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PAIN MANAGEMENT AND PULMONARY DYSFUNCTION
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PAIN MANAGEMENT AND PULMONARY DYSFUNCTION Pankaj M. Desai, MBBS, FRCA
Pain and pulmonary dysfunction (PD) co-exist in a number of clinical scenarios, including burns, trauma, and a variety of acute abdominal diseases (e.g., pancreatitis).’ The two conditions are, however, encountered with the greatest frequency in the postoperative setting. This setting has given us much information on the possible mechanisms by which the two are related. The nature of PD can range from transient aberrations in arterial blood gases (ABG), to overt lobar pneumonia or pulmonary thromboembolism (PTE), both severe enough to cause significant morbidity and, not infrequently, mortality. This article examines the extent to which pain contributes to PD in each of these common scenarios; it also discusses options available to attenuate the extent of this contribution. Owing to the larger body of published literature on this subject, postoperative pulmonary dysfunction (PPD) will be addressed separately. POSTOPERATIVE PULMONARY DYSFUNCTION Pathophysiology of PPD
As far back as 1910, P a s t e ~ described r ~ ~ ~ lobar collapse of the lung following abdominal operations. In 1932, Beecher2”speculated that the functional residual capacity (FRC) was the most important of all the lung volumes that were reduced following laparotomy. In the years following those early observations, a clinical syndrome often referred to From the Department of Anesthesiology, The University of Alabama at Birmingham, Birmingham, Alabama ~~
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as ”the postoperative chest” has come to be recognized as a frequent complication following certain types of major surgery. Postoperative chest includes fever, tachycardia, dyspnea, chest pain, retained sputum, auscultatory, and radiologic changes. Current evidence would suggest that the condition is mediated by abdominal pain, muscle spasms, and other reflexes, which restrict the diaphragm and chest wall movement. The pain of the abdominal incision and peritoneal inflammation is accompanied by spasms or guarding of the muscles of the abdominal l9 Since the rectus transversus abdominis and the internal and external oblique are muscles of forced expiration, their contraction increases the abdominal pressure, raises the diaphragm, and thereby the transpulmonary pressure, which forces gas out of the lungs. In patients with pain in the postoperative period, their sustained contraction maintains a reduction in the size of the lungs throughout normal tidal ventilation, thus leading to a reduction in FRC. Studies have demonstrated that airways, mainly in dependent lung regions, could close This condition reduces or during part or all of the respiratory completely abolishes ventilation of the subtended lung units, leaving them at risk of undergoing resorption atelectasis. The volume of lung that is at risk increases as the FRC falls. Tidal volume decreases and respiratory rate increases presumably as an adaptive response to worsening pressure-volume relationships resulting from atelectasis. Intermittent sighs, which are an important part of normal respiratory pattern and allow ventilation of basal alveoli, are absent. As lung volume decreases, areas of low V/Q develop and contribute to the venous admixture, or shunt, or both, resulting in hypoxemia. On the other hand, carbon dioxide elimination is not significantly reduced and may in fact be enhanced because of the rapid respiratory rate often seen in patients with unrelieved pain. Thus, it is not unusual to see patients in this condition with arterial blood gases consistent with a respiratory alkalosis. Since the respiratory drive is no longer dependent on the CO, level, a dangerous situation leading to apnea may arise if the respiratory drive is depressed by sedatives, or if the patient were to fall asleep as a result of his or her pain relief. Provision of adequate analgesia coming after a prolonged period of unrelieved pain may paradoxically place the patient at greater risk of harm. When FRC and forced vital capacity (FVC) are reduced for prolonged periods postoperatively, the patient’s inability to cough effectively leads to retained secretions, bacterial contamination of the airway, and pneumonia. Pain not only leads to localized guarding of muscles around the area of pain, but also to generalized muscle rigidity. There is also an associated immobility of trunk and limb muscles in an attempt to reduce any movement, which would lead to an increase in pain. Vasoconstriction occurs as a result of pain-induced sympathetic discharge throughout the body. This situation predisposes the patient to PD of a different kind. Immobility and venous stasis can lead to venous thrombosis. The end result may be the occurrence of a PTE, which is the most common cause
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of sudden death in the first 10 days after surgery. Other predisposing factors to venous thrombosis include obesity, surgical procedures of prolonged duration, upper abdominal operations, prostatectomy, pancreatitis, and oral contraceptives.
Physiologic Aberrations In the hospital setting, a number of physiologic aberrations are found among patients in pain. Behavioral aberrations include immobility, a tendency to maintain the supine in preference to the upright posture, and reduced ambulation. Respiratory aberrations include decreased FRC, FVC, forced expiratory volume over 1 second (FEV,), tidal volume (TV), cough, and absence of sigh. CraigI2found that vital capacity (VC) troughed immediately after upper abdominal surgery while FRC and Paoz troughed on the first postoperative day (Fig. 1).There is also a marked dysfunction of the diaphragm. Other abnormalities include decreased immunity, which relates to the stress response, of which pain is the principal factor. The reductions in FRC, FVC, FEV,, cough,
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Figure 1. Postoperative vital capacity (squares), functional residual capacity (circles), and arterial oxygen pressure (diamonds)as a percentage of preoperative values following upper abdominal surgery. (From Craig DB: Postoperative recovery of pulmonary function. Anesth Analg 60:46-52,1981; with permission.)
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and the behavioral aberrations are affected by pain and are therefore, in most cases, improved by generic analgesia. Some of these parameters, however, may be worsened or indeed caused by the analgesic technique used. Thus, the patient who has been oversedated with narcotics may also fail to ambulate, sit up, and cough. Incidence/Diagnostic Criteria
Although transient physiologic aberrations such as decreased FRC, FVC, and VT can progress to overt pathology such as pneumonia, distinction should be made between the two conditions when considering incidence of PPD. Furthermore, atelectasis is a noninfectious complication that develops in up to 90% of patients after cardiac surgery and resolves without adverse effects in most patients, although it is often the first clinically apparent postoperative abnormality in a pathophysiologic sequence that results in bacterial contamination and development of pneumonia in 1%to 3% of all surgical procedures. Diagnostic criteria for postoperative pulmonary complications usually include radiographic abnormalities (e.g., atelectasis, lobar collapse, or infiltrate) and clinical signs or symptoms that reflect newly acquired pulmonary pathology (e.g., fever, leukocytosis, rales, bronchial breath sounds, cough, sputum production, or dyspnea). Although postoperative complication rates vary widely depending on the specific radiographic or clinical criteria used for detection, pulmonary complications after upper abdominal surgery are as common today as they were 20 years ago. However, clinical complications requiring some kind of intervention are fairly rare, occurring in about 1%to 3% of patients after elective surgery and up to 10% in patients requiring emergency surgery. The majority of studies pertaining to postoperative pulmonary dysfunction have focused on subclinical complications such as radiographic evidence of atelectasis, excessive cough, and fever. With this broad definition of complications, the incidence increases dramatically from 25% to 75% after abdominal surgery (Table 1). The contribution of atelectasis to significant morbidity and mortality is unclear, with some believing that its presence does not necessitate therapeutic intervention. Diaphragmatic Dysfunction
Typical respiratory changes after upper abdominal (UA) or thoracic (Th) surgery include a change in the pattern of breathing, increased work of breathing, and respiratory muscle dysfunction. Following cardiac surgery, left lower lobe atelectasis is present in 85% to 90% of patients in the immediate postoperative period as a result of cardiac and phrenic nerve cooling and frank manipulation. In 1983, Ford et alZo measured changes in transdiaphragmatic pressure swings and external abdominal dimensions in patients who had undergone open cholecystec-
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Table 1. INCIDENCE OF PULMONARY COMPLICATIONS AFTER UPPER ABDOMINAL SURGERY Criteria Author 1968-1 980 Wightman Latimer Van De Water Bartlett Craven Lyager
Jung 1981-1988 Alexander Celli Stock Ricksten Schwieger O’Connor Roukema
Number of Patients
PE
CXR
20 76 30 17 59 37 41
118 46 30 150 70 103 126 134 174 65 43
40 40 153
Incidence of PPC (percent)
+ + + + +
+
+ + + +
35 46 37 16
35 35 41
PPC, Postoperative pulmonary complications; PE, physical examination; CXR, chest radiography. From Miller CF, Martin J L Changes in lung function following anesthesia and surgery. In Breslow MJ, Miller CF, Rogers MC (eds): Perioperative Management. St. Louis, CV Mosby, 1990, pp 195-211; with permission.
tomy. They concluded that diaphragm function was significantly decreased after surgery. The pattern of breathing, which had previously been predominantly abdominal before surgery, became predominantly thoracic.22These findings were confirmed in another study by Simonneau et a P Interestingly, they also observed that the provision of analgesia with 150 pg of epidural fentanyl had no beneficial effect on diaphragmatic dysfunction. Fratacci et alZ2observed that thoracotomy and pulmonary resections produce a marked reduction in active diaphragmatic shortening that is not reversed by thoracic epidural anesthesia despite improvement of other indices of respiratory function. Pansard et a1 inserted electromyogram (EMG) electrodes in the diaphragms of patients undergoing abdominal aortic surgery and observed that the diaphragm EMG signal was significantly decreased on the first postoperative day.35Phrenic nerve stimulation studies on patients who had undergone upper abdominal surgery showed that there was no diminution in the contractility of the diaphragm muscle, but, rather, a reflex inhibition of phrenic nerve output was induced by surgical trauma. Ford et aPoahad previously shown the existence of such a reflex in anesthetized spontaneously breathing dogs after gall bladder manipulation. The short interval between the gall bladder stimulation and the decrease in diaphragmatic contraction suggested that a neural reflex was probably involved. The persistence of these effects following vagotomy implied that the afferents in the reflex did not travel via the
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vagus. Subsequently, Mannikian et a1 showed that provision of a thoracic epidural blockade with 0.5% bupivacaine restored the diaphragmatic function after upper abdominal surgery as measured by transdiaphragmatic pressures or by diaphragmatic EMG The epidural block also reduced the postoperative respiratory rate and increased the tidal volume to preoperative levels. It has been suggested that thoracic epidural blockade may interrupt both the afferent and the efferent portions of the neural arc. Risk Factors Obesity, chronic obstructive pulmonary disease (COPD), and smoking are major risk factors for PPD. Smokers generally suffer from chronic airflow obstruction and have increased closing volumes. Because of the perioperative decrease in FRC, a patient with obstruction who receives general anesthesia will experience greater airway closure during tidal ventilation than a patient without obstruction. A smoker also has more secretions in the lungs than a non-smoker. These two factors increase the risk of PPD after a surgical procedure in the smoker. The lung volume at which airways collapse during expiration increases with age, but is not affected by body position and presumably not by anesthesia. On the other hand, FRC is reduced by the cephalad displacement of the diaphragm on assuming the supine position. Thus, airway closure can occur early in many elderly patients when lying supine in the postoperative period. A condition termed micro-atelectasis occurs frequently, especially in obese patients undergoing upper abdominal surgery. These patients experience significant hypoxemia caused by ventilation perfusion mismatch. Site of Surgery PPD is most common after upper abdominal surgery, less common after lower abdominal surgery, and rare after surgery on the limbs and the body surface. It is less common after midthoracic than upper abdominal surgery.24Among upper abdominal incisions, the vertical midline incision is associated with greater dysfunction than the transverse (bicostal) incision. The advent of laparoscopic surgery has greatly reduced the severity of PPD.ll,38 FRC decreases more after abdominal or thoracic incisions than after lower abdominal procedures. Superficial and peripheral procedures are not associated with postoperative FRC reduction. Oxygenation (Pao,) increases postoperatively in direct proportion to the amount that FRC increases.12FVC and FEV, also decrease more after upper abdominal than after lower abdominal or superficial incisions. A subcostal incision results in a 40% to 50% fall in VC and FRC, even in patients without preexisting pulmonary disease; however,
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the ratio of FEV,/FVC usually remains normal. FRC and FVC slowly return to preoperative values over 12 days to 14 days after abdominal or thoracic procedures.12Thus, postoperative patients develop acute restrictive pulmonary defects that vary in duration and severity according to the site of surgical incisions and degree of preexisting pulmonary disease. Effects of Anesthesia
Alterations of pulmonary function commonly develop during and after anesthesia for surgery.34Clearance of mucus and inhaled particulate matter by airway cilia is markedly reduced at anesthetic concentrations of volatile agents. Tracheal mucous flow is also impaired during inhalation of either cold air or air at relative humidity less than 75%. While cuffed endotracheal tubes prevent tracheal aspiration, they also reduce tracheal mucous velocity. Using CT scanning of the chest, Hedenstierna et a1 confirmed that the combined effects of decreased cross-sectional area of the chest and cephalad displacement of the diaphragm account for reduced thoracic volume associated with decreased FRC after induction of general anesthesia.26Decreased lung volumes caused by general anesthesia, however, rapidly return to preoperative values in the early postoperative periods. Ravin et a1 found that both spinal and general anesthesia techniques were associated with identical reductions in FVC, FEV,, and Pao, at 24 hours and 48 hours following lower abdominal surgery.3yTherefore, anesthetic metabolites do not appear to mediate postoperative pulmonary abnormalities. Another argument against anesthesia as a primary mediator of late postoperative pulmonary restrictive dysfunction is the rapid return of lung volume, mechanical function, and gas exchange to preoperative values after peripheral procedures. Thus, while decreased FRC, Pao,, and varying degrees of atelectasis frequently follow the administration of general anesthesia in all patients, these abnormalities are seen postoperatively for a prolonged period only in those patients in whom the thoracic or abdominal cavity has been opened. Effect of Analgesic Therapy on Pulmonary Function Tests
Although measurements of FRC in patients before and after the provisions of anesthesia are similar, effort dependent spirometric values do show an i m p r ~ v e m e n t .Thus, ~ , ~ ~FVC and FEV, are increased. Furthermore, a positive correlation exists between a lowered FVC and the development of postoperative pulmonary complications.26b Thus, properly titrated analgesia may decrease the incidence of postoperative pulmonary complications. Wahba et a146also found that when pain was eliminated by the
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administration of epidural lidocaine, FVC increased from 37% to 55% of preoperative values. Bromage et a17 gave parenteral morphine to postoperative patients with pain and found that FEV, increased from 37% to 45% of preoperative values. Administration of either epidural local anesthetic or epidural narcotic further increased FEV, from 45% to 67% of preoperative values after upper abdominal or thoracic procedures. Functional residual capacity was not measured. Jakobsen et a P b measured FRC after providing pain relief with intercostal nerve blocks using mepivacaine 24 hours after cholecystectomy and found no change when compared to control patients. These studies suggest that pain relief may decrease postoperative splinting and partially correct spirometric abnormalities; however, pulmonary restriction remains unchanged. Furthermore, it seems unlikely that pulmonary restriction results from the effects of epidural or intercostal neural blockade because neither technique decreased FRC in volunteers who had not had surgical interventions. The usefulness of effective analgesia was further investigated by Ricksten et a140awho combined it with aggressive respiratory therapy in the form of cough and deep-breathing exercises and continuous positive airway pressure. With this combination, this group was able to show a significant decrease in the incidence of postoperative pulmonary complications in high-risk surgical patients. In an earlier study, Rawal et a140 also showed that the provision of effective analgesia in grossly obese patients undergoing gastroplasty for weight reduction, the provision of effective analgesia with epidural morphine allowed these patients to participate in more vigorous physiotherapy and allowed them to ambulate earlier compared with a similar group receiving intramuscular morphine. Thus, adequate analgesia leads to an increase in FVC, FEVI, and peak expiratory flow (PEF) and allows earlier ambulation together with improved compliance with respiratory therapy. ANALGESIC TECHNIQUES Parenteral Narcotics
Traditionally, narcotic analgesia has been administered to patients by intramuscular injection on an as-needed basis (prn). There is a large amount of interpatient variability in the minimum effective analgesic concentration (MEAC). For instance, the MEAC for meperidine can vary from 0.24 to 0.76 kg/mL for the same surgical procedure in different patients. Narcotic requirements via patient-controlled analgesia (PCA) during the first 2 to 3 days after a surgical procedure decreases, probably demonstrating that tolerance during this short postoperative time period does not develop.
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Currently, the most commonly used method of analgesia is intravenous (IV) narcotic administration. Intravenous patient-controlled analgesia (ivPCA) is gaining popularity over prn IV or IM bolus administration. Of the noninvasive techniques, it is considered to be the standard control technique by which newer techniques are compared. Intercostal nerve blocks may be used to provide postoperative analgesia in patients undergoing upper abdominal procedures. The dermatoma1 distribution of analgesia may not match the ribs anatomically, and therefore it is necessary to block two nerves above and below the affected intercostal space. Pain relief lasting up to to 18 hours after a single dose of local anesthetic has been observed. Cryoanalgesia, the application of a cryoprobe to the chosen intercostal nerves to create a temporary neurapraxia, decreases postoperative pain and narcotic requirement. In patients receiving cryoanalgesia, the occurrence of pain was usually not incisional, but was related to shoulder and arm pain as a result of pleural irritation caused by the chest tube. Analgesia from cryotherapy lasts longer than the apparent time required for wound healing. The return of sensation ranges from 2 to 3 weeks to 6 to 8 months. Return of normal sensation may take up to 1 year, and there is a high incidence of intercostal neuralgia. Interpleural analgesia, transcutaneous electrical nerve stimulation (TENS),and paravertebral nerve blocks have all been used with varying degrees of success in the treatment of acute pain (Table 2).
TYPES OF ANALGESIC TECHNIQUES AVAILABLE Epidural Opioids and Local Anesthetics
In 1976, Yaksh and R u d y observed that opioids have analgesic properaties when applied to the spinal cord; this observation was immediately applied by clinicians. Bromage et a1 were able to show that The epidural narcotics could partially restore the FEV, po~toperatively.~ advantage with epidural narcotics is they are longer acting and do not cause motor blockade or significant changes in vascular tone; they increase the ability of the patient to perform PFTs. The maximum expiratory flow rate (MEFR), FVC, and FEV, may also increase. Thus, the patient may be able to cough and breathe more deeply. Side effects, however, may include delayed respiratory depression, urinary retention, and itching. In recent years, combination narcotic and low-dose local anesthetic has gained popularity. In experimental studies, local anesthetics have been demonstrated to potentiate spinal morphine antinociception even at doses at which the drugs by themselves had little or no effect. In clinical studies, the combination of epidural local anesthetics with opioids has been demonstrated to maintain sensory analgesia and to improve pain relief after abdominal, thoracic, and gynecologic surgery,
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Table 2. TYPES OF ANALGESIC TECHNIQUES AVAILABLE Technique
Oral narcotics Parenteral narcotics
Neuraxial narcotics Neuraxial local anesthetics Intercostal nerve block Paravertebral nerve block Interpleural analgesia NSAIDs TENS Cryotherapy
Advantages
Disadvantages
Patients generally NPO after surgery IM injection painful, Ease of administration subtherapeutic & toxic levels, respiratory depression Intense analgesia Invasive, requires special expertise Good dynamic pain control Invasive, requires special expertise hypotension Good dynamic pain control Hypotension, risk of pneumothorax Good dynamic pain control Invasive, requires special Less hypotension than epidural expertise Local anesthetics Invasive, requires special Good analgesia for thoracostomy tubes expertise Risk of gastric ulceration and Good analgesia for pain of musculoskeletal origin hemorrhage, renal dysfunction Only moderately effective for Non invasive, no side effects severe pain Neuralgia is a common afterLong-term analgesia effect Ease of administration
compared with epidural local anesthesia alone, thus confirming previous experimental data.'3*25 In contrast, clinical studies comparing epidural local anesthesiaopioid mixtures with epidural opioid alone are contradictory. All but two studies addressing the administration of high-dose epidural local anesthetic showed no advantages to added epidural opioids; however, these studies failed to assess pain during activity. A shortcoming of many of the studies that have addressed pros and cons of neuraxial analgesia is that they have failed to recognize the importance of treating dynamic pain (i.e., pain upon movement). This should be held distinct from rest pain. There is an increasing body of evidence that neuraxial analgesia, especially when combined with local anesthetic, can significantly reduce dynamic pain in the postoperative period. Since deep breathing and ambulation both contribute significantly to incisional pain, they would be expected to be two of the activities that the under-analgesed patient is least likely to participate in, thereby leading to PPD. Bell found that the improvement in FEV, and inspiratory force (IF) following epidural analgesia in patients after abdominal aortic aneurysmal surgery was seen only if dynamic pain control was a~hieved.~ In another study, patients undergoing thoracic or abdominal surgery for cancer, patients who had dynamic pain control with a combination of morphine and bupivacaine epidural analgesia, recovered more quickly as judged by shorter mechanical ventilation,
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surgical intensive care unit (SICU), and hospital days.I5 This study bolsters the findings from Yeager et a1 which showed that high-risk patients undergoing epidural anesthesia and analgesia had lower costs and morbidity associated with their hospital stay than those who had undergone general anesthesia with parenteral a n a l g e ~ i a . ~ ~ Side Effects
With the discovery of spinally mediated opioid analgesia, there was some expectation that adequate analgesia could perhaps be delivered selectively to regions in the torso while avoiding changes in sensorium and respiratory depression commonly seen at higher doses of parenterally delivered narcotics. Reports of respiratory depression from rostra1 spread of spinal morphine temporarily dampened this initial enthusiasm for neuraxial opioids. Stenseth, in a series of 1085 patients using bolus doses of morphine with or without bupivacaine, reported a respiratory depression rate of o.9%.45DeLeon-Casasola et a1 reported an incidence of only 0.07% in a series of 4227 patients receiving infusions of morphine and bupivacaine.16As a result of these series, it would seem that using infusions of narcotic in the epidural space is safer than boluses. The incidence of respiratory depression has been quoted to be as high as 0.9% for intramuscular opioid therapy. Other Benefits of Epidurals
FRC is often further reduced by wound dressings, ascites, and bowel gas caused by ileus. Early mobilization and early initiation of bowel regimens would thus be expected to promote pulmonary function. Since abdominal distension caused by ileus will further increase cephalad movement of the diaphragm, any measures leading to a reduction in the duration of postoperative ileus would help pulmonary function. Liu et a129afound that an infusion of bupivacaine and morphine given epidurally in the postoperative period led to a faster resolution of ileus, when compared to IV morphine, while at the same time providing effective analgesia. Epidural infusions using local anesthetic have also been shown to decrease the incidence of deep venous thrombosis (DVT). Pain from Traumatic Injury
The issue of pain as a result of blunt chest trauma is one which deserves special mention. These patients consistently report very high pain scores as a result of continued disruption of rib periosteum during the respiratory cycle. Not surprisingly, VC, FEV,, MIP, and cough are significantly reduced. This setting lends itself to pulmonary complica-
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tions which typically occur in the first 24 hrs, especially with coexisting pulmonary contusion, and after 48 hrs in the absence of it. The latter occurs as a result of the inhibitory effects of pain on respiratory effort. All the analgesic modalities used for upper abdominal surgery have been used to treat the pain of rib fractures (Table 2). There is evidence to suggest that avoidance of tracheal intubation and mechanical ventilation may decrease morbidity in these patients, especially in the elderly. Bollinger et a1 observed that the duration of treatment and the number of days spent in the ICU were reduced in those patients treated with continuous positive airway pressure (CPAP), as opposed to those treated with mechanical ventilation and positive end-expiratory pressure (PEEP). There was also a reduction in the percentage of patients incurring infectious complication^.^ Therefore, aggressive analgesic techniques would seem logical. Aggressive treatment of pain using parenteral narcotics can lead to increased somnolence and respiratory depression. Several studies have shown an advantage to using neuraxial analgesia. Cicala et a1 compared thoracic epidural ropivacaine with lumbar epidural morphine with IV narcotic.'O Groups receiving thoracic epidural ropivacaine and lumbar epidural morphine had equivalent analgesia, which was superior to the analgesia provided with IV narcotics. The thoracic epidural group had an increased VC and FEV, and a decreased respiratory rate. Mackersie et a1 compared epidural fentanyl with IV f e n t a n ~ lBoth . ~ ~ groups had equivalent analgesia; however, the epidural fentanyl group had an increase in MIP and VC. The IV fentanyl group had an increase in VC; however, this was accompanied by an increase in PCO, and a decrease in PO,. Dittmann et a1 also studied the effects of thoracic epidural analgesia in these patients and found that use of this modality was a successful alternative to mechanical ventilation for patients who had sustained multiple rib fractures.ls There was an increase in FRC, dynamic compliance, VC, and an increase in Po2 in patients treated with the thoracic epidurals. Wisner et a1 found an improvement in analgesia, ventilatory function, morbidity, and mortality in elderly patients treated with epidural analgesia as compared to IV or IM narcotics.47 Post-Thoracotomy Pain
The pain from thoracotomy incisions has been recognized as being one of the most intense. The nociceptive afferents arise primarily from the surgical incision site, caused by disruption of the intercostal musculature and often an adjacent rib and parietal pleura. The pain arising from these structures is thus transmitted by intercostal nerves and sensed as intense, localized wound pain. Pain from the lungs and mediastinal structures is transmitted by the vagus, and although intense, is deep and poorly localized. Diaphragmatic irritation can cause pain referred to the scapula. Postoperatively, the frequent use of a thoracostomy tube ensures a continuous painful stimulus triggered with each breath. This
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intense negative reinforcement to deep breathing, combined with the fact that many of these patients have pre-existing pulmonary pathology, sets the stage for PPD. Thus the elimination of this pain is an important aspect of the postoperative care of these patients. Each of the techniques previously performed has been used for the treatment of this pain entity. Traditionally, post-thoracotomy pain has been treated with systemic opioids, most frequently administered by PCA; however, respiratory depression is of special concern in these patients since the resulting hypercarbia carries the potential risk of resultant increases in pulmonary hypertension and pulmonary edema. More recently, epidural administration of opioids, local anesthetics, or a combination of the two, has gained popularity. Several studies have compared lumbar epidurals with thoracic, since elimination of the small but not inconsequential risk of trauma to the spinal cord would be desirable. Current literature appears to support the use of a continuous infusion of either morphine or fentanyl via a thoracic catheter. Addition of LA to either of these has led to an improvement in pain scores, but also carries a greater potential for hemodynamic instability. Lumbar epidural morphine was also associated with excellent analgesia, but analgesia from lumbar epidural with fentanyl was equivalent to IV fentanyl. Nonsteroidal anti-inflammatory drugs (NSAIDs) have been found to be beneficial as adjuvants to narcotics, but do not provide any additional benefit in patients receiving optimal neuraxial analgesia. Their potential for causing gastric evasions and renal insufficiency, however, should be considered prior to initiation. In the author’s experience, the pain arising from the thoracostomy tube is significant and can be difficult to treat at times. Our institution has had good results with intermittent instillation of bupivacaine into the thoracostomy tube, followed by clamping for 10 minutes to 15 minutes (e.g., intrapleural analgesia). Shulman and colleagues43evaluated patients undergoing thoracotomy predominantly for lobectomy and evaluated the efficacy of epidural morphine and intramuscular morphine. Pain relief during the first 8 hours to 24 hours was superior for the patients receiving epidural morphine; however, at 24 hours, pain relief was similar in both groups. Also, decrements in pulmonary function were observed to be significantly less during the first 24 hours in patients who received epidural morphine. CONCLUSION
The humanitarian desire to relieve postoperative pain is sometimes overridden by the fear of potential respiratory and central nervous system side effects of opioid analgesics. Pain affects pulmonary function in a variety of ways. The intensity of the pain is important to the extent that it will inhibit mobilization of the patient in a graded manner. As a result, the quality of pain relief afforded to the patient will have a
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bearing on the speed of recovery. The quality of dynamic analgesia provided by epidural narcotic and local anesthetic combination techniques is superior to that achieved by giving narcotics by traditional methods. The best results have been shown with the use of multimodality therapy. Unfortunately, even complete relief of pain will not overcome the diaphragmatic inhibition that occurs following upper abdominal surgery. The main goals in restoring pulmonary function and reducing complications should be To eliminate pain (thus allowing clearance of secretions by coughing and deep breathing) To restore FRC to normal by early mobilization, allowing the patient to ambulate and maintain the upright posture. This will also aid restoration of gastrointestinal function, thus reducing any migration of the diaphragm. To maintain respiratory muscle function by minimizing the size of the surgical incision. To use the appropriate prophylactic measures to reduce the risk of DVT. References 1. Basran GS, Ramasubramanian R, Verma R Intrathoracic complications of acute pancreatitis. British Journal of Diseases of the Chest 81:326-331, 1987 2. Becker JM, Pemberton JH, DiMagno EP, et al: Prognostic factors in pancreatic abscess. Surgery 96:455-461, 1984 2a. Beecher HK: Effect of laparotomy on lung volume: Demonstration of a new type of pulmonary collapse. J Clin Invest 12651-658, 1932 3. Bell SD: The correlation between pulmonary function and resting and dynamic pain scores in post aortic surgery patients. (Abstract.) Anesth Analg 72 (Suppl):S18, 1991 4. Benhamou D, Samii K, Noviant Y Effect of analgesia on respiratory muscle function after upper abdominal surgery. Acta Anesthesiol Scand 2722-25, 1983 5. Bolliger CT, Van Eeden SF Treatment of multiple rib fractures: Randomized controlled trial comparing ventilatory with nonventilatory management. Chest 97943-948, 1990 6. Bonnet F, Blery C, Zatan M, et al: Effect of epidural morphine on post-operative pulmonary dysfunction. Acta Anaesthesiol Scand 28:147-151, 1984 7. Bromage PR, Camporesi E, Chestnut D: Epidural narcotics for post-operative analgesia. Anesth Analg 59:473480, 1980 8. Catley DM, Thornton C, Jordan C, et al: Pronounced, episodic oxygen desaturation in the postoperative period: Its association with ventilatory pattern and analgesic regimen. Anesthesiology 6320-28, 1985 9. Chalmers TC, Ballantyne JC, Carr DR, et al: Comparative effects of analgesic therapies upon postoperative pulmonary function: Meta-alaysis (Abstract #358). 7th World Congress of Pain, p 136, 1993 10. Cicala RS, Voeller GR, Fox T, et al: Epidural analgesia in thoracic trauma: Effects of lumbar morphine and thoracic bupivacaine on pulmonary function. Crit Care Med 18:229-231, 1990 11. Couture JG, Chartrand D, Gagner M, et al: Diaphragmatic and Abdominal Muscle Activity after endoscopic cholecystectomy. Anesth Analg 78:733-739, 1994 12. Craig DB: Postoperative recovery of pulmonary function. Anesth Analg 60:46-52,1981 13. Cuschieri RJ, Morran CG, Howie JC, et a1 Postoperative pain and pulmonary complications: Comparison of three analgesic regimens. Br J Surg 72495498, 1985
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14. Dahl JB, Rosenbert J, Hansen BL Differential analgesic effects of low-dose epidural morphine and morphine-bupivacaine at rest and during mobilization after major abdominal surgery. Anesth Analg 74:362-365, 1992 15. De Leon-Casasola OA, Parker BM, Lema MJ, et al: Epidural analgesia versus intravenous patient-controlled analgesia. Regional Anesthesia 19:307-315, 1994 16. De Leon-Casasola OA, Parker BM, Lerna MJ, et al: Post-operative epidural bupivacaine-morphine therapy. Anesthesiology 81:368-375, 1998 17. Dittmann M, Keller R, Wolff G: A rationale for epidural analgesia in the treatment of multiple rib fractures. Intensive Care Medicine 4:193-197, 1978 18. Dittmann M, Steenblock U, Kranzlin M, et al: Epidural analgesia or mechanical ventilation for multiple rib fractures? Intens Care Med 8(2):89-92, 1982 19. Duggan J, Drummond GB: Activity of lower intercostal and abdominal muscle after upper abdominal surgery. Anesth Analg 66:852-855, 1987 20. Ford GT, Whitelaw WA, Rosenal TW, et al: Diaphragmatic function after upper abdominal surgery in humans. Am Rev Respir Dis 127431435, 1987 20a. Ford GT, Grant DA, Rideout KS, et al: Inhibition of breathing associated with gallbladder stimulation in dogs. J Appl Physiol 65:72-79, 1988 21. Forster EL, Kramer JF, Lucy SD, et al: Effect of TENS on pain, medications, and pulmonary function following coronary artery bypass graft surgery. Chest 106(5):1343-1348, 1994 22. Fratacci MD, Kimball WR, Wain JC, et al: Diaphragmatic shortening after thoracic surgery in humans. Anesthesiology 79:654-665, 1993 23. Frazee RC, Roberts JW, Okeson GC, et al: Open vs laparoscopic cholecystectomy: A comparison of postoperative pulmonary function. Ann Surg 213:651-654, 1991 24. Garibaldi RA, Britt MR, Coleman ML, et al: Risk factors for postoperative pneumonia. Am J Med 70:670-680, 1981 25. George KA, Chisakuta AM, Gamble JAS, et al: Thoracic epidural infusion for postoperative pain relief following abdominal aortic surgery: Bupivacaine, fentanyl or a mixture of both? Anaesthesia 47:38-394, 1992 26. Hedenstierna H, Strandberg A, Brismar B, et al: Functional Residual Capacity, thoracoabdominal dimensions and central blood volume during general anesthesia with muscle paralysis and mechanical ventilation. Anesthesiology 62:247-254, 1985 26a. Hendolin H, et al: The effect of thoracic epidural analgesia on respiratory function after cholecystectomy. Acta Anesth Scand 31:645-651, 1987 26b. Jakobson S, et al: Effects of intercostal nerve blocks (0.5% etidocaine) on chest wall mechanics in cholecystectomized patients. Acta Anesth Scand 21:497-503, 1997 27. Jayr C, Thomas H, Rey A, et al: Postoperative pulmonary complications. Anesthesiology 78:666-676, 1993 28. Jayr C, Mollie A, Bourgain JL: Postoperative pulmonary complications: General anesthesia with postoperative parenteral morphine compared with epidural analgesia. Surgery 104(1):57-63, 1988 29. Johnston JR, McCaughey W Epidural morphine: A method of management of multiple fractured ribs. Anaesthesia 35(2):155-157, 1980 29a. Liu SS, Carpenter RL, Mackey DC, et al: Effects of perioperative analgesic technique on rate of recovery after colon surgery. Anesthesiology 83:757-765, 1995 30. Mackersie RC, Shackford SR, Hoyt DB, et al: Continuous epidural fentanyl analgesia: Ventilatory function improvement with routine use in treatment of blunt chest injury. J Trauma 27(11):1207-1212, 1987 31. Mackersie RC, Karagianes TG, Hoyt DB, et al: Prospective evaluation of epidural and intravenous administration of fentanyl for pain control and restoration of ventilatory function following multiple rib fractures. J Trauma 31(4):443449, 1991 32. Manikian 8, Cantineau TP, Bertrand M, et al: Immovement of dianhragmatic function by a thoracic extraduraiblock after upper abdokinal surgery. Anesthesiology 68:379386. ~~. , 1988 -~ 33. Miller CF, Martin JL: Changes in lung function following anesthesia and surgery. In Breslow MJ, Miller CF, Rogers MC (eds): Perioperative Management. St. Louis, CV Mosby, 1990, pp 195-211 34. Nunn JF: Effects of Anesthesia on respiration. Br J Anaesth 65:54-62, 1990 I
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35. Pansard JL, Mankikian B, Bertrand M, et al: Effects of thoracic extradural block on diaphragmatic electrical activity and contractility after upper abdominal surgery. Anesthesiology 78:63-71, 1993 35a. Pasteur W: Active lobar collapse of the lung after abdominal operations: A contribution to the study of postoperative lung complications. Lancet 2:1080-1083, 1910 36. Pflug AE, Murphy TM, Butler SH, et al: The effects of postoperative peridural analgesia on pulmonary therapy and pulmonary complications. Anesthesiology 41% 17, 1974 37. Polaner DM, Kimball WR, Fratacci MD, et al: Thoracic epidural anesthesia increases diaphragmatic shortening after thoracotomy in the awake lamb. Anesthesiology 79(4):808-816, 1993 38. Rademaker BM, Ringers J, Odoom JA, et al: Pulmonary function and stress response after laparoscopic cholecystectomy comparison with subcostal incision and influence of thoracic epidural analgesia. Anesth Analg 75:381-385, 1992 39. Ravin MB: Comparison of spinal and general anesthesia for lower abdominal surgery in patients with COPD. Anesthesiology 35:319-322, 1971 40. Rawal N, Sjostrand U, Christoffersson E, et al: Comparison of intramuscular and epidural morphine for postoperative analgesia in the grossly obese: Influence on postoperative ambulation and pulmonary function. Anesth Analg 63:583-592, 1984 40a. Rickston S, et al: Effects of periodic airway pressure by mask on postoperative pulmonary function. Chest 89:774-781, 1986 41. Scott NB, Murphy M, Kehlet H: Continuous thoracic epidural analgesia versus combined spinal/ thoracic epidural analgesia on pain, pulmonary function and the metabolic response following colonic resection. Acta Anaesthesiol Scand 40691496, 1996 42. Scott NB, Mogensen T, Greulich A, et al: No effect of continuous i.p. infusion of bupivacaine on postoperative analgesia, pulmonary function and the stress response to surgery. Br J Anaesth 61(2):165-168, 1988 43. Shulman M, Sandler AN, Bradley JW, et al: Postthoracotomy pain and pulmonary function following epidural and systemic morphine. Anesthesiology 61:569-575, 1984 44. Simonneau G, Vivien A, Sartene R, et al: Diaphragm dysfunction induced by upper abdominal surgery: Role of postoperative pain. Am Rev Respir Dis 128:899-903, 1983 45. Stenseth R, Sellevold 0, Breivik H: Epidural morphine for postoperative pain: Experience with 1085 patients. Acta Anaesthesiol Scand 29:148-156, 1985 46. Wahba WM, Don HF, Craig DB: Post-operative epidural analgesia: Effects on lung volumes. Can Anaesth SOCJ 22:519-527, 1975 47. Wisner DH: A stepwise logistic regression analysis of factors affecting morbidity and mortality after thoracic trauma: Effect of epidural analgesia. J Trauma 30:799-804,1990 47a. Yaksh TL, Rudy TA: Analgesia mediated by a direct spinal action of narcotics. Science 192:1357-1358, 1976 48. Yeager MP, Glass DD, Neff RK, et al: Epidural anesthesia and analgesia in high-risk surgical patients. Anesthesiology 66729-736, 1987 Address reprint requests to Pankaj M. Desai, MBBS, FRCA Department of Anesthesiology The University of Alabama at Birmingham 845 Jefferson Tower 619 South 19th Street Birmingham, AL 35233-6810
e-mail: PANKAJ.DESAI8CCC.UAB.EDU
PAIN MANAGEMENT
+ .OO
PAIN MANAGEMENT AND PULMONARY DYSFUNCTION Pankaj M. Desai, MBBS, FRCA
Pain and pulmonary dysfunction (PD) co-exist in a number of clinical scenarios, including burns, trauma, and a variety of acute abdominal diseases (e.g., pancreatitis).’ The two conditions are, however, encountered with the greatest frequency in the postoperative setting. This setting has given us much information on the possible mechanisms by which the two are related. The nature of PD can range from transient aberrations in arterial blood gases (ABG), to overt lobar pneumonia or pulmonary thromboembolism (PTE), both severe enough to cause significant morbidity and, not infrequently, mortality. This article examines the extent to which pain contributes to PD in each of these common scenarios; it also discusses options available to attenuate the extent of this contribution. Owing to the larger body of published literature on this subject, postoperative pulmonary dysfunction (PPD) will be addressed separately. POSTOPERATIVE PULMONARY DYSFUNCTION Pathophysiology of PPD
As far back as 1910, P a s t e ~ described r ~ ~ ~ lobar collapse of the lung following abdominal operations. In 1932, Beecher2”speculated that the functional residual capacity (FRC) was the most important of all the lung volumes that were reduced following laparotomy. In the years following those early observations, a clinical syndrome often referred to From the Department of Anesthesiology, The University of Alabama at Birmingham, Birmingham, Alabama ~~
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as ”the postoperative chest” has come to be recognized as a frequent complication following certain types of major surgery. Postoperative chest includes fever, tachycardia, dyspnea, chest pain, retained sputum, auscultatory, and radiologic changes. Current evidence would suggest that the condition is mediated by abdominal pain, muscle spasms, and other reflexes, which restrict the diaphragm and chest wall movement. The pain of the abdominal incision and peritoneal inflammation is accompanied by spasms or guarding of the muscles of the abdominal l9 Since the rectus transversus abdominis and the internal and external oblique are muscles of forced expiration, their contraction increases the abdominal pressure, raises the diaphragm, and thereby the transpulmonary pressure, which forces gas out of the lungs. In patients with pain in the postoperative period, their sustained contraction maintains a reduction in the size of the lungs throughout normal tidal ventilation, thus leading to a reduction in FRC. Studies have demonstrated that airways, mainly in dependent lung regions, could close This condition reduces or during part or all of the respiratory completely abolishes ventilation of the subtended lung units, leaving them at risk of undergoing resorption atelectasis. The volume of lung that is at risk increases as the FRC falls. Tidal volume decreases and respiratory rate increases presumably as an adaptive response to worsening pressure-volume relationships resulting from atelectasis. Intermittent sighs, which are an important part of normal respiratory pattern and allow ventilation of basal alveoli, are absent. As lung volume decreases, areas of low V/Q develop and contribute to the venous admixture, or shunt, or both, resulting in hypoxemia. On the other hand, carbon dioxide elimination is not significantly reduced and may in fact be enhanced because of the rapid respiratory rate often seen in patients with unrelieved pain. Thus, it is not unusual to see patients in this condition with arterial blood gases consistent with a respiratory alkalosis. Since the respiratory drive is no longer dependent on the CO, level, a dangerous situation leading to apnea may arise if the respiratory drive is depressed by sedatives, or if the patient were to fall asleep as a result of his or her pain relief. Provision of adequate analgesia coming after a prolonged period of unrelieved pain may paradoxically place the patient at greater risk of harm. When FRC and forced vital capacity (FVC) are reduced for prolonged periods postoperatively, the patient’s inability to cough effectively leads to retained secretions, bacterial contamination of the airway, and pneumonia. Pain not only leads to localized guarding of muscles around the area of pain, but also to generalized muscle rigidity. There is also an associated immobility of trunk and limb muscles in an attempt to reduce any movement, which would lead to an increase in pain. Vasoconstriction occurs as a result of pain-induced sympathetic discharge throughout the body. This situation predisposes the patient to PD of a different kind. Immobility and venous stasis can lead to venous thrombosis. The end result may be the occurrence of a PTE, which is the most common cause
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of sudden death in the first 10 days after surgery. Other predisposing factors to venous thrombosis include obesity, surgical procedures of prolonged duration, upper abdominal operations, prostatectomy, pancreatitis, and oral contraceptives.
Physiologic Aberrations In the hospital setting, a number of physiologic aberrations are found among patients in pain. Behavioral aberrations include immobility, a tendency to maintain the supine in preference to the upright posture, and reduced ambulation. Respiratory aberrations include decreased FRC, FVC, forced expiratory volume over 1 second (FEV,), tidal volume (TV), cough, and absence of sigh. CraigI2found that vital capacity (VC) troughed immediately after upper abdominal surgery while FRC and Paoz troughed on the first postoperative day (Fig. 1).There is also a marked dysfunction of the diaphragm. Other abnormalities include decreased immunity, which relates to the stress response, of which pain is the principal factor. The reductions in FRC, FVC, FEV,, cough,
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90 80 h
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.-$
50
f
40
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Q 0
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Figure 1. Postoperative vital capacity (squares), functional residual capacity (circles), and arterial oxygen pressure (diamonds)as a percentage of preoperative values following upper abdominal surgery. (From Craig DB: Postoperative recovery of pulmonary function. Anesth Analg 60:46-52,1981; with permission.)
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and the behavioral aberrations are affected by pain and are therefore, in most cases, improved by generic analgesia. Some of these parameters, however, may be worsened or indeed caused by the analgesic technique used. Thus, the patient who has been oversedated with narcotics may also fail to ambulate, sit up, and cough. Incidence/Diagnostic Criteria
Although transient physiologic aberrations such as decreased FRC, FVC, and VT can progress to overt pathology such as pneumonia, distinction should be made between the two conditions when considering incidence of PPD. Furthermore, atelectasis is a noninfectious complication that develops in up to 90% of patients after cardiac surgery and resolves without adverse effects in most patients, although it is often the first clinically apparent postoperative abnormality in a pathophysiologic sequence that results in bacterial contamination and development of pneumonia in 1%to 3% of all surgical procedures. Diagnostic criteria for postoperative pulmonary complications usually include radiographic abnormalities (e.g., atelectasis, lobar collapse, or infiltrate) and clinical signs or symptoms that reflect newly acquired pulmonary pathology (e.g., fever, leukocytosis, rales, bronchial breath sounds, cough, sputum production, or dyspnea). Although postoperative complication rates vary widely depending on the specific radiographic or clinical criteria used for detection, pulmonary complications after upper abdominal surgery are as common today as they were 20 years ago. However, clinical complications requiring some kind of intervention are fairly rare, occurring in about 1%to 3% of patients after elective surgery and up to 10% in patients requiring emergency surgery. The majority of studies pertaining to postoperative pulmonary dysfunction have focused on subclinical complications such as radiographic evidence of atelectasis, excessive cough, and fever. With this broad definition of complications, the incidence increases dramatically from 25% to 75% after abdominal surgery (Table 1). The contribution of atelectasis to significant morbidity and mortality is unclear, with some believing that its presence does not necessitate therapeutic intervention. Diaphragmatic Dysfunction
Typical respiratory changes after upper abdominal (UA) or thoracic (Th) surgery include a change in the pattern of breathing, increased work of breathing, and respiratory muscle dysfunction. Following cardiac surgery, left lower lobe atelectasis is present in 85% to 90% of patients in the immediate postoperative period as a result of cardiac and phrenic nerve cooling and frank manipulation. In 1983, Ford et alZo measured changes in transdiaphragmatic pressure swings and external abdominal dimensions in patients who had undergone open cholecystec-
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Table 1. INCIDENCE OF PULMONARY COMPLICATIONS AFTER UPPER ABDOMINAL SURGERY Criteria Author 1968-1 980 Wightman Latimer Van De Water Bartlett Craven Lyager
Jung 1981-1988 Alexander Celli Stock Ricksten Schwieger O’Connor Roukema
Number of Patients
PE
CXR
20 76 30 17 59 37 41
118 46 30 150 70 103 126 134 174 65 43
40 40 153
Incidence of PPC (percent)
+ + + + +
+
+ + + +
35 46 37 16
35 35 41
PPC, Postoperative pulmonary complications; PE, physical examination; CXR, chest radiography. From Miller CF, Martin J L Changes in lung function following anesthesia and surgery. In Breslow MJ, Miller CF, Rogers MC (eds): Perioperative Management. St. Louis, CV Mosby, 1990, pp 195-211; with permission.
tomy. They concluded that diaphragm function was significantly decreased after surgery. The pattern of breathing, which had previously been predominantly abdominal before surgery, became predominantly thoracic.22These findings were confirmed in another study by Simonneau et a P Interestingly, they also observed that the provision of analgesia with 150 pg of epidural fentanyl had no beneficial effect on diaphragmatic dysfunction. Fratacci et alZ2observed that thoracotomy and pulmonary resections produce a marked reduction in active diaphragmatic shortening that is not reversed by thoracic epidural anesthesia despite improvement of other indices of respiratory function. Pansard et a1 inserted electromyogram (EMG) electrodes in the diaphragms of patients undergoing abdominal aortic surgery and observed that the diaphragm EMG signal was significantly decreased on the first postoperative day.35Phrenic nerve stimulation studies on patients who had undergone upper abdominal surgery showed that there was no diminution in the contractility of the diaphragm muscle, but, rather, a reflex inhibition of phrenic nerve output was induced by surgical trauma. Ford et aPoahad previously shown the existence of such a reflex in anesthetized spontaneously breathing dogs after gall bladder manipulation. The short interval between the gall bladder stimulation and the decrease in diaphragmatic contraction suggested that a neural reflex was probably involved. The persistence of these effects following vagotomy implied that the afferents in the reflex did not travel via the
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vagus. Subsequently, Mannikian et a1 showed that provision of a thoracic epidural blockade with 0.5% bupivacaine restored the diaphragmatic function after upper abdominal surgery as measured by transdiaphragmatic pressures or by diaphragmatic EMG The epidural block also reduced the postoperative respiratory rate and increased the tidal volume to preoperative levels. It has been suggested that thoracic epidural blockade may interrupt both the afferent and the efferent portions of the neural arc. Risk Factors Obesity, chronic obstructive pulmonary disease (COPD), and smoking are major risk factors for PPD. Smokers generally suffer from chronic airflow obstruction and have increased closing volumes. Because of the perioperative decrease in FRC, a patient with obstruction who receives general anesthesia will experience greater airway closure during tidal ventilation than a patient without obstruction. A smoker also has more secretions in the lungs than a non-smoker. These two factors increase the risk of PPD after a surgical procedure in the smoker. The lung volume at which airways collapse during expiration increases with age, but is not affected by body position and presumably not by anesthesia. On the other hand, FRC is reduced by the cephalad displacement of the diaphragm on assuming the supine position. Thus, airway closure can occur early in many elderly patients when lying supine in the postoperative period. A condition termed micro-atelectasis occurs frequently, especially in obese patients undergoing upper abdominal surgery. These patients experience significant hypoxemia caused by ventilation perfusion mismatch. Site of Surgery PPD is most common after upper abdominal surgery, less common after lower abdominal surgery, and rare after surgery on the limbs and the body surface. It is less common after midthoracic than upper abdominal surgery.24Among upper abdominal incisions, the vertical midline incision is associated with greater dysfunction than the transverse (bicostal) incision. The advent of laparoscopic surgery has greatly reduced the severity of PPD.ll,38 FRC decreases more after abdominal or thoracic incisions than after lower abdominal procedures. Superficial and peripheral procedures are not associated with postoperative FRC reduction. Oxygenation (Pao,) increases postoperatively in direct proportion to the amount that FRC increases.12FVC and FEV, also decrease more after upper abdominal than after lower abdominal or superficial incisions. A subcostal incision results in a 40% to 50% fall in VC and FRC, even in patients without preexisting pulmonary disease; however,
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the ratio of FEV,/FVC usually remains normal. FRC and FVC slowly return to preoperative values over 12 days to 14 days after abdominal or thoracic procedures.12Thus, postoperative patients develop acute restrictive pulmonary defects that vary in duration and severity according to the site of surgical incisions and degree of preexisting pulmonary disease. Effects of Anesthesia
Alterations of pulmonary function commonly develop during and after anesthesia for surgery.34Clearance of mucus and inhaled particulate matter by airway cilia is markedly reduced at anesthetic concentrations of volatile agents. Tracheal mucous flow is also impaired during inhalation of either cold air or air at relative humidity less than 75%. While cuffed endotracheal tubes prevent tracheal aspiration, they also reduce tracheal mucous velocity. Using CT scanning of the chest, Hedenstierna et a1 confirmed that the combined effects of decreased cross-sectional area of the chest and cephalad displacement of the diaphragm account for reduced thoracic volume associated with decreased FRC after induction of general anesthesia.26Decreased lung volumes caused by general anesthesia, however, rapidly return to preoperative values in the early postoperative periods. Ravin et a1 found that both spinal and general anesthesia techniques were associated with identical reductions in FVC, FEV,, and Pao, at 24 hours and 48 hours following lower abdominal surgery.3yTherefore, anesthetic metabolites do not appear to mediate postoperative pulmonary abnormalities. Another argument against anesthesia as a primary mediator of late postoperative pulmonary restrictive dysfunction is the rapid return of lung volume, mechanical function, and gas exchange to preoperative values after peripheral procedures. Thus, while decreased FRC, Pao,, and varying degrees of atelectasis frequently follow the administration of general anesthesia in all patients, these abnormalities are seen postoperatively for a prolonged period only in those patients in whom the thoracic or abdominal cavity has been opened. Effect of Analgesic Therapy on Pulmonary Function Tests
Although measurements of FRC in patients before and after the provisions of anesthesia are similar, effort dependent spirometric values do show an i m p r ~ v e m e n t .Thus, ~ , ~ ~FVC and FEV, are increased. Furthermore, a positive correlation exists between a lowered FVC and the development of postoperative pulmonary complications.26b Thus, properly titrated analgesia may decrease the incidence of postoperative pulmonary complications. Wahba et a146also found that when pain was eliminated by the
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administration of epidural lidocaine, FVC increased from 37% to 55% of preoperative values. Bromage et a17 gave parenteral morphine to postoperative patients with pain and found that FEV, increased from 37% to 45% of preoperative values. Administration of either epidural local anesthetic or epidural narcotic further increased FEV, from 45% to 67% of preoperative values after upper abdominal or thoracic procedures. Functional residual capacity was not measured. Jakobsen et a P b measured FRC after providing pain relief with intercostal nerve blocks using mepivacaine 24 hours after cholecystectomy and found no change when compared to control patients. These studies suggest that pain relief may decrease postoperative splinting and partially correct spirometric abnormalities; however, pulmonary restriction remains unchanged. Furthermore, it seems unlikely that pulmonary restriction results from the effects of epidural or intercostal neural blockade because neither technique decreased FRC in volunteers who had not had surgical interventions. The usefulness of effective analgesia was further investigated by Ricksten et a140awho combined it with aggressive respiratory therapy in the form of cough and deep-breathing exercises and continuous positive airway pressure. With this combination, this group was able to show a significant decrease in the incidence of postoperative pulmonary complications in high-risk surgical patients. In an earlier study, Rawal et a140 also showed that the provision of effective analgesia in grossly obese patients undergoing gastroplasty for weight reduction, the provision of effective analgesia with epidural morphine allowed these patients to participate in more vigorous physiotherapy and allowed them to ambulate earlier compared with a similar group receiving intramuscular morphine. Thus, adequate analgesia leads to an increase in FVC, FEVI, and peak expiratory flow (PEF) and allows earlier ambulation together with improved compliance with respiratory therapy. ANALGESIC TECHNIQUES Parenteral Narcotics
Traditionally, narcotic analgesia has been administered to patients by intramuscular injection on an as-needed basis (prn). There is a large amount of interpatient variability in the minimum effective analgesic concentration (MEAC). For instance, the MEAC for meperidine can vary from 0.24 to 0.76 kg/mL for the same surgical procedure in different patients. Narcotic requirements via patient-controlled analgesia (PCA) during the first 2 to 3 days after a surgical procedure decreases, probably demonstrating that tolerance during this short postoperative time period does not develop.
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Currently, the most commonly used method of analgesia is intravenous (IV) narcotic administration. Intravenous patient-controlled analgesia (ivPCA) is gaining popularity over prn IV or IM bolus administration. Of the noninvasive techniques, it is considered to be the standard control technique by which newer techniques are compared. Intercostal nerve blocks may be used to provide postoperative analgesia in patients undergoing upper abdominal procedures. The dermatoma1 distribution of analgesia may not match the ribs anatomically, and therefore it is necessary to block two nerves above and below the affected intercostal space. Pain relief lasting up to to 18 hours after a single dose of local anesthetic has been observed. Cryoanalgesia, the application of a cryoprobe to the chosen intercostal nerves to create a temporary neurapraxia, decreases postoperative pain and narcotic requirement. In patients receiving cryoanalgesia, the occurrence of pain was usually not incisional, but was related to shoulder and arm pain as a result of pleural irritation caused by the chest tube. Analgesia from cryotherapy lasts longer than the apparent time required for wound healing. The return of sensation ranges from 2 to 3 weeks to 6 to 8 months. Return of normal sensation may take up to 1 year, and there is a high incidence of intercostal neuralgia. Interpleural analgesia, transcutaneous electrical nerve stimulation (TENS),and paravertebral nerve blocks have all been used with varying degrees of success in the treatment of acute pain (Table 2).
TYPES OF ANALGESIC TECHNIQUES AVAILABLE Epidural Opioids and Local Anesthetics
In 1976, Yaksh and R u d y observed that opioids have analgesic properaties when applied to the spinal cord; this observation was immediately applied by clinicians. Bromage et a1 were able to show that The epidural narcotics could partially restore the FEV, po~toperatively.~ advantage with epidural narcotics is they are longer acting and do not cause motor blockade or significant changes in vascular tone; they increase the ability of the patient to perform PFTs. The maximum expiratory flow rate (MEFR), FVC, and FEV, may also increase. Thus, the patient may be able to cough and breathe more deeply. Side effects, however, may include delayed respiratory depression, urinary retention, and itching. In recent years, combination narcotic and low-dose local anesthetic has gained popularity. In experimental studies, local anesthetics have been demonstrated to potentiate spinal morphine antinociception even at doses at which the drugs by themselves had little or no effect. In clinical studies, the combination of epidural local anesthetics with opioids has been demonstrated to maintain sensory analgesia and to improve pain relief after abdominal, thoracic, and gynecologic surgery,
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Table 2. TYPES OF ANALGESIC TECHNIQUES AVAILABLE Technique
Oral narcotics Parenteral narcotics
Neuraxial narcotics Neuraxial local anesthetics Intercostal nerve block Paravertebral nerve block Interpleural analgesia NSAIDs TENS Cryotherapy
Advantages
Disadvantages
Patients generally NPO after surgery IM injection painful, Ease of administration subtherapeutic & toxic levels, respiratory depression Intense analgesia Invasive, requires special expertise Good dynamic pain control Invasive, requires special expertise hypotension Good dynamic pain control Hypotension, risk of pneumothorax Good dynamic pain control Invasive, requires special Less hypotension than epidural expertise Local anesthetics Invasive, requires special Good analgesia for thoracostomy tubes expertise Risk of gastric ulceration and Good analgesia for pain of musculoskeletal origin hemorrhage, renal dysfunction Only moderately effective for Non invasive, no side effects severe pain Neuralgia is a common afterLong-term analgesia effect Ease of administration
compared with epidural local anesthesia alone, thus confirming previous experimental data.'3*25 In contrast, clinical studies comparing epidural local anesthesiaopioid mixtures with epidural opioid alone are contradictory. All but two studies addressing the administration of high-dose epidural local anesthetic showed no advantages to added epidural opioids; however, these studies failed to assess pain during activity. A shortcoming of many of the studies that have addressed pros and cons of neuraxial analgesia is that they have failed to recognize the importance of treating dynamic pain (i.e., pain upon movement). This should be held distinct from rest pain. There is an increasing body of evidence that neuraxial analgesia, especially when combined with local anesthetic, can significantly reduce dynamic pain in the postoperative period. Since deep breathing and ambulation both contribute significantly to incisional pain, they would be expected to be two of the activities that the under-analgesed patient is least likely to participate in, thereby leading to PPD. Bell found that the improvement in FEV, and inspiratory force (IF) following epidural analgesia in patients after abdominal aortic aneurysmal surgery was seen only if dynamic pain control was a~hieved.~ In another study, patients undergoing thoracic or abdominal surgery for cancer, patients who had dynamic pain control with a combination of morphine and bupivacaine epidural analgesia, recovered more quickly as judged by shorter mechanical ventilation,
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surgical intensive care unit (SICU), and hospital days.I5 This study bolsters the findings from Yeager et a1 which showed that high-risk patients undergoing epidural anesthesia and analgesia had lower costs and morbidity associated with their hospital stay than those who had undergone general anesthesia with parenteral a n a l g e ~ i a . ~ ~ Side Effects
With the discovery of spinally mediated opioid analgesia, there was some expectation that adequate analgesia could perhaps be delivered selectively to regions in the torso while avoiding changes in sensorium and respiratory depression commonly seen at higher doses of parenterally delivered narcotics. Reports of respiratory depression from rostra1 spread of spinal morphine temporarily dampened this initial enthusiasm for neuraxial opioids. Stenseth, in a series of 1085 patients using bolus doses of morphine with or without bupivacaine, reported a respiratory depression rate of o.9%.45DeLeon-Casasola et a1 reported an incidence of only 0.07% in a series of 4227 patients receiving infusions of morphine and bupivacaine.16As a result of these series, it would seem that using infusions of narcotic in the epidural space is safer than boluses. The incidence of respiratory depression has been quoted to be as high as 0.9% for intramuscular opioid therapy. Other Benefits of Epidurals
FRC is often further reduced by wound dressings, ascites, and bowel gas caused by ileus. Early mobilization and early initiation of bowel regimens would thus be expected to promote pulmonary function. Since abdominal distension caused by ileus will further increase cephalad movement of the diaphragm, any measures leading to a reduction in the duration of postoperative ileus would help pulmonary function. Liu et a129afound that an infusion of bupivacaine and morphine given epidurally in the postoperative period led to a faster resolution of ileus, when compared to IV morphine, while at the same time providing effective analgesia. Epidural infusions using local anesthetic have also been shown to decrease the incidence of deep venous thrombosis (DVT). Pain from Traumatic Injury
The issue of pain as a result of blunt chest trauma is one which deserves special mention. These patients consistently report very high pain scores as a result of continued disruption of rib periosteum during the respiratory cycle. Not surprisingly, VC, FEV,, MIP, and cough are significantly reduced. This setting lends itself to pulmonary complica-
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tions which typically occur in the first 24 hrs, especially with coexisting pulmonary contusion, and after 48 hrs in the absence of it. The latter occurs as a result of the inhibitory effects of pain on respiratory effort. All the analgesic modalities used for upper abdominal surgery have been used to treat the pain of rib fractures (Table 2). There is evidence to suggest that avoidance of tracheal intubation and mechanical ventilation may decrease morbidity in these patients, especially in the elderly. Bollinger et a1 observed that the duration of treatment and the number of days spent in the ICU were reduced in those patients treated with continuous positive airway pressure (CPAP), as opposed to those treated with mechanical ventilation and positive end-expiratory pressure (PEEP). There was also a reduction in the percentage of patients incurring infectious complication^.^ Therefore, aggressive analgesic techniques would seem logical. Aggressive treatment of pain using parenteral narcotics can lead to increased somnolence and respiratory depression. Several studies have shown an advantage to using neuraxial analgesia. Cicala et a1 compared thoracic epidural ropivacaine with lumbar epidural morphine with IV narcotic.'O Groups receiving thoracic epidural ropivacaine and lumbar epidural morphine had equivalent analgesia, which was superior to the analgesia provided with IV narcotics. The thoracic epidural group had an increased VC and FEV, and a decreased respiratory rate. Mackersie et a1 compared epidural fentanyl with IV f e n t a n ~ lBoth . ~ ~ groups had equivalent analgesia; however, the epidural fentanyl group had an increase in MIP and VC. The IV fentanyl group had an increase in VC; however, this was accompanied by an increase in PCO, and a decrease in PO,. Dittmann et a1 also studied the effects of thoracic epidural analgesia in these patients and found that use of this modality was a successful alternative to mechanical ventilation for patients who had sustained multiple rib fractures.ls There was an increase in FRC, dynamic compliance, VC, and an increase in Po2 in patients treated with the thoracic epidurals. Wisner et a1 found an improvement in analgesia, ventilatory function, morbidity, and mortality in elderly patients treated with epidural analgesia as compared to IV or IM narcotics.47 Post-Thoracotomy Pain
The pain from thoracotomy incisions has been recognized as being one of the most intense. The nociceptive afferents arise primarily from the surgical incision site, caused by disruption of the intercostal musculature and often an adjacent rib and parietal pleura. The pain arising from these structures is thus transmitted by intercostal nerves and sensed as intense, localized wound pain. Pain from the lungs and mediastinal structures is transmitted by the vagus, and although intense, is deep and poorly localized. Diaphragmatic irritation can cause pain referred to the scapula. Postoperatively, the frequent use of a thoracostomy tube ensures a continuous painful stimulus triggered with each breath. This
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intense negative reinforcement to deep breathing, combined with the fact that many of these patients have pre-existing pulmonary pathology, sets the stage for PPD. Thus the elimination of this pain is an important aspect of the postoperative care of these patients. Each of the techniques previously performed has been used for the treatment of this pain entity. Traditionally, post-thoracotomy pain has been treated with systemic opioids, most frequently administered by PCA; however, respiratory depression is of special concern in these patients since the resulting hypercarbia carries the potential risk of resultant increases in pulmonary hypertension and pulmonary edema. More recently, epidural administration of opioids, local anesthetics, or a combination of the two, has gained popularity. Several studies have compared lumbar epidurals with thoracic, since elimination of the small but not inconsequential risk of trauma to the spinal cord would be desirable. Current literature appears to support the use of a continuous infusion of either morphine or fentanyl via a thoracic catheter. Addition of LA to either of these has led to an improvement in pain scores, but also carries a greater potential for hemodynamic instability. Lumbar epidural morphine was also associated with excellent analgesia, but analgesia from lumbar epidural with fentanyl was equivalent to IV fentanyl. Nonsteroidal anti-inflammatory drugs (NSAIDs) have been found to be beneficial as adjuvants to narcotics, but do not provide any additional benefit in patients receiving optimal neuraxial analgesia. Their potential for causing gastric evasions and renal insufficiency, however, should be considered prior to initiation. In the author’s experience, the pain arising from the thoracostomy tube is significant and can be difficult to treat at times. Our institution has had good results with intermittent instillation of bupivacaine into the thoracostomy tube, followed by clamping for 10 minutes to 15 minutes (e.g., intrapleural analgesia). Shulman and colleagues43evaluated patients undergoing thoracotomy predominantly for lobectomy and evaluated the efficacy of epidural morphine and intramuscular morphine. Pain relief during the first 8 hours to 24 hours was superior for the patients receiving epidural morphine; however, at 24 hours, pain relief was similar in both groups. Also, decrements in pulmonary function were observed to be significantly less during the first 24 hours in patients who received epidural morphine. CONCLUSION
The humanitarian desire to relieve postoperative pain is sometimes overridden by the fear of potential respiratory and central nervous system side effects of opioid analgesics. Pain affects pulmonary function in a variety of ways. The intensity of the pain is important to the extent that it will inhibit mobilization of the patient in a graded manner. As a result, the quality of pain relief afforded to the patient will have a
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bearing on the speed of recovery. The quality of dynamic analgesia provided by epidural narcotic and local anesthetic combination techniques is superior to that achieved by giving narcotics by traditional methods. The best results have been shown with the use of multimodality therapy. Unfortunately, even complete relief of pain will not overcome the diaphragmatic inhibition that occurs following upper abdominal surgery. The main goals in restoring pulmonary function and reducing complications should be To eliminate pain (thus allowing clearance of secretions by coughing and deep breathing) To restore FRC to normal by early mobilization, allowing the patient to ambulate and maintain the upright posture. This will also aid restoration of gastrointestinal function, thus reducing any migration of the diaphragm. To maintain respiratory muscle function by minimizing the size of the surgical incision. To use the appropriate prophylactic measures to reduce the risk of DVT. References 1. Basran GS, Ramasubramanian R, Verma R Intrathoracic complications of acute pancreatitis. British Journal of Diseases of the Chest 81:326-331, 1987 2. Becker JM, Pemberton JH, DiMagno EP, et al: Prognostic factors in pancreatic abscess. Surgery 96:455-461, 1984 2a. Beecher HK: Effect of laparotomy on lung volume: Demonstration of a new type of pulmonary collapse. J Clin Invest 12651-658, 1932 3. Bell SD: The correlation between pulmonary function and resting and dynamic pain scores in post aortic surgery patients. (Abstract.) Anesth Analg 72 (Suppl):S18, 1991 4. Benhamou D, Samii K, Noviant Y Effect of analgesia on respiratory muscle function after upper abdominal surgery. Acta Anesthesiol Scand 2722-25, 1983 5. Bolliger CT, Van Eeden SF Treatment of multiple rib fractures: Randomized controlled trial comparing ventilatory with nonventilatory management. Chest 97943-948, 1990 6. Bonnet F, Blery C, Zatan M, et al: Effect of epidural morphine on post-operative pulmonary dysfunction. Acta Anaesthesiol Scand 28:147-151, 1984 7. Bromage PR, Camporesi E, Chestnut D: Epidural narcotics for post-operative analgesia. Anesth Analg 59:473480, 1980 8. Catley DM, Thornton C, Jordan C, et al: Pronounced, episodic oxygen desaturation in the postoperative period: Its association with ventilatory pattern and analgesic regimen. Anesthesiology 6320-28, 1985 9. Chalmers TC, Ballantyne JC, Carr DR, et al: Comparative effects of analgesic therapies upon postoperative pulmonary function: Meta-alaysis (Abstract #358). 7th World Congress of Pain, p 136, 1993 10. Cicala RS, Voeller GR, Fox T, et al: Epidural analgesia in thoracic trauma: Effects of lumbar morphine and thoracic bupivacaine on pulmonary function. Crit Care Med 18:229-231, 1990 11. Couture JG, Chartrand D, Gagner M, et al: Diaphragmatic and Abdominal Muscle Activity after endoscopic cholecystectomy. Anesth Analg 78:733-739, 1994 12. Craig DB: Postoperative recovery of pulmonary function. Anesth Analg 60:46-52,1981 13. Cuschieri RJ, Morran CG, Howie JC, et a1 Postoperative pain and pulmonary complications: Comparison of three analgesic regimens. Br J Surg 72495498, 1985
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14. Dahl JB, Rosenbert J, Hansen BL Differential analgesic effects of low-dose epidural morphine and morphine-bupivacaine at rest and during mobilization after major abdominal surgery. Anesth Analg 74:362-365, 1992 15. De Leon-Casasola OA, Parker BM, Lema MJ, et al: Epidural analgesia versus intravenous patient-controlled analgesia. Regional Anesthesia 19:307-315, 1994 16. De Leon-Casasola OA, Parker BM, Lerna MJ, et al: Post-operative epidural bupivacaine-morphine therapy. Anesthesiology 81:368-375, 1998 17. Dittmann M, Keller R, Wolff G: A rationale for epidural analgesia in the treatment of multiple rib fractures. Intensive Care Medicine 4:193-197, 1978 18. Dittmann M, Steenblock U, Kranzlin M, et al: Epidural analgesia or mechanical ventilation for multiple rib fractures? Intens Care Med 8(2):89-92, 1982 19. Duggan J, Drummond GB: Activity of lower intercostal and abdominal muscle after upper abdominal surgery. Anesth Analg 66:852-855, 1987 20. Ford GT, Whitelaw WA, Rosenal TW, et al: Diaphragmatic function after upper abdominal surgery in humans. Am Rev Respir Dis 127431435, 1987 20a. Ford GT, Grant DA, Rideout KS, et al: Inhibition of breathing associated with gallbladder stimulation in dogs. J Appl Physiol 65:72-79, 1988 21. Forster EL, Kramer JF, Lucy SD, et al: Effect of TENS on pain, medications, and pulmonary function following coronary artery bypass graft surgery. Chest 106(5):1343-1348, 1994 22. Fratacci MD, Kimball WR, Wain JC, et al: Diaphragmatic shortening after thoracic surgery in humans. Anesthesiology 79:654-665, 1993 23. Frazee RC, Roberts JW, Okeson GC, et al: Open vs laparoscopic cholecystectomy: A comparison of postoperative pulmonary function. Ann Surg 213:651-654, 1991 24. Garibaldi RA, Britt MR, Coleman ML, et al: Risk factors for postoperative pneumonia. Am J Med 70:670-680, 1981 25. George KA, Chisakuta AM, Gamble JAS, et al: Thoracic epidural infusion for postoperative pain relief following abdominal aortic surgery: Bupivacaine, fentanyl or a mixture of both? Anaesthesia 47:38-394, 1992 26. Hedenstierna H, Strandberg A, Brismar B, et al: Functional Residual Capacity, thoracoabdominal dimensions and central blood volume during general anesthesia with muscle paralysis and mechanical ventilation. Anesthesiology 62:247-254, 1985 26a. Hendolin H, et al: The effect of thoracic epidural analgesia on respiratory function after cholecystectomy. Acta Anesth Scand 31:645-651, 1987 26b. Jakobson S, et al: Effects of intercostal nerve blocks (0.5% etidocaine) on chest wall mechanics in cholecystectomized patients. Acta Anesth Scand 21:497-503, 1997 27. Jayr C, Thomas H, Rey A, et al: Postoperative pulmonary complications. Anesthesiology 78:666-676, 1993 28. Jayr C, Mollie A, Bourgain JL: Postoperative pulmonary complications: General anesthesia with postoperative parenteral morphine compared with epidural analgesia. Surgery 104(1):57-63, 1988 29. Johnston JR, McCaughey W Epidural morphine: A method of management of multiple fractured ribs. Anaesthesia 35(2):155-157, 1980 29a. Liu SS, Carpenter RL, Mackey DC, et al: Effects of perioperative analgesic technique on rate of recovery after colon surgery. Anesthesiology 83:757-765, 1995 30. Mackersie RC, Shackford SR, Hoyt DB, et al: Continuous epidural fentanyl analgesia: Ventilatory function improvement with routine use in treatment of blunt chest injury. J Trauma 27(11):1207-1212, 1987 31. Mackersie RC, Karagianes TG, Hoyt DB, et al: Prospective evaluation of epidural and intravenous administration of fentanyl for pain control and restoration of ventilatory function following multiple rib fractures. J Trauma 31(4):443449, 1991 32. Manikian 8, Cantineau TP, Bertrand M, et al: Immovement of dianhragmatic function by a thoracic extraduraiblock after upper abdokinal surgery. Anesthesiology 68:379386. ~~. , 1988 -~ 33. Miller CF, Martin JL: Changes in lung function following anesthesia and surgery. In Breslow MJ, Miller CF, Rogers MC (eds): Perioperative Management. St. Louis, CV Mosby, 1990, pp 195-211 34. Nunn JF: Effects of Anesthesia on respiration. Br J Anaesth 65:54-62, 1990 I
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35. Pansard JL, Mankikian B, Bertrand M, et al: Effects of thoracic extradural block on diaphragmatic electrical activity and contractility after upper abdominal surgery. Anesthesiology 78:63-71, 1993 35a. Pasteur W: Active lobar collapse of the lung after abdominal operations: A contribution to the study of postoperative lung complications. Lancet 2:1080-1083, 1910 36. Pflug AE, Murphy TM, Butler SH, et al: The effects of postoperative peridural analgesia on pulmonary therapy and pulmonary complications. Anesthesiology 41% 17, 1974 37. Polaner DM, Kimball WR, Fratacci MD, et al: Thoracic epidural anesthesia increases diaphragmatic shortening after thoracotomy in the awake lamb. Anesthesiology 79(4):808-816, 1993 38. Rademaker BM, Ringers J, Odoom JA, et al: Pulmonary function and stress response after laparoscopic cholecystectomy comparison with subcostal incision and influence of thoracic epidural analgesia. Anesth Analg 75:381-385, 1992 39. Ravin MB: Comparison of spinal and general anesthesia for lower abdominal surgery in patients with COPD. Anesthesiology 35:319-322, 1971 40. Rawal N, Sjostrand U, Christoffersson E, et al: Comparison of intramuscular and epidural morphine for postoperative analgesia in the grossly obese: Influence on postoperative ambulation and pulmonary function. Anesth Analg 63:583-592, 1984 40a. Rickston S, et al: Effects of periodic airway pressure by mask on postoperative pulmonary function. Chest 89:774-781, 1986 41. Scott NB, Murphy M, Kehlet H: Continuous thoracic epidural analgesia versus combined spinal/ thoracic epidural analgesia on pain, pulmonary function and the metabolic response following colonic resection. Acta Anaesthesiol Scand 40691496, 1996 42. Scott NB, Mogensen T, Greulich A, et al: No effect of continuous i.p. infusion of bupivacaine on postoperative analgesia, pulmonary function and the stress response to surgery. Br J Anaesth 61(2):165-168, 1988 43. Shulman M, Sandler AN, Bradley JW, et al: Postthoracotomy pain and pulmonary function following epidural and systemic morphine. Anesthesiology 61:569-575, 1984 44. Simonneau G, Vivien A, Sartene R, et al: Diaphragm dysfunction induced by upper abdominal surgery: Role of postoperative pain. Am Rev Respir Dis 128:899-903, 1983 45. Stenseth R, Sellevold 0, Breivik H: Epidural morphine for postoperative pain: Experience with 1085 patients. Acta Anaesthesiol Scand 29:148-156, 1985 46. Wahba WM, Don HF, Craig DB: Post-operative epidural analgesia: Effects on lung volumes. Can Anaesth SOCJ 22:519-527, 1975 47. Wisner DH: A stepwise logistic regression analysis of factors affecting morbidity and mortality after thoracic trauma: Effect of epidural analgesia. J Trauma 30:799-804,1990 47a. Yaksh TL, Rudy TA: Analgesia mediated by a direct spinal action of narcotics. Science 192:1357-1358, 1976 48. Yeager MP, Glass DD, Neff RK, et al: Epidural anesthesia and analgesia in high-risk surgical patients. Anesthesiology 66729-736, 1987 Address reprint requests to Pankaj M. Desai, MBBS, FRCA Department of Anesthesiology The University of Alabama at Birmingham 845 Jefferson Tower 619 South 19th Street Birmingham, AL 35233-6810
e-mail: PANKAJ.DESAI8CCC.UAB.EDU