Postoperative Respiratory Care

Chapter 29 

Postoperative Respiratory Care Daniel Bainbridge, MD  •  Davy C.H. Cheng, MD, MSC  •  Thomas L. Higgins, MD, MBA  •  Daniel T. Engelman, MD

Key Points 1. Cardiac anesthesia has fundamentally shifted from a high-dose narcotic technique to a more balanced approach using moderate-dose narcotics, shorter-acting muscle relaxants, and volatile anesthetic agents. 2. This new paradigm has also led to renewed interest in perioperative pain management involving multimodal techniques that facilitate rapid tracheal extubation such as regional blocks, intrathecal morphine, and supplementary nonsteroidal antiinflammatory drugs. 3. This approach has prompted a change from the classical model of recovering patients in the traditional intensive care unit manner, with weaning protocols and intensive observation, to management more in keeping with the recovery room practice of early extubation and rapid discharge. 4. Fast-track cardiac anesthesia appears to be safe in comparison with conventional high-dose narcotic anesthesia, but if complications occur that would prevent early tracheal extubation, the management strategy should be modified accordingly. 5. The initial management in the postoperative care of fast-track cardiac surgical patients consists of ensuring an efficient transfer of care from operating room staff to cardiac recovery area staff, while at the same time maintaining stable patients’ vital signs. 6. Pulmonary complications following cardiopulmonary bypass are relatively common, with up to 12% of patients experiencing some degree of acute lung injury and approximately 1% requiring tracheostomy for long-term ventilation. 7. Risk factors for respiratory insufficiency include advanced age, presence of diabetes or renal failure, smoking, chronic obstructive lung disease, peripheral vascular disease, previous cardiac operations, and emergency or unstable status. 8. Patients with preexisting chronic obstructive lung disease have higher rates of pulmonary complications, atrial fibrillation, and death. 9. Operating room events that increase risk include reoperation, blood transfusion, prolonged cardiopulmonary bypass time, and low–cardiac output states, particularly if a mechanical support device is required. 10. Hospital-acquired infections are important causes of postoperative morbidity. Strategies to reduce the incidence of ventilator-associated pneumonia include early removal of gastric and tracheal tubes, formal infection control programs, hand washing, semirecumbent positioning of the patient, use of disposable heat and moisture exchangers, and scheduled drainage of condensate from ventilator circuits. 11. Patients at risk for acute lung injury and those developing acute respiratory distress syndrome should be switched to a lung-protective ventilation strategy, which involves maintaining peak inspiratory pulmonary pressure less than 35 cm H2O and restricting tidal volumes to 6 mL/kg of ideal body weight. 12. Permissive hypercapnia may be necessary to implement a lung-protective ventilation strategy. It should be used judiciously in patients with pulmonary hypertension because

742

Postoperative Respiratory Care

acidosis can exacerbate pulmonary vasoconstriction and further impair right ventricular function and cardiac output. 13. Impediments to weaning from mechanical ventilation and extubation include delirium, unstable hemodynamic status, respiratory muscle dysfunction, renal failure with fluid overload, and sepsis. 14. Short-term weaning success can be achieved with any variety of ventilation modes. The patient receiving long-term ventilatory support requires an individualized approach that may encompass pressure-support ventilation, synchronized intermittent mandatory ventilation weaning, or T-piece trials. Noninvasive ventilation may assist in the transition from full support to liberation from mechanical ventilation. 15. A few patients are not able to be weaned from ventilation support. Characteristics of these patients include a persistent low-output state with multisystem organ failure. Long-term weaning may be best accomplished in a specialized unit rather than an acute cardiovascular recovery area.

Cardiac anesthesia itself has fundamentally shifted from a high-dose narcotic technique to a more balanced approach using moderate-dose narcotics, shorter-acting muscle relaxants, and volatile anesthetic agents. This change primarily has been driven by a realization that high-dose narcotics delay extubation and recovery after surgical procedures. This new paradigm also has led to renewed interest in perioperative pain management. In addition to changes in anesthetic practice, the type of patients presenting for cardiac operations is changing. Patients are now older and have more associated comorbidities (stroke, myocardial infarction [MI], renal failure). Change also has taken place in the recovery of patients undergoing cardiac procedures. Although cardiac surgical procedures often were associated with a high mortality rate and long intensive care unit (ICU) stays, the use of moderate doses of narcotics has allowed for rapid ventilator weaning and discharge from the ICU within 24 hours. This change has prompted a shift from the classical model of recovering patients in the traditional ICU manner, with weaning protocols and intensive observation, to management more in keeping with the recovery room practice of early extubation and rapid discharge. 29

FAST-TRACK CARDIAC SURGICAL CARE Anesthetic Techniques Few trials have compared inhalation agents for fast-track cardiac anesthesia (FTCA). Several studies examined the effectiveness of propofol versus an inhalation agent; these studies demonstrated reductions in myocardial enzyme release (creatine kinase myocardium band [CK-MB], troponin I) and preservation of myocardial function in patients receiving inhalation agents. The choice of muscle relaxant in FTCA is important to reduce the incidence of muscle weakness in the cardiac recovery area (CRA) that may delay tracheal extubation. Several randomized trials compared rocuronium (0.5–1 mg/kg) with pancuronium (0.1 mg/kg) and found significant differences in residual paralysis in the ICU, with delays in the time to extubation in the pancuronium-treated group. Several trials examined the use of different short-acting narcotic agents during FTCA. In these trials, fentanyl, remifentanil, and sufentanil all were found to be efficacious for early tracheal extubation. The anesthetic drugs and their suggested dosages are listed in Box 29.1. 743

Postoperative Care

BOX 29.1 

Suggested Dosages for Fast-Track Cardiac Anesthesia

Induction Narcotic Fentanyl 5–10 µg/kg Sufentanil 1–3 µg/kg Remifentanil– infusions of 0.5–1.0 µg/kg per min Muscle Relaxant Rocuronium 0.5–1 mg/kg Vecuronium 1–1.5 mg/kg Hypnotic Midazolam 0.05–0.1 mg/kg Propofol 0.5–1.5 mg/kg

Maintenance Narcotic Fentanyl 1–5 µg/kg Sufentanil 1–1.5 µg/kg Remifentanil infusions of 0.5–1.0 µg/kg per min Hypnotic Inhalational 0.5–1 MAC Propofol 50–100 µg/kg per min

Transfer to Cardiac Recovery Area Narcotic Morphine 0.1–0.2 mg/kg Hypnotic Propofol 25–75 µg/kg per min

VI

MAC, Minimum alveolar concentration. Data from Mollhoff T, Herregods L, Moerman A, et al. Comparative efficacy and safety of remifentanil and fentanyl in ‘fast track’ coronary artery bypass graft surgery: a randomized, double-blind study. Br J Anaesth. 2001;87:718; Engoren M, Luther G, Fenn-Buderer N. A comparison of fentanyl, sufentanil, and remifentanil for fast-track cardiac anesthesia. Anesth Analg. 2001;93:859; and Cheng DC, Newman MF, Duke P, et al. The efficacy and resource utilization of remifentanil and fentanyl in fast-track coronary artery bypass graft surgery: a prospective randomized, double-blinded controlled, multi-center trial. Anesth Analg. 2001;92:1094.

Evidence Supporting Fast-Track Cardiac Recovery Several randomized trials and one metaanalysis of randomized trials addressed the question of safety of FTCA. None of the trials was able to demonstrate differences in outcomes between the fast-track anesthesia group and the conventional anesthesia group. The metaanalysis of randomized trials demonstrated a reduction in the duration of intubation by 8 hours (Fig. 29.1) and in the ICU length of stay (LOS) by 5 hours in favor of the fast-track group. However, the hospital LOS was not statistically different. FTCA appears safe in comparison with conventional high-dose narcotic anesthesia. It reduces the duration of ventilation and ICU LOS considerably without increasing the incidence of awareness or other adverse events. FTCA appears effective at reducing costs and resource use. As such, it is becoming the standard of care in many cardiac 744

Postoperative Respiratory Care

Favors FTCA

Favors TCA

Slogoff Cheng Myles 1997 Michalopoulos Sakaida Silbert Berry Myles 2002 Overall (95%Cl) –20

–15

–10

–5

0

5

10

Weighted mean difference (h) Fig. 29.1  Forrest plot showing the weighted mean difference in extubation times. The overall effect was an 8.1-hour reduction in extubation times. CI, Confidence interval; FTCA, fast-track cardiac anesthesia; TCA, traditional cardiac anesthesia. (Data from Myles PS, Daly DJ, Djaiani G, et al. A systematic review of the safety and effectiveness of fast-track cardiac anesthesia. Anesthesiology. 2003;99[4]:982–987.)

centers. The usual practice at many institutions is to treat all patients as candidates for FTCA with the goal of allowing early tracheal extubation for every patient. However, if complications occur that would prevent early tracheal extubation, the management strategy is modified accordingly. Investigators have demonstrated that the risk factors for delayed tracheal extubation (>10 hours) are increased age, female sex, postoperative use of intraaortic balloon pump (IABP), inotropes, bleeding, and atrial arrhythmia. The risk factors for prolonged ICU LOS (>48 hours) are those of delayed tracheal extubation in addition to preoperative MI and postoperative renal insufficiency. Care should be taken to avoid excessive bleeding (antifibrinolytic agents) and to treat arrhythmias either prophylactically or when they occur (β-blockers, amiodarone).

INITIAL MANAGEMENT OF PATIENTS IN FAST-TRACK CARDIAC ANESTHESIA: THE FIRST 24 HOURS On arrival in the CRA, initial management of cardiac patients consists of ensuring an efficient transfer of care from operating room (OR) staff to CRA staff while at the same time maintaining stable patient vital signs. The anesthesiologist should relay important clinical parameters to the CRA team. To accomplish this, many centers have devised handoff sheets to aid in the transfer of care. The patient’s temperature should be recorded, and, if low, active rewarming measures should be initiated with the goal of rewarming the patient to 36.5°C. Shivering may be treated with low doses of meperidine (12.5–25 mg, intravenously). Hyperthermia, however, is common later within the first 24 hours after cardiac operations and may be associated with an increase in neurocognitive dysfunction, possibly a result of hyperthermia exacerbating cardiopulmonary bypass (CPB)–induced neurologic injury (Box 29.2). 745

29

Postoperative Care

BOX 29.2

Initial Management of the Fast-Track Cardiac Anesthesia Patient

Normothermia Hemoglobin >7 g/dL Paco2 35–45 mm Hg Sao2 >95% Mean blood pressure >50–70 mm Hg Potassium: 3.5–5.0 mEq/L Blood glucose <10.0 mmol/L (<200 mg/dL) PaCO2, Partial pressure of arterial carbon dioxide; SaO2, arterial oxygen saturation.

BOX 29.3 

Ventilation Management Goals During the Initial Trial of Weaning From Extubation

Initial Ventilation Parameters A/C at 10–12 beats/min Tidal volume 8–10 mL/kg PEEP 5 cm H2O

Maintenance of Arterial Blood Gases pH 7.35–7.45 Paco2 35–45 mm Hg Pao2 >90 mm Hg Saturations >95%

Extubation Criteria VI

Arterial blood gases as above Awake and alert Hemodynamically stable No active bleeding (<400 mL/2 h) Temperature >36°C Return of muscle strength (>5 s, head lift/strong hand grip) A/C, Assist-controlled ventilation; PaCO2, partial pressure of arterial carbon dioxide; PaO2, partial pressure of arterial oxygen; PEEP, positive end-expiratory pressure.

Ventilation Management: Admission to Tracheal Extubation Ventilatory requirements should be managed with the goal of early tracheal extubation in patients (Box 29.3). Arterial blood gases (ABGs) are initially drawn within one-half hour after admission and then repeated as needed. Patients should be awake and cooperative, hemodynamically stable, and have no active bleeding with coagulopathy. Respiratory strength should be assessed by hand grip or head lift to ensure complete reversal of neuromuscular blockade. The patient’s temperature should be more than 746

Postoperative Respiratory Care

36°C, preferably normothermic. When these conditions are met and ABG results are within the reference range, tracheal extubation may take place. ABGs should be drawn approximately 30 minutes after tracheal extubation to ensure adequate ventilation with maintenance of partial pressure of arterial oxygen (PaO2) and partial pressure of arterial carbon dioxide (PaCO2). Inability to extubate patients as a result of respiratory failure, hemodynamic instability, or large amounts of mediastinal drainage necessitates more complex weaning strategies. Some patients may arrive after extubation in the OR. Careful attention should be paid to these patients because they may subsequently develop respiratory failure. The patient’s respiratory rate should be monitored every 5 minutes during the first several hours. ABGs should be drawn on admission and 30 minutes later to ensure that the patient is not retaining carbon dioxide. If the patient’s respirations become compromised, ventilatory support should be provided. Simple measures such as reminders to breathe may be effective in the narcotized or anesthetized patient. Low doses of naloxone (0.04 mg, intravenously) also may be beneficial. Trials of continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP), or noninvasive ventilation (NIV) may provide enough support to allow adequate ventilation. Reintubation should be avoided because it may delay recovery; however, it may become necessary if the earlier mentioned measures fail, with resulting hypoxemia, hypercarbia, and a declining level of consciousness.

Management of Bleeding Chest tube drainage should be checked every 15 minutes after ICU admission to assess a patient’s coagulation status. Although blood loss is commonly divided into two types, surgical or medical, determining the cause of bleeding is often difficult. When bleeding exceeds 400 mL/hour during the first hour, 200 mL/hour for each of the first 2 hours, or 100 mL/hour over the first 4 hours, returning the patient to the OR for chest reexploration should be considered. The clinical situation must be individualized for each patient, however, and in patients with known coagulopathy, more liberal blood loss before chest reexploration may be acceptable (Box 29.4).

Electrolyte Management

29

Hypokalemia is common after cardiac surgical procedures, especially if diuretic agents were given intraoperatively. Hypokalemia contributes to increased automaticity and may lead to ventricular arrhythmias, ventricular tachycardia, or ventricular fibrillation.

BOX 29.4 

Management of the Bleeding Patient

Review activated coagulation time, prothrombin time, international normalized ratio, and platelet count Administer protamine if bleeding is caused by excess heparin (reinfusion of pump blood) Treat the medical cause with platelets, fresh-frozen plasma, and cryoprecipitate if bleeding is secondary to decreased fibrinogen Factor VIIa should be considered if bleeding continues despite a normal coagulation profile Treat the surgical cause with reexploration

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Postoperative Care

BOX 29.5 

Common Electrolyte Abnormalities and Possible Treatment Options

Hypokalemia (Potassium <3.5 mmol/L) SSx: muscle weakness, ST-segment depression, “u” wave, T-wave flat, ventricular preexcitation Rx: IV KCl at 10–20 mEq/h by central catheter

Hyperkalemia (Potassium >5.2 mmol/L) SSx: muscle weakness, peaked T wave, loss of P wave, prolonged PR/QRS Rx: CaCl2 1 g, insulin/glucose, HCO3−, diuretics, hyperventilation, dialysis

Hypocalcemia (Ionized Calcium <1.1 mmol/L) SSx: hypotension, heart failure, prolonged QT interval Rx: CaCl2 or calcium gluconate

Hypercalcemia (Ionized Calcium >1.3 mmol/L) SSx: altered mental state, coma, ileus Rx: dialysis, diuretics, mithramycin, calcitonin

Hypermagnesemia (Magnesium >0.7 mmol/L) SSx: weakness, absent reflexes Rx: stop magnesium infusion, diuresis

Hypomagnesemia (Magnesium <0.5 mmol/L) SSx: arrhythmia, prolonged PR and QT intervals Rx: magnesium infusion 1 to 2 g CaCl2, Calcium chloride; HCO3−, bicarbonate; IV KCl, intravenous potassium chloride; Rx, treatment; SSx, signs and symptoms.

VI

Treatment consists of potassium infusions (20 mEq potassium in 50 mL of D5W infused over 1 hour) until the potassium level exceeds 3.5 mEq/mL. In patients with frequent premature ventricular contractions caused by increased automaticity, a serum potassium level of 5.0 mEq/mL may be desirable. Hypomagnesemia contributes to ventricular preexcitation and may contribute to atrial fibrillation (AF). This disorder is common in malnourished and chronically ill patients, a frequent occurrence in the cardiac surgical setting. Management consists of intermittent boluses of magnesium: 1 to 2 g over 15 minutes. Hypocalcemia also is frequent during cardiac operations and may reduce cardiac contractility. Intermittent boluses of calcium chloride or calcium gluconate (1 g) may be required (Box 29.5).

Pain Control Pain control after cardiac surgical procedures has become a concern as narcotic doses have been reduced to facilitate fast-track protocols. Intravenous morphine or hydromorphone is still the mainstay of treatment in patients after cardiac operations. The most common approach is patient-demanded, nurse-delivered intravenous morphine, and this treatment remains popular because of the 1 : 1 to 1 : 2 nursing typically 748

Postoperative Respiratory Care

BOX 29.6 

Pain Management Options After Cardiac Surgical Procedures

Patient-Controlled Analgesia Possible benefit in a step-down unit Reduced 24-hour morphine consumption in two of seven randomized trials

Intrathecal Morphine Doses studied: 500 µg to 4 mg Possible benefit in reducing intravenous morphine use Possible benefit in reducing VAS pain scores Potential for respiratory depression Ideal dosing not ascertained; range, 250–400 µg

Thoracic Epidural Regimens Common dosages from literature: Ropivacaine 1% with 5 µg/mL fentanyl at 3–5 mL/h Bupivacaine 0.5% with 25 µg/mL morphine at 3–10 mL/h Bupivacaine 0.5–0.75% at 2–5 mL/h Reduced pain scores Shorter duration of intubation Risk for epidural hematoma difficult to quantify

Nonsteroidal Antiinflammatory Drugs Common dosages from literature: Indomethacin 50–100 mg PR bid Diclofenac 50–75 mg PO/PR q8h Ketorolac 10–30 mg IM/IV q8h Reduces narcotic utilization Many different drugs studied; difficult to determine superiority of a given agent Possible increase in serious adverse events (trial using cyclooxygenase-2–specific inhibitors) bid, Twice daily; IM, intramuscularly; IV, intravenously; PO, orally; PR, rectally; VAS, visual analog scale.

29

provided during cardiac recovery. However, with a change to more flexible nurse coverage and therefore higher nurse-to-patient ratios, patient-controlled analgesia (PCA) morphine use has become increasingly popular. However, young patients, those who took opioids preoperatively, or patients transferred to a regular ward on the day of the operation may benefit from PCA for pain management (Box 29.6).

MANAGEMENT OF POSTOPERATIVE COMPLICATIONS Complications are frequent after cardiac surgical procedures. Although many are short-lived, some complications (eg, stroke) are long-term catastrophic events that seriously affect a patient’s functional status. The incidence and predisposing risk factors are well studied for many of these complications. Many complications have specific management issues that may improve postoperative recovery (Box 29.7). 749

Postoperative Care

BOX 29.7 

Treatment for Complications After Cardiac Surgical Procedures

Stroke • Supportive treatment • Avoidance of potential aggravating factors (eg, hyperglycemia, hyperthermia, severe anemia)

Delirium • Usually self-limited • Close observation required • Sedatives (midazolam, lorazepam) possibly required

Atrial Fibrillation • Rate control: calcium channel blockers, β-blockers, digoxin • Rhythm control: amiodarone, sotalol, procainamide • Thromboembolic prophylaxis: for atrial fibrillation >48 h

Left Ventricular Dysfunction • Volume • Inotropes: epinephrine, milrinone, norepinephrine • Mechanical support: intraaortic balloon pump

Renal Failure • Removal of the causative agent (nonsteroidal antiinflammatory drugs, antibiotics) • Hemodynamic support if necessary • Supportive care

RISK FACTORS FOR RESPIRATORY INSUFFICIENCY VI

Some cardiac surgical patients can be expected to have respiratory complications. Acute lung injury (ALI), sometimes progressing to acute respiratory distress syndrome (ARDS), can occur in up to 12% of postoperative cardiac patients. Approximately 6% of cardiovascular surgical patients require more than 72 hours on the ventilator, and approximately 1% of patients undergo tracheostomy to facilitate recovery and weaning from prolonged support with mechanical ventilation. The lung is especially vulnerable because disturbances may affect it directly (atelectasis, effusions, pneumonia) or indirectly (from fluid overload in heart failure; as the result of mediator release from CPB, shock states, or infection; or from changes in respiratory pump function, as with phrenic nerve injury). Postoperative status is determined in part by the patient’s preoperative pulmonary reserve, as well as by the level of stress imposed by the procedure. Thus a patient with reduced vital capacity as a result of restrictive lung disease who is undergoing a minimally invasive surgical procedure may have fewer postoperative pulmonary issues than a relatively healthy patient who is undergoing simultaneous coronary artery bypass grafting (CABG) and valve replacement with its longer accompanying operative, anesthetic, and CPB times. Respiratory muscle weakness contributes to postoperative pulmonary dysfunction, and prophylactic inspiratory muscle training has been shown to improve respiratory 750

Assessing Risk Based on Preoperative Status The Society of Thoracic Surgeons National Adult Cardiac Surgery Database is widely used in the United States, and it offers, in addition to a mortality prediction, a model customized to predict prolonged ventilation. The European System for Cardiac Operative Risk Evaluation (EuroSCORE) is commonly used in Europe. Factors common to outcome risk adjustment models include age, sex, body surface area, presence of diabetes or renal failure, chronic lung disease, peripheral vascular disease, cerebrovascular disease, previous cardiac operation, and emergency or unstable status. Patients with preexisting chronic obstructive pulmonary disease have higher rates of pulmonary complications (12%), atrial fibrillation (27%), and death (7%).

Postoperative Respiratory Care

muscle function, pulmonary function test results, and gas exchange, as well as reducing the incidence of delayed extubation.

Operating Room Events Identification of the patient who is difficult to intubate is important for planning extubation for a time when sufficient personnel and equipment are available to implement a potentially difficult reintubation. Patients undergoing reoperation are at risk partly because of longer CPB times with reoperation, increased use of blood transfusion, and the additional likelihood of bleeding in this population. Length of time on CPB is repeatedly identified as a risk factor, and a correlation between CPB time and inflammatory cytokine release has been demonstrated.

Postoperative Events The expected ICU course, if the patient is not extubated “on the table,” is a short period of ventilation support while the patient is warmed, allowed to awaken, and observed for bleeding or hemodynamic instability. In low-risk patients, shortstay (8-hour) protocols can deliver clinical results at lower cost comparable to a standard overnight ICU stay. Preoperative risks, issues with difficult intubation, and operating room events should be communicated from the operating room team to the ICU team at the time of ICU admission. Box 29.8 outlines criteria to be met before routine extubation. Health care–acquired infections are important causes of postoperative morbidity and increased costs, and include pneumonia, sepsis, and Clostridium difficile colitis. Hospital-acquired pneumonia, and specifically ventilator-acquired pneumonia (VAP), may occur in any patient receiving continuous mechanical ventilation. Studies quote rates of hospital-acquired pneumonia of 3% to 8% for cardiac surgical patients, when assessed by criteria used by the Centers for Disease Control and Prevention (CDC), but these rates are lower when assessed by clinicians taking into account alternate explanations for new infiltrates, tachypnea, or hypoxemia. The historical risk of VAP in ICU patients was approximately 1%/day of ventilation when VAP was diagnosed using protected specimen brush and quantitative culture techniques. Strategies believed to be effective at reducing the incidence of VAP include early removal of nasogastric or endotracheal tubes, formal infection control programs, hand washing, semirecumbent positioning of the patient, daily sedation “vacations,” avoidance of unnecessary reintubation, adequate nutritional support, avoidance of gastric overdistension, use of the oral rather than the nasal route for intubation, scheduled drainage of condensate from ventilator circuits, and maintenance of adequate endotracheal tube cuff pressure. 751

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Postoperative Care

BOX 29.8 

Criteria to Be Met Before Early Postoperative Extubation

Neurologic: Awake, neuromuscular blockade fully dissipated (head lift ≥5 s); following instructions, able to cough and protect airway Cardiac: Stable without mechanical support; cardiac index ≥2.2 L/m2 per min; MAP ≥70 mm Hg; no serious arrhythmias Respiratory: Acceptable CXR and ABGs (pH ≥7.35); minimal secretions, comfortable on CPAP or T-piece with spontaneous respiratory rate ≤20 breaths/min; MIP ≥25 cm H2O; alternatively, a successful SBT defined as an RSBI <100 and a Pao2/Fio2 ≥200 Renal: Undergoing diuresis well; urine output >0.8 mL/kg per h; not markedly fluidoverloaded from operative or CPB fluid administration or SIRS Hematologic: Chest tube drainage minimal Temperature: Fully rewarmed; not actively shivering ABG, Arterial blood gas; CPAP, continuous positive airway pressure; CPB, cardiopulmonary bypass; CXR, chest radiograph; MAP, mean arterial pressure; MIP, maximal inspiratory pressure; PaO2/FIO2, ratio of arterial partial pressure of oxygen to fraction of inspired oxygen; RSBI, rapid shallow breathing index; SBT, spontaneous breathing trial; SIRS, systemic immune response syndrome.

Diagnosis of Acute Lung Injury and Acute Respiratory Distress Syndrome

VI

ARDS may develop as a sequela of blood transfusion or CPB, or, more commonly in the postoperative patient, it is associated with cardiogenic shock, sepsis, or multisystem organ failure. Components of ARDS include diffuse alveolar damage resulting from endothelial and type I epithelial cell necrosis and noncardiogenic pulmonary edema caused by breakdown of the endothelial barrier with subsequent vascular permeability. The exudative phase of ARDS occurs in the first 3 days after the precipitating event and is thought to be mediated by neutrophil activation and sequestration. Ultimately the alveolar spaces fill up with fluid as a result of increased endothelial permeability. The clinical presentation is typically an acute onset of severe arterial hypoxemia refractory to oxygen therapy, with a ratio of arterial oxygen partial pressure to fraction of inspired oxygen (PaO2/FIO2 or P/F ratio) of less than 200 mm Hg. ARDS is classically diagnosed only in the absence of left ventricular failure, a factor that complicates the diagnosis in the postoperative cardiac patient, who may also be in heart failure. Other findings in ARDS include decreased lung compliance (<80 mL/cm H2O) and bilateral infiltrates on chest radiographs. The proliferative phase of ARDS occurs on days 3 to 7 as inflammatory cells accumulate in response to chemoattractants released by the neutrophils. At this stage, the normal repair process removes debris and begins repair, but a disordered repair process may result in exuberant fibrosis, stiff lungs, and inefficient gas exchange. Evidence suggests that careful fluid and ventilator management may affect this process. Current clinical practice in patients with known or suspected lung injury is to limit inflation pressures. The maximal “safe” inflation pressure is not known, but evidence favors keeping peak inspiratory pressures lower than 35 cm H2O and restricting tidal volumes to less than 6 mL/kg of ideal body weight in patients at risk for ALI. 752

Maintaining a lung-protective ventilatory strategy involves permissive hypercapnia if normal partial pressure of carbon dioxide (PCO2) levels cannot be achieved with low tidal volumes. The acid-base changes must be monitored carefully, especially in patients with reactive pulmonary vasculature. Lower tidal volumes with increasing amounts of positive end-expiratory pressure (PEEP) may promote alveolar recruitment and thus improve oxygenation. Taken to an extreme, patients with ALI may be ventilated with high-frequency oscillation, which is essentially high PEEP with tiny (smaller than dead space), frequently delivered tidal volumes. Other techniques for patients in whom conventional therapy is failing include extracorporeal CO2 removal, extracorporeal membrane oxygenation (ECMO), inhaled nitric oxide, and inhaled prostacyclin. Inhaled nitric oxide has an established role in reducing right ventricular dysfunction when pulmonary hypertension compromises heart transplantation. Healthy cardiac surgical patients generally do not require much PEEP. Higher levels of PEEP may decrease cardiac output, unless volume loading is used to stabilize preload by maintaining transmural filling pressures. The effects of PEEP are most marked in the presence of abnormal right ventricular function, particularly if the right coronary artery is compromised. PEEP neither protects against the development of ARDS nor reduces the amount of mediastinal bleeding after cardiac surgical procedures involving CPB. Most clinicians routinely use 5 cm H2O of PEEP in ventilated patients. However, higher levels of PEEP (often 8–15+ cm H2O) may be necessary to maintain adequate oxygenation with ALI or developing ARDS; application of PEEP in the postsurgical patient usually involves balancing cardiac and pulmonary goals.

Postoperative Respiratory Care

ADDITIONAL THERAPY IN PATIENTS WITH ACUTE LUNG INJURY OR ACUTE RESPIRATORY DISTRESS SYNDROME

IMPEDIMENTS TO WEANING AND EXTUBATION Factors limiting the removal of mechanical ventilatory support include delirium, neurologic dysfunction, unstable hemodynamic status, respiratory muscle dysfunction, renal failure with fluid overload, and sepsis. Fig. 29.2 outlines one approach to identifying readiness to wean from ventilation and possible alternative approaches to weaning. Early mobilization, including formal exercise programs, can enhance recovery from the catabolic muscle loss with critical illness.

MODES OF VENTILATOR SUPPORT Positive-pressure ventilators used outside the operating room have a non-rebreathing circuit, may be volume- or pressure-limited, and may be triggered by changes in flow or changes in pressure. All modern ventilators contain multiple modes of ventilation support that accommodate both mandatory and patient-triggered breaths. The most common modes of positive-pressure ventilation are assist-control (A/C), synchronized intermittent mandatory ventilation (SIMV), and pressure-support ventilation (PSV). With volume modes, the inspiratory flow rate, targeted volume, and inspiratory time are set by the clinician, and inspiratory peak pressure varies depending on the patient’s lung compliance and synchrony with the ventilator. Volume cycling ensures consistent delivery of a set tidal volume, as long as the pressure limit is not exceeded. With nonhomogeneous lung disorders, however, delivered volume tends to flow to areas of low resistance; this may result in overdistension of healthy segments of lung and 753

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Postoperative Care

Examine patient and assess readiness for weaning (must satisfy all criteria below) Hemodynamically stable off pressor/inotrope infusions Minute ventilation < 12 L/min PO2 > 60 mm Hg at FIO2 < 0.60 and PEEP < 10 cm H2O f/VT < 105 on brief trial of spontaneous breathing MIP < –25 cmH2O and spontaneous VT ≥ 5 mL/kg Respiratory drive intact (neurologic status, drugs)

Criteria met? Yes

No

Trial of spontaneous breathing through ETT

Fail

Sustained for > 30 minutes without distress? (RR < 35, SpO2 > 90%; HR < 20% increase, SBP 90 to 180; minimal anxiety or diaphoresis) Pass Upper airway patent? (consider leak test) Able to cough and clear secretions? Capable of protecting airway? Yes Extubate Tube feeding must be off for 1 hour

No

Leave ETT in place, perhaps with low-level pressure support while addressing airway patency, neurologic status and/or secretions

VI

• Full support modes: Assist/control or SIMV sufficient to ablate spontaneous respiratory drive • Weaning modes: If patient is on SIMV plus PSV, convert to PSV alone. Initial PSV level usually 2/3 peak inspiratory pressure delivered on A/C or SIMV • Wean PSV in small increments (1 to 2 cm H2O as long as f/VT ≤ 50 and RR ≤ 30 bpm • Alternate weaning modes: see box below

Resume mechanical ventilation with either pressure support or assist/control; continue once-daily trials of spontaneous breathing

Progress stalled? Search for and correct causes: Renal/fluids Neurologic Hematologic Psychological Cardiac Infectious Iatrogenic Respiratory Nutritional

Institute ancillary measures: • Physical and occupational therapy (patient must be able to support weight and eventually walk with assistance) • Tracheostomy for > 14 days anticipated ETT • Involve patient in weaning process • Prevent decubitus (specialized beds)

Alternate approaches: IMV weaning: Set initial rate low enough to encourage breathing over machine rate; decrease IMV rate by 2 as long as RR < 24; pH > 7.32 and patient remains stable and comfortable T-Piece weaning: Begin with 1- to 2-minute spontaneous trials every 2 hours and increase duration as tolerated without patient distress

Fig. 29.2  This flow chart addresses care of patients receiving both short-term and long-term ventilatory support in the cardiothoracic intensive care unit. All patients require periodic assessment for readiness for weaning, and if they meet criteria they are eligible for spontaneous trials leading to extubation. Patients who do not meet the criteria should have mechanical ventilation maintained until criteria are met. Pressure-support ventilation (PSV) weaning may be possible; if not, alternative approaches include intermittent mandatory ventilation (IMV) weaning and T-piece weaning. Patients who stall in their weaning progress should have a comprehensive examination and an assessment of organ systems to search for correctable causes. A/C, Assist-control mode; bpm, breaths per minute; ETT, endotracheal tube; FIO2, ratio of arterial partial pressure of oxygen to fraction of inspired oxygen; f/VT, frequency-to-tidal volume ratio; HR, heart rate; MIP, maximal inspiratory pressure; PEEP, positive end-expiratory pressure; PO2, partial pressure of oxygen; RR, respiratory rate; SBP, systolic blood pressure; SIMV, synchronized intermittent mandatory ventilation; SpO2, oxygen saturation measured with pulse oximetry.

underinflation of atelectatic segments with consequent ventilation/perfusion (V̇ /Q̇ ) mismatching. Intermittent mandatory ventilation (IMV) and later SIMV were developed to facilitate weaning from mechanical ventilatory support. With either IMV modality, a basal respiratory rate is set by the clinician that may be supplemented by patientinitiated breaths. In contrast to A/C ventilation, however, the tidal volume of the patient’s spontaneous breaths is determined by the patient’s own respiratory strength and lung compliance rather than delivered as a preset volume. SIMV mode is appropriate for patients with normal lungs who are recovering from opioid anesthesia. Weaning is accomplished by reducing the mandatory IMV rate and allowing the patient to assume more and more of the respiratory effort over time. SIMV mode has been used for weaning in patients with complex cases, but the weaning effort may stall at very low IMV rates if the patient cannot achieve spontaneous volumes sufficient to 754

Pressure-Support Ventilation PSV, which is primarily a weaning tool, must be distinguished from pressure-control ventilation, which is generally used during the maintenance phase of ventilation. PSV may be used in conjunction with CPAP or SIMV modes. Pressure support augments the patient’s spontaneous inspiratory effort with a clinician-selected level of pressure. Putative advantages include improved comfort for the patient, reduced ventilatory work, and faster weaning. The volume delivered with each PSV breath depends on the pressure set for inspiratory assist, as well as the patient’s lung compliance. The utility of PSV in weaning from long-term ventilation support is that it allows the patient’s ventilatory muscles to assume part of the workload while augmenting tidal volume, thus preventing atelectasis, sufficiently stretching lung receptors, and keeping the patient’s spontaneous respiratory rate within a reasonable physiologic range.

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activate the pulmonary stretch receptors. Under these circumstances, the patient is likely to become tachypneic, and weaning attempts will fail.

LIBERATION FROM MECHANICAL SUPPORT (WEANING) When terminating mechanical ventilation, two phases of decision making are involved. First, resolution of the initial process for which mechanical ventilation was begun should occur. The patient cannot have sepsis, be hemodynamically unstable, or be burdened with excessive respiratory secretions. If these general criteria are met, then specific weaning criteria can be examined. These include oxygenation (typically a PaO2 >60 mm Hg on 35% inspired oxygen and low levels of PEEP), adequate oxygen transport (measurable by oxygen extraction ratio or assumed if the cardiac index is adequate and lactic acidosis is not present), adequate respiratory mechanics (tidal volume, maximal inspiratory pressure) and adequate respiratory reserve (minute ventilation at rest of <10 L/min), and a low frequency-to–tidal volume ratio (f/Vt <100; see next section) indicating adequate volume at a sustainable respiratory rate. 29

Weaning: the Process The actual process of weaning from mechanical ventilatory support must be individualized. No “one size fits all” method exists. While gradually lowering the SIMV rate in increments of two breaths/minute generally works for short-term ventilatory support, patients receiving long-term ventilatory support often have difficulty making the transition from SIMV rates of two breaths/minute to CPAP. The time-honored method of weaning by maintaining a patient on full ventilatory support and alternating with increasingly longer periods of spontaneous ventilation on a T-piece is effective, but it is time consuming because it requires setting up additional equipment and also requires a nurse or respiratory therapist to be immediately available at the bedside during each weaning attempt. Diaphragmatic effort is significantly lower during a T-piece trial with a deflated tracheostomy tube cuff than with the cuff inflated. Weaning trials with the cuff deflated may thus be more physiologic when attempting weaning from the ventilator in a patient for whom this process is difficult. Breath-to-breath monitoring, display of tidal volumes, and ventilator alarms are not available during a T-piece trial. More commonly, pressure support is used as an adjunct to weaning either with IMV or CPAP while the patient is still connected to the ventilator and its alarm system. 755

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Our preference is to conduct CPAP weaning with pressure support alone (ie, no additional IMV rate) because mechanical ventilation introduces one more variable into the evaluation of a patient’s progress. Sufficient CPAP is applied to maintain open alveoli (generally 5–8 cm H2O, but often higher when recovering from ALI or ARDS), and then the pressure-support level is titrated to provide the patient with sufficient tidal volume to achieve a respiratory rate lower than 24 breaths/minute. Rapid rates are detrimental to weaning, because diaphragmatic blood flow is limited during contraction. As the patient’s exercise tolerance improves, the pressure-support level can be lowered in increments of 2 to 3 cm H2O. It is usually necessary to address fluid overload, nutritional support, and other nonpulmonary factors to achieve the pressure-support reduction.

Specific Impediments to Weaning Weaning from ventilator support affects cardiac output in response to changes in pulmonary vascular resistance. Increased pulmonary vascular resistance can lead to septal shifts and consequent changes in the efficiency of right ventricular and left ventricular function. Thus it makes little sense to attempt weaning in the hemodynamically unstable patient. Our approach has been to keep these patients on full ventilator support with sedation and neuromuscular blockade if necessary until the acute cardiac problem is resolved.

Tracheostomy Prolonged endotracheal intubation results in damage to the respiratory epithelium and cilia and may lead to vocal cord damage and airway stenosis. If mechanical ventilation is anticipated for longer than 14 days, consideration should be given to early tracheostomy. Other indications for tracheostomy include copious or tenacious secretions in debilitated patients who are unable to clear secretions spontaneously. Tracheostomy is relatively contraindicated in patients with ongoing mediastinitis or local infection at the tracheostomy site because of the potential for mediastinal contamination with respiratory secretions. VI

Inability to Wean A few patients are not able to be weaned from ventilator support despite all efforts. Predictive models, however, are rarely useful for deciding which patients will not benefit from further intensive care. It is rarely a single problem, but rather the interactions among multiple morbidities that create a situation in which the patient may never be able to achieve the “escape velocity” needed to separate from the ventilator. At this point, a discussion with the patient (if he or she has decisional capacity) or the health care proxy can be helpful in defining the benefits and burdens of further therapy and the patient’s desires. Consultation with the hospital’s ethics team may be very helpful. A frank assessment of which problems can be “fixed” versus those that are irreversible will define care options. Patients who remain in low–cardiac output states cannot resolve their multiple organ failure, and thus their dependence on high-technology support continues, including ventilation and hemodialysis. Unless patients are candidates for long-term ventricular assist devices or heart transplantation, they are facing a slow, technologyassisted decline that will end in an untreatable infection. Conversely, malnutrition and deconditioning in the absence of ongoing sepsis and organ system failure sometimes respond to prolonged rehabilitation, which may be better handled by a long-term 756

SUGGESTED READINGS Badhwar V, Esper S, Brooks M, et al. Extubating in the operating room after adult cardiac surgery safely improves outcomes and lowers costs. J Thorac Cardiovasc Surg. 2014;148:3101–3109. Baghban M, Paknejad O, Yousefshahi F, et al. Hospital-acquired pneumonia in patients undergoing coronary artery bypass graft: comparison of the center for disease control clinical criteria with physicians’ judgment. Anesth Pain Med. 2014;17:e20733. Bainbridge D, Martin JE, Cheng DC. Patient-controlled versus nurse-controlled analgesia after cardiac surgery: a meta-analysis. Can J Anaesth. 2006;53(5):492–499. Branca P, McGaw P, Light R. Factors associated with prolonged mechanical ventilation following coronary artery bypass surgery. Chest. 2001;119:537–546. Bucerius J, Gummert JF, Borger MA, et al. Predictors of delirium after cardiac surgery delirium: effect of beating-heart (off-pump) surgery. J Thorac Cardiovasc Surg. 2004;127(1):57–64. Canver CC, Chanda J. Intraoperative and postoperative risk factors for respiratory failure after coronary bypass. Ann Thorac Surg. 2003;75:853–857. Chacko B, Peter JV, Tharyan P, et al. Pressure-controlled versus volume-controlled ventilation for acute respiratory failure due to acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Cochrane Database Syst Rev. 2015;(1):CD008807. Cheng DC, Newman MF, Duke P, et al. The efficacy and resource utilization of remifentanil and fentanyl in fast-track coronary artery bypass graft surgery: a prospective randomized, double-blinded controlled, multi-center trial. Anesth Analg. 2001;92(5):1094–1102. Engelman D, Higgins TL, Talati R, et al. Maintaining situational awareness in a cardiac intensive care unit. J Thorac Cardiovasc Surg. 2014;147:1105–1106. Gerstein NS, Gerstein WH, Carey MC, et al. The thrombotic and arrhythmogenic risks of perioperative NSAIDs. J Cardiothorac Vasc Anesth. 2014;28:369–374. Gilstrap D, MacIntyre N. Patient-ventilator interactions: implications for clinical management. Am J Respir Crit Care Med. 2013;188:1058–1068. Haddad F, Couture P, Tousignant C, et al. The right ventricle in cardiac surgery, a perioperative perspective: II. Pathophysiology, clinical importance, and management. Anesth Analg. 2009;108(2):422–433. Kuiper AN, Trof RJ, Groeneveld AB. Mixed venous O2 saturation and fluid responsiveness after cardiac or major vascular surgery. J Cardiothorac Surg. 2013;22(8):189. Lopes CR, Brandao CM, Nozawa E, et al. Benefits of non-invasive ventilation after extubation in the postoperative period of heart surgery. Rev Bras Cir Cardiovasc. 2008;23:344–350. Myles PS, Daly DJ, Djaiani G, et al. A systematic review of the safety and effectiveness of fast-track cardiac anesthesia. Anesthesiology. 2003;99(4):982–987. Probst S, Cech C, Haentschel D, et al. A specialized post anaesthetic care unit improves fast-track management in cardiac surgery: a prospective randomized trial. Crit Care. 2014;18(4):468. Pronovost P, Berenholtz S, Dorman T, et al. Improving communication in the ICU using daily goals. J Crit Care. 2003;18:71–75. Raghunathan K, Murray PT, Beattie WS, et al. Choice of fluid in acute illness: what should be given? An international consensus. Br J Anaesth. 2014;113(5):772–783. Schweickert WD, Gehlbach BK, Pohlman AS, et al. Daily interruption of sedative infusions and complications of critical illness in mechanically ventilated patients. Crit Care Med. 2004;32(6):1272–1276. Zhu F, Gomersall CD, Ng SK, et al. A randomized controlled trial of adaptive support ventilation mode to wean patients after fast-track cardiac valvular surgery. Anesthesiology. 2015;122:832–840.

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ventilation facility than an acute care hospital. The critical issue is the patient’s reserve because, unless the patient has adequate cardiac and pulmonary reserve to tolerate stress once all remediable problems have been addressed, indefinite technologic support (ventilation, dialysis) will be required.

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