- Email: [email protected]
Postoperative Respiratory Management
PostoperativeRespiratoryManagement* John H. Lecky, M.D.e
and Alan I. Omin.iky, M.D.±
Or, Leeky
‘J1his article provides our answers to the following questions: (1) which patients are especially likely to require postoperative mechanical ventilation? (2) what special intraoperafiee approaches should be taken with such patients? (.3) what postoperative observations uid measurements are necessary to permit safe, systematic respiratory management decisions? We recognize that the answers to these questions must vary with differences in intensive care facilities, patient populations, ancillary personnel and surgical techniques. PREOPERATIVE MANAGEMENT OF PATIENTS WHO ESPECIALLY LIKELY TO REQUIRE PosToP nATIvE MECHANICAL VENTILATION
The conditions which, in our experience, predispose to postoperative respiratory failure are listed in Table 1. Careful history and physical examination will identify most patients who fall frito the categories listed in Table 1. Preoperative pulmonary function testing and blood gas measurement are used not for the identification of patients at risk, but rather for the provision of a baseline from which improve. mean (or deterioration) car, be judged. The preoperative measurements tnat have been of the greatest use to us are: (1) the arterial Po2 with the patient breathing room air and (2) measurements of the speed of gas flow such as the forced expiratory volume (FEV1) in the first second, the peak flow rate, or the maximum breathing capacity. After identifying patients in whom the potential exists for intraoperative or postoperative respiratory
failure, we take whatever steps we can preoperatively to treat bronchospasm, sputum production, infection, or congestive heart failure. Vigorous postural drainage, bronchodilator therapy, antibiotics, and pulmonary’ physiotherapy are continued so long as there is effective mobilization of secretions and continued improvement in the objective measurements of lung function. In patients in congestive heart failure, an attempt is made to achieve optimal digitalization and diuresis. Should a need for postoperative mechanical ventilation seem likely, we describe the experience preoperatively in some detail and reassure our patients that they will receive as much sedation as necessary to keep them comfortable. Whenever possible, such patients also receive preoperative training in deep breathing and coughing techniques from a pulmonary physiotherapist. Premedication in patients with respirators’ impairment is ordered at reduced dosage levels. We usually avoid narcotics entirely unless an anesthesiologist can guarantee adequate oxygenation and ventilation thereafter. There is presently no effective narcotic that is not equally effective as a respiratory- depressant. Barbiturates and tranquilizers do not significantly impair ventilation in less than sleep-producing closes. hut very small doses may produce delirium or sleep in old or sick patients. Table I-.-Condit,o.,
W ,kh Pred .po, Respiratory Failure
go Po top.’rwh’e
1. Decreased levels of consciousness due to residual general anesthesia or central nervous system disease 2. Muscular weakness (tale to residual muscle relaxant effect or neuromuscular disease 3. Cardiac failure and/or fluid overload 4. Upper abdominal surgery or cardiac surgery 5. The ‘#{176}cniched chest” syndrome 6. Chronic lung disease and/or a history of heavy smoking 7. Systemic gram-negative infection 8. Severe obesity 9. Advanced age
‘From the Cardiorespiratory Anesthesia Service, Department of Anesthesia, University of Pennsylvania School of Medidne, Philadelphia. Thi’ work was supported (in part) by U.S.P.H.S. Research Center Grant, 5-P0I-GM.15430-04, and U.S.P.H.S. Research Training Grant, 5-T01-CM-00215-13, from the National Institute of General Medical Sciences, National Institutes of Health.
Research Fellow,
tAssociate Professor. Reprint requexts: Dr. Omiiasky, Departnuent of Anectlueria, 3400 Spruce Street. Phih de1phia 19104
50S
51S
POSTOPERATIVERESPIRATORYMANAGEMENT Although the use of atropine is often helpful in patients with copious secretions, we prefer to withhold atropine until the patient arrives in the operating room. Since the duration of action of atropine is short, this maximizes the drug’s effectiveness during induction,’ It also prevents unnecessary discomfort and injury from inspissated secretions during the hour prior to surgery. THE JNTRAOPERATIVE PHASE The skill of the anesthesiologist and the adequacy of the monitoring systems he employs are far more important for patient safety than is a particular agent or technique.2 While local and spinal anesthesia may leave less postoperative depression of consciousness and of respiratory drive, they also reduce the simplicity with which periodic intraoperative hyperinflation and tracheobronchial toilet can be achieved. \Ve do not hesitate to provide general anesthesia for patients with chronic lung disease when such anesthesia seems desirable for adequate surgical management. However, in the extremely ill patient, “general anesthesia” may represent a small amount of analgesia mixed with a large amount of mechanical ventilation, tracheobronchial toilet, and circulatory support. We try to provide inspired oxygen concentrations above 60 percent in the patient with serious (Or potentially serious) respiratory problems. Even the “normal” patient runs a risk of hypoxia during major surgery despite the use of slightly enriched oxygen mhtures (eg, 30 percent). The most common causes for such intraoperative hypoxia include (1) hypoventilation (the easiest to correct), (2) ateleetasis (produced by abdominal packs, lung retraction, or lack of periodic hyperinflation) and (3) an increase in physiologic shunt produced by the anesthetic agents themselves. We maintain a strong preference for halothane anesthesia in patients who are predisposed to problems with secretions and bronchospasm since such anesthesia rarely adds to these potentially lifethreatening difficulties.5 Virtually all patients with serious or potentially serious respiratory problems undergo percutaneous radial artery catheterization prior to the induction of anesthesia. With the patient breathing room air, an arterial blood gas determination is made to serve as a baseline. Subsequent blood gas determinations are made as often as necessary to insure the presence of a safe Po2, Pco2, and pH. Depending on the seriousness of the problem or on changing operative conditions, these measurements are repeated as often as every 15 minutes or as infrequently as once an hour. As an example, the schedule for obtaining
Table
2-buraope,utk’e Arte rid Blood as PJrn itorh.g ha the Ope...Heart Putie.a*
Time Sample Obtained 1. Prior to induction of anesthesia, patient breathing room air 2. After induction, prior to opening chest or sternum 3. After chest or sternum has been opened 4. Shortly after bypass begins
5. Ten minutes before bypass ends 8. Ten minutes after bypass ends
7. One-halfhour before
going to recovery room
Reason fo Obtaining a Sample To establish a baseline value
To determine if AaDo2has increased after induction of anesthesiaand to check that
is adequate that lung compression or contusion has not led to an increase in dead space or AaDo2 To insure that oxygen transport and CO2 elimination by the heart-lung device are satisfactory To insure that no systemic acidosis has developed To insure that the bypass period has not produced unsuspected pulmonary damage To provide information for choosing the Fao..and V, in recovery room.
To insure
intraoperative blood gas determinations in cardiotomy patients is given in Table 2. Nonscheduled blood gas determinations are made whenever there is an arrhythmia, unexplained hypotension. cyanosis or dark blood, change in Fio2 or ventilator settings, or if more than 45 minutes have elapsed since the previous sample. Arterial blood gases are measured in the anesthesia department s clinical laboratory,8 and the results are available in less than five minutes. routine
T IMMEDIATE POSTOPERATIVE PHASE In some high-risk patients the decision to mechanically ventilate the patient postoperatively is fairly straightforward. Such patients include most of those who experience intraoperative problems with oxygen transport, CO2 clearance, or congestive heart failure. \\‘hen the decision is less clear-cut, patients are evaluated for extubation by the same systematic procedure (to be described later) that is used in the intensive care unit. The arterial Po2 can vary markedly in the immediate postoperative period. The most common causes of hypoxia in the recovery room and ICU are listed in Table 3. Our initial responses to an hypoxic patient are listed in Table 4. The most common cause of postoperative hypercarbia during controlled ventilation is an increase in physiologic dead space which may occur quite rapidly and often without well-defined cause. A minute ventilation that was adequate intraopera. tively may become inadequate postoperatively and
CHEST, VOL. 62, NO. 2, AUGUST 1972 SUPPLEMENT
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LECKY AND OMINSKY Table 3-.-I tioiogk
o/
Hypo io
Table 5-Approach
collapse due to endobronchial intubation, pneumothorax, hemothorax, or endobronchial blood clots. 2. Patchy atelectasis caused by unmobilized secretions, low airway “closing” pressures, lack of periodic hyperinilation, or the patient “fighting” the ventilator 3. Ventilation/perfusion mismatcha 4. The presence of interstitial lung water and/or congestive heart failure 5. Disconnected oxygen supply or leaks in the delivery system. Faulty valves 6. Pulmonary embolism 7. Pericardial tamponade Rarely an important clinical problem in patients breathing enriched oxygen mixtures (eg Fmz > 0.4).
1. Pulmonary
by as much as two to three times. The most common causes of carbon dioxide retention during controlled mechanical ventilation and our diagnostic approach are presented in Table 5. Note that the approach to COz retention during spontaneous ventilation is quite different (Table 6) than that during controlled ventilation. We follow no rigid schedule for obtaining arterial blood gases postoperatively. If the cardiovascular status is stable and our recovery room blood gas values acceptable, we obtain our next values in about five hours. More frequent determinations are mandatory in the presence of unexplained disorientation, arrhythmia, or hypotension. A major danger to any mechanically ventilated patient is mechanical disaster, je, disconnection, plugging or kinking of the endotracheal tube, failure of the humidification system, disconnection of the O line, or mechanical problems with the ventilator. These dangers should be minimal in a good intensive care unit, but preclude our suggested management in the absence of such a unit or recovery area. Our patients are routinely turned, hyperinflated, lavaged, and suctioned every’ hour (more frequently if thick secretions are a problem). Chest physiotherapy is routinely used to facilitate mobilization of secretions. We employ disposable endotracheal tubes, and large-volume, low-pressure cuffs inflated just to the point where there is no air have to be increased
Table 4-Appro reh 1. Increase (Pa0
<60
to the Hyporrk Pet.ens
if the condition appears life-threatening
torr)
2. Carefully inspect and auscultate the chest to rule out the problems listed in Table 3; check the inspired 02 concentration with an oximeter; check expired ventilation at the endotracheal tube to rule out leaks or faulty valves 3. Perform careful tracheobronchial toilet and hyperinllation 4. Get a chest x-ray film; measure the CV? 5. Consider administering a diuretic even if there is no other evidence of excessive interestitial pulmonary water 8. Consider the use of continuous positive end-expiratory pressure
to CO Retention during Co,,trofled Eenlilation
Mehonird
A. Rule out increased dead space by: I. Directly measuring dead space and CO2 production or 2. Noting whether the V is appropriate to patient’s size and temperature. A normal adult patient requires ventilation of approximately 90 mI/kg/win to maintain a normal arterial Pco2. This reqinirennent is increased by 5 percent for each F of temperature rise above 98.OcF. It is rare for CO2 production to be increased by more than 20-30 percent in ICU patients because of fever or s,tller causes. Hence, large increase in ventilatory refluirenients are almost invariably due to increases in dead space. B. Rule out hypoventilation by direct ri,eastirenwnt of V with a Wright respirorneter. It is vital to make this measurement at the endr,tracheal tul,e or trac-heostornv rather than ‘downstream.” Measurement at the endotracheal tube nih-s out the presence of undetected leaks or of fault,, valves.
leak. We do not routinely deflate the cuffs. \Ve prefer volume-cycled ventilators that permit the patient to trigger inspiration if desired. At present the most frequently employed ventilator in our
institution is the Bennett MA-i.
EVALUATION FOR EXTUBATION
On the first postoperative
recovery
morning (or in the
room if that seems appropriate)
the pa-
tient is evaluated for discontinuing mechanical ventilation and extubation. We employ a systematic scoring system to aid in deciding when extubation is safe. There are at least two important advantages to using such a scoring system. First, it greatly reduces the chance of overlooking critical information. Secondly, it is a useful teaching guide for students and residents. However, no objective” evaluation system can completely replace clinical judgment; our system is an aid to decision-making, not an automatic decision-maker. It is important first to identify those patients who cannot safely tolerate a trial of spontaneous ventilaTable 6-.4pproach
to CO Retention Occurring during Spontaneous Ventitation
A. Rule out weakness by measuring vital capacity and/or
inspiratory force ventilation by measuring V5. If hypoventilation is present the most likely cause is respiratory depression resulting horn recent administration of narcotics even in small doses. A rarer cause is the depression of ventilation by oxygen in a patient dependent on hypoxic drive Pain will rarely if ever diminish V enough to cause CO 4retention C. If the measured V5 is high, a o thination of problems is probably present, such as: 1. fever + weakness or 2. increased dead space + exhaustion
B. Rule out decreased
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POSTOPERATIVERESPIRATORYMANAGEMENT Table 7-.Controindkations
to a Trial o/ Spon*an.o .s ‘engiIation on a
1. Coma 2. Serious arrhythmia or uncontrolled congestive heart failure 3. Vital capacity helosv 8 nil/kg 4. PaO below 80 ton with 60%inspired 0 .5. More than 180 rI/kg/mm of minute ventilation required to maintain PaCO2 at or below 40 ton
tion. \Ve have listed contraindications to such a trial in Table 7. In the absence of the listed contraindica. tions, we undertake a one-hour ‘T’-piece trial of spontaneous ventilation (while the patient is still intubated), (Fig 1). Unless the trial must be abandoned because of marked increase in respiratory rate, significant deterioration in circulatory status, or patient agitation or fatigue, the scoring system is reapplied at the end of one hour of spontaneous ventilation. Data are recorded on the form shown in Figure 2. The evaluation system is divided into six categories; of these, three are laboratory and three are clinical (Fig 3). We have tried to select categories that are as independent of one another as possible. Although we occasionally see deterioration in a single area, it is common for several categories to improve, or deteriorate together. While the scoring system was originally derived from our experience with 200 open-heart patients,7 it is equally useful in evaluating the respiratory status of noncardiotomy patients in the first week following surgery. It is less uscful for evaluating patients who have been on longterm mechanical ventilation where psychologic
FIGURE 1. A typical ‘T ’-piece trial.
dependence on the ventilator may have developed. We have not observed psychologic dependence on mechanical ventilation in the first few postoperative days in patients who were not mechanically ventilated prior to surgery. When a postoperative patient indicates a desire for mechanical ventilatory support, that desire almost always rests on strong physiologic ground.s. To sedate such a patient in order to discontinue mechanical ventilation is to court disaster. How to Use These Criteria A maximum of 18 points is possible. The highe.r the score, the better. However, a high score does not insure a successful extubation. We prefer to base decisions on the absence of low scores in any category, rather than on the overall sum. The presence of a zero in any category or “one’s” in two or more categories makes discontinuance of mechanical ventilation a risky business. In the presence of such low scores, we usually elect to maintain mechanical ventilation for an additional 24 hours. An Explanation of the Criteria State of Consciousness. The patient who adamantly and unmistakably demands removal of the endotracheal tube after a trial of spontaneous ventilation almost always does well when extubated. A patient who wants to be placed back on the ventilator should have his wishes met. It is usually hazardous to extubate comatose or disoriented patients since they will not be able to defend their pulmonary function by voluntary deep breathing or coughing. Respiratory. Thick or copious secretions by themselves do not necessarily prevent us from extubating a patient. However, when such secretions are combined with a depressed state of consciousness or poor vital capacity, they greatly diminish the chances for a benign course after extubation. The respiratory rate during a trial of spontaneous centilation is prognostically useful. A rate of 25/mm bodes well, whereas a rate that climbs to over 40/mm suggests an ominous postextubation course. Such rapid rates are often associated with greatly diminished vital capacities and indicate minimal respiratory reserve. Circulatory. A patient in poorly compensated congestive heart failure during positive-pressure ventilation will almost certainly get worse in the absence of such ventilation. Increased venous return will follow the removal of positive pressure. Oi e objective index of the degree of circulatory failure is the amount of inotropic drug required.
CHEST,VOL. 62, NO. 2, AUGUST1972 SUPPLEMENT
LECKY AND OMINSKY
54S DEPARTMENT 04 JIESTNESI* tWfiC*t c* R*7O #{149}GI uCtSfl
____________
.oO_
to-
,-,.
I iu
#{176}. -
I i. 13 r
I
,
._
._
0
-.
#{149}0 ‘ “‘‘“#{176}C.”
F,cunE 2. Respiratory care data sheet.
not much matter which of these causes a low V . A patient who cannot or will not take a deep breath is not likely to keep his alveoli expanded or his secretions cleared. It is difficult to set a minimum safe limit on Vc in terms of mi/kg hodyweight. An important consideration, however, is whether the vital capacity is increasing or decreasing. Ve might he willing to extubate a postcardiotomy patient with a Vi. of 8 mllkg on the second postoperative day provided
Similarly, the presence of an arrhythmia requiring significant amounts of lidocaine (Xylocamne) (1 mg/mm) makes us reluctant to discontinue positivepressure ventilation even if the arrhythmia is due to nonrespiratorv causes. Vital Capacity (Vt). Vc is affected not only by the strength of the respiratory muscles, but also by the pulmonary pathology, by the presence or absence of congestive heart failure, and by the patient’s willingness to cooperate. However, it does
EXTUBATIONCRITERIA FLOW SHEET Poti*ntS Nonle
Operative Procedure Dateof Extubotioo TracheostOflly 0 Score CoflWIOSEof de-
STATE OF
CONSCIOUSNESS
Sites FTtICIIOOICOI
.flt,iOt.Ofl
Actually
CIRCULATION RESPIRATION
reCtlvri
r.Ofrop.. esw Or.
ontiorrflytttmic
5o,n n
SECOETIONS
8
V (o I/kg) 0 yQ.notion .
Ratiot
I.4
2O
vE’lTll A tOP.fl iO
CO2Elinminotion
P O 4P n,)
‘50
nd rising
2
I Diw,ents,
UnC000erOtIVe
SudS drug, berig
tSIdefed
40-50/nsin
4.0 he
cc “Set
SC.,,. ObSO.m,t.t, fl PUllS 0’ CCd pa.sw.. DOt to dr,jQS ,tqO,rtd Sr
-. ...,..
3 Awne.won,, tube Qul
No CbnOrmol,t.s
4O/n,in
.c40/ns,n
thick or copku
modest
neghgible
8-13
14-20
2I
1.5- 2.4
2.5-3.4
35
1.7- 2.0
o
and stable
Postoperative Scoring DAY DAY DAY DAY I 2 3 4
1.3-1.7
.3
S49
49
TOTAL SCORE calculateOxygenatmnratio divide Pa ,1in tort by inspiredO in percent To coloulate VefltiIOt.Ofl ratio I) C lcuIote90 mI/kg Mt. fl kg 40 #{149} _______ (A) 2) Calculate actual x actual ‘.f (mi/mm) #{149} ________ (B) A n,t fl o y ‘cite’, Osoallyp,SCI.thtSttTuOtu!ofl 3) Divide B by A #{149} Ventilotiot, ratio A c.... floCily #{149},.CtoOfl t.lUbOf,Gfl criteria Place potient in lowest category consistent with either factor
re
FIGuRE 3. Ext,ihation flow sheet.
CHEST,VOL. 62, NO. 2, AUGUST1972 SUPPLEMENT
55S
POSTOPERATIVERESPIRATORYMANAGEMENT that this represented an increase from the day before. On the other hand, we would probably intubate a myasthenic patient whose Vc was 15 mi/kg and falling. (We measure Vc using a \Vright respirometer or a disposable volume respirometer.) I PaO., (torr) \ Oxygenation Ratio -F----(%) -)The ratio of Pa02 to the inspired O concentration provides a simple index of the adequacy of pulmonary oxygen transfer (AaDo2). A 5.0 ratio is excellent: eg, Po2 = 500 torr on 100 percent inspired 02. A 1.0 ratio is poor: eg, Po2 = 60 torr on 60 percent inspired 02. Ve have found this ratio to be the most simple, understandable, and useful method to train a novice to relate arterial to inspired oxygen levels and to interpret that relationship. The change noted in this ratio during a trial of spontaneous ventilation is often of greater use for decision.making than is the ratio in the mechanically ventilated patient. A drop in the ratio from 4 to 1.5 during a one-hour T’piece trial would make us wary of extubation. It is not unusual for a decreasing oxygenation ratio during spontaneous ventilation to be the only objective evidence for fluid overload; in fact, patients with falling ratios often improve dramatically after di uresis. Pco2 and Ventilation Ratio. Weakness or depression of the respiratory center is never a cause for CO2 retention during controlled mechanical ventilation. Our approach to CO2 retention during mechanical ventilation is presented in Table 5. During spontaneous ventilation CO2 retention is caused by exhaustion, weakness, and/or central nervous system depression often combined with increased CO2 production or increased dead space (Table 6). While the clinical consequences of moderate CO2 retention in a well-oxygenated healthy person are minimal, minor elevations of Paco2 may contribute to right-heart failure following cardiac surgery in a patient with pulmonary hypertension. Sympathetic stimulation resulting from elevated PaCO2 may also threaten cardiac patients because of increased mvocardial work or the production of arrhythmias. \ Ventilation ratio iI ActualV, \ Predicted v /I. This ratio reflects the efficiency with which the patient eliminates CO2. If V greater than the predicted V is required to maintain a P of 40 torr, then either dead space or CO2 production must be increased. Gross errors in data-taking are possible here. It is important to do the yE and Pcoz determinations at the same time. A patients can change markedly .
‘Boebringer
Laboratories,
Wynnewood,
Penn.sylvania
19006.
in response to the stimuli of arterial puncture, manipulation of the endotracheal tube, etc. V determined at a time other than when the blood gas is obtained is of little use. More sophisticated approaches to measuring Vo/V.r can be undertaken, but their increased complexity is not rewarded by any increase in clinical utility. Our approach to deciding when to extubate a patient is a tvvo.step one: first, the patient is evaluated iii six categories while respiration is being mechanically supported; second, if there are no contraindications, a trial of spontaneous ventilation is given. The response to this trial of spontaneous respiration is the most important factor in determining whether extubation and discontinuance of mechanical ventilation are safe. Very few patients who do well during a one-hour trial of spontaneous ventilation on a “T”-piece fare poorly after extubation. (If we are in doubt at the end of one hour on a ‘T’-piece, we sometimes employ a second consecutive hour as an additional test.) Vhen reintubation is required, the need usually develops six to ten hours after extubation and is manifested by patient fatigue or by an increasing respiratory rate and a falling arterial Po2.T Less than 5 percent of our patients have required reintubation, and no patient has experienced a serious respiratory or circulatory accident when the above system was being employed. If a patient is not extubated on the first postoperative day, he is ventilated overnight and re-evaluated the following morning. Tracheostomy may become necessary if the patient cannot be extubated by the third or fourth day. Because of increased risk to the larynx, we prefer not to leave an endotracheal tube in place more than three days. However, we will not perform a tracheostomy if we believe, on the basis of the present day’s data, that safe extubation is likely within 24 hours. For this reason, patients will on rare occasions be ventilated by an oral endotracheal tube for a week or more. During the last three years we have ventilated over 400 patients without any developing laryngeal stenosis or requiring surgical resection for tracheal stenosis. It has been our experience that oral endotracheal tubes are as well tolerated by the postoperative patient as are nasal tracheal tubes. While oral hygiene is easier to maintain with nasal tubes, the increased length and decreased lumen of the nasal tube may cause mechanical difficulties (eg, kinking or difficulty with suction catheter passage). \Ve, therefore, do not routinely switch to nasal tubes in our patients. However, should reintubation be necessary, it may be easier and less traumatic to
CHEST, VOL. 62, NO. 2, AUGUST 1972 SUPPLEMENT
LECKYAND OMINSKY
56$ Table 8-Po wb.gion
Protoeol
Table 9-Care
I. Chest physiotherapy (postural drainage and vibration) is employed as necessary, usually four times a day. Intermittent positive-pressure breathing is given in conjunction with physiotherapy. 2. Oxygen is given by face mask at the concentration used during the “T”-piece trial 3. An arterial blood gas is ched ed three to four hours after extnbation to determine the minimal safe inspired oxygen level. Additional blood gas or gases are obtained thereafter as indicated 4. Because the larynx is usually not competent for some hours after extubation, no oral intake is permitted for at least six hours. After this the patient is permitted only clear liquids until the following morning
pass a nasal endotracheal awake laryngoscopy. Tiw
tube than to perform
POSTEXTUBATION
PERIOD
After the patient has been extubated, the protocol outlined in Table 8 is followed. Arterial blood gases, Vc, and ‘ 7 are measured at least once a day until a satisfactory arterial Poa (above 60 torr) is obtained with the patient breathing room air. We usually do not discharge a patient from the intensive care unit until this arterial P02 (Pa02) is reached. Most patients can achieve this PaOz within the first day or two after extubation. However, such a Pa02 is unlikely to be reached in the patient whose pulmonary function preoperatively was very poor. Even with these patients, a Pa02 of 50 ton on room air is usually an obtainable objective. We keep such patients in the intensive care unit until: (1) no further improvement in PaO2 is occurring, and! or (2) a value comparable
to the best preoperative
value and compatible with life is achieved. It is this approach that makes a preoperative baseline value for Pa02 breathing room air especially useful. TEACHEOS’IDMYCARE
Those patients who require tracheostomy present special problems. The details of tracheostomy care are summarized in Table 9. Patients are usually more comfortable and mechanical ventilation is more readily tolerated after an endotracheal tube has been replaced by a tracheostomy. Patients who have had one or two weeks or more of mechanical ventilation usually require gradual “weaning.” Because of disuse, their respiratory muscles may require “retraining.” Psychologic dependence on the ventilator may also be observed in 1t is difficult to guarantee that an oxygen mask or nasal prongs will remain properly positioned outside the continuous observation of an intensive care unit. Thus, discharge from the unit demands that such disconnection will not result in major complication or fatality.
0/u
Tracheosfo,ny Voile,,:
I - The cuff is inflated only enough to avoid air leak 2. The tie around the neck is loose enough that one finger may slide under it 3. A fresh tracheostomy tube is not electively changed for 72 hours, Ic, until the tract is reasonably vell defined. A tracheal spreader, laryngoscope, siuccinlycholine and an endotracheal tube are mandatory at the first changing of a tracheostomy tube 4. Tracheostomy tubes are then usually changed every two days to reduce accumulation of dried secretions artnancl the cuff ai-nd to remove exudate that tends to accumulate around the tube 5. We are very cautious about feeding a patient with a tracheostomy in place. Aspiration can occur decgntc an inflated cuff. We perform a niethylene-blue tests daily before feeding such patients, and if the test is positive. only parenteral feeding is permitted 6. Suctioning, lavage, hvperinflation, periodic turning, and chest physiotherapy are provided on the same schedule as for patients who have an endotracheal tube in place #{176}The test is performed as follows: 2 ml of nirthylene blue are dissolved in one-half cup a1 water. The patient drinks this. Tracheal aspiration is then clone two to five minutes later. Methylene-blue in the aspirate constitutes a positive test and indicates leakage of material around the cuff
such patients. A typical “weaning” schedule is outlined in Table 10. Patients who have oral or nasal endotracheal tubes in place are never “weaned.” They receive a “T”.piece trial and if they fail such a trial, they are Table 10-A
T pkd “WeonMg” &hedd
1. Periods of .5 to 15 minutes of spontaneous ventilation on a “T”-piece are alternated with hvo hours on the ventilator. Patients receive continuous overnight ventilation 2. The duration of spontaneous breathing periods is gradually increased to one hour and the periods of ventilatory support decreased to one hour. Continuous overnight ventilation is continued 3. The patient is allowed to ventilate spontaneously as long as he is comfortable and upto the entire daytime period. This usually takes a minimum of three days after the weaning process begins. The patient is ventilated (,Vernight that night, and then allowed to breathe spontaneously thereafter unless signs of troul,le develop 4. Once mechanical ventilation has been discontinued for 24 consecutive hours, the size of the tracheostomy hibe is decreased by one size each day for two Or three days. The tracheostomy tube is then plugged so that the patient can breathe around the tube and through his Vocal cords. This passage of air through the cords seems to aid recovery oi laryngeal competence. Supplemental 02 can be given by face mask during the periods when the tube is plugged. The patient is decimnulated 24 hours after the tube is plugged. The tracbeostomy site is closed with adhesive tape only 5. Oral feeding should be dime only with great caution during the period just before and after decannulation. Nlethylene-blue tests (see above) are done at least daily.#{176} The patient is fed parenterally when there is any evidence of laryngeal incompetence In this case the test is for laryngeal competence.
CHEST, VOL. 62, NO. 2, AUGUST 1972 SUPPLEMENT
POSTOPERATIVERESPIRATORYMANAGEMENT continuously ventilated until the next trial. There is no need to “wean” any patient who has been on a ventilator for less than a week. Unlike the situation with tracheostomy, it is harder to breathe spontaneously through an oral endotracheal tube than it is to breathe through an unobstructed natural airway. Hence, spontaneous ventilation through such tubes for prolonged periods may result in deterioration of pulmonary
function.
SUMMARY
This paper describes our present method of handling postoperative respiratory problems at the
University of Pennsylvania. The preoperative and intraoperative evaluation and management of patients with potential problems are discussed. A systematic scoring system designed to make postoperative extubation decisions less intuitive is preseated, along with some specific guidelines for dealing with postoperative hypoxia and hypercar-
57S bia. Lastly, our approach to tracheostomy following surgery is reviewed. REFERENcES
care
1 DePadua CB: Effects of atropine and scopolamine on the cardiovascular system in man. Anesthesiolo ’ 25:123, 1964 2 Conahan Ti III, Omimky AJ, Woilman H, et a!: A pro. spective, random comparison of halothane and morphine for open heart anesthesia A one year’s experience. American Society of Anesthesiologists Annual Meeting (Abstract) 1071, p 137 3 Paskin S, Roshnan T, Smith TC: The effect of spinal anesthesia on the pulmonary function of patients with chronic obstructive pulmonary disease. Ann Surg 169:35, 1969 JF, Bergman NA, Coleman AJ: Factors influencing 4 Nunn the arterial oxygen tension during anesthesia with artificial ventilation. BrJ Anaesth 37:898, 1965 5 Shnider SM, Papper EM: Anesthesia for the asthmatic patient. Anesthesiology 22:888, 1961 8 Wollman The laboratory in the operating area. thesiology H: 31:176, 1969 7 Lecky JH, Omimky AJ, Woliman HW: In preparation Lecky JH, Denlinger JK: In preparation
s
CHEST, VOL. 62, NO. 2, AUGUST 1972 SUPPLEMENT
and Alan I. Omin.iky, M.D.±
Or, Leeky
‘J1his article provides our answers to the following questions: (1) which patients are especially likely to require postoperative mechanical ventilation? (2) what special intraoperafiee approaches should be taken with such patients? (.3) what postoperative observations uid measurements are necessary to permit safe, systematic respiratory management decisions? We recognize that the answers to these questions must vary with differences in intensive care facilities, patient populations, ancillary personnel and surgical techniques. PREOPERATIVE MANAGEMENT OF PATIENTS WHO ESPECIALLY LIKELY TO REQUIRE PosToP nATIvE MECHANICAL VENTILATION
The conditions which, in our experience, predispose to postoperative respiratory failure are listed in Table 1. Careful history and physical examination will identify most patients who fall frito the categories listed in Table 1. Preoperative pulmonary function testing and blood gas measurement are used not for the identification of patients at risk, but rather for the provision of a baseline from which improve. mean (or deterioration) car, be judged. The preoperative measurements tnat have been of the greatest use to us are: (1) the arterial Po2 with the patient breathing room air and (2) measurements of the speed of gas flow such as the forced expiratory volume (FEV1) in the first second, the peak flow rate, or the maximum breathing capacity. After identifying patients in whom the potential exists for intraoperative or postoperative respiratory
failure, we take whatever steps we can preoperatively to treat bronchospasm, sputum production, infection, or congestive heart failure. Vigorous postural drainage, bronchodilator therapy, antibiotics, and pulmonary’ physiotherapy are continued so long as there is effective mobilization of secretions and continued improvement in the objective measurements of lung function. In patients in congestive heart failure, an attempt is made to achieve optimal digitalization and diuresis. Should a need for postoperative mechanical ventilation seem likely, we describe the experience preoperatively in some detail and reassure our patients that they will receive as much sedation as necessary to keep them comfortable. Whenever possible, such patients also receive preoperative training in deep breathing and coughing techniques from a pulmonary physiotherapist. Premedication in patients with respirators’ impairment is ordered at reduced dosage levels. We usually avoid narcotics entirely unless an anesthesiologist can guarantee adequate oxygenation and ventilation thereafter. There is presently no effective narcotic that is not equally effective as a respiratory- depressant. Barbiturates and tranquilizers do not significantly impair ventilation in less than sleep-producing closes. hut very small doses may produce delirium or sleep in old or sick patients. Table I-.-Condit,o.,
W ,kh Pred .po, Respiratory Failure
go Po top.’rwh’e
1. Decreased levels of consciousness due to residual general anesthesia or central nervous system disease 2. Muscular weakness (tale to residual muscle relaxant effect or neuromuscular disease 3. Cardiac failure and/or fluid overload 4. Upper abdominal surgery or cardiac surgery 5. The ‘#{176}cniched chest” syndrome 6. Chronic lung disease and/or a history of heavy smoking 7. Systemic gram-negative infection 8. Severe obesity 9. Advanced age
‘From the Cardiorespiratory Anesthesia Service, Department of Anesthesia, University of Pennsylvania School of Medidne, Philadelphia. Thi’ work was supported (in part) by U.S.P.H.S. Research Center Grant, 5-P0I-GM.15430-04, and U.S.P.H.S. Research Training Grant, 5-T01-CM-00215-13, from the National Institute of General Medical Sciences, National Institutes of Health.
Research Fellow,
tAssociate Professor. Reprint requexts: Dr. Omiiasky, Departnuent of Anectlueria, 3400 Spruce Street. Phih de1phia 19104
50S
51S
POSTOPERATIVERESPIRATORYMANAGEMENT Although the use of atropine is often helpful in patients with copious secretions, we prefer to withhold atropine until the patient arrives in the operating room. Since the duration of action of atropine is short, this maximizes the drug’s effectiveness during induction,’ It also prevents unnecessary discomfort and injury from inspissated secretions during the hour prior to surgery. THE JNTRAOPERATIVE PHASE The skill of the anesthesiologist and the adequacy of the monitoring systems he employs are far more important for patient safety than is a particular agent or technique.2 While local and spinal anesthesia may leave less postoperative depression of consciousness and of respiratory drive, they also reduce the simplicity with which periodic intraoperative hyperinflation and tracheobronchial toilet can be achieved. \Ve do not hesitate to provide general anesthesia for patients with chronic lung disease when such anesthesia seems desirable for adequate surgical management. However, in the extremely ill patient, “general anesthesia” may represent a small amount of analgesia mixed with a large amount of mechanical ventilation, tracheobronchial toilet, and circulatory support. We try to provide inspired oxygen concentrations above 60 percent in the patient with serious (Or potentially serious) respiratory problems. Even the “normal” patient runs a risk of hypoxia during major surgery despite the use of slightly enriched oxygen mhtures (eg, 30 percent). The most common causes for such intraoperative hypoxia include (1) hypoventilation (the easiest to correct), (2) ateleetasis (produced by abdominal packs, lung retraction, or lack of periodic hyperinflation) and (3) an increase in physiologic shunt produced by the anesthetic agents themselves. We maintain a strong preference for halothane anesthesia in patients who are predisposed to problems with secretions and bronchospasm since such anesthesia rarely adds to these potentially lifethreatening difficulties.5 Virtually all patients with serious or potentially serious respiratory problems undergo percutaneous radial artery catheterization prior to the induction of anesthesia. With the patient breathing room air, an arterial blood gas determination is made to serve as a baseline. Subsequent blood gas determinations are made as often as necessary to insure the presence of a safe Po2, Pco2, and pH. Depending on the seriousness of the problem or on changing operative conditions, these measurements are repeated as often as every 15 minutes or as infrequently as once an hour. As an example, the schedule for obtaining
Table
2-buraope,utk’e Arte rid Blood as PJrn itorh.g ha the Ope...Heart Putie.a*
Time Sample Obtained 1. Prior to induction of anesthesia, patient breathing room air 2. After induction, prior to opening chest or sternum 3. After chest or sternum has been opened 4. Shortly after bypass begins
5. Ten minutes before bypass ends 8. Ten minutes after bypass ends
7. One-halfhour before
going to recovery room
Reason fo Obtaining a Sample To establish a baseline value
To determine if AaDo2has increased after induction of anesthesiaand to check that
is adequate that lung compression or contusion has not led to an increase in dead space or AaDo2 To insure that oxygen transport and CO2 elimination by the heart-lung device are satisfactory To insure that no systemic acidosis has developed To insure that the bypass period has not produced unsuspected pulmonary damage To provide information for choosing the Fao..and V, in recovery room.
To insure
intraoperative blood gas determinations in cardiotomy patients is given in Table 2. Nonscheduled blood gas determinations are made whenever there is an arrhythmia, unexplained hypotension. cyanosis or dark blood, change in Fio2 or ventilator settings, or if more than 45 minutes have elapsed since the previous sample. Arterial blood gases are measured in the anesthesia department s clinical laboratory,8 and the results are available in less than five minutes. routine
T IMMEDIATE POSTOPERATIVE PHASE In some high-risk patients the decision to mechanically ventilate the patient postoperatively is fairly straightforward. Such patients include most of those who experience intraoperative problems with oxygen transport, CO2 clearance, or congestive heart failure. \\‘hen the decision is less clear-cut, patients are evaluated for extubation by the same systematic procedure (to be described later) that is used in the intensive care unit. The arterial Po2 can vary markedly in the immediate postoperative period. The most common causes of hypoxia in the recovery room and ICU are listed in Table 3. Our initial responses to an hypoxic patient are listed in Table 4. The most common cause of postoperative hypercarbia during controlled ventilation is an increase in physiologic dead space which may occur quite rapidly and often without well-defined cause. A minute ventilation that was adequate intraopera. tively may become inadequate postoperatively and
CHEST, VOL. 62, NO. 2, AUGUST 1972 SUPPLEMENT
52S
LECKY AND OMINSKY Table 3-.-I tioiogk
o/
Hypo io
Table 5-Approach
collapse due to endobronchial intubation, pneumothorax, hemothorax, or endobronchial blood clots. 2. Patchy atelectasis caused by unmobilized secretions, low airway “closing” pressures, lack of periodic hyperinilation, or the patient “fighting” the ventilator 3. Ventilation/perfusion mismatcha 4. The presence of interstitial lung water and/or congestive heart failure 5. Disconnected oxygen supply or leaks in the delivery system. Faulty valves 6. Pulmonary embolism 7. Pericardial tamponade Rarely an important clinical problem in patients breathing enriched oxygen mixtures (eg Fmz > 0.4).
1. Pulmonary
by as much as two to three times. The most common causes of carbon dioxide retention during controlled mechanical ventilation and our diagnostic approach are presented in Table 5. Note that the approach to COz retention during spontaneous ventilation is quite different (Table 6) than that during controlled ventilation. We follow no rigid schedule for obtaining arterial blood gases postoperatively. If the cardiovascular status is stable and our recovery room blood gas values acceptable, we obtain our next values in about five hours. More frequent determinations are mandatory in the presence of unexplained disorientation, arrhythmia, or hypotension. A major danger to any mechanically ventilated patient is mechanical disaster, je, disconnection, plugging or kinking of the endotracheal tube, failure of the humidification system, disconnection of the O line, or mechanical problems with the ventilator. These dangers should be minimal in a good intensive care unit, but preclude our suggested management in the absence of such a unit or recovery area. Our patients are routinely turned, hyperinflated, lavaged, and suctioned every’ hour (more frequently if thick secretions are a problem). Chest physiotherapy is routinely used to facilitate mobilization of secretions. We employ disposable endotracheal tubes, and large-volume, low-pressure cuffs inflated just to the point where there is no air have to be increased
Table 4-Appro reh 1. Increase (Pa0
<60
to the Hyporrk Pet.ens
if the condition appears life-threatening
torr)
2. Carefully inspect and auscultate the chest to rule out the problems listed in Table 3; check the inspired 02 concentration with an oximeter; check expired ventilation at the endotracheal tube to rule out leaks or faulty valves 3. Perform careful tracheobronchial toilet and hyperinllation 4. Get a chest x-ray film; measure the CV? 5. Consider administering a diuretic even if there is no other evidence of excessive interestitial pulmonary water 8. Consider the use of continuous positive end-expiratory pressure
to CO Retention during Co,,trofled Eenlilation
Mehonird
A. Rule out increased dead space by: I. Directly measuring dead space and CO2 production or 2. Noting whether the V is appropriate to patient’s size and temperature. A normal adult patient requires ventilation of approximately 90 mI/kg/win to maintain a normal arterial Pco2. This reqinirennent is increased by 5 percent for each F of temperature rise above 98.OcF. It is rare for CO2 production to be increased by more than 20-30 percent in ICU patients because of fever or s,tller causes. Hence, large increase in ventilatory refluirenients are almost invariably due to increases in dead space. B. Rule out hypoventilation by direct ri,eastirenwnt of V with a Wright respirorneter. It is vital to make this measurement at the endr,tracheal tul,e or trac-heostornv rather than ‘downstream.” Measurement at the endotracheal tube nih-s out the presence of undetected leaks or of fault,, valves.
leak. We do not routinely deflate the cuffs. \Ve prefer volume-cycled ventilators that permit the patient to trigger inspiration if desired. At present the most frequently employed ventilator in our
institution is the Bennett MA-i.
EVALUATION FOR EXTUBATION
On the first postoperative
recovery
morning (or in the
room if that seems appropriate)
the pa-
tient is evaluated for discontinuing mechanical ventilation and extubation. We employ a systematic scoring system to aid in deciding when extubation is safe. There are at least two important advantages to using such a scoring system. First, it greatly reduces the chance of overlooking critical information. Secondly, it is a useful teaching guide for students and residents. However, no objective” evaluation system can completely replace clinical judgment; our system is an aid to decision-making, not an automatic decision-maker. It is important first to identify those patients who cannot safely tolerate a trial of spontaneous ventilaTable 6-.4pproach
to CO Retention Occurring during Spontaneous Ventitation
A. Rule out weakness by measuring vital capacity and/or
inspiratory force ventilation by measuring V5. If hypoventilation is present the most likely cause is respiratory depression resulting horn recent administration of narcotics even in small doses. A rarer cause is the depression of ventilation by oxygen in a patient dependent on hypoxic drive Pain will rarely if ever diminish V enough to cause CO 4retention C. If the measured V5 is high, a o thination of problems is probably present, such as: 1. fever + weakness or 2. increased dead space + exhaustion
B. Rule out decreased
CHEST,VOL. 62, NO. 2, AUGUST1972 SUPPLEMENT
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POSTOPERATIVERESPIRATORYMANAGEMENT Table 7-.Controindkations
to a Trial o/ Spon*an.o .s ‘engiIation on a
1. Coma 2. Serious arrhythmia or uncontrolled congestive heart failure 3. Vital capacity helosv 8 nil/kg 4. PaO below 80 ton with 60%inspired 0 .5. More than 180 rI/kg/mm of minute ventilation required to maintain PaCO2 at or below 40 ton
tion. \Ve have listed contraindications to such a trial in Table 7. In the absence of the listed contraindica. tions, we undertake a one-hour ‘T’-piece trial of spontaneous ventilation (while the patient is still intubated), (Fig 1). Unless the trial must be abandoned because of marked increase in respiratory rate, significant deterioration in circulatory status, or patient agitation or fatigue, the scoring system is reapplied at the end of one hour of spontaneous ventilation. Data are recorded on the form shown in Figure 2. The evaluation system is divided into six categories; of these, three are laboratory and three are clinical (Fig 3). We have tried to select categories that are as independent of one another as possible. Although we occasionally see deterioration in a single area, it is common for several categories to improve, or deteriorate together. While the scoring system was originally derived from our experience with 200 open-heart patients,7 it is equally useful in evaluating the respiratory status of noncardiotomy patients in the first week following surgery. It is less uscful for evaluating patients who have been on longterm mechanical ventilation where psychologic
FIGURE 1. A typical ‘T ’-piece trial.
dependence on the ventilator may have developed. We have not observed psychologic dependence on mechanical ventilation in the first few postoperative days in patients who were not mechanically ventilated prior to surgery. When a postoperative patient indicates a desire for mechanical ventilatory support, that desire almost always rests on strong physiologic ground.s. To sedate such a patient in order to discontinue mechanical ventilation is to court disaster. How to Use These Criteria A maximum of 18 points is possible. The highe.r the score, the better. However, a high score does not insure a successful extubation. We prefer to base decisions on the absence of low scores in any category, rather than on the overall sum. The presence of a zero in any category or “one’s” in two or more categories makes discontinuance of mechanical ventilation a risky business. In the presence of such low scores, we usually elect to maintain mechanical ventilation for an additional 24 hours. An Explanation of the Criteria State of Consciousness. The patient who adamantly and unmistakably demands removal of the endotracheal tube after a trial of spontaneous ventilation almost always does well when extubated. A patient who wants to be placed back on the ventilator should have his wishes met. It is usually hazardous to extubate comatose or disoriented patients since they will not be able to defend their pulmonary function by voluntary deep breathing or coughing. Respiratory. Thick or copious secretions by themselves do not necessarily prevent us from extubating a patient. However, when such secretions are combined with a depressed state of consciousness or poor vital capacity, they greatly diminish the chances for a benign course after extubation. The respiratory rate during a trial of spontaneous centilation is prognostically useful. A rate of 25/mm bodes well, whereas a rate that climbs to over 40/mm suggests an ominous postextubation course. Such rapid rates are often associated with greatly diminished vital capacities and indicate minimal respiratory reserve. Circulatory. A patient in poorly compensated congestive heart failure during positive-pressure ventilation will almost certainly get worse in the absence of such ventilation. Increased venous return will follow the removal of positive pressure. Oi e objective index of the degree of circulatory failure is the amount of inotropic drug required.
CHEST,VOL. 62, NO. 2, AUGUST1972 SUPPLEMENT
LECKY AND OMINSKY
54S DEPARTMENT 04 JIESTNESI* tWfiC*t c* R*7O #{149}GI uCtSfl
____________
.oO_
to-
,-,.
I iu
#{176}. -
I i. 13 r
I
,
._
._
0
-.
#{149}0 ‘ “‘‘“#{176}C.”
F,cunE 2. Respiratory care data sheet.
not much matter which of these causes a low V . A patient who cannot or will not take a deep breath is not likely to keep his alveoli expanded or his secretions cleared. It is difficult to set a minimum safe limit on Vc in terms of mi/kg hodyweight. An important consideration, however, is whether the vital capacity is increasing or decreasing. Ve might he willing to extubate a postcardiotomy patient with a Vi. of 8 mllkg on the second postoperative day provided
Similarly, the presence of an arrhythmia requiring significant amounts of lidocaine (Xylocamne) (1 mg/mm) makes us reluctant to discontinue positivepressure ventilation even if the arrhythmia is due to nonrespiratorv causes. Vital Capacity (Vt). Vc is affected not only by the strength of the respiratory muscles, but also by the pulmonary pathology, by the presence or absence of congestive heart failure, and by the patient’s willingness to cooperate. However, it does
EXTUBATIONCRITERIA FLOW SHEET Poti*ntS Nonle
Operative Procedure Dateof Extubotioo TracheostOflly 0 Score CoflWIOSEof de-
STATE OF
CONSCIOUSNESS
Sites FTtICIIOOICOI
.flt,iOt.Ofl
Actually
CIRCULATION RESPIRATION
reCtlvri
r.Ofrop.. esw Or.
ontiorrflytttmic
5o,n n
SECOETIONS
8
V (o I/kg) 0 yQ.notion .
Ratiot
I.4
2O
vE’lTll A tOP.fl iO
CO2Elinminotion
P O 4P n,)
‘50
nd rising
2
I Diw,ents,
UnC000erOtIVe
SudS drug, berig
tSIdefed
40-50/nsin
4.0 he
cc “Set
SC.,,. ObSO.m,t.t, fl PUllS 0’ CCd pa.sw.. DOt to dr,jQS ,tqO,rtd Sr
-. ...,..
3 Awne.won,, tube Qul
No CbnOrmol,t.s
4O/n,in
.c40/ns,n
thick or copku
modest
neghgible
8-13
14-20
2I
1.5- 2.4
2.5-3.4
35
1.7- 2.0
o
and stable
Postoperative Scoring DAY DAY DAY DAY I 2 3 4
1.3-1.7
.3
S49
49
TOTAL SCORE calculateOxygenatmnratio divide Pa ,1in tort by inspiredO in percent To coloulate VefltiIOt.Ofl ratio I) C lcuIote90 mI/kg Mt. fl kg 40 #{149} _______ (A) 2) Calculate actual x actual ‘.f (mi/mm) #{149} ________ (B) A n,t fl o y ‘cite’, Osoallyp,SCI.thtSttTuOtu!ofl 3) Divide B by A #{149} Ventilotiot, ratio A c.... floCily #{149},.CtoOfl t.lUbOf,Gfl criteria Place potient in lowest category consistent with either factor
re
FIGuRE 3. Ext,ihation flow sheet.
CHEST,VOL. 62, NO. 2, AUGUST1972 SUPPLEMENT
55S
POSTOPERATIVERESPIRATORYMANAGEMENT that this represented an increase from the day before. On the other hand, we would probably intubate a myasthenic patient whose Vc was 15 mi/kg and falling. (We measure Vc using a \Vright respirometer or a disposable volume respirometer.) I PaO., (torr) \ Oxygenation Ratio -F----(%) -)The ratio of Pa02 to the inspired O concentration provides a simple index of the adequacy of pulmonary oxygen transfer (AaDo2). A 5.0 ratio is excellent: eg, Po2 = 500 torr on 100 percent inspired 02. A 1.0 ratio is poor: eg, Po2 = 60 torr on 60 percent inspired 02. Ve have found this ratio to be the most simple, understandable, and useful method to train a novice to relate arterial to inspired oxygen levels and to interpret that relationship. The change noted in this ratio during a trial of spontaneous ventilation is often of greater use for decision.making than is the ratio in the mechanically ventilated patient. A drop in the ratio from 4 to 1.5 during a one-hour T’piece trial would make us wary of extubation. It is not unusual for a decreasing oxygenation ratio during spontaneous ventilation to be the only objective evidence for fluid overload; in fact, patients with falling ratios often improve dramatically after di uresis. Pco2 and Ventilation Ratio. Weakness or depression of the respiratory center is never a cause for CO2 retention during controlled mechanical ventilation. Our approach to CO2 retention during mechanical ventilation is presented in Table 5. During spontaneous ventilation CO2 retention is caused by exhaustion, weakness, and/or central nervous system depression often combined with increased CO2 production or increased dead space (Table 6). While the clinical consequences of moderate CO2 retention in a well-oxygenated healthy person are minimal, minor elevations of Paco2 may contribute to right-heart failure following cardiac surgery in a patient with pulmonary hypertension. Sympathetic stimulation resulting from elevated PaCO2 may also threaten cardiac patients because of increased mvocardial work or the production of arrhythmias. \ Ventilation ratio iI ActualV, \ Predicted v /I. This ratio reflects the efficiency with which the patient eliminates CO2. If V greater than the predicted V is required to maintain a P of 40 torr, then either dead space or CO2 production must be increased. Gross errors in data-taking are possible here. It is important to do the yE and Pcoz determinations at the same time. A patients can change markedly .
‘Boebringer
Laboratories,
Wynnewood,
Penn.sylvania
19006.
in response to the stimuli of arterial puncture, manipulation of the endotracheal tube, etc. V determined at a time other than when the blood gas is obtained is of little use. More sophisticated approaches to measuring Vo/V.r can be undertaken, but their increased complexity is not rewarded by any increase in clinical utility. Our approach to deciding when to extubate a patient is a tvvo.step one: first, the patient is evaluated iii six categories while respiration is being mechanically supported; second, if there are no contraindications, a trial of spontaneous ventilation is given. The response to this trial of spontaneous respiration is the most important factor in determining whether extubation and discontinuance of mechanical ventilation are safe. Very few patients who do well during a one-hour trial of spontaneous ventilation on a “T”-piece fare poorly after extubation. (If we are in doubt at the end of one hour on a ‘T’-piece, we sometimes employ a second consecutive hour as an additional test.) Vhen reintubation is required, the need usually develops six to ten hours after extubation and is manifested by patient fatigue or by an increasing respiratory rate and a falling arterial Po2.T Less than 5 percent of our patients have required reintubation, and no patient has experienced a serious respiratory or circulatory accident when the above system was being employed. If a patient is not extubated on the first postoperative day, he is ventilated overnight and re-evaluated the following morning. Tracheostomy may become necessary if the patient cannot be extubated by the third or fourth day. Because of increased risk to the larynx, we prefer not to leave an endotracheal tube in place more than three days. However, we will not perform a tracheostomy if we believe, on the basis of the present day’s data, that safe extubation is likely within 24 hours. For this reason, patients will on rare occasions be ventilated by an oral endotracheal tube for a week or more. During the last three years we have ventilated over 400 patients without any developing laryngeal stenosis or requiring surgical resection for tracheal stenosis. It has been our experience that oral endotracheal tubes are as well tolerated by the postoperative patient as are nasal tracheal tubes. While oral hygiene is easier to maintain with nasal tubes, the increased length and decreased lumen of the nasal tube may cause mechanical difficulties (eg, kinking or difficulty with suction catheter passage). \Ve, therefore, do not routinely switch to nasal tubes in our patients. However, should reintubation be necessary, it may be easier and less traumatic to
CHEST, VOL. 62, NO. 2, AUGUST 1972 SUPPLEMENT
LECKYAND OMINSKY
56$ Table 8-Po wb.gion
Protoeol
Table 9-Care
I. Chest physiotherapy (postural drainage and vibration) is employed as necessary, usually four times a day. Intermittent positive-pressure breathing is given in conjunction with physiotherapy. 2. Oxygen is given by face mask at the concentration used during the “T”-piece trial 3. An arterial blood gas is ched ed three to four hours after extnbation to determine the minimal safe inspired oxygen level. Additional blood gas or gases are obtained thereafter as indicated 4. Because the larynx is usually not competent for some hours after extubation, no oral intake is permitted for at least six hours. After this the patient is permitted only clear liquids until the following morning
pass a nasal endotracheal awake laryngoscopy. Tiw
tube than to perform
POSTEXTUBATION
PERIOD
After the patient has been extubated, the protocol outlined in Table 8 is followed. Arterial blood gases, Vc, and ‘ 7 are measured at least once a day until a satisfactory arterial Poa (above 60 torr) is obtained with the patient breathing room air. We usually do not discharge a patient from the intensive care unit until this arterial P02 (Pa02) is reached. Most patients can achieve this PaOz within the first day or two after extubation. However, such a Pa02 is unlikely to be reached in the patient whose pulmonary function preoperatively was very poor. Even with these patients, a Pa02 of 50 ton on room air is usually an obtainable objective. We keep such patients in the intensive care unit until: (1) no further improvement in PaO2 is occurring, and! or (2) a value comparable
to the best preoperative
value and compatible with life is achieved. It is this approach that makes a preoperative baseline value for Pa02 breathing room air especially useful. TEACHEOS’IDMYCARE
Those patients who require tracheostomy present special problems. The details of tracheostomy care are summarized in Table 9. Patients are usually more comfortable and mechanical ventilation is more readily tolerated after an endotracheal tube has been replaced by a tracheostomy. Patients who have had one or two weeks or more of mechanical ventilation usually require gradual “weaning.” Because of disuse, their respiratory muscles may require “retraining.” Psychologic dependence on the ventilator may also be observed in 1t is difficult to guarantee that an oxygen mask or nasal prongs will remain properly positioned outside the continuous observation of an intensive care unit. Thus, discharge from the unit demands that such disconnection will not result in major complication or fatality.
0/u
Tracheosfo,ny Voile,,:
I - The cuff is inflated only enough to avoid air leak 2. The tie around the neck is loose enough that one finger may slide under it 3. A fresh tracheostomy tube is not electively changed for 72 hours, Ic, until the tract is reasonably vell defined. A tracheal spreader, laryngoscope, siuccinlycholine and an endotracheal tube are mandatory at the first changing of a tracheostomy tube 4. Tracheostomy tubes are then usually changed every two days to reduce accumulation of dried secretions artnancl the cuff ai-nd to remove exudate that tends to accumulate around the tube 5. We are very cautious about feeding a patient with a tracheostomy in place. Aspiration can occur decgntc an inflated cuff. We perform a niethylene-blue tests daily before feeding such patients, and if the test is positive. only parenteral feeding is permitted 6. Suctioning, lavage, hvperinflation, periodic turning, and chest physiotherapy are provided on the same schedule as for patients who have an endotracheal tube in place #{176}The test is performed as follows: 2 ml of nirthylene blue are dissolved in one-half cup a1 water. The patient drinks this. Tracheal aspiration is then clone two to five minutes later. Methylene-blue in the aspirate constitutes a positive test and indicates leakage of material around the cuff
such patients. A typical “weaning” schedule is outlined in Table 10. Patients who have oral or nasal endotracheal tubes in place are never “weaned.” They receive a “T”.piece trial and if they fail such a trial, they are Table 10-A
T pkd “WeonMg” &hedd
1. Periods of .5 to 15 minutes of spontaneous ventilation on a “T”-piece are alternated with hvo hours on the ventilator. Patients receive continuous overnight ventilation 2. The duration of spontaneous breathing periods is gradually increased to one hour and the periods of ventilatory support decreased to one hour. Continuous overnight ventilation is continued 3. The patient is allowed to ventilate spontaneously as long as he is comfortable and upto the entire daytime period. This usually takes a minimum of three days after the weaning process begins. The patient is ventilated (,Vernight that night, and then allowed to breathe spontaneously thereafter unless signs of troul,le develop 4. Once mechanical ventilation has been discontinued for 24 consecutive hours, the size of the tracheostomy hibe is decreased by one size each day for two Or three days. The tracheostomy tube is then plugged so that the patient can breathe around the tube and through his Vocal cords. This passage of air through the cords seems to aid recovery oi laryngeal competence. Supplemental 02 can be given by face mask during the periods when the tube is plugged. The patient is decimnulated 24 hours after the tube is plugged. The tracbeostomy site is closed with adhesive tape only 5. Oral feeding should be dime only with great caution during the period just before and after decannulation. Nlethylene-blue tests (see above) are done at least daily.#{176} The patient is fed parenterally when there is any evidence of laryngeal incompetence In this case the test is for laryngeal competence.
CHEST, VOL. 62, NO. 2, AUGUST 1972 SUPPLEMENT
POSTOPERATIVERESPIRATORYMANAGEMENT continuously ventilated until the next trial. There is no need to “wean” any patient who has been on a ventilator for less than a week. Unlike the situation with tracheostomy, it is harder to breathe spontaneously through an oral endotracheal tube than it is to breathe through an unobstructed natural airway. Hence, spontaneous ventilation through such tubes for prolonged periods may result in deterioration of pulmonary
function.
SUMMARY
This paper describes our present method of handling postoperative respiratory problems at the
University of Pennsylvania. The preoperative and intraoperative evaluation and management of patients with potential problems are discussed. A systematic scoring system designed to make postoperative extubation decisions less intuitive is preseated, along with some specific guidelines for dealing with postoperative hypoxia and hypercar-
57S bia. Lastly, our approach to tracheostomy following surgery is reviewed. REFERENcES
care
1 DePadua CB: Effects of atropine and scopolamine on the cardiovascular system in man. Anesthesiolo ’ 25:123, 1964 2 Conahan Ti III, Omimky AJ, Woilman H, et a!: A pro. spective, random comparison of halothane and morphine for open heart anesthesia A one year’s experience. American Society of Anesthesiologists Annual Meeting (Abstract) 1071, p 137 3 Paskin S, Roshnan T, Smith TC: The effect of spinal anesthesia on the pulmonary function of patients with chronic obstructive pulmonary disease. Ann Surg 169:35, 1969 JF, Bergman NA, Coleman AJ: Factors influencing 4 Nunn the arterial oxygen tension during anesthesia with artificial ventilation. BrJ Anaesth 37:898, 1965 5 Shnider SM, Papper EM: Anesthesia for the asthmatic patient. Anesthesiology 22:888, 1961 8 Wollman The laboratory in the operating area. thesiology H: 31:176, 1969 7 Lecky JH, Omimky AJ, Woliman HW: In preparation Lecky JH, Denlinger JK: In preparation
s
CHEST, VOL. 62, NO. 2, AUGUST 1972 SUPPLEMENT