PRO AND CON J. Earl Wynands, MD, Editor

Pro: Early Endotracheal Extubation is Preferable to Late Extubation in Patients Following Coronary Artery Surgery Thomas

L. Higgins, MD

0

PIOID-BASED anesthesia continues to be the most popular technique for patients undergoing coronary artery bypass grafting (CABG), primarily since this approach promotes hemodynamic stability. High-dose opioid anesthesia is technically straightforward, leaving the anesthesiologist free to concentrate on other aspects of patient care. The tost of these advantages, prolonged mechanica1 ventilatory support, has been accepted by many anesthesiologists and surgeons, partly because of habit, and partly due to the belief that overnight ventilation is somehow beneficial to the patient’s respiratory and cardiovascular systems. Observations that early postoperative ischemia is related to adverse cardiac outcomei have prompted interest in continuing an infusion of high-dose opioids wel1 into the postoperative period,* potentially expanding the period of ventilatory support. Whereas control of the stress response probably reduces ischemia, this may not provide sufficient justification for prolonged mechanica1 ventilation, particularly because other methods of stress control and hemodynamic control may accomplish the task without the disadvantages of prolonged mechanica1 ventilation. The author hopes to convince the reader that early trachea1 extubation following CABG is not only possible, but preferable to intentionally delayed extubation, once the risks and benefits of prophylactic ventilation are fully taken into account. What constitutes “early” extubation? For the purposes of this discussion, early extubation wil1 be defined as removal of the endotracheal tube from the patient within 8 hours of the patient’s arrival in the postoperative unit, an arbitrary time limit that encompasses data from prior studies (Table 1).3-7Early extubation, by this definition, is more commonly used than assumed, often because of local habit or staffing considerations. Overnight ventilation with extubation on the first postoperative day has many adherents, particularly in institutions with a high volume of complex cases, and also when postoperative care and the decision to extubate are controlled by individuals other than the operating room anesthesiologist.

From the Cleveland Clinic Foundation, Cleveland, OH. Address reprints to Thomas L. Higgins, MD, Cleveland Clinic Foundation, Cleveland, OH 44195. Copyright 0 1992 by W.B. Saunders Company 1053-0770/92/0604-0018$03.00/0 Key words: extubation, coronary artey surgery, cardiac anesthesia, coronay artey disease 488

DEFINING THE CANDIDATE

FOR EARLY EXTUBATION

The truism that healthy patients tend to do wel1 and sick patients do poorly influences decision-making on extubation. In the healthy patient, even the minima1 risks of prolonged ventilation are outweighed by advantages of early extubation. Conversely, in the higher risk patient, the chance of infrequent but major events, such as reoperation for continued mediastinal bleeding, relegate the risks of continued ventilation to a secondary status. It is, thus, necessary to distinguish between patients likely to succeed after early extubation from those requiring further support. Patients with inadequate postoperative cardiovascular performance are best managed by controlling ventilation to reduce the work of breathing and to allow adequate sedation and, if necessary, neuromuscular blockade. Time to ICU discharge in these patients wil1 be governed by issues other than time of extubation, in any case. Postoperative morbidity and mortality are, to a large extent, predictable based on preoperative status.s Patients likely to have respiratory complications after cardiac surgery can be identified by the presence of congestive heart failure (CHF), emergency procedures, reoperation, impaired renal function, chronic obstructive pulmonary disease (COPD), prior vascular surgery, age greater than 70 years, and presence of significant aortic stenosis or mitral insufficiency.9 Unexpected events in the operating room (aspiration, incomplete revascularization, poor left ventricular performance post-cardiopulmonary bypass) may dictate prolonged postoperative ventilation. Table 2 outlines one approach to identifying the candidate for early extubation based on preoperative, intraoperative, and postoperative characteristics. RESPIRATORY

SYSTEM

BENEFITS OF EARLY EXTUBATION

Trachea1 intubation and mechanica1 ventilation, while safe, are not entirely benign. Endotracheal intubation contributes to morbidity, which increases with length of time intubated. Vocal cord granulomas and ulcerations can be detected in about two-thirds of patients intubated for more than 24 hours.lO An inflated, cuffed endotracheal tube produces significant depression of trachea1 mucus velocity after 1 hour. i1 Experimental animals subjected to intubation demonstrate complete cessation of mucus transport, epithelial damage, and loss of cilia.r2 Disruption of these host defenses may contribute to colonization of the tracheobronchial tree.

Journal of Cardiothoracic and VascularAnesthesia, Vol 6, NO4 (August), 1992: pp 488-493

489

PRO: EARLY EXTUBATION

Table 1. Early vs Late Extubation After Cardiac Surgery Number

Prakash3

Anesthetic

Type of Study

Author

1977/Not

Timing of Extubation

and

(% of Patients Able

Type of Patientl

Year Publishedi

First

randomized pro-

Technique

142 mixed (62 CABG)/Opioid

Findings

to be Extubated)

5 3 hr (87%)

Fewer ICU days NO increase in morbidity

spective

Earlier mobilization Klineberg4

1977/Retrospective

Quashas

1980/Randomized

72 CABG/Not stated

I 5 hr (62%)

38 CABG/lnhalation

I 8 hr (89%)

Earlier mobilization NO increase in morbidity

prospec-

NSD in intrapulmonary shunt NSD in ICU time

tive

NSD in hemodynamics NSD in plasma NE Less cardiopulmonary

mor-

bidity Less postop sedation Cost savings $70/patient Foster6

1984/Not

randomized pro-

< 8 hr (83%)

63 CABG/Opioid

Lower costs ABG sampling reduced 42%

spective

NSD in morbidity Impression: More comfortable Lichtenthal’

1983/Not

randomized pro-

100 mixed (69 CABG)/lnhalational

spective

7.35 on spontaneous ventilation Hemodynamically

stable without significant dysrhythmias

Well-perfused with adequate urine output (> 1.0 mL/kg/hr) Mediastinal bleeding < 100 mL/hrfor

22 hrs

Fully rewarmed (core temp > 36°C; no shivering)

NE, norepinephrine levels; CABG, coronary artery bypass grafting.

ability to cough. Clinical observation confirms that “it is usual for the patient to cough up a large amount of secretions immediately after the endotracheal tube is removed, in spite of previous suctioning.“14 Prophylactic ventilation was championed in the early days of cardiac surgery to reduce the work of breathing, allow greater postoperative analgesia, and promote better gas exchange.15J6 Machine-imposed work-of-breathing was a significant problem with early ventilators such as the Engstrom (LKB, Medical AB, Solna, Sweden) and Bird (Bird Corporation, 3M, St Paul, MN) respirators used in these studies, but became less important with the advent of IMV-mode ventilators, improved demand valves, and microprocessor-controlled ventilators with rapid response times. Early studies did not always distinguish between atelectasis and increased alveolar-arteriolar oxygen gradients resulting from other causes. More recent studies do not support the use of prophylactic ventilation to prevent atelectasis. Shackford et al” studied 35 high-risk, elderly patients undergoing abdominal aortic reconstruction, and found no differente in intrapulmonary shunt and oxygen delivery between those randomized to early extubation (3.3 ?Z0.5 hr) versus prophylactic overnight ventilation (18 t 0.5 hr). Similarly, Dantzker et al, examining gas exchange following CABG, found no differente in the leve1 of intrapulmonary shunt whether the patient was intubated or breathing spontaneously.‘* One retrospective analysis of cardiac surgical patients noted a greater incidence of postoperative atelectasis and longer ICU stay in those whose extubation was delayed beyond 24 hours.” Positive end-expiratory pressure (PEEP) has been shown to be of benefit in the treatment of noncardiogenic pulmonary edema or adult respiratory distress syndrome (ARDS).

490

THOMAS

However, prophylactic PEEP does not protect against development of ARDS. In a randomized trial of 24 well-matched cardiac surgical patients, PEEP did not result in significant roentgenographic improvement in the degree or frequency of left lower lobe atelectasis, or produce a clinically significant improvement in arterial-alveolar oxygen ratios. *l The argument for using PEEP to reduce postoperative mediastinal bleeding has also been discounted in the one randomized study examining this issue.2Z The key to adequate postoperative respiratory function is adequate analgesia, which can be attained via conventional means, patient-controlled infusions,24 intrathecal morphine,25 or thoracic epidural analgesia.26 CIRCULATORY

BENEFITS OF EARLY EXTUBATION

Adverse circulatory effects of positive-pressure ventilation are wel1 documented.27-29 In theory, increased intrathoracic pressure associated with positive-pressure mechanica1 ventilation andfor PEEP should decrease preload to both ventricles, while increasing right-sided afterload by virtue of increased pulmonary artery impedance from lung inflation. This expected decrease in cardiac output (CO) with PEEP has been documented in the CARG population, using thermodilution and nuclear radiography.29 Addition of PEEP at 5, 10, and 15 cmHzO results in progressively decreased CO; a 15% decrease at a PEEP of 15 cmH20. Guyton et al noted that modest volume loading attenuated the deleterious effect of PEEP, and estimated that the change in transmural pressure (in mmHg) approximately equals the change in PEEP (in cmH20) multiplied by 0.4.29 Other investigations suggest that changes in cardiac filling are not sufficient to explain the hemodynamic effects of positive pressure, because stroke volume may remain depressed even after volume expansion.30 The influence of PEEP on right ventricular dysfunction appears to be most marked in the presence of right coronary artery stenosis. Hemodynamic effects of positive airway pressure are not limited to the heart. PEEP-induced decreases in CO are accompanied by significant reductions in myocardial, splanchnic, and skeletal muscle flow, although renal and cerebral vascular beds are relatively unaffected.31 Even so, ventilation Koning et al 32 found that positive-pressure resulted in substantial decreases in renal perfusion, consistent with increased renal venous pressure due to impaired venous return to the heart. Exaggerated hemodynamic responses to positive-pressure ventilation occur in patients with COPD when exhalation times are insufficient to prevent air-trapping. This phenomenon, known as auto-PEEP, can produce lung hyperexpansion and dramatic rises in pleura1 pressure, even in the absente of significant extrinsic PEEP.33 In a clinical study of 28 low-risk, stable postoperative CARG patients, Prakash et a134noted that the transition from controlled ventilation to either spontaneous ventilation or intermittent mandatory ventilation (IMV) was associated with increases in oxygen consumption, CO2 production, and cardiac index. They were “unable to demonstrate adverse cardiorespiratory effects of early extubation in patients who fulfilled extubation criteria.” In a randomized comparison, Quasha et al5 were unable to find

L. HIGGINS

differences between early and late extubation groups in the incidence of postoperative hypertension, use of sodium nitroprusside, cardiac index, systemic vascular resistance index, pulmonary vascular resistance index, or ratepressure product. Gal1 et al instrumented six patients undergoing routine CABG with left ventricular micromanometers, left ventricular minor axis dimension crystals, and left atria1 and intrapleural pressure catheters.35 Physiologic data recorded during controlled mandatory ventilation and again following extubation (7.2 hours after ICU arrival) demonstrated significant declines in intrapleural pressure, and significant increases in LV end-diastolic diameter, stroke work, and CO following extubation. The authors attributed the improved ventricular function following extubation to increased preload associated with a shift of capacitance blood volume towards the chest. While the Gal1 study suggests that early extubation is clinically beneficial, caution must be exercised in patients with left ventricular dysfunction. The increased preload and afterload seen with termination of ventilation have been shown to provoke acute left ventricular failure in this subset of patients.36 STRESS RESPONSE

Slogoff and Keats,37 the S.P.I. Research Group38 and others have focused awareness on perioperative ischemia. It has been suggested that stress, reflected by ECG changes, might be controlled with opioid infusions wel1 into the postoperative period, perhaps even beyond the traditional extubation time on the morning of the first postoperative day.* It is not clear, however, that even high doses of opioids are capable of completely suppressing the catecholamine responses.39,40 In addition, at some point the clinician must awaken and extubate the patient, and thus decrease plasma concentrations of opioids below the respiratory depressant threshold. Clearly, it would be impractical to keep patients intubated and on high-dose opioid infusions for several days. The question then becomes not whether to control the response, but when the switch from high-dose opioids to other methods is best achieved. Reversal of opioid action with naloxone or mixed agonist-antagonist drugs such as nalbuphine appears to be ill-advised.41 Hemodynamic responses to extubation itself appear to be relatively modest.42 If the stress response must be controlled wel1 into the postoperative period, then early extubation, before operative opioids have been entirely metabolized, followed by either opioid-sedative infusions andlor regional techniques43+ may more efficiently control the stress response than prolonged intubation with inherent stresses from coughing and suctioning. Though it is possible to achieve postoperative sedation with agents such as propofol or midazolam,45,46 it remains to be seen if nonnarcotic sedative regimens can control the stress response and reduce the incidence of perioperative ischemia. Further study is needed to determine which approach results in less stress and less ischemia: extubation at the earliest opportunity, or prolonged sedation, with the possibility of “break-through” stress should the patient awaken and gag on the endotracheal tube. Examining hemodynamics and plasma norepinephrine as a marker of stress response, Quasha et al5

491

PRO: EARLY EXTUBATION

found no differente between early and late extubation groups. However, the early extubation group did require less morphine and diazepam for sedation. ECONOMIC

Early Risks

-

Late Complications

BENEFITS

Earlier extubation permits earlier discharge from the ICU, particularly by avoiding oversedation and resultant depression of the brainstem respiratory center. Though Prakash et als documented fewer ICU days in their study, Quasha et al5 failed to find a differente in ICU time, although his group did document tost savings from earlier extubation. At approximately $1,500 per ICU day, the savings from earlier ICU discharge add up quickly. Indirect economie benefits also accrue: earlier mobilization of the patient,4J lesser need for sedation, and less cardiopulmonary morbidity” presumably reduce nursing demands and need for additional laboratory testing. A patient whose surgery is postponed because of the lack of ICU beds represents a tost to the hospital: operating room time and associated staffing costs cannot be recovered. The patient also pays a tost in additional anxiety, with the possibility of myocardial ischemia occurring prior to operation with obvious sequellae such as high-risk emergency operation, or even death. Early extubation with early ICU discharge reduces the chance of “ICU gridlock” and case cancellations. WHEN IS THE OPTIMAL

--------.

TIME FOR EXTUBATION?

The criteria for extubation in the cardiac surgical patient are no different than for other major operations, once the late effects of cardiopulmonary bypass (CPB) are considered. Patients are generally adequately rewarmed at this institution by the third or fourth ICU hour, consistent with results reported elsewhere. 47The hypermetabolic response after hypothermie CPB occurs simultaneously with maximum spontaneous rewarming, and this represents the period of highest risk for decompensation.48 The nadir of ventricular function occurs about 4 hours following conclusion of CPB,49 or about 1 to 3 hours into the ICU stay. The best markers of compromised cardiopulmonary function, indicating need for continued ventilation, are low mixed venous oxygen saturation and high ( > 20 mmHg) left atria1 pressure.’ Poor urine output correlates with need for reintubatior9O and also suggests ventilation should be maintained. Otherwise, the decision to extubate follows conventional criteria. In fact, it may not be necessary in the cardiac surgical patient to satisfy the usual criteria of a 15 mL/kg vita1 capacity or maxima1 inspiratory force of more than 25 cmH*O, because rigid adherente to these guidelines may unnecessarily prolong intubation.51 Given that most patients can meet al1 of the above criteria for extubation beginning in the third or fourth hour of ICU stay, and that complications from intubation increase with time, the “window of opportunity” for extubation would appear to occur between 3 and 10 hours after ICU admission (Fig 1). CAVEATS

Changing from a routine of overnight ventilation to early extubation may require education of and cooperation from

Additional 0

24

4

Hom

After ICU Arrival

Fig 1. Early risks include hemodynamic instabilii, hypermetabolism, shivering, and mediastinal bleeding. Late complications encompass ciliary dysfunction, inability to cough and clear secretions, and patient discomfort. Costs escalate markedly if late extubation delays ICU discharge for an additional day.

the surgical team, ICU staff, nurses, and respiratory therapists. The conduct of patient care of those identified for early extubation wil1 differ in a number of ways, ranging from altered preoperative education to ensuring adequate rewarming to avoid late shivering. Some revisions of protocols and coordination of effort may be required on busy services to avoid peak extubation demands occurring at certain times of minima1 staffing. One argument frequently voiced against early extubation is that continued intubation protects the patient in the event of unusual and unexpected problems. However, this institution experienced a very unusual and unexpected problem: total failure of normal and backup electrical power sources.52 This occurred at 4 AM, and lasted 1 hour. Because 6 of the 14 cardiac surgical patients that day were already extubated, immediate attention and hand ventilation could be concentrated on the remaining ventilatordependent patients, potentially averting morbidity. While chances of a repeat occurrence are slim, this anecdote does illustrate that prolonged intubation is not necessarily protective against every unexpected occurrence.

SUMMARY

AND CONCLUSIONS

Prolonged mechanica1 ventilation following CABG should not be uncritically considered “routine,” and should only be used where indicated. A thorough physiologic and clinical evaluation with attention to hemodynamics, neurologie status, temperature and metabolism, hemostasis, and respiratory reserve should precede extubation. Continued postoperative ventilation is indicated in patients at high risk for complications, and it is possible to identify this subset preoperatively and upon arrival in the postoperative ICU. Early extubation (within 8 hours of arrival) should otherwise be the goal. The benefits of early extubation include improved cardiac function and patient comfort, reduction in respiratory complications, ease in management, and tost savings as the result of shortened length-of-stay in expensive postoperative units. More research is needed to clarify unanswered questions regarding ablating the stress response and avoiding myocardial ischemia.

492

THOMAS

L. HIGGINS

REFERENCES

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48. Chiara 0, Giomarelli PP,&agioli B, et al: Hypermetabolic response after hypothermie cardiopulmonary bypass. Crit Care Med 15:995-1000,1987 49. Breisblatt WM, Stein KL, Wolfe CJ, et al: Acute myocardial dysfunction and recovery: A common occurrence after coronary bypass surgery. J Am Col1 Cardiol15:1261-1269,199O 50. Tahvanainen J, Salmenpera M, Nikki P: Extubation criteria after weaning from intermittent mandatory ventilation and continuous positive airway pressure. Crit Care Med 11:702-707,1983 51. Michel L, McMichan JC, Marsh HM, Rehder K: Measurement of ventilatory reserve as an indicator for early extubation after cardiac operation. J Thorac Cardiovasc Surg 78:761-764, 1979 52. O’Hara JF, Higgins TL: Total electrical power failure in a cardiothoracic intensive care unit. Crit Care Med 20:840-843, 1992