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(Chest. 2001;120:445S-453S.)
© 2001 American College of Chest Physicians

Trials Comparing Early vs Late Extubation Following Cardiovascular Surgery*

Maureen O. Meade, MD; Gordon Guyatt, MD; Ron Butler, MD; Brad Elms, RRT; Lori Hand, RRT; Andie Ingram, RRT and Lauren Griffith, MSc

* From the Departments of Medicine (Drs. Meade and Guyatt) and Clinical Epidemiology & Biostatistics (Ms. Griffith), McMaster University, Hamilton, Ontario, Canada; the Department of Anesthesia (Dr. Butler), University of Western Ontario, London, Ontario, Canada; and the Department of Respiratory Therapy (Messrs. Elms and Ingram, and Ms. Hand), Hamilton Health Sciences Corporation, Hamilton, Ontario, Canada.

Correspondence: Deborah J. Cook, MD, McMaster University, Faculty of Health Sciences Center, Department of Clinical Epidemiology & Biostatistics, 1200 Main St West, Hamilton, Ontario, Canada; e-mail: debcook{at}mcmaster.ca


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
We identified 10 randomized trials that compared alternative management approaches to patient care during and following cardiovascular surgery. One overall strategy involved a modification of anesthesia, in particular, a reduction in the dosage of fentanyl and benzodiazepine or the substitution of fentanyl for propofol (five randomized controlled trials [RCTs]). Pooled results show a shorter duration of ventilation (7 h) and a shorter duration of hospital stay (approximately 1 day) associated with lower anesthetic doses. The second strategy involved early vs late extubation once patients were admitted to the ICU (five RCTs). Pooled results show a shorter duration of ventilation (13 h) and a shorter duration of ICU stay (half a day) associated with early extubation. An additional 8 nonrandomized trials had findings that were consistent with the 10 RCTs. Reintubation, complications, and mortality rates were too low to draw conclusions about these outcomes. Overall, these studies indicate that anesthetic, sedation, and early-extubation strategies in selected cardiac surgery patients are associated with a shorter duration of mechanical ventilation and shorter lengths of ICU and hospital stays.

Key Words: cardiac surgery • coronary artery bypass • early extubation • extubation • mechanical ventilation • meta-analysis • systematic reviews • weaning


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Routine overnight postoperative ventilation following cardiovascular surgery was adopted in the 1960s after the demonstration of frequent postoperative respiratory complications.1 2 The development of high-dose opioid anesthetic techniques for use in patients undergoing cardiac surgery reinforced the need for postoperative mechanical ventilation.3 4 In the last decade, this approach has been challenged, and early extubation following cardiac surgery has been championed for many patients as safer and more cost-effective.5

Cardiovascular surgery provides special challenges, and special opportunities, for optimizing the weaning process. Much of cardiovascular surgery is elective, and a relatively small team of surgeons, anesthesiologists, and intensivists in each hospital can, should they choose to do so, standardize a number of aspects of care. Furthermore, strategies for minimizing the duration of intubation can include anesthetic and sedation regimens.

Investigators have taken advantage of these unique features to test a number of interventions designed to facilitate the early extubation of patients after cardiovascular surgery. As in all situations in which clinicians try to hasten weaning, the risk is that they will precipitate complications resulting from the premature termination of mechanical ventilation. The concern is greater in patients who have just undergone cardiac surgery, in which physiologic stress may induce cardiac ischemia and heart failure. In this section, we describe the results of studies that have examined the impact of strategies to reduce the duration of mechanical ventilation in patients after cardiovascular surgery.


   Materials and Methods
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 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
We have described the methods of our reviews in detail in the introduction to this supplement and in the article concerning alternative discontinuation assessment methods and weaning modes. Herein, we summarize these methods briefly, focusing on aspects specific to this topic.

Eligibility Criteria
We included all studies of adult and pediatric patients who had received mechanical ventilation following cardiovascular surgery that compared alternative strategies, one of which was designed to reduce the duration of time patients spent intubated, and measured the duration of mechanical ventilation. We included randomized controlled trials (RCTs) and controlled nonrandomized studies.

Search for Relevant Studies
To identify relevant studies, we searched MEDLINE, EMBASE, HEALTHStar, CINAHL, the Cochrane Controlled Trials Registry and the Cochrane Data Base of Systematic Reviews from 1971 to September 1999, and we examined the reference lists of all included articles for other potentially relevant citations.

Data Abstraction and Assessment of Methodological Quality
In duplicate, we abstracted data and rated methodological quality of all eligible RCTs or nonrandomized controlled cohort studies addressing treatment issues. One of the investigators rechecked the final data abstraction.

The methodological features of RCTs that we abstracted included the following: the method of randomization and whether randomization was concealed; the criteria for weaning, extubation, and reintubation; the extent to which groups were similar with respect to important prognostic factors; whether investigators conducted an intention-to-treat analysis; whether patients, clinicians, and those assessing outcome were blind to allocation; the extent to which the groups received similar cointerventions; and the reporting of the reasons for study withdrawal.

For nonrandomized controlled clinical trials, we considered the extent to which groups were similar with respect to important prognostic factors, whether the investigators adjusted for differences in prognostic factors, and the extent to which the groups received similar cointerventions.

Statistical Analysis
We abstracted or, when necessary, calculated effect sizes in terms of relative risks (RRs) and associated 95% confidence intervals (CIs) for binary outcomes, and mean differences and 95% CIs for continuous variables.

We pooled data from different studies when, based on the underlying physiology, we expected more or less the same treatment effect. For instances in which we could pool data, for continuous variables we considered the mean in each group and an estimate of variability from each group, which determined the weight given to the study in the pooled analysis. For pooling binary data, we calculated risk ratios using the methods described by Fleiss.6


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
We identified 10 RCTs, 9 from MEDLINE and 1 from EMBASE, comparing alternative management approaches to patient care during and following cardiovascular surgery.7 8 9 10 11 12 13 14 15 16 Investigators have tested two types of interventions to try to reduce the duration of mechanical ventilation. One strategy involves the modification of anesthesia, in particular a reduction in the doses of fentanyl and benzodiazepine or the substitution of fentanyl for propofol, and the other involves different approaches to care once patients are admitted to the ICU. We identified five trials of each type of intervention.

Table 1 describes these 10 RCTs. In addition to the methodological limitations of the RCTs shown in Table 1 , in particular the consistent lack of information concerning concealment, these studies failed to conduct intention-to-treat analyses. Some RCTs restricted the analysis to patients who achieved early extubation or to the extubation goals of the study arm to which the patients were allocated. We have chosen to report only outcomes in which at least 80% of the randomized patients in both groups were included in the analysis.


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  		Table 1.. Methodological Characteristics of RCTs Comparing Early vs Late Extubation Following Cardiovascular Surgery*

 
Four RCTs7 8 9 10 that tested lower doses of fentanyl in patients after coronary artery bypass surgery enrolled between 85 and 144 patients, and a fifth RCT tested fentanyl vs propofol in 70 patients (Table 1) . The results of all five RCTs suggested a reduction in the duration of mechanical ventilation with the lower anesthetic doses. No other outcomes consistently differed between the early-intervention and late-intervention groups in the five trials (Table 2 2A 2B )


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  		Table 2.. Results of Individual RCTs Comparing Early vs Late Extubation Following Cardiovascular Surgery*

 

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  		Table 2A.. Continued*

 

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  		Table 2B.. Continued*

 
The pooled results (Table 3 ) confirm a reduction in the duration of mechanical ventilation, with a mean effect of approximately 7 h. Although there is considerable heterogeneity among studies, both the smallest mean effect seen in an individual study and the lower boundary of the CI are approximately 1 h. The pooled results also showed a difference in the reduction of hospital length of stay (1 day) with early extubation, with a very narrow 95% CI.


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  		Table 3.. Pooled Results of RCTs Comparing Early vs Late Extubation Following Cardiovascular Surgery*

 
With respect to mortality and important morbidity, even after pooling across the four studies there were very few events, and as a result the 95% CIs were so wide as to be uninformative (Table 3) . Except for the outcome of reintubation, the observed trends favored the early-extubation strategy.

Five RCTs that used other approaches to achieve early extubation included the following more varied populations: elderly patients undergoing elective abdominal aortic reconstruction,13 mitral valvulotomy14 ; and three trials12 15 16 in patients undergoing coronary artery bypass surgery. Two RCTs reversed neuromuscular blockade to achieve early extubation12 14 and one RCT16 discontinued sedation at an earlier point, while two RCTs simply instituted early efforts at extubation.13 15 Sample sizes varied from 35 to 404 patients, and only Reyes et al15 recruited > 100 patients.

The results of all five trials suggested that they achieved, on average, a shorter duration of ventilation in the early-extubation group (Table 2) . Morbid events were rare and similar in the two groups. The pooled analysis confirms these findings and suggests, in addition, a decrease of half a day in ICU stay in the early-extubation group (Table 3) .

There are an additional eight nonrandomized controlled studies17 18 19 20 21 22 23 24 of early vs late extubation following cardiovascular surgery (Table 4 ). These were large studies conducted primarily in adults, and all studies evaluated a combination of altered anesthetic techniques and altered ICU care to achieve early extubation. The results were very similar to the RCT results (Table 5 5A ). The duration of intubation was reduced with the implementation of early-extubation strategies by 1 to 28 h, although associated reductions in ICU and hospital lengths of stay were relatively small and inconsistent, ranging from 1 to 53 h, and 0.3 to 2.6 days, respectively. Complication rates varied across studies in the early-extubation vs late-extubation groups, and these event rates were rather small.


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  		Table 4.. Methodological Characteristics of Clinical Non-RCTs Comparing Early vs Late Extubation Following Cardiac Surgery*

 

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  		Table 5.. Results of Non-RCTs Comparing Early vs Late Extubation Following Cardiovascular Surgery*

 

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  		Table 5A.. Continued

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
These studies unequivocally demonstrate that extubation following cardiac surgery can be achieved a few hours earlier than was the case with previous conventional practices, and that this reduction likely leads to patients spending fewer hours in the ICU, and possibly less time in the hospital. This benefit can be achieved through lowering the intensity of intraoperative anesthesia, decreasing postoperative sedation, or instituting a policy of early extubation without other specific interventions. Investigators have not rigorously tested the simultaneous use of all these interventions. These RCTs were consistently limited by a failure to do an intention-to-treat analysis, which is a potentially serious problem.

In these highly selected cardiac surgery patients, significant morbidity occurs infrequently enough that the 95% CIs around RRs with early vs late extubation are very wide. In fact, the 95% CIs are so wide that they are consistent both with a substantial increase or a substantial decrease in RR with early extubation. Another way to look at this result, however, is that event rates remain low in patients receiving early extubation. These low event rates, and the safety of early extubation, may well be restricted to the relatively low-risk patients undergoing coronary artery bypass grafting. The results of non-RCTs corroborated these findings.

Since lower doses of sedation and anesthesia, early reversal of neuromuscular blockade, and early attempts to discontinue mechanical ventilatory support all can reduce the duration of mechanical ventilation in patients undergoing cardiac surgery, cardiac programs should, and most now do, consider any or all approaches. It is likely that their implementation will reduce the duration of stay in the ICU, but the reduction will likely be less than a day, and possibly less than half a day. Nevertheless, this reduction could have a large impact, particularly if extubated patients no longer require ICU admission or if they require less intense nursing care.

While research has not unequivocally established the safety of early extubation, serious adverse event rates are so low that a trial of thousands of patients (or, with even a combined morbidity end point, at least many hundreds of patients) would be required to definitively establish the effect. Given the widespread adoption of early extubation following cardiovascular surgery, and suggestions of cost-effectiveness, spending scarce resources on further studies to detect small but clinically important increases in morbidity following early extubation may not be warranted.

The data included in this systematic review and a more comprehensive discussion of the original articles are included in an Evidence Report of the Agency for Healthcare Research and Quality.25


   Footnotes
 
Abbreviations: CI = confidence interval; RCT = randomized controlled trial; RR = relative risk

This article is based on work performed by the McMaster University Evidence-based Practice Center, under contract to the Agency for Healthcare Research and Quality (Contract No. 290-97-0017), Rockville, MD.


   References
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 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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