Early Extubation After Cardiac Surgery: No Increase in Ischemia

Abstract & Commentary

Synopsis: In a randomized study of patients undergoing coronary artery bypass surgery (CABG), those extubated between one and two hours after surgery had no more evidence of ischemia than those extubated after 10-12 hours.

Source: Berry PD, et al. Brit J Anaesth 1998;80:20-25.

In an attempt to shorten hospital and icu stay, patients undergoing CABG are being extubated sooner following surgery. They are often hypothermic, marginally compensated hemodynamically, and still experiencing the effects of anesthesia. Adverse effects of early extubation include the need for re-intubation, hemodynamic deterioration, and cardiac stress. Berry and associates studied the incidence of electrocardiographic (ECG) ischemia in a prospective, randomized study of 98 patients with good ventricular function and no lung disease undergoing elective CABG surgery. Three ECG leads were recorded for 24 hours following surgery in all patients. The time-weighted sum of all ST-segment changes was calculated. Acute ischemia was defined as ST-segment changes of more than 2 mm in any lead. An acute myocardial infarction (MI) was diagnosed by characteristic elevations of blood MB-CPK levels or the appearance of new Q waves on ECG.

Thirteen patients were excluded due to bundle branch blocks, poor arterial blood gases, excessive bleeding, death in the early postoperative period,1 and failed early extubation (3 patients), which left 85 patients for analysis. The early extubation group, E (43 patients) differed from the late group L (42 patients) only in that more E were being treated for hypertension and more were receiving beta blocker therapy (P = 0.030). There was no difference in preoperative ischemia, surgical success, operative length, or complications.

The number of patients experiencing postoperative ST-changes was similar in both groups (22 in E vs 17 in L; P = 323). ST depression was more frequent in the E group (20 vs 11; P = 0.029), although when the effect of preoperative hypertension was included in a multivariate analysis, no independent association with E or L extubation was found in the development of ST-changes or ischemia. Nitroglycerine was used more frequently in the E group and epinephrine more frequently in the L group. Four patients developed non-fatal MIs, two in each group, and two patients died, both in the L group. Ischemic burden (mm ST change times hours it was present, divided by the total hours of monitoring), CPK levels, hospital length of stay, and ICU length of stay were not different between the groups.

COMMENT BY CHARLES G. DURBIN, Jr., MD, FCCM

This is an interesting study demonstrating a lack of correlation between early extubation and development of ischemia following elective CABG surgery. Its conclusions must be viewed cautiously for several reasons. The initial randomization failed to control for beta blocker therapy use. Although multivariate analysis can help separate the issues, it essentially reduces the power of the experiment to show a difference when one actually exists (type I error). A second problem is that three patients failed early extubation and were dropped from analysis. The hazards of reintubation may adversely affect patient outcome and should be recognized. This may not have affected the ischemia analysis but certainly should affect enthusiasm for early extubation.

Another issue is the surgical technique used. Many of these patients underwent normothermic bypass with electrical fibrillation with a short cross clamp time. This is an unusual technique in the United States. The effect of surgical technique was not analyzed in the study. Body temperature was not reported or compared. Anesthesia may have been different in the two groups as well, lowdose narcotic and propofol in E and higher dose narcotic with propofol in L. The increased use of nitrates in the E group and epinephrine in the L group is concerning. Were these patients being treated for identified problems? How did drug use correlate with outcomes?

It is difficult to do the "perfect" study looking for adverse outcomes. This paper suggests that ischemia is not a major concern when considering early extubation following elective CABG surgery, but more information is needed before this technique can be advocated universally.