The effect of preoperative beta-blocker therapy on cardiovascular responses to weaning from mechanical ventilation and extubation after coronary artery bypass grafting.

The hemodynamic and electrocardiographic changes during weaning from mechanical ventilation and tracheal extubation were studied in 75 patients after elective coronary artery bypass surgery. Transfer from synchronized intermittent mandatory ventilation to spontaneous respiration through a T-piece was associated with an increase greater than 20% over baseline in systolic (SBP) and diastolic (DBP) blood pressure in 27% of patients, and in heart rate (HR) in 5% of patients. Although baseline SBP, DBP, and HR differed significantly between the patients taking chronic beta-blocker therapy and those not on beta-blockers (P values all < 0.003), there were no differences between these groups in their response to transfer to the T-piece. (P values: SBP = 0.98; DBP = 0.46; HR = 0.20). Tracheal extubation was associated with an increase greater than 20% of baseline in SBP in 18.9%, DBP in 16.2%, and HR in 5% of patients. However, there were significant differences between the chronically beta-blocked and non-beta-blocked groups, both in baseline values for SBP, DBP, and HR (P values all < 0.001), and also in the SBP response (P = 0.007) and HR response (P = 0.02) to extubation. Extubation was associated with a greater than 20% increase in SBP in 8.2% and DBP in 12.2% of chronically beta-blocked patients, compared to 40% and 23% of non-beta-blocked patients, although the DBP response was not statistically different (P = 0.14) between the groups. Similar proportions of patients in both groups increased their HR more than 20% above baseline, but the increase was much greater in the non-beta-blocked group (P = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)