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

Abstract

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 β-blocker therapy and those not on β-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 β-blocked and non-β-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 β-blocked patients, compared to 40% and 23% of non-β-blocke 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-β-blocked group ( P = 0.02). Only one episode of myocardial ischemia was recorded. This occurred in a β-blocked patient during extubation, was not associated with a significant hemodynamic response, and had resolved by 1 minute after extubation. It is concluded that after coronary artery surgery a clinically significant hemodynamic response to weaning from mechanical ventilation occurs in approximately one third of all patients, and that the response is sustained. A clinically significant response to extubation occurs in less than 10% of chronically β-blocked and in 40% of non-β-blocked cases, and this response is short-lived. Routine use of drugs immediately before extubation to attenuate the hemodynamic response is not justified for patients on chronic (3-blocker therapy when medication is continued up to the morning of surgery.