Pharmacodynamics of fentanyl citrate in patients undergoing aortocoronary bypass.

The pharmacodynamics of fentanyl citrate were studied in two groups of patients. One group underwent surgery with cardiopulmonary bypass (CPB) and the other group had surgery without CPB; the latter group represented the controls. Apneic periods were considerably longer (2.70 +/- 0.90 hr) for the CPB patients than for the control patients (1.75 +/- 0.75 hr). The total plasma fentanyl concentration at which apnea ceased was not statistically different between the two groups. Minor differences were attributed to the massive dilution of plasma proteins after the adding of priming fluid to the heart-lung machine. This prolongation of apnea is of considerable clinical importance because it means that CPB patients must remain mechanically ventilated for longer periods.