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Plasma fentanyl concentrations were measured by radioimmunoassay in patients during aortocoronary bypass surgery and correlated with hemodynamic responses to surgical stimulation. Thirty patients scheduled for aortocoronary bypass surgery were divided into three groups of 10. Patients in group 1 received fentanyl, 30 micrograms/kg, as a loading dose followed by an infusion of 0.3 microgram/kg/min; those in group 2 received 40 micrograms/kg as a loading dose followed by an infusion of 0.4 microgram/kg/min; and those in group 3 received 50 micrograms/kg as the loading dose followed by an infusion of 0.5 microgram/kg/min. The total dose of fentanyl administered to each group up to the time of rewarming on cardiopulmonary bypass was 60 micrograms/kg, 90 micrograms/kg, respectively. Each of the dose regimens produced stable plasma concentrations starting approximately 20 minutes after induction and continuing until the infusion was discontinued. Patients in group 1 had a mean plasma concentration of 10 to 12 ng/ml in the stable period compared with 12 to 14 ng/ml in group 2 and 15 to 18 ng/ml in group 3. Fewer patients in group 3 responded to intubation and surgical stimulation than in the other groups, although the differences between groups were not statistically significant. Response to stimulation was treated by the administration of droperidol or volatile anesthetic agents. At a plasma concentration of 15 ng/ml, 50% of patients had an increase in systolic blood pressure which required treatment. This minimal intra-arterial concentration, analogous to MAC, can be achieved by the administration of fentanyl as a loading dose of 50 micrograms/kg followed by an infusion of 0.5 microgram/kg/min.

We examined whether different plasma fentanyl concentrations could maintain hemodynamic stability during coronary artery surgery. Two randomly selected groups of 10 patients were studied. Patients in group 1 received a single 75-micrograms/kg intravenous dose of fentanyl; patients in group 2 received the same dose but it was followed by an infusion of fentanyl at a rate of 0.75 micrograms/kg/min. The total dose of fentanyl in group 2 was 162 +/- 6.5 micrograms/kg (mean +/- SEM). At some point during surgery, all 10 patients in group 1 and 7 of 10 patients in group 2 had a hypertensive response. Plasma fentanyl concentrations in the two groups were not significantly different in the period 10-45 min after induction of anesthesia. At 60 min, corresponding to the time of aortic root dissection, mean plasma fentanyl concentration was statistically significantly lower in group 1 than in group 2 (13.5 +/- 1.4 ng/ml and 24 +/- 2.3 ng/ml, respectively, P less than 0.01). However, no significant difference was observed in the frequency of hypertensive response between the two groups in the period before cardiopulmonary bypass. During cardiopulmonary bypass, plasma fentanyl concentrations in group 1 were 2-3 times lower than those in group 2, and hypertension was observed in all 10 patients in group 1 but in only 2 patients in group 2 (P less than 0.05). Patients in group 1 were ventilated for 16.6 +/- 1.5 h, and those in group 2 for 19.1 +/- 1.8 h, postoperatively (P greater than 0.05). Six patients in group 1 required vasodilating drugs, whereas eight patients in group 2 required alpha-adrenergic agonists. Although the plasma fentanyl concentrations achieved were not successful in totally suppressing a hypertensive response, this study suggests that a plasma fentanyl concentration might be attainable to effect this.

MAC BAR, the minimum end-tidal alveolar anesthetic concentration that inhibits adrenergic response to a noxious stimulus in 50% of subjects, is a quantifiable physiological parameter that can be used to determine potency and therapeutic indices of volatile anesthetics. We wished to determine whether there is a minimal intraarterial plasma concentration (MIC BAR) of an opiate such as fentanyl that will prevent a hypertensive response to noxious stimuli in 50% of patients undergoing aortocoronary bypass surgery (ACBP). Forty-three patients with good left ventricular function were studied. All patients were premedicated with diazepam, morphine, and scopolamine. Five groups of patients were anesthetized with different fentanyl anesthesia protocols, each designed to produce different plasma fentanyl concentrations (PFC). A 20% increase in systolic blood pressure compared to control was considered an adrenergic response that related to the plasma fentanyl concentration inferred from each patient's PFC time-concentration curve. Only four patients became hypertensive with a PFC greater than 20 ng/ml. One patient became hypertensive at intubation with a PFC of 12.3 ng/ml. There was no statistically significant difference in the mean PFC in patients who became hypertensive at each event. During aortic dissection, when significantly more patients became hypertensive, there was no difference in the incidence of hypertension in patients with a PFC above or below 20 ng/ml. Two patients became hypertensive at skin incision with a PFC over 30 ng/ml. A MIC BAR could not be identified because of the great variability in the PFC of patients who became hypertensive.(ABSTRACT TRUNCATED AT 250 WORDS)

In an attempt to prevent the decrease in nasopharyngeal temperature (NPT) ("afterdrop") after cardiac surgery, 30 patients undergoing hypothermic cardiopulmonary bypass (CPB) were randomly assigned to receive humidified heated inspired gases at 45 degrees C at the proximal end of the endotracheal tube (group I) or dry gases at room temperature (group II), from the time of termination of CPB. All patients received high flow rates on CPB during the rewarming period with the use of vasodilator drugs when necessary. Both groups were comparable with respect to total bypass time, rewarming time, and temperature at termination of CPB. In addition, the NPT was compared with the tympanic membrane temperature (TMT) in group I to assess the validity of the NPT under these conditions. The results indicate that heating and humidifying inspired gases do not prevent afterdrop and do not falsely increase the nasopharyngeal temperature. The reasons for the ineffectiveness of heated humidified gases may include a large heat deficit at termination of CPB despite a normal NPT, and the very small heat content of heated gases. Monitoring the temperature of a site that reflects the heat deficit, and a more complete rewarming during CPB are suggested as a better approach to the prevention of afterdrop.