[Effects of propofol and fentanyl on the baroreceptor reflex in geriatric patients]

Increasing age and anaesthetics diminish the baroreflex response to acute changes in blood pressure. This study was designed to investigate the effects of propofol and the combination of propofol with fentanyl on the baroreflex activity in geriatric patients.

Baroreflex sensitivity was studied by the method of Smyth et al. in 10 elderly (72 +/- 6 yrs) and in 10 younger (48 +/- 6 yrs) patients. Nitroprusside (depressor test) and phenylephrine (pressor test) were used to induce changes in blood pressure of 20 mmHg each to alter the stimulation of the baroreceptor sites. Anaesthesia was induced with propofol, 2 mg x kg-1 b.w.m, and maintained by a continuous infusion of 12 mg x kg-1 x h-1 for 10 min and thereafter with 6 mg x kg-1 x h-1. Then a bolus of fentanyl, 7 micrograms x kg-1 b.w. was injected. Haemodynamic parameters and baroreflex activity were measured in the awake state, 10 min after induction of anaesthesia and 10 min after the administration of fentanyl. Plasma propofol concentrations were determined by HPLC 10 min after induction of anaesthesia with propofol and 10 min after injection of fentanyl. The slope of the linear regression changes in RR-interval [ms] per changes in systolic pressure [mmHg] was used as an index of the baroreflex sensitivity.

In the awake state the depressor slopes were significantly reduced by 60% in the elderly patients when compared to the younger patients. In both groups propofol decreased reflex sensitivity by 38% and 41% respectively; this effect was enhanced by the addition of fentanyl in the younger patients, while there was no further effect in the elderly. The pressor slopes did not change significantly in both groups neither with propofol nor with the combination of fentanyl, but again reflex response was significantly less in the elderly patients.

Our data demonstrate that in geriatric patients the baroreflex control of heart rate already is attenuated in the awake state. Propofol produces a further reduction in reflex sensitivity to an acute decrease in blood pressure; this effect is more pronounced in elderly patients as compared to younger individuals. Acute changes in posture or circulating blood volume during propofol anaesthesia may result in greater cardiovascular instability in older patients due to the greater impairment of circulatory control mechanisms.