ARE ALL EFFECTS OF ESMOLOL EQUALLY RAPID IN ONSET

The purpose of this study was to compare the time course of the bradyc ardic and hypotensive effects of esmolol. Ten patients undergoing cran iotomy requiring hypotension were anesthetized with nitrous oxide and isoflurane. During steady state anesthesia, the response to an infusio n of esmolol 500 mu g . kg(-1). min(-1) for 90 s followed by 300 mu g . kg(-1). min(-1) was measured over 60 min. Heart rate (HR), mean arte rial pressure (MAP), and plasma renin activity (PRA) responses did not occur with equal rapidity. The half-time for the 14% decrease in HR ( 81 +/- 13 bpm to 70 +/- 9 bpm) was 1.2 min. MAP decreased by 26% (85 /- 7 mm Hg to 63 +/- 6 mm Hg) with a 17.8 min half-time. This delay in MAP response may, in part, be related to the gradual 44% decline in P RA (9.5 +/- 4.5 ng degrees mL(-1). h(-1) to 5.3 +/- 2.5 ng . mL(-1). h (-1)) occurring with a half-time of 11.9 min. The times to attainment of 90% maximum decreases were 4.8 +/- 3.0 min for HR, 42.5 +/- 8.9 min for MAP, and 32.1 +/- 15.0 min for PRA. Thus although esmolol has an ultrashort kinetic half-life, only the HR effect can be considered to have an ultrashort onset.