Potentialisation par le captopril de l'hypotension induite par l'halothane

Abstract

In a double-blind study, twenty-four ASA 1 and II patients scheduled for otosclerosis surgery were randomized in two groups according to the premedication given orally 1 h before anaesthesia : placebo (group P ; n = 12) or 25 mg captopril (group C ; n = 12). Anaesthesia was induced with thiopentone, fentanyl and vecuronium and was maintained, after oral tracheal intubation, with N 2O/O 2 (50/50) ; 5 min after intubation, the inspired halothane concentration ( Fih) was set at 1.8–2 % in order to obtain a mean arterial pressure (P̄a) of 45–55 mmHg ; thereafter, Fih was increased or decreased (± 0.5 % every 3 min) in order to maintain this P̄a value. Ventilation was controlled in order to assure normocapnia (35–40 mmHg). Inspired and expired ( Feh) halothane concentrations were monitored by halothane analyser. The plasma renin (ARP) and conversion enzyme activities (AEC) were measured before anaesthesia (ARP 1, AEC 1), 5 min (ARP 2) and 55 min (ARP 3, AEC 2) after the start of anaesthesia. In group C, AEC 1 and AEC 2 were reduced by half, confirming the efficiency of captopril in inhibiting the conversion enzyme. ARP 1 and ARP 2 were increased in group C (5.42 ± 4.2 and 9.92 ± 7.35 μg · l −1 · h −1. ARP 3 increased in both groups (20.75 ± 8.42 μg · l −1 · h −1 in group C, and 24.60 ± 15.40 in group P). Pa decreased to 55 mmHg more rapidly in group C (9 min in group C ; 18 min in group P ; p < 0.05) and Feh could be reduced by a third (1.38 ± 0.29 % in group P ; 0.90 ± 0.17 % in group C ; p < 0.05). In conclusion, captopril 25 mg was active when given as premedication 60 to 90 min before surgery ; the renin angiotensin system was stimulated during this surgery and hypotension was induced more quickly with halothane in the presence of captopril. During hypotension, the halothane concentration could be reduced by one third.