[Response of the cervical sympathetic activity to acute hypoxemia in dogs and its modification by volatile anesthetics].

Response of the cervical sympathetic activity (CSA) to acute hypoxemia was studied in dogs in the absence and in the presence of either halothane (H), enflurane (E), isoflurane (I) or sevoflurane (S). Multifiber potentials of CSA, EEG, heart rate (HR), arterial blood pressure (ABP) and arterial oxygen saturation (SaO2) were continuously monitored. CSA increased responding to acutely induced hypoxemia at a speed of -6 - 9% (SaO2).min-1. The response of CSA was estimated in two ways as a function of SaO2: The threshold was determined at the SaO2 level where CSA increased by 3% over the basal level and the gain was determined by the slope of CSA increase divided by the SaO2 span. They were 92% and -1.88 in the absence of volatile anesthetics, respectively. The threshold and the gain decreased markedly in the presence of various concentrations of volatile anesthetics. They were 89.2% and -1.16; 81% and -0.74; 84.2% and -1.16 and 86.2% and -0.94 with 1 MAC of H, E, I and S, respectively. The depressant effects of volatile anesthetics on the CSA responses to acutely induced hypoxemia can cause depressed control of the autonomic nervous system against hypoxemia and conceal the manifestation of clinical signs of hypoxemia.