Forty-eight patients scheduled to undergo spinal anaesthesia were allocated to three groups of 16 each according to ASA classification I-II-III. Each patient received a fluid load of 7 ml kg-1 and either ephedrine 12.5 mg i.v. and 37.5 mg i.m., or placebo. Twelve patients in the placebo groups developed a maximal decrease in mean arterial pressure exceeding 20%. Five of these (one in ASA II and four in ASA III) developed a decrease exceeding 33% and required treatment. In ASA risk group III, all patients in the placebo group had a decrease in mean arterial pressure exceeding 20%; in 50% of these patients, the decrease exceeded 33%. We conclude that prophylactic ephedrine is desirable for spinal anaesthesia, especially in ASA III patients.
A significant correlation was found between the inhibition produced by 1% halothane with nitrous oxide and oxygen on platelet aggregation in vitro and the increase in bleeding time during anaesthesia with halothane, nitrous oxide and oxygen in 10 patients. It is suggested that halothane in nitrous oxide with oxygen inhibits platelet aggregation in vivo and in vitro. The inhibition is not seen when platelet aggregation is studied in platelet-rich plasma from anaesthetized patients because the agents evaporate during preparation of platelet-rich plasma and during analysis in the aggregometer.
Treatment with alpha adrenergic receptor blocking agents has been used clinically for many years to obviate peripheral vasoconstriction in patients suffering from circulatory or thermoregulatory distress. Various reports indicating that administration of these agents may be followed by an increased plasma concentration of catecholamines, and subsequently an increased oxygen demand, led to 29 investigations on humans who were placed in a horizontal position in a thermoneutral environment and given 25 mg chlorpromazine intravenously, dissolved in 500 cc low molecular weight dextran. Blood pressure and heart rate remained unchanged during the infusions and significant changes in plasma noradrenaline (average fall: 4.42 nmol X 1(-1), range: -31.9- + 5.1) and in plasma adrenaline (average fall: 1.06 nmol X 1(-1), range: -16.3- + 5.11) were observed (P less than 0.01). The results indicate that as long as any baro-reflex activation of the sympathetic nervous system and acceleration of the nonshivering thermogenesis is avoided, the recommended treatment with alpha adrenergic receptor blocking agents can be performed without any increase in plasma concentration of catecholamines.
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