COMPARISON OF THE ANAESTHETIC AND HAEMODYNAMIC EFFECTS OF CHLORMETHIAZOLE AND THIOPENTONE

Two groups of eight women (60 – 85 yr) undergoing gynaecologicaloperations of 50 to 130 min duration were compared. Anaesthesiawas induced with either thiopentone (mean 4.5mg kg^–) orchlormethiazole(mean 6.0 ing kg^–1) and maintained withnitrous oxide and pethidine in combination with the drug usedfor the induction. The hourly maintenance dose and the plasmaconcentration determined at equilibrium were greater for chlormethiazole(means 4.7mg kg^–1 h^–1 and 27(µmol litre^–1)compared with 1.3 mgkg ^–1h ^–1 (P< 0.01) and 16µmollitre^–1 respectively for thiopentone (P< 0.02). Impedancecardiography showed that cardiac output was decreased by 30–40%in the thiopentone group (P < 0.01), whereas ho significantchange was observed in the chlormethiazole group. Chlormethiazoleanaesthesia was followed by a significant increase (P<0.02)in stroke volume. No correlations were found between the plasmaconcentrations and changes in the haemodynamic indices for eitherof the drugs.