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In 10 patients subjected to craniotomy for supratentorial cerebral tumours in neurolept anaesthesia, cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) were measured twice peroperatively by a modification of the Kety & Schmidt technique, using 133Xe. The relative CO2 reactivity was assessed indirectly as the % change of the arteriovenous oxygen difference (AVDO2) per mm change in PaCO2. The patients were premedicated with diazepam 10-15 mg perorally. For induction, thiopentone 4-6 mg/kg, droperidol 0.2 mg/kg and fentanyl 5 micrograms/kg were used, and for maintenance N2O 67% and fentanyl 4 micrograms/kg/h. During the first flow measurement the median and range of CBF was 30 ml/100 g/min (range 17-45), of AVDO2 8.0 vol % (range 4.1-9.5), and of CMRO2 2.28 ml O2/100 g/min (range 1.57-2.84). During the second CBF study, AVDO2 increased to 9.3 vol % (range 3.4-11) (P less than 0.05), and CMRO2 increased to 2.51 ml O2/100 g/min (range 1.88-3.00) P less than 0.05, while CBF was unchanged. The CO2 reactivity was present in all studies, median 1.8%/mmHg (range 0.5-15.1). The correlation coefficients between jugular venous oxygen tension/saturation, respectively, and CBF were high at tensions/saturations exceeding 4.0 kPa and 55%, indicating that hyperperfusion is easily unveiled by venous samples from the jugular vein during this anaesthesia.

The CO2-production and degree of relaxation after increasing doses of suxamethonium were measured in seven patients undergoing alloplastic surgery of the hip. The study indicates that the CO2-production rises following the injection of increasing doses of suxamethonium. Another group of patients received diazepam 0.1 mg kg-1 before the injection of suxamethonium 1 mg kg-1. CO2-production was significantly reduced compared to CO2 production when suxamethonium was not preceded by diazepam. It is suggested that diazepam in doses larger than 0.1 mg kg-1 might be effective in preventing fasciculations and postoperative muscle pains before the injection of suxamethonium in a dose of 0.5 mg kg-1.

Eighteen patients undergoing alloplastic surgery of the hip were divided into three groups, each consisting of six patients. All operations were performed under endotracheal intubation using halothane N2O-O2 anaesthesia. After a steady state as to CO2-production had been obtained, suxamethonium 1 mg kg-1 was given intravenously to the patients in Group I. A maximum rise in CO2-production of 14.8% (range: 12.9-16.8) was observed after 5 min. In Group II, patients were pretreated with pancuronium 0.01 mg kg-1: no increase in CO2-production was observed. The third group received a continuous infusion of suxamethonium. In this group there was an increase in CO2-production of 17.6% (range: 6.7-22.0) 5 min after start of infusion. The CO2-production then fell to the preinfusion level over the next 10 min.

The Venturi circuit was studied with regard to CO2 elimination in a model experiment. A mean concentration of 0.6% CO2 in the fresh gas supply to the patient was accepted. The experiments demonstrated that a soda-lime charge of 200 g will cover the elimination requirements of CO2 in a Venturi circuit for any patient below 100 kg b.w. for a period of 3 h, while a soda-lime charge of 300 g will suffice for 5 h. The utilization of the soda lime charge is of the same order of magnitude as that of the much larger canisters used in circle circuits. In the Venturi circuit, the size of the soda-lime charge can be adjusted to suit the body weight of the patient and the expected length of the anaesthetic procedure. One soda-lime charge for each anaesthetic procedure is preferable from the point of view of hygiene. The charge should not be less than 200 g.

Carbon dioxide production was measured in 20 adult patients undergoing alloplastic operation of the hip. Body weight ranged from 40 to 81 kg. Anaesthesia consisted of lumbar plexus block, i.v. diazepam, pethidine, pavulon and N2O/O2 under controlled ventilation. CO2 production was 2.13 ml kg-1 min-1 (interquartile range 2.09-2.23). A fresh gas flow rate of about 30 ml kg-1 min-1 was required for the elimination of CO2 produced when using the Venturi system for inhalation anaesthesia.

Measurements of carbon dioxide production were carried out on 20 patients undergoing arthroplastic operation of the hip joint, under halothane anaesthesia supplemented with lumbar plexus block. Compared to spontaneous respiration, the carbon dioxide production during controlled ventilation, with and without muscular relaxation, showed a decrease of 19% and 12%, respectively.