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The central placement rate of central venous catheters inserted via the external jugular veins was assessed using two different types of catheter. In 50 patients a catheter-through-cannula design was used, in 50 a catheter-through-needle design; central placement rates were 72% and 60% respectively. Complications were few and never serious. The catheter-through-cannula design is recommended.

Difficulties were experienced in weaning a patient from a ventilator by means of intermittent mandatory ventilation (IMV). The difficulty was overcome by installing an alternative IMV system (Hudson "disposable IMV valve") through which the patient drew her spontaneous breaths. Laboratory measurements showed that the resistance of the ventilator breathing system was much higher than that of the alternative system, mainly as a result of the resistance of the humidifier. It was calculated from measurements with a preset pattern of simulated breathing that the extra, external, work of breathing through the ventilator breathing system was approximately 1.5 times the normal internal mechanical work of breathing for a normal patient; with the alternative system, the extra work was only 0.5 times the normal. It is stressed that the breathing systems of IMV ventilators should be judged with the same rigour as other systems through which the patient is required to breathe spontaneously. It is recommended that manufacturers should provide the necessary information.

The pressure in the internal jugular vein was measured with the head in three different positions using, first, a short cannula and then a catheter with a round occluded end and two side-holes. These pressures were compared with the central venous pressure. In the horizontal position using the catheter, the two venous pressure measurements were similar. With the open-ended cannula, results could be unreliable with the head turned towards the side of cannulation.

In 15 patients anaesthesia for elective Caesarean section was maintained with 50% nitrous oxide in oxygen and a 0.65% halothane supplement. In a further 15 mothers a 0.2% halothane supplement was used. In those mothers receiving 0.65% halothane intermittent measurements were made of maternal arterial halothane concentrations during the uptake and the excretion of the agent. At delivery the foetal umbilical venous concentrations were measured also. The mean time between administering halothane and delivery was 10.5 min (SD 3.5). The mean maternal arterial halothane concentration at delivery was 6.03 mg/100 ml (SD 0.75) and the mean umbilical vein concentration was 2.13 mg/100 ml (SD 0.69). The regression of Apgar scores at 1 min after delivery on umbilical vein halothane concentration at delivery was not significant. In the mothers receiving 0.2% halothane measurements of halothane concentration were made in five patients only. The mean maternal arterial halothane concentration at delivery was 1.56 mg/100 ml (SD 0.52) and the mean umbilical vein and artery concentrations were 0.8 and 0.38 mg/100 ml respectively. The use of 0.2% and 0.65% halothane supplements prevented awareness in all the mothers. However, dreaming occurred in two patients given a 0.2% halothane supplement. Studies are required to establish the minimum halothane supplement required to prevent awareness in a larger series of patients.

Mean venous pressures were measured in 20 patients in whom a catheter, inserted via the external jugular vein, failed to pass centrally. The catheter used had a rounded end and two side holes. Pressures were measured with the patient's head in three different positions. The pressures were compared with the central venous pressures measured from a catheter inserted through an antecubital vein (and confirmed to be placed centrally). In all patients the differences between the mean pressures from the two sites were all within 3 mm Hg and were not influenced by alteration in head position or the side of jugular catheterization.