A pressure and volume-limited inflation syringe.

Excessive pressures generated in balloon-tipped pulmonary artery (PA) catheters, which have migrated distally, contribute to the morbidity and mortality associated with their use. A simple syringe modification is described by which additional dead space is added to the inflation syringe. The volume of injected gas is also increased to compensate for the dead space, thus ensuring correct balloon inflation. The added dead space acts as a compression chamber should normal balloon inflation be restricted (Safety Syringe). An additional modification is described in which the syringe nozzle is reduced to a pinhole, thus decreasing the rate of gas escape and lessening the possibility of rapid lateral impact of the balloon on the PA wall (Super Safety Syringe). The syringes were compared with a standard volume-limited syringe. Pressures were recorded at the intraluminal site of balloon contact in rigid tubes, live porcine PA, and human cadaver PA. The Safety Syringe consistently generated pressures of less than 975 mmHg, the lowest pressure at which human PA rupture has been demonstrated, under the most adverse simulated clinical conditions. The currently used volume-limited syringe generated a pressure of approximately 1500 mmHg when balloon inflation was restricted, and in one human cadaver PA, produced rupture. The pinhole modification of the Super Safety Syringe increased the time to generate maximum pressure from less than 0.25 s to about 1.5 s.

A comparison of oesophageal and central venous pressures in the measurement of transpulmonary pressure change.

Oesophageal (oes) and central venous pressure (CVP) were compared as indices of transpulmonary pressure change (deltap). The mean increase of deltaPoes over deltapCVP was 2.8 cm H2O. The size and variability of the increase were similar to the expected difference between oesophageal and pleural pressure fluctuations occurring in the supine patient. Central venous pressure may be more accurate and reliable than oesophageal pressure for estimations of transpulmonary pressure change in the supine position.

Intravenous anaesthesia by infusion. A technique using alphaxolone/alphadolone (althesin).

Two hundred and seventy-three patients were anaesthetised using aphaxolone/alphadolone as a sole anaesthetic agent, administered in either a 10% solution or in increments of neat drug. Analgesics were given where necessary. This technique was instituted to provide a method of anaesthesia that avoided pollution of the atmosphere, with its possible harmful effects. As experience was gained, better results were obtained. Overall, 86% of the anaesthetics administered were without problems, 12% presented some difficulty, usually minor movement of the patient, and in 2% this technique was abandoned.

The effect of carbon dioxide on the neuromuscular and haemodunamic effects of AH 8265, a new non-depolarizing muscle relaxant.

The influence of carbon dioxide on the neuromuscular and haemodynamic effects of AH 8165, a new non-depolarizing muscle relaxant, was determined in nine healthy patients before the onset of minor elective surgery. Five patients (hypocapnic, group I) were maintained at an arterial Pco2 ranging from 25 to 31 mm Hg; four patients (hypercapnic, group II) at a Cco2 from 54 to 57 mm Hg. AH 8165 0.25 MG/KG (one-quarter of the dose required for intubation) was given by rapid central venous injection. Haemodynamic responses were similar in the two groups; there were increases in heart rate ranging from 45 to 60 per cent, increases in mean arterial pressure of 17 - 20 percent, and increases in cardiac output of 22-32 per cent. The intensity of neuromuscular blockade of the forearm muscles after AH 8165 was similar in the two groups, and there was no significant difference in recovery rates; group I patients were 80 percent recovered in 36.6 min. group II patients in 47.3 min. It was concluded that the activity of AH 8165 was not influenced by moderate changes in respiratory acid base status.