Biomedical subjects
Publications and source records attributed to P J Venn.
A case of stridor is described which was due to the presence of a foreign body in the larynx of an infant. Following partial removal, compression of the right main bronchus was detected because of continuing low arterial oxygen saturation. The use of pulse oximetry allowed this complication to be identified, and the advantages of this method of monitoring are discussed.
We have assessed a Venturi driven device for delivering continuous positive airway pressure (CPAP) using a reservoir bag and expiratory valve under conditions of continuous flow and simulated spontaneous breathing. The system performed well and was economical, consuming only 3.5 litre min-1 of fresh gas. One Venturi was partially blocked and performed inadequately, but the function of a second one was close to the manufacturer's specification (inspired oxygen 33%, flow 20 litre min-1 against end-expiratory pressures of 0-1.8 kPa). Compliance curves for two reservoir bags (new and old) were defined; these showed that compliance increased as the pressure in the circuit increased. The characteristics of the expiratory valve approached those of a threshold resistor. Small fluctuations in airway pressure occurred at all settings of CPAP and decreased with the increasing compliance of the circuit at higher values of CPAP. The method provided to monitor the airway pressure was inaccurate and overestimated the true pressure by 20% at pressures greater than 1 kPa.
We studied the effect on systemic arterial pressure of fluid preloading with 1 litre of crystalloid fluid before spinal anaesthesia in 40 patients undergoing minor lower abdominal or lower limb surgery. Fluid was given at a rate of either 1 ml min-1 (no preload group), or 1000 ml in the 15 min (preload group) immediately before induction of spinal anaesthesia with 3 ml of 0.75% glucose-free bupivacaine. There was no difference between the groups in the character of anaesthesia or motor block in the lower limbs. The cephalad spread of analgesia ranged from L1 to C8. Analgesia was insufficient for surgery without supplementary analgesia in three patients in each group. The group not given a fluid preload had significantly lower arterial pressures (P less than 0.05) when anaesthesia extended above the T5 dermatome. The mean time before the lowest arterial pressure was recorded was twice as long in the preloaded group as in the non-preloaded group. Glucose-free 0.75% bupivacaine did not give a reliable extent of anaesthesia for lower abdominal surgery.
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