Speed of collapse of the non-ventilated lung during one-lung anaesthesia: the effects of the use of nitrous oxide in sheep

By enhancing gaseous uptake from the non-ventilated lung during procedures performed thoracoscopically, the rapid diffusion properties of nitrous oxid e would be expected to speed lung collapse and so facilitate surgery. To as sess the effect of nitrous oxide on the speed of absorptive lung collapse, a study was conducted using 11 anaesthetised sheep. Speed of collapse was a ssessed in an indirect manner by recording the time required in a closed-ch est situation for the airway pressure distal to a single lung airway occlus ion to decrease to -1.0 kPa. The influence of nitrous oxide was assessed by comparing the time taken for this decrease in airway pressure when the ani mal was being mechanically ventilated with 50% nitrous oxide in oxygen with the time taken when using 100% oxygen. In all assessments, it was found th at the decrease in airway pressure to -1.0 kPa occurred in a shorter time w hen nitrous oxide was used. The findings lend support to the hypothesis tha t during thoracoscopic surgery, mechanical lung ventilation with an oxygen/ nitrous oxide mixture will increase the rate of gaseous uptake from the non -ventilated lung and so hasten its absorptive collapse.