Ventilation during bronchoscopy.

Abstract

A brief review of techniques used to provide anaesthesia and ventilation during bronchoscopy indicates the advantage of Sanders’ technique of ventilation, using the injector principle. A jet of oxygen, attached to an endotracheal tube or bronchoscope, entrains a volume of air several times greater than its own flow volume. The flow can be used to generate pressures sufficient for inflation of the lung. Intermittent positive pressure ventilation can then be produced by periodic interruption of the flow through the jet with the help of a manually operated valve or with a Bird Mark II ventilator. The pressure generated depends on the volume of flow through the jet and the cross sectional area of the tube. An increase in the volume flow through the jet will produce a proportional rise in inflation pressure; reduction of the cross sectional area of the tube, leaving the jet unchanged, will produce an exponential increase in inflation pressure. This explains the higher inflation pressures obtained with a tube of uniform diameter, e.g., the Jackson type of bronchoscope in comparison to bronchoscopes with a cone shaped end. Blood gas determinations in 20 patients show that adequate ventilation can be obtained during bronchoscopy while allowing the bronchoscopist complete freedom for observation and instrumentation through the bronchoscope. The only practical problem is a leak of air around the instrument which can prevent the attainment of adequate inflation pressures; this leak can be overcome by increasing the driving pressure of the jet and may be minimized by external supraglottic pressure. In children, the scope produces a snug fit, smaller jets and lower driving pressures must be used to avoid excessive inflation pressures.