Investigation of High Frequency Jet Ventilation (HFJV) in a model of bronchopleural fistula (BPF)

The management of patients with a bronchopleural fistula (BPF) undergoing surgery or respiratory support in Intensive Care involves complex decision making. The two most commonly used types of artificial ventilation are Intermittent Positive Pressure Ventilation (IPPV) and High Frequency Jet Ventilation (HFJV). Each of these have advantages and disadvantages and the clinician must balance the need to maintain an adequate tidal volume for gas exchange against the risks of increasing gas leak through the BPF caused by the higher pressures and volumes which may be required. In this thesis, experiments investigating the effects of HFJV and IPPV on ventilation and leak volumes whilst ventilating various sizes and positions of simulated BPFs are described. A survey was also conducted to gauge the current airway management of BPFs by specialist anaesthetists in the UK.A bench top model was used to ventilate (HFJV or IPPV) standard artificial ‘test’ lungs and/or cadaveric porcine lungs whilst data were collected (i.e. entrained/expired/leak volumes).Whilst ventilating with HFJV, leak and entrained volumes were shown to increase progressively with more proximally situated BPFs, whereas the measured expired volume decreased. The leak volume approximately halved when the BPF decreased from 1cm to 2mm across all ventilatory frequencies. The effects of alterations in applied pressure (Drive pressure) and duration over which positive pressure was applied (‘Inspiratory Time, IT %’) were determined. Changes in Drive Pressure affected the measured volumes with the best tradeoff between leak volume and expired volume being 1.5bar, in particular with a distal BPF. The optimum IT% varied depending on the position of the BPF and consideration of the tradeoff between leak volume and expired volume. The use of IPPV generated larger leak volumes with all positions of BPFs compared with the use of HFJV and the leak volume was proportional to both the tidal volume and ventilator frequency. These data suggest that using HFJV to ventilate lungs with a BPF, independent of size or position, would be preferable in order to minimize gas leak whilst maintaining ventilation through the provision of adequate tidal volume. This however is not the practice of the UK anaesthetists who responded to the survey, who stated that their preferred practice is to use conventional ventilation (IPPV) using a double lumen endobronchial tube.