Abstract
Transportation of patients critically dependent on positive end expiratory pressure (PEEP) can be problematic, as a patient of ours with adult respiratory distress syndrome (ARDS) and bilateral broncho-pleural fistulae demonstrated. He required intermittent positive pressure ventilation (IPPV) (Siemens 900C) with 100% O2 and PEEP of 2 kPa to maintain his arterial O2 saturation (SaO2)>90%. Severe hypoxemia (SaO2<75%) occurred on change to a portable ventilator (Oxylog, Dräger) with a PEEP valve (Ambu 20) at its expiratory port, despite adjusting the valve to 2 kPa, continuing use of 100% O2, and varying the ventilatory pattern. The problem appeared due to loss of PEEP because of gas leak from the lungs via his intercostal catheters. It was solved by introducing a continuous O2 flow of 51/min into the circuit between the Oxylog non-rebreathing valve and endotracheal tube. We used a model lung to investigate the effect of a gas leak from the lungs or circuit on the performance of the Oxylog IPPV/PEEP system. Lung compliance and ventilatory pattern were adjusted so that tidal volume (VT)=0.61, peak inspiratory Airway pressure (PIP)=5 kPa, PEEP=1.5 kPa, and respiratory rate=10/min. A small leak was introduced from the lung resulting in a decrease in PIP, VT, and PEEP. Adjustment of ventilator minute volume to restore PIP to 5 kPa failed to restore PEEP, airway pressure continuing to fall throughout the expiratory pause. PEEP was restored by providing a compensatory flow of O2 of 5l/min to the system between the Oxylog nonrebreathing valve and the lung. We conclude that significant loss of PEEP can occur in patients with gas leaks from the lung when ventilators, such as the Oxylog, are used that do not provide a compensatory flow of gas into the lung during expiration and the expiratory pause. If the patient is critically dependent on PEEP this loss will result in severe hypoxemia.
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McQuillan, P.J., Hillman, D.R. & Woods, W.P.D. Positive end expiratory pressure and critical oxygenation during transport in ventilated patients. Intensive Care Med 16, 513–516 (1990). https://doi.org/10.1007/BF01709403
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DOI: https://doi.org/10.1007/BF01709403