Positive end expiratory pressure and critical oxygenation during transport in ventilated patients

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) greater than 90%. Severe hypoxemia (SaO2 less than 75%) occurred on change to a portable ventilator (Oxylog, Dräger) with a PEEP value (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 5 l/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 5 l/min to the system between the Oxylog non-rebreathing valve and the lung.(ABSTRACT TRUNCATED AT 250 WORDS)