Gas-powered and portable ventilators: an evaluation of six models

Gas-powered resuscitators (ventilators) designed to be used primarily for resuscitation should be basic and simple to use. They offer many advantages over manual methods of ventilation during in-hospital cardiopulmonary resuscitation. Portable ventilators intended for critical care transport require additional, more sophisticated features such as: adjustable pressure limiting valves, air-mixing, airway pressure gauge, independent tidal volume and rate controls, and a Positive End-Expiratory Pressure (PEEP) valve. The performance of six gas-powered resuscitators/portable ventilators (TransPAC, Oxylog, Ambu Matic, ERA 2000, Uni-Vent, and MARS) was evaluated.

The accuracy of volumes delivered to a test lung at three different compliance and resistance settings, was assessed for each ventilator prior to clinical evaluation during cardio-pulmonary resuscitation (CPR) and patient transport.

In each circumstance, measured tidal volumes and level of minute ventilation decreased as resistance was increased and compliance reduced. Much of this loss of measured tidal volume occurred through inspiratory pressure relief valves that tended to start leaking at pressures below the preset level. Increasing levels of back-pressure resulted in further reductions in tidal volume when the ventilators were tested using the air-mix mode (available on three of the devices). In general, each resuscitator functioned well when used during CPR within the hospital.

Each resuscitator tested failed to deliver the preset volumes and this must be considered during their use. Inspiratory pressure relief valves for all but one of the ventilators tested would not permit the delivery of adequate levels of ventilation in patients with low pulmonary compliance and/or high airway resistance.