Modification of a critical care ventilator for anesthesia use

Some critically ill patients require ventilatory support during surgery that exceeds the capabilities of most anesthesia ventilators. We modified an Emerson 3MV ventilator for anesthesia use and measured delivered concentrations of isoflurane during simulated ventilation of a test lung with oxygen flow rates ranging from 5 to 45 L/min. Each measurement was made at atmospheric pressure and incremental levels of 5, 10, 15, and 20 cm H2O PEEP. The delivered anesthetic concentrations were stable at oxygen flow rates of 12.5 to 20 L/min and were unaffected by PEEP changes.