VentPlan assists physicians, nurses, and respiratory therapists in the management of artificial respiration for critically ill patients in the intensive-care unit (ICU). VentPlan interprets clinical observations, monitored data, and arterial-blood-gas analyses to make recommendations for setting the ventilator. The VentPlan interface allows users to examine the physiologic model, to inspect details of the data on which the model is based, and to exercise the model to try out different ventilator settings before they implement a new setting. We also report here a preliminary evaluation of VentPlan's ability to predict the arterial oxygen and carbon-dioxide tensions following adjustments to the ventilator. We conclude that VentPlan's physiologic models are acceptably accurate for predicting the effects of small adjustments of the ventilator.