Efficient gas exchange with low tidal volume ventilation in acute respiratory distress syndrome

摘要

The immediate and ultimate objectives of mechanical ventilation in the acute respiratory distress syndrome (ARDS) are to maintain gas exchange, ensure survival and allow the patient to regain a high quality of life. To achieve these goals, ventilation must be adequate and ventilator-induced lung injury minimal. A trade-off between the immediate and ultimate goals is required in order to secure adequate gas exchange with respect to CO_2 and O_2, and this can be achieved with lung-protective ventilation (LPV). LPV is achieved with low tidal volume ventilation, an adequate positive end-expiratory pressure (PEEP) and a limited plateau pressure. These features tend to compromise gas exchange. Dead space is large in ARDS. In this review, methods to enhance gas exchange, even at low tidal volume, by decreasing the huge dead space in ARDS are discussed. Optimizing the ventilator setting involves combining the best values for respiratory rate, minute ventilation and tidal volume, PEEP, the flow or pressure pattern of gas delivery and the ratio of inspiratory to expiratory time. This can be difficult or even impossible given the complex physiology of the individual patient. Computer analysis of physiological parameters followed by simulation of ventilator function is a method that allows the physician to define immediate therapeutic goals and let the computer suggest how ventilation should be delivered to reach those goals.