Complications of Mechanical Ventilation and Positive End-Expiratory Pressure

Complications from mechanical ventilation have been frequently reported. Some can be prevented by careful ventilatory monitoring and by the establishment of protocols, while others can be avoided by an understanding of mechanical ventilation's effects on cardiopulmonary physiology. The major cardiovascular complication of mechanical ventilation is depression of cardiac output, the magnitude of which is influenced by the mode of mechanical ventilation used. PEEP with controlled mechanical ventilation produces a greater cardiac output depression than does PEEP with intermittent mandatory ventilation (IMV), and PEEP with continuous positive airway pressure (CPAP) produces the least depression of the three. Because this depression of cardiac output during PEEP can be marked, oxygen delivery must be monitored after PEEP has been initiated. Recent studies have shown that the extent of oxygen delivery is not reliably reflected by the mixed venous oxygen tension measurement, so oxygen delivery to the tissues must be calculated. Another major cardiovascular complication of mechanical ventilation is pulmonary barotrauma, the risk of which can be minimized by the use of low tidal volumes with PEEP. High-frequency positive-pressure ventilation (HFPPV) may solve the problem of providing adequate alveolar ventilation at low mean airway pressures with little depression of cardiac output and low risk of pulmonary barotrauma; however, more research needs to be done on this ventilatory mode before it can be used routinely. The ideal ventilator circuit of the future will provide a constant tidal volume, a low compressible volume, and a low internal compliance.