Patterns of ventilation
Postoperative disturbances of pulmonary function were common when open heart surgery was first undertaken. Attempts to restore spontaneous ventilation postoperatively usually failed and a policy of elective mechanical ventilation for virtually all patients was established in most centers. Now that the factors contributing to pulmonary complications are understood more clearly, many can be avoided. At the same time, the emphasis in cardiac surgery has changed from valvular to ischemic heart disease, so fewer patients are likely to suffer from notable pulmonary disease as a result of their cardiac condition.
The reduction in pulmonary morbidity has prompted a reevaluation of the need for mechanical ventilation as a routine after open heart surgery. A policy of early extubation with the resumption of unassisted spontaneous ventilation is receiving growing support. Prakash et al1 reported extubation within 3 hours of operation in 123 of 142 adult patients after open heart surgery; five subsequently required reintubation. They proposed criteria for selecting suitable patients based on common variables that are usually monitored routinely (Table).
Alternative criteria in common use are vital capacity per kilogram of body weight and maximum inspiratory force. Figures of at least 15 ml/kg vital capacity (VC), and −28 cm H2O maximum inspiratory force (MIF) are quoted by Hilberman et al,2 who carried out an extensive computer-based study of the predictive value of many physiological variables in cardiac surgical patients. In other circumstances, lower values have often been regarded as acceptable, e.g., VC, 10 to 15 ml/kg; and MIF, −20 cm H2O.
Although . . .