The measurement of the work of breathing for the clinical assessment of ventilator dependence.

The work of breathing was measured in 10 normal subjects and in 28 critically ill patients with acute complications of obstructive pulmonary disease treated with assisted ventilation. The measurement of the work of breathing was found to be a useful objective variable for determining the capability for independent ventilation. Dependence on mechanical ventilation was observed when the respiratory work was greater than or equal to 1.7 kg-m/min. Patients were ordinarily capable of spontaneous ventilation when the respiratory work was less than or equal to 1.0 kg-m/min. Discontinuation of assisted ventilation was likely to be successful in those patients whose respiratory work was less than or equal to 1.5 kg-m/min if the patient was able to increase and maintain his work capability by a factor of two when breathing against an inspiratory resistance of 5 cm H2O for 10 min. Failure to increase the respiratory work when breathing against an inspiratory resistance indicated limitations in respiratory mechanics and was associated with the need for prolonged assisted ventilation. The measurement of the work of breathing against an inspiratory resistance of 5 cm H2O was useful in the identification and quantification of ventilatory reserve in patients with obstructive pulmonary disease.