WORK OF BREATHING IN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE IN ACUTE RESPIRATORY-FAILURE

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Abstract
In 11 spontaneously breathing patients with chronic obstructive pulmonary disease (COPD) in acute ventilatory failure, the total inspiratory (.ovrhdot.WItot) and total resistive (.ovrhdot.WI + Eres) work rate of breathing, together with lung mechanics (dynamic pulmonary elastance and inspiratory and expiratory pulmonary flow resistance) was measured. All variables were markedly increased compared with those in normal subjects. No significant correlation was found between .ovrhdot.WItot and .ovrhdot.WI + Eres with lung mechanics data. When .ovrhdot.WItot and .ovrhdot.WI + Eres were expressed per liter of ventilation, a significant positive correlation was found with all lung mechanics data. Although in patients acutely ill with COPD, work rate and work per liter of ventilation are increased, only the latter is related to the severity of pulmonary mechanical impairment, and it could be used as one of the criteria for extubation. At end-expiration the alveolar pressure was positive (range, 6-13 cm H2O) in all patients (intrinsic PEEP [peak end-expiratory pressure]), a fact that must necessarily affect hemodynamics; furthermore, it imposes an extra burden on the inspiratory muscles.