No abstract

Continuous positive airway pressures (CPAP) of 0.49 kPa and 0.98 kPa were applied to ten healthy volunteers and nine critically ill patients with acute respiratory failure. A modified Godart-Statham NV 16003 spirometer was used to measure respiratory frequency (f), tidal volume (VT), oxygen consumption (Vo2), and changes in functional residual capacity (AFRC). During CPAP of 0.49 kPa, volunteers had a decrease in f, and increased VT and minute volume (MV). At 0.98 kPa CPAP, f did not change but VT and MV significantly increased. Vo2 did not change at either pressure. The volume of ~.FRC increased with an increased level of CPAP. The entire volunteer group was comfortable throughout the whole study.When CPAP was applied to acutely ill patients, f decreased. VT and MV increased at both CPAP pressures. AFRC was similar to the volunteers. Vo2 in the patient group rose significantly at 0.49 and 0.98 kPa CPAP. Some of the patients were uncomfortable with 0.49 kPa pressure, while all the patients were distressed at 0.98 kPa CPAP.The effects of increased oxygen consumption and patient discomfort should be considered in critically ill patients receiving CPAP therapy.CONTINUOUS POSITIVE AIRWAY PRESSURE (CPAP) has been employed to improve pulmonary gas exchange in spontaneously breathing patients. CPAP has been utilized in the treatment of the idiopathic respiratory distress syndrome of infants,~ and has been applied to adults with acute respiratory failure. 2'3 Adult respiratory distress syndrome is associated with a decrease in functional residual capacity (FRC). CPAP increases FRC to prevent or reverse closure of small airways and consequently improves oxygenation. In addition, the possible advantages of CPAP over mechanical ventilation with end-expiratory pressure include lower peak airway pressures and a lesser effect on cardiac output. 2 We applied CPAP to groups of healthy volunteers and to patients with acute respiratory failure in order to compare the oxygen cost of breathing and tolerance in subjects with normal and severely compromised respiratory function. Respiratory frequency (f), tidal volume (VT), and oxygen consumption (Vo:) were measured during CPAP. Oxygen consumption was used as a measure of the work of breathing. 4

No abstract