Biphasic positive airway pressure (BiPAP) is a ventilatory mode in which two pressure levels (higher (Phigh) and lower (Plow)) acting as continuous positive airway pressure (CPAP) alternate at preset time intervals. BiPAP combines pressure-controlled ventilation with unrestricted spontaneous breathing. BiPAP has not yet been evaluated in patients with chronic obstructive pulmonary disease (COPD). Therefore, the effects of BiPAP (15 cmH2O Phigh and 5 cmH2O Plow) pressure support (PS; 15 cmH2O and positive end-expiratory pressure (PEEP) 5 cmH2O) and CPAP (5 cmH2O) on respiratory mechanics in COPD patients were compared. Twenty-one COPD patients were supported in randomized order with BiPAP, PS and CPAP. Pressure-time product (PTP), work of breathing (WOB), change in oesophageal pressure (deltaPoes), mouth occlusion pressure (p = 0.1), intrinsic PEEP (PEEPi), tension time index (TTI), respiratory frequency, and tidal volume (VT) were measured. During BiPAP, the COPD patients showed a significantly higher PTP, WOB, deltaPoes, P0.1, TTI and PEEPi than during PS. Comparing the Plow phases of BiPAP and CPAP, the breaths during the Plow phases of BiPAP had a lower VT and a greater WOB and PTP due to a higher PEEPi than on CPAP alone. In conclusion, biphasic positive airway pressure carries the risk of increased work of breathing in spontaneously breathing chronic obstructive pulmonary disease patients. Pressure support is superior for reducing their respiratory muscle effort.
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