Continuous flow biphasic positive airway pressure by helmet in patients with acute hypoxic respiratory failure : effect on oxygenation

Purpose: We investigated the effects of periodical high pressure breaths (SIGH) or biphasic positive pressure ventilation (BIPAP) during helmet continuous positive airway pressure (CPAP) in patients with acute hypoxic respiratory failure. Methods: We used a recently developed electromechanical expiratory valve (TwinPAP®, StarMed, Mirandola, Italy), which is time-cycled between two customizable positive end-expiratory pressure (PEEP) levels. We studied 21 patients (67 ± 17 years old) undergoing helmet CPAP. Continuous flow CPAP system was set at 60 l/min flow rate while maintaining clinical FiO2 (51 ± 15%). Five steps, lasting 1 h each, were applied: (1) spontaneous breathing with PEEP 0 cmH2O (SB), (2) CPAP with PEEP 8 cmH2O (CPAPbasal), (3) low PEEP, 8 cmH2O, for 25 s and high PEEP, 25 cmH2O, for 5 s (SIGH), (4) low PEEP, 8 cmH2O, for 3 s and high PEEP, 20 cmH2O, for 3 s (BIPAP), (5) CPAP with PEEP 8 cmH2O (CPAPfinal). We randomized the sequence of SIGH and BIPAP. Results: PaO2 was significantly higher during all steps compared to SB. When compared to CPAP basal, both SIGH and BIPAP induced a further increase in PaO 2. PaO2 during SIGH and BIPAP were not different. The oxygenation improvement was maintained during CPAPfinal. Conclusions: Superimposed, nonsynchronized positive pressure breaths delivered during helmet CPAP by means of the TwinPAP® system may improve oxygenation in patients with acute hypoxemic respiratory failure, even at a rate as low as two breaths per minute.