Continuous flow biphasic positive airway pressure by helmet in patients with acute hypoxic respiratory failure: effect on oxygenation
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. 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. PaO2 was significantly higher during all steps compared to SB. When compared to CPAPbasal, both SIGH and BIPAP induced a further increase in PaO2. PaO2 during SIGH and BIPAP were not different. The oxygenation improvement was maintained during CPAPfinal. 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.