E. Calderini M. Confalonieri P.G. Puccio N. Francavilla L. Stella C. Gregoretti Patient-ventilator asynchrony during noninvasive ventilation: the role of expiratory trigger Received: 5 June 1998 Accepted: 24 February 1999 E.Calderini ´ P. G. Puccio ´ N. Francavilla ´ L. Stella Terapia Intensiva Malattie Infettive CSL, IRCCS H San Raffaele, I-20 127 Milano, Italy M. Confalonieri ( ) ) U.O. di Pneumologia, Ospedale Civile, via Crotti, 24, I-29 100 Piacenza, Italy e-mail: mconfalonieri@qubisoft.it Tel. + 39 05 23 30 25 33 Fax + 39 05 23 38 59 00 C. Gregoretti Servizio di Anestesia e Rianimazione, Centro Traumatologico Ortopedico, Torino, Italy Abstract Objective: Air leaks around the mask are very likely to occur during noninvasive ventila- tion, in particular when prolonged ventilatory treatment is required. It has been suggested that leaks from the mask may impair the expiratory trigger cycling mechanism when in- spiratory pressure support ventila- tion (PSV) is used. The aim of this study was to compare the short-term effect of two different expiratory cycling mechanisms (time-cycled vs flow-cycled) during noninvasive in- spiratory pressure support ventila- tion (NIPSV) on patient-ventilator synchronisation in severe hypoxe- mic respiratory failure. Study population: Six patients with acute lung injury (ALI) due to ac- quired immunodeficiency syndrome (AIDS)-related opportunistic pneu- monia were enrolled in the protocol. Intervention: Each subject was first studied during spontaneous breath- ing with a Venturi oxygen mask (SB) and successively submitted to a ran- domly assigned 20 ¢ conventional flow-cycling (NIPSVfc) or time-cy- cling inspiratory pressure support ventilation (NIPSVtc). The pre-set parameters were: inspiratory pres- sure of 10 cm H 2 O, PEEP of 5 cm H 2 O for the same inspired oxygen fraction as during SB. A tight fit of the mask was avoided in order to fa- cilitate air leaks around the mask. The esophageal pressure time prod- uct (PTPes) and tidal swings (DPes) were measured to evaluate the pa- tient's respiratory effort. A subjec- tive ªcomfort scoreº and the differ- ence between patient and machine respiratory rate [DRR(p-v)], calcu- lated on esophageal and airway pressure curves, were used as indices of patient-machine interaction. Results: Air leaks through the mask occurred in five out of six patients. The values of PEEPi (< 1.9 cm H 2 0) excluded significant expiratory muscle activity. NIPSVtc signifi- cantly reduced PTPes, DPes, and DRR(p-v) when compared to NIPS- Vfc [230  41 (SE) vs 376  72 cm H 2 O × s × min ±1 ; 8  2 vs 13  2 cm H 2 O; 1  1 vs 9  2 br × min ±1 ; re- spectively] with a concomitant sig- nificant improvement of the ªcom- fort scoreº. Conclusions: In the presence of air leaks a time-cycled expiratory trig- ger provides a better patient-ma- chine interaction than a flow-cycled expiratory trigger during NIPSV. Key words Noninvasive positive pressure ventilation × Hypoxemia × Acute respiratory failure × Acquired immunodeficiency syndrome Intensive Care Med (1999) 25: 662±667 Ó Springer-Verlag 1999 ORIGINAL