Effects of inspiratory pause on CO2 elimination and arterial PCO2 in acute lung injury

1 Medical Intensive Care Unit, AP-HP, INSERM Unit 841, Centre Hospitalier Albert Chenevier-Henri Mondor, Créteil, France; 2 Department of Clinical Physiology, University Hospital, Lund, Sweden Submitted 22 May 2008 ; accepted in final form 17 September 2008 A high respiratory rate associated with the use of small tidal volumes, recommended for acute lung injury (ALI), shortens time for gas diffusion in the alveoli. This may decrease CO 2 elimination. We hypothesized that a postinspiratory pause could enhance CO 2 elimination and reduce Pa CO 2 by reducing dead space in ALI. In 15 mechanically ventilated patients with ALI and hypercapnia, a 20% postinspiratory pause (Tp20) was applied during a period of 30 min between two ventilation periods without postinspiratory pause (Tp0). Other parameters were kept unchanged. The single breath test for CO 2 was recorded every 5 min to measure tidal CO 2 elimination (VtCO 2 ), airway dead space (V Daw ), and slope of the alveolar plateau. Pa O 2 , Pa CO 2 , and physiological and alveolar dead space (V Dphys , V Dalv ) were determined at the end of each 30-min period. The postinspiratory pause, 0.7 ± 0.2 s, induced on average