Am. J. Respir. Crit. Care Med., Vol 153, No. 6, Jun 1996, 1825-1830.
Mean airway pressure as an index of mean alveolar pressure
P Valta, C Corbeil, M Chasse, J Braidy and J Milic-Emili
Respiratory Division, Hopital Saint-Luc, Universite de Montreal, Quebec, Canada.
Mean airway pressure (Pao) has been advocated as a useful index for
monitoring hemodynamic performance and risk for barotrauma during
mechanical ventilation. This is based on the assumption that Pao closely
reflects mean alveolar pressure (Palv). In the present study we have
compared Pao with Palv in 12 sedated, paralyzed, mechanically ventilated
patients. External PEEP ranged from 0.3 to 8.9 cm H2O. Palv was estimated
by measuring Pao after rapid flow interruptions made at different points in
time of the breathing cycle, using a modification of the method of Fuhrman
and coworkers (4). All subjects exhibited intrinsic PEEP (PEEPi), which
ranged from 0.5 to 9.4 cm H2O. A significant negative correlation (p <
0.001) was found between Pao/Palv and PEEPi. On average, at PEEPi of 10 cm
H2O, Pao underestimated Palv by about 50%. We conclude that Pao cannot be
taken as an index of Palv in patients who exhibit dynamic hyperinflation
and PEEPi caused by expiratory flow limitation.