Proximal mean airway pressure: a good estimator of mean alveolar pressure during continuous positive-pressure breathing

Although airway and alveolar pressures are not instantly equal during positive-pressure ventilation, proximal mean airway pressure (Paw) is the simplest available indirect gauge of mean alveolar pressure (Palv). To ascertain the relation of Paw to Palv and the limits of agreement between the two measures, real-time curves of proximal airway pressure (at the hub of the endotracheal tube) and alveolar pressure were generated by repeated airway occlusion at numerous PEEP levels in four groups of ventilated lambs or piglets: normal controls, oleic acid-injured and serotonin stimulated lambs, and preparatations with mechanically induced air trapping. From these curves, Paw and Palv were determined. In all groups, Paw proved to be a precise estimator of Palv during volume-regulated, time-cycled, continuous positive-pressure breathing.