Equipment review: Measurement of occlusion pressures in critically ill patients

Abstract

The evaluation of airway pressure tracings during complete airway occlusion provides interesting functional data for weaning patients from mechanical ventilation. The occlusion manoeuvre may be achieved either by maintaining occlusion for a prolonged period during maximal inspiratory effort (PiMax) or for a shorter time period (200–300 ms). The inspiratory depression of airways pressure, achieved after 100 ms of occlusion, is generally defined as the occlusion pressure or P0.1 and represents a valid indirect measurement of the activity of the respiratory centres. P0.1 is a reliable measurement of the intensity of the stimuli from the neurological centres to the peripheral respiratory muscles [1,2]. Whitelaw et al elegantly demonstrated the reliability of this measurement [1] in human healthy volunteers spontaneously breathing at rest and during hypercapnic challenge. P0.1 can represent a more precise respiratory drive measurement than other measurements such as tidal volume, respiratory rate, minute ventilation or mean inspiratory flow (VT/Ti) since it is relatively independent of modification by respiration machines. The aim of this article is to analyse the technical aspects relating to the acquisition of occlusion pressures, taking into account the possible bias represented by specific physiopathologic situations and to define some future uses of P0.1 during weaning procedures. A complete review of the literature dedicated to P0.1 measurement in different clinical settings has been recently published [3].