A novel sensor for routine continuous spirometry of intubated patients.

Measurement of gas flow and airway pressure at the Y-piece of an endotracheal tube provides valuable information about airway integrity and basic pulmonary function. We describe the working principle and design of the D-lite sensor (Datex Division, Instrumentarium Corporation, Helsinki, Finland), which, in a single, lightweight adapter piece, encloses flow, airway pressure, and sidestream gas measurement. The main emphasis in the design of this instrument was on reliable and accurate operation during continuous monitoring with exposure to humidity and mucus. Therefore, a robust flow-restrictor element with a pick-off arrangement resembling a Pitot tube was employed. This arrangement has nonlinear characteristics with potential difficulties in the measurement of small flows. However, these inherent drawbacks, together with compensations required because of varying gas fractions and pressure, can be handled by sophisticated computer algorithms at the host-monitor end (Capnomac Ultima [Datex Division, Instrumentarium Corporation, Helsinki, Finland]). Validation methods with main results and a brief review of applications are given.