287 AUTOMATED—MEASUREMENT OF RESPIRATORY MECHANICS IN MECHANICALLY VENTILATED NEONATES

Abstract

Monitoring of respiratory mechanics is not a well developed technique in neonatal intensive care units. The aim of this report was to describe an automated system that could be routinely used at bedside in neonatal and pediatric intensive care units. This system is composed of a microcomputer IBM 486 PC equipped with an analog-to-digital data acquisition board (12 bits resolution). Flow was measured by a Fleisch pneumotachometer n°00 inserted between the endotracheal tube and the breathing circuit and connected to a pressure transducer (± 2 cmH2O). Pressure variations were measured at airway opening. Signals were sampled at 256 Hz. Data processing includes “time fi notion” and “loop function”. Time function provides data processing (low pass and high pass filtering, gain and sweep frequency tuning, numeric integration) and real time computing of several parameters (tidal volume, respiratory frequency, inspiratory time, peak inspiratory pressure, mean pressure, positive end expiratory pressure and air leak ratio). With Loop function, flow/volume, volume/pressure and pressure/flow loops are displayed in real time at each ventilatory cycle. At any time, the operator can freeze the display and calculate respiratory mechanic parameters (resistances, compliance, time constant, trapped volume and intrinsic positive end expiratory pressure) by using the passive inflation method. This system provides qualitative informations by displaying loops and quantitative data. The use of microcomputer makes this technique attractive and highly suitable for understanding the pathophysiology of the underlying disease, for optimizing ventilator settings and/or for evaluating drug efficiency.