Development and testing of a PC-based system with menu-driven software for evaluating lung function in ICU patients

This paper describes a portable PC-based system for measuring respiratory system resistance (Rrs) and dynamic lung compliance (Cdyn) in intubated and mechanically ventilated patients. A pneumotachometer placed immediately proximal to the endotracheal tube measures flow, and a pressure catheter with its tip at the distal end of the endotracheal tube measures lateral airway pressure. The software is menu driven and allows the user to select from options including patient information display and entry, data collection, data editing, and waveform display. Up to ten consecutive breaths can be analyzed per run. Rrs and Cdyn are calculated on a breath by breath basis. Results are displayed to the screen, output to the system printer, and written to a user-specified ACSII data file. The system was tested by measuring resistance and compliance in a model of the lung, and results compared with those calculated from analog signals. It was then used to make measurements in intubated post-operative patients. Results were comparable to those previously reported in intubated ICU patients without primary lung disease. We conclude that our system provides reliable measurements of lung mechanics in the intubated patient, and represents an inexpensive and more versatile alternative to microprocessor-based ventilator systems currently being marketed.