Utility of monitoring capnography, pulse oximetry, and vital signs in the detection of airway mishaps: A hyperoxemic animal model

This study was undertaken to determine the time interval for changes in end tidal CO2, oxygen saturation (SaO(2)), heart rate (HR), and blood pressure (BP) in response to an acute airway obstruction or hypopharyngeal extubation in a hyperoxemic model. Complete and partial airway obstructions were simulated with complete and partial cross-clamping of an endotracheal (ET) tube in five anesthetized, nonparalyzed, mechanically ventilated Yorkshire minipigs with initial PaO2 of >400 mm Hg. Placement of the ET tube into the hypopharynx was performed to simulate accidental extubation. Both sidestream (SS) and mainstream (MS) capnography were used. Continuous pulse oximetry monitored SaO(2), femoral arterial catheter monitored systolic BP, and electrocardiograph monitored HR. The time intervals for the capnograph wave to flatten and for the monitor to display zero were recorded after each airway alteration. The time interval to a change in the initial HR of 10 beats/min, a change of initial systolic BP of 10 mm Hg, and a change of initial SaO(2) of 5% were recorded. Experiments were carried out for 180 seconds, and 25 trials were performed. HR, systolic BP, and SaO(2) did not change for the 180-second duration of the trials. Complete obstruction produced a flattening of the SS and MS waveform in 8 +/- 2 seconds and 6 +/- 2 seconds, respectively. The SS and MS monitors displayed zero in 19 +/- 1 seconds and 68 +/- 7 seconds, respectively. Partial obstruction did not produce flattening of the wave or a monitor displaying zero. Hypopharyngeal extubation produced a flattening of the SS and MS waveform in 7 +/- 1 seconds and 7 +/- 2 seconds, respectively. The SS and MS monitors displayed zero in 18 +/- 3 seconds and 76 +/- 16 seconds, respectively. Continuous end-tidal CO2 capnography detects acute airway obstruction and hypopharyngeal extubation more rapidly than does pulse oximetry or vital sign monitoring in a hyperoxemic porcine model. (Am J Emerg Med 1998;16:350-352. Copyright a 1998 by W.B. Saunders Company).