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October 17-21, 2009 New Orleans, LA Home Abstract Archive Search Abstracts 2009 Session Grid 2009 Meeting Website Policy Statements ASA Website Feedback 
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A-524
2003 |
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| Recognizing an Increased Arterial to End-Tidal Carbon Dioxide Gradient (PaCO2 - EtCO2) Due to Equipment Failure: A Full Human Simulator Study | ||||||||||||||||||||
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W. Bosseau Murray, MB, ChB, Terry T. Durbin, D.D.S., Jody L. Henry, B.S. Simulation Development and Cognitive Science Lab, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States. |
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Introduction: Capnography is a sensitive, yet nonspecific indicator of physiological and mechanical maladies that occur in an intubated patient. Knowledge of the relationship between capnogram morphology, end tidal carbon dioxide (EtCO2) values, and their correlation to a patient's condition is essential. Tripathy and Pandey¹ discovered a "new" capnogram pattern when they used a side stream gas analyzer with a leaking sampling tube. The leak of the sampling tube produced an abnormal capnographic pattern during pressure controlled breathing called "tails-up". The tails-up waveform is such a bizarre pattern it is readily distinguishable from an abnormal ETCO2 reading with a physiological etiology. We wished to determine if a normal waveform, coupled with a false (low) end tidal carbon dioxide reading, could be produced by altering the location and size of holes (leaks) along the gas sampling tube. Methods: We punctured several side stream sampling tubes by at various positions along the length of the tube. A simulator (METI, Sarasota, FL) was intubated, and connected to an anesthesia machine. We set the simulator for positive pressure and spontaneous respiration at rates and depths to establish a baseline EtCO2 value between 38 and 52 mmHg. EtCO2 was measured and the capnogram recorded using a Rascal II Gas Analyzer (Ohmeda Corporation, Madison, WI) using the various altered (“penetrated and leaking”) tubes. Results: All capnograms obtained when using positive pressure ventilation produced a tails-up trace. The terminal section of the capnograph trace demonstrates a sudden, brief increased CO2 value. All results from spontaneous respiration produced waveforms of normal morphology, albeit with significantly altered (decreased) values depending on the position of the breach. The closer the breach to the analyzer, the greater the contamination with room air, and the greater the error. (Figure 1 and Table 1).Figure1Legend: Spontaneous breathing. See Table 1 for positions of holes in sampling tubes. Discussion: During spontaneous breathing, false low EtCO2 values were obtained, translating into clinically significant PaCO2 – EtCO2 gradients. While the tails-up waveform is easily recognizable as non-physiological and an error, the waveform with spontaneous breathing is normal and the erroneous reading is not obvious. The simulator enables residents to manipulate variables in order to produce, examine and understand the abnormal waveforms. This ability to reproduce abnormalities at will in a protected teaching environment increases understanding and improves knowledge retention, which we believe can translate into greater patient safety. References: Tripathy M, Pandey M. Atypical "Tails-Up" Capnograph due to Breach in the Sampling Tube of Side-Stream Capnometer, J of Clin Monit, 2000;16:17-21. Anesthesiology 2003; 99: A524 |
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Figure 1
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