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A86
October 13, 2007 9:00 AM - 11:00 AM Room Hall D, Area C, |
| Respiratory Rate Monitoring during Conscious Sedation Using an Electronic Precordial Stethoscope |
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Dwayne Westenskow, Ph.D., Bryce Hill, B.S., Joseph Orr, Ph.D., Ken Johnson, M.D. Anesthesiology, University of Utah, Salt Lake City, Utah |
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Introduction: When propofol and opioids are used to provide sedation and analgesia for less invasive procedures such as endoscopy and colonoscopy, patients are at risk from airway obstruction and central respiratory depression. An electronic stethoscope and digital signal processing may provide a warning of inadequate respiration that could precede oxygen desaturation, especially when patients receive supplemental oxygen. A stethoscope has the potential to be less expensive than capnometry and provide automatic detection of airway obstruction. Methods: After obtaining IRB approval, 24 volunteers received propofol and remifentanil in graded steps until they lost consciousness (OAA/S < 1), became unresponsive to the esophageal insertion of a bougie and/or unresponsive to a 50mA tetanic stimulus. At each step we recorded airway flow, tidal volume and respiratory rate using a face mask and a COSMO+ respiratory monitor (Respironics, Walingford, CT). Breath sounds were recorded with 24 bit accuracy at 22 kHz using a condenser microphone (WM-56A103 Panasonic) placed in a precordial stethoscope. The recorded audio signals were processed off-line to calculate respiratory rate. Respiratory rate calculated from the breath sounds signal was compared to the rate calculated from the simultaneously collected respiratory flow (pneumotachograph) data. Results: The figure shows the results from two volunteers. The correlation coefficient between the respiratory rate calculated using the breath sounds and the respiratory rate from the pneumotachograph was r2 = 0.82. The average difference between the two measurements was 0.2 ± 1.8 breaths per minute. Conclusion: We found an electronic stethoscope and digital signal processing to be an effective means of monitoring respiratory rate and thus central respiratory depression in volunteers receiving propofol and remifentanil for sedation. The presence of partial airway obstruction may be monitored by automatically detecting abnormal breath sounds that occurred during snoring. Simple and inexpensive monitoring may be especially important in obese patients or those with a history of obstructive sleep apnea.[figure1] Anesthesiology 2007; 107: A86 |
Figure 1
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