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A101
October 13, 2007 9:00 AM - 11:00 AM Room Hall D, Area C, |
| Breath to Breath Variability during Deep Sedation May Be Indicative of Partial Airway Obstruction |
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Frank J. Overdyk, M.D., M.S.E.E., Heather Beeson, Ph.D., Caroline Hunter, B.S., Jarred Callura, B.S., Ike Gaines, M.D. Dapartment of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, South Carolina |
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INTRODUCTION: Capnography is important monitor of ventilation during procedural sedation1. Complete airway obstruction is manifest by a sustained absence of CO2 and an apnea alarm. Partial airway obstruction (PAO) is more difficult to detect. Although the capnograph during PAO has an irregular contour, the respiratory rate (RR) may not change, since any detectable CO2 is counted as a breath and averaged. Highly variable breath to breath intervals (BBI) have been found in obstructive sleep apnea patients (OSA) and correlate with the apnea-hypopnea index2. We hypothesized that deeply sedated patients may demonstrate BBI patterns similar to OSA patients due to PAO during deep sedation. METHODS: After informed consent, patients undergoing ERCP under deep sedation with propofol/fentanyl and spontaneous ventilation had CO2 sampled via nasal cannula (Oridion MicrostreamTM Capnograph). Depth of sedation was recorded using the bispectral index (BIS; AspectTM Med Systems). After manual removal of artifact, our MatLab© algorithm calculated BBI as the time between upstroke of the CO2 tracing for successive breaths. The kurtosis, an index of variability of a sample as compared to a Normal distribution, was measured for BBI during periods of deep sedation (BIS<70) and compared to BBI for periods of light sedation (BIS>=70) using the Mann-Whitney U test. Kurtosis values <0.5 are consistent with highly variable BBI, as established during polysomnography2. Results are mean +/- stand dev. RESULTS: Twelve adult patients provided 4.2 hours of capnography data, including two obese patients (body mass index BMI >30) and one morbidly obese patient (BMI = 44).The mean kurtosis was significantly less for patients during deep sedation (0.44 +/- 0.32, BIS = 42 +/- 9.2) than for periods during light sedation (2.4 +/- 0.41; p<0.05, BIS = 84 +/- 8.5). An example of the wider distribution of BBI during deep sedation is shown in the Figure (patient #11). Four patients, however, showed minimal BBI variability (kurtosis > 1.0) during deep sedation, including one obese patient. CONCLUSIONS: Some deeply sedated patients demonstrate variability of breath duration similar to OSA patients, which may be indicative of PAO. Further research will correlate this finding with indicators and risk factors for PAO, such as capnograph shape, snoring, response to chin lift, BMI, and desaturation, to determine whether real-time BBI measurement can help diagnose PAO during deep sedation. REFERENCES: Vargo JJ, et. al. Gastrointestinal Endoscopy. Vol 55, No. 7, 2002. Kowallik P, et. al. Chest 119(2), p451-59, Feb 2001. Study supported in part by a grant from the National Patient Safety Foundation.[figure1][figure2] Anesthesiology 2007; 107: A101 |
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