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Assessment of Preoxygenation using Real-Time End-Tidal Oxygen Measurements Versus Single-Breath End-Tidal Oxygen
Steven Lindsey1, Tim P Moran1, John Diehl1
1Department of Emergency Medicine, Emory University School of Medicine, Emory University, Atlanta, Georgia, USA.
Objective:
Preoxygenation decreases morbidity for patients requiring endotracheal intubation. However, rigorous means for determining adequate pre-oxygenation are limited in the emergency department (ED). End-tidal oxygenation (EtO2) monitoring could potentially improve preoxygenation in the ED. The accuracy of nasal cannula (NC) EtO2 in patients receiving supplemental oxygen is unknown. Our study examined the correlation between NC EtO2 and single-breath (SB) EtO2.
Methods:
Healthy volunteers were randomized to receive supplemental oxygen via a nonrebreather mask (NRBM) or a noninvasive ventilation mask (NIV). Participants underwent 3-minute trials at 3 different settings: NRBM at 15 liters per minute (LPM), 35 LPM, and 55 LPM, or NIV at 40% fraction of inspired oxygen (FiO2), 70% FiO2, and 100% FiO2. NC EtO2 and SB EtO2 were obtained at the end of each trial.
Results:
Complete data were obtained for 104 participants. Beta regression analysis revealed a strong correlation between NC EtO2 and SB EtO2 in the NIV group (pR2 = 0.7) and a moderate correlation (pR2 = 0.4) in the NRBM group. Mean differences in the NRBM arm were 13.1% (15 LPM), 18.0% (35 LPM), 17.1% (55 LPM), and 1.8% (40% FiO2), 5.1% (70% FiO2), and 10.1% (100% FiO2) in the NIV arm.
Conclusions:
Supplemental oxygen led to an overestimation of NC EtO2 across both groups, with NRBM more than NIV. The correlation between SB EtO2 and NC EtO2 suggests NC EtO2 may be useful in assessing preoxygenation in real-time. Further study is needed to examine its clinical efficacy in preventing desaturation events during endotracheal intubation in the ED.
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