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GENERAL ARTICLES

A Pilot Study of Pharyngeal Pulse Oximetry with the Laryngeal Mask Airway: A Comparison with Finger Oximetry and Arterial Saturation Measurements in Healthy Anesthetized Patients

C. Keller, MD^*, J. Brimacombe, MB, ChB, FRCA, MD, F. Agrò, MD, and J. Margreiter, MD^*

*Department of Anaesthesia and Intensive Care Medicine, Leopold-Franzens University, Innsbruck, Austria; University of Queensland, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, Cairns, Australia; and Department of Anaesthesia, University School of Medicine LIU Campus Bio-Medico, Rome, Italy

Address correspondence and reprint requests to Dr. J. Brimacombe, Department of Anaesthesia and Intensive Care Medicine, University of Queensland, Cairns Base Hospital, Cairns 4870, Australia. Address e-mail to 100236,2343{at}compuserve.com

We compared pharyngeal SpO₂ by using the laryngeal mask airway (LMA) to finger SpO₂ and oxygen saturation from arterial blood samples (SaO₂). We studied 20 hemodynamically stable, well oxygenated, anesthetized patients (ASA physical status I–III, aged 18–80 yr). A single-use pediatric pulse oximeter was attached to the back plate of a size 5 LMA. Pharyngeal and finger SpO₂ (dominant index finger) and SaO₂ (nondominant radial artery) were measured with the cuff volume at 0–40 mL in the neutral position. The intracuff pressure was then set at 60 cm H₂O in the neutral position, and readings were taken with the head-neck flexed, extended, and rotated. SaO₂ was the same as pharyngeal SpO₂ at 20 and 30 mL cuff volume, but higher than pharyngeal SpO₂ at all other cuff volumes and head-neck positions (P < 0.04). SaO₂ was always higher than finger SpO₂ (P < 0.01). Pharyngeal SpO₂ was higher than finger SpO₂ at cuff volumes 10–40 mL and in the flexed and rotated head-neck positions (all: P < 0.007), but was lower at 0 cuff volume (P < 0.0001) and similar in the extended head-neck position. There was an increase in pharyngeal SpO₂ between 0 and 10 mL cuff volume (P < 0.0001), but no changes thereafter. Pharyngeal SpO₂ was similar in the flexed, rotated and extended head-neck positions. Pharyngeal SpO₂ agrees more closely with SaO₂ (mean difference < 0.7%) than finger SpO₂ (mean difference > 1.1%) at 10–40 mL cuff volume and in head-neck flexion. The standard error of limits was identical (0.09) for both finger SpO₂ and pharyngeal SpO₂ if data at 0 cuff volume are excluded. We conclude that pharyngeal SpO₂ with the LMA is feasible and generally provides more accurate readings than finger SpO₂ in hemodynamically stable, well oxygenated, anesthetized patients.

Implications: Pharyngeal oximetry with the laryngeal mask airway is feasible and generally provides more accurate readings than finger oximetry in hemodynamically stable, well oxygenated, anesthetized patients.

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