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

We compared pharyngeal Spo(2) by using the laryngeal mask airway (LMA) to finger Spo(2) and oxygen saturation from arterial blood samples (Sao(2)). 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 Spo(2) (dominant index finger) and Sao(2) (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. Sao(2) was the same as pharyngeal Spo(2) at 20 and 30 mL cuff volume, but higher than pharyngeal Spo(2) at all other cuff volumes and head-neck positions (P < 0.04). Sao(2) was always higher than finger Spo(2) (P < 0.01). Pharyngeal Spo(2) was higher than finger Spo(2) 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 Spo(2) between 0 and 10 mL cuff volume (P < 0.0001), but no changes thereafter. Pharyngeal Spo(2) was similar in the flexed, rotated and extended head-neck positions. Pharyngeal Spo(2) agrees more closely with Sao(2) (mean difference < 0.7%) than finger Spo(2) (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 Spo(2) and pharyngeal Spo(2) if data at 0 cuff volume are excluded. We conclude that pharyngeal Spo(2) with the LMA is feasible and generally provides more accurate readings than finger Spo(2), 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.