Does pulse oximetry accurately monitor a patient's ventilation during sedated endoscopy under oxygen supplementation?

Arakawa H, Kaise M, Sumiyama K, Saito S, Suzuki T, Tajiri H
Correspondence: Dr Hiroshi Arakawa, endosc-arakawa@jikei.ac.jp

ABSTRACT
Introduction Pulse oximetry (SpO_²) measures oxygen saturation but not alveolar ventilation. Its failure to detect alveolar hypoventilation during sedated endoscopy under oxygen supplementation has been reported. The aim of this study was to measure the masking effect of oxygen supplementation in SpO₂ when alveolar hypoventilation develops during sedated endoscopy.
Methods A total of 70 patients undergoing sedated diagnostic colonoscopy were randomly divided into two groups – oxygen supplementation group (n = 35) and room air breathing group (n = 35). SpO₂ and end-tidal carbon dioxide (etCO₂) were measured by non-intubated capnography during the procedure for all the patients.
Results The rise of etCO₂caused by alveolar hypoventilation was comparable in the two groups after sedation. SpO₂ was significantly higher in the oxygen supplementation group than in the room air breathing group (98.6% ± 1.4% vs. 93.1% ± 2.9%; p < 0.001) at peak etCO₂, and oxygen supplementation caused SpO₂ to be overestimated by greater than 5% when compared with room air. SpO2 at peak etCO2 was reduced from the baseline before sedation for the oxygen supplementation and room air breathing groups by 0.5% ± 1.1% and 4.1% ± 3.1%, respectively (p < 0.001).
Conclusion SpO₂ alone is not adequate for monitoring alveolar ventilation during sedated endoscopy under oxygen supplementation due to possible delays in detecting alveolar hypoventilation in patients. Even if SpO₂ decreases by only 1% during the procedure and its level remains near 100%, physicians should consider the onset of severe alveolar hypoventilation, which requires immediate intervention.

Keywords: capnography, endoscopy, hypoventilation, pulse oximetry, sedation
Singapore Med J 2013; 54: 212-215; http://dx.doi.org/10.11622/smedj.2013075

http://smj.org.sg/sites/default/files/5404/5404a3.pdf

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