Source: Annual Congress 2002 - Monitoring respiratory parameters in critically ill patients
Disease area: Airway diseases, Respiratory critical care

Abstract

Pulse oximeter saturation (SpO₂) readings are delayed when measured at the finger site as compared to the ear site, due to the circulatory transit time, but the influence of this time lag on the amplitude of the SpO₂ readings during transient oxygen desaturation has not been investigated. Using 2 identical pulse oximeters (Datex-Ohmeda, model 3900P, Louisville, Colorado), we measured simultaneously ear and finger SpO₂ in 6 normal subjects during transient oxygen desaturation induced by one or 2 fast nitrogen inhalations followed by deep air inhalation. We choose the fastest oximeter response (3 s). At least 12 trials were done for each subject. Measurements at each site were done with the specific site sensor, but in each subject, the electronic modules were inverted for half of the trials to ensure the same electronic processing of the sensor signals. For each subject and oximeter, SpO₂ was measured at both sites during constant 11.5 % F_iO₂ breathing to assess the static response of the measuring system. With subjects breathing 11.5% F_iO₂, SpO₂ decreased from 98.7% ±] 1.0% to 84.1% ±] 5.6% at the ear site and from 99.3% ±] 0.8% to 85.2% ±] 6.1% at the finger site (non significantly different) whereas minimal SpO₂ during transient oxygen desaturation was 83.1% ±] 2.5% at the ear site and 93.2% ±] 1.8% at the finger site (p < 0.001) . In all 6 subjects, the maximal decrease in SpO₂ during transient hypoxia, expressed as a percentage of the decrease in SpO₂ during constant 11.5 % F_iO₂ breathing, was higher at the ear than at the finger site (p<0.001 for all the subjects).
The ratio of finger/ear maximal oxygen desaturation was negatively correlated to the time lag between ear and finger SpO₂ signals (r = 0.59, p<0.001) indicating that the difference between ear and finger SpO₂ during transient oxygen desaturation might presumably be, at least in part, of physiological origin.

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Citations should be made in the following way:
H. Normand, A. Mouadil (Caen, France). Ear or finger pulse oximetry during transient arterial oxygen desaturation: does it matter?. Eur Respir J 2002; 20: Suppl. 38, 625

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