Defining hypoxemia from pulse oximeter measurements of oxygen saturation in well children at low altitude in Bangladesh: an observational study
Authors: McCollum Eric D. , King Carina , Ahmed Salahuddin , Hanif Abu A.M. , Roy Arunangshu D. , Islam ASMD Ashraful , Colbourn Tim , Schuh Holly B. , Ginsburg Amy Sarah , Hooli Shubhada , Chowdhury Nabidul H. , Rizvi Syed J.R. , Begum Nazma , Baqui Abdullah H. , Checkley William 
Published: June 2021

Background

The World Health Organization defines hypoxemia, a low peripheral oxyhemoglobin saturation (SpO2), as <90%. Although hypoxemia is an important risk factor for mortality of children with respiratory infections, the optimal SpO2 threshold for defining hypoxemia is uncertain in low-income and middle-income countries (LMICs). We derived a SpO2 threshold for hypoxemia from well children in Bangladesh residing at low altitude.

Methods

We prospectively enrolled well, 3-35 month old children participating in a pneumococcal vaccine evaluation in Sylhet district, Bangladesh between June and August 2017. Trained health workers conducting community surveillance measured the SpO2 of children using a Masimo Rad-5® pulse oximeter with a wrap sensor. We used standard summary statistics to evaluate the SpO2 distribution, including whether the distribution differed by age or sex. We considered the 2.5th, 5th, and 10th percentiles of SpO2 as possible lower thresholds for hypoxemia.

Results

Our primary analytical sample included 1,470 children (mean age 18.6 +/- 9.5 months). Median SpO2 was 98% (interquartile range, 96–99%), and the 2.5th, 5th, and 10th percentile SpO2 was 91%, 92%, and 94%. No child had a SpO2 <90%. Children 3– 11 months old had a lower median SpO2 (97%) than 12–23 month olds (98%) and 24– 35 month olds (98%) (p=0.039). The SpO2 distribution did not differ by sex (p=0.959).

Conclusion

A SpO2 threshold for hypoxemia derived from the 2.5th, 5th, or 10th percentile of well children is higher than <90%. If a higher threshold than <90% is adopted into LMIC care algorithms then decision-making using SpO2 must also consider the child’s clinical status to minimize misclassification of well children as hypoxemic. Younger children in lower altitude LMICs may require a different threshold for hypoxemia than older children. Evaluating the mortality risk of sick children using higher SpO2 thresholds for hypoxemia is a key next step.

Key Messages

What is the key question? The ideal peripheral oxyhemoglobin saturation (SpO2) threshold for defining hypoxemia among children in low-income and middle-income countries is unknown.

What is the bottom line? A SpO2 threshold for hypoxemia set at any of the 2.5th, 5th, or 10th percentiles of SpO2 measurements from well children in a lower altitude setting is higher than the <90% threshold currently recommended by the World Health Organization.

Why read on? This study is a possible model for other research seeking to establish SpO2 thresholds for hypoxemia in children and provides evidence for health policy makers to consider before implementing higher SpO2 thresholds than currently in practice in lower altitude settings of low-income and middle-income countries.