Defining hypoxaemia from pulse oximeter measurements of oxygen saturation in well children at low altitude in Bangladesh: An observational study

Background WHO defines hypoxaemia, a low peripheral arterial oxyhaemoglobin saturation (SpO 2), as <90%. Although hypoxaemia is an important risk factor for mortality of children with respiratory infections, the optimal SpO 2 threshold for defining hypoxaemia is uncertain in low-income and middle-income countries (LMICs). We derived a SpO 2 threshold for hypoxaemia from well children in Bangladesh residing at low altitude. Methods We prospectively enrolled well, children aged 3-35 months participating in a pneumococcal vaccine evaluation in Sylhet district, Bangladesh between June and August 2017. Trained health workers conducting community surveillance measured the SpO 2 of children using a Masimo Rad-5 pulse oximeter with a wrap sensor. We used standard summary statistics to evaluate the SpO 2 distribution, including whether the distribution differed by age or sex. We considered the 2.5th, 5th and 10th percentiles of SpO 2 as possible lower thresholds for hypoxaemia. Results Our primary analytical sample included 1470 children (mean age 18.6±9.5 months). Median SpO 2 was 98% (IQR 96%-99%), and the 2.5th, 5th and 10th percentile SpO 2 was 91%, 92% and 94%. No child had a SpO 2 <90%. Children 3-11 months had a lower median SpO 2 (97%) than 12-23 months (98%) and 24-35 months (98%) (p=0.039). The SpO 2 distribution did not differ by sex (p=0.959). Conclusion A SpO 2 threshold for hypoxaemia 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 SpO 2 must also consider the child's clinical status to minimise misclassification of well children as hypoxaemic. Younger children in lower altitude LMICs may require a different threshold for hypoxaemia than older children. Evaluating the mortality risk of sick children using higher SpO 2 thresholds for hypoxaemia is a key next step.