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), as <90%. Although hypoxaemia is an important risk factor for mortality of children with respiratory infections, the optimal SpO threshold for defining hypoxaemia is uncertain in low-income and middle-income countries (LMICs). We derived a SpO 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 of children using a Masimo Rad-5 pulse oximeter with a wrap sensor. We used standard summary statistics to evaluate the SpO distribution, including whether the distribution differed by age or sex. We considered the 2.5th, 5th and 10th percentiles of SpO as possible lower thresholds for hypoxaemia.

Results: Our primary analytical sample included 1470 children (mean age 18.6±9.5 months). Median SpO was 98% (IQR 96%-99%), and the 2.5th, 5th and 10th percentile SpO was 91%, 92% and 94%. No child had a SpO <90%. Children 3-11 months had a lower median SpO (97%) than 12-23 months (98%) and 24-35 months (98%) (p=0.039). The SpO distribution did not differ by sex (p=0.959).

Conclusion: A SpO 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 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 thresholds for hypoxaemia is a key next step.