Respiratory rates among rural Gambian children: a community-based cohort study

Abstract Background: Although ranges of normal respiratory rates (RR) have been described for children under five years old living in the tropics, there are few datasets recording rates in older children. The present study was designed to capture the changes in RR with age and to examine its association with nutritional status and environmental factors. Methods: A cohort of rural Gambian children aged from six months to 14 years had their RR recorded during home visits twice weekly during two annual rainy seasons. Measurements were made by trained field assistants using an electronic timer during a one-minute period. Age, sex, nutritional status, health status, time of day of data collection were recorded. A generalized additive model for location, scale and shape was used to construct the RR reference curves and a linear mixed effect model used to examine factors associated with RR. We also assessed the agreement between repeat measurements taken from a subset of study subject. Results: A total of 830 children provided 67,512 RR measurements. The median age was 6.07 years (interquartile range (IQR), 4.21–8.55) and 400 (48.2%) were female. The centile chart showed a marked nonlinear decline in RR measurements with increasing age up to six years old, after which the decline was minimal (predicted median RR of 31 breaths/minute (IQR: 29–34) among one-year-olds, 22 breaths/minute (IQR: 21–23) among six-year-olds and 21 breaths/minute (IQR: 21-22) among 13-year-olds. Age (non-linear effect, p<0.001), stunting (0.84 breaths/minute [95%CI: 0.40-1.28, p<0.001]), ambient temperature (0.38 breaths/minute [95%CI: 0.33-0.42, p<0.001] for every 1oC increase in ambient temperature) and time of day when RR measurements were taken (non-linear effect, p<0.001) were independent predictors of respiratory rate. Strikingly, children with signs of illness were associated with higher intra-observer variability. Interpretation: We constructed a RR reference chart for children aged one to 13 years and proposed a cutoff of >26 breaths/minute for raised RR among children aged >5 years bridging an important gap in this age group. Although time of data collection, nutritional status and ambient temperature were predictors of RR, the evidence is not clinically significant to warrant a change in the current WHO guidelines owing to the prevailing uncertainty in the measurement of RR. The finding that RR between repeat measurements were more variable among children with signs of illness suggests that a single RR measurements may be inadequate to reliably assess the status of sick children - a population in which accurate diagnosis is essential to enable targeted interventions with lifesaving treatment.