Resus.me has recently brought our attention to a new BMJ article describing a combined derivation (1555 kids) and validation(671 kids) paper that studied children at one hospital in the Netherlands and observed the respiratory rate response to fever, producing this graph. They found that using the 97th centile as cut off values was more useful as ruling in LRTI (specificity 94%, positive LR 3.66) than the APLS thresholds (specificity 53%, positive LR 1.59). However centile cut offs could not discriminate between pneumonic and non-pneumonic LRTI.
The study estimated an increase in RR of 2.2 breaths/min per 1 degree Celsius rise in temperature.
A previous larger derivation study estimated 0.5-2 breaths/min RR increase and an approximately 10 beat/min HR increase for each 1 degree Celsius rise.