Conservatively, the best current data suggest an increase in 10 bpm for every 1°C rise in body temperature for fever in children presenting to the ED. Although some studies may suggest larger responses, 10 bpm/1°C is likely the best ballpark number to currently attribute to fever. Although not an ED study, an inpatient pediatric study of 60,863 children found a similar association.⁶

“Are there any places we may need to consider where children can ‘hide’ disease that may be suggested by tachycardia?”

Although almost any disease can potentially present with tachycardia, two to consider may be pneumonia and myocarditis. In adults, pulmonary embolism (PE) should be considered in cases of persistent or disproportionate tachycardia. Although PE should be considered in children also, it is very uncommon, with a reported rate in the pediatric community of 0.14 to 0.9 cases per 100,000. Anecdotally, pneumonias can sometimes be difficult to diagnose in children. Some lower lobe pneumonias manifest as upper abdominal pain; some simply present as persistent tachycardia. A prospective cohort study of 570 children ages one to 16 years found an odds ratio of 1.3 (95 percent CI; 1.0-1.6) for tachycardia in the setting of a consolidated pneumonia.⁷ Regarding myocarditis, a separate prospective observational study of 63 cases of pediatric myocarditis found tachycardia (96.8 percent) to be the most common arrhythmia found in these children.⁸ Although these results don’t suggest that everyone with tachycardia needs a chest radiograph or cardiac evaluation, they do suggest that pneumonia and myocarditis should be on our differential diagnosis when considering the evaluation of children with tachycardia.

“When discharging a child with tachycardia, does having tachycardia suggest that they will bounce back more easily?”

A 2017 study over 44 months retrospectively reviewed children ages two months to 17 years who were discharged from a pediatric ED.⁹ The authors specifically looked at those patients who discharged with an abnormal heart rate, respiratory rate, temperature, or oxygen saturation level. The primary goal of this study was to evaluate the frequency and nature of significant adverse events within 72 hours in children who had abnormal vital signs at discharge. During this 44-month time period, the pediatric ED discharged 33,185 children—of whom 5,540 (17 percent) had at least one abnormal vital sign. Abnormal vital signs were defined as temperature ≥ 38°C, oxygen saturation < 95 percent, or heart rate and respiratory rate outside published age-specific ranges. Of the 5,540 children discharged with one or more abnormal vital signs, 24 (0.43 percent) had a significant adverse event within the next 72 hours (defined as re-presentation to hospital and admission for greater than or equal to five days, CPR, endotracheal intubation, or unexpected surgery). Death related to the initial visit, even though it may have happened outside the 72-hour window, was explored and included on a case-by-case basis. In the group discharged with at least one abnormal vital sign—compared to the normal vital sign group—the relative risk for a significant adverse event was 2.5 (95 percent CI 1.6-4.2), and the number needed to harm was 380 (95 percent CI 252-767). In the 24 children who were discharged with at least one abnormal vital sign and returned with a significant adverse event, 67 percent demonstrated tachycardia at discharge. In children who were discharged with at least one abnormal vital sign and had no adverse events, 56.1 percent had tachycardia at discharge. Thus, heart rate had poor discrimination for predicting adverse events. There were two deaths in the group with abnormal vitals at discharge; one was an unrelated accidental death and the other was due to infection “not believed to be potentially preventable by hospital observation.” In the group with normal vitals at discharge, there were no deaths. Although discharging a child with abnormal vital signs does appear to increase the risk of bounce back, the likelihood of a significant event is still very low (0.43 percent)—emphasizing the importance of good discharge instructions. Although the most common abnormal vital sign in this study was tachycardia, it was a poor predictor of adverse events.