18 Respiratory Tract Normal ranges of heart rate and respiratory rate in children from birth to 18 years of age: a systematic review of observational studies Fleming S, Thompson M, Stevens R, et al (Oxford Univ, Headington, UK; et al) Lancet 377:1011-1018, 2011 Background.dAlthough heart rate and respiratory rate in children are measured routinely in acute settings, current reference ranges are not based on evidence. We aimed to derive new centile charts for these vital signs and to compare these centiles with existing international ranges. Methods.dWe searched Medline, Embase, CINAHL, and reference lists for studies that reported heart rate or respiratory rate of healthy children between birth and 18 years of age. We used non-parametric kernel regres- sion to create centile charts for heart rate and respiratory rate in relation to age. We compared existing reference ranges with those derived from our centile charts. Findings.dWe identified 69 studies with heart rate data for 143 346 children and respiratory rate data for 3881 children. Our centile charts show decline in respiratory rate from birth to early adolescence, with the steepest fall apparent in infants under 2 years of age; decreasing from a median of 44 breaths per min at birth to 26 breaths per min at 2 years. Heart rate shows a small peak at age 1 month. Median heart rate increases from 127 beats per min at birth to a maximum of 145 beats per min at about 1 month, before decreasing to 113 beats per min by 2 years of age. Comparison of our centile charts with existing published reference ranges for heart rate and respiratory rate show striking disagree- ment, with limits from published ranges frequently exceeding the 99th and 1st centiles, or crossing the median. Interpretation.dOur evidence-based centile charts for children from birth to 18 years should help clinicians to update clinical and resuscitation guidelines. : Measurements of heart rate and respiratory rate are extraordinarily funda- mental to the assessment of the physiologic status of both well and unwell chil- dren. Infancy and childhood are periods of enormous physiological and developmental changes, particularly in the early months and years of life. Over the years, investigators have attempted to establish what constitutes normal heart and respiratory rates at different ages, but these investigations have taken place in various populations, settings, and geographical locations using different measurement techniques. The result is that evidence for what 521