When a child develops a fever, their heart rate, or pulse, provides valuable information about the body’s response to illness. The heart rate is the number of times the heart beats each minute, measuring how hard the organ works to circulate blood. When body temperature rises, the heart rate increases as a direct result of the fever. Understanding this relationship and knowing what is normal helps caregivers assess a child’s condition accurately.
Standard Heart Rates by Age
A child’s baseline heart rate is naturally much faster than an adult’s and gradually decreases with age. These rates are measured when the child is calm, resting, and healthy. For a newborn up to one month old, the normal resting heart rate ranges broadly from 70 to 190 beats per minute (bpm).
Infants (one month to one year old) typically have a resting rate between 80 and 160 bpm. For toddlers and preschoolers (one to four years), the expected range narrows to 80 to 120 bpm. School-aged children (five to 12 years old) have a resting heart rate closer to adult values, usually falling between 70 and 110 bpm.
The Physiological Link Between Fever and Heart Rate
The body’s temperature regulation center, located in the hypothalamus, raises its set point during a fever to fight infection. This change drives the metabolic rate upward, requiring more oxygen and nutrients to be delivered to tissues. The cardiovascular system compensates for this increased demand by speeding up the heart’s pumping action.
This response is amplified by the body’s attempt to dissipate heat through the skin, causing peripheral blood vessels to widen (vasodilation). To maintain adequate blood pressure and ensure blood flow to organs despite this widening, the heart must beat faster. The heart rate typically increases by about 10 beats per minute for every one degree Celsius rise in body temperature (or 1.8 degrees Fahrenheit).
Studies suggest this increase can be more pronounced in children, particularly during the initial fever spike, rising up to 12.3 bpm per degree Celsius. This predictable increase, known as “sinus tachycardia” in the context of fever, is a normal physical reaction. Treating the fever with an antipyretic medication, such as acetaminophen or ibuprofen, typically causes the heart rate to slow down as the temperature drops.
Identifying Dangerous Heart Rate Increases
A heart rate that is excessively high, even after accounting for the fever, is known as pathological tachycardia and may signal a serious underlying issue. This suggests the heart is working too hard due to complications like dehydration, which reduces the volume of blood available to pump. Specific threshold rates have been established for febrile children that indicate the need for medical evaluation.
For an infant younger than 12 months, a heart rate consistently above 160 bpm is a concern. Children between 12 and 24 months should be assessed if the rate exceeds 150 bpm. A child aged two to four years requires medical assessment if their heart rate is sustained above 140 bpm.
These high rates, especially when persisting after the fever has been reduced with medication, are predictive of a potential serious bacterial infection. An alarming heart rate accompanied by other symptoms, such as difficulty breathing, pale or mottled skin, or difficulty rousing the child, warrants immediate emergency medical attention.
How to Check a Child’s Pulse Accurately
Obtaining an accurate heart rate measurement requires the child to be calm and still, ideally after resting for several minutes. To find a pulse on an older child, gently place your index and middle fingers on the inside of the wrist, just below the base of the thumb (the radial artery). Avoid using your thumb, as it has its own distinct pulse that can confuse the count.
For infants, the pulse is easiest to locate on the inner upper arm, between the elbow and shoulder, at the brachial artery. Once the rhythmic throbbing is located, count the number of beats for 15 seconds. Multiplying this number by four provides the heart rate in beats per minute.