Which pulse rate in an 18-month-old child would be cause for concern?

In children, particularly those around 18 months old, the normal resting pulse rate typically ranges from 80 to 130 beats per minute. A pulse rate that is significantly elevated above this range can indicate a potential issue.

The selected response, which indicates a pulse rate of 150 bpm, is concerning because it exceeds the upper limit of the normal range for this age group. Such a high pulse rate could be indicative of several possible conditions, including infection, fever, dehydration, or underlying cardiovascular issues. It may warrant further evaluation to determine the cause of the tachycardia and to assess the child's overall health status.

The other pulse rates presented—in the low end of the range—are not alarming. A pulse rate of 90 bpm is within the normal parameters and does not typically raise concern. Rates of 100 bpm and 120 bpm also fall comfortably within the expected range for this age, indicating that the child is likely in a stable condition. Hence, the stark difference in the case of a 150 bpm pulse makes it the one that requires attention.