Abstract: To study the effects of ketamine and midazolam on heart rate variability (HRV) in children. Methods Forty-four children aged 5 to 6 years old (ASA I) were randomly divided into two groups, and intravenously received 2mg/kg ketamine (n=23) or 0.2mg/kg midazolam (n=21). All patients kept spontaneous respiration. Heart rate (HR), mean arterial pressure (MAP) and pulse oxygen saturation (SpO₂) were monitored. HRV parameters including total power (TP), low frequency component (LF) and high frequency component (HF) were recorded before and after drug administration. Normalized unit power was derived as follows: nuLF=LF/TP×100%, nuHF = HF/TP×100%. ResultsThe levels of TP and HF decreased (P<0.05), nuLF increased from （63±16）% to （71±13）% (P<0.05) and nuHF attenuated from （32±15）% to （21±13）% (P<0.05) after ketamine administration. While after receiving midazolam, the value TP and LF reduced（P<0.05）, nuLF decreased from（65±15）% to （48±16）%（P<0.05）and nuHF increased from （33±15）% to（ 42±16）%（P<0.05）. ConclusionKetamine and midazolam have different effects on HRV in children, indicating enhancement of sympathetic nerve tension by ketamine and inhibition of sympathetic nerve tension by midazolam.

Key words: Ketamine, Midazolam, Heart rate variability, Child