The role of autonomic nervous system function in hypothermia-mediated sepsis protection.

OBJECTIVE: The objective of this study is to determine whether hypothermia will lessen decreases in heart rate variability and improve outcome in a rat model of sepsis. METHODS: Thirty-six male Sprague-Dawley rats were randomized into 3 groups: control, low sepsis, and high sepsis groups. These groups were each subdivided into a normothermia (37°C) (n = 6) and a hypothermia group (34°C) (n = 6). Cyclophosphamide (100 mg/kg) was administered 5 days before Staphylococcus aureus injection to produce conditions in which sepsis could be induced reliably. Hypothermic rats received temperature reduction for 1 hour post injection. Electrocardiogram was recorded before, after, and 1 day after staphylococcal injection, and the low frequency, high frequency (HF), and LF/HF ratio measurements of heart rate variability and the frequencies of arrhythmia were recorded. The effects of time, sepsis severity, and hypothermia on these variables were analyzed using a multivariate generalized estimation equation mode. RESULTS: Four deaths occurred in the normothermic group, and none, in the hypothermic group. Sepsis of both low and high severity increased low frequency and HF 1 day after sepsis induction. Hypothermia significantly decreased HF in low, but not high sepsis severity. CONCLUSIONS: Hypothermia decreased mortality in septic rats. The influence of hypothermia on HF depended on the severity of the sepsis.