Brief hyperthermia does not worsen outcome after striatal hemorrhage in rats

Hyperthermia accelerates and increases ischemic brain damage. Owing to overlapping mechanisms of injury, many assume that hyperthermia also worsens outcome after intracerebral hemorrhage (ICH). However, clinical data do not conclusively prove this, and there is only one animal study examining the impact of hyperthermia. In that study (MacLellan and Colbourne, 2005), several hyperthermia protocols were administered after collagenase-induced ICH in rats; none worsened injury. While the collagenase model is widely used, it differs in important ways from another common model - injecting autologous blood directly into the brain. Thus, we evaluated the impact of immediate hyperthermia (HYP, 39 °C for 3 hr) after a 100-µL infusion of blood into the striatum of rats. This treatment, which markedly increases ischemic damage, was compared to control rats kept normothermic (NOR, 37 °C). Three separate experiments were done to measure: 1) edema at 24 hr, 2) edema at 72 hr, and 3) behavioral impairment and lesion size out to 1 month post-ICH. The HYP treatment did not significantly affect edema at 24 hr, but surprisingly, it modestly reduced edema at 72 hr and partly improved behavioral outcome. However, there were no lasting effects of HYP on behavior (e.g., skilled reaching) or the volume of tissue lost (NOR: 14.0 mm(3) vs. HYP: 14.5 mm(3)). In summary, our findings do not support the common belief that hyperthermia worsens outcome after ICH. Additional research is needed to determine whether more severe or prolonged heating or fever and its cause (e.g., infection) affect morbidity and mortality after ICH.