A 46-year-old woman is brought back to the neurologic intensive care unit (NeuroICU) after undergoing coiling of a right middle cerebral artery aneurysm that had ruptured the previous day. On examination, she requires mild sternal rub to remain awake and is able to follow simple, one-step commands. There are no cranial nerve abnormalities, but a mild left pronator drift is noted. Overall, examination is unchanged from presentation. While in the operating room, a left subclavian central line and radial arterial line is placed along with a right external ventricular drain. On posthemorrhage day 5 (postoperative day 4), she develops a fever with a temperature of 39°C.
Why is controlling fever after brain injury important?
Fever after brain injury independently worsens outcome. One of the important mechanisms is by exacerbating inflammatory cascades. Postinjury elevations in temperature have been shown to increase inflammatory processes, including elevations in proinflammatory cytokines, the increased accumulation of polymorphonuclear leukocytes in injured tissue.1 Vascular and inflammatory cascades appear to be extremely sensitive to mild elevations in temperature following central nervous system (CNS) injury.
Several studies also suggest that one of the key impacts of fever is an increase in neuronal excitotoxicity. Elevations in temperature have been reported to increase neurotransmitter release, accelerate free-radical production, increase intracellular glutamate concentrations, and potentiate the sensitivity of neurons to excitotoxic injury.1 In an experimental microdialysis study of focal ischemia, glutamate release was significantly higher in hyperthermic than normothermic rats, indicating the importance of focal brain temperature on neurotransmitter release.2 Other investigators have observed increases in cellular depolarization in the ischemic penumbra surrounding damaged neuronal tissue, increased neural intracellular acidosis, and inhibition of enzymatic protein kinases, which are responsible for synaptic transmission and cytoskeletal function in relation to elevations in core body temperature.3 At the molecular level, elevations in temperature have been shown to enhance the expression of heat-shock proteins, as well as receptor expression associated with glutamate neurotransmission.4 Fever affects cerebral hemodynamics, and cerebral blood flow (CBF) velocity and pulsatility index has been shown to increase in parallel with rising temperatures.5 Experimental mild hyperthermia has been shown to increase contusion areas and volumes and most severe loss of neuronal nuclear (NeuN)-positive cells in animal models with mild traumatic brain injury (TBI).6
Experimental and clinical studies have suggested that fever can also directly induce nervous system injury.7 In these circumstances, it is usually a temperature > 40°C for extended periods that produces abnormalities in the blood-brain barrier, as well as profound cardiovascular, metabolic, and hemodynamic dysfunction. The hypothalamus is a key center for thermoregulation, and damage to this structure can result in hyperthermia. Thus, mechanisms underlying hyperthermia-induced pathophysiology and secondary hyperthermia following CNS injury are similar.
A meta-analysis of all brain injury types found that fever was consistently associated with mortality and worse outcomes across multiple outcome measures of morbidity.8...