Prolonged unintended brain cooling may inhibit recovery from brain injuries: case study and literature review

Tracheal intubation of comatose patients is common, but contrary to most standards for respiratory care, heated nebulizers are not always used. This deviation from recommendations appears to be widespread.

In the case examined, a tracheotomized patient suffering from severe anoxic brain injury was unintentionally exposed to chilled air, 17 degrees C (63 degrees F) at the cannula, for a period of 31 months. A month after upper respiratory tract warming was restored the vegetative state lifted, as marked by the patient's ability to verbalize responses to questions.

This clinical experience led us to a review of the literature. Among other findings, we learned that brain temperature is strongly affected by the temperature of arterial blood flow. Arterial blood, in turn, is strongly affected by the air temperature in the lungs. Experiments have shown that the introduction of colder air in the lungs will produce rapid cooling of at least some surface brain tissues. Chilled aortic blood is also more viscous and less efficient in transfer of oxygen. Hypothermia of brain tissue may significantly affect the endocrine system and neurochemistry. Through inferences from the literature, we also identify other possible effects. We hypothesize that intubated delivery of air into the lungs at a temperature significantly below body temperature, especially over a prolonged period, is likely to inhibit recovery and may even produce iatrogenic effects. We recommend the use of heated nebulizers. Research strategies are recommended.