KEEPING A COOL HEAD, POSTHYPOXIC HYPOTHERMIA - AN OLD IDEA REVISITED

Hypoxia-ischaemia produces permanent brain damage by processes that co ntinue for many hours after reoxygenation/reperfusion. This provides a window of opportunity for therapy aimed at preventing further loss of brain cells. Reducing brain temperature by 2-6 degrees C for 3-72 h a fter reoxygenation/reperfusion has been shown to reduce brain damage b y 25-80% in controlled trials with six different neonatal animal model s of hypoxia-ischaemia. No adverse effects from mild hypothermia have been documented. The mechanisms of protection are unknown but may incl ude a reduction in extracellular excitotoxic amino acids, reduced nitr ic oxide synthesis and inhibition of apoptosis. Mild hypothermia is cu rrently the most promising clinically feasible neural rescue therapy f or full-term infants at risk of developing hypoxic-ischaemic encephalo pathy, but clinical use must be restricted to approved trial protocols .