HOW THER­A­PEU­TIC HY­POTHER­MIA WORKS

BBC Earth (Asia) - - Science -

Within the first 20 sec­onds of car­diac ar­rest, tis­sues start to de­plete their re­serves of oxy­gen, and tox­ins build up in

the brain.

Cool­ing the body after car­diac ar­rest re­duces the

brain’s meta­bolic rate,

slow­ing re­ac­tions that

cause cell dam­age. For each 1°C drop

in core tem­per­a­ture,

the brain’s meta­bolic rate de­creases by 6-7 per cent.

After re­sus­ci­ta­tion, pa­tients are kept cold and un­con­scious for 12-24 hours. This pre­vents brain dam­age when pa­tients are re­vived.

Drugs pre­vent shiv­er­ing, which raises body tem­per­a­ture.

Once sta­ble, the pa­tient is

warmed slowly – some­times by as lit­tle as

0.1°C every hour.

After be­ing suf­fi­ciently warmed, the pa­tient is re­vived. Pa­tients who’ve been hy­pother­mic for many hours will of­ten show signs of fever, or

de­velop res­pi­ra­tory in­fec­tions.

The sooner pa­tients can be cooled the bet­ter, although cool­ing pa­tients after they have been re­sus­ci­tated can still

be ben­e­fi­cial.

Doc­tors use cool­ing

blan­kets, pads or ice-cold in­stru­ments to re­duce the body tem­per­a­ture to 33-36°C. Cruder

tem­po­rary mea­sures, such as ap­ply­ing bags of frozen food, have also been em­ployed.

If blood flow is re­stored, tis­sue dam­age in the brain con­tin­ues. Such ‘reper­fu­sion in­jury’ is thought to be caused by the pro­duc­tion of free rad­i­cals when blood re­turns to oxy­gen-de­pleted

cells.

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