Temperature management and modern post-cardiac arrest care

A new global study that used Australian patients has cast doubt on the usefulness of induced hypothermia to treat unconscious survivors who have a heart attack outside hospital.

Unconscious patients admitted to critical care units after out-of-hospital cardiac arrest are at high risk of death, and brain injury is common in those who do survive.

The new trial, published recently in The New England Journal of Medicine, revisited the outcomes of two 2002 trials that changed the way cardiac arrest patients were treated in hospitals.

The 2002 trials showed that lowering patients’ temperature to 33C for 12 or 24 hours increased survival and improved brain injury outcomes for a select group of heart attack patients.

As a result, induced hypothermia became widely used in hospitals and advocated by international guidelines.

Australian lead investigator, from The George Institute and Liverpool Hospital, Associate Professor Anders Aneman, led a team of researchers from The George Institute as part of the worldwide re-examination of this type of treatment.

He said: “Some investigators argued that the evidence for induced hypothermia change was weak, owing to the risk of bias and small samples.

“The far larger new trial has now raised questions over whether lower temperatures actually benefit cardiac-arrest patients.”

The trial looked at 939 patients around the world, including 44 in Australia, and found that there was little difference in outcomes between patients whose temperatures were lowered to 33C and those whose temperatures were maintained at near normal, at 36C.

At the end of the trial, 50 per cent of patients in the 33C group had died, compared to 48 per cent of patients in the 36C group.

“Our trial does not provide evidence that targeting a body temperature of 33C confers any benefit for unconscious patients admitted to hospital after cardiac arrest, compared to those whose temperature is maintained at 36C,” said Professor Aneman.

The study was nearly three times larger than the original two studies combined. Most patients experienced cardiac arrest at home or in public places.

“Reducing temperature affects the whole body, not just the brain, and any potential benefits should be balanced against the possible side effects,” Professor Aneman said.

“The population of patients with cardiac arrest is made up of many different people, and the potential risks and benefits of temperature intervention may not be the same across subgroups.”

The team from The George Institute included Sharon Micallef, Ann Gould, Meg Harward, Kelly Thompson, Naomi Hammond, Parisa Glass, John Myburgh AO. Patients came from Royal North Shore Hospital, St George Hospital and Liverpool Hospital.