Patients who have a cardiac arrest outside of the hospital setting may receive a placebo instead of adrenaline as part of a study into whether adrenaline works in resuscitation.

Current UK and Australian guidelines used by ambulance services recommend routinely giving adrenalin during the resuscitation of patients who have suffered cardiac arrest.

However, there are concerns that adrenaline may cause severe brain damage and may not help overall survival at all say UK researchers.

Researchers from the UK and Australia who are conducting the study, called Paramedic 2: the adrenalin trial, say that despite being used for close to 40 years adrenalin is an unproven treatment for cardiac arrest and, increasingly, there are safety and efficacy concerns about its use in this setting.

While most studies have found that adrenaline increases the chance of return of spontaneous circulation for short periods, many studies found harmful effects on the brain and raise concern that adrenaline may reduce overall long term survival and lead to worse neurological outcomes, the researchers said in their study protocol published in Resuscitation.

“This creates the paradox of better short-term survival at the cost of worse long-term outcomes, in other words a ‘double-edged sword,” they wrote.

The trial is seen to be controversial because patients will not be able to consent to taking part. What’s more, relatives of patients who may die having taken part in the trial will not automatically be made aware of their involvement in the study.

During the trial, paramedics will be given randomised treatment packs and will not know whether they are injecting adrenalin or a saline solution placebo.

All other resuscitation including heart massage and defibrillation would be conducted on every patient as recommended by current guidelines.

Researchers say that advertisements where the trial is due to take place will tell people what is happening and allow them to say in advance that they would not consent to taking part if they suffered a cardiac arrest.

However they acknowledge that it might be difficult to check up on pre-registered refusal during the scramble to save someone’s life, confirming the consent of the trial participants could be difficult.

Some 8,000 people will be recruited to the study over three years and survivors will be followed for 30 days.

Researchers say the data would be reviewed at regular intervals and if it were clear that the intervention group or the control group was doing better the study would be stopped.