A new study suggests that survival rates of adults who suffer cardiac arrest are not improved by the lowering of their body temperature prior to hospital arrival. This is according to a study published in JAMA.
Cardiac arrest occurs when the heart stops pumping blood around the body. The most common cause of the condition is an irregular heart rhythm known as ventricular fibrillation (VF).
According to the researchers from Harborview Medical Center in Seattle, WA, led by Francis Kim, cardiac arrest can cause brain injury and because of this, many patients do not awake after resuscitation.
Putting the body into a state of hypothermia (lowering of the body temperature) can help the brain recover from cardiac arrest, the investigators note.
It is thought that better outcomes occur when body cooling is carried out as soon as patients show the return of spontaneous circulation – the resumption of sustained cardiac activity – prior to hospital arrival.
To see how pre-hospital body cooling impacts patients’ survival rates, the researchers analyzed 1,359 patients, of which 583 had ventricular fibrillation and 776 did not.
All patients suffered pre-hospital cardiac arrest and were resuscitated by paramedics. Patients were randomly assigned to receive standard care with or without pre-hospital cooling.
The pre-hospital cooling was carried out by infusing the patients with up to 2 liters of normal saline (sterile solution of sodium chloride) at 4°C as soon as the patient showed return of spontaneous circulation.
The investigators note that almost all of the patients who were resuscitated from VF and admitted to the hospital received hospital cooling regardless of which group they were randomized to.
Patients who received pre-hospital cooling experienced a reduced core temperature of more than 1°C and reached the goal temperature (34°C) around 1 hour sooner, compared with patients who did not receive pre-hospital cooling.
However, on monitoring the survival rates of all VF patients up to their discharge from hospital, the investigators found there was no significant difference between those who had pre-hospital cooling and those who did not, with rates of 62.7% and 64.3% respectively.
Among the patients who did not have VF, survival rates stood at 19.2% for those who underwent pre-hospital cooling and 16.3% for those who did not.
Furthermore, the researchers found that pre-hospital cooling was not associated with any improvements seen in the neurological status of full recovery or mild impairment patients with or without VF.
Commenting on their findings, the researchers say:
“Although hypothermia is a promising strategy to improve resuscitation and brain recovery following cardiac arrest, the results of the current study do not support routine use of cold intravenous fluid in the pre-hospital setting to improve clinical outcomes.”
The researchers hypothesize that pre-hospital cooling may need to take place during resuscitation and not after return of spontaneous circulation in order to have a beneficial impact on patient outcomes.
“Early cooling during resuscitation might attenuate the cascade of reperfusion injury that begins with return of spontaneous circulation,” they add. “This use of intra-arrest cooling is supported by animal studies. Whether earlier cooling will improve survival and outcomes in humans awaits further study.”
Last year, Medical News Today reported on research suggesting that a person’s risk of cardiac arrest depends on where they live.