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Rationale

Cooling Rationale

Active cooling is a treatment method whereby energy is dynamically extracted from the body in order to reduce core temperature for the benefit of health. This treatment may be sought in order to reduce abnormally or dangerously elevated core temperatures, as in hyperthermia or pyrexia, or to instigate a treatment method known as therapeutic hypothermia. During therapeutic hypothermia, a patient’s body temperature is lowered in a controlled manner in order to reduce tissue damage following a loss of blood perfusion, especially to the brain which is highly sensitive to hypoxia (or oxygen depletion).

Cardiac Arrest

The advised treatment for cardiac arrest is rapid defibrillation (if the heart is in a shockable rhythm), reversing treatable causes (such as giving intravenous fluids if there has been blood loss from the circulation), and cardiopulmonary resuscitation to provide circulatory support. Once the heart has restarted, the patient is described as having achieved a return of spontaneous circulation (ROSC). Beyond this, the only treatment which has been shown to confer significant patient benefit is the provision of mild therapeutic hypothermia in the form of targeted temperature management (TTM).

The use of TTM was adopted as part of the standard treatment protocol for SCA in October 2002 with the publication of an Advisory Statement by the Advanced Life Support Task Force of the International Liaison Committee on Resuscitation (ILCOR) which stated:

“Unconscious adult patients with spontaneous circulation after out-of-hospital cardiac arrest should be cooled to 32°C to 34°C for 12 to 24 hours when the initial rhythm was ventricular fibrillation (VF).” and;

“Such cooling may also be beneficial for other rhythms or in-hospital cardiac arrest.”

The new 2015 guidelines, in light of new research, maintain the importance of cooling but amend the target temperature range to 32°C to 36°C, with emphasis on preventing fever.

Hospitals have been quick to adopt the treatment as a standard of care: 86% of UK ICU departments were implementing this therapy by 2009. Studies have shown that the earlier cooling can be applied, the greater the patient benefit is likely to be. CAERvest® allows paramedics and other first responders to deliver core body cooling in the critical pre-hospital environment, prior to receiving conventional powered methods of cooling in hospital.

Potential Mechanisms of Hypothermia Benefit (for more information see here)

  • Decreasing neuronal metabolism in the early stage of ischaemic injury
  • Decreasing glucose and oxygen consumption by the brain which reduces supply/demand mismatch
  • Decreasing the release of excitatory amino acids (e.g. glutamate) that normally trigger cytotoxic cascades in the intermediate phase of injury
  • Reducing the production of harmful reactive oxygen species
  • Maintaining cellular pH
  • Reducing cell death
  • Slowing the breakdown of the blood-brain barrier that worsens cerebral oedema

Heatstroke

Following heatstroke, the basic premise of rapidly lowering the core temperature to about 39°C remains the primary goal. Where cold water immersion is not available, CAERvest® offers an effective method of cooling the core body temperature quickly to safe levels.

Other

Active cooling also has potential for use across a range of other pathophysiologies and it is our intention to support further research as to the benefits of therapeutic hypothermia in each case.

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