Hypothermia: Ice cold little heart

5. June 2014
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In the instance of a cardiac arrest, the brain is often affected as well. Doctors try to counteract it using therapeutic hypothermia. From a scientific viewpoint a lot speaks in favour of this method, whereas some lingering doubts have not yet been dispelled.

In recent decades pieces of indicative evidence have accumulated showing that patients, after cardiac arrest and successful resuscitation, profit from mild hypothermia. One goal is to slow down brain metabolism, thus reducing tissue damage. Temperature reduction slows down biochemical processes by about six percent per degree: reason enough for it to be recommended for its use in practice.

ERC Guidelines-justified hypothermia

An example: The European Resuscitation Council (ERC) writes in its guideline on cardiopulmonary resuscitation that comatose patients should after the return of spontaneous circulation (ROSC) be cooled to 32 to 34 degrees. Sufficient sedation and muscle relaxation in the instance of shivering are also actions to be followed with vigilance here. After at least 12 to 24 hours of hypothermia treatment the patient concerned should go through a rewarming process – by way of a 0.25 to 0.5 degrees Celsius increase per hour. It must be said however that the data-set at the time of the publication of the guideline at the end of 2010 was still very limited.

Cold or colder

In 2012, Esteban Lopez-de-Sa, Madrid, published results of a study. His aim was to investigate which temperature brings the maximum benefit. Lopez-de-Sa divided 36 patients who had survived a cardiac arrest randomly into two groups. With each of the 18 patients in each group he cooled the body respectively to a temperature of 32 degrees or 34 degrees. Eight patients (44 percent) of the 32-degree group reached the primary end point, they survived six months without serious harm. In the 34-degree group, there were only two such patients (eleven percent). Large differences with regard to complications did not occur. The only exception: In the 32-degree group there was increased bradycardia incidence (39 versus 11 percent). “The results of this pilot study suggest that a lower level of cooling correlates with better results,” writes Lopez-de-Sa. He calls for larger studies in order to extrapolate what the consequences should be for clinic practice.

Hypothermia without value?

It’s quite clear that cardiologists have continued to deal with this issue. At the end of 2013 Niklas Nielsen, Helsingborg, together with colleagues published surprising results. He drew 939 unconscious individuals who had suffered cardiac arrest into his study. 466 of them were treated with the aim of reaching 36 degrees Celsius body temperature. A further 473 had their temperature set to 33 degrees. The groups differed in their primary endpoint, ie. mortality rate at the end of the study, insignificantly from one another. When the authors combined mortality and neurological outcomes, no benefit was shown by the lower temperature. Are hypothermia treatments therefore obsolete? Not necessarily. With this in mind, let’s take a look at Nielsen’s study design. Patients with non-shockable heart rhythms where excluded by the doctor. The rate of resuscitation by non-specialists stood at 73 percent – nearly four times more than in Germany. According to Nielsen, the median average time until the point of resuscitation was a period of just 60 seconds. The respective vertice values might have inherently destroyed the genuine additional value of hypothermia treatment.

Fatal fever

But that’s not all: Jon C. Rittberger and Clifton W. Callaway, Pittsburgh, in an editorial regarding Nielsen’s work evaluated hypothermia treatments to be valuable. They suspect that through the cooling, prognostically unfavourable hyperthermia would be prevented. How unfavourably fever affects things is shown by the work of John Bro-Jeppesen, Copenhagen. He observed 270 patients after a cardiac arrest. They went through a 24-hour hypothermia protocol involving target temperatures of 32-34 degrees Celsius. Fever of 38.5 °C or more was associated with a 36 percent mortality rate. In the comparison group, only 22 percent died. The observation period selected by Bro-Jeppsen was one of 30 days. He identified maximum temperature and the duration of fever as prognostic parameters.

more cooling …

What does the data available now bring to doctors? “The German Society of Internal Intensive Care and Emergency Medicine (DGIIN) recommended that until further study results exists, unconscious adults having experienced spontaneous circulation after preclinical ventricular fibrillation still be cooled for twelve to 24 hours at 32 to 34 degrees Celsius”, it says in a statement. “In addition, a target temperature of 36 degrees Celsius should be actively pursued with all other unconscious patients after having heart circulatory arrest”. Increased temperatures are to be avoided in every case.

but at the correct time …

According to Francis Kim, Seattle, hypothermia treatment still should not be initiated in the prehospitalisation phase. The scientist took 1,359 patients with cardiac arrest into her randomised clinical trial. With around 50 percent of all those affected, before arrival in the hospital body temperature had been cooled using saline solution. In the comparison group only standard treatment was used. Differences were found neither for mortality nor with regard to neurological status. The problematic matter was that with early application of hypothermia treatment lung oedema and repeat cardiac arrest occurred.

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1 comment:

Nurse / Hospital nurse

Although known by me as certified ERC-NRR CPR+AED instructor it is nice to see it here, so that a lot of professionals learn about it.

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