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What is core body cooling?

Various strategies have been devised to cool patients; the most important aim is to cool organs that may deteriorate in the absence of oxygen or if overheated. The most apparent damage is to brain tissue, but significant damage occurs to all tissues. It is therefore inappropriate to employ strategies that only cool the brain by local cooling as this does nothing for the rest of the body.

Is CAERvest® safe?

CAERvest® is made of biocompatible thermoplastic polyurethane and filled with a blend of chemicals that are chosen, in part, for their extremely low toxicity. They are non-flammable and non-explosive. They can however be corrosive to metals so, in the unlikely event of any leaks, it is good practice to rinse any escaped fluids away with fresh water. Standard precautions should be taken for infection control and in the event of defibrillation being required, although CAERvest® is designed to be left in place during defibrillation and cardiopulmonary resuscitation (CPR).

What do I do with CAERvest® after use?

CAERvest® can be disposed of with normal waste, and should be discarded immediately after use. In the event that it may have been in contact with body fluids during use however, we recommend that the device is disposed of as clinically contaminated waste.

How do I check CAERvest® isn’t cooling too much?

CAERvest® is a powerful device, and will cool a person rapidly. Your own organisation will have protocols for evaluating patient temperature, and we encourage you to follow these. We recommend that patient temperature is measured using an oesophageal probe. A rectal probe may also be used, but responds a little more slowly. It is also possible to use an infrared thermometer, but take care in using this in a markedly hot person – over 40° C (104° F) particularly if the skin feels paradoxically cold. We DO NOT recommend tympanic thermometers. The cooling power of CAERvest® can readily be adjusted by folding back the device or even removing it altogether as required. It is however important not to let the patient rewarm. As CAERvest® has a defined mass, it will eventually run out of cooling power and should be replaced.

How do I know when CAERvest® is depleted?

There are two ways to check this. Firstly, the device will obviously feel less cold, and will feel soft to the touch instead of gritty. Secondly, the patient temperature will cease declining and may even start to rise. If this is not desired, then a second device should be prepared and deployed and the first discarded.

What does TTM stand for?

TTM means targeted temperature management. It is used to describe reducing the core body temperature of patients below normal. It indicates that a target temperature is set, and that there is active monitoring and control of temperature to that target. It does not imply any particular target temperature.

What is the difference between TTM and therapeutic hypothermia (TH)?

TH is an older term that has been superseded by the more accurate description TTM.

What is the set point?

Every animal has an optimum temperature at which its enzyme reaction systems work most efficiently. In mammals and birds the internal systems maintain a specific temperature within tight limits. See our FAQ on the difference between hyperpyrexia and hyperthermia.

What is the difference between hyperpyrexia and hyperthermia?

Humans are homeotherms. This means that like nearly all mammals and birds, they have internal mechanisms for creating and retaining heat so as to maintain a body temperature irrespective of the ambient temperature within wide limits. The body temperature varies between species and, to a lesser extent, individuals within that species. For humans, the accepted (‘normal’) range is 36.8°C ± 0.5°C – 36.3°C to 37.3°C. While this is maintained by various metabolic processes, the control of temperature is performed by a small group of cells at the base of the brain. They create a set temperature point that the remainder of the body attempts to maintain through various strategies such as cooling by sweating or warming by shivering, amongst others.

Hyperthermia is the term used to describe a high temperature in a previously well patient with a normal set point in whom the heat rejection processes are overwhelmed – such as an athlete running on a hot day who generates more heat from exercise than can be shed. The effect is to raise the core body temperature despite measures like sweating, wearing light clothing and radiating heat to the environment. Additional cooling will increase heat loss, and when the person cools the body temperature will return to the set point.

Hyperpyrexia describes a patient with an elevated set point – normally because of infection. Pyrexia is considered an appropriate response to infection, and while excessively high temperatures that in themselves may be harmful and are termed hyperpyrexia should be treated, a mild pyrexia is tolerable and probably assists fighting infection. Hyperpyrexia with confusion or fitting should be treated.

What is an endothermic reaction?

Whenever substances are mixed to interact with each other, energy is either released or absorbed. If energy is released the mix becomes hot, may catch fire or even explode. This is an exothermic reaction. If energy is absorbed, cooling ensues. This is an endothermic reaction. CAERvest® has a specially formulated mix that absorbs energy at a rate suitable for use on humans when activated, for which the technical term is an endothermic dissolution.

What is the difference between in-hospital and out of hospital cooling?

Cooling requires energy. In a hospital this can be achieved using mains electricity to run refrigeration units, but this is impractical outside hospital. Ice and cool boxes have conventionally been used, but start warming immediately they are taken outside. CAERvest® gets around these issues by remaining inactive until the fluid is added. The cooling starts immediately without any need for external power.

Why does CAERvest® have no batteries?

It doesn’t need any. The user squeezes the fluid in manually and this triggers the endothermic reaction. This means that it can be carried on any vehicle including aeroplanes without any special precautions or testing.

Can I defibrillate a patient with CAERvest® in place?

CAERvest® may be used in conjunction with defibrillation. There is a theoretical risk that a short could occur between the pads, however modern defibrillators are designed to detect low impedance between the electrodes and inhibit shock, alerting the user. Steps have also been taken to ensure that this risk is minimised by careful product design.

Can I perform CPR with CAERvest® in place?

CAERvest® is specifically designed to allow good-quality CPR to continue. It only takes a moment to fit, and the panel in the centre with the logo is designed to help place hands in the right place on the torso for compressions. It may be used with the LUCAS mechanical CPR device, but must be turned round with the neck extensions over the groins, so that the LUCAS suction cup can be placed in the correct position on the chest. CAERvest® has been used effectively in this configuration. Research is being undertaken at present to establish that CAERvest® is compatible with the Autopulse® CPR device.

Why is CAERvest® a single use device? Can’t it be reactivated?

There are two reasons. Firstly, it is designed for use in emergency situations and therefore it is extremely likely to become contaminated with body fluids so cleaning would be a complex, intensive and difficult process. Secondly, while the non-toxic reagents can readily be recycled, CAERvest® is a sealed device with specific features such as air vents that cannot be replaced or reused. Thus for both clinical and technical reasons CAERvest® has to be single use.

How difficult is CAERvest® to use?

We want CAERvest® to be as easy to use as possible, and we think that we have perfected a design that fulfils that requirement. Take a look at our training video and see for yourself!

Why is the carrying bag silver?

Two reasons. Firstly, nothing else used in an emergency has a silver bag, so this helps it to stand out when you are working fast, and secondly, the bag can be used as a cold retaining device; when placed over CAERvest® on the patient, it reflects sunlight away and reflects the cold back to the casualty, thus intensifying the cooling power.


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