Commercially available hypothermia induction devices are based on invasive and non-Invasive methods. As a rule, invasive methods provide higher heat transfer rates than non-invasive methods, but they require specially trained physicians for initiation and are associated with much higher range of possible side effects Invasive methods include:
- Endovascular cooling catheters tipped with a balloon percolated by cold water.
- Irrigation of the body cavities with cold water.
- Intravenous or intraosseous infusion of cold fluids.
- ECMO cooling.
Non-invasive methods include:
- Plastic body wraps percolated by cold water.
- Imitation of cold water immersion.
- Spraying evaporating coolant into the nasal cavity .
- Cooling cervical collar.
Endovascular cooling catheters (Alsius CoolGard 3000®, Zoll Medical; Thermogard XP®; Philips InnerCool RTx Endovascular System) do not provide fast heat loss. Their cooling rates are about the same as the cooling rates of cooling body wraps. Endovascular cooling catheters are invasive, they require use of systemic anticoagulation, making them unsuitable for use out of hospital settings. The adverse effects include bleeding, infection, vascular punctures, and deep vein thrombosis (26) They are not suitable for targeted temperature maintenance or rewarming. ECMO allows very rapid rate of heat loss by pumping blood through a cooler. ECMO allows controlled re-warming. However, it is invasive, requires the presence of a specially trained physician, perfusionist and nurses and requires systemic anticoagulation. It can be used only either in Intensive Care Unit or Operating Room settings. Due to the technical complexity ECMO requires a longer time to start than other methods. ECMO is associated with significant side effects, including bleeding, infection, deep vein thrombosis and stroke. It is unsuitable for out of hospital use. Intravenous or intraosseus infusion of cold saline produces fast heat loss, can be used in pre-hospital settings and is inexpensive, but it requires administration of non-physiologically large volumes of fluids, which can lead to respiratory and/or cardiac failure, which can be detrimental. In addition, it does not allow accurate control of temperature reduction, temperature maintenance and precise re-warming. Irrigation of body cavities with cold saline (Veratherm®) does not offer higher heat transfer than cooling blankets. It is invasive, relies on the presence of a trained physician, can’t be used in pre-hospital settings, and may lead to fluid overload. Cooling body wraps (MTRE Allon system; Arctic Sun Temperature Management System; Cincinnati Sub Zero Blanketrol III; Gaymar MediTherm®) are the most widely used cooling methods, representing about 90% of hypothermia equipment market. The do not provide fast heat loss in adult patients, requiring up to 6 to 8 hours to achieve target temperature. They are relatively large and are not suitable for out of hospital use. They cover almost the entire body and obstruct access for care or physical examination or performance of CPR. Accurately controlled rewarming is hard to achieve. Cold water immersion imitating device (ThermoSuit®) offers high rate of heat loss. The drawbacks include large size, restriction of access to the patient, inability to use in prehospital settings, and inability to maintain target temperature or re-warming. Irrigation of nasal cavity with evaporative coolant device is compact and can be used in pre-hospital settings, but it does not provide fast heat loss and can cause thermal injury to the nose and nasal cavity. It does not allow targeted temperature maintenance or re-warming. Intranasal balloon tipped cooling catheter (Quickcool®) is portable and can be used in prehospital settings, but offers very slow rate of cooling and it does not allow targeted temperature maintenance or re-warming. Excel Cryo Cooling® cervical collar is easy to use and compact and it allows for the initiation of hypothermia in prehospital settings. This device has a slow cooling rate and it does not allow targeted temperature maintenance or re-warming. All of the currently used methods for the induction of therapeutic hypothermia have numerous shortcomings. Most of them can’t be used in prehospital settings, which leads to significant delays in achieving therapeutic level of cooling. Most of them are not able to maintain steady targeted temperature. Only several devices allow rewarming, however, none of them allow rewarming at precise rate. Methods that can be used in prehospital settings are incapable of producing a fast rate of cooling. In conclusion, either due to technical complexity, or to low effectiveness, all commercially available methods of induction of hypothermia do not allow achieving targeted body temperature within desirable time. Some methods are invasive, or rely on bulky devices with restricted access to the patient. In conclusion: none of the currently used methods for the induction of therapeutic hypothermia is ideal.
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