February 2008 - The body regulates its core temperature by reducing the blood flow to the extremities, but anesthesia interferes with this process and affects the temperature control center in the hypothalamus, allowing the normal temperature control limits to be increased and compromising the body's normal response to cold. For these reasons clinicians need to warm patients in the OR, and there are a variety of products available.
When the body goes into hypothermia (when the body core temperature is less than 36 C/96.8 F) it can cause slower processing of anesthetics, promote surgical site infection, alter drug metabolism, impair blood clotting, cause cardiovascular ischemia, and prolong recovery after surgery. These factors can add additional costs for hospitals, so experts say it is easier to maintain normothermia instead of treating the effects of hypothermia.
The old-fashioned way to keep patients warm includes use of warmed blankets. However, blankets quickly lose their heat. Consistent heat can be delivered using several methods, including forced air blankets, electric, liquid or gel pads, and IV fluid warming
Forced air systems use a heater/blower unit to blow warmed air through a flexible hose, into disposable blankets. One of these systems is Gaymar's Thermacare Patient Warming System, which features a lightweight, portable, warm-air blower unit offering three temperature settings for the OR/ICU and four for the PACU. The company says the unit's flexible, covered hose is lightweight and easy to clean. It can be mounted on an IV pole, foot end of bed or on a portable stand. The blower unit is used with disposable Thermacare quilts, which come in five sizes and have perforated areas that can be opened for better patient access.
Some critics of forced air systems say they are noisy and can be cumbersome because the blower unit must be located in the OR and the attached hose adds to OR clutter. Critics also say the tiny jets of air escaping from the blankets can help spread dust and bacteria in the OR. Augustine Biomedical Design collected evidence that shows bacteria can contaminate the inside of blower machines and the inner most part of corrugations on blower hoses can trap bacteria and are difficult to clean.
To prevent these issues Cincinnati Sub-Zero’s (CSZ) WarmAir and FilteredFlo blankets use a 0.2 micron HEPA filter before the air is distributed to the blanket to prevent airborne bacterial contamination. The warmed air is then filtered again as it leaves the blanket. CSZ also uses a lower velocity blower to minimize the spread of contaminants.
Warming can also be done using encapsulation of one extremity. Dynatherm Medical recently introduced the vitalHEAT vH2 Temperature Management System using heat under low vacuum to open AVAs (thermo-regulatory structures) in the palm and fingers. The company says the vH2 warms blood in the hand and arm then delivers this heat directly to the core through the venous vasculature, bypassing the need to cover large body surface areas. The maker says it is easy to apply and operate, and it warms patients with minimal interference with surgical drapes or the surgical site.
Low-level electric current is also used for warming. Augustine Biomedical offers its Hot Dog series of blanket warmers, which use a radiant carbon fabric technology to produce heat. The blanket has a control unit box and attached cord. The blanket has a cleanable antimicrobial polymer shell, so it can be sterilized and reused. The company claims it is up to 80 percent more energy efficient than forced air or water warming systems.
Another electric warmer is the LMA PerfecTemp pad, which uses a heating element consisting of India ink on a Mylar backing that begins heating when pressure is applied. The pad temperature is monitored via built-in fiber optics,and the pad is designed to be permanently mounted on an operating table. Visco elastic foam inside reduces pressure as a patient lays on the table. The pad is covered in a pliable, stain-resistant, antibacterial fabric that can be cleaned.
The pads are hooked up to a monitor, which will regulate the heat and record up to 100 hours of heating history. The machine can perform a self-diagnosis and tell the operator how to fix most issues. The language of the unit can also be changed.
CSZ last year introduced its Gelli-Roll Hypothermia/Hyperthermia System, which consists of a reusable, temperature controlled jell-filled pad to heat or cool a patient. In addition to temperature management, the pad is placed under the patient to help reduce tissue pressure.
Gaymar's Medi-Therm MTA7900 heats or cools water that circulates body wraps/blankets. It can provide a blanket temperature from 39 to 107 F. The blankets are available in single-use and reusable options.
Many of the warming devices use an internal temperature monitor, which can warn clinicians if the temperature is not operating as programmed.
Several companies also offer IV fluid warmers. German-based Barkley offers a series of IV warming products. The Autocontrol 3XPT warms IV fluid prior to it entering the patient. The Warming Center II warms IV fluid bottles and bags in a heated cabinet. The company also makes the Plasmatherm, a tabletop warmer for blood transfusion bags.