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Forced-Air Warming Systems Explained

25 October, 2011 | Anesthesiology Equipment

Forced-Air Warming Systems Explained

How Can Hypothermia be Prevented in Medical Settings?


Unplanned hypothermia (a core temperature of less than 36 degrees C) can negatively impact patients in many ways. Even mild hypothermia may contribute to complications such as: surgical site infection, altered drug metabolism, impaired blood clotting, cardiovascular ischemia, prolonged recovery following surgery and shivering.

It is maintained by many professionals in the field that active patient warming is associated with normalizing patient temperature. The literature supports the use of forced air warming devices for normalizing patient temperature and reducing shivering. In addition, the literature suggests that forced-air warming is associated with reduced time in recovery. Also, it is agreed that both the perioperative maintenance of normothermia and the use of forced-air warming reduce shivering and improve patient comfort and satisfaction. It is recommended that normothermia should be a goal during emergence and recovery, and that when available, forced-air warming systems should be used for treating hypothermia.

Inadvertent perioperative hypothermia is a common and preventable complication of surgery. Inadvertent perioperative hypothermia is defined when the core body temperature is drops below 360C and is associated with poor outcomes for patients.

The possible consequences of hypothermia are:

  • Increased risk of wound infection
  • Increased perioperative blood loss
  • Longer post-anesthetic recovery
  • Postoperative shivering and thermal discomfort
  • Morbid cardiac events including arrhythmia
  • Altered drug metabolism
  • Increased risk of pressure sores
  • Reduced patient satisfaction with the surgical experience
  • Longer hospital stay

Prevention of hypothermia requires the use of simple measures, such as warm clothing, use of a duvet (comforter) or blankets preoperatively and active warming of the patient and intravenous fluids, especially in the operating room. A range of active patient warming devices have been designed for use in the perioperative and critical care environment, including: electric blankets, heated fluid filled mattresses, radiant warmers and forced air warming devices.

A forced air warming system is a medical electrical device used to help keep patients warm during anesthesia and surgery. The device comprises a reusable controller and disposable, single-use blankets.

A forced air warming system comprises a controller plus a compatible disposable blanket. The controller contains the following components:

  • Electric motor and fan
  • Electric heating element
  • Thermostats
  • Air filter
  • Hose

In operation the fan draws in air through the filter and the heating element heats it to a selected temperature, controlled by the thermostats. Heated air travels through the hose to the blanket, which connects to the hose nozzle.

The blanket is double layered and inflates in operation. The patient contact surface is permeable to air and the warm air exits the blanket and moves over the patient’s skin and transfers heat to the patient by convection.

The most significant operational factors relate to the single use blankets. It is essential that the blankets are compatible with the controller and the range of blankets available for the controller is an important factor in the purchasing decision.

The blankets are bulky and require storage space.

The cost of disposable blankets is the most significant cost of forced air warming and purchasers should make use of bulk purchasing arrangements in order to benefit from volume discounts.

The function of the fan which drives the air flow and the high airflow in the blanket generates significant noise. Noise in operating is a potential hazard, because it can disturb the concentration of staff or may even interfere with communications among the team. Small differences in noise level (a few dBA’s) may result in significant differences in the perceived noise.