Patient warming

About patient hypothermia

By: Mölnlycke Health Care, March 29 2012Posted in: Patient warming

Perioperative hypothermia is when a patient’s core body temperature drops considerably before, during or after surgery. It is a common but preventable complication of surgical procedures that most commonly appears after induction of general anesthesia. Through clinical studies and among healthcare practitioners it is well-established that patients benefit from being warmed prior to, during and after surgery.

The outcome for patients as a result of perioperative hypothermia is poorer, with an increase in surgical site infections, cardiac complications and bleeding as common complications. Patients' distress and discomfort as well as increased treatment costs and prolonged hospitalization are other consequences associated with perioperative hypothermia. Preoperative patient warming in order to increase body warmth and reduce the drop in temperature during surgery as well as active warming during surgery, has been effective in avoiding inadvertent perioperative hypothermia.

Human body temperature varies

The normal range of human body temperature varies due to an individual’s metabolic rate, the higher (faster) it is the higher the normal body temperature; the slower the metabolic rate the lower the normal body temperature (normothermia).

Other factors that might affect the body temperature of an individual may be the time of day or the part of the body in which the temperature is measured. The body temperature is lower in the morning, due to rest during night, and higher at night after a day of muscular activity and after food intake. Body temperature also varies at different parts of the body.

Why does variation in body temperature occur?

Common sources of increased temperature are elevated environmental temperature, eating and exercise. The body’s most efficient way of decreasing an increased body temperature is by sweating. Maximum sweat production can be as much as five litres in a day. The body temperature can also be lowered through widening of the superficial blood vessels.

The most common source of decreased body temperature is a cold environment. The body temperature can be elevated through shivering. We can also narrow our peripheral blood vessels to decrease the amount of blood in the more peripheral parts of the body – by doing so we expose less of the blood volume to cold and stay warmer.

From where does hypothermia arise?

Hypothermia may result from environmental conditions and traumatic injuries, and from (adverse) reactions to patient therapies as diverse as anaesthesia, neurosurgery, induced hypothermia (e g, during cardiac surgery when the heart and sometimes the entire patient is cooled to reduce metabolism and oxygen consumption), medication and ventilation.

The hypothermic state ranges from mild to profound. Most people tolerate mild hypothermia (35.0°C to 35.9°C body temperature), which is not associated with significant morbidity or mortality. The mortality rate for patients with moderate hypothermia (34.0°C to 34.9°C body temperature) has been estimated at 21.0 percent, and is even higher in severe hypothermia (i.e., core temperature < 33.9°C). Despite hospital-based treatment, mortality from moderate or severe hypothermia approaches 40 percent.

How can hypothermia occur?

  • Patient lying on cold O.R. beds
  • Evaporative heat loss from open body cavities
  • Exposure to cold ambient temperatures in the preoperative and surgical suites
  • Reduction in metabolic heat production (i.e., no muscle activity)
  • Room-temperature antimicrobial skin preparations and room-temperature IV fluids
  • Various forms of anaesthesia (vasodilation)
  • Various pharmacological agents (e.g., midazolam)

Effects of hypothermia

The effects of hypothermia are proportional to the change in temperature. Metabolic rate is reduced by up to 10 percent for every 1°C decrease in body temperature.
There is an increased risk of complications:

  • Increased incidence of infection
  • Bleeding; the blood coagulation is enzyme-dependent (enzymes have an optimum temperature for their action) and blood platelet function is temperature-dependent
  • Delayed wound healing
  • Decreased oxygen delivery to body tissues, which can be dangerous for the heart (infarctions and rhythm disturbances) and brain (infarction = stroke)
  • Decreased metabolism, also of pharmaceuticals (drugs) and prolonged duration of action
  • Shivering

Who is at risk?

Healthy people have a mechanism that regulates internal body temperature within a very narrow range. This mechanism is not fully developed in infants and young children.

Elderly people cannot widen and narrow the blood vessels as much as younger adults; therefore, the very young and the very old are more susceptible to hypothermia (and also the opposite, hyperthermia, elevated body temperature). In addition, several medical conditions may affect the body’s normal thermoregulation.

Trauma patients comprise another group of people at high risk for hypothermia. The greater the traumatic injury, the greater the likelihood that hypothermia will become a complication; in fact, hypothermia occurs in 21 to 66 percent of all trauma patients and often indicates a poor prognosis for survival.

Hypothermia can be prevented

Effective, continuous patient warming helps managing the risk of hypothermia.

Read how BARRIER EasyWarm helps prevent hypothermia

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