Prevention and Care of Intraoperative Hypothermia - Part 1

Prevention and Care of Intraoperative Hypothermia - Part 1

I. The concept of hypothermia:

• Core temperature below 36℃ is hypothermia

• Core temperature is the temperature in the body's pulmonary artery, tympanic membrane, esophagus, nasopharynx, rectum and bladder, etc.

• Perioperative hypothermia (Inadvertentperioperativehypothermia, IPH)，Mild hypothermia may occur in 50%-70% of anesthesiology and surgical patients.

II. Hypothermia grading:

• Clinically, a core temperature of 34℃-36℃ is generally referred to as mild hypothermia

• 34℃-30℃as shallow hypothermia

• 30℃-28℃ is moderate hypothermia

• <20℃ for deep hypothermia

• <15℃ ultra-deep hypothermia

III. Causes of intraoperative hypothermia

(I) Self-caused:

A.  Age:

Seniors: Poor thermoregulation function (muscle thinning, low muscle tone, skin blood, tube contractile strain capacity decreased, low cardiovascular reserve function).

Premature babies, low birth weight babies: The thermoregulatory center is underdeveloped.

B. Physique (body fat)

Fat is a strong heat insulator, it can prevent the loss of body heat.

All fat cells can sense temperature, and they heat up by releasing energy. The Harvard University study found that this heating process depends on a protein called coupling protein-1. When the body is exposed to cold, the amount of coupling protein-1 doubles.

Under normal circumstances, patients need to fast for about 12 hours before surgery. If their physical fitness is poor, they will be more sensitive to cold stimulation, resulting in weakened resistance. The cold stimulation caused by surgery can easily cause body temperature to drop.

C. State of mind

The patient's emotional fluctuations such as fear, tension, and anxiety cause the blood to be redistributed, affecting the return of blood to the heart and microcirculation, and it is easy to cause hypothermia during the operation.

D. Critical illness

Critically ill, extremely debilitated: low heat production capacity.

Impaired skin integrity: major trauma, degloving wounds, severe burns.

(II)Environmental

The temperature in the operating room is generally controlled at 21-25°C. below body temperature.

The conventional temperature of the laminar flow operating room and the rapid convection of the indoor air will increase the heat dissipation of the patient's body, which is more likely to cause the patient's body temperature to drop.

(III)Body heat dissipation

A. Skin disinfection:

The temperature of the disinfectant is low, and the purpose of disinfection can only be achieved after the disinfection is dry. The volatilization of the disinfectant takes away a lot of heat and lowers the body temperature.

B. Heavy flushing:

Washing with a large amount of normal saline or water for injection during the operation also leads to the loss of body heat, which is the reason for the patient's body temperature to drop.

C. Major surgery takes a long time, and the exposure time of chest and abdomen organs is longer

D. Medical staff lack awareness of heat preservation

IV.Anesthesia

Drugs can alter the set point of the thermoregulatory center.

General anesthesia - many anesthetics can directly dilate blood vessels, and muscle relaxants can inhibit the response to shivering.

Regional block anesthesia - the afferent fibers of peripheral cold sensation are blocked, so that the center mistakenly believes that the blocked area is warm.

V.Fluid and blood transfusion

Infusion of a large amount of liquid and stock blood at the same room temperature or a large amount of flushing fluid at room temperature during the operation will achieve the effect of "cold dilution" and cause hypothermia.

Intravenous infusion of 1L of liquid at room temperature or 1 unit of 4C blood in adults can reduce the core body temperature by about 0.25°C.

Excerpted from: Wu Zhimin. Yue Yuan. Research and Nursing of Hypothermia During Liver Transplantation Anesthesia Operation]. Chinese Journal of Practical Nursing, 2005