Maintaining normothermia during and after surgical procedures has a direct impact on treatment efficacy and is associated with a reduced risk of complications. A drop in the patient’s core body temperature can have serious health consequences. What is normothermia, and what factors disrupt it in the context of surgical care? This article provides an explanation.
What Is normothermia? Definition of normothermia and thermoregulation
Thermoregulation is the body’s ability to maintain a stable internal temperature by balancing heat production and heat loss. The thermoregulatory center is located in the hypothalamus, which receives input from thermoreceptors located, among other places, in the skin[1].
Normothermia refers to the physiological state in which the human body maintains a core temperature within the normal range. This condition is essential for the proper and optimal functioning of physiological processes.
What is the temperature range of normothermia?
In humans, normothermia is defined as a core body temperature ranging from 36.5 °C to 37.5 °C. Body temperature undergoes natural circadian fluctuations, with differences of up to 1 °C observed in healthy individuals.
Heat in the human body is primarily generated in the liver, muscles, brain, heart, and kidneys. These organs account for approximately 85% of total heat production at rest. Heat loss, on the other hand, occurs through four main mechanisms: radiation, convection, conduction, and evaporation[2].
Normothermic temperature – how can it be disrupted by surgery?
Surgical procedures pose a significant challenge to the body’s thermoregulatory mechanisms. The combination of the surgical intervention itself, the operating room environment, anesthesia, and the patient’s overall health status creates conditions that promote uncontrolled heat loss. This may ultimately lead to hypothermia.
Hypothermia – a condition below the normothermic range
Hypothermia is defined as a decrease in core body temperature (Tc) below 35 °C. It is classified into three categories: mild (35–32 °C), moderate (32–28 °C), and severe (below 28 °C). Severe hypothermia can result in profound bradycardia and even cardiac arrest[3]. Unfortunately, surgical procedures inherently carry the risk of uncontrolled body heat loss, increasing the likelihood of hypothermia.
General anesthesia and the risk of hypothermia
General anesthesia and the anesthetic agents used during its administration are primary contributors to the development of hypothermia in surgical patients. This occurs due to several mechanisms:
- The patient under anesthesia is unable to consciously respond to cold sensations, such as by adjusting body position;
- Anesthesia reduces endogenous heat production by slowing metabolic rate;
- It impairs the function of the thermoregulatory center in the hypothalamus;
- It induces redistribution of heat from the core (central compartment) to the periphery[4].
Operating room environment and hypothermia
The operating room is a space specifically designed for performing surgical procedures; however, paradoxically, it promotes the development of hypothermia in patients. Environmental parameters necessary to maintain sterility and ensure the surgical team’s comfort often conflict with the patient’s thermoregulatory needs. Factors that facilitate heat loss include:
- Low ambient temperature in the operating room;
- Airflow generated by ventilation and air conditioning systems;
- Low relative humidity;
- Exposure to metal surfaces, surgical instruments, and equipment components[5].
Patient-related factors and hypothermia
The risk of developing hypothermia during surgical procedures is not uniform across all patients. Individuals with neuropathies that impair thermal signal conduction are particularly susceptible. Additional risk factors include hypothyroidism, which reduces metabolic heat production, and extensive burns, which compromise the skin’s thermoregulatory function and increase heat loss[6].
What impact can a body temperature below the normothermic range have on the patient?
A decrease in body temperature below the normothermic range exerts multifaceted and sometimes severe effects on patient physiology.
Uncontrolled hypothermia impairs blood coagulation, leading to increased perioperative bleeding. Consequently, the patient may require frequent transfusions of blood and blood products.
Reduced body temperature also elevates the risk of myocardial ischemia, cardiac arrhythmias, and infarction—particularly in patients with coronary artery disease. Hypothermia slows wound healing and significantly diminishes patient comfort during hospitalization.
Moreover, patients experiencing uncontrolled hypothermia impose increased healthcare costs on the hospital due to the need for treatment of associated complications.
Prevention of intraoperative and postoperative hypothermia should be a standard component of perioperative care. Investing in patient warming systems, medical warming cabinets, and specialized monitoring devices contributes to improved treatment outcomes and reduced healthcare costs. Implementing these measures as standard practice enhances patient safety and minimizes the incidence of hypothermia-related complications.
Sources:
- M. Kostyra, B. Lisowska, E. Nowacka, M. Wielgus Zaburzenia termoregulacji w trakcie zabiegów laparoskopowych (Thermoregulation disorders during laparoscopic operations), w: Anestezjologia i Ratownictwo 2015; 9: 345-349.
- https://podyplomie.pl/medycyna/29550,hipotermia-jak-nie-odebrac-choremu-szansy-na-przezycie
- Targeted Temperature Management
[1] https://www.ncbi.nlm.nih.gov/books/NBK556124/
[2] M. Kostyra, B. Lisowska, E. Nowacka, M. Wielgus Zaburzenia termoregulacji w trakcie zabiegów laparoskopowych (Thermoregulation disorders during laparoscopic operations), w: Anestezjologia i Ratownictwo 2015; 9: 345-349.
[3] https://podyplomie.pl/medycyna/29550,hipotermia-jak-nie-odebrac-choremu-szansy-na-przezycie?srsltid=AfmBOorSvOPIxViDoCzPb1bLdzW8-Xu_HP9PTqmtiHcr1BIdookzf-q7
[4] M. Kostyra, B. Lisowska, E. Nowacka, M. Wielgus Zaburzenia termoregulacji w trakcie zabiegów laparoskopowych (Thermoregulation disorders during laparoscopic operations), w: Anestezjologia i Ratownictwo 2015; 9: 345-349.