Maintaining Normothermia

Chris PfaffelMedina General Hospital

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Introduction

• Maintaining normothermia, during the entire perioperative experience, lessens the chances of complications resulting from hypothermia and increases the patient’s comfort.

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OBJECTIVES• Explain how the body’s thermoregulation system works.

• Define and explain the principle mechanisms of heat loss in the surgical patient.

• Define unintended perioperative hypothermia.

• Identify adverse patient outcomes associated with unintended perioperative hypothermia.

• Identify areas where cost savings can be recognized by maintaining normothermia.

• Identify the effectiveness of currently available warming modalities.

• Explain the benefiet of prewarming to help prevent unintended perioperative hypothermia.

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Overview

• Our patients come to us with numerous disadvantages already in play. They are experiencing pre-operative anxiety, prolonged fasting, all their clothes taken away, issued a thin backless gown, and given a thin cotton blanket. This predisposes our patient to being hypothermic before they reach the OR door.

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Vocabulary• Normothermia: Core body temperature

36 C to 38 C (96.8 to 100.4)

• Hypothermia: Core body temperaturebelow 36* C (96.8* F)

• Ideal thermic state: Near 37.0*C (98.6*F)

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• Passive Insulation: Method of containingbody heat and insulating the body fromheat loss through radiation.(e.g., blankets, clothing).

• Active skin warming: The application ofconductive, convective, or radiativewarming to the skin. (e.g., bair hugger)

• Ambient temperature: The temperature of the immediate environment, usuallyranging from 20 C to 25 C (68 to 77 F

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NORMOTHERMIA

• In a resting patient a large portion of their heat is generated by the organs of the thermal core, (brain, organs of the chest and abdomen)

• Under normal conditions the body can control the rate of heat loss from the core.

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• Thermic state is aggressively maintained at a set point determined by the CNS.

• The core body temperature seldom varies more than +or- 2*C above or below ideal state.

• Behavior is the mechanism that helps maintain the core body temperature.

• We adjust our behavior in accordance to thermal discomfort.

• Our surgical patient is unable to do this.8

• Surgical patients rely on the autonomic thermoregulation system to regulate temperature.

• Interthreshold Range is the narrow limit above and below the body’s normothermic state of 37.0*C ( + or – 0.2*C).

• Temps below the lower limit of the interthreshold triggers the body’s cold responses of thermoregulation: vasoconstriction, non-shivering thermogenesis, and shivering. (compliments of the hypothalamus)

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Core temperature

Metabolic rate

Produces more heat

Humans have a limited metabolic heat production potential.

Heat productionSHIVER

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Administration of Anesthetic Drugs• Hypothermia can result from general as

well as regional anesthetic agents.• Anesthetized patients rely on the autonomic

thermoregulation system to respond to changes in temperature.

• Anesthetic agents inhibit this system by reducing metabolism and depressing the hypothalmus.

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• Research has shown that in the first 60 minutes of anesthesia unwarmed surgical patients can lose up to 1.6 degrees Celsius.

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• Maintaining normothermia during surgery is important not only for patient comfort, but also for prevention of the complications that result from hypothermia.

Complications:

• wound infections, increased mortality, coagulopathy

• Myocardial ischemia and cardiac disturbance, delayed emergence from anesthesia

• Prolonged and altered drug effects, shivering, pain, thermal discomfort 13

HYPOTHERMIA• Core body temperature of less than 36*

C• JCAHO patient safety issue• Several factors that contribute to heat

loss:– General and regional anesthesia– Cold temperature maintained in OR– Surgical procedure and exposed body cavities– Infusion of cold fluids and blood

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Anesthesia-Impaired Response to Temperature

Depressed hypothalamus—interthreshold widens to + or – 4*C

Patient gets either warmer or colder before thermoregulatory responses are triggered.

Vasoconstriction and shivering are three times more likely that vasodilation and sweating.’

Patient cannot shiver due to anesthesia.

Heat redistribution occurs-blood flows freely to the periphery-as the body can no longer maintain temp gradient between core and periphery-heat is lost by radiation.

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Heat redistribution is responsible for 81% of initial loss of core body temperature.

After initial effect of heat redistribution patient will lose heat to the environment by four ways

• Radiation

• Convection

• Conduction

• Evaporation

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• A study done in an ICU– 24% of patients who were hypothermic for 2 hours died

compared to 4% who had been normothermic.

– 64% less nosocomial infections when the patients were normothermic

– 44% less myocardial infarctions with normothermic patients

– 34% less likely to need mechanical ventilation with the normothermic group

– 55% lower mortality rate in normothermic group

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• Optimal management of patient core temperature is such an important issue that new guidelines were required for patient care.

• Consensus Conference on Intraoperative Thermoregulation convened in February 1998 to develop and evaluate such guidelines.

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•WHAT CAN BE DONE?

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PRE-WARMING PATIENTS• HYPOTHERMIA IS EASIER TO

PREVENT THAN TO TREAT!• Can reduce core temperature drop by

banking heat• Yes you can prevent hypothermia by

prewarming, intraoperative warming, and post-op warming.

• STOP HYPOTHERMIA BEFORE IT HAS A CHANCE TO BEGIN.

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PRE-WARMING

• Studies have shown that a 30 min period of pre-warming reduces infection rates from 14% to 5%.

• If applied according to the manufacturers’ guidelines, pre-warming appears to have no adverse side-effects.

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SO NOW YOU COVER YOUR

PATIENT WITH A WARMED

COTTON BLANKET

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• Patients prefer the warmed ones.

• Heat contained in the warmed blankets is likely to dissipate rapidly to the environment.

• Will have to replace the blanket every 15 min with fresh warmed ones.

• Warmed blankets reduced heat loss more than unwarmed ones, but the benefit dissipated in approximately 10 minutes.

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• Rapid dissipation of the heat in warmed cotton blankets is due to the fact that the heat capacity of cotton is low.

• Even when blankets are replaced with freshly warmed ones at 10-min intervals cutaneous heat loss remains high compared with the best active warming systems.

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SO NOW YOU HAVE ACTIVELY AND PASSIVELY WARMED YOUR PATIENT, NEXT WOULD BE THE ENVIRONMENT

• Temperature of the immediate environment should fall between 68* F to 77* F (20* C to 25* C)

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The patient is being warmed,

The room is set at 68* F

Now your team at the field is sweating

• 9-20% of healthy men are heavy staphylococcal dispersers.

• 1% of premenopausal and 5% of postmenopausal women are staphylococcal dispersers.

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• Contamination of the surgical field by sweating could occur by several mechanisms:– Sweat droplets or exfoliated skin flakes falling

from exposed skin.– Seepage through the hood or mask dripping

directly onto the field.– Droplets from exhaled air from the sides of the

mask– Sweat may track onto the forearm of the gown

at the interface between the gloves and gown cuff.

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• The present studies indicates that shedding is increased by sweating and may contribute to surgical site infections.

• Keeping the surgical team, at the field, cool by lowering the temperature of the operating room could reduce sweating and therefore potentially reduce contamination of the surgical field.

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• Proactive and judicious use of nursing interventions, safety report protocols, and warming cabinets are essential in temperature management of the perioperative patients.

• Perioperative nurses must focus on patient comfort as well as maintaining normothermia for improved patient outcomes.

• IT IS EVERYONES RESPONSIBILITY TO WARM THE PATIENT.

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• CAREFUL AND THOUGHTFUL ACTIONS DIRECTED AT MAINTAINING NORMOTHERMIA CAN SIGNIFICANTLY AFFECT THE COURSE OF THE PATIENT’S PERIOPERATIVE EXPERIENCE

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