Temperature Management in Surgical Patient

Dr. Asifa IqbalBDS,M.Phil

PGR FCPS II(OMFS)

Body Temperature• Normal Body Temperature (NBT) –

98.60F(370C)• Range of NBT ----- (970F to 990F)• Rectal Temp ----- (0.50F to 10F) above

the Oral• Rectal Temp reflects the internal body Temp

(Core Body Temp)• Core Body Temp remain almost constant• Skin Temp (Shell Temp)-----Variable

circadian (daily) rhythm, exercise, food intake, infection,hypothyroidism, hyperthyroidism, women’s menstrual cycle, anesthetics and other drugs such as alcohol, sedatives and/or nicotine can alter the threshold

Thermoregulatory regulatory responses

Exposure to ColdShiveringIncrease voluntary activityIncrease TSH secretionIncrease CatecholaminesVasoconstrictionHorripilationCurling up

Exposure to HeatVasodilatationSweatingIncrease in RespirationAnorexiaApathyDecrease TSH secretion

• Normothermia : body core temperature between 36.5 - 37.5C ± 0.5C.

• Any core body temperature below 1C in “Homothermics” is therefore considered hypothermia.

• Mild hypothermia : 1C to 2C below body core temperature • Moderate hypothermia :temperature of 35C. • Severe hypothermia : body core temperature below 35C

• Any temperature below 28C is considered deep hypothermia

• consciousness is lost, sinoatrial pacing becomes erratic, ventricular irritability increases,

• below 26C rigidity and myoclonus ensues.

•All general anesthetics and regional anesthesia can impair normal autonomic thermoregulatory control.

•Volatile and nonvolatile anesthetics predispose patient’s to heat loss because of their vasodilatory properties.

• Most narcotics reduce vasoconstriction mechanisms for heat conservation because of their sympatholytic properties

• Muscle relaxants reduce muscle tone and prevent shivering.

Redistribution Hypothermia

Core37°C

Vasoconstricted

Periphery31-35°C

Anesthesia

Periphery33-35°C

Core36°C

Vasodilated

Intraoperative Heat Transfer

Evaporation

Conduction

ConvectionRadiation

Cardiovascular - Increased pulse and blood pressure (postoperatively), systemic vascularresistance (SVR), contractility, ventricular dysrhythmias and irritability, myocardial depressionand secretion of catecholamines. Cardiac output and heart rate are decreased (intraoperative)

Respiratory - Strength is diminished at body core temperature of less than 33C, but CO2ventilatory response is unaffected.

Hepatic - Blood flow and function are diminished which will decrease significantly themetabolism of some drugs.

Renal - Decrease in renal blood flow due to increase in renal vascular resistance. Inhibition oftubular resorption maintains normal urinary volume until progressively lower temperaturesinhibit reabsorption of sodium and potassium and an antiduiretic hormone (ADH) mediateddiuresis results. Plasma electrolyte usually remain normal.

Neurologic - Decreased cerebral blood flow, increased cerebrovascular resistance, decreasedminimum alveolar concentration, delayed emergence from anesthesia due to direct depressanteffects of hypothermia, altered mental sensorium to include drowsiness and confusion.

Metabolic - Decreased metabolic rate, decreased tissue perfusion leading to metabolic acidosis, and hyperglycemia from catecholamines may occur. Increased oxygen consumption may occur due to shivering postoperatively.

Hematologic - Increased blood viscosity, thrombocytopenia, leftward shift of the hemoglobin dissociation curve causing increase difficulty of oxygen unloading from hemoglobin leading to hypoxia, alterations in coagulation via impaired platelet function, decreased coagulation factor activity leading to a greater intraoperative bleeding and blood loss.

Immunologic - Impaired immune system function increasing rate of postoperative woundinfection.

Drug Pharmacology - Decreased hepatic blood flow, and metabolism coupled with decreased renal blood flow and clearance result in decreased anesthetic requirement, delayed awakening due to reduced rates of drug clearance.

Shivering and Wound Healing - Increased shivering which can increase heat production by100% - 300% with concomitant oxygen consumption up to 500% and increased production ofCO2. Vasoconstriction and the reduced delivery of oxygen to injured tissues also leads to a delay in wound healing and a significant rate of postoperative infection rate.

Special Medical Conditions - Hypothermia can precipitate a sickle cell crisis in sickle cell anemia patient since sickling of erythrocytes occur with decreasing arterial oxygen tension.

The three most common complications associated with mild hypothermia are

oa three-fold increase in morbid myocardial events, oa three-fold increase in the risk of surgical wounds infection and prolonged hospitalization,o increased blood loss and transfusion requirements

•The best management for hypothermia, like most complications in anesthesia, is prevention.

•Intraoperative hypothermia can be minimized by any technique which limits cutaneous heat loss to the environment, evaporation from surgical sites and respiratory tract, conductive cooling from excessive gas flow rates, cold intravenous fluids or irrigating solutions.

•The initial 1-1.5 C reduction in core temperature change is not possible to prevent. It will happen Mean body temperature will decrease when heat loss to the environment is greater than metabolic heat production.

•The body will loss about 1C per hour when the heat lost to the environment is greater than twice the metabolic production.

• Pre-warming• Operating room environment• Anesthesia Circuits, Airway Heating and

Humidification• Warming IV Fluids and Blood Products• Postoperative Considerations

•During the postoperative recovery period, the bodies thermal heat transfer situation is significantly different.

•As the anesthetic-induced peripheral vasodilation dissipates away, the thermoregulatory vasoconstriction ensues. Now, heat transfer from the periphery to the central core compartment is significantly impaired due to this vasoconstriction. Because the postoperative thermoregulatory vasoconstriction decreases peripheral-to-core heat transfer, applied warming to the skin is most effective during surgery when patients are vasodilated.

•Postoperative shivering should be treated with warming of the patient most effectively via forced-air systems and warm blankets to not only psychologically help make the patient feel better but institute physiologic measures to re-warm the patient. Intravenous administration of 12.5 - 25mg of meperidine IV or ketanserin IV can be use to treat the postoperative shivering caused by hypothermia. The mechanism by which this works is by lowering the thremoregulatory threshhold for shivering thermogenesis.

Hyperthermia (T > set-point )

Physiological elevation

Pathologica elevation

Fever (T ＝ set-point )

elevation of body temperature(>0.5 C)

Types of the elevation of body temperature

Hyperthermia Fever

Arising from changes within the body or by changes in environment

Resulting from pyrogen

Set-point remains unchanged or damaged, or effector organs fails

Ability to regulate set-point remains intact, but is turned up at a high level functionally

Body temperature may rise to a very high level

Rise of body temperature has an upper limit

Treatment with water-alcohol bathing Treatment with antipyretics and measures and drugs to eliminate the causes

Comparison between hyperthermia and fever

Malignant hyperthermia

•- A rare complication of anaesthesia

“It is a biochemical chain reaction response triggered by commonly used general anesthetics and the paralyzing agent succinylcholine, within the skeletal muscles of susceptible individuals” –MHAUS.org

Has autosomal dominant inheritance

Incidence of 1-5 : 100,000, < 5% mortality rate

Triggered by anesthetic drugs such as all inhalation agents (except NO) and succinylcholine (depolarising muscle relaxant)

Clinical pictureIt's onset can be immediate or hours after agent is administered

There will be increase in:

- Oxygen consumption

- ETco2 on capnograph

- Tachycardia/dysrythmia

- Tachypnia/cyanosis

- Diaphoresis

- Hypertension

- Temperature

Muscular symptoms- Trismus (occurs in 1% of children given SCh

together with halothane)- Tender and swollen muscles due to

rhabdomyolysis- Trunk or total body rigidity

PathophysiologyAlteration in the Ca induced ca release impairment in the ability of the sarcoplasmic reticulum to sequester calcium via the ca transporter

After trigger agent is administered, there is a sudden and prolonged release of ca which causes

- Massive muscle contraction

- Lactic acid production

- Increased body temperature

Dantrolene stops the calcium released by binding to the ryanodine receptor and blocking the opening of the channel therefore stopping the release of calcium.

Triggering vs safe anaesthetics

Triggering agents•Volatile gaseous inhalation anesthetics:

–IsofluraneSevofluraneDesofluraneHalofluraneEnfluraneMethoxyflurane

•Succinylcholine–Suxamethoniumdecamethonium

Non-triggering agents

•PropofolKetamineNitrous oxideAll local anestheticsAll narcoticsNon depolarizing muscle relaxants:

•Vecuronium•Rocuronium•pancuronium

ComplicationsComa

DIC

Rhabdomyolysis

Myoglobinuric renal failure/hepatic dysfunction

Electrolyte abnormalities (hyperkalemia) and secondary arrhythmias

ARDS

Pulmonary edema

Can be fatal if untreated

PreventionCheck family history

Avoid trigger medication, use regional anaesthesia if possible and use clean equipment

Central body temperature and ETco2 monitoring

Used to use dantrolene as prophylaxis but not commonly used anymore

Management

1. Notify surgeon, discontinue agents, hyperventilate with 100% Oxygen at >10l/min, halt procedure if possible

2. Dantrolene 2.5mg/kg IV every 5 min (1mg/kg/dose, max dose = 10 mg/kg)

- Repeat until control is obtained

3. Bicarbonate 1-2 mEq/kg if blood gas values are not available for metabolic acidosis

4. Cool patient with core temp >39C

- Lavage open body cavities, stomach, bladder, rectum, apply ice to surface, infuse cold saline IV

- Stop cooling if temp reaches 38C

Remember"Some Hot Dude Better Give Iced Fluids Fast!"(Hot dude = hypothermia):

Stop triggering agentsHyperventilate/ Hundred percent oxygenDantrolene (2.5mg/kg)BicarbonateGlucose and insulinIV Fluids and cooling blanketFluid output monitoring/ Furosemide/ Fast heart [tachycardia] 

Take Home Message

In emergency patient

In preoperative patient

In Immediate post operative period