Thermoregulation

Question 1

Thermoregulation definition

Answer 1

The concept of thermoregulation is a balance between the production, gain or loss of heat which is kept within a tight homeostatic range.

Question 2

Where are temperature receptors located

Answer 2

Skin
Spinal cord
abdominal viscera
great veins

Question 3

What are the three internal process to regulate heat production and loss

Answer 3

1. BMR: generates heat to maintain core body temp at rest.
2. Sweating when hot to cook skin by evaporation
3. Arteriole vasodilation/vasoconstriction

Question 4

What are the four means of heat transfer

Answer 4

Radiation e.g. sunlight, fire
Evaporation ege applying water to burns to increase cooling.
Conduction: warming blankets to heat a cold surface (or vice versa)
Convection (wind)e.g. turning heater or air con on

Question 5

State Hypothermia categories

Answer 5

Mild: 32 - 35 degrees
Moderate: 28-32 degrees
Severe: <28 degrees

Question 6

Discuss the pathophysiology of hypothermia

Answer 6

• Exposure to cold
• Peripheral vasoconstriction, increased catecholamine release, increase BMR = increased SNS activity (Increased HR, RR and BP)
• As temperature drops, shivering initiated to increase activity of muscles to generate heat and increase core temp.
• When temp <35 degrees, ECG changes (Osborne wave present)
• <32 degrees, shivering stops as body no longer compensating for temp falling.
• <30 degrees, glucose transfer ceases to occur as insulin no longer available and liver glycogen stores exhausted.
• Rapid decrease in core temp, and decrease in HR< BP, RR, tidal volume & pH
• Fluid shifts from intravascular to interstitial space
• Progessive bradycardia and ECG changes (AF, VF, asystole)
• Core temp 20 degrees = cardiac and respiratory arrest.

Question 7

Discuss the pathophysiology of hyperthermia

Answer 7

Excessive heat denatures proteins, destabilizes phospholipids and lipoproteins, and liquefies membrane lipids, leading to cardiovascular collapse, multi organ failure, and, ultimately, death. The exact temperature at which cardiovascular collapse occurs varies among individuals
Thermo sensors located in the skin, muscles, and spinal cord send information regarding the core body temperature to the anterior hypothalamus, where the information is processed and appropriate physiologic and behavioural responses are generated.

Physiologic responses to heat include an increase in the blood flow to the skin (as much as 8 L/min), which is the major heat-dissipating organ; dilatation of the peripheral venous system; and stimulation of the sweat glands to produce more sweat. When heat gain exceeds heat loss, the body temperature rises. The redistribution of blood flow to the periphery, coupled with the loss of fluids and electrolytes in sweat, place a tremendous burden on the heart, which ultimately may fail to maintain an adequate cardiac output, leading to additional morbidity and mortality.

Heat directly influences the body on a cellular level by interfering with cellular processes along with denaturing proteins and cellular membranes. In turn, an array of inflammatory cytokines and heat shock proteins (HSPs) are produced. If the stress continues, the cell will succumb to the stress (apoptosis) and die. Progression to heatstroke may occur through thermoregulatory failure, an amplified acute-phase response, and alterations in the expression of HSPs. This can then lead to Multi Organ Dysfunction (MODS), Coma and Death.

Question 8

Discuss the management of the cardiac arrested hypothermic patient with a temperature less than 30°C. What modifications need to be made?

Answer 8

· CPR/One defibrillation shock only (for VF or pulseless VT).
· Advanced airway management.
· IV access/One dose of Adrenaline only.
· Continue CPR and rewarming measures until temperature rises above 30°C.

Question 9

Causes of hyperthermia

Answer 9

Exercise, fever, shivering, tremors, convulsions, thyrotoxicosis, sepsis, sympathomimetic drugs, external factors, and many other conditions can increase heat production,

Question 10

Hyperthermia definition

Answer 10

Core body temp >40 degrees for more than 60 mins.
Occurs when there is an imbalance between the heat inside the body and ability to dissipate the heat.

Question 11

Fever defintion and how differs from hyperthermia

Answer 11

Body temp over 37.5 due to an increase in temperature regulatory set point.
Differs from hyperthermia in that hyperthermia is elevated above the thermoregulatory set point due to excessive heat production

Question 12

Hyperthermia and cellular & organ damage

Answer 12

Temp >41,5 results in progressive denaturing of proteins and cell membrane causing APO, rhabdo, DIC, electrolyte dysfunction

Question 13

Heat exhaustion (moderate)

Answer 13

• Recognised by core temp <40 and patient feeling between when lying down and shade
• Recognised by fatigue, headache, nausea, vomiting and dizziness, balance problems

Question 14

Heat stroke (severe)

Answer 14

• Causes unconsciousness and death
• > 41 degrees with hot, dry skin
• Profuse sweating or complete cessation, tacky, hyperventilation, seizures, combing, hypotension

Question 15

Hyperthermia management

Answer 15

• Cooling <38 degrees: shelter, airflow, remove clothing, water
• ypovolaemia: fluids if tachycardic/hypotensive
• BGL management
• Airway and ventilation