Hypothermia

Question 1

What is hypothermia?
What are the classes of hypothermia?

Answer 1

A core body temperature below 35 degrees

Mild = 32 - 35 (alert and shivering)
Moderate = 28 - 32 (reduced consciousness, diminished shivering, loss of fine motor control)
Severe = 20 - 28 (25 - 28 causes loss of shivering and arrhythmias, 20 - 25 causes cardiac arrest)
Absent vital signs below 20 degrees

Question 2

What are the causes of hypothermia?

Answer 2

Increased heat loss or impaired thermogenesis

Environmental causes:
Exposure
Drowning
Poverty
Drugs
Sepsis
Shock
CNS disorders e.g. hypothalamic lesions
Endocrine disorders e.g. hypothyroidism
Trauma/burns
Skin disorders

Question 3

How is heat lost during an operation?

Answer 3

Radiation (the majority of heat is lost in this way via vasodilation)
Evaporation
Conduction

Question 4

What are the risk factors for surgical hypothermia?

Answer 4

Open surgery
Long procedure
Sepsis
Pre-operative hypothermia
Large areas exposed e.g. trauma surgery
High pre-operative risk
General anaesthesia (propofol causes vasodilation, neuromuscular blockers prevent shivering, opiates depress thermoregulatory control)

Question 5

What are the signs and symptoms of hypothermia?

Answer 5

Mild: signs of sympathetic drive e.g. tachycardia and shivering, behavioural changes e.g. putting on clothes and curling up

Moderate: confusion, slurred speech, decreased reflexes, loss of fine motor skills

Severe: bradycardia, hypotension, hallucinations, fixed pupils, paroxysmal undressing, terminal burrowing

Question 6

What are the ECG changes seen in hypothermia?

Answer 6

Bradycardia
Widening of QRS complex
Increased PR interval
J waves (positive deflection at the end of the QRS complex)

Risk of VF below 20 degrees

Question 7

What are the complications of hypothermia?

Answer 7

Arrhythmias - bradycardia, VF

Oxygen dissociation shifts to the left - higher Hb affinity so less oxygen delivery to tissue which leads to ischaemic complications

Decreased drug metabolism, protein and enzyme actions

Clotting dysfunction

Infections

Wound breakdown

Hyperglycaemia due to reduced glucose uptake by cells and sympathetic-driven release of glucose from the liver

Question 8

How to initially approach hypothermia?

Answer 8

A to E
Continuous ECG monitoring
Rectal thermometer
Catheter
Regular glucose monitoring

Question 9

How to treat hypothermia?

Answer 9

Mild and conscious: passive warming
E.g. keeping in a warm place, removing wet clothes, warming the environment, blankets, allowing mobilisation

Moderate: peripheral active warming
E.g. bare huggers, thermal blankets, hot water bottles, IV fluids

Severe: central active warming
E.g. heated humidified oxygen, bladder and intraperitoneal warm fluid infusion, cardiopulmonary bypass, extracorporeal blood warming