From the Guidelines
Hypothermia has several physiological effects on the body, including reducing brain metabolism, lowering intracranial pressure, and decreasing the initiation of brain cell apoptosis.
Physiological Effects of Hypothermia
- Reducing brain metabolism, which restores a favourable balance with cerebral blood flow in injured brain tissue 1
- Lowering the intracranial pressure
- Reducing the initiation of brain cell apoptosis, notably the caspase activation pathway, and of necrosis
- Decreasing the local release of lactate and of excitotoxic compounds, such as glutamate, that is associated with alteration in calcium homoeostasis during brain ischaemia
- Reducing brain tissue inflammatory response and systemic inflammatory response syndrome
- Decreasing the production of free radicals
- Limiting the vascular and cell membrane permeability as seen in brain ischaemia
Systemic Effects of Hypothermia
- Increasing systemic vascular resistance and causing arrhythmias (usually bradycardia) 1
- Causing a diuresis and electrolyte abnormalities such as hypophosphataemia, hypokalaemia, hypomagnesaemia and hypocalcaemia
- Decreasing insulin sensitivity and insulin secretion, and causing hyperglycaemia
- Impairing coagulation and may increase bleeding
- Impairing the immune system and increasing infection rates
Clinical Implications
Hypothermia is considered an independent risk factor for mortality, related to its initial impairment of cardiovascular function, coagulation, and lactic acidosis followed by respiratory compromise 1. Rewarming therapy should begin in the prehospital phase with passive and active warming strategies.
Management of Hypothermia
- Maintain a constant, target temperature between 32 and 36 °C for those patients in whom temperature control is used 1
- Use of sedation protocols to reduce shivering
- Monitoring and management of electrolyte abnormalities and hyperglycaemia
- Use of antibiotics to prevent infection
- Rewarming therapy to prevent further morbidity and mortality 1
From the Research
Physiological Effects of Hypothermia
The physiological effects of hypothermia on the body are complex and can be both beneficial and detrimental. Some of the key effects include:
- Disruption of physiological processes at the molecular, cellular, and system level 2
- Decrease in tissue oxygen demand, which can reduce the risk of cerebral or cardiac ischemic damage 2, 3
- Inhibition or mitigation of destructive processes in injured tissue, such as excitotoxicity, neuroinflammation, and apoptosis 3
- Stimulation of protective systems, such as early gene activation 3
- Reduction of intracranial hypertension and brain edema 3
- Decrease in myocardial contractility and cardiac output due to hypothermia-induced bradycardia, but maintenance of the balance between supply and demand 3
- Potential side effects, including immunosuppression, cold diuresis and hypovolemia, electrolyte disorders, insulin resistance, impaired drug clearance, and mild coagulopathy 3, 4
Systemic Effects of Hypothermia
Hypothermia can affect various organ systems, including:
- Nervous system: hypothermia can influence the function of the nervous system and improve neurologic outcome after cardiac arrest 4, 5
- Cardiovascular system: hypothermia can reduce myocardial contractility and cardiac output, but also reduce the risk of cardiac ischemic damage 2, 3
- Renal system: hypothermia can cause cold diuresis and hypovolemia 3
- Endocrine system: hypothermia can cause insulin resistance and impaired drug clearance 3
Therapeutic Applications of Hypothermia
Hypothermia has been used therapeutically in various clinical applications, including:
- Cardiac arrest: hypothermia has been shown to improve neurologic outcome after cardiac arrest 2, 3, 5
- Neurosurgery: hypothermia has been used to reduce the risk of cerebral ischemic damage during neurosurgical procedures 2, 5
- Organ transplantation: hypothermia has been used to protect organs during transplantation 6
- Neonatal encephalopathy: hypothermia has been used as a therapeutic adjuvant for cerebral protection in neonatal encephalopathy 6