Therapeutic hypothermia

Induced (therapeutic) hypothermia is being increasingly used as a tool to achieve neuroprotection and/or cardioprotection. Clear benefit in terms of neurological outcome exists for victims of cardiac arrest following VT or VF, and following asphyxia in neonates. Ongoing work is examining its efficacy in ischaemic stroke, traumatic head injury, subarachnoid haemorrhage, hepatic encephalopathy, and haemorrhagic shock. Study results are either conflicting or too preliminary to make firm recommendations.

Timing and duration

The optimal period following neurological injury for which outcomes may be positively influenced by hypothermia is uncertain. Human studies show benefit from treatment durations ranging from 12–72h. From animal experiments, optimal effects are achieved when hypothermia is induced as rapidly as possible ‘time is brain’. Studies show benefits can be realised even after delays of 8h before commencement. Ideally, target temperature (currently 32–34*C) should be maintained as closely as possible, and rewarming should be slow and controlled to minimise reperfusion injury. Various cooling systems are currently available, each with specific advantages and disadvantages.

Cooling techniques

These can be subdivided into non-invasive and invasive.

Non-invasive

• Air- or water-circulating cooling blankets or pads.

• Ice packs in groins and axillae.

• Covering body in wet sheets or spraying with alcohol.

• Exposing head.

• Fans to increase air circulation.

• Immersion of body in cold water.

Invasive

• Infusion of cold fluids.

• Irrigating (or instilling and draining at regular intervals) bladder and/or stomach and/or peritoneum with iced water.

• Specialised endovascular catheters placed in a central vein, with iced sterile saline pumped through integral cooling balloons.

• Extracorporeal circulation.

Infusion of cold fluid can be used in the induction phase of hypothermia maintained by non-invasive methods.

Potential side effects

• Infection.

• Pressure sores.

• Electrolyte disorders.

• Hyperglycaemia.

• Arrhythmias (low risk if core temperature kept >30*C).

• Increased bleeding tendency.

• Alterations in drug metabolism.

• Bradycardia.

• Thrombocytopaenia, leucopaenia.