An unresposnive patient with a chilling ECG (hypothermia management)

Winter has finally arrived and a new season brings new environmental factors that may play a part in a patients presentation. As we move into the coldest months of the year the identification and management of hypothermia is something which we may all need to revise.

Hypothermia can be categorised into:
Mild - 32-35'C
Moderate- 28 - 32'C
Severe - less than 28'C

In these cold months be sure to consider hypothermia in elderly patients and the young when presenting acutely unwell.

The  identification of hypothermia is seemingly easy with use of a thermometer however the usual oral or tympanic thermometers become less accurate in truly cold patients and a central thermometer (rectal/ oesophageal / bladder) should be used.

Signs and symptoms of moderate to severe hypothermia include:
Shivering
Reduced GCS and sluggish to fixed dilated pupils
Bradycardia and hypotension
Slow AF
Hyperglycaemia
AKI can develop if left untreated

The ECG can be a clincher in the diagnosis before a temperature is gained and there are characteristic ECG findings that you should be aware of.

A specific finding is the "J" or Osborn wave, a positive deflection at the J-point, seen below:

The height of the J wave is roughly proportional to the degree of hypothermia.

Other ECG findings include:
Prolonged PR, QRS and QT intervals
Shivering artefact
Ventricular ectopics
Cardiac arrest due to VT, VF or asystole

Below is an example of severe hypothermia demonstrating these features (temp 26 degrees) found on life in the fast lane. This ECG is very similar to a patient recently presenting unresponsive to the ED with a temp of 27'C.

Management
Search for and treat secondary cause for hypothermia or leading to unprotected exposure to the cold (i.e sepsis, myxoedema, CVE, overdose, DKA etc).

Rewarming strategies:

Mild-moderate hypothermia
Passive re-warming

• keep dry
• insulated blankets
• encourage patient to move around

Peripheral active re-warming

• Chemical heat pads
• bair hugger

Severe hypothermia
Central active warming

• Warmed IV fluids (running fluid through a warmer or level 1 infuser)
• Warmed humidified inspired gasses (if intubated)
• Body cavity lavage  - bladder irrigation, R sided thoracic lavage
• Renal replacement therapy
• ECMO

Be very careful transferring a hypothermic patient (particularly patients with temperatures <32'C) as moving the patient alone can trigger VF.

Resuscitation
Changes to ALS in a hypothermic arrest:

• Palpate pulse for up to 1 minute (consider point of care echo but do not delay CPR).
• Delay adrenaline and other drugs until  temp is greater than 30'C.
• Between 30-35'C double the dose intervals between ALS drugs.
• Shock VF up to 3 times if necessary, then no further shocks until the temperature is  greater than 30'C.
• Do not stop CPR until the patients temperature is greater than 30'C unless all attempts at rewarming have been futile or the cause of the hypothermia is thought to be non reversible. (Of note a very high potassium, greater than 8 has an extremely poor predictive value for a positive outcome in hypothermic cardiac arrest)

Further reading:
https://litfl.com/hypothermia/
​https://www.rcemlearning.co.uk/reference/hypothermia/

Martin Dore Dec 20