Tests
1st tests to order
core temperature measurement
Test
Do not use a standard clinical thermometer to measure core temperature. This may be inadequate as it will not measure temperatures below 94°F (34.4°C). Conventional mercury thermometers are also not recommended, owing to the risk of breakage and poisoning. Where feasible (usually in hospital), an esophageal probe is preferred as it correlates well with the temperature of the pulmonary artery.[19][20][51] This is usually only possible in critically ill patients as readings must be obtained from the lower third of the esophagus when the airway is secured (i.e., tracheal tube or a supraglottic device with an esophageal channel in place).
Alternatively, a low-reading tympanic membrane thermistor-based thermometer (where the thermistor touches the tympanic membrane) can be used if the patient is spontaneously breathing.[20][48]
Bladder catheter temperature sensors can be used in patients who require a urinary catheter, but bladder and rectal temperature lag behind core temperature and are only recommended for stable patients in a hospital setting.[19][20] Never measure rectal temperature if the patient is in a cold environment because this method requires the patient to be further exposed, which will increase heat loss and potentially worsen hypothermia.
Result
<95°F (<35°C)
12-lead ECG
Test
Continuous ECG monitoring is essential for detecting arrhythmias, which may be fatal. Where possible, ECG monitoring should also be used to detect cardiac arrest.[20][48]
Arrhythmias can occur at any stage of hypothermia, and also during rewarming.
Initially, in mild hypothermia, the ECG may show tachycardia. In more severe cases of hypothermia, the ECG may show progressive sinus bradycardia, atrial or ventricular fibrillation, junctional rhythms, ST segment changes, T-wave inversion, prolongation of the QT interval, and eventually asystole.[11] With the exception of ventricular fibrillation, these changes are likely to improve without treatment as the patient’s core temperature increases.[20][48]
J waves (or Osborn waves) occur in most, but not all, patients.[50] However, they do not correlate well with temperature.[51]
Result
sinus bradycardia; atrial fibrillation; J wave or Osborn wave; ST elevation or depression; T wave inversion; prolonged PR, QT, and QTc interval; broad QRS complexes
CBC
Test
Hemoglobin and hematocrit may be elevated due to hemoconcentration. Platelets and WBCs are abnormally low due to sequestration in the spleen.
Result
elevated hemoglobin and hematocrit, low WBC and platelet counts
serum electrolytes
Test
Renal function may be impaired due to dehydration, cold exposure, or rhabdomyolysis. Hypokalemia may occur as a result of hypothermia or the associated treatment. Hyperkalemia may occur during rewarming.
For a patient in cardiac arrest, hyperkalemia can also indicate that hypoxia preceded hypothermia (e.g., if the patient was found in an avalanche).[48] Initial serum potassium >12 mEq/L (>12 mmol/L) is associated with irreversible death if the patient is in cardiac arrest.[48] Serum potassium is part of the HOPE (Hypothermia Outcome Prediction after ECLS rewarming for hypothermic arrested patients) score for prognostication of successful rewarming.[20][48] [ Hypothermia outcome prediction after ECLS (HOPE) score Opens in new window ]
Result
hypokalemia, hyperkalemia
blood glucose
Test
Glucose levels may be normal, high (owing to increased secretion of stress hormones - cortisol, growth hormones, and catecholamines - and reduced insulin secretion, together with increased peripheral resistance to insulin), or low (owing to cold-induced inhibition of hepatic glucose production). Monitor blood glucose even after the patient is normoglycemic because rebound hypoglycemia may develop when normal insulin production resumes. Treat hypoglycemia promptly. Hypoglycemia can stop shivering (because the central control of shivering is dependent on glucose), leading to subsequent heat loss.[53]
Result
may be elevated, often normal, sometimes low
ABG
Test
May show respiratory alkalosis, metabolic acidosis, or a mixed picture. As core temperature decreases, respiration is depressed, resulting in hypoxemia and hypercapnia. A combined respiratory and metabolic acidosis occurs as a result of hypoventilation, retention of carbon dioxide, decreased bicarbonate, impaired hepatic metabolism of organic acid production (owing to impaired hepatic perfusion), and increased lactic acid production. It is important to note that blood pH rises by 0.015 for every 1.8°F (1°C) drop in body temperature. In general, use blood gas results without adjustment for temperature to guide treatment decisions.[52]
Result
respiratory alkalosis, metabolic acidosis, or mixture of both; respiratory acidosis is suggested by pH <7.35 and carbon dioxide partial pressure >40 mmHg; metabolic acidosis is suggested by pH <7.35, bicarbonate ≤24 mEq/L, and a normal partial pressure of carbon dioxide, although it may be low with compensation; PaO₂ may be low with severe hypothermia, and/or if there are pulmonary infiltrates or edema
clotting screen
Test
Prothrombin time (PT) and PTT are prolonged due to inhibition of enzymatic activity in both the intrinsic and the extrinsic coagulation cascade. The cause of coagulopathy is unknown.[54]
Result
elevated PT and PTT
chest x-ray
Test
Particularly important if the patient has an altered level of consciousness.
May show pulmonary edema or infiltrates.
If the patient has been immersed in water, it may show inhaled foreign bodies, such as false teeth or debris from the water, which will need to be removed. See Foreign body aspiration.
Result
may be normal or may show pulmonary infiltrates and/or edema
Tests to consider
serum creatinine kinase
Test
Should be checked for rhabdomyolysis if the patient may have been lying on the ground outdoors for a long time and they have not been immersed in water. See Rhabdomyolysis.
Result
>5 times the upper limit of normal indicates rhabdomyolysis
myoglobin levels
Test
Should be checked for rhabdomyolysis if the patient may have been lying on the ground outdoors for a long time and they have not been immersed in water. See Rhabdomyolysis.
Result
increased levels in blood and/or urine is an indicator of rhabdomyolysis
end-tidal CO₂
Test
Used to detect cardiac arrest, where possible, in the absence of vital signs.[20][48] See Cardiac arrest.
Result
low or absent in cardiac arrest
ultrasound
Test
Used to detect cardiac arrest, where possible, in the absence of vital signs.[20][48] See Cardiac arrest.
Result
ventricular fibrillation or absence of cardiac activity in cardiac arrest
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