Additional Diagnostic Measures
Laboratory investigations should be driven by the clinical situation.
What to obtain
In most cases, it would be reasonable to obtain the following:
- Urea and electrolytes (U&E)
- Full blood count (FBC)
- Clotting screen
- Arterial blood gas
- Creatinine kinase level
- Blood alcohol
- Urine toxicology screen
These investigations should be repeated during the rewarming phase.
Physiological changes
Some of the physiological changes seen with hypothermia include:
- A shift of the oxyhaemoglobin dissociation curve to the left
- Increased haematocrit due to the decrease in circulating plasma volume
- Low-to-normal white blood cell count, even in the setting of infection
Blood gases
Arterial blood gases should not be corrected for temperature.
The blood gas analyser warms the blood to 37oC and the uncorrected values for pH and PaCO2 correspond almost perfectly to normal temperature values.
An uncorrected pH of 7.4 and a PaCO2 of 5.3 kPa confirm acid-base balance at all temperatures.
Respiratory response
The normal respiratory response to hypothermia is hyperventilation, resulting in a respiratory alkalosis.
As the hypothermia worsens, respiratory depression predominates and this results in a respiratory acidosis.
In a series of 135 hypothermic patients, 30% were acidotic and 25% were alkalotic. This reflects the unpredictability of the acid-base milieu in the hypothermic patient.
Imaging studies should be geared toward the clinical situation.
Learning bite
Do not correct for hypothermia when analysing the acid-base status. Normal values can be assumed to meet the needs of the hypothermic tissue.