Psychology
Hypothermia kills, but it can be a lifesaver for people with brain injuries.
Hypothermia kills, but it can be a lifesaver for people with brain injuries.
It’s easy to believe that Wellington holds the crown for the most reliably dry Christmas in New Zealand. Niwa said so. Admittedly, it also said Wellington shared the honour with Christchurch, but I shall take what I can get.
Yesterday, however, I saw snow. But this was because I am in Boston. Today’s high was a balmy 3°C, but on New Year’s Day it got down to -10°C, with blizzard conditions. There are piles of snow on the footpaths, the Charles River has iced over and people are skating on Frog Pond.
However, it’s a far cry from the coldest winters on Earth. On the Antarctic coast, the temperature drops to below -40°C and in the depths of winter it hits below -80°C. Talk about chilly.
Humans are not designed to cope with extreme cold. More than a thousand people die from hypothermia each year in the US, and although New Zealand’s rates are harder to find, it’s probably a couple of dozen a year.
Unsurprisingly, our hearts and brains are particularly sensitive to the effects of the cold, and because they’re quite important, we want to keep them warm. One of the things our bodies try to do when the temperature drops is divert blood from lessimportant extremities to our vital organs.
Temperature regulation is part of the job of the hypothalamus, when it’s not looking after other basic physiological processes such as hunger, thirst, sleep and libido. If our core temperature continues to drop, the electrical activity in our hearts and brains does too, and organs start to fail.
Normal human body temperature is about 37°C, but if you’ve had kids (or a fever), you know it doesn’t take much of a deviation from that for us to start worrying. Hypothermia starts when our internal temperature drops below 35°C. The heart starts to become erratic at around 28°C, and at 20°C … well, the brain will take a rest.
Long before that point, though, we get rather less good at stuff – mild hypothermia comes with such neurological effects as dizziness and difficulty with speech and co-ordination. If we get colder, expect slurred speech, confusion and apathy – no longer caring.
Hypothermia has some uses, though, or at least mild hypothermia does. Lowering core temperature under controlled conditions is now a common way to improve outcomes for acute brain-injury sufferers. Deliberate therapeutic hypothermia, or “target temperature management”, has been around for more than 70 years but has become almost standard since the early 2000s, because randomised studies showed that dropping core temperature to 33°C for up to a day improved the end result.
This is because, as well as the bad stuff that can happen, hypothermia reduces brain energy load and the associated mechanisms involved and reduces the inflammation that usually accompanies a brain injury.
The heart starts to become erratic at 28°C, and at 20°C the brain will take a rest.
As a result, the brain gets a rest and doesn’t back up with juices as much.
This last is particularly important, because excessive pressure of cerebrospinal fluid on the brain (or intracranial hypertension) is one of the biggest predictors of brain-injury outcomes.
This presents me with the tricky decision of whether to go ice skating. The US has about 2000 skating-related head injuries annually. The upside is that it will be cold.