Lady walking in the park

Understanding Heatstroke

1. What exactly is heat stroke and what causes it – what is going on inside the body on a cellular level?

Heat stroke is the worse end of a big spectrum of heat related conditions.

Exertional heat stroke is the type that is associated with exercising in the heat, it is a very serious condition when our body can no longer control its temperature and it starts to sky rocket.

Usually when we work out we have lots of great mechanisms for helping our body cool off. Aside from our fancy work out gear our body cleverly sends more blood flow to the skin to help our skin produce more sweat which helps our body stay cool. To get more blood flow to the skin we send less blood to our digestive system which is why lots of people can find it hard to digest foods after exercise. In extreme heat this though can cause problems with less water being absorbed in our gut and even the gut becoming leaky and allowing toxins to enter our blood stream.

If we become dehydrated during exercise it gets worse as our heart struggles to pump enough to keep up our circulation and becomes strained. If we can’t get enough blood to our muscles, they can start to overheat too and produce harm toxins which can actually damage the muscle tissue itself.

We really start to worry about people when the body temperature is above 40 degrees centigrade. This is because this is called the ‘thermal threshold’, above this temperature the membranes, or outer layer of our cells, can become damaged, this can cause enough harm to cause the death of cells. In the worst-case scenario, the combination of these events can lead to unconsciousness, coma, multiple organ failure and even death.

2. What can trigger heat stroke?

The biggest risk of heat stroke is when the temperature outdoors is above 28°C, in combination with doing some strenuous activity or high intensity exercise for an hour or more. So even an outdoors exercise class or a fast run could be a risky time.

Definitely if you are not used to that exercise there is a bigger risk. So, the current brilliant weather is a great reason to enjoy being outdoors but not the perfect time to try out that boot camp class.

If you have another complicating factor it can also be enough to get your body in trouble, even if you are super fit. Common things are having a virus or mild illness, being dehydrated before you start exercises, inappropriate clothing and being tired. Some medications such as anti-depressant medicines can also add to the risk.

3. What are the symptoms of heat stroke? – from the most obvious to some which are perhaps a bit more surprising?

Most of us have probably experienced mild symptoms such as feeling a headache and unwell after a long afternoon in the sun. These kind of exhaustion symptoms are probably a really good way our body tries to make sure we don’t keep exerting ourselves and put ourselves at risk of overheating even further

Heatstroke though can progress really quickly, there is often a severe headache, feeling generally confused and restless. It might surprise people that the skin is often dry, they are no longer sweating which is part of the problem and they are usually quite red and dry skinned. Their pulse might be racing. If you measured your temperature it would usually be above 40 degrees centigrade. When symptoms have become this severe it is an emergency to cool that person, they can quickly deteriorate to becoming drowsy and then unconscious.

4. What are the best forms of heat stroke prevention and management?

As in most things prevention is much better than cure. So, try to make sure you are not putting yourself in a high-risk group. Keep well hydrated before exercise, if you are doing a long event such as a marathon it is important you keep hydrated but take care not to over drink. Pre-cooling by using cooling clothing, cold water immersion and taking cool drinks before exercise can help too.

If you know you are not well or are just recovering from an illness, then it is sensible not to push yourself in hot conditions. Make sure you have clothing on which will allow your skin to sweat freely and keep cool. If you are concerned about any medication or illness you may have please check with your doctor before strenuous exercise. Stomach upsets and having had too much alcohol in the day before are common triggers.

Anyone planning to take part in an event or exercise in hot conditions should plan to get their body used to this beforehand. Ideally this would be training in the same environment but if that’s not possible then a training in a hot room can help, it takes the body at least 7 days and up to 14 days to really get used to exercising in a hot climate. Start with 30 minutes at a time and build up to 100 minutes, your body will learn to cool itself better. Ideally this should be daily, but even every day or two will help. Heart rate monitors can help you check you are not pushing yourself too hard. Unfortunately, when it comes to getting used to exercising in heat we are not all equal, women are more at risk than men.

Ice packs and cool flannels can help to reduce body temperature quickly, the back of the neck, underarms and groins are the best places for these. Plus using fans and cold-water sprays to help the body lose heat through the skin. Cool fluids and slushy ice drinks are useful too.

If you or someone you are with is showing signs of heat stroke then it is important to get them to medical care quickly, this would usually be an Accident and Emergency department. Even young and fit people can deteriorate quite quickly. In hospital other techniques such as fluids via a drip and medicines can be used, as well as blood tests and checks to make sure that the person is not suffering any organ damage.

Dr Lucy Hooper
Coyne Medical