It doesn’t seem like a huge difference to me but even a 1 degree increase of body temp can make you so tired and have fever. Why is that?
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Hi. First I’m a registered nurse.
You feel tired when you have a pyrexia (high body temperature above 38 celsius) for several reasons:
You are losing moisture and become dehydrated. This will cause your breathing rate (respiration rate) and heart rate to increase. You may not notice it because moisture doesn’t condense on hot skin as sweat, you ‘ll notice you feel tired because your heart and lungs are working harder than normal already you have less capacity for exercise. A few days at this high heart rate and breathing rate, without a period of rest to recover can cause the heart, lungs and breathing muscles to become fatigued and eventually fail.
With a core body temperature above 39 Celsius your ability to lose heat gradually diminishes to the point it can no longer effectively cool you down, sweating and breathing no longer removes excess heat fast enough your heart and lungs are working at maximum capacity even while at rest, extended periods above 39 Celsius lead to body organ failure, heart and lungs failure, dehydration and death. (Muscles produce heat and carbon dioxide when they are working, that includes the heart and the muscles you use to breathe, that’s more heat and acidity your body has to remove, it becomes a vicious feedback loop).
People with high skin temperature often complain they feel cold because the air temperature is colder than their skin. A person who has had a high temperature for a while can look very pale and their skin feels cool because they have dehydrated to the point their brain says there is only enough blood circulation for the important body organs and it doesn’t want to lose more fluid as evaporated sweat, so it directs blood away from the skin and this further reduces cooling capacity.
While feeling unwell you eat and drink less which adds to the feeling of fatigue because your body switches to burning it”s own reserves to maintain the high metabolic rate, this produces toxic chemicals which get into the bloodstream, your heart and lungs, your liver and kidneys have to work harder to remove these toxins. Kidney cells and their chemical processes are very sensitive to pH levels. Taking in less fluid means your heart and kidney’s work less efficiently and there is less fluid to dilute the acidity from carbon dioxide (CO2).
Your immune system requires energy to produce a response. When body cells are working normally they produce toxins which are removed by the circulation, lungs, liver and kidneys, as the metabolic rate increases with temperature the systems that remove these toxins can no longer cope and the toxins build up in the body. Increased metabolic rate of the cells produces CO2 which dissolves in the blood and makes it more acidic, body cells are sensitive to blood pH too much acid damages the cells and disrupts chemical functions. The cells which conduct electricity to make your heart beat are very sensitive to pH levels.
Your brain cells work efficiently within a narrow range of 35.5 to 37.5 degrees Celsius and pH levels. As your brain heats up there is a risk that some parts of the brain’s activity becomes disorganised, this causes epileptic type fits particularly in babies and the elderly. When we see a temperature spike we give anti-pyretics like NSAID’s to stop the temperature spiking to harmful levels. We can do this because we know in most cases we have drugs to deal with the problem if the immune system can’t cope but most of the time it does.
Infection can be localized to a part of the body, while locally hot at the infection site the body core temperature usually stays below 38 Celsius because your heart, lungs kidneys and liver are coping. If the core temp goes above 38 Celsius it is an indication that the infectious agent has overwhelmed the immune response and is now bloodborne. It has also gone beyond the body’s ability to cool itself for extended periods. We take blood samples to find out what the infectious organism is and start broad spectrum antibiotics. Common viruses don’t usually cause the core body temperature to rise above 38 Celsius unless the person has some other underlying illness. They also don’t cause symptoms to last more than 3-5 days usually. Uncommon viruses usually have other symptoms which medical staff check for on examination.
If there is a temperature spike to 40 Celsius or above the person can become confused, disorientated, agitated and there is a significant risk of epileptic-type fitting, in which case we would begin active cooling methods such as applying tepid water to the skin, or even ice, as well as the previous methods we used to bring the temperature down, we also give IV fluids. If a core temperature doesn’t reduce with NSAID’s this is indicative that the problem is more serious than a routine illness. If the pH of the blood falls to acidic levels that we know cause damage, because the lungs aren’t removing the CO2 well enough we put them on a machine that assists their breathing to remove the CO2, a ventilator. We might also give alkaline IV infusions.
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