Rehydration
It has been a long hot summer and everyone seems to be waiting for the weather to change. With the hot weather comes an increased risk of dehydration due to fluid and salt losses from increased sweating.
Our body chemistry works best when our core (internal) temperature is 36.9*C. Core temperature can be raised in two ways, either through infection or from exposure to a high environmental temperature. This latter effect is exacerbated by exertion or exercise when the weather is hot, as the exercise also generates heat due to the metabolism of glucose in energy production.
As the body absorbs or produces more heat blood vessels dilate in the skin bringing blood to the surface of the body where heat can be lost through radiation. This gives that “red-in-the-face look” indicating the person is hot. At the same time increased sweating puts a layer of moisture on the skin surface that increases heat loss through evaporation. The physics of this means that the surface of the skin is cooled down. This effect is increased if there is air blowing over the skin surface. Hence the well known “wind chill factor” effect that can cause hypothermia (abnormally low core temperature) in cold, wet climatic conditions.
One question I have been asked is how much fluid should be drunk when the weather is hot. In estimating this amount it is necessary to understand that even at rest, when doing nothing, fluid is being lost from the body during respiration, in sweat and from urine production. This fluid loss is about 1 litre in 24 hours. If working in hot conditions, whether outside, in the galley or engine room another 2 litres of fluid can easily be lost due to sweating and an increased respiratory rate. So, just to replace this loss 3 litres of fluid should be imbibed every 24 hours. For most people replacing fluid loss with water will be sufficient.
Sweat contains salts as well as water but these losses are minimal, unless sweating is excessive and prolonged, and will be replaced quickly in healthy people eating a balanced diet. It is not normally necessary to take salt tablets or special drinks containing extra salts. However if dehydration occurs due to failure to replace fluid, it is necessary to replace both water and salts. Drinks such as “Gatorade” can be useful in preventing dehydration, but should not be taken in excess as they could cause an overdose of salts, which can also be harmful.
It is also possible to drink too much water as is illustrated by an interesting report in the press recently about a well-known British actor. He was rehearsing long hours for a new play in London and the rehearsal rooms were very hot. He was aware of the need to take extra fluids, but did so to excess consuming 8 litres of water every day for some time. The effect of this was to wash out salts in the urine and overload the body tissues with fluid. The effects of this eventually led to him collapsing and requiring several days in hospital to re-establish a normal electrolyte (or salts) balance. If he had pre-existing heart, lung or kidney problems the outcome could have been far worse, even fatal.
My guess would be that most people working on boats do not drink enough fluids during the hot season. By being aware of the need to drink a minimum of 3 litres of fluid per day problems of dehydration should be avoided.
Dr Ian Marshall, MCA Approved Doctor, Medical Centre, Club de Mar, Palma. Telephone (+34) 629 818 826.