NSW Nordic Ski Club
Hypoglycaemia and Heat Exhaustion
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This article on hypoglycaemia and heat exhaustion is based on a lecture which was given at a club meeting last year. I bet it comes as some surprise that heat exhaustion can occur whilst we are at the snow! However, it is important to be aware of that these conditions can occur and to increase our knowledge on how to avoid them.
The basic principle underlying these conditions is that the brain requires oxygen and glucose for metabolism and energy. Low levels of oxygen in the blood is known as hypoxia and low levels of glucose is known as hypoglycaemia.
Hypoglycaemia
Hypogylcaemia is defined as a low blood glucose level. Glucose is the primary energy source for the brain. Insufficient glucose to the brain significantly impairs function and, if prolonged, will lead to coma. Of course, other organs are affected adversely as well, but the brain is exquisitely sensitive to low blood glucose levels. This is due to the fact that the brain cannot utilize proteins, complex carbohydrates or fat without these products first being metabolized to glucose. The body's requirements for glucose is increased by physical exertion, stress, and illness, and there are several medical conditions that also lead to increased glucose requirement and utilization.
Types of Hypoglyaceamia
Postprandial hypoglycaemia occurs after eating and results in the failure of a normal rise in blood glucose following a meal. Fasting hypoglycaemia occurs where there is a failure of metabolism to respond to fasting by breaking down stores of energy in order to raise blood glucose.
The causes of postprandial hypoglycaemia include medical conditions such as gastrointestinal enzyme defects, surgery to the gastrointestinal tracts and abnormal glucose metabolism (diabetes mellitus). Insufficient intake of food for example during physical exertion and during environmental exposure to extremes of temperature, such as hypothermia or heat exhaustion, will also result in hypoglycaemia particularly in those individuals that have lower levels of physical fitness.
Fasting hypoglycaemia occurs where there is failure of metabolism to respond to fasting by increasing glucose production from body energy stores. Underproduction of glucose from metabolism occurs with enzyme disorders, liver disease, drugs including alcohol, pregnancy and insufficient fat stores (malnutrition). Increased utilization of glucose is a less common but important cause of fasting hypoglycaemia. This occurs in severe infections, tumours (cancer) and exposure to drugs.
For the purposes of our sport, hypoglycaemia due to exertion is of greater relevance. Physical exertion increases tissue demand for glucose due to increased tissue utilization of glucose. These symptoms of hypoglycaemia include weakness, feeling empty in the stomach, hunger, sweating, palpitations and tremor. If the blood glucose level is not restored by eating a meal, the individual may develop headache and eventually dizziness, disorientation and confusion. In the worst scenario if low blood glucose level is prolonged, the individual may pass into coma.
Prevention of hypoglycaemia
Good general medical health is important to ensure safety in the snow with respect to hypoglycaemia. An exercise program several weeks prior to the snow season will improve fitness and cardiovascular efficiency. It is important for individuals to be aware of their limitations and not to push themselves beyond their ability if they are clearly having difficulty keeping up with their friends in the group. It is wise to discuss your individual needs with the tour leader or instructor to ensure that you are not undertaking a physical activity that is beyond your level of fitness. When you are in the snow, and particularly with cross-country skiing which requires a high level of physical fitness, it is important to have regular breaks and to eat regularly especially when exercising over a prolonged period. Refined sugar alone will not be sufficient to sustain your blood glucose level. Complex carbohydrates and protein rich foods should be eaten while exercising. Ensure adequate fluid intake whilst exercising and take it easy.
Treatment of hypoglycaemia
When symptoms are detected early it is important to sit down, have a break and eat a carbohydrate/protein rich snack or meal. Ensure adequate fluid intake. If you are overheating remove a layer of clothing. Return to base if symptoms are not improving or if progression of symptoms occur as described above.
Where the individual has returned to base for more serious symptoms, medical attention is required. Bed rest for a few hours with monitoring of pulse, blood pressure, sugar level and hydration will be necessary. Oral glucose is given in the first instance, but intravenous glucose may be necessary in more serious conditions. The important message is that if hypoglycaemia is treated early and effectively, full recovery will occur.
Heat Exhaustion
Heat exhaustion occurs where there is failure of the cardiovascular system to respond to high environmental temperature. The condition is not uncommon and can occur in both sedentary and active individuals. Heat exhaustion is more likely to occur in the elderly and the frail at rest; and in unfit and overweight individuals during exercise. Predisposing factors includes low level of physical fitness, medical conditions that affect cardiovascular function, and drugs such as anti-hypertensive and diuretic medication.
Prevention of heat exhaustion
Improve fitness prior to commencement of prolonged exercise such as cross-country skiing. Ensure adequate fluid intake whilst exercising. Remove items of clothing during exercise if overheating and take it easy in hot weather. Cool drinks help to lower body core temperature. The symptoms of heat exhaustion include weakness, dizziness, headache, loss of appetite, nausea, vomiting and fainting. The physical signs to the observer include cool, clammy skin, pallor of the face, a weak pulse and the individual may appear anxious. Further symptoms include over breathing, unsteadiness on the feet, disorientation and confusion. The latter signs indicate that the individual requires urgent attention.
Treatment of heat exhaustion
Remove the individual to a cool, shady place and encourage them to rest and lie down if necessary. If the individual is feeling faint encouraging them to lie down is beneficial as this will result in improve blood flow to the brain. Encourage the individual to drink fluid. These basic steps will usually result in improvement, but if improvement does not occur then medical assistance is required. In these circumstances intravenous fluids to replenish blood volume may be necessary.
The final message in relation to hypoglycaemia and heat exhaustion is to tell someone in your group when you are not feeling well. Do not suffer in silence as others are not able to assist you if they are not aware that you are having difficulties. This is especially relevant because early appropriate measures will avoid the need for medical assistance.
And remember to "take it easy in the snow".
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