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Chapter 16
ORAL FLUID AND ELECTROLYTE REPLACEMENT
Recommendations are considered Category 1B by the WMS Panel of Expert Reviewers
I. GENERAL INFORMATION
Oral rehydration/electrolyte solutions (ORS) are useful in three circumstances when
fluids and electrolytes may be lost in significant amounts: 1) heavy, prolonged exercise
with high-volume sweat losses, 2) treatment of mild to moderate heat illness, and 3)
illness with diarrhea and/or vomiting. Significant hemorrhage also requires fluid
replacement.
A. Fluid replacement during exercise.
Large fluid losses may occur during exercise in heat and at high altitudes. Sweat losses of
1 L/h are common during moderate exercise in a hot environment or at high levels of
exertion in a temperate environment. The rate is individual, and depends on the degree of
heat acclimatization. Dehydration disposes to heat illness. In high altitude
mountaineering, the scarcity of surface water, difficulty adjusting clothing to changing
levels of exertion or weather conditions, and respiratory fluid losses from
hyperventilation in dry, cold air (averages 1.5 L/day for moderate exertion at 15,000 feet
[4,500 meters]) commonly creates fluid needs of 7 to 8 L/day. Dehydration in this
environment disposes to altitude sickness, hypothermia, frostbite and venous thrombosis.
During exercise, frequent fluid replacement is critical. Inadequate fluid intake
decreases exercise performance and increases the risk of heat illness. Too much fluid may
lead to dilutional hyponatremia. For most situations, at least
300-500mls per hour will be required. Hydration needs will be higher with extreme
exertion or environment. The fluid is best consumed in volumes of approximately 200
mls at a time as this promotes emptying of the stomach. Dark urine suggests that the body
is struggling to maintain normal hydration and can be used as a sign that fluid intake
should be increased.
Sweat contains electrolytes: sodium (average 20 to 60 mEq/L), chloride, and
small amounts of potassium. In most instances, replacement of electrolytes during sweat
loss, especially during less than 60 minutes of exercise, is not necessary so ORS have no
advantage over plain water. Electrolyte needs during prolonged physical activity can
usually be met by regular meals and snacks, which also provide more calories than
electrolyte solutions.
In endurance events or work/exercise for in a very hot environment with high
sweat losses, electrolyte supplements are recommended. During exercise, a solution
containing 2 to 6% glucose and 30 mEq/L sodium is optimal to maintain palatability.
Higher glucose concentrations may delay gastric emptying and promote osmotic diarrhea,
but new long-chain carbohydrates that break down to simple sugars during digestion can
provide larger amounts of sugar. Excessive sodium can cause nausea. Do not ingest salt
tablets directly because they can cause gastric irritation and vomiting. One or two salt
tablets, however, can be dissolved in a liter of water. Commercial sports drinks contain
