Heat cramps Associated with whole-body salt deficiency.
Cramps occur in the abdominal and large muscles of the extremities but differ from exertion-induced cramps since the entire muscle is not involved; cramp appears to wander because individual motor units contract. Plasma Na deficit with urine specific gravity Observed mostly in unacclimatized individuals. Heat syncope Brief fainting spell without a significant increase in rectal temperature. Pale skin is obvious. Pulse and breathing rates are slow. Presyncope warning signals include weakness, vertigo, nausea, or tunnel vision.
Abbreviations: IV intravenous, gram, Na sodium, NaCl sodium chloride table salt, tsp teaspoon.
IV solutions, used when symptoms include nausea and vomiting, bring rapid relief with no lasting complications.
Lay the patient in the shade and elevate feet above the level of the head. Replace fluid and salt losses. Avoid sudden or prolonged standing.
Adapted, by permission, from L.E. Armstrong and R.W.Hubbard,Hyperthermia: New thoughts on an old problem, The Physician and Sportsmedicine :. sodium lost its favored position among medical professionals, because it was recognized as a key etiological factor in the development of salt-sensitive hypertension. Ina select committee of the U.S. Senate McGovern Committee on Nutrition and Human Needs recommended that U.S. residents reduce their salt consumption to about NaCl/day. Currently, the Food and Nutrition Board of the National Research Council recommends that adults limit their daily intake of sodium to NaCl/day.
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The exact amount of sodium required by humans, at any stage of development or during any specific activity, is difficult to measure because the absolute need is determined almost entirely by nonrenal losses such as sweating. Despite this fact, investigations have shown that the basal metabolic requirement for salt is remarkably small. For example, Dahl reported that hospitalized patients required only NaCl/day. Except for a few cases of renal impairment, maintenance of sodium balance and health was not a problem. Clearly, the average daily salt intake of U.S. adults NaCl far exceeds their physiological needs.
It also is difficult to determine the sodium requirements of individuals who leave modern lifestyles in mild climates and move to hot climates. Many factors affect sodium turnover, including sweat production, state of heat acclimatization, dietary intake of sodium, and daily duration of exposure to heat. One analytical method involves measuring the dietary salt levels of healthy residents of hot environments. For example, studies have shown that the Masai warriors of Africaand Galilean Naturalists who eat no livestockg NaCl/day, maintain year-round health on low-salt diets. These studies support Dahl’s findings, and suggest that extreme hormonal sparing of sodium in sweat and urine, controlled water intake, careful dietary practices, as well as clothing may affect sodium balance in a hot climate. Because many diverse populations have been studied, it is unlikely that there are major hereditary influences on basal sodium needs.
In contrast to these studies, many experts formerly recommended large sodium intakes. These were published between andand involved recommended daily levels of -NaCl for continuous desert living. Hubbard and colleagues reviewed these studies and concluded that such recommendations were unnecessarily large, in light of aldosterone-mediated sodium conservation that occurs during heat acclimatization. They noted that excess dietary salt results in reduced plasma aldosterone levels, exactly opposite the hormonal status desired during prolonged thermal stress. This is especially true if secondary challenges reduced food intake, occupational distractions, increased work requirements occur concurrently.
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