aniadrg
13.09.05, 00:27
Hyponatremia in Distance Athletes
Pulling the IV on the 'Dehydration Myth'
Timothy D. Noakes, MB ChB, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 28 - NO. 9 - SEPTEMBER 2000
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The strength of modern medicine is its relentless quest for an elusive
perfection. That quest requires that we examine our errors even more closely
than our successes. It is for this reason that the case report of Flinn and
Sherer ("Seizure After Exercise in the Heat: Recognizing Life-Threatening
Hyponatremia," page 61) is so important. For it records a potential tragedy
that was prevented by expeditious and appropriate medical care (1)--care that
conflicted with popular dogma. The timeworn understanding is that collapse
during or after prolonged exercise is caused by heat exhaustion; heat
exhaustion is caused by dehydration; both are prevented by inordinate fluid
ingestion; and immediate treatment should be intravenous fluids. I have
termed this traditional litany the "dehydration myth" (2,3). It has been
relentlessly perpetuated, always in the guise of good science.
Drinking (Water) to Death
Flinn and Sherer conclude that their recruit developed the complications of
hyponatremia as a result of drinking too much plain water during a series of
exercises that included a 10-km hike with an 18-kg pack. He had been actively
encouraged by his military leadership to drink water, presumably in copious
amounts, to prevent exertional heat injury.
The debate of whether exercisers drink too little, too much, or the correct
amount during endurance exercise--and whether such fluid ingestion actually
influences the risk of heat injury--has been contested with vigor in the
pages of this journal for more than a decade (3-9). In addition, the journal
has previously reported a case of water intoxication in a marathon runner
(10). Despite drinking copiously during and after the race, that runner
(whose case was also described in the American Review of Respiratory Disease)
received 1.5 L of intravenous fluids because "the emergency room physicians
assumed that the patient was suffering from volume depletion, as they had
observed repeatedly that day in other marathon runners" (11). The illogic in
such assumptions has been repeatedly argued (1-3,9,12-15).
A characteristic of this debate has been the inability of some to comprehend
the obvious. Whereas there are no case reports or clinical trials that
unambiguously link exercise-induced dehydration with specific, life-
threatening, exercise-related disorders (2,3,13), the evidence that
iatrogenic fluid overload can have very serious consequences is absolute and
irrefutable. Indeed, there are now at least 21 publications describing the
life-threatening consequences of fluid overload in runners (10,11,16-24),
triathletes (16,25-27), army personnel (28-30), and even recreational hikers
(31-33). How is it possible that this evidence can be so long ignored and
that athletes can continue to be encouraged to "consume the maximum amount
that can be tolerated" during exercise (34), without any cautionary reference
whatsoever to the dangers of drinking too much? It is a scientific paradox,
for which any logical explanation continues to elude me.
Moderate Dehydration Not Hazardous
Compared with this irresistible proof, the evidence is nonexistent that the
modest levels of dehydration in endurance athletes--body mass losses of 2% to
8% (12)--have any health consequences during exercise (2).
Consider first the definitive series of studies undertaken in the Nevada
desert during World War II (35). There, in one study (36), groups of army
conscripts exercised during the day in desert heat for as long as they could,
usually up to 8 hours, without any fluid ingestion whatsoever. During this
time they would cover up to 34 km. At the point of fatigue, caused
by "dehydration exhaustion," subjects exhibited the following symptoms and
signs: They "grew peevish and intractable; others walked in silence and were
unresponsive." All developed marked physical fatigue and ultimately
became "incapable of even mild physical effort." Yet "there were no obvious
aftereffects of dehydration. . . . We do know that man can suffer a water
deficit so incapacitating that he can neither walk nor stand; yet he recovers
his walking ability within a few minutes of water ingestion, and his feelings
of well-being within half an hour or less after he begins drinking. With a
meal or two intervening, his recovery is practically complete in 6 to 12
hours."
If these army subjects, who developed levels of dehydration twice as great as
those usually measured in modern endurance athletes, were able to recover
within minutes of drinking fluids orally, where did the idea arise that much
lesser degrees of dehydration are (1) life-threatening and (2) must be
treated immediately with intravenous fluids? (8)
The second body of evidence--also conveniently ignored--is that up to 1969,
endurance athletes were encouraged not to drink during exercise (2,12). Yet
there are almost no documented case reports of complications experienced by
these athletes. Thus, the impressively titled review article "Heat Stroke and
Hyperthermia in Marathon Runners" (37) mentions only one case of heatstroke
in a competitive marathon runner, that of Jim Peters in the 1954 Empire Games
Marathon in Vancouver. The reasons other than dehydration that explained
Peters' only collapse in a remarkable competitive career have been described
(38). Generations of competitive distance runners were, like Peters, able to
set world records at a wide range of running distances without ever consuming
anything (let alone maximal quantities) and without apparently suffering life-
threatening complications (as is now frequently reported in those who drink
too much).
Perpetuated Error
The first error identified by the case reported in this issue may well be the
perpetration and perpetuation of the dehydration myth within the United
States Army (28,29) (and among other groups) despite an avalanche of
contradictory evidence. So ingrained is this myth that attempts by a local
Chicago columnist (39) to warn runners about the dangers of overhydration
following the death of a runner in the 1998 Chicago Marathon were met with
howls of indignant protests from runners, doctors, and exercise scientists
(Eric Zorn, personal communication, October 1999).
I suggest that the resulting desire to administer intravenous fluids to
collapsed exercisers, commendably avoided by Flinn and Sherer, has developed
because the physiologic term dehydration has become established as a specific
medical diagnosis encompassing almost any form of collapse in endurance
athletes (2,3). But dehydration is not a diagnosis of a specific medical
condition, and there is no proven relationship between dehydration and any
condition associated with collapse in distance athletes (2,3). In my view,
intravenous fluids are almost never required in the management of
postexercise collapse, for the simple reason that they have no effect on the
physiologic abnormality that is most usually present: postural hypotension
secondary to peripheral blood pooling and inadequate peripheral
vasoconstriction immediately on the cessation of exercise (3,14,15,40).
Diagnose, Then Treat
To return to the specifics of this case report, two points are of note
regarding overall management. First, definitive treatment was not begun until
diagnosis was complete. An intravenous line was placed at the field aid
station only to provide intravenous access (not to treat a presumed
dehydration with rapid infusion of a large volume of fluids), and the blood
sodium concentration was measured as an immediate prio
