Hyponatremia in Distance Athletes: Pulling the IV on the 'Dehydration Myth'

Management of Suspected Fluid Balance Issues in Participants of Wilderness Endurance Events

Dehydration and exercise-associated hyponatremia (EAH) are both relatively common conditions during wilderness endurance events. Whereas dehydration is treated with fluids, EAH is appropriately managed with fluid restriction and a sodium bolus but can worsen with isotonic or hypotonic fluids. Therefore, caution is recommended in the provision of postevent rehydration in environments where EAH is a potential consideration because accurate field assessment of hydration status can be challenging, and measurement of blood sodium concentration is rarely possible in the wilderness. Dehydration management with oral rehydration is generally adequate and preferred to intravenous rehydration, which should be reserved for athletes with sustained orthostasis or inability to tolerate oral fluid ingestion after some rest. In situations where intravenous hydration is initiated without known blood sodium concentration or hydration status, an intravenous concentrated sodium solution should be available in the event of acute neurological deterioration consistent with the development of EAH encephalopathy.

Injuries and Health Considerations in Ultramarathon Runners

Ultramarathon runners are a relatively small and unique group of distance runners with somewhat different medical issues than other distance runners. This article outlines some of those differences so that clinicians caring for these runners in the clinic or at competitions might be better prepared.

Managing collapsed or seriously ill participants of ultra-endurance events in remote environments

Increasing participation in ultramarathons and other ultra-endurance events amplifies the potential for serious medical issues during and immediately following these competitions. Since these events are often located in remote settings where access may be extremely limited; the diagnostic capabilities, treatment options, and expectations of medical care may differ from those of urban events. This work outlines a process for assessment and treatment of athletes presenting for medical attention in remote environments, with a focus on potentially serious conditions such as major trauma, acute coronary syndrome, exertional heat stroke, hypothermia, hypoglycemia, exercise-associated hyponatremic encephalopathy, severe dehydration, altitude illness, envenomation, anaphylaxis, and bronchospasm. A list of suggested medical supplies is provided and discussed. But, given that diagnostic and treatment options may be extremely limited in remote settings, it is important for medical providers to understand how to assess and manage the most common serious medical issues with limited resources, and to be prepared to make presumptive diagnoses when necessary.

Characterization of medical care at the 161-km Western States Endurance Run

OBJECTIVE

To examine the medical care at a highly competitive 161-km mountain ultramarathon.

METHODS

Encounter forms from the 2010 through 2013 Western States Endurance Run were analyzed for trends in consultation and use of intravenous fluids.

RESULTS

A total of 63 consultations (8.2% of starters) were documented in 2012 and 2013, of which 10% involved noncompetitors. Most (77%) of the consultations with competitors occurred on the course rather than at the finish line, and were generally during the middle third of the race. Of the on-course consultations, the runner was able to continue the race 55% of the time, and 75% of those who continued after consultation ultimately finished the race. Relative number of consultations did not differ among competitors within 10-year age groups (P = .7) or between men and women (P = .2). Overall, consultations for medical issues were predominant, and nausea and vomiting accounted for the single highest reason for consultation (24%). Although there was an overall decrease in finish line consultations and intravenous fluid use from 2010 through 2013 (P < .0001 for both) that was independent of maximum ambient temperature (P = .3 and P = .4), the proportion of those being treated with intravenous fluids relative to those receiving consultation at the finish line was directly related to maximum ambient temperature (r = .93, P = .037). Both 2012 and 2013 had a single medical emergency that required emergency evacuation.

CONCLUSIONS

This work demonstrates that the medical needs in a 161-km ultramarathon are mostly for minor issues. However, occasional serious issues arise that warrant a well-organized medical system.

Drinking guidelines for exercise: what evidence is there that athletes should drink "as much as tolerable", "to replace the weight lost during exercise" or "ad libitum"?

The most recent (1996) drinking guidelines of the American College of Sports Medicine (ACSM) propose that athletes should drink "as much as tolerable" during exercise. Since some individuals can tolerate rates of free water ingestion that exceed their rates of free water loss during exercise, this advice has caused some to overdrink leading to water retention, weight gain and, in a few, death from exercise-associated hyponatraemic encephalopathy. The new drinking guidelines of the International Olympic Committee (IOC), recently re-published in this Journal, continue to argue that athletes must drink enough to replace all their weight lost during exercise and to ingest sodium chloride since sodium is "the electrolyte most critical to performance and health". In this rebuttal to that Consensus Document, I argue that these new guidelines, like their predecessors, lack an adequate, scientifically proven evidence base. Nor have they been properly evaluated in appropriately controlled, randomized, prospective clinical trials. In particular, these new guidelines provide erroneous recommendations on five topics. If novel universal guidelines for fluid ingestion during exercise are to be promulgated by important international bodies including the IOC, they should first be properly evaluated in appropriately controlled, randomized, prospective clinical trials conducted under environmental and other conditions that match those found in "out-of-doors" exercise. This, and the potential influence of commercial interests on scientific independence and objectivity, are the two most important lessons to be learned from the premature adoption of those 1996 ACSM drinking guidelines that are not evidence-based. These concerns need to be addressed before the novel IOC guidelines are accepted uncritically. Otherwise the predictable consequences of the premature adoption of the 1996 ACSM guidelines will be repeated.

Intravenous Fluids Post Marathon

The medical management of marathon casualties involves several potential treatment pathways. It is helpful to develop defined treatment protocols for commonly experienced conditions addressing intervention selection criteria and monitoring response to therapy. Providing intravenous (IV) fluids for runners post marathon should be scrutinised based upon the effectiveness and safety of the intervention. Commonly agreed upon indications for IV fluids are replacement for clinical dehydration and support for unconscious, hypoglycaemic or persistently hypotensive athletes. Most clinicians recommend serum sodium evaluation prior to IV initiation. IV fluid use in athletes with persistent nausea, generalised muscle cramping and to augment whole-body cooling is commonly deployed despite the paucity of supporting scientific evidence and remains an area for further study. Marathon medical support leaders should develop and disseminate guidelines to direct the administration of IV fluids at their medical aid stations.

The downed runner

Race coverage can be a rewarding experience for the sports medicine clinician. Several conditions are likely to present to the medical tent, and accurate diagnosis is critical to proper treatment. An algorithm approach as outlined in this article can provide a starting point for the assessment of the downed runner. Recognition of the primary causes for collapse can help to instigate the correct treatment approach. A proper history and physical examination often can help to differentiate significant cardiac events from the more innocuous EAC. Furthermore, avoiding immediate i.v. fluids in the downed runner is prudent, at least until an appropriate diagnosis is made. This will help to prevent iatrogenic hyponatremia. In sum, proper preparation and knowledge of the ailments that affect long distance runners will help to maintain an effective medical tent on race day.

Exercise-Associated Hyponatraemia

In 1958, Edelman and colleagues empirically showed plasma sodium concentration ([Na+]p) to be primarily a function of the sum of exchangeable sodium and potassium (E) divided by total body water (TBW). Based on Edelman's equation, Nguyen and Kurtz derived an equation to show how [Na+]p changes as a function of TBW, change in TBW (DeltaTBW), and change in the sum of exchangeable sodium and potassium (DeltaE). Using the Nguyen-Kurtz equation, the present study examines the sensitivity of [Na+]p to these parameters: [Na+]p is very sensitive to DeltaTBW and moderately sensitive to DeltaE, and is modulated by TBW. For example, for a person with 50 L TBW, a net increase of 1L water lowers [Na+]p by 3.2 mEq/L, but for a person with 25 L TBW it lowers [Na+]p by 6.3 mEq/L (assuming initial [Na+]p is 140 mEq/L). In each case, a loss of 159 mEq of sodium plus potassium (roughly equivalent to 1.5 teaspoons of table salt) would be required to produce the same effect as the net increase of 1 L water. The present review demonstrates why fluid overload predominates over electrolyte loss in the aetiology of exercise-associated hyponatraemia (EAH), and why the excretion of electrolyte-dilute urine is highly effective in correcting EAH (nonetheless, loss of sodium and potassium is significant in long events in warm weather). Sports drinks will, if overconsumed, result in hyponatraemia. Administration of a sports drink to an athlete with fluid overload hyponatraemia further lowers [Na+]p and increases fluid overload. Administration of either a sports drink or normal (0.9%) saline increases fluid overload.

Recommendations for treatment of hyponatraemia at endurance events

This review focuses on possible pathophysiology of exercise-associated hyponatraemia and its implication on evaluation and treatment of collapsed athletes during endurance events. Rehydration guidelines and field care have traditionally been based on the belief that endurance events create a state of significant fluid deficit in athletes, which must be corrected by liberal hydration. Beliefs in the necessity of liberal hydration may have contributed to cases of hyponatraemia. Assumptions that fluid loss accounts for the entire weight loss during exercise and that fluid ingestion is the only source of water gain during exercise may lead to an overestimation of the degree of volume depletion and the amount of fluid needed for replacement. Increasing evidence suggests that hyponatraemic athletes are fluid overloaded; ingestion of large amount of hypotonic fluid in combination with inappropriate or inadequate physiological responses leads to excessive retention of free fluid. Risk factors include hot weather, female sex, slower finishing time, and possibly the use of nonsteroidal anti-inflammatory medications. Symptoms of hyponatraemia can be subtle and can mimic those of other exercise-related illnesses, thereby complicating its diagnosis and leading to possible inappropriate treatment. Most athletes who collapse at the finish line experience exercise-associated collapse, a benign and transient form of postural hypotension that can be treated simply by continued ambulation after finishing or elevation of legs while in a supine position for those who cannot walk. Care providers should consider the use of intravenous hydration with normal saline carefully since it is not needed by most collapsed athletes and may worsen the condition of patients with unsuspected hyponatraemia. Historic information and clinical signs of volume depletion should be elicited prior to its use. Most hyponatraemic athletes will recover uneventfully with careful observation while awaiting spontaneous diuresis. Use of hypertonic saline should be reserved for patients with severe symptoms. Moderate consumption of carbohydrate-electrolyte solution during exercise may allow the maintenance of adequate hydration and the prevention of hyponatraemia.

Fluid replacement during marathon running

During endurance exercise, about 75% of the energy produced from metabolism is in the form of heat, which cannot accumulate. The remaining 25% of energy available can be used for movement. As running pace increases, the rate of heat production increases. Also, the larger one's body mass, the greater the heat production at a particular pace. Sweat evaporation provides the primary cooling mechanism for the body, and for this reason athletes are encouraged to drink fluids to ensure continued fluid availability for evaporation and circulatory flow to the tissues. Elite level runners could be in danger of heat illness if they race too quickly in hot/humid conditions and may collapse at the end of their event. Most marathon races are scheduled at cooler times of the year or day, however, so that heat loss to the environment is adequate. Typically, this postrace collapse is due simply to postural hypotension from decreased skeletal muscle massage of the venous return circulation to the heart on stopping. Elite athletes manage adequate hydration by ingesting about 200-800 mL/hour, and such collapse is rare. Athletes "back in the pack" are moving at a much slower pace, however, with heat accumulation unlikely and drinking much easier to manage. They are often urged to drink "as much as tolerable," ostensibly to prevent dehydration from their hours out on the race course. Excessive drinking among these participants can lead to hyponatremia severe enough to cause fatalities. A more reasonable approach is to urge these participants not to drink as much as possible but to drink ad libitum (according to the dictates of thirst) no more than 400-800 mL/hour.

Weight changes, sodium levels, and performance in the South African Ironman Triathlon

OBJECTIVE

To establish relationships between body weight changes and serum sodium during and after an Ironman Triathlon, and postrace fluid status and rectal temperature, including the incidence of hyponatremia.

DESIGN

Descriptive research.

SETTING

The 2000 South African Ironman Triathlon, in which each athlete swam 3.8 km, cycled 180 km, and ran 42.2 km.

PARTICIPANTS

All entrants in the race were invited to participate in the study.

METHODS

Athletes were weighed at registration, immediately prerace, immediately postrace, and 12 hours later. Blood samples were drawn at registration and immediately postrace. Rectal temperatures were measured postrace.

RESULTS

Starting body weight was significantly related to total finishing time (r = 0.27) and to cycling (r = 0.20) and running (r = 0.28) time. Body weight decreased significantly (p < 0.0001) during the race and had not returned to prerace values 12 hours later (p < 0.0001). Percentage change in body weight was unrelated to postrace rectal temperatures and inversely related to the postrace serum sodium concentrations (r = -0.45). Postrace serum sodium concentrations fell within a normal distribution (141.8 +/- 3.1 mmol.L(-1), mean +/- SD) and were negatively correlated to overall triathlon time (r = -0.22). Three sodium values (0.6%) were below 135 mmol.L(-1). Percentage change in body weight was unrelated to time in the marathon leg.

CONCLUSIONS

Percentage change in body weight was linearly related to postrace serum sodium concentrations but unrelated to postrace rectal temperature or performance in the marathon. There was no evidence that in this study, more severe levels of weight loss or dehydration were related to either higher body temperatures or impaired performance.

The collapsed athlete

Athletic collapse is rare, but personnel caring for athletes at sporting events must be prepared for it. Most cases are nonfatal and, with proper management, can have good outcomes. Medical personnel should expect the typical causes of athletic collapse that occur at the events they are covering, but rare causes should also be anticipated.