Hyponatremia in ultradistance triathletes

The incidence, risk factors, and clinical manifestations of hyponatremia in marathon runners

OBJECTIVE

To report on the incidence, identify the risk factors, and clarify the clinical manifestations of acute hyponatremia in marathon runners.

DESIGN

An observational and retrospective case-controlled series.

SETTING

The medical care area of the 2000 Houston Marathon.

PATIENTS

Marathon finishers treated in medical area receiving intravenous fluids (N=55), including a more detailed analysis of 39 runners completing a retrospective questionnaire.

MAIN OUTCOME MEASURES

Vital signs, serum electrolytes, and finish time were analyzed via ANOVA studies between all non-hyponatremic (NH: N=34)) and hyponatremic (H: N=21)) runners. Fluid intake, training variables, NSAID use, and Symptomatology were further analyzed to delineate all significant differences between groups.

RESULTS

There were no significant differences in vital signs, training variables, or NSAID use between H and NH groups, although there was a trend towards the less experienced runners presenting with lower post-race sodium levels. H runners had lower potassium [K] (p=.04), chloride [Cl] (p<.001), and blood urea nitrogen [BUN] (p=.004) levels than NH runners. There was a significant inverse linear relationship between both finish time versus [Na] (r2 =.51) and total amount of fluid ingested versus [Na] (r2 =.39). The total cups of water (p=.004), electrolyte/carbohydrate solution (p=.005) and total amount of fluid ingested (p<.001) were significantly higher in H compared to NH runners and the degree of hyponatremia was related in a dose dependent manner. Vomiting was observed more frequently in H than NH runners (p=.03).

CONCLUSION

21 runners presented to the medical area of the Houston Marathon with hyponatremia (.31% of entrants). Excessive fluid consumption and longer finishing times were the primary risk factors for developing this condition. Vomiting was the only clinical sign differentiating hyponatremia from other conditions that induce exercise-associated collapse.

Food intake and electrolyte status of ultramarathoners competing in extreme heat

OBJECTIVE

To relate changes in laboratory indices to dietary intake during extremely prolonged running and to determine if dietary intake influences the ability of runners to finish an 160 km trail race.

METHODS

We monitored intake and serum chemistries of 26 runners competing in an 160 km foot race in temperatures which peaked at 38 degrees C. Blood was drawn pre-, mid- and post-race. Dietary intake and incidence of gastrointestinal distress or changes in mental status were determined by interview with runners approximately every 13 km. Twenty-three runners completed at least 88 kms and, of these 23 runners, 13 finished 160 km in a mean time of 26.2 +/- 3.6 hours.

RESULTS

Finishers ingested nearly 30,000 J, 19.4 +/- 8.1 L of fluid and 16.4 +/- 9.5 g of sodium (Na). Sodium and fluid intake per hour was estimated to be 0.6 g/hour and 0.7 L/hour, respectively. Electrolyte intake during the first half of the race was similar between those that finished the race and those that did not. Finishers ingested fluid at a greater rate than non-finishers (p = 0.01) and tended to meet their caloric needs more closely than did non-finishers (p = 0.09). Body weight was unchanged over time (ANOVA, p = 0.52). Serum Na concentration tended to fall from 143 to 140 mEq/L during the race (p = 0.06), and was inversely correlated with weight loss (p = 0.009). Serum Na concentration was lower mid-race in runners experiencing changes in mental status than in runners without changes (p = 0.04). Fluid intake was inversely correlated with serum Na concentrations (p = 0.04). Most of the runners experienced nausea or vomiting; these symptoms were not related to serum sodium concentration. Hyponatremia (<135 mEq/L) was seen in one runner at 88 kms, but resolved by 160 km. Urinary sodium excretion decreased (p = 0.002) as serum aldosterone concentration increased pre- to post-race (p < 0.001). From start to finish of the race plasma volume increased by 12%.

CONCLUSIONS

Food and fluid was ingested at a greater rate than described previously. Runners consumed adequate fluid to maintain body weight although dietary sodium fell far short of the recommended 1 g/hour. The rate of fluid intake was greater in finishers than in non-finishers, and finishers tended to more nearly meet their energy needs. Maintenance of body mass despite large exercise energy expenditures in extreme heat is consistent with fluid overload during a running event lasting more than 24 hours in hot and humid conditions.

Oral salt supplementation during ultradistance exercise

OBJECTIVE

The objective of this study was to determine whether sodium supplementation 1) influences changes in body weight, serum sodium [Na], and plasma volume (PV), and 2) prevents hyponatremia in Ironman triathletes.

SETTING

The study was carried out at the South African Ironman triathlon.

PARTICIPANTS

Thirty-eight athletes competing in the triathlon were given salt tablets to ingest during the race. Data collected from these athletes [salt intake group (SI)] were compared with data from athletes not given salt [no salt group (NS)].

INTERVENTIONS

Salt tablets were given to the SI group to provide approximately 700 mg/h of sodium.

MAIN OUTCOME MEASUREMENTS

Serum sodium, hemoglobin, and hematocrit were measured at race registration and after the race. Weights were measured before and after the race. Members of SI were retrospectively matched to subjects in NS for 1) weight change and 2) pre-race [Na].

RESULTS

The SI group developed a 3.3-kg weight loss (p < 0.0001) and significantly increased their [Na] (delta[Na] 1.52 mmol/L; p = 0.005). When matched for weight change during the race, SI increased their [Na] compared with NS (mean 1.52 versus 0.04 mmol/L), but this did not reach statistical significance (p = 0.08). When matched for pre-race [Na], SI had a significantly smaller percent body weight loss than NS (-4.3% versus -5.1%; p = 0.04). There was no significant difference in the increase of [Na] in both groups (1.57 versus 0.84 mmol/L). PV increased equally in both groups. None of the subjects finished the race with [Na] < 135 mmol/L.

CONCLUSIONS

Sodium ingestion was associated with a decrease in the extent of weight loss during the race. There was no evidence that sodium ingestion significantly influenced changes in [Na] or PV more than fluid replacement alone in the Ironman triathletes in this study. Sodium supplementation was not necessary to prevent the development of hyponatremia in these athletes who lost weight, indicating that they had only partially replaced their fluid and other losses during the Ironman triathlon.

Biochemical changes as a result of prolonged strenuous exercise

OBJECTIVE

To briefly review biochemical changes that may result from prolonged strenuous exercise and to relate these changes to health risk.

METHODS

Medline and Sports Discus databases were searched for relevant articles. Additional articles were found using cross referencing and the authors' knowledge of the subject area.

RESULTS

Prolonged strenuous exercise may result in a series of biochemical changes that are of concern from a health point of view. Generally, these changes are benign, but some, especially hyponatraemia, are potentially life threatening occurrences.

CONCLUSION

Doctors and athletes should be aware of the potentially adverse biochemical changes, especially hyponatraemia, that may result from prolonged strenuous exercise.

Hyponatremia in runners requiring on-site medical treatment at a single marathon

STUDY OBJECTIVE

Literature reports indicate an increasing number of cases of hyponatremia in athletes participating in moderate endurance events such as standard marathons. In this study, we evaluated the incidence of hyponatremia in marathon finishers requiring medical treatment on-site and attempted to assess the contribution of fluid type ingested and nonsteroidal antiinflammatory drug (NSAID) use to the development of hyponatremia.

METHODS

We examined a prospective, convenience sample of runners requiring intravenous hydration at the final medical tent of a standard marathon course and a comparison group of finishers who did not require intravenous hydration. After giving informed consent, subjects had blood drawn and answered a questionnaire regarding fluid intake on the course and NSAID use before the race. Blood samples were analyzed on-site for serum sodium values as well as other hematologic parameters.

RESULTS

Fifty-one subjects requiring intravenous hydration as well as 11 subjects who did not were enrolled. Three subjects (5.6%; 95% CI, 0-11.9%; missing = 8) in the intravenous hydration group had serum sodium less than 130 mEq/L. None of the three runners suffered neurologic or pulmonary consequences and only one required overnight hospital admission for hydration. The small number of hyponatremic subjects precluded the analysis of the role of fluid type or NSAID use in the development of hyponatremia or the development of a model for prediction.

CONCLUSION

This study found a 5.6% incidence of hyponatremia in marathon runners requiring medical treatment.

Response to a fluid load in athletes with a history of exercise induced hyponatremia

PURPOSE

To determine whether athletes who had previously developed hyponatremia during an ultradistance triathlon show an impaired ability to excrete a large fluid load compared with athletes who had completed the same race without developing hyponatremia.

METHODS

Six athletes who had developed hyponatremia ([Na] < 135 mmol x L(-1)) in the 1997 Ironman Triathlon (study cases) were compared with six athletes who completed the same race without hyponatremia (controls). All participants consumed 3.4 L of water over 2 h at rest. Weight, urine output, urine electrolytes, serum [Na(+)], hemoglobin, and hematocrit were measured every 30 min. Changes in plasma volume and residual fluid volume in the gut were estimated from these data.

RESULTS

There were no significant differences between cases and controls in any parameters measured. Maximal rates of urine production (+/- SD) (1043 +/- 331 mL x h(-1) for cases, 878 +/- 168 mL x h(-1) for controls) were substantially behind the rate of fluid intake (1500 mL x h(-1)). Consequent to fluid retention, serum [Na(+)] fell progressively in both groups. Five cases and four controls developed hyponatremia. There was an inverse correlation between change in body weight and change in [Na(+)] (r = -0.67). Estimated changes in the intra- and extra-cellular fluid volumes could account for all the retained fluid, and there was little evidence for fluid accumulation in the bowel.

CONCLUSION

When evaluated at rest, there does not appear to be any unique pathophysiological characteristic that explains why some athletes develop hyponatremia in response to fluid overload during prolonged exercise. Rather, hyponatremia was induced with equal effect in both cases and controls, consequent to progressive fluid overload of all the body fluid compartments and without evidence for fluid retention in the small bowel.

Hyponatremia associated with exercise: risk factors and pathogenesis

Exercise-related hyponatremia is an infrequent but potentially life-threatening accompaniment of prolonged exercise. This condition results from sodium losses in sweat, excessive water intake, or both. We review the risk factors for development of this condition and discuss evidence that there is a population at increased risk of hyponatremia during prolonged exercise.

Exercise-associated hyponatremia in marathon runners: a two-year experience

This study was conducted to better define the pathophysiology, risk factors, and therapeutic approach to exercise-associated hyponatremia. Medical records from all participants in the 1998 Suzuki Rock 'N' Roll Marathon who presented to 14 Emergency Departments (EDs) were retrospectively reviewed to identify risk factors for the development of hyponatremia. Hyponatremic patients were compared to other runners with regard to race time and to other marathon participants seen in the ED with regard to gender, clinical signs of dehydration, and use of nonsteroidal anti-inflammatory drugs (NSAIDs). An original treatment algorithm incorporating the early use of hypertonic saline (HTS) was evaluated prospectively in our own ED for participants in the 1999 marathon to evaluate improvements in sodium correction rate and incidence of complications. A total of 26 patients from the 1998 and 1999 marathons were hyponatremic [serum sodium (SNa) < or =135 mEq/L] including 15 with severe hyponatremia (SNa < or = 125 mEq/L). Three developed seizures and required intubation and admission to an intensive care unit. Hyponatremic patients were more likely to be female, use NSAIDS, and have slower finishing times. Hyponatremic runners reported drinking "as much as possible" during and after the race and were less likely to have clinical signs of dehydration. An inverse relationship between initial SNa and time of presentation was observed, with late presentation predicting lower SNa values. The use of HTS in selected 1999 patients resulted in faster SNa correction times and fewer complications than observed for 1998 patients. It is concluded that the development of exercise-associated hyponatremia is associated with excessive fluid consumption during and after extreme athletic events. Additional risk factors include female gender, slower race times, and NSAID use. The use of HTS in selected patients seems to be safe and efficacious.

Changes in respiratory function during a wilderness multisport endurance competition

OBJECTIVE

To document the changes in respiratory function seen in competitors during a typical wilderness multisport endurance event.

METHODS

A prospective observational cohort study measuring forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) at baseline, midrace, and end of race in competitors in a 105-km ski/run/cycle/paddle race held midwinter in the mountains of Victoria, Australia.

RESULTS

Twenty-five adult subjects (22 men) between 20 and 42 years of age were studied. The mean decline in FEV1 was 15.1% (95% CI 10.3-19.8) and for FVC was 13.0% (95% CI 8.1-17.9). Fourteen (56%) of the 25 subjects had a >10% decline in FEV1 and FVC, and 7 (28%) of the 25 subjects had a >20% decline. In 9 control subjects, aged between 21 and 55 years, there was no significant change in FEV1 or FVC from prerace to end of race.

CONCLUSIONS

Significant declines in FEV1 and FVC are common during wilderness multisport endurance events. The focus of future research should be the etiology, which as yet remains speculative.

Factors affecting performance in an ultraendurance triathlon

In the recent past, researchers have found many key physiological variables that correlate highly with endurance performance. These include maximal oxygen uptake (VO2max), anaerobic threshold (AT), economy of motion and the fractional utilisation of oxygen uptake (VO2). However, beyond typical endurance events such as the marathon, termed 'ultraendurance' (i.e. >4 hours), performance becomes harder to predict. The ultraendurance triathlon (UET) is a 3-sport event consisting of a 3.8 km swim and a 180 km cycle, followed by a 42.2 km marathon run. It has been hypothesised that these triathletes ride at approximately their ventilatory threshold (Tvent) during the UET cycling phase. However, laboratory assessments of cycling time to exhaustion at a subject's AT peak at 255 minutes. This suggests that the AT is too great an intensity to be maintained during a UET, and that other factors cause detriments in prolonged performance. Potential defeating factors include the provision of fuels and fluids due to finite gastric emptying rates causing changes in substrate utilisation, as well as fluid and electrolyte imbalances. Thus, an optimum ultraendurance intensity that may be relative to the AT intensity is needed to establish ultraendurance intensity guidelines. This optimal UET intensity could be referred to as the ultraendurance threshold.

Exercise-associated hyponatremia: a review

This paper reviews the extensive literature on hyponatremia, a common and potentially serious complication of ultra-distance exercise. Fluid overload is the likely aetiology. Fluid intakes are typically high in athletes who develop hyponatremia, although hyponatremia can occur with relatively modest fluid intakes. The development of fluid overload and hyponatremia in the presence of a modest fluid intake raises the possibility that athletes with this condition may have an impaired renal capacity to excrete a fluid load. The bulk of evidence favours fluid retention in the extracellular space (dilutional hyponatremia) rather than fluid remaining unabsorbed in the intestine. Female gender is an important risk factor for the development of hyponatremia. Management and prevention of exercise-associated hyponatremia are discussed.

Fluid balance during and after an ironman triathlon

OBJECTIVE

To record weight changes, fluid intake and changes in serum sodium concentration in ultradistance triathletes.

DESIGN

Descriptive research.

SETTING

Ironman triathlon (3.8 km swim, 180 km cycle, 42.2 km run). Air temperature at 1200 h was 21 degrees C, (relative humidity 91%). Water temperature was 20.7 degrees C.

PARTICIPANTS

18 triathletes.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Subjects were weighed and had blood drawn for serum sodium concentration [Na], hemoglobin, and hematocrit, pre-race, post-race, and at 0800 h on the morning following the race ("recovery"); subjects were also weighed at transitions. Fluid intake during the race was estimated by athlete recall.

RESULTS

Median weight change during the race = -2.5 kg (p < 0.0006). Subjects lost weight during recovery (median = -1.0 kg) (p < 0.03). Median hourly fluid intake = 716 ml/h (range 421-970). Fluid intakes were higher on the bike than on the run (median 889 versus 632 ml/h, p = 0.03). Median calculated fluid losses cycling were 808 ml/h and running were 1,021 ml/h. No significant difference existed between pre-race and post-race [Na] (median 140 versus 138 mmol/L) or between post-race and recovery [Na] (median 138 versus 137 mmol/L). Plasma volume increased during the race, median + 10.8% (p = 0.0005). There was an inverse relationship between change in [Na] pre-race to post-race and relative weight change (r = -0.68, p = 0.0029). Five subjects developed hyponatremia ([Na] 128-133 mmol/L).

CONCLUSIONS

Athletes lose 2.5 kg of weight during an ultradistance triathlon. most likely from sources other than fluid loss. Fluid intakes during this event are more modest than that recommended for shorter duration exercise. Plasma volume increases during the ultradistance triathlon. Subjects who developed hyponatremia had evidence of fluid overload despite modest fluid intakes.

Joint Position Statement: nutrition and athletic performance. American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada

It is the position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition. These organizations recommend appropriate selection of food and fluids, timing of intake, and supplement choices for optimal health and exercise performance. This position paper reviews the current scientific data related to the energy needs of athletes, assessment of body composition, strategies for weight change, the nutrient and fluid needs of athletes, special nutrient needs during training, the use of supplements and nutritional ergogenic aids, and the nutrition recommendations for vegetarian athletes. During times of high physical activity, energy and macronutrient needs-especially carbohydrate and protein intake-must be met in order to maintain body weight, replenish glycogen stores, and provide adequate protein for building and repair of tissue. Fat intake should be adequate to provide the essential fatty acids and fat-soluble vitamins, as well as to help provide adequate energy for weight maintenance. Overall, diets should provide moderate amounts of energy from fat (20% to 25% of energy); however, there appears to be no health or performance benefit to consuming a diet containing less than 15% of energy from fat. Body weight and composition can affect exercise performance, but should not be used as the sole criterion for sports performance; daily weigh-ins are discouraged. Consuming adequate food and fluid before, during, and after exercise can help maintain blood glucose during exercise, maximize exercise performance, and improve recovery time. Athletes should be well-hydrated before beginning to exercise; athletes should also drink enough fluid during and after exercise to balance fluid losses. Consumption of sport drinks containing carbohydrates and electrolytes during exercise will provide fuel for the muscles, help maintain blood glucose and the thirst mechanism, and decrease the risk of dehydration or hyponatremia. Athletes will not need vitamin and mineral supplements if adequate energy to maintain body weight is consumed from a variety of foods. However, supplements may be required by athletes who restrict energy intake, use severe weight-loss practices, eliminate one or more food groups from their diet, or consume high-carbohydrate diets with low micronutrient density. Nutritional ergogenic aids should be used with caution, and only after careful evaluation of the product for safety, efficacy, potency, and whether or not it is a banned or illegal substance. Nutrition advice, by a qualified nutrition expert, should only be provided after carefully reviewing the athlete's health, diet, supplement and drug use, and energy requirements.

Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance

It is the position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition. These organizations recommend appropriate selection of food and fluids, timing of intake, and supplement choices for optimal health and exercise performance. This position paper reviews the current scientific data related to the energy needs of athletes, assessment of body composition, strategies for weight change, the nutrient and fluid needs of athletes, special nutrient needs during training, the use of supplements and nutritional ergogenic aids, and the nutrition recommendations for vegetarian athletes. During times of high physical activity, energy and macronutrient needs--especially carbohydrate and protein intake--must be met in order to maintain body weight, replenish glycogen stores, and provide adequate protein for building and repair of tissue. Fat intake should be adequate to provide the essential fatty acids and fat-soluble vitamins, as well as to help provide adequate energy for weight maintenance. Overall, diets should provide moderate amounts of energy from fat (20% to 25% of energy); however, there appears to be no health or performance benefit to consuming a diet containing less than 15% of energy from fat. Body weight and composition can affect exercise performance, but should not be used as the sole criterion for sports performance; daily weigh-ins are discouraged. Consuming adequate food and fluid before, during, and after exercise can help maintain blood glucose during exercise, maximize exercise performance, and improve recovery time. Athletes should be well-hydrated before beginning to exercise; athletes should also drink enough fluid during and after exercise to balance fluid losses. Consumption of sport drinks containing carbohydrates and electrolytes during exercise will provide fuel for the muscles, help maintain blood glucose and the thirst mechanism, and decrease the risk of dehydration or hyponatremia. Athletes will not need vitamin and mineral supplements if adequate energy to maintain body weight is consumed from a variety of foods. However, supplements may be required by athletes who restrict energy intake, use severe weight-loss practices, eliminate one or more food groups from their diet, or consume high-carbohydrate diets with low micronutrient density. Nutritional ergogenic aids should be used with caution, and only after careful evaluation of the product for safety, efficacy, potency, and whether or not it is a banned or illegal substance. Nutrition advice, by a qualified nutrition expert, should only be provided after carefully reviewing the athlete's health, diet, supplement and drug use, and energy requirements.

Exercise-induced hyponatremia in ultradistance triathletes is caused by inappropriate fluid retention

OBJECTIVE

To study fluid and sodium balance during overnight recovery following an ultradistance triathlon in hyponatremic athletes compared with normonatremic controls. CASE CONTROL STUDY: Prospective descriptive study.

SETTING

1997 New Zealand Ironman Triathlon (3.8 Km swim, 180 Km cycle, 42.2 Km run).

PARTICIPANTS

Seven athletes ("subjects") hospitalized with hyponatremia (median sodium [Na] = 128 mmol L(-1)). Data were compared with measurements from 11 normonatremic race finishers ("controls") (median sodium = 141 mmol L(-1)).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Athletes were weighed prior to, immediately after, and on the morning after, the race. Blood was drawn for sodium, hemoglobin, and hematocrit immediately after the race and the following morning. Plasma concentrations of arginine-vasopressin (AVP) were also measured post race.

RESULTS

Subjects were significantly smaller than controls (62.5 vs. 72.0 Kg) and lost less weight during the race than controls (median -0.5% vs. -3.9%, p = 0.002) but more weight than controls during recovery (-4.4% vs. -0.8%, p 0.002). Subjects excreted a median fluid excess during recovery (1,346 ml): controls had a median fluid deficit (521 ml) (p = 0.009). Estimated median sodium deficit was the same in subjects and controls (88 vs. 38 mmol L(-1), p = 0.25). Median AVP was significantly lower in subjects than in controls. Plasma volume fell during recovery in subjects (-5.9%, p = 0.016) but rose in controls (0.76%, p = NS).

CONCLUSIONS

Triathletes with symptomatic hyponatremia following very prolonged exercise have abnormal fluid retention including an increased extracellular volume, but without evidence for large sodium losses. Such fluid retention is not associated with elevated plasma AVP concentrations.

Seizure after exercise in the heat: recognizing life-threatening hyponatremia

A 20-year-old military recruit suffered a generalized tonic-clonic seizure following 9 hours of moderate activity in a hot, humid environment. He had drunk at least 5.8 L of plain water before the seizure, and laboratory studies revealed that his serum sodium concentration was 113 mmol/L. Overconsumption of fluids during exercise may precipitate acute hyponatremia, a potentially life-threatening medical condition. Prompt correction of serum sodium in acute exertional hyponatremia is important to reduce the risk of permanent neurologic sequelae or death. Recommendations for prevention include ingesting the correct amount of fluid for the activity (the most important method) and consuming adequate salt through diet or beverage.

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

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.

A guide to treating ironman triathletes at the finish line

The unique physiologic characteristics of an ironman triathlete present challenges to physicians covering ultraendurance events. Cardiovascular emergencies at the finish line are rare. Occult blood in postrace urine is common but rarely of clinical significance. Medical volunteers must distinguish between signs of dehydration, heatstroke, hyponatremia, and postural hypotension and offer appropriate treatment. Recumbent positioning and oral hydration often suffice to stabilize a conscious collapsed athlete, but serious abnormalities require swift evacuation to a hospital.

Hyponatremia, cerebral edema, and noncardiogenic pulmonary edema in marathon runners

BACKGROUND

Noncardiogenic pulmonary edema is often associated with increased intracranial pressure and can be the initial manifestation of hyponatremic encephalopathy. Marathon runners tend to develop conditions that lead to hyponatremia.

OBJECTIVE

To describe the development and treatment of noncardiogenic pulmonary edema in marathon runners that was associated with hyponatremic encephalopathy.

DESIGN

Case series.

SETTING

One university hospital and two community hospitals.

PATIENTS

Seven healthy marathon runners who had a history of nonsteroidal anti-inflammatory drug use. The runners collapsed after competing in a marathon and were hospitalized with pulmonary edema.

MEASUREMENTS

Plasma sodium levels, chest radiograph, electrocardiogram, cardiac enzyme levels, and magnetic resonance imaging or computed tomographic scans of the brain.

RESULTS

Patients had nausea, emesis, and obtundation. The mean (+/-SD) plasma sodium level was 121 +/- 3 mmol/L, and oxygen saturation was less than 70%. Electrocardiograms and echocardiograms were normal. Chest radiographs showed pulmonary edema with a normal heart. Creatine phosphokinase-MB bands, troponin levels, and pulmonary wedge pressure were not elevated. Scanning of the brain showed cerebral edema. All patients were intubated and mechanically ventilated. Treatment with intravenous NaCl, 514 mmol/L, increased plasma sodium levels by 10 mmol/L in 12 hours. Pulmonary and cerebral edema resolved as the sodium level increased. One patient had unsuspected hyponatremic encephalopathy and died of cardiopulmonary arrest caused by brainstem herniation. All six treated patients recovered and were well after 1 year of follow-up.

CONCLUSIONS

In healthy marathon runners, noncardiogenic pulmonary edema can be associated with hyponatremic encephalopathy. The condition may be fatal if undiagnosed and can be successfully treated with hypertonic NaCl.

A prospective study of exercise-associated hyponatremia in two ultradistance triathletes

OBJECTIVE

To study fluid and sodium balance in two ultradistance triathletes.

DESIGN

Prospective case study.

SETTING

An ultradistance triathlon (3.8 km swim, 180 km cycle, 42.2 km run), and during overnight recovery. Ambient air temperature at 12:00 p.m. race day was 21 degrees C, with a relative humidity of 91%. Water temperature was 20.7 degrees C.

SUBJECTS

Two female ultradistance triathletes, ages 30 and 39 years, who were participating in a larger study investigating weight and electrolyte changes in the Ironman triathlon.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Subjects were weighed and had blood drawn for serum sodium concentration, hemoglobin, hematocrit, arginine vasopressin, and aldosterone concentration prior to and after the race, and at 8:00 a.m. the following morning. Sodium and fluid intake and urinary output were measured during recovery.

RESULTS

Both subjects developed mild hyponatremia (Na 131 and 130 mmol/L) during the race, with a weight gain (0.5 and 1.5 kg). Neither subject had large sodium losses (24 mmol and 20 mmol). Fluid consumption was 733 ml/h and 764 ml/h. Plasma volume increased during the race (25 and 16%). Arginine vasopressin (AVP) levels were not elevated in either subject (1.2 and 1.9 pmol/L). Both subjects demonstrated a water excess during the race (1.5 and 2.5 L), and lost weight during recovery (2.0 and 4.5 kg).

CONCLUSIONS

Hyponatremia resulted from fluid retention in the extracellular space, without evidence of large sodium losses or inappropriate AVP secretion.

Diagnosis and prevention of hyponatremia at an ultradistance triathlon

OBJECTIVE

To evaluate a method of medical care at an ultradistance triathlon, with the aim of reducing the incidence of hyponatremia.

DESIGN

Descriptive research.

SETTING

New Zealand Ironman triathlon (3.8 km swim, 180 km cycle, 42.2 km run).

PARTICIPANTS

117 of 134 athletes seeking medical care after the triathlon (involving 650 race starters).

INTERVENTIONS

A prerace education program on appropriate fluid intake was undertaken. The number of support stations was decreased to reduce the availability of fluid. A body weight measurement before the race was introduced as a compulsory requirement, so that weight change during the race could be included in the triage assessment. An on-site laboratory was established within the race medical tent.

MAIN OUTCOME MEASURES

Numbers of athletes and diagnoses, including the incidence of symptomatic hyponatremia (defined as symptoms of hyponatremia in association with a pretreatment plasma sodium concentration [Na] < 135 mmol/L); weight changes; and changes in [Na].

RESULTS

The common diagnoses in the 117 athletes receiving attention were exercise-associated collapse (27%), musculoskeletal complaints (26%), and dehydration (12%). There was a significant reduction in the number of athletes receiving medical care for hyponatremia, from 25 of the 114 athletes who received care in 1997 (3.8% of race starters) to 4 of the 117 athletes who received care in 1998 (0.6% of race starters). Mean weight change among athletes in the 1998 race was -3.1 kg, compared with -2.6 kg in 1997.

CONCLUSION

A preventive strategy to decrease the incidence of hyponatremia, including education on fluid intake and appropriate placement of support stations, was associated with a decrease in the incidence of symptomatic hyponatremia.

Hyponatremia and seizures in an ultradistance triathlete

Hyponatremia is being increasingly recognized as a complication of participation in ultra-endurance sports. Reported is the case of an Ironman triathlete who collapsed at the end of the race, having gained 5% in body weight. His serum sodium concentration at the finish was 116 mmol/L. After an Intensive Care Unit course complicated by recurrent seizures, he eventually made a complete neurologic recovery. The pathogenesis of hyponatremia and its management in such cases is discussed.