Exertional Heat Illness

Response to Heat Stress Thermoregulation is very efficient –1*C change in core temperature for every 25* to 30*C in ambient temperature For every 0.6*C increase in core temperature there is a 10% increase in basal metabolic rate Hypothalamus controls thermoregulation –Ability to dissipate heat to control your core temperature

Thermoregulation Four processes at work –Conduction - transfer –Convection - current –Radiation - dissipation –Evaporation - sweat

Physiology Heat illness occurs when the heat generated by the body and its environment overwhelms its regulatory systems

Role of the GI & Immune Systems In order to bring more blood flow to the skin to dissipate heat, the body compensates by shunting blood away from the gut Epithelial damage causes release of endotoxins (ACSM 2003) Exaggerated immune response –Heat shock proteins generated –Release of INF, TNF, IL1, IL6, IL2r

Heat Illness Spectrum Heat cramps Heat syncope Heat exhaustion Heat stroke Exertional Rhabdomyolysis

Definitions Heat cramps - cramping of muscles –Profuse sweating –Etiology: sodium depletion (?controversial?) Heat Exhaustion –Heat cramps, sweating, nausea, vomiting, headache, malaise, lightheadedness, confusion, oliguria, poor coordination –Sodium depletion or water depletion Heat Syncope –Fainting –Inability to maintain cardiac output from peripheral blood vessel dilation

Definitions Heatstroke - core body temp > 40*C (104*F) –GI and CNS effects during or after exercise –Continue to perspire –Nausea, vomiting, headache, hypotension, confusion, irritability, delirium, seizure –Complications: rhabdomyolysis, shock, DIC, cerebral edema, death

Heat Illness Spectrum Heat cramps Heat syncope Heat exhaustion Heat stroke Exertional Rhabdomyolysis

Injury to skeletal muscle resulting in lysis of cell with subsequent leakage of contents into plasma Known to be a complication of vigorous exercise What predisposes an athlete to develop this condition?

Exertional Rhabdomyolysis Predisposing factors –Overweight or unfit –Fever, diarrhea viremia, or heat stress –Drugs –Novel overexertion –Inherited muscle enzymopathy –Sickle Cell Trait??

Exertional Rhabdomyolysis Novel Exertion ->Too much, too fast –Rhabdo in Football two a days GG Ehlers et al, Journal of Athletic Training 2002;37:151-6 –Muscle Meltdown Medical Journal of Australia mile fun run, hot(88F) & hilly Rhabdo:hind quarter amputation

Exertional Rhabdomyolysis Muscle enzymopathy –Inherited disorders implicated in recurrent exertional rhabdomyolysis or ongoing rhabdomyolysis McArdles or Myotonic dystropy Treem 1987, Argov and Dimauro 1983

Exertional Rhabdomyolysis Sickle Cell Trait –1 in 12 African Americans –Generally benign with no anemia –Cramping & hyperventilation due to lactic acidosis –Sickling collapse in all-out exertion Over 80 cases; 10 deaths in college football –Unlike heatstroke: Collapse early in 1 st few minutes running Athlete can talk after they hit the ground

Exertional Rhabdomyolysis Recognition –> 5 times the normal serum CK level –Absolute height does not = severity –Levels hours –Failure to decline indicates and ongoing process –Myoglobinuria increases risk of ARF Urine dip: positive for blood Urine micro: no red cells seen

Exertional Rhabdomyolysis Treatment –Maintain vital signs –Get to ER fast –IV fluids to maintain urine flow –Can give 50% of sodium as bicarb Corrects acidosis, controls hyperkalemia, makes myoglobin more soluble –Consider mannitol and furosemide –Dialyze as necessary for ARF –Hospital at >50,000 CK, increased creatinine ?or myoglobinuria present –RTP at serum CK of 2-3,000 if asymptomatic

Heat Illness Spectrum Heat cramps Heat syncope Heat exhaustion Heat stroke Exertional Rhabdomyolysis

Prevention in Athletic Competition What factors increase the risk? Is water enough? What is safe for competition? Are there different consideration for different athletes? Are there different concerns for different sports?

Risk Factors for Heat Illness Drugs: alcohol, ephedra Poor nutrition: eating disorders Poor hydration or dehydration Chronic diseases: Diabetes, HTN, sweat gland dysfunction Acute illness: URI, gastroenteritis, sunburn

Dehydration Debate Is water enough to overcome risk factors? –Noakes: argues that people still develop this condition even why they exercise in a fully hydrated state –ACSM: ml of water or sports drink every 15 minutes Avoid preoccupation with H2O intake

What is safe for competition? More emphasis on acclimatization Work-rest cycles during different heat loads Monitor daily weights in an athlete When should an event or practice be cancelled?

Are there different considerations for different athletes? Sickle cell trait –Should we be screening for the condition? –Precautions No one day fitness test No sprinting >600m No timed miles No stadium steps to exhaustion Regular fluids Stop at first cramp

Are there different concerns for different sports? Football –Full practice gear –New NCAA guidelines

Final Points Maintain a high index of suspicion in an athlete playing under extreme conditions Appropriate monitoring of athletes by medical personnel is important in preventing heat illness –Daily weights –Consider risk of sickle cell trait Water is not the only answer Slower is better than dead –Graded training programs –Work- Rest cycles