Heat-Related Illness

David E. Olson, M.D. U of MN

TPC 2013 Miami

Agenda

• Physiology • Predisposition • Acclimatization • Heat related illnesses • Prevention

Physiology

• We are homeothermic – Regulate or own warm-blooded body temp

• Maintain “normal” range – 96.4 - 99.1 degrees F

Physiology

• Body’s ability to regulate core temp depends on internal and external factors

• How heat is produced: – Basal Metabolism

• Increases with increased core temp – 10 percent elevation in BMR per 0.6 degree C rise

– Exercise • Heat production 15-20x greater during exercise

– External Heat Sources

Physiology • Hypothalamus is critical in heat physiology (the

thermoregulation center) – Helps to control:

• Cutaneous blood flow (sympathetic) • Sweat glands (parasympathetic) • Cardiac output • Stroke volume

• Usually efficient in a healthy individual

– 1 degree C change in core temp for every 25-30 degree C change in ambient temp

• Chronic Disease/Meds/Poor Conditioning are risks for impaired control

Physiology

• How do athletes control heat? – Conduction – Convection – Radiation – Evaporation

• Work simultaneously

Conduction

• Occurs when the body comes in contact with something cooler

• Heat is transferred to the cooler object

Convection

• When cool air passes over the skin • Lifts heat away • Windy days • Fans

Radiation

• Heat released from the body directly into the environment

Evaporation

• Sweat on the skin taking heat away from the body

• **The primary thermoregulatory mechanism when the ambient temp is above 20 degree C (68 degrees F)

• Need to be hydrated to maximize this! • Incorporates processes of convection and

radiation

Physiology

• Assuming healthy athlete – These 4 mechanisms are dependent on

gradients of temp and moisture – As temp and humidity increase these are less

efficient – Evaporation becomes the key in hot

conditions!! • Any process that limits this causes issues

– Dehydration – Clothing

Risk Factors Endogenous

• Acute Illness (fever, gastroenteritis) • Chronic Illness (DM, CAD) • Sleep deprivation • Obesity • Eating disorders • Poor acclimatization • Inexperience • Motivation • Dehydration

– 1% decrease in body weight can increase risk of heat illness • Sickle Cell Trait • History of Heat Illness • Extremes of age (Elderly and Kiddos)

Risk Factors Exogenous

• Alcohol • Stimulants • Drugs of abuse • Meds

– Anticholinergics, antihistamines, beta blocker, diuretics, neuroleptics, benzos, calcium channel blockers, tricyclic antidepressants and stimulants

• Environment – Temperature, humidity

Children and Heat

• Special cases – Produce more metabolic heat proportionately – Core temp rises faster when dehydrated – Smaller organ systems – Less efficient with heat dissipation

Acclimatization • Physiological adaptation to hot, humid

environment • 7-10 days • Changes:

– Increase in blood volume (10-25%) – Increase in stroke volume – Decrease in resting HR – Sweat changes (earlier, more, dilute) – Skin vasodilates earlier

Heat Illness

• A spectrum of issues can occur • Can occur anytime • More likely in hot/humid weather • Remember:

– Heat production is 15-20 greater with exercise!!!

• 240 deaths annually • 3rd leading cause of death among US high

school athletes

Heat Illness Monitoring

• Patient monitoring – Rectal temperatures – Pill monitoring devices

Heat Index Air Temp/Humidity

Heat Illness Monitoring Major Risk in Heat Illness is high ambient temp

with combined high level humidity • Wet Bulb Globe Temperature

– Helps quantify the risk of heat injury

• Takes in to account – Ambient temp – Radiant heat – Humidity

• WBGT=0.7WB + 0.2BG + 0.1DG

WBGT • WB

– Thermometer with bulb covered with a wet cotton wick

– Simulates the evaporation of sweat – Integrates effects of humidity, wind and rad

• BG – 6 inch black globe – Radiation and wind

• DG – Shielded thermometer from radiation – What is usually reported as the temp

Wet Bulb Globe Temperature

Different Classifications of WBGT: Military ACSM Green/Low 80-84 <65 Yellow/Medium 85-88 65-73 Red/High 88-90 73-82 Black/Very High >90 >82

WBGT Devices

Heat Illness Spectrum

• Heat Edema • Heat Syncope • Heat Cramps • Heat Exhaustion • Heat Stroke

Heat Edema

• Mild • Transient peripheral

vasodilation • Orthostatic pooling • Mild dependent

edema on exam

Heat Syncope • Syncope or pre-syncope caused by decrease in

vasomotor tone causing venous pooling • Un-acclimatized or dehydrated athletes • Usually at conclusion of exercise (worry if athlete

collapses prior to finish) • Treated with rest, elevation of legs and fluids • Can return to activity after resolution of

symptoms

Heat Cramps

• Localized, involuntary and sustained contractions of skeletal muscle

• Causes: – Sodium and/or chloride depletion – Dehydration

• Poorly conditioned athlete can lose more sodium along with fluid than a conditioned athlete

– Impaired circulation in working muscles – Alterations in spinal neural reflex activity increased by

fatigue

Heat Cramps

• Intensity dependent • Poorly conditioned • Fatigue • Dehydration

• Individuals predisposed

• Sickle Trait? • Game vs Practice • Supplement use

Heat Cramps: Treatment

• Stretching • Massage/Ice • Fluids

– Oral – IV

• Drugs – Valium – Quinine

Heat Cramps

• Return to Play – Rule out further Heat Illness – Resolution of symptoms – Correction of any underlying issues – Can be same day

Heat Exhaustion

• Most common form of Heat Illness • Temp usually from 38 degrees C (100.4 F)

to 40 degrees C (104 F) • Numerous symptoms or signs that happen

with exercise in warm humid conditions • Can result from volume/sodium depletion

Heat Exhaustion Signs and symptoms

• Elevated temp • Elevated respiratory

rate • Elevated pulse • Narrowed pulse

pressure • Headache • Malaise • Fatigue

• Weakness • Thirst • Nausea • Vomiting • Dizziness • Cramps • Sweating • Mild Mental Status

Alteration

Heat Exhaustion Evaluation/Treatment

• Obtain Core Temp!!!!! – Rectal

• Rest – Decrease heat production

• Shelter/Shade – Remove from the hot

environment – Minimize exposure to heat

• Cooling – Fans/Ice tub/Towels

• Fluids – PO usually in these case – IV

Heat Exhaustion Return to play

• Resolution of symptoms • Normal Vitals • Normal hydration status • If in doubt……hold ‘em out

– Symptoms can return quickly and progress to Heat stroke!!

• Transfer if not improving or progressing to heat stroke

Heat Stroke

• Life threatening clinical syndrome characterized by loss of temperature regulation capabilities

• Second most common cause of death in athletes in US

• Risk dependent upon: – Endogenous heat production – Temperature/humidity – Individual predisposition

Heat Stroke Presentation

• Core temp now getting over 40 degrees C (104 F)

• Similar presentation to Heat exhaustion • Onset can be sudden

Heat Stroke Additional Signs/Symptoms

• Classic Triad – Hyperpyrexia – Anhydrosis – Mental Status

Changes • Confusion • Delerium • Ataxia • Seizures • Coma

Heat Stroke Additional Signs/Symptoms

• Tachycardia • Hypotension • Arrhythmias • Metabolic disturbance • Clotting disturbances • Rhabdo (Sickle Trait) • Renal and Hepatic collapse

Heat Stroke Treatment

• REMOVE FROM HEAT!! • Obtain Rectal Core Temp • ABC’s • Immediate cooling, if able, prior to

transport • Then transport!!!

Heat Stoke

• With prompt recognition and treatment survival rate is high (90-100 percent)

• The key is early recognition and treatment (cooling)

Heat Stroke

Cooling Methods • Ice water immersion • Ice water blankets

– Fans • Ice packs • Evaporative cooling

– Cool water/Warm air – .31 degrees C/min

How we roll in Minnesota

Heat Stroke

• Prognosis- dependent of length of time and severity of hyperthermia

• Return to play – May take some time – Normalize labs – Symptom resolution – Hydration status – Gradual

Exertional Hyponatremia

• Low sodium due to over-hydration in prolonged exercise with dilute fluids

• Presents with: disorientation, pulmonary edema, seizures, coma

• Rx- recognize and transfer • Prevention- avoid over hydration with

dilute fluids during prolonged exercise • More frequent seen with extreme

endurance events

Heat Illness Prevention

• Acclimatization • Fitness • Conditioning • Clothing • Nutrition • Hydration • Sleep

• Illness control • Medications • Education • Environment risk

assessment • Timing of event • Monitoring of

conditions at event!

Heat Illness Case • 25 yo AA football

player at his second day of training camp. Sickle Cell Trait positive.

• Long history of heat cramps.

• Practice the first day consisted of two 90 minute practices. Temp 83 degrees.

• Mild cramps after first practice of second day

• Down 8 pounds • Pushing PO fluids • Resolves • Eats • 4 hour break inside air

conditioning • Checks in before second

practice • Feels “good”

Case

• Returns to afternoon

practice in 85 degree heat.

• Cramps return – Full body

Treatment

• IV fluids • Not improving • Sent to Hospital • CK max to 120k • Inpatient for 2 days • Return to play issues!

– Follow CK to normal? – Symptoms? – Gradual increase activity

What could have helped prevent issues??

• More time to acclimatize

• Shorter practice time • Early/later practice • Better hydration • Hold out after first

practice • Better training prior to

camp

Should there be special considerations for sickle trait patients??

• NCAA Testing/Protocols

• Mandatory testing unless waiver is signed

• Started April 2010

Summary • Understanding basic physiology of heat transfer

and balance provides the framework for understanding heat illness and treatment

• Identify who may be predisposed to problems

• Have a plan for monitoring the heat

• Heat illness can be life threatening; early diagnosis and treatment can be life saving

Thank You!!

Resources

• Bently S. Exercise induced muscle cramp. Sports Med 1996 Jun:21 (6); p 409-420 • Miners. The diagnosis and emergency care of heat related illness. The Journal of the

Canadian Chiropracitc Association, June 2010. • Carter R, et al. Epidemiology of hospitalizations and deaths from heat illness in

soldiers. Med Sci Sports Ex 37(8), August 2005, pp 1338-1334. • Coris EE et al. Heat illness in athletes. The dangerous combination of heat, humidity

and exercise. Sports Med 2004; 34(1) p 9-16. • Eichner ER. Treatment of suspected heat illness. Int J Sports Med 19: S150-153. • Maughan RJ. Exercise in the heat; limitations to performance and the impact of fluid

replacement strategies. Can J Appl Physiol 24(2): 149-151, 1999 • Seto CK, et al. Environmental illness in athletes. Clin Sports Med 21 (2005) p695-718 • Wexler Randall, Evaluation and Treatment of Heat Illness, American Family

Physician. June 1, 2002