Lecture 21: Heat and Hydration

What is Exertional Heat Injury?

• 46 high school football players died of heatstroke between 1995 and 2010

• 5-year period of 2005-2009 saw more Exertional Heat Stroke deaths in organized sports in the United States (US) than any other 5 year period in the past 35 years.

What is temperature?

As atmospheric temperature increases, the temperature gradient between air and body decreases

When lose heat via radiation?

Tbody > Tenvironment

Over 27C (80F) the body absorbs heat.

• Heat loss is from evaporation only.

What is heat generated by?

Endogenous

Muscle activity and metabolism

What are exogenous sources of heat?

Transfer to body when Tenviron>T bod

What happens when an athlete exercises in a hot environment?

they sweat to dissipate heat

• An increase in humidity will decrease the vapour gradient, therefore there will be less evaporation.

• + increase T body due to decreased evaporation of sweat

What is the risk of exertional heat injury?

• We must also take the humidity into consideration.

• Substantial humidity, even at low temperatures can be dangerous

What is Exertional heat stroke (EHS)?

occurs when the patient presents with exertion-related hyperthermia (core body temperature > 40 C) and associated central nervous system disturbance or evidence of other end organ system damage.

What do people experience with What is Exertional heat stroke (EHS)?

• They first may experience dizziness, weakness nausea, fast pulse and respiration, and mental confusion. They may collapse and suddenly become unconcious.

The individual may stop sweating (hot, dry skin), but this is unreliable

What is heat exhaustion?

characterized by an inability to continue functioning in the heat without evidence supporting the diagnosis of EHS. i.e. no temperature greater than 40 C

What are some signs and symptoms of heat exhaustion?

• Signs and symptoms are variable and may include-Heavy sweating with pale, moist, cool skin; headache, weakness, dizziness, nausea (with or without vomiting)

Non-severe- (Heat exhaustion) hard signs?

Primary (Hard signs)

• Conscious

• Alert

• Temp < 40C

• Systolic >100 mmHg

Non-severe- (Heat exhaustion) soft signs?

Secondary (soft signs) May or may not be present

• Sweating

• Pale , moist, cool skin

• Cramping ?

• Nausea

Severe- (Heat Stroke) hard signs?

Primary (Hard signs)

• Unconscious or

• Decreased Mental status

• Disoriented

• Irrational behaviour

• Temp > 40C

• Systolic<100 mmHg

Severe- (Heat Stroke) soft signs?

Secondary (soft signs) May or may not be present

• No Sweat

• Hot, dry skin

• Weakness/flaccid

• Nausea

What is the management of heat exhaustion?

Alert with appropraite behavior, near-normal /stable vital signs, and able to drink fluids

• Care on side-line for up to one hour with up to 2 liters of fluids

• Rest in the shade, cooling, rehydration, frequent vital signs and mental status assessment (every 5-10 min)

• Upon realization that recovery will require more than this, or if the patient is not improving, then evacuation to an Emergency Room should be quickly arranged.

What is the management of heat stroke?

Mental status changes, amnesia, syncope, seizure, unable to drink fluids, unstable vital signs, or temp >40 C

• cool first, transport second

• Care on side-lines includes aggressive cooling withing golded first ½ hour

• remove gear

• ice/water submersion (best) or on core starting with armpits and groin) /fanning,

• rehydration,

• frequent vital signs and mental status assessment (every 5-10 min),

• Quickly arranging evacuation to an Emergency Room

How bad is heat stroke?

THIS IS LIFE THREATENING - These patients require immediate evaluation by an experienced clinician, and laboratory tests

What are intrinic factors for EHS?

• Lack of acclimatization

• Fever

• Overweight/obesity

• dehydration

• Recent alcohol use

• Sunburn

What are extrinsic factors for EHS?

• Hot, humid environment

• Exercise Intensity

• Inappropriate work-to-rest ratios

• Equipment/clothing • Education

- Athlete

- Coaches and medical staff

• Lack of emergency plans to identify and treat EHS

• Lack of proper infrastructure (heat acclimatization

• Access to fluids

• Access to preventative cooling strategies

What are the five concepts for combatting heat Injuries?

1. Get an accurate temperature

2. Keep them/Get them cool

3. Allow time for acclimatization

4. Train Coaches and players on the signs of EHI

5. Keep them hydrated!

Why do you need to get an accurate temperature?

• Know what you are dealing with

• Devices to measure ''core body temperature'' via direct contact with the forehead, or radiation from the ear canal may not be accurate and/or validated in controlled experiments involving athletes and are potentially dangerous! • While a definitive diagnosis of EHS requires a rectal temperature of > 40 C, it is wise to assume EHS if the patient is displaying CNS signs, even if the temperature is slightly lower than 400C

What are the NCCA guidelines fro keeping them cool?

• number and duration of football practice sessions

• Work to rest ratios

• the uniform items that should be worn, during the initial days of summer training

• Material- convection • Such procedures provide football players with the most effective nonmedical means to reduce the risk of EHS

What is the best cooling method?

• Cold water and ice water immersion provide superior cooling rates (i.e., rectal temperature decreases 5-14 times faster than packing with ice) • Cold water and ice water immersion administered to more than 2000 patients with EHS during mass participation running events and military training exercises; were 100 % effective in preventing death

What is allowing time for acclimatization?

• Most EHS deaths occur among non-acclimatized players during the initial 3 days of summer practices.

• Acclimatization improves cooling mostly through increased sweating (evaporation)

• Less effective in high humidity

• May need to add electrolytes

How does acclimatization occur?

By progressive and prolonged elevation of the body's core temperature

• Living in a hot environment without exercising in the environment provides little acclimatization.

• Working/sleeping in air conditioning?

What does acclimatization look like for an athelete?

• Conditioned athletes acclimatize after 4-7 progressive exercise sessions of 1-4 h total duration each over a period of 1-2 weeks.

• Studies indicate that military units (various levels of individual conditioning) acclimatize about 40% at 1 wk, 80% at 2 wk, and 100% at 3 wk. • Four high-intensity intermittent acclimation sessions, in a 10-day period, is sufficient to improve games-type exercise capacity.

What is the bottom line for acclimatization?

• Physiological adaptations will occur during 1-3 weeks of exercise-heat exposure. These include:

• reduced rectal temperature, cardiovascular strain, and perceived exertion, as well as increased plasma volume.

What does training coaches and players on the signs of EHI do?

• EHS deaths among football players occur almost exclusively on the football practice field.

• Athletes pushed beyond the point at which they otherwise would stop to rest, rehydrate, and cool the body

What is the bottom line for team education?

Coaches/trainers are responsible for removing a player from practice when he or she exhibits signs and symptoms of EHS • Some coaches do not understand or accept this responsibility!

• The medical team MUST educate staff and players on signs and symptoms and ensure EAP's are completed, understood and followed!

What is keeping the athlete hydrated?

• More than 50% of athletes arrive at training sessions hypo hydrated.

• Usually only replace 2/3 of sweat loss while training

• Specific individual recommendations are calculated based on sweat rates, activity, equipment and dynamics, as well as individual tolerance.

• The goal of drinking during exercise is to prevent excessive (>2 % body weight loss from water deficit) dehydration and excessive changes in electrolyte balance to avert compromised performance

What are the physiological implication of dehydration?

• Increase Fluid loss= Increase Systemic compromise

• Increase Tcore during physical activity,

• with Tcore increase 0.15 to 0.20°C for every 1% of body weight lost (due to sweating) during the activity.

• Cardiovascular strain as characterized by

• Decreased SV

• Increased HR

• 3-5 bpm/ Decreased 1% of body weight lost

How can you track hydration changes>

1. Acute hydration changes can be measured by taking nude body mass before and after exercise.

• Hydration status can be reliably estimated using as few as three consecutive days of first-morning euhydrated body weights, measured after voiding.

• If body mass changes more than 2%, the individual is drinking too little; if body mass increases, the individual is drinking too much. 2

. Check Urine Concentration/colour in morning

3. Thirst- First morning thirst is correlated with hypohydration

• Thirst at rest increases at roughly 2% hypohydration

• Thirst during exercise is NOT reliable

What are the concepts of rehydration?

• The primary goal is the immediate return of physiologic function (especially if another bout will follow before 24 hrs). • Compensate for urine losses by drinking 50% more than sweat losses to assure optimal hydration, if recovery time is less than 4 hours

• When recovery time is greater than 12 hours, an athlete can eat and drink as needed and should recover.

• 2/3 glasses per lb (or per ½ kg) of body weight lost

• A balanced diet that provides about 2500 to 3000 kcal will generally provide about 1 liter of water per day from food alone.

Hydration- Bottom Line individual?

rehydration planning is important and shoul be reassessed and altered as needed

Hydration- Bottom Line Pre exercise?

•Need to start exercise in a state of euhydration

•body water within its optimal range

Hydration- Bottom Line During Exercise

• Try to maintain water levels...drink early and often

• Use CHO drink if exercising for periods greater than 1 hour

• Optimal concentration is between 3-8 percent. • Those over 5% may slow gastric emptying

Hydration- Bottom Line Post Exercise?

• Need to correct fluid loss ASAP. Much of this through general nutrition and H2O. May need to add CHO and electrolytes

Hydration factors and consideration?

• Hydration plans need to be individualized and consider many factors • An athlete who exercises for more than 4 hours and hydrates excessively (well beyond sweat loss) only with water or lowsolute beverages may be susceptible to a relatively rare condition known as hypontremia (also known as water intoxication).

• Everyone associated with the team needs to take responsibility!