(3) Lecture 20: Heat + Hydration Flashcards
Temperature
as atmospheric temp increases, the temp gradient btwn air and body decreases
when body temp > environ temp, we lose heat via radiation
Over 27C, the body ABSORBS heat (issues dissipation heat)
How is heat lost?
Heat loss is from evaporation only (through sweat)
Exercise in the heat
- heat is generated by ENDOGENOUS sources (muscle activity + metabolism)
- heat can be generated from exogenous sources - transfer to body when environ temp > body temp
- when an athlete exercises in a hot environ., they sweat to dissipate heat
What does an increase in humidity do?
An increase in humidity decreases the vapour gradient = LESS evaporation
- increases body temp due to decreased evaporation of sweat
more humid = less sweat = increase in body temp
Risk of Exertional Heat Injury
substantial humidity even at low temps can be dangerous
Exertional Heat Stroke
when the patient has exertion-related hyperthermia (core body temp > 40C) and associated CNS disturbance or evidence of other end organ system damage
- May first experience dizziness, weakness, nausea, fast pulse and respiration, and mental confusion
- May collapse and become unconscious
- May stop sweating (hot, dry skin → red flag) but UNRELIABLE
Heat Exhaustion
PRECURSOR to heat stroke
inability to continue functioning in the heat without evidence supporting diagnosis of EHS (no temp greater than 40C)
Variable signs and symptoms: heavy sweating w/ pale, moist, cool skin; headache, weakness, dizziness, nausea (+/- vomiting)
Athlete with Exertional Heat Injury
Less severe (Heat Exhaustion)
Primary (hard signs)
- Conscious
- Alert
- Temp < 40C
- Systolic > 100mmHg
Secondary (soft signs)
- Sweating
- Pale, moist, cool skin
- Nausea
Severe (Heat Stroke)
Primary (hard signs)
- Unconscious OR decreased mental state (disoriented, irrational)
- TEMP > 40C
- Systolic < 100mmHg
Secondary (soft signs)
- No sweat
- Hot, dry skin
- Weakness
- Nausea
Management of Heat Exhaustion
Patient is alert w/ appropriate behaviour, near-normal/stable vital signs + able to drink fluids
- care on sideline for up to 1 hour w/ up to 2L of fluids
- rest in shade, cooling, rehydration, frequent vital signs + mental status assessment
Management of Heat Stroke
Mental status changes, amnesia, syncope (LOC), seizure, unable to drink fluids, temp > 40C, unstable vitals
COOL FIRST THEN TRANSPORT second
Aggressive cooling in sidelines within golden first 1/2 hour
- remove gear
- ice/water SUBMERSION (best) or on core starting w/ armpits + groin/fanning
- rehydration (if mental status allows)
- frequent vitals and mental assessment
- quickly arrange evacuation to ER
- this is LIFE THREATENING
Risk factors for EHS
Intrinsic
- Lack of acclimatization
- Fever
- Overweight/obesity
- Dehydration
- Recent alcohol use
- Sunburn
Extrinsic
- Hot, humid environment
- Exercise intensity
- Inappropriate work-rest ratios
- Equipment/clothing
- Education of early signs
- Lack of emergency plans to identify + treat EHS
- Lack of proper acclimatization
- Access to fluids
- Access to preventative cooling strategies
5 Concepts for combatting heat illness
- Get an ACCURATE temperature
- Keep them/get them cool
- Allow time for acclimatization
- Train coaches and players on signs of EHI
- Keep them hydrated
Getting an accurate temperature
definitive EHS diagnosis requires a RECTAL TEMPERATURE of > 40C
- devices to measure “core body temp” from forehead or ear canal may not be accurate –> potentially dangerous
- wise to assume EHS if patient displays CNS signs. even if temp is slightly lower
Keeping/getting athletes cool
KEEPING them cool
NCAA has guidelines for
- # and duration of football practice sessions (work to rest ratios)
- uniform items that should be worn during initial days of summer training = acclimatization (material - convection)
these guidelines provide football players w/ most effective nonmedical ways to reduce risk of EHS
GETTING them cool
- cold water and ice IMMERSION provides superior cooling rates
Allowing time for acclimatization
- most EHS deaths occur to non-acclimatized players during initial 3 days of summer practices
Acclimatization improves cooling most through increased SWEATING (evap.)
- less effective in high humidity
- may need to add electrolytes
Acclimatization happens by progressive and prolonged elevation of body core temp
Conditioned athletes acclimatize after 4-7 progressive exercise sessions of 1-4h total duration over 1-2 weeks
Living in a hot environment w/o exercising in the environment does NOT provide acclimatization
Acclimatization bottom line
Physiological adaptations occur during 1-3 weeks of EXERCISE-HEAT EXPOSURE
adaptations include
- reduced rectal temp
- reduced CV strain
- reduced perceived exertion
- increased plasma volume
Team education
- EHS deaths in football players happen almost exclusively in PRACTICE b/c athletes are pushed
- coaches/trainers are responsible for removing a player from practice when they exhibit S&S of EHS
medical team MUST educate staff and players on signs and symptoms and ensure EAPs are completed, understood and followed
Keeping athletes hydrated
- more than 50% of athletes arrive at training sessions hypohydrated
- usually only replace 2/3 of sweat loss while training
Goal of drinking during exercise is to prevent excessive dehydration (>2% of body weight loss from water deficit) and excessive changes in electrolyte balance
Physiological implications of dehyrdation
↑ Fluid loss = ↑ systemic compromis
↑ core temp during physical activity
CV strain:
↓ SV
↑ HR
Factors that contribute to risk of hypohydration or rehydration
Availability of fluids
Water breaks, water stations, types of fluids, temp of fluids
Environmental conditions
Air flow, radiant heat, humidity, ambient temp, clothing and equipment
Exercise structure
Exercise intensity, duration of exercise, number of exercise sessions per day
Intrinsic factors
Sex, thirst drive, acclimatization status, body size + composition
Sport Specific Factors
Weight loss in weight division, acrobatic and appearance-based sports
Tracking hydration changes
- acute hydration changes can be measured by taking NUDE BODY MASS before and after exercise
- use first-morning euhydrated (ideally hydrated) body weights
- if body mass drops more than 2%, individual is drinking too little - check urine concentration/colour in morning
- thirst - first morning thirst = hypohydration
- thirst during exercise is NOT reliable
Rehydration concepts
Primary goal: immediate return of physiologic function
- compensate for urine losses by drinking 50% more than sweat losses if recovery time is < 4 hours (if you’re down 1kg, drink 1.5L of water)
- 2-3 glasses per lbs of body weight fat
Foods with high water content
- watermelon
- cucumber
- lettuce (iceberg)
Questions to ask to establish a hydration plan
Are athletes in a state of euhydration?
- assess hydration status
- pee scales, measure sweat rates
Prolonged or intense exercise?
- increase availability of fluids
- more/longer duration breaks
What are environmental conditions?
- breaks based on conditions/modify practice
Is fluid constantly available?
- fluid made readily available
- make sure athletes use breaks to drink
Intrinsic factors?
- identify those w/ high sweat rates or low thirst drives
- develop individual hydration plans
Extrinsic/sport specific factors?
Hydration pre exercise
need to start exercise in a state of euhydration
- body water within its optimal range
Hydration during exercise
- try to maintain water levels .. drink early and often
- Use CHO (carbs) drink if exercising for periods more than 1 hour (optimal conc of 3-8%)
Hydration post exercise
need to correct fluid loss ASAP
- much of this through general nutrition and water
- may need to add CHO (carbs) + electrolytes
Bottom line of hydration
Hydration plans need to be INDIVIDUALIZED + consider many factors
- athlete who exercises for more than 4 hours and hydrates excessively (beyond sweat loss) only w/ water may be susceptible to hyponatremia
Hyponatremia
water intoxication
- can cause organ failure
- common in marathoners
athlete who exercises for more than 4 hours hydrates excessively (well beyond sweat loss) only with water or low-solute beverages
