Exertional Heat Illness

1
Exertional Heat Illness
John W. Gardner, MD, DrPH COL(ret), MC, FS, US
Army
Uniformed Services University of the Health
Sciences Bethesda, MD
2
Less than 20 of energy expended during exercise
is converted to mechanical energy The
remainder is released as HEAT

3
Heat Dissipation

• Heat must be dissipated or the body temperature
  rises
• Rise in body temperature stimulates
  thermoregulatory mechanisms (in proportion to
  amount of rise)
• Heat is dissipated primarily at the SKIN (and
  some through respiration)

4
Body Cooling Mechanisms

• Conduction
• Convection
• Radiation
• Evaporation

5
Body Cooling Mechanisms

• Efficiency of body cooling depends upon the
  differential between skin and environmental
  temperatures
• When there is no gradient between skin and
  environmental temperatures, the only mechanism
  for heat dissipation is through evaporation
• In high humidity, evaporation is also ineffective
  (dripping sweat does not cool, but simply
  induces further dehydration)

6
Hydration Requirements

• Maximal sweating is 2-3 liters/hour
• GI water absorption during exercise is limited to
  about 1.5 liters/hour
• Maximal sweat rates cannot be maintained
  indefinitely, as dehydration always progresses
  even when drinking maximally

7
Estimated Distribution of Cardiac Output
8
Exertional Heat Illness

• The combination of dehydration, circulatory
  demands, and metabolic processes induce tissue
  injury organ dysfunction
• The heart must work harder to meet circulatory
  demands
• Redistribution of blood flow may compromise vital
  organs
• bloody diarrhea in marathoners?
• acute renal failure?
• encephalopathy?
• Acidosis and electrolyte imbalance may disrupt
  other metabolic processes or induce organ
  dysfunction
• High temperature may alter metabolic rates and
  induce organ dysfunction
• Inflammatory processes initiated? (release of
  endotoxin through gut compromise?)

9
THE SPECTRUM OF EXERTIONAL HEAT ILLNESS
Heat Exhaustion
Hyperthermia Dehydration Nephropathy Cell
Lysis Encephalopathy
Shock
Heat Injury
Renal Failure
Rhabdomyolysis
Heatstroke
Moderate
Severe
10
Key Points

• Severe exertional heat illness
• can occur in cool weather
• can occur without high body temperature
• Mental status change
• may reflect severe illness
• Vital signs Laboratory values
• must be closely monitored
• early rapid cooling essential
• Dehydration Acidosis
• early aggressive IV therapy
• Sickle Cell Trait Patients
• have higher risk of death

11
Wet-Bulb Globe Temperature Index

• The WBGT Index takes into account air
  temperature, humidity, radiant heat, and air
  movement.

W Aspirated Wet-Bulb Temperature G Matte
Black Globe Temperature D Dry-Bulb Temperature
WBGT Index 0.7W 0.2G 0.1D
12
PARRIS ISLAND MARINE CORPS RECRUIT TRAINING
DEPOT, SC
13
PARRIS ISLAND MARINE CORPS RECRUIT TRAINING
DEPOT, SC
14
PARRIS ISLAND MARINE CORPS RECRUIT TRAINING
DEPOT, SC
15
Acclimatization

• Thermoregulatory mechanisms initiate at lower
  levels of elevated temperature
• Sweating begins sooner and in higher volume
• Sweat has much lower sodium content
• Blood volume and cardiac capacity expand, with
  more efficient redistribution of blood flow
• In well-conditioned individuals most of
  acclimatization is accomplished in 3-5 days

16
PARRIS ISLAND MARINE CORPS RECRUIT TRAINING
DEPOT, SC
June 3, 1991
17
PARRIS ISLAND MARINE CORPS RECRUIT TRAINING
DEPOT, SC
18
PARRIS ISLAND MARINE CORPS RECRUIT TRAINING
DEPOT, SC
19
PARRIS ISLAND MARINE CORPS RECRUIT TRAINING
DEPOT, SC
20
Military and ACSM Flag Conditions
21
Body Mass Index (BMI) on Arrival by Case and
Control Status,Male Marine Recruits, MCRD-PI,
1988-1992
BMI CATEGORY
OR (95 CI)
CASES
CONTROLS
lt22 kg/m2 22-lt26 kg/m2 26 kg/m2 Total
449 659 340 1448
62 156 172 390
1.0 1.7 (1.3-2.4) 3.6 (2.5-5.0)
22
1.5 mile PFT1 Run Time by Case and Control
Status,Male Marine Recruits, MCRD-PI, 1988-1992
Run Time CATEGORY
OR (95 CI)
CASES
CONTROLS
lt10 minutes 10-lt12 minutes 12 minutes Total
204 884 329 1417
1.0 1.5 (0.9-2.4) 5.6 (3.4-9.1)
28 156 193 377
23
Odds Ratios Combining PFT1 Run Timeand BMI
Category for Exertional Heat Illness,Male Marine
Recruits, MCRD-PI, 1988-1992
1.5 Mile PFT1 Run Time
BMI CATEGORY
lt10 minutes
10-lt12 minutes
12 minutes
3.5 8.5 8.8
1.5 2.0 3.3
1.0 1.6 3.7
lt22 kg/m2
22-lt26 kg/m2
26 kg/m2
24
Percent of Population Producing Heat Illness Cases
PARRIS ISLAND MARINE CORPS RECRUIT TRAINING
DEPOT, SC
35
65
18
47
17
18
25
Percent of Cases with Neurologic Heat Stroke
PARRIS ISLAND MARINE CORPS RECRUIT TRAINING
DEPOT, SC
26
Does Rectal Temperature 106F Predict Heat
Stroke (Delirious or worse)?
RectalTemperature
Delirious
Total
Yes
No
106 F
35
36
71
lt 106 F
34
363
397
Total
69
399
468
Sensitivity 35 / 69 51
Specificity 363 / 399 91
Predictive Value () 35 / 71 49
27
Risk of Exercise-Related Threatened or Completed
Sudden Cardiac DeathRecruits, Parris Island, SC
1979-90 95 confidence limits
Cases (deaths)
Recruits/Cadre
Population
Incidence
137 1,800 267,500
7 (2) 0 4(4)
5.1 2.5-10 0.0015 0-0.004
w/ Heat Stroke
w/ Other EHI
w/o EHI
28
Types of Exercise-related Recruit Deaths (96
military recruit deaths, 1979-90)
29
Percent of Exercise-related Recruit
DeathsExposed to Environmental Heat Stress
(N 96)
(N 20)
(N 25)
(N 45)
(N 6)
Same or Prior Day WBGT gt 75F
30
Clinical Assessment of Heat Illness

• Non-Specific Symptoms
• weakness, thirst, headache, cramps, poor
  concentration
• Progressive Orthostatic Symptoms
• faintness, dizziness, wobbly, visual symptoms,
  collapse

31
Clinical Assessment of Heat Illness

• Exertional Syncope
• brief loss of consciousness
• Orthostatic Hypotension
• positive tilt tests
• sustained hypotension
• Shock/Cardiac Arrhythmia
• Metabolic Complications

32
Scale of Encephalopathy in Heat Illness

• 8 Normal - alert, oriented, cooperative
• 7 Drowsy - lethargic, slow mentation
• 6 Confused Appropriate - cooperative
• 5 Confused Inappropriate - disoriented
• 4 Delirious - disoriented, agitated
• 3 Obtunded - minimal mental response
• 2 Light coma - reflex responses
• 1 Deep coma - no reflex responses

33
RECOMMENDED LABORATORY TESTS IN EXERTIONAL HEAT
ILLNESS

• CBC Hgb, Hct, WBC, Platelet Count
• Urinalysis S.G., pH, evidence of myoglobin
• Chemistries Na, K, Cl, HCO3, Glu, BUN,
  Creatinine,
• CKCPK, ASTSGOT, Uric Acid, LDH,
  ALTSGPT
• If severe ABG Ca, Phos PT, PTT, FSP,
  Fibrinogen

34
Immediate Management ofHeat Illness Casualties

• Get a Rectal Temperature
• Assess Mental Status
• Immediate Cooling with Ice Water
• Rapid Rehydration
• Monitor Vital Signs and Serum Chemistries
• Limit Duty after Treatment

35
Predictors of HospitalizationParris Island
Recruits, 1988-92
Clinical Variable Score
Maximum body temperature 106 ?F 1 Min
systolic blood pressure lt100 mmHg 1 Disorientat
ion duration 1-29 minutes 1 30
minutes 2 Minimum serum potassium lt 3.7
mEq/L 1 Maximum serum creatinine 1.8
mg/dL 1 Maximum serum LDH 400 U/mL 1
A score of 2 or more may require hospitalization.
36
Prevention of Exertional Heat Illness

• Schedule Training / Exercises During Cool Hours
• Consider Accumulative Effects of Heat Exposure
• Minimize Heavy or Retentive Clothing
• Minimize Unnecessary Strenuous Exercise (Running
  )
• Tailor exercise to physical and medical condition
  of participants

37
Prevention of Exertional Heat Illness

• Maintain Good Hydration
• Provide Shade, Water and Rest Periods
• Have Medical Personnel On-Site During Strenuous
  Exercise

38
Prevention of Exertional Heat Illness
Forget
NO PAIN, NO GAIN
Remember
TRAIN, NOT PAIN
39
The notion that courage and esprit de corps can
somehow defeat the principles of physiology is
not only wrong but dangerously wrong.
Sir Roger Bannister (1989)
40
Example Combat Confidence Course
Modifications to Reduce Risk for Exertional Heat
Illness

• Location with Access to Shade and Water
• Showers for Wet-Down During Run/Between Events
• Clothing T-shirts vs. Full Combat Gear
• Cover None vs. Helmet
• Run Formation vs. Individual (non-competitive )
• Hydration Status Checked by Urine Color

41
Exertional Heat Illness Outbreaks, Ft. Bragg,
2000-2001

9/22/00 EFMB March (12 miles) 6
hospitalizations 11/4/00 Perimeter Challenge (60
miles) 5 hospitalizations 4/12/01 EFMB March
(12 miles) 9 hospitalizations 6/14/01 Army
Birthday Run (10 miles) 6 hospitalizations 7/20/
01 EIB March (12 miles) 19 hospitalizations
8/9/01 Corps Birthday Run (4 miles) 4
hospitalizations
42
Exertional Heat Illness Ft. Bragg, 2000-2001

• STUPIDITY
• Death related to 6 mile run in new transfer at
  pace faster than his 2-mile PFT run (coronary
  heart disease)
• Three heat stroke cases related to 8 mile run in
  new transfers on their first day of arrival
• Heat stroke related to chemical gear at Black
  Flag conditions
• Permanent mental disability related to recurrent
  heat injury when on medical restriction after
  release from hospital for heat stroke -
  commander insisted on 100 field participation
• Numerous heat casualties related to use of
  ephedra-containing nutritional supplements

43
Career Implications of Heat Stroke Diagnosis

• Mandatory MEB with 3-month P3 medical
  restriction, followed by 6-12 month P2 medical
  restriction
• Airborne operations restricted
• Pilots grounded for a minimum of 3 months, then
  can request waiver recurrent episode - waiver
  not to be recommended
• Single episode of heat stroke may preclude flight
  school entry
• Medical restrictions usually make soldiers
  non-deployable for a prolonged period of time

44
Diagnosis of Heat Stroke

• Recommendations
• In the setting of heat exposure or exertion, any
  of the following (elevated body temperature not
  required)
• persistent (at least 10-20 minutes)
  disorientation, confusion, or combativeness
• delirium or obtundation beyond 3-5 minutes
• coma beyond the three minutes of a simple faint
• amnesia beyond 10-15 minutes surrounding the
  event
• elevated CKgt700, ASTgt60, ALTgt60, or LDHgt400 at
  24 hours post-event (particularly if rising
  after initial values, or if associated with
  myoglobinuria)

45
Diagnosis of Heat Exhaustion

• Recommendations
• In the setting of heat exposure or exertion, all
  patients not meeting heat stroke criteria who
  experience exercise-related collapse/illness and
  require medical intervention (e.g., more than two
  liters of IV fluids) and/or more than one hour to
  recover (unable to return to work at light-duty
  within one hour)
• Includes exertional dehydration, cramps, syncope
• These patients should all be evaluated by an
  experienced clinician, preferably in an Emergency
  Room setting and with laboratory workup

46
Field Management of Exertional Heat Illness

• Mild patients - Alert with appropriate behavior,
  near-normal and rapidly stabilizing vital signs,
  and able to drink fluids
• Care in the field for up to one hour with up to 2
  liters of fluids (NS if IV)
• 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
• No patient leaves medical care until providing
  urine

47
Field Management of Exertional Heat Illness

• Moderate/Severe patients - Mental status changes,
  amnesia, syncope, seizure, unable to drink
  fluids, unstable vital signs, or temp gt104
• Care in the field includes rest in the shade,
  cooling, rehydration, frequent vital signs and
  mental status assessment (every 5-10 min), while
  quickly arranging evacuation to an Emergency Room
• These patients require immediate evaluation by an
  experienced clinician, and laboratory tests (CBC,
  electrolytes, creatinine, liver enzymes, CK,
  urinalysis)
• No patient leaves medical care until providing
  urine

48
ER Management of Exertional Heat Illness

• ACLS procedures as needed, to include aggressive
  cooling and rehydration
• Stop aggressive cooling at 102 to avoid
  hypothermia
• Repeat vital signs and mental status assessments
  every 5-10 minutes until stable and temp lt100
• Lab assessment is usually required, with
  follow-up the next day in all but very mild
  patients
• All ER and hospitalized patients to be
  followed-up in the Preventive Medicine clinic for
  reporting, medical restrictions, MEB referral,
  and review of need for further medical management
  or follow-up

49
Disposition of Exertional Heat Illness Cases

• Mildly ill patients who appear to be fully
  recovered in the ER and have no laboratory
  abnormalities may return to light duty the next
  day maximal exercise should be avoided for
  several days
• Patients not fully recovered or who have
  laboratory abnormalities require next day
  follow-up by an experienced clinician, with
  laboratory evaluation
• All patients remain on quarters, convalescent
  leave, or P4 medical restriction until all
  symptoms have completely resolved and laboratory
  tests are normal
• When fully recovered, the patient may begin
  exercise at own pace, building slowly up to
  maximal efforts

50
MEB for Heat Stroke Cases

• All heat stroke or rhabdomyolysis cases require
  MEB
• If no complications, MEB will provide P3
  restriction for 3 months which limits vigorous
  exercise to periods no longer than 15 minutes, no
  maximal efforts, no PFT, and no chemical gear or
  significant heat exposure
• If after 3 months there has been no indication of
  heat intolerance, the restriction is changed to
  P2 through the next hot season, which allows
  normal work but restricts significant heat
  exposure and maximal exertion
• If no heat intolerance, return to full duty after
  the hot season if signs of heat intolerance,
  refer to PEB

51
Surveillance and Reporting of Exertional Heat
Illness

• Report all cases from the Emergency Room, and
  none from the field
• Cases admitted to the hospital are interviewed
  there by Preventive Medicine, and case summaries
  developed for discussion with commanders
• All ER and hospital cases are followed-up in the
  Preventive Medicine clinic for reporting
  purposes, as well as to assure that the soldier
  is properly restricted and referred to MEB, if
  appropriate
• If we take the soldiers away from their
  commanders through the mandatory restriction and
  MEB process, it will emphasize the seriousness of
  inducing heat stroke

52

• EFMB Safety
• Prevention of Exertional Heat Illness
• PROBLEM
• 2 deaths from heat stroke during 12-mile march
  in EFMB testing (9/98 6/99)
• Numerous episodes of exertional heat illness
  during 12-mile march in EFMB testing (Ft.
  Bragg examples)
• CHALLENGES
• Unlike EIB, EFMB candidates are generally
  medical personnel who do not march for a living
  
• Use of ergogenic aids as nutritional
  supplements

53

• EFMB Safety
• Prevention of Exertional Heat Illness
• PROBLEM
• EFMB candidates often arrive physically
  unprepared for the 3-hour 12-mile road march
  requirement
• SOLUTION
• Require prerequisite physical conditioning per
  FM 21-18, section 5-11
• Certified by individuals unit, and
• Perhaps tested at beginning of course with
  12-mile march in 3-hours without pack

54

• EFMB Safety
• Prevention of Exertional Heat Illness
• PROBLEM
• EFMB candidates often often use ergogenic
  nutritional supplements or are taking other
  medications
• SOLUTION
• Prohibit use of ergogenic nutritional
  supplements within 30-days of EFMB testing
• Require medical clearance of all candidates to
  determine medication and supplement hazards

55

• EFMB Safety
• Prevention of Exertional Heat Illness
• PROBLEM
• Inadequate hydration during the road march
• SOLUTION
• It is important to begin the march
  fully-hydrated
• Prior day should have minimal physical
  activity and heat stress exposure
• Hydration early in the march is important
• Staff should ensure that candidates actually
  drink

56

• EFMB Safety
• Prevention of Exertional Heat Illness
• PROBLEM
• Overzealous candidates and staff put
  themselves and others at risk
• SOLUTION
• Staff should do periodic mental status checks
• Staff must be authorized to immediately
  disqualify candidates when medical risks
  warrant
• Staff should not be overzealous in enforcing
  detailed course requirements to the detriment of
  candidates

57

• EFMB Safety
• Prevention of Exertional Heat Illness
• PROBLEM
• Medical care at the event is often inadequate
• SOLUTION
• Plan for mass casualties and evacuation
  procedures
• Every candidate should be medically evaluated
  before being released from the event
• Maintain complete records
• Report all injuries / illness
• Accurate weights before and after the march
  are helpful

58
PM TEAM FORT BRAGG
ALL THE WAY, AIRBORNE