Exertional Heat Stroke: Pathophysiology Discussion

1
Exertional Heat Stroke PathophysiologyDiscussio
n

• Steve Blivin, MD, FAAFP, CAQSM
• Commander, U.S. Navy
• Head, Sports Medicine Department
• Naval Hospital
• Camp Lejeune, NC
• ACSM/DOD Roundtable Conference
• Exertional Heat Stroke
• Bethesda, MD
• 22-23 OCT 2008

2
Disclaimer

• The following is my professional opinion based on
  the literature, unpublished data, experts
  opinions, and personal experience. It is not
  U.S. Navy or DoD official policy or opinion.

3
Agenda

• Definitions
• Epidemiology and Evidence
• Risk factors
• Signs
• Dual pathway model
• If true, what does it mean?
• Pathophysiology discussion points and questions

4
Definitions Exertional Heat Injury (EHI)

• Heat Exhaustion (HE)
• Exerting AND
• Cant go on, may be confused
• Heat Stroke (HS)
• Not strictly defined by Tgt104F (40C)
• ExertingSx of HEAND
• End Organ Damage
• Mental Status Change
• Study Abnormalities

5
EHI Data Okinawa (U.S. Military)

• 2004 32 HE, 14 HS (1 death)
• Stop Spray, Fan, Cool packs / Ice packs
• Start Ice / Water cooling more Training
• Model Parris Is. and Quantico USMC methods
• 2005 16 HE, 4 HS
• 1 HE discharged post muscle biopsy
• 2006 26 HE, 4 HS
• 2007 30 HE, 1 HS

6
EHI Mortality Time at Temperature

• WWI Brits in Mesopotamia, 600 EHI (?deaths)
  until ice, water, and activity mods
• WWII 200 DEATHS at US training bases
• Parris Island, SC USMC Training
• 1.5 (2/137) HS cardiac Mortality 1979-1990
  Paris Is.
• Total HS mortality quoted 1 - 5 during this
  time
• 0 Since ice water rapid cooling adopted
• Quantico, VA USMC Training
• 0 Since ice water rapid cooling adopted

7
Exertional Heat Illness Cases by Year and
Hospitalization 1979-97Parris Island, South
Carolina
Number of cases
8
Quantico Officer Candidate School EHI
9
Quantico EHI Candidates Dropped

• 2000 10
• 2001 6
• 2002 10
• 2003 11
• 2004 2006 exact s not provided
• All were from USMC Officer Candidate School (OCS)
• 2003-2006 2 at risk for repeat HS and
  permanently NPQd
• Candidates are dropped if not full duty gt 4 days
• Many not motivated to return to full duty
• Many return for a later class and graduate
• USMC Officer The Basic School (TBS) had 1
  repeat EHI (HS with HE in past) who graduated to
  attend flight school.
• Data reported by personal e-mail from CDR
  Scott Pyne (OCS / TBS 2000-2002) and CAPT Bruce
  Adams (OCS / TBS 2003-2007)

10
Quantico OCS EHI Data 2000-2002 Incomplete and
Retrospective

• 6 (7) HS Dx in 82 total EHI data available
• Data mostly missing for 50 out of ? HS
  transported (32) of 155 actual EHIs
• All (100) of HS during 3 mile run (1 PFT)
• HS Temp 106.1F (41.2C) to 107.8F (42.1C)
• 17 of the 72 HE Dx had Tgt104F (40C)
• 5 T gt 107F (41.7C)
• 6 T gt 106F lt 107F (41.1C lt 41.7C)
• 3 T gt 105F lt 106F (40.6C lt 41.1C)
• 3 T gt 104F lt 105F (40C lt 40.6C)

11
Parris Is. Unpublished EHI Data 1998-99

• No Dx noted on data. Mental Status not known.
  So, arbitrary HS CKgt3K and/or ASTgt100
• 32 HS in 142 EHI (23) by labs alone
• 10 HS had Temp lt 104F (40C)
• Range 97.9F (36.6C) to 103.1F (39.5C)
• T101F (38.3C), CK6K, AST209
• 21 HE T gt 104F (40C)some probably HS by mental
  status
• 1 T 109.2F (42.9C)normal labs common in HS
  with rapid cooling
• 3 T gt 107F lt 109F (41.7C lt 42.9C)
• 3 T gt 106F lt 107F (41.1C lt 41.7C)
• 7 T gt 105F lt 106F (40.6C lt 41.1C)
• 7 T gt 104F lt 105F (40C lt 40.6C)

12
Temperature

• Level of core temperature elevation NOT
  diagnostic of HS
• Parris Is. study - 468 EHI cases
• 1/2 cases with HS had Tlt 106F (41.5C)
• 1/2 cases with Tgt106F (41.5C) had HS

13
Thermoregulation ? Thermo-tolerance
Byrne, Lee, Tan and Lim MSSE (38 803-810, 2006)
14
(No Transcript)
15
EHI Risk Factors Environment

• Competitive or group activities peer pressure
• Kevlar, Flak, Packadd 10F (5.6C) to WBGT
• HUMID, sunny, hot (WBGT Flag system)
• Most EHI occur at WBGT 70F 85F (21.1C 29.4C)
• Military Heat Stress Flags
• Green 80F 85F (26.7C -29.4C) , Yellow 85F - 88F
  (26.7C 31.1C), Red 88F 90F (31.1C 32.2C)
  Activity cautions
• Black 90F (32.2C) Activity suspended unless
  required
• NOTE ACSM black flag starts at 82F (27.8C)
• Preceding day MAX heat stress
• Most EHI had preceding day WBGTMAX gt85F (29.4C)

16
Exertional Heat Illness Cases by Hour 1982 -
1996 (excluding 1992)Parris Island, South
Carolina
Number of cases
0800
1500
17
EHI Risk Factors Personal

• Overweight
• BMI 22-26 (OR 1.7)
• BMI gt26 (OR 3.6)
• Slow gt8 min/mile runner (OR 5.6)
• Overexertion (pushing beyond ability)
• Febrile, GI, or Respiratory illness
• Dietary Supplements, Drugs
• Dehydration, Prior EHI, poor acclimatization
• In literature but not noted in recent deaths or
  EHS cases70-100 acclimatized, fully/over
  hydrated.

18
EHI Signs (think heat stroke)

• Trect 103F to 110F (39.4C to 43.3C)
• If Tlt103F think other Dx like hyponatremia
• Tachycardia /-
• Hypotension /-
• SWEATING. NOT DRY (as in classic heat stroke)
• All EHS victims sweat in Quantico, Parris Is, and
  Okinawa. - Survey of all Navy sports docs 2006
• Mental Status Change Obtunded, Giddy, Crying,
  Combative
• Collapse
• Seizure

19
Immune Response to Intense Exercise
Open Window Theory
Intense exercise
Intense exercise
Immune function
Intense exercise
Normal immune function
Exercise
Suppressed Immune function
3 to 72 h
Suppressed Immune function
Chronically suppressed immune function
Post-exercise
Time
Smith L.L. Sports Med. 33347-364, 2003
20
Working Hypothesis
Heat sepsis triggers the primary pathway of heat
stroke
Heat intolerance results from a transient shift
in physiological state
Heat Stroke
Direct thermal effect drives the secondary
pathway of heat stroke
Exercise- induced immune changes
Pre-existing or sub-clinical infection
Facilitator
Pathology
Outcome HS
Heat
Sepsis
Clinical state
21
USMC Marathon October 2001Pentagon
22
If true, what does it mean?

• Dual pathway theory supported 1. SIRS likely.
  2. Direct heat damage over time possible.
• T97F with EHS
• Tgt106F not always EHS.
• Rapid ice-water cooling prevents sequela even at
  T110.5F (Quantico 2006)
• Role for cooling in other SIRS?
• Prior EHS not a risk factor for future EHS?
• No repeat EHScould prior EHS protect against
  future EHS?
• Role of heat tolerance testing?
• Hydration, WBGT based flags and acclimatization
  protection?
• Increased performance increased EHS risk
• Decreased performance decreased EHS risk
• EHS not a sweating failure.
• EHS victims SWEAT in hot, humid environments

23
Questions?
24
REFERENCES

• 1. Lim CL, Mackinnon LT. The Roles of Exercise
  induced Immune system Disturbances in the
  Pathology of Heat Stroke. The Dual pathway Model
  of Heat Stroke. Sports Med 2006 36(1) 39-64
• 2. Lim Cl et al. Preexisting inflammatory state
  compromises Heat Tolerance in Rats Exposed to
  Heat Stress. Am J Physio- Regulatory,
  Integrative and Comp Physiol. 2007 292 16-194
• 3. Ng QY et al. Plasma Endotoxin and Immune
  Responses During a 21-Km Road Race Under a Warm
  and Humid Environment. Ann Acad Med Singapore
  2008 37 307-14
• 4. Lim Cl. Heat Injury Prevention The Singapore
  Experience. Presented at Heat Lessons Learnt or
  Ignored Seminar. Australian Department of
  Defence.  Canberra AU. 20 NOV 2006.
• 5. Cotter J. Heat Injury Pathophysiology.
  Presented at Heat Lessons Learnt or Ignored
  Seminar. Australian Department of Defence. 
  Canberra AU. 20 NOV 2006.
• 6. Holtzhausen L Noakes TD, KorningB, et al.
  Clinical and biochemical characteristics of
  collapsed ultramarathon runners. Med Sci Sports
  Exerc 1994261095-1101.
• 7. Laird RH Medical care at ultraendurance
  athlete proposed mechanisms and approach to
  management. Clin J Sports Med 1997(4)292-301.
• 8. Holtzhausen L Noakes TD, Collapsed
  ultraendurance athlete proposed mechanisms and
  an approach to management. Clin J Sports Med
  19977(4)292-301.
• 9. Sandor RP Heat illness. Phys and Sports Med
  199725(6).
• 10. Gardner JW, Kark JA Heat-associated illness.
  In Strickland GL. Hunters Tropical Medicine.
  8th ed. 2000140-147.
• 11. BMC Parris Island 2000 Clinical Guidelines
  for Management of EHI Based on Symptoms and
  Clinical Chemistry Presentation.
• 12. Environmental illness in athletes. Seto CK -
  Clin Sports Med - 01-JUL-2005 24(3) 695-718, x
• 13. Gardner JW, Kark JA, Wenger BC et al.
  Exertional Heat Illness in U.S. Marine Recruits,
  presentation (no date) 1990s
• 14. Personal communication and U.S. Marine Corps
  and Navy Exertional Heat Injury experience survey
  including all Navy Sports Medicine Physicians
  with Steve Blivin. NOV 2006 and OCT 2007.
• 15. Byrne C, Lee JKW, Chew SAN et al. Continuous
  Thermoregulatory Responses to Mass-Participation
  Distance Running in Heat.. Med Sci Sports Exerc
  38(5) pp 803-810, 2006
• 16. Gardner JW, Gutmann FD, Potter RN, Kark JA.
  Nontraumatic exercise-related deaths in the U.S.
  military, 1996-1999. Mil Medicine. 167
  (12)964-70, Dec. 2002
• 17. Gaffin SL, Gardner JW, Flinn SD. Cooling
  Methods for Heatstoke Victims. Ltr to editor.
  Annals Int Med. 132(8) pp678-9, 18 APR 200021.
• 18. Climatic Injuries in the Armed Forces
  Prevention and Treatment 2003. Defense Medical
  Services Department, Ministries of Defense (U.K.)
• 19. Personal Communications Dr. Jim Cotter,
  Exercise and Environmental Physiology, University
  of Otago, Duedin, New Zealand with Dr Steve
  Blivin OCT 08.