Heat Stress from the Sidelines

Dan Foster, PhD, ATC

August 20, 2009

Case #1

• 20 yo Div-I FB• 6’3” / 274 lbs (BMI 33.5, VO2 40.1)

• HIIS = high

• Day 15, On field WBGT 91oF

• Tc = 103.6oF

• Nausea and dizziness after 1.5 hr

Emerson C, et al. Unpublished FIU. 2006.

• Rested in shade - 101.7oF

• Returned to drills and conditioning

• Progressive dizziness, nausea, disorientation, pallor, transient LOC, sensation of heat – 102.7oF

• Ice bags at neck and axilla – 102.7oF 10 min later could walk

• Cool water bath (72oF)

• In 14 min temp at 100.4oF

BMI

• Normal– 18.5-25

• Overweight– 25-30

• Obese– >30

Gardner J, et al. MSSE 1996; 28:939-944

kg/m2

> Heat production

< Heat dissipation

low specific heat

VO2

• Acclimation to heat 10-14 days

• Poor CV fitness 3 fold increase in risk

Gardner J, et al. MSSE 1996; 28:939-944

ml/kg/min

Davies H. Cross training; 2009

WBGT

Reading• <18oC (<65oF)

• 18-23oC (65-73oF)

• 23-28oC (73-82oF)

• >28oC (>82oF)

Comments• Low risk still exists

• Level inc as progress through day

• At-risk should not compete

• Reschedule, delay, or high alert

Roberts W. 1998; Medical Manual.NATA

WBGT = 0.7Twb + 0.2Tbg + 0.1Tdb

Mild Heat Illness Symptom Scale

• Feeling tired• Cramps• Nausea• Dizziness• Thirst• chills

• Vomiting• Confusion• Muscle

weakness• Heat sensations• Feeling

lightheadedLow-risk positions: QB, P, K

Mid-risk positions: DB, RB, LB, R

High-risk positions: OL, DLCoris E, et al. SMJ; 2006.

0-10 scale with anchors

Exertional Heat Illness

Exertional Cases

• Heat edema/rash• Muscle cramps• Syncope• Exhaustion• Stroke• Hyponatremia

Management

• Elevation of legs/keep dry• Sports drinks, IV• Shade, rehydrate• Cool, shade, rehydrate• Immersion, transport• Transport, IV

Rectal temp* Return is possible for the first 4, and gradual for last 2

Recruit Heat Illness by WBGT Category at Time of Illness, 7-9 am Cases

0

1

2

3

4

5

6

<6

0

60

-<6

5

65

-<7

0

70

-<7

5

75

-<8

0

80

-<8

5

85

-<8

8

88

-<9

0

90

+

WBGT Category (°F)

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10

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rs

050100150200250300350400450

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Case Rates

Case Counts

PARRIS ISLAND MARINE CORPS RECRUIT TRAINING DEPOT, SC

Recruit Heat Illness by WBGT Category of Prior Day Maximum, 7-9 am Cases

0

2

4

6

8

10

12

<6

0

60

-<6

5

65

-<7

0

70

-<7

5

75

-<8

0

80

-<8

5

85

-<8

8

88

-<9

0

90

+

WBGT Category (°F)

Ca

se

s p

er

10

0,0

00

pe

rso

n-d

ay

s

0

50

100

150

200

250

300

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Ca

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Case Rates

Case Counts

PARRIS ISLAND MARINE CORPS RECRUIT TRAINING DEPOT, SC

Volleyball Pre-season 2009

Should we develop a formal index for risk?

• Risk Factors– High fat– Low fitness– Past Hx– Not acclimatized– Dehydration– Meds/Supplem*– Heavy clothing

– Fever or illness– Sunburn/skin– Prepubescent– Over-exertion– Stoic– CV disease– Sickle-cell traitAntihistamines

AntipsychoticAntidepressantDiureticsErgogenic stimulantsbetablockers

Previous day WBGTDark colored clothing

Risk Assessment Matrix

• WBGT• # days Cat 5• Past work load• Work load today• Acclimatization d• Rest in past day

• Category 4-5• >4• Hard• Hard• <3• <2 h

7-13=extreme risk Hard Work = speed >7 mph, resistance >70% maxUS Army 2009

Adjusted

Matrix Actions

• Know the players– Individual risk factors

• Check hydration status– Do after each practice– Require extra fluids as needed– Check urine color

• Check illness and Meds

Should ATs be trained in IV administration?

• Heat cramps

• Heat syncope

• Exercise exhaustion

• Exertional hyponatremia

Emerson C, et al. Unpublished FIU; 2006.

Is rectal temp necessary?

• Oral

• Tympanic

• Axillary

• Skin

Casa D. JAT. 2007; 42:333-342

How far should we go to measure sweat rate?

• NATA recommends calculating sweat rate on each athlete:– (BWpre – BWpost + fluid in – urine

vol)/ex time)– Do this for a variety of

environmental conditions, practices, competition

– 95% CI reported 0.5-2.5 L/h

Casa D, et al. JAT. 2008; 42:333-342

Thanks!