Exertional Heat Illness Flashcards
Exertional Heat Illness
Collapse on exertion
Body core temperature >39 degrees
Recover very quickly
Usually caused by drop in blood pressure
- struggle between pumping blood to surface to decrease heat and pumping blood to working muscles
Exertional Heat Stroke
More severe
Collapses on exertion
Body core temperature >40 degrees
Neurological disturbance - more sustained in severe cases
Multiple organ failure in very severe cases
EHI Incidence - Sport
Varies between sports and events but increases with rising ambient temperature and humidity
Observed more frequently in road races and other activities that involve continuous high intensity metabolic activity
EHI Incidence - Military
Training - on average ~100 personnel are admitted to hospital each year during training
Operations
- average maximum air temp. in excess of 40 degrees in Iraq and Afghanistan
- 849 cases of heat illness during first 6 months of Op Telic
Proposed new framework classification for ‘heat-illness’
Conditions in which there is a pathological increase in body heat storage
- Exercise and environmentally induced heat stroke:
- –> due to inadequate heat loss
- –> due to excessive endogenous heat production
- –> combination
Conditions in which there is no pathological increase in body heat storage
- Exercise - associated postural hypotension
Risk factors
Sleep deprivation
Lack of fitness
High solar radiation
Training at hottest hours
Absence of medical support
Heat stressors
Clothing thermal properties
Intensity and duration of exercise
Thermal environment
- Temperature
- Humidity
- Air velocity
Individual heat tolerance
Wet Bulb Globe Temperature
Environmental stress measured
Threshold Limit Values
Takes into account
- temperature
- solar radiation
- humidity
- air velocity
Gives WBGT index
Physical Fitness
Rectal temperature increases as exercise intensity increases (Saltrin & Hermansen, 1994)
Mortality of sedentary rats occur at lower core temperature than endurance trained rats (Fruth & Gisolfi, 1983)
Menstrual Cycle Phase
Temperature higher in luteal phase of cycle
Endurance time reduced
Age
Increased cases of heat stroke in older individuals - probably related to physical fitness (Armstrong, 2003)
Children have a smaller surface to body mass ratio
- lower sweat rates
- slower rate of acclimatisation
- greater core temperature before sweating
Treatment
Every minute counts
Rectal temperature is best gauge
Cool first, transport second
Ice-water or cold-water is best (Casa et al., 2005)
Monitor closely - remove athlete from tub when rectal temperature = 38.9 degrees
Patient can be cooled from ~42 degrees to 38.9 degree in 15-30 mins (Roberts, 1989)
Send patient to hospital after cooling
Survival rates approach 100% with fast cooling
Recovery
90% of heat stroke patients have normal heat tolerance within 2 months (Armstrong et al., 1990)
Only 1% of Marine recruits who suffered heat illness had subsequent occurrence per year (Phiney et al., 2001)
Role of Arteriovenous Anastomoses (AVAs) in Heat Loss
Location
- Palmar side of fingers
- Plantar side of toes, palm, sole, ear and nose
Will not constrict - allow continued blood flow to periphery even when skin temperature is low
Proposed Mechanisms - Incidence & Pathophysiology of EHI in Parachute Regiment Trainees - source
Bilzon, Walsh and Jackson, 2008
