Taking the Heat

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Taking the Heat
HKCEM College Tutorial

• Author
• Dr. C C Lau
• Dr. T W Wong
• Revised by Dr. Shek Kam Chuen
• Oct., 2013

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Heat illness is not an uncommon presentation to
ED in summer months.

• Exertional heat stroke had been reported in
  healthy military recruits in Hong Kong.
• One local study revealed that heat illness (24.4
  of total cases) was one of major reasons for
  helicopter transfer from June 1998 through
  November 1998.
• Among 17 casualty evacuation cases of Oxfam
  Trailwalker 2006, 2 of them were heat cramp and 3
  of them were heat exhaustion.

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Heat related illness is expected to increase
since the emerge of global warming.
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You are the GFS doctor on duty on a hot Sunday

• What problems will you anticipate?

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Heat illnesses

• What are the predisposing factors?
• Who cannot take the heat?

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Predisposing factors to heat illness

• Environmental Factors
• 1) Working in hot, humid environment close to or
  above body temperature
• 2) Limited water and salt access
• B) Patient Factors

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Heat Index
http//en.wikipedia.org/wiki/Heat_index
Can you name the other two meteorological factors
affecting the heat stress?
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Heat stress

• The "heat stress" perceived by humans depends on
  many factors.
• The four relevant meteorological factors are
• air temperature,
• relative humidity,
• wind speed and
• solar radiation.

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Acclimatization

• Ability to adapt the heat stress
• 7 days to several weeks
• Change the onset of sweating
• Increase volume of sweating
• Improve skin blood flow, CVS function
• alteration of the thermoregulatory set point.

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Predisposing factors to heat illness

• B) Patient Factors
• 1) Drugs (anticholinergics, diuretics, CVS
  drugs, phenothiazines, amphetamines,
  salicylates)
• 2) Disease (cardiovascular diseases,
  diabetes, hyperthyroidism, skin ds)
• 3) Days--Extreme ages
• 4) Dehydration

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You are called to treat a group of hikers.

• Ms. Bookworm is not feeling well.
• Mr. Man is stretching his calf muscle.

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Miss Bookworm

• Sudden severe dizziness with black outsensation
• Well after lying flat for 2 min.
• No convulsion, no head injury
• Good past health
• diagnosis and management?

What is the problem here? What is the tx?
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Heat Syncope

• in non-acclimatized persons during early stage of
  heat exposure
• postural hypotension
• peripheral vasodilatation
• decreased vasomotor tone
• relative volume depletion
• treatment removal from heat source, rehydration,
  rest, and look for secondary traumatic injury

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Mr Man

• c/o calf pain while walking
• Good past health
• Has taken 4 bottles of distilled water because of
  heavy exercise and sweated a lot
• What is the diagnosis and management?
• What is he suffering from?

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Heat Cramps

• painful, involuntary, spasmodic contractions of
  (calf) muscles
• persons sweating liberally replace fluid loss
  with water
• self limiting, exact pathogenesis unknown
  (relative deficiency of Na, K, and fluid at
  cellular level)

What is the treatment ?
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Heat Cramps

• Treatment
• rest in cool environment with salt and fluid
  replacement
• Prevention
• maintaining adequate dietary intake of salt and
  fluid

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As you are taking care of Ms Bookworm and Mr Man

• Down the path, someone is waving fanatically.
• Someone seems to be in trouble !

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A man is down

• M/40 hiking in Sai Kung
• Complains of dizziness/fatigue
• Found confused hot moist flushed skin

Outdoor temp. 33ºC Relative humidity 95
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What is the likely diagnosis?

• ? Heat Stroke
• ? Heat Exhaustion

• How to differentiate between the 2 conditions ?

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HEAT EXHAUSTION HEAT STROKE

• The major heat-related illnesses, occur along a
  continuum of severity
• Clinical features of dehydration, electrolyte
  losses and failure of thermoregulatory mechanisms

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HEAT EXHAUSTION

• Acute heat injury with hyperthermia due to
  dehydration
• Impaired heat dissipation due to extreme
  environmental conditions or increased endogenous
  heat production
• May progress to heat stroke

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HEAT EXHAUSTION

• Clinical Features
• Often non-specific and insidious in onset similar
  to viral illness
• fatigue and weakness
• nausea and vomiting
• headache, dizziness, irritability
• myalgia and muscle cramps
• Preserve cognitive function with no impaired
  conscious state

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HEAT STROKE

• Extreme hyperthermia with thermoregulatory
  failure
• Clinical features of end organs damage
• Characterised by CNS involvement and elevated
  core temperature gt 41ºC
• Mortality and morbidity from cerebral,
  cardiovascular, hepatic, and renal damage

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Which dx is likely for our patient?

• Heat Stroke
• Which type?

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HEAT STROKE

• Traditionally 2 types according to underlying
  etiology, but clinically indistinguishable
• exertional typically in young athletic patients
  exercising heavily in the heat
• classic commonly in older patients with
  underlying diseases exposed to extreme
  environmental conditions

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Characteristics of Heat stroke
Exertional Classic
Healthy Chronic ill/on medication
younger older
Strenuous exercise sedentary
sporadic Heat wave
diaphoresis Sweating may be absent
hypoglycemia normoglycemia
DIC mild coagulopathy
Rhabdomyolysis Mild increase CPK
20-30 Acute renal failure lt5 Acute renal failure
Marked lactic acidosis Mild acidosis
hypocalcaemia normocalcaemia
Waters TA, Al-Salamah MA. Heat Emergencies. In
Tintinalli JE, et al. Tintinallis Emergency
Medicine.(7th Ed) New YorkMcGraw-Hill, 2011
p.1339-44.
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Differential Diagnosis of Heatstroke

• Intracranial haemorrhage
• Toxins/ Drug
• e.g. anticholinergic, salicylate, sympathomimetic
  
• Seizures
• Malignant hyperthermia
• Neuroleptic malignant syndrome
• Serotonin syndrome
• Thyroid storm
• Sepsis/ infection
• e.g. Encephalitis, Meningitis, Typhoid, Malaria

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Clinical Features
Heat Stroke

• All symptoms of heat exhaustion
• Critical feature of CNS dysfunction with sudden
  onset in 80 cases
• bizarre behaviour, hallucinations, confusion,
  disorientation, convulsion, coma
• hyperpyrexia gt 41ºC
• sweating may be present (gt50), anhydrosis is
  usually a late finding

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Heat illness symptoms, signs and treatment
Symptoms Signs Treatment
Heat cramps Painful muscle cramps, Normal to mild elevated temperature, sweating Palpable muscular spasm Stretch, ice massage, oral fluids(salt-con- taining)
Heat syncope Syncope Loss of consciousness Rest, supine with feet up, monitor vital signs
Heat exhaustion Fatigue, inability to continue exercise, dizziness, nausea, vomiting, syncope, chills of head and neck Orthostatic hypotension, elevated core temperature (up to 40C), syncope ABCs, cool, rest,monitor temp/ Vital Signs, oral fluids (salt-con-Taining)
Heat stroke Pronounced mental status changes, confused, fatigue, nausea, vomiting, seizures, anhidrosis or sweating Elevated core temp gt40C, hypotension, tachycardia, tachypnoea, possible cessation of sweating, coma, DIC, ARF ABCs, cool urgently, IVF, intensive care support
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What is your initial mx for this patient?

• Support ABC
• Cooling fast!

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First aid treatment

• move patient to shady area
• improve heat loss by physical means
• Fanning, spray water, immersion
• oral rehydration if no contraindication
• close monitoring and immediate transfer to
  hospital

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Transfer by helicopter
Continue cooling en route
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Treatment in ED

• What are your priorities?

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ED Treatment

• 1) ABC, oxygen
• 2) Immediate cooling by physical means to correct
  hyperthermia in 45-60 min
• Remove clothing, water spraying, fanning,
• ice packs
• Peritoneal lavage with cold potassium-free
  dialysate
• How about immersion method?

Glass Hg thermometer can register temp. up to ?
Deg. C
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Mechanisms of heat transfer

• Radiation
• Conduction
• Convection
• Evaporation

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ED Treatment

• 3. Rehydration, electrolyte replacement, maintain
  adequate urine output, alkaline diuresis if
  myoglobinuria
• 4. Supportive treatment and continuous close
  monitoring
• 5. Look for predisposing cause

What is the prognosis?
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Prognosis

• Related to degree and duration of hyperthermia
• Mortality 10-70, highest with treatment delayed
  beyond 2 hours
• Mild cases, rapid and complete recovery, except
  in the ill elderly
• Severe, may die suddenly, or recover with
  residual cerebellar or cortical signs

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Target Temperature

• Heat stroke patients should be cooled rapidly to
  a core temperature of 38.5C to 39C, after which
  point active cooling should be stopped to avoid
  hypothermia.
• Continuous core temperature monitoring is needed
  to keep temperatures between 37C and 38C and to
  identify any rebound of hyperthermia requiring
  further treatment.

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Other treatment

• Dantrolene
• Panadol or other antipyretics
• No evidence to support the use the above drugs

Smith JE. Cooling methods used in the treatment
of exertional heat illness. Br J Sports Med
200539(8)503-7.
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Heat stress causes damage

• heat is directly toxic to cells.
• heat stress results in release of inflammatory
  cytokines
• elevated temperatures seem to result in injury to
  vascular endothelium, resulting in enhanced
  vascular permeability, activation of the
  coagulation cascade, and disseminated
  intravascular coagulation (DIC)

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Left untreated

• severe heat illness can be seen as a combination
  of direct cytotoxicity and a severe systemic
  inflammatory response in which encephalopathy
  predominates early in the course of the disease.
• If left unchecked, acute renal failure(ARF),
  coagulopathy, hepatic dysfunction, and ultimately
  multiple organ dysfunction system will result.

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Disposition

• Admit ICU
• Other mild and uncomplicated heat related illness
  like heat syncope or heat exhaustion can be
  managed in EMW or observation ward.

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How to prevent heat illness ?

• Most heat illness are preventable

• The "Heat Stress Monitoring System" developed by
  the Observatory uses three types of temperature,
  namely Natural Wet Bulb Temperature (Tnw), Globe
  Temperature (Tg) and Dry Bulb temperature (Ta),
  to calculate a combined temperature index called
  Wet Bulb Globe Temperature (WBGT) according to
  the following formula
• WBGT 0.7 Tnw 0.2 Tg 0.1 Ta
• Air temperatures, humidity, wind speed, solar
  radiation

• WBGT above 27.8C is considered very high risk.
  WBGT between 22.827.8C is considered high
  risk. WBGT between 18.322.8C is considered
  moderate risk.
• The American College of Sports Medicine
  recommends canceling sporting events when the
  WBGT index is above 28C.
• http//www.weather.gov.hk/education/edu01met/wxphe
  /ele_heat-stress_e.htm

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• The Hong Kong Observatory maintains a close watch
  on the local temperature changes.
• It issues Very Hot Weather Warning whenever
  Hong Kong is threatened by very hot weather, to
  alert members of the public to the risk of
  heatstroke.

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Actions to be taken for Very Hot Weather Warning

• When engaged in outdoor work or activities,
  drink plenty of water and avoid over exertion. If
  not feeling well, take a rest in the shade or
  cooler place as soon as possible.
• People staying indoors without air-conditioning
  should keep windows open as far as possible to
  ensure that there is adequate ventilation.
• Avoid prolonged exposure under sunlight. Loose
  clothing, suitable hats and UV-absorbing
  sunglasses can reduce the chance of sunburn by
  solar ultraviolet radiation.
• Swimmers and those taking part in outdoor
  activities should use a sunscreen lotion of SPF
  15 or above, and should re-apply it frequently.

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Three bring home messages

• Heat illnesses encompass a spectrum of syndromes
  ranging from muscle cramps to life threatening
  heat stroke.
• The cardinal features of heat stroke are
  hyperthermia (gt40C) and altered mental state.
  (not found in heat exhaustion)
• Heat stroke is a true medical emergency and
  patient warrants admission to intensive care unit
  for further treatment and monitoring.

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Thank You