heat stress txolan 2012
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Heat Stress Heat Stress HyperthermiaHyperthermia
Benjamin Buchanan, DVM
Diplomate American College of Veterinary Internal Medicine
Diplomate American College of Veterinary Emergency and Critical Care
Brazos Valley Equine Hospital, Navasota Texas
Who is BVEH?Who is BVEH?
Group of Large Equine Hospitals– Navasota– Stephenville– Rockdale
Navasota– Full service referral facility– Started admitting camelids in 2008
Who is BVEH?Who is BVEH?
Two Internal Medicine Specialists– Ben Buchanan
Residency in Knoxville, TN at UTK 50% Equine, 50% Food Animals Trained under Sarel Van Amstel Second residency in Emergency and Crtical Care
– University of Pennsylvania
Navasota - 2005
Who is BVEH?Who is BVEH?
Two Internal Medicine Specialists– Tiffany Hall
Residency at UC Davis– Finished in 2010
Started as Emergency and Critical Fellow at BVEH in 2010.
Goal of LectureGoal of Lecture
Lecture will cover heat stress, cause, prevention, diagnosis, treatment at the ranch before transport and what to expect after treatment.
Include original data from BVEH
DefinitionsDefinitions
Heat Stress– General name for several medical conditions
(heat exhaustion, heat cramps, heat stroke).
DefinitionsDefinitions
Hyperthermia– “Elevated body temperature due to failed
thermoregulation” – Wikipedia– Occurs when body absorbs or produces more
heat than it can dissipate
DefinitionsDefinitions
Heat Exhaustion– “A condition characterized by faintness, rapid
pulse, nausea, profuse sweating, cool skin, and collapse, caused by prolonged exposure to heat accompanied by loss of adequate fluid and salt from the body” – Dictionary.com
DefinitionsDefinitions
Heat Cramps– Muscle cramps causes by electrolyte and water
loss secondary to heat related illness.
DefinitionsDefinitions
Heat Stroke– “Hyperthermia caused by environmental
exposure to heat accompanied by phsical symptoms including changes in nervous system function” – Medicinenet.com
– Can be exertional or non-exertional– Damages brain, heart, kidneys, muscles– Medical emergency
DiscussionDiscussion
Based on literature Based on BVEH
experience Based on collective
veterinary experience
DiscussionDiscussion
Normal Metabolism Heat Distribution Definitions Effects of
Hyperthermia Risk Factors Symptoms Diagnosis
Treatment Prevention Complications Prognosis BVEH – Cases
– Demographics– Survival– Cost
MetabolismMetabolism
Requires waterHuman
– Ingest 2.3 liters per day– Output
Skin 350 ml per day Lungs 350 ml per day Sweat 100 ml per day Feces 100 ml per day Urine 1400 ml per day
MetabolismMetabolism
Camelids– 67% of body weight is water– ~1 liter per 100 pounds of body
weight in thermoneutral environment
– ~5 liter per 100 pounds on pasture
Includes water in forage
MetabolismMetabolism
Camelids– Will intake less water when food intake is
restricted.– Lactation increase water demand significantly– All same social factors that impact feeding may
impact water consumption– Water intake is critical!
MetabolismMetabolism
Requires waterCarries nutrients to cell
– Turned into energy, ATP, fat, polysaccharidesCarries waste products away from cell
– Carbon dioxide– HEAT
End product of ALL chemical reactions
MetabolismMetabolism
Water requirement is equal to metabolismFor every kCal of energy need 1 ml of waterIncreased energy demands = more HEAT =
more water– Exercise– Late Pregnancy
MetabolismMetabolism
Requires waterWaste products carried in blood
– Requires adequate blood volume– Requires perfusion
Poor perfusion to skin = poor heat transfer
MetabolismMetabolism
Getting rid of HEAT– RADIATION
Transfer of heat via infared heat waves Requires environmental temp next to skin be less
than core body temp Major source of heat loss
MetabolismMetabolism
Getting rid of HEAT– CONDUCTION
Transfer of heat to objects touching the body– Minor source of heat loss normally– Laying on cool ground
Transfer of heat to air– Significant source of heat loss– Requires air to be cooler than skin– Air movement important (air convection)
Cooling effect of wind proportional to speed of wind– Not linear but SqRt of velocity
MetabolismMetabolism
Getting rid of HEAT– EVAPORATION
Loss of heat via conversion of liquid to gas Insensible loss in lungs Sweat
MetabolismMetabolism
Impact of Fiber as Insulator– Holds air next to skin and impacts Conduction
and Convection– Insulation is impacted when fiber gets wet
Fat is also an insulator!
MetabolismMetabolism
High Environmental Heat– Stops Radiation– Stops Conduction
Actually gains heat via Radiation and Conduction
– Only route of heat loss is Evaporation
MetabolismMetabolism
Heat Index– Temp + Humidity– <120 is ok (80 F and 40% humidity)– 120 to 160 is slight risk– 160 to 180 is significant risk (80 F and 80%
humidity)– >180 is severe risk (105 F and 80% humidity)
MetabolismMetabolism
Dehydration– Camelids can sustain a 25% loss in body weight
from dehydration with no ill effects Shape of RBC allows for swelling and contraction
– Loss of 40% of plasma volumeImpacts ability to respond to heat stress
MetabolismMetabolism
Impacts ability to respond to heat stress– Lack of blood plasma reduces delivery of blood
to skin Less heat transfer Less sweating
– Must increase heat transfer via respiration– Increased respiratory rate compared to
normohydration
Effects of HyperthermiaEffects of Hyperthermia
104 F threshold in humans and other species for heat stroke
Increases tissue oxygen demand– Core temp above 105 F– Unable to take in enough oxygen
Supplement with nasal oxygen
Proteins denatures at 113 F
Effects of HyperthermiaEffects of Hyperthermia
Three important control mechanisms for cooling– Vasodilation– Sweating– Decrease in heat production
Effects of HyperthermiaEffects of Hyperthermia
Vasodilation– All areas of the skin
Helps carry heat to skin Increase delivery 8 times above normal May drop blood pressure
– Radiation and conduction heat transfer
Effects of HyperthermiaEffects of Hyperthermia
Sweating– Instantaneous with core temp increase– 2 degree increase in body temp causes 10 fold
increase in sweating (HUMAN)– Sweat glands in SAC are poorly developed
Located over entire body Concentrated on ventrum
Effects of HyperthermiaEffects of Hyperthermia
Decrease heat production– Inhibition of excess heat
production Shivering
Effects of HyperthermiaEffects of Hyperthermia
Sequence of Events– Increase in Core Body Temp– Adaptation with increase RR and HR– Sweating– Dehydration – fluid shifts– Muscle cramps = Recumbency and stiffness– Loss of blood pressure control– Heat Stroke
Effects of HyperthermiaEffects of Hyperthermia
Heat Stroke– Circulatory collapse
Lack of vasomotor control Loss of adequate blood volume
– Disseminated Intravascular Coagulation (DIC) Bleeding and clotting disorder Damages other organs and spine
– Teratogenic effects
Risk FactorsRisk Factors
Geography and TravelHeat Index and DurationFat and FiberIncreased activity (fighting,
packing, etc)
Risk FactorsRisk Factors
Food and Water intakePregnancy and Lactation Lack of appropriate shelterGeneral health / Parasitism
SymptomsSymptoms
Clinical Signs– Increase HR and RR – Nose flaring– Open mouth breathing– Drooling– Cushed over water or leaning forward– Laying in abnormal positions
SymptomsSymptoms
Clinical Signs– Scrotal swelling– Decreased GI function– Poor appetite– Frequent cooling in sprinkler or pools– Stiff gait – Neurologic deficits
DiagnosisDiagnosis
Clinical Signs and HistoryLab Values
– High CK/AST – muscle damage Most consistent abnormality
– Low Platelets– Stress response– Other organ damage– CTnI and Lactate
TherapyTherapy
Emergency Cooling– RADIATION
Shade
– CONDUCTION Fans Concrete A/C
– EVAPORATION Water Fans
– DO NOT PUT ICE ON SKIN
– Contact Veterinarian
TherapyTherapy
Veterinary care– Fluids
Blood Pressure Cold – Core Cooling Correct Acid-Base and
Electrolyte Issues
– Enema Cold water
– Oxygen
TherapyTherapy
Veterinary care– Pain Management
Critical Muscle damage is painful Nephrotoxic?
– Vitamins Target at metabolism and muscle repair B Vitamins, Vitamin E
TherapyTherapy
Veterinary care– Antibiotics
Especially with recumbency
– Slings and Pools Helpful in recovery Not in acute stage
TherapyTherapy
Veterinary care– Recumbency management
Physical therapy Supportive care Nutritional therapy
PreventionPrevention
Environment– Air quality
Lots of fans and misters– Consider humidity when using mister
– Consider fan quality
Adequate space for herd
– Sprinklers and ponds
PreventionPrevention
Environment– Shade and Shelter
Important year round
– Try to avoid traveling in heat of day July and August
PreventionPrevention
General Health– Body Condition Score– Weigh Frequently
Identify dehydration and body water loss early
– Monitor temps Microchips
PreventionPrevention
General Health– Screen for parasites– SHEAR! and repeat in July
or August if necessary
PreventionPrevention
Breeding– Plan breeding
Not heavy pregnant in July, August, September >30 days pregnant by July 1
– Weaning Not lactating in July, August, September Wean before July
– Heat temporarily damages sperm quality
PreventionPrevention
Nutrition– Monitor food intake
Decreased food intake = decreased water intake
– Provide excessive amounts of clean water in multiple locations
– Vitamins Vit E?
– Herbs and Minerals?
ComplicationsComplications
Complications– Acute death– Chronic neurologic impairment– Increased susceptibility to future hyperthermia– GI dysfunction
ComplicationsComplications
Complications– Problems of recumbency
Pneumonia Eye ulcers Bed sores Urine/fecal scalding
PrognosisPrognosis
Prognosis?– People
Rarely leads to permanent deficit with heat stroke Not always true
– Chicago study 58 heat strokes
– 25% died within 3 months after discharge
– Remainder had permanent neuro impairment
– Half had chronic organ damage (Kidney)
– Age not a factor
PrognosisPrognosis
Prognosis?– Alpacas
Not known Restrospective Case Evaluation of BVEH
– 2008 through 2011
– Seasons
– Laboratory
– Therapy
– Cost
– Survival
Case DiscussionCase Discussion
BVEH Cases– 22 Records
2008 – 1 patient 2009 – 6 patients 2010 – 7 patients 2011 – 8 patients
Case DiscussionCase Discussion
BVEH Cases– Season
June – 2 cases July – 2 cases August – 13 cases September – 4 cases April – 1 case
Case DiscussionCase Discussion
BVEH Cases– Laboratory Values
CK/AST – 100% increased– < 10 % of recumbent alpaca had increase
Glucose – 30% increased Lactate – 20% increased (all died!) CTnI – Elevated in 3 cases (2 died)
Case DiscussionCase Discussion
BVEH Cases– Laboratory Values
CK/AST– Internal component of muscle cell
– Requires lysis of cell for increase
– CK goes up first
– AST remains elevated longest
Case DiscussionCase Discussion
BVEH Cases– Laboratory Values
Lactate– Indication of oxygen debt
• Increased metabolism beyond normal
• Decrease in oxygen delivery
– Poor delivery
• Blood pressure control
• Lack of blood volume
Case DiscussionCase Discussion
BVEH Cases– Laboratory Values
CTnI– Internal component of HEART muscle
– Cleared rapidly
– Elevation is indication of ongoing damage
Case DiscussionCase Discussion
BVEH Cases– Therapy
Air conditioning Most received IV fluids Most received ESE
– Non-surviors more likely to not receive ESE
– Likely due to acute nature of death
– Added to therapy in 2010
Case DiscussionCase Discussion
BVEH Cases– Cost
Average length of stay = 9 days (range 4 to 30 days) Average invoice total = $1,374.63 (range $466.70 to
$4,571.07)
Case DiscussionCase Discussion
BVEH Cases– Survival
14 out of 22 discharged alive 63%– 1 to 7 years of age
– Rectal temp at presentation – 103.7 F
– Non survivors 8 out of 22 died in hospital 37%
– 2 to 10 years of age
– Rectal temp at presentation 105.1 F
Case DiscussionCase Discussion
BVEH Cases– Long term
Not officially completed Several relapsed and presented the following or
subsequent years Several had neurologic deficits One aborted cria Several euthanized at home for variety of reasons
Case #1 Case #1
Adult male– Houston Weather on August 21, 2009
0.73 inches of rain High of 100 F Humidity ~ 71% with high of 100% Wind 5 to 32 mph
– 8 consecutive days of > 95 F and 95%
Case #1 Case #1
Aug 21– Acutely recumbent 5 pm on farm with fever
Given banamine by owner
– Presentation 106.8 on arrival Increased RR at 40 bpm Lateral recumbency Transported into ICU (air conditioned)
Case #1 Case #1
Aug 21– 7 pm
Fans and water bath Placed IV catheter (jugular) Bolus 2 liters of room temp electrolyte fluids Switched to cold fluids post bolus
– Laboratory CK unmeasureable, AST unmeasureable, Glu 300
mg/dl, Creatinine 2.2 mg/dl
Case #1 Case #1
Aug 22– 9 pm
Temp 97.7 F, HR 52, RR 24
– 2 am Temp 95.7 F
– 8 am Temp 97.2, HR 40, RR 12 Unable to stand
Case #1 Case #1
Aug 22– 8 am
Given banamine IV ESE IM
– 5 pm T – 95.7 F, HR 40, RR 16 Good appetite unable to stand
Case #1 Case #1
Aug 23 to Aug 25– Kept in ICU, but taken off 24 observation and
care– Continued banamine and physical therapy
Aug 26 moved out of ICU– Temp spiked to 102.4 – 104.3– Continued banamine and physical therapy
Case #1 Case #1
Laboratory– Aug 26– CK – decreasing 1497– AST – unmeasurable– Glu – 170 mg/dl– Creatinine 1.3 mg/dl
Case #1 Case #1
Aug 26 – 31– Continued to have rectal temp 103 F to 104 F– Continued PT and banamine
August 31– Stood with assistance– CK – 407 IU/L, AST – 1988 IU/L– Went home
Case #1 Case #1
Conclusions– Muscle damage is part of syndrome not
recumbency Returned to normal despite being recumbent
– CK / AST values indicative of severity and possibly level of pain.
– Need to address muscle issues with recumbency
Take HomeTake Home
5 Most Important Points– Combination of heat and humidity is important– Understand and manipulate cooling– Shear early and repeat– Monitor appetite and water intake– Diagnose early and treat aggresively
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