heat stress txolan 2012

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


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


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 StressHyperthermiaHeat ExhaustionHeat CrampsHeat Stroke


Heat Stress– General name for several medical conditions

(heat exhaustion, heat cramps, heat stroke).


Hyperthermia– “Elevated body temperature due to failed

thermoregulation” – Wikipedia– Occurs when body absorbs or produces more

heat than it can dissipate


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


Heat Cramps– Muscle cramps causes by electrolyte and water

loss secondary to heat related illness.


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


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


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!


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


Water requirement is equal to metabolismFor every kCal of energy need 1 ml of waterIncreased energy demands = more HEAT =

more water– Exercise– Late Pregnancy


Requires waterWaste products carried in blood

– Requires adequate blood volume– Requires perfusion

Poor perfusion to skin = poor heat transfer


Getting rid of HEAT– Three Methods

RADIATION CONDUCTION EVAPORATION


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


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


Getting rid of HEAT– EVAPORATION

Loss of heat via conversion of liquid to gas Insensible loss in lungs Sweat


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!


High Environmental Heat– Stops Radiation– Stops Conduction

Actually gains heat via Radiation and Conduction

– Only route of heat loss is Evaporation


High Humidity– Impacts efficiency of

Evaporation


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)


Combination of Heat and Humidity is KILLER


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


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


Three important control mechanisms for cooling– Vasodilation– Sweating– Decrease in heat production


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


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


Decrease heat production– Inhibition of excess heat

production Shivering


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


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


Environment– Shade and Shelter

Important year round

– Try to avoid traveling in heat of day July and August


General Health– Body Condition Score– Weigh Frequently

Identify dehydration and body water loss early

– Monitor temps Microchips


General Health– Screen for parasites– SHEAR! and repeat in July

or August if necessary


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


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


BVEH Cases– Season

June – 2 cases July – 2 cases August – 13 cases September – 4 cases April – 1 case


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)



CK/AST– Internal component of muscle cell

– Requires lysis of cell for increase

– CK goes up first

– AST remains elevated longest



Lactate– Indication of oxygen debt

• Increased metabolism beyond normal

• Decrease in oxygen delivery

– Poor delivery

• Blood pressure control

• Lack of blood volume



CTnI– Internal component of HEART muscle

– Cleared rapidly

– Elevation is indication of ongoing damage


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


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)


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


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

Questions?

heat stress txolan 2012

Education

definitions heat exhaustion

water consumption water

metabolism water requirement

water human

water demand

water exercise

water loss secondary

metabolism camelids