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Accidental Hypothermia François Dufresne McGill Emergency Medicine May 2 nd 2001 The Case of Tommy 23h10 Call from MD working in James Bay Male, 27 y.o. Unresponsive. Found in snow, cross-country skiing Normal Airway. Breathing.  O 2 sat. Femoral pulse + (35)  BP.

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accidental hypothermia

Accidental Hypothermia

François Dufresne

McGill Emergency Medicine

May 2nd 2001

the case of tommy
The Case of Tommy
  • 23h10
  • Call from MD working in James Bay
  • Male, 27 y.o. Unresponsive.
  • Found in snow, cross-country skiing
  • Normal Airway. Breathing.  O2 sat.
  • Femoral pulse + (35)  BP.
  • GCS=3 TR = 28C.
  • IV. Monitor. Mask with 100% O2
the case of tommy3
The Case of Tommy…
  • Friend told MD:
    •  PMH.  Rx.  drugs.  EtOH
  • Major foot deformity
  • Looks like fell in ski and could not return home by himself…
  • MD has some questions for you…
the case of tommy4
The Case of Tommy…
  • Should he intubate? Are there risks to precipitate dysrythmias?
      • Cold myocardium prone to arythmias?
  • How should he rewarm the patient?
      • Danger of afterdrop?
  • He wants an ABG but should he ask for the blood to be warmed to normal T for analysis…or it doesn’t matter?

Answer: You’ll call him back…

the case of tommy5
The Case of Tommy…
  • MD calls you back 30 minutes later
  • Pt in cardiac arrest : V.fib. Now 27C
  • 3 shocks
  • Epinephrine + re-shock
  • Having Amiodarone prepared…
  • How long should he do CPR and rescussitation?

Answer ?

Anything wrong ?

introduction
Introduction
  • Maritime / War litterature
  • Hannibal experience in 218 B.C
introduction8
Introduction
  • EtOH 
  • Mental illness 
  • Homelessness 
  • Province of Quebec  Cold
slide9
Plan
  • Definitions
  • Physiology
  • Pathophysiology
  • Labs findings : ABG, ECG
  • Rewarming methods
  • Afterdrop
  • ACLS 2000 guidelines
definitions
Definitions
  • Primary VS Secondary
  • Primary
    • Normal thermoregulation
    • Overwhelming cold exposure
  • Secondary
    • Abnormal thermogenesis
    • Multiple causes
definitions11
Definitions
  • Hypothermia : < 35C
  • Mild : 32-35C
  • Moderate : 28-32C
  • Severe : < 28C
physiology heat production
Physiology: Heat production
  • Basal metabolism (Metabolic rate)
    • Heart / Liver
  • Anterior hypothalamus
  • Thyroid / Sympathetic
  • Preshivering muscle tone (2x)
  • Shivering (2-5x)
  • Posterior hypothalamus
physiology heat dissipation
Physiology: Heat dissipation
  • Radiation (55-65%)
      • Gradient between environement and exposed body area.
  • Conduction (2-3%)
      • Direct contact with cold substance
  • Convection (10-15%)
      • Wind…
  • Evaporation (20-35%)
physiology
Physiology…
  • Above 32C:
    • Vasoconstriction
    • Shivering
    • Basal metabolic rate
  • Below 32C:
    • No shivering
  • Below 24C:
    • No basal metabolic rate
pathophysiology
Pathophysiology

Cardiovascular

  • Initial tachycardia
  • Gradual bradycardia : HR 50% at 28C.
  • Not consistent ?
    • Hypoglycemia, intoxication, hypovolemia,…?
  • Refractory to atropine
  •  BP  CI
  • A.fib (T < 32C)
  • V.fib (T < 28C)
pathophysiology16
Pathophysiology…

CNS

  • Cerebral metabolism  6% / 1C
  • Normal autoregulation until 25C
  • EEG flat at 19C

Renal

  • Cold diuresis
    • Peripheral vasoconstriction
    • Failure to reabsorb Na+ and water.
pathophysiology17
Pathophysiology…

Respiratory

  • CO2 production  50% at 30C
  • Decreased RR
  • ARDS possible

Hematology

  • Hemostasis and coagulation impaired
  • Problems with CPB
mild 32 c
Mild (> 32C)
  • Increase metabolic rate
  • Maximum shivering thermogenesis
  • Amnesia / dysarthria / ataxia
  • Loss of coordination
  • Tachycardic, tachypneic
  • Normal BP
moderate 28 32 c
Moderate (28– 32C)
  • Stupor
  • No shivering
  • Bradycardic / A.fib
  •  BP  RR
  • Pupils dilated (< 30C)
severe 28 c
Severe (<28C )
  • Coma
  • No corneal or oculocephalic reflexes
  •  BP
  • V.fib (Maximum risk: 22C)
  • Apnea
  • Asystole
  • Areflexia / fixed pupils
  • Flat EEG (19C)
lab findings ecg
Lab findings : ECG
  • Woman, 75 y.o
  • Found unconscious in her apartment
osborn j wave
Osborn (J) Wave
  • Mr. John J. Osborn in the early ’50’s.
  • When T< 33C
  • 25%-30% of patients
  • Positive-negative deflection

Osborn JJ: Experimental hypothermia: respiratory and blood pH changes in relation to cardiac function. Am J Physiol 1953; 175:389.

osborne j wave
Osborne (J) Wave…
  • Amplitude proportionnal to degree of hypothermia
  • Usually V3-V6
  • At junction of QRS and ST segment

Osborn JJ: Experimental hypothermia: respiratory and blood pH changes in relation to cardiac function. Am J Physiol 1953; 175:389.

ecg in hypothermia
ECG in Hypothermia
  • Muscle tremors artifacts
  • Early changes
    • Bradycardia
    • T wave inversion
    • Prolonged PR, QRS and QT intervals
  • A.fib when T < 32C
  • V.fib when T < 28C
lab findings abg
Lab findings : ABG
  • Man, 45 y.o,.
  • Rectal T= 30C. LOC Intubated.
  • Acid-base status?
  • Technician asks you if he should warm the blood before analysis…

A) Don’t warm it : 30C

B) Warm it to 37C

C) heu…(30+37)/2….33.5C

D) Both and I’ll pick the best one.

abg in hypothermia
ABG in Hypothermia
  • 1st ABG (30C):
      • pH = 7.5
      • pCO2 = 27
  • 2nd ABG (37C):
      • pH = 7.4
      • pCO2 = 40
  • Which one do you pick?
  • Will you try to  RR or VT to  pCO2 ?
  • Everything’s perfect, I don’t touch the ventilator ?
  • The answer ? ….

The Good One !!!

abg in hypothermia the rationale
ABG in Hypothermia……the rationale
  • pH of water at any given T defines neutrality
  • H2O  H+ + OH-
  • As T , less free H+ and OH- are generated and pH of neutrality .
  • As T , CO2 content is the same but pCO2 .

Delaney KA and al. Assessment of Acid-Base Disturbances in Hypothermia and their physiologic consequences. Ann Emerg Med, Jan 1989; 18:72-82.

slide31
So…
  • 1st ABG (30C):
      • pH = 7.5
      • pCO2 = 27
  • 2nd ABG (37C):
      • pH = 7.4
      • pCO2 = 40
abg in hypothermia the rationale32
ABG in Hypothermia……the rationale
  • ABG machines usually warms blood to 37C.
  • So use the UNCORRECTED ABG for normal T .

Delaney KA and al. Assessment of Acid-Base Disturbances in Hypothermia and their physiologic consequences. Ann Emerg Med, Jan 1989; 18:72-82.

rewarming methods passive rewarming
Rewarming methods :Passive rewarming
  • Endogenous heat production
    • Shivering, metabolic rate, TSH, sympathetic,…
  • Involves decreasing heat loss
    • Remove from cold environnement
    • Remove wet clothes
    • Provide blanket
passive rewarming
Passive rewarming…
  • O2 consumption can > 90%
  • CO2 production can by 65%
  • Possible anaerobic metabolism Rewarming rate : 0.5C - 2.0C /h
  • Method of choice for mild hypothermia
  • Adjunt for moderate hypothermia
rewarming methods active external rewarming
Rewarming methods :Active external rewarming
  • Heat to body surfaces
    • Heating blankets (fluid filled)
    • Air blankets
    • Radiant warmers
    • Immersion in hot bath
    • Water bottles / Heating pads
  • Less effective than internal rewarming if vasoconstricted +++
active external rewarming
Active external rewarming…
  • Concern about afterdrop.
  • Rewarming rates : 1C – 2.5C / h
  • Circulatory problem may be  by applying devices to trunk only.
  • Very few prospective controlled study comparing methods.
forced air blankets
Forced Air Blankets
  • ED patients
  • Moderate to severe hypothermia (< 32C)
  • Exclusion criteria
    • Cardiac arrest
    • Hypothalamic lesions
  • 16 patients
  • Randomized to passive insulation with cotton blanket or forcedair blanket @ 43C .

Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484.

forced air blanket
Forced Air Blanket…
  • All patients: warm iv fluids @ 38C
  • Warm O2 (40C)
  • End point: T = 35C
  • Looked at:
    • Rates of rewarming
    • Skin damage by blankets

Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484.

forced air blanket39
Forced Air Blanket…

Results

  • No afterdrop in both groups
  • No skin erythema/damage
  • Rewarming rates (p=0.01)
    • Forced-Air: 2.4C / h
    • Regularblanket: 1.4C / h

Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484.

slide40

Forced air

Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484.

electrical heating blanket
Electrical heating blanket
  • Carbon fiber-resistive blanket

VS Passive rewarming

  • 8 patients
  • Induced-hypothermia (33C)
  • Skin thermal flux transducer
  • CO2 concentration production through mask
  • Compared:
    • rates of rewarming
    • core heat content

Greif R and al, Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: a randomized controlled trial. Ann Emerg Med. April 2000; 35: 337-345.

electrical heating
Electrical heating

Results

  • Core heat content >> electrical heating
  • Rates  1.5C/h > with electical heating
  • No afterdrop both groups

Greif R and al, Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: a randomized controlled trial. Ann Emerg Med. April 2000; 35: 337-345.

rewarming methods active internal core rewarming
Rewarming methods :Active internal (core) rewarming
  • Warm iv fluids
  • Warm, humid oxygen
  • Peritoneal lavage
  • Gastric / Esophageal lavage
  • Bladder / Rectal lavage
  • Pleural / Mediastinal lavage
  • Microwaves (Diathermy)
  • Extracorporeal circulatory rewarming
warm iv fluids
Warm iv fluids
  • Up to 45C shown to be safe
  • 65C fluid studied in dogs
    • Journal of Trauma 1993 (8 dogs)
    • American Journal of Surgery 1996 (10 dogs)
    • Through IVC
    • Safe. No Complications
    • 2.9C/h compared to 1.25C/h (J Trauma)
    • 3.7C/h compared to 1.75C/h (Am J Surg)
warm iv fluids45
Warm iv fluids…
  • Saline…Not RL
  • Long tubulure = lost of heat
  • Can use microwave for saline (No D5W)
    • Annals of EM, 1984 and 1985
    • 1L of NS to 39C : 2 minutes at high power.
  • No microwave rewarming for PRBC
    • Hemolysis
    • Hemoglobinuria
    • Transfusion reaction
warm humidified o 2
Warm, humidified O2
  • 42C-46C
  • Prevent heat loss
  • Negligible heat gain
  • Very important in management of hypothermic patient:
    • Up to 30% of heat production lost through airway.
gastric oesophageal bladder rectal lavage
Gastric/Oesophageal/ Bladder/Rectal lavage
  • Not shown to be better than external rewarming.
  • Limited surface area
  • Limited heat exchange
  • Limited utility (!)
  • Recommend as last resort when other modalities not available.
peritoneal lavage
Peritoneal lavage
  • Fluid at 40-45C
  • Up to 12 L/h
  • KCl free
  • Hepatic rewarming
  • Renal support when dialysate is used
  • 2C-4C / h
  • C.I.
    • Abdominal trauma
    • Acute abdomen
    • Free intra-abdominal air
peritoneal lavage49
Peritoneal lavage…
  • Almost all studies before 1980
  • Almost all animal studies
  • Critical Care Medicine 1988
    • 11 dogs
    • Comparing peritoneal/pleural lavage and heated aerosol inhalation
    • Peritoneal and pleural lavage equivalent
    •  6C/h/m2
    • Heated inhalation alone : little heat gain
pleural lavage closed thoracic lavage continuous thoracic cavity lavage
Pleural lavageClosed-thoracic lavageContinuous thoracic cavity lavage
  • Two large (38F) ipsilateral chest tubes
  • 1: 2nd or 3rd anterior intercostal space, midclavicular.
  • 2: 5th or 6th intercostal space, posterior axillary line.
  • NS or tap water @ 42C
  • Rewarms heart + greater vessels

Hall KN and al. Closed thoracic cavity lavage in the treatment of severe hypothermia in human beings. Ann Emerg Med, Feb 1990;19:204-206.

mediastinal lavage
Mediastinal lavage
  • Requires certain expertise
  • Limited clinical experience
  • Case reports
  • Internal cardiac massage
  • 8C / h

Douglas D. Brunette, Hypothermic cardiac arrest: An 11 year review of ED management and outcome. Am J Emerg Med 2000; 18:418-422.

extracorporeal blood rewarming techniques
Extracorporeal blood rewarming techniques
  • Hemodialysis
  • Arteriovenous rewarming
  • Venovenous rewarming
  • Cardiopulmonary bypass
extracorporeal blood rewarming
Extracorporeal blood rewarming…
  • Hemodialysis : renal dysfunction
  • AV depends on the pt’s BP
  • CPB is the « Gold Standard ».
  • CPB improves long term survival and neurologic outcome.
    • 15 of 32 long term survivors and none had neurologic deficits (7 years later).

B.H. Walpoth and al. Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming, N Engl J Med, 1997;337:1500-5

diathermy
Diathermy
  • Ultrasonic waves
  • Microwaves
  • Short waves
  • Few studies
  • Radio wave regional hyperthermia: Experience with Tx of tumors.
  • Not widespread because of dosages in human poorly defined.
diathermy55
Diathermy…
  • Prospective
  • Radio Wave vs. Peritoneal lavage
  • 6 dogs
  • Rate of rewarming 3x > for Radio wave.

J.D. White and al. Controlled comparison of Radio Wave regional hyperthermia and peritoneal lavage rewarming after immersion hypthermia, J Trauma, 1985; (25)10: 989-993.

the afterdrop phenomenon
The Afterdrop Phenomenon
  • Continued fall in deep core T during the initial period of rewarming.
  • First described by James Currie in 1798
  • Theory of Burton and Edholm (1955):
    • Attributed to peripheral vasodilatation
    • Return of cold blood to central circulation
    • Cooling of myocardium
  • Accepted theory until mid ’80’s

Burton, A.C., and O.G. Edholm. Man in Cold Environment. London: Arnold, 1955, p.216.

paul webb an alternative explanation j appl physiol 1986
Paul Webb,An alternative explanation.J. Appl. Physiol. 1986
  • Fall of T during active rewarming:
    • Up to 2C
    • 10 – 30 min
  • Used calorimeter, rectal, esophageal and tympanic probes.
  • Heat loss calculation

Webb, Paul. Afterdrop of body temperature during rewarming: an alternative explanation. J.Appl.Physiol. 60(2): 385-390, 1986.

2 mecanisms for afterdrop
2 mecanisms for afterdrop
  • Convection mecanism
    • Return of cold blood from periphery
    • Minimal is any contribution
  • Conduction mecanism
    • Thermal gradient principal
    • Heat flow principal

Webb, Paul. Afterdrop of body temperature during rewarming: an alternative explanation. J.Appl.Physiol. 60(2): 385-390, 1986.

conduction mecanism
Conduction Mecanism

Environement

Skin/Tissues

Blood vessel

Heat transfer

Heat transfer

afterdrop an alternative explanation
Afterdrop: an alternative explanation
  • Active external rewarming  increase threat of further cooling of the heart…as much as thought before.
  • Correlated by many other papers
  • Savard, G.K., K.E. Cooper, W.L. Veale, and T.J. Malkinson. Peripheral blood flow during rewarming from mild hypothermia in humans. J. Appl. Physiol. 58(1): 4-13, 1985.
  • Romet, Tiit T. Mechanism of afterdrop after cold water immersion. J.Appl.Physiol. 65(4): 1535-1538, 1988.
the alcatraz san francisco swim study
The Alcatraz/San Francisco Swim Study
  • San Francisco Bay…contest…
  • Swims from Alcatraz Island to shore
  • No wetsuits or protective clothing
  • Water T = 12C (53F)
  • Outside : T = 10C
  • 3 Km
  • 11 subjects for study
  • 23 y.o to 70 y.o (!)
  • Measured T after contest.

Thomas J. Nuckton and al. Hypothermia and afterdrop following open water swimming: The Alcatrax/San Francisco Swim Study. Am J Emerg Med 2000; 18:703-707.

afterdrop conclusion
Afterdrop conclusion
  • Rectal T lags behing esophageal T and is often > than esophageal and pulmonary T.
  • Think about it but you can probably not prevent it.
  • Issue with active external rewarming
  • Other concerns about external rewarming:
    • Acidosis
    • Hypotension
management ed issues
Management: ED issues

Intubation

  • General belief it can induce arythmias
  • Danzl, Multicenter Hypothermia Survey, Annals Emerg Med, Sept.87.
    • Data from 13 ED
    • 428 cases
    • 117 intubation
    • NO arythmias
management ed issues66
Management: ED issues

Bretylium

  • Recommended for V.fib in hypothermia
  • Removed from new ACLS 2000:
      •  availability and limited supply
      •  occurrence of side effects
  • Still recommend in textbooks (Rosen)
  • Recommended by US Wilderness Emergency Medical Services Institute
  • Based on Dogs studies
  • Good for prophylaxis only
management ed issues67
Management: ED issues

Drugs / Shocks

  • NO drugs if T < 30C
    • Not efficacious
    • Not metabolised
  • If > 30C,  intervals between doses
  • If < 30C and failure of 3 shocks
management ed issues68
Management: ED issues

Drugs / Shocks

  • NO drugs if T < 30C
    • Not efficacious
    • Not metabolised
  • If > 30C,  intervals between doses
  • If < 30C and failure of 3 shocks

Defer subsequent shock + Rx until T > 30C

acls 2000
ACLS 2000

The algorithm…

conclusion
Conclusion
  • Hypothermia is rare but treatable
  • Good outcome after prolonged arrests
  • Include Hypothermia in your  Dx
  • Include T as a 5th vital sign…
  • Call early to organize CPB if available if patient in cardiac arrest
  • Prevention is still the best…and…
play carefully
Play carefully…

From Journal Le Soleil, february 2001