Accidental Hypothermia François Dufresne McGill Emergency Medicine May 2 nd 2001.

Accidental Hypothermia

François Dufresne

McGill Emergency Medicine

May 2nd 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. O2 sat.• Femoral pulse + (35) BP.• GCS=3 TR = 28C.• IV. Monitor. Mask with 100% O2

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…


• 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…


• MD calls you back 30 minutes later

• Pt in cardiac arrest : V.fib. Now 27C• 3 shocks

• Epinephrine + re-shock

• Having Amiodarone prepared…

• How long should he do CPR and rescussitation?

Anything wrong ?Answer ?

Introduction

• Maritime / War litterature

• Hannibal experience in 218 B.C

Hannibal against Rome

Introduction

• EtOH • Mental illness • Homelessness • Province of Quebec Cold

Plan

• Definitions

• Physiology

• Pathophysiology

• Labs findings : ABG, ECG

• Rewarming methods

• Afterdrop

• ACLS 2000 guidelines

Definitions

• Primary VS Secondary

• Primary– Normal thermoregulation– Overwhelming cold exposure

• Secondary– Abnormal thermogenesis– Multiple causes

Definitions

• Hypothermia : < 35C

• Mild : 32-35C• Moderate : 28-32C• Severe : < 28C

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

• 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…

• Above 32C:– Vasoconstriction– Shivering– Basal metabolic rate

• Below 32C:– No shivering

• Below 24C:– No basal metabolic rate

Pathophysiology

Cardiovascular– Initial tachycardia– Gradual bradycardia : HR 50% at 28C.– Not consistent ?

• Hypoglycemia, intoxication, hypovolemia,…?

– Refractory to atropine BP CI– A.fib (T < 32C)– V.fib (T < 28C)

Pathophysiology…

CNS– Cerebral metabolism 6% / 1C– Normal autoregulation until 25C– EEG flat at 19C

Renal– Cold diuresis

• Peripheral vasoconstriction

• Failure to reabsorb Na+ and water.

Pathophysiology…

Respiratory– CO2 production 50% at 30C– Decreased RR– ARDS possible

Hematology– Hemostasis and coagulation impaired– Problems with CPB

Mild (> 32C)

• Increase metabolic rate

• Maximum shivering thermogenesis

• Amnesia / dysarthria / ataxia

• Loss of coordination

• Tachycardic, tachypneic

• Normal BP

Moderate (28– 32C)

• Stupor

• No shivering

• Bradycardic / A.fib BP RR

• Pupils dilated (< 30C)

Severe (<28C )

• Coma• No corneal or oculocephalic reflexes BP• V.fib (Maximum risk: 22C)• Apnea• Asystole• Areflexia / fixed pupils• Flat EEG (19C)

Lab findings : ECG

• Woman, 75 y.o

• Found unconscious in her apartment

Osborn (J) Wave

• Mr. John J. Osborn in the early ’50’s.

• When T< 33C• 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…

• 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

• Muscle tremors artifacts

• Early changes– Bradycardia– T wave inversion– Prolonged PR, QRS and QT intervals

• A.fib when T < 32C• V.fib when T < 28C

Lab findings : ABG

• Man, 45 y.o,. • Rectal T= 30C. LOC Intubated.• Acid-base status?• Technician asks you if he should warm

the blood before analysis…A) Don’t warm it : 30CB) Warm it to 37CC) heu…(30+37)/2….33.5CD) Both and I’ll pick the best one.

ABG in Hypothermia

• 1st ABG (30C):• pH = 7.5• pCO2 = 27

• 2nd ABG (37C):• 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

• 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.

So…

• 1st ABG (30C):• pH = 7.5

• pCO2 = 27

• 2nd ABG (37C):• pH = 7.4

• pCO2 = 40

ABG in Hypothermia……the rationale

• ABG machines usually warms blood to 37C.

• 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

• Endogenous heat production– Shivering, metabolic rate, TSH, sympathetic,…

• Involves decreasing heat loss– Remove from cold environnement– Remove wet clothes– Provide blanket

Passive rewarming…

• O2 consumption can > 90%

• CO2 production can by 65%

• Possible anaerobic metabolism Rewarming rate : 0.5C - 2.0C /h

• Method of choice for mild hypothermia

• Adjunt for moderate hypothermia

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…

• Concern about afterdrop.

• Rewarming rates : 1C – 2.5C / h

• Circulatory problem may be by applying devices to trunk only.

• Very few prospective controlled study comparing methods.

Forced Air Blankets

• ED patients• Moderate to severe hypothermia (< 32C)• Exclusion criteria

– Cardiac arrest

– Hypothalamic lesions

• 16 patients• Randomized to passive insulation with cotton

blanket or forced air blanket @ 43C .

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

Forced Air Blanket…

• All patients: warm iv fluids @ 38C• Warm O2 (40C)

• End point: T = 35C• Looked at:

– Rates of rewarming– Skin damage by blankets


Forced Air Blanket…

Results

• No afterdrop in both groups

• No skin erythema/damage

• Rewarming rates (p=0.01)– Forced-Air: 2.4C / h– Regular blanket: 1.4C / h



Forced air

Electrical heating blanket

• Carbon fiber-resistive blanket VS Passive rewarming

• 8 patients• Induced-hypothermia (33C)• 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

Results

• Core heat content >> electrical heating

• Rates 1.5C/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

• 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

• Up to 45C shown to be safe

• 65C fluid studied in dogs– Journal of Trauma 1993 (8 dogs)– American Journal of Surgery 1996 (10 dogs)– Through IVC – Safe. No Complications– 2.9C/h compared to 1.25C/h (J Trauma)– 3.7C/h compared to 1.75C/h (Am J Surg)

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 39C : 2 minutes at high power.

• No microwave rewarming for PRBC– Hemolysis

– Hemoglobinuria

– Transfusion reaction

Warm, humidified O2

• 42C-46C• 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

• 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

• Fluid at 40-45C• Up to 12 L/h• KCl free• Hepatic rewarming• Renal support when dialysate is used• 2C-4C / h• C.I.

– Abdominal trauma– Acute abdomen– Free intra-abdominal air

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 6C/h/m2

– Heated inhalation alone : little heat gain

Pleural lavageClosed-thoracic lavage

Continuous 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 @ 42C• 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

• Requires certain expertise

• Limited clinical experience

• Case reports

• Internal cardiac massage

• 8C / 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

• Hemodialysis

• Arteriovenous rewarming

• Venovenous rewarming

• Cardiopulmonary bypass

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

• 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.

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• 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

• Fall of T during active rewarming:– Up to 2C– 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

• 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.

Skin/Tissues

Blood vessel

Environement

Heat transfer

Conduction Mecanism

Heat transfer

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

• San Francisco Bay…contest…

• Swims from Alcatraz Island to shore

• No wetsuits or protective clothing

• Water T = 12C (53F)

• Outside : T = 10C• 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

• 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

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


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


Drugs / Shocks

• NO drugs if T < 30C– Not efficacious– Not metabolised

• If > 30C, intervals between doses

• If < 30C and failure of 3 shocks


Drugs / Shocks

• NO drugs if T < 30C– Not efficacious– Not metabolised

• If > 30C, intervals between doses

• If < 30C and failure of 3 shocks

Defer subsequent shock + Rx until T > 30C

ACLS 2000

The algorithm…

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…

From Journal Le Soleil, february 2001

The End

Accidental Hypothermia François Dufresne McGill Emergency Medicine May 2 nd 2001.

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Transcript of Accidental Hypothermia François Dufresne McGill Emergency Medicine May 2 nd 2001.