Hypothermia

1
Hypothermia

• By
• Paul Rega MD, FACEP

2
Key Celsius/Fahrenheit Conversions

• 19C 66F
• 20C 68F
• 25C 77F
• 28C 82F
• 30C 86F

• 32C 90F
• 33C 91F
• 34C 93F
• 35C 95F
• 43C 109F

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Diagnosis of Hypothermia

• Requires
• 1) High index of suspicion
• 2) Low-reading thermometer (down to 25C)
• At least 10cm into rectum
• Check for fecal cache
• Impaction will give a falsely elevated reading

4
Definition

• Core temperature lt35º C (95º F)
• Mild 32.1º C-35º C
• Moderate 28º C-32º C
• Severe lt28º C

5
Classification

• Accidental
• Primary Patients with normal intact
  thermoregulatory system
• Usually exposed to extreme cold
• Secondary Patients with impaired
  thermoregulatory system
• Intentional

6
Frequency

• 700 die annually from accidental primary
  hypothermia
• Majority
• Urban setting due to environmental exposure
• Aggravated by homelessness, illicit drug use,
  alcoholism, mental illness
• Minority
• Outdoor setting hunters, swimmers, hikers, etc.

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Mortality

• Mild (32-35 C) No significant
  morbidity/mortality
• Moderate (29 C-32 C) 21 mortality
• Severe (lt28 C) Even higher mortality rate

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Hypothermia and Trauma

• 38,520 trauma patients (2000-2002)
• 16 yo and greater
• 1,921 (5) hypothermic on admission
• Hypothermia independently tripled chances of
  death
• Isolated head injury hypothermia associated with
  gttwice risk of death
• CCM 331296-1301

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At risk populations

• Very young/elderly
• May present with symptoms not clinically obvious
  (e.g. altered mental status)
• Those with decreased muscle mass
• Trauma, burns, and other stressors worsen bodys
  response to cold.

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Normal Physiology

• Body regulates core temp through mechanisms of
  heat loss and heat gain
• Hypothalamus controls thermoregulation
• Rest 40-60kcal heat/m² produced
• Shivering Heat production increases 2-5 times
• Hindered by endocrine derangements

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Heat Loss

• Conduction (Transfer of heat from body to
  environment)
• Water has 25-35 times heat conduction ability of
  air
• Convection
• Heat transfer from movement of liquid or gases
  over a victim
• e.g. Wind chill
• Conduction convection 15 heat loss
• Cold water immersion increases conductive heat
  loss up to 25 times
• Radiation (Heat transfer by electromagnetic waves
  through space)
• 55-65 of heat loss
• Evaporation (sweat, exhaled breath)
• Heat loss from conversion of water to a gas
• Respiration evaporation Remainder of heat loss

12
Heat Gain

• Peripheral vasoconstriction
• Increased metabolic rate
• Shivering
• Behavior
• Warm clothes
• Removal from cold environment

13
Hypothermic Predisposing Factors

• Impede circulation
• Dehydration, DM, Peripheral vascular disease,
  tight clothes, tobacco
• Increase heat loss
• Burns, skin diseases, environment, alcohol/drugs,
  infancy,
• Decrease heat production
• Endocrine failure, hypoadrenalism, hypoglycemia,
  hypopituitarism, hypothyroidism, infancy, old
  age, malnutrition
• Impair thermoregulation
• DM, Parkinsons, spinal cord injuries, stroke

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What is the lowest recorded temperature for a
survivor of accidental hypothermia?
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Answer
15.2C (59.2F) 23-day-old infant
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The lowest temperature recorded in an adult
survivor?
17
Answer
16C (60.8F)
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System Response to Hypothermia
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CNS in Hypothermia

• All organ systems affected
• lt33C Abnormal brain activity
• 19-20C EEG consistent with brain death

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Cardiovascular Response in Hypothermia

• Osborne J waves
• T-wave inversion
• Prolonged PR, QRS, and QT intervals
• Bradycardia, slow a fib, v fib, asystole
• Bradycardia Decreased depolarization of
  pacemaker cells
• Refractory to atropine since not vagally mediated
• Atrial/ventricular arrhythmias
• 25C Asystole/ventricular fibrillation
• Increased risk of thrombosis and embolism
• Due to decreased intravascular volume and
  increased blood viscosity

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Osborne or J wave was first described in 1938.
It is best seen in leads aVL, aVF, and the
lateral chest leads. Its presence is suggestive
of, but no pathognomonic for, hypothermia. May
appear at temperatures below 32C.
22
Bradycardia appears in 50 of patients with
temperatures below 28C.
23
The presence of acute atrial fibrillation often
precedes ventricular fibrillation.
24
These rhythms may be refractory to electricity
and drugs in severe hypothermia
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Pulmonary Response in Hypothermia

• Rate initially increases then decreases below
  32ºC.
• Tidal volume decreases
• Cough/gag reflexes fail
• Risk of aspiration grows
• Decreased O2 delivery to tissues
• Higher O2 and CO2 levels and a lower pH than a
  patients actual values because analyzers warm
  blood to 37 C
• Interpret uncorrected ABGs (i.e. at the patients
  core temp)
• Aspiration pneumonia and pulmonary edema common

26
Renal Response

• Loss of ability to concentrate urine
• Cold diuresis initially result of increased blood
  flow to kidneys with peripheral vasoconstriction
• Volume depletion can result in decreased renal
  blood flow.
• Decreased renal blood flow (depressed by 50 at
  27-30C) and increased tissue breakdown products
• Acute tubular necrosis
• Renal failure

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Clinical Manifestations According to
Temperature Change
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Mild Hypothermia (32-35 C)

• Lethargy
• Increased metabolic activity
• Superficial vessels constrict
• Confusion
• Altered judgment, amnesia, dysarthria lt34 C
• Shivering
• Greatest between 34 -35 C
• Loss of fine motor coordination
• Ataxia apathy at 33 C
• Respiratory rate may be higher
• Pulse/blood pressure intact
• May be increase in CO, Heart rate, and B/P

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Moderate Hypothermia (28-32 C)

• Delirium
• Stupor
• Shivering dissipates
• Metabolic activity slows
• Drop in O2 and CO2 production
• Slowed reflexes
• Drop in CO, heart rate, B/P
• Arrhythmias may begin at 30 C
• Atrial fibrillation
• Ventricular hyperactivity
• Pupils dilate and minimally react to light (may
  mimic death)

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Severe Hypothermia (lt28 C)

• Very cold skin
• Unresponsive
• Coma
• Difficulty breathing to apnea
• Shock
• Arrhythmias
• Markedly susceptible to v. fib.
• Rigidity
• Pupils fixed

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Patient Management
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General Care

• Remove wet clothes
• Insulate victim from environment
• Dont delay urgent procedures (e.g. intubation,
  IVs)
• Remember Because of rigidity of jaw and chest
  wall, it may be next to impossible to intubate
  orotracheally as well as to ventilate a patient.

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Caution

• Perform procedures gently
• Monitor cardiac rhythm
• May go into V. fib.

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Rewarming Techniques

• Passive external
• Active external
• Active internal (core)

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Passive External Rewarming

• Usually adequate for mild hypothermia
• Place in warm environment
• Remove wet clothing
• Cover with blankets
• Rewarming rate 0.5C-1C/hour

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Active External Rewarming

• Added for moderate-severe hypothermia
• Hot water bottles to groin/axillae (43C)
• Radiant heaters
• Heating pads, circulating hot water mattresses
• Forced air rewarming
• Rewarming rate 2.4C/hour
• Warm IV solutions
• Rate 1C-2.5C/hour

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Complications of External Rewarming

• Core Temp afterdrop Cold blood returning from
  periphery further cools body core
• Rewarming acidosis Cold blood returning from
  periphery brings lactic acid with it.
• Rewarming shock Relative hypovolemia occurs
  secondary to peripheral vasodilatation
• Note Complications minimized using combo of
  external rewarming with active core rewarming.

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Active Core Rewarming

• Core temp lt30C
• Best especially if core temp is lt30ºC or cardiac
  instability is present
• Techniques
• Warmed (42C-45C) humidified O2
• Warmed (42C-44C) IV fluids (D5NS preferred)
  150-200cc/hr
• Gastric, colonic, bladder, peritoneal lavage
  (40C-45C) with warm saline potassium-free
  solutions
• Rewarming rate 1C-3C/hour

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Active Core Rewarming

• Closed thoracic cavity lavage
• Chest tube anteriorly, chest tube posteriorly
• 14 cases (8-72 yrs of age) Thoracic cavity
  lavage
• Mean core temp 24.5C
• most without B/P or pulse
• Predominant rhythm V. fib.
• 7 Thoracotomy 7 thoracostomy
• Median rewarming rate 2.95C/hour
• Median time to sinus rhythm 120 min.
• Median length of hospital stay 2 weeks
• 4 died
• Survivors 8 neurologically intact 2 with
  residual impairments

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Active Core Rewarming (Extracorporeal)

• Hemodialysis, AV rewarming, VV rewarming
• Cardiopulmonary bypass (CPB)
• Provides central rewarming and circulatory
  support
• 32 patients (mean age 25.2 years)
• Mean time from discovery to CPB 141 min.
• 15 long-term survivors
• All in cardiopulmonary arrest at hospital
• All intubated and receiving CPR prior to hospital
• Mean core temp rose from21.8C to 35.6C within
  97.9 min after rewarming (other CPB reports
  8C-10C/hour)
• Follow-up no or minimal cerebral impairment
• Keys to success
• Hypothermia deep
• No prior hypoxic brain damage prior to
  hypothermia
• Young
• Great medical infrastructure in Switzerland
• Hypothermia maintained prior to CPB

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Key Points

• Method of rewarming dependent on core temp and
  patient stability
• Active rewarming recommended with
  life-threatening dysrhythmias
• All hypothermic patients must be examined for any
  trauma or underlying medical condition

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Pre-hospital Care

• Avoid needless sudden movements
• Especially with cold-water immersion
• Supine to avoid postural hypotension
• O2
• Monitors
• CPR and intubation should not be withheld if
  needed
• Trauma immobilization as needed
• Intense vasoconstriction at lt30 C may make IV
  meds ineffective
• Lidocaine/atropine ineffective
• Prophylactic (lt30 C) and therapeutic bretylium
• Treat life-threatening arrhythmias only the
  remainder will self-correct with re-warming
• Attempt defibrillation up to 3 times and no
  re-attempts until core temp reaches 30ºC
• Magnesium sulfate Helpful in spontaneous
  resolution of v fib
• Reduce further heat loss
• Begin re-warming
• Heat packs in axillae, groin, belly
• Intubate as needed pre-oxygenate first
• Resuscitate cold and dead to warm and dead (at
  least by 30-33ºC)

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ER Care

• Baseline studies
• CBC, lytes, BUN. Cr, BS, ABGs, PT/PTT
• Tox screen where appropriate
• EKG
• CXR

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Labs in Hypothermia

• Coagulation mechanism can fail
• Failure of enzymatic reactions of the clotting
  cascade
• Coag studies typically performed at 37 C and so
  results may be deceptively normal
• DIC may develop
• Hyperglycemia in acute hypothermia
• Hypoglycemia in chronic or secondary hypothermia
• K Levels of 10mmol/L associated with low
  likelihood of recovery
• Classic EKG changes of hyperkalemia may be absent
  or diminished
• Hct may be deceptively high
• Hypothermic patients are volume contracted
  because of cold diuresis
• Increase 2 for each 1 C drop in core temp

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Differential Diagnosis

• Alcohol/other intoxicants
• Endocrine problems
• Hyper/hypoglycemia
• Hypoxemia
• Narcotics
• Uremia
• Trauma
• Infection
• Psychiatric
• CNS SAH, space-occupying lesions

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Positive Benefit of Hypothermia

• May exert a protective effect on brain and organs
  in cardiac arrest.

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Hypothermia with Perfusing Rhythm

• Mild (gt 34C or 93.2F) Passive rewarming
• Warmed blankets
• Warm environment

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Hypothermia with Perfusing Rhythm

• Moderate (30 C-34 C or 86 F
• 93.2 F) Active external rewarming
• Heating blankets
• Forced hot air
• Warmed infusions
• Warmed water packs
• Carefully monitor for hemodynamic changes

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Hypothermia with Perfusing Rhythm

• Severe (lt30C or 86 F) Active internal
  rewarming
• Peritoneal lavage
• Esophageal rewarming tubes
• CP bypass
• Extracorporeal circulation

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Cardiac Arrest at 30 -34 C(Moderate
Hypothermia)Overview

• CPR
• Defib once
• IV
• Intubate
• IV medications
• Active Internal Rewarming

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Cardiac Arrest at lt 30 (Severe
Hypothermia)Overview

• CPR
• Defib once
• IV
• Intubate
• IV medications when at core temp gt34 C
• Active Internal Rewarming

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BLS Modifications

• Check breathing and pulse for 30-45 sec. to
  confirm arrest state.
• If doubt, commence CPR anyway
• Warmed humidified O2 if possible (42-46 C)
• 1 defib attempt and defer further attempts until
  patient warmed to 30-32 C

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ALS Modifications

• Intubation
• Delivers warmed O2 better
• Prevents aspiration
• Focus on active core rewarming warmed humidified
  O2 (42-46 C), warmed IV fluids (43 C, warm
  peritoneal lavage fluids, pleural lavage
  extracorporeal blood warming)
• Hypothermic heart unresponsive to drugs,
  pacemakers, and defib
• Drug metabolism reduced
• Cardioactive drugs can accumulate to toxic levels
  in peripheral circulation
• IV drugs often withheld at temps lt30 C
• IV meds given at gt30 C but at increased
  intervals
• May not need to pace bradycardic rhythm since it
  may be physiologic due to hypothermia
• If after rewarming and return of pulse, the B/P
  is low push fluids to compensate for vasodilation

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References

• Li J. Hypothermia. www.emedicine.com/emerg/topi
  c279.htm Accessed 11/18/05
• Ulrich AS, Rathlev NK. Hypothermia and localized
  Cold Injuries. Emerg Med Clin N Am 2004
  22281-298.
• Phillips TG. Hypothermia. www.emedicine.com/med/t
  opic1144.htm.
• Wang HE, Callaway CW, et al. Admission
  Hypothermia and Outcome after Major Trauma. Crit
  Care Med 33(6)1296-1301
• Hypothermia. www.vnh.org/GMO/ClinicalSection/19Hy
  pothermia.html. Accessed 12/11/05

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References

• Plaisier BR. Thoracic Lavage in Accidental
  Hypothermia with Cardiac Arrest Report of a
  Case and Review of the Literature. Resuscitation
  2005 6699-104.
• Walpoth BH, Walpoth-Aslan BN, et al. Outcome of
  Survivors of Accidental Hypothermia with
  Circulatory Arrest Treated with Extracorporeal
  Blood Warming. NEJM 1997 3371500-1505.
• Rice R. Hypothermia Potentially Deadly All
  Year Around. JAAPA 2005 1847-52.
• 2005 American Heart Association Guidelines for
  Cardiopulmonary Resuscitation and Emergency
  Cardiovascular Care, Part 2 Hypothermia.
  Circulation 2005 112(suppl IV)IV-136-139.