Hypothermia

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Hypothermia

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Although mortality from hypothermia is most
common in cold-weather areas,it is not uncommon
in temperate zones and often occurs indoors as
well.Variables contributing to the development
of cold injury include age,systemic
illness,medication,and intoxicants.
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• Patients at the extremes of age and those with
  underlying medical conditions are at great risks.
• Early recognition and prompt management are
  crucial to survival.

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Case presentation

• 78 Y/O women in lethargic state over the past
  3days the pt became weaker and weaker and more
  confused and that she seemed to have lost her
  appetite. The Pt offers no complaints in the
  ED.There is no fever ,chills,cough,headache,trauma
  ,abd pain,urinary frequency,or diarrhea.
• PHDM,H/T,and hypothyroidism.Drug
  historyinsulin,atenolol,and levothyroxine.

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Case presentation

• PEE3V5M6 100/60,31ºc,56,20.
• BS decreased in both base and shallow
  respirations.
• NE no focal sign.
• WBC15000 78 neutrophils,sugar
  345,Ketone().CO2.
• Brain CT negative.
• CXR shows a right middle lobe infiltrate.

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Critical decisions

• Which mechanisms are most likely to cause serious
  hypothermia?

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Increased heat loss

• Radiation,convection,conduction,evaporation,and
  respiration.radiative loss 55,conductive2,plus
  water exposures50
• Vasodilatation induced by drugs can increased
  heat loss.
• Ethanol ingestion is associate with paradoxical
  undressing and inhibited shiver response.

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Inadequate heat production

• Heat production can be increased by food
  ingestion,muscular activity,fever,or shivering.
• Generation of heat can be impaired by
  hypoadrenalism or hypothyroidism,or chronic
  malnutrition,or hypoglycemia.
• Failure of the shivering mechanism results in
  decreased heat production by as much as 2 to 5
  times.
• This loss of thermoregulation results from CNS
  dysfunction involving the hypothalamus, pituitary
  and spinal cord or from trauma,toxic
  exposures,carcinomas,or sepsis.

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• Hypothermia mild
  core T 32º -35ºC moderate 28º32º C
  severe
• Cutaneous vasoconstriction and shivering are the
  primary methods of heat conservation and
  production,these mechanisms begin to fail at T 35º C.

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Critical decisions

• What are the presenting signs and symptoms of
  worsening hypothermia?

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• In mild hypothermia,the Pt may present with
  initial tachycardia and transient hyperglycemia
  reflecting a high catecholamine state.The Pt
  will be shivering and vasoconstrictor and the
  basal metabolic rate will be increased.
• Mentation often is slowedthe Pt can exhibit
  confusion and impaired judgment,and there may be
  focal symptoms such as ataxia and slurred speech.

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• Mildly hypothermic Pt can present with polyuria
  secondary to peripheral vasoconstriction and
  shunting of blood to the core.The end result is
  dehydration.

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• Moderate hypothermia is heralded by the loss of
  protective mechanisms limiting heat loss.
• Shivering is extinguished.
• Mental status worsens,and there can be loss of
  peripheral reflexes.RR decreased,an initial
  polyuria may be replaced by oliguria,with
  decreased renal perfusion,ileus,and impaired
  coagulation.

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• Severe hypothermia can be confused with death.
• Pulse and BP can be undetectable, with decreases
  in O2 consumptions,spontaneous respiration,and
  reflexes.
• Resp. acidosis predominates.Pt can present in
  coma with a decline in brain EEG and absence of
  corneal reflexes.
• However,the absence of a pupillary reflex above
  22c should not be attributed to hypothermia
  alone.

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Critical decision

• What cardiac complication should EP be prepared
  for in hypothermic Pts?

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• Dysrhymia are common in Pts with a core Temp.
  below 30ºC.
• Af is most common.
• Bradycardia occurs secondary to decreased
  depolarization of myocardial cells and is
  refractory to atropine.
• Tachycardia at this temp. ,consider pain,
  toxidromes,or hypovolemia as potential causes.
• The myocardium is prone to VF in severe
  hypothermia.

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• Arrhythmia can be refractory to pharmacological
  Tx in hypothermic Pts,but most will resolve
  spontaneously with rewarming.
• At T lower than than 30ºC,Pt may not respond to
  defibrillation.

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Medications

• Such as epinephrine ,lidocaine,and procainamide
  have limited usefulness at these Temp and can
  accumulate to toxic levelsthey should be given
  at longer than standard intervals.

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Critical decision

• What are the Tx options in the setting of
  hypothermia?

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• Pt with mild hypothermia (those who are
  shivering )are most often treated with passive
  rewarming.
• These are methods that are minimize heat loss and
  allow Pt to generate heat to restore a normal
  core Temp.,include removing wet
  clothing,insulating Pts in a worm
  environment,and decreasing air flow over them by
  keeping door shut.
• Head covering also is of great importance.

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Critical decision

• When is active rewarming recommended?

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• Pt with moderate to severe hypothermia should be
  treated with active rewarming.
• Management techniques should achieve a rewarming
  rate of at least 0.5ºC to 1ºC per hour.
• In Pt who are hemodynamically stable ,heating
  blankets,hot water bottles,and radiant air
  warmer.
• A forced-air warming system that circulate heated
  air through a blanket allows a conductive and
  convective heat transfer to the Pt.

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• Active internal rewarming techniques are used to
  actively rewarm the core.these techniques are
  indicated for hemodynamically unstable Pts who
  required faster rewarming.
• Warmed IV fluids should be provided at 40ºC to
  42ºC using a short length of IV tubing.
• A liter bag may be micro waved for 2 min on high
  power.
• Heated inhaled O2 cab be used too.

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• Invasive internal rewarming allows for more rapid
  rates of Temp.increase.
• Peritoneal lavage with warm saline 45ºC is
  administered as exchanges of up to 2 L every 20
  min.
• Thoracic lavage are better,two thoracostomy tubes
  are inserted into one hemi thorax( right is
  better),one ant. and one post.
• Hemodialysis ,cardiopulmonary bypass and A-V or
  V-V are most aggressive methods.

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Summary and case
resolution
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• This case illustrates the multifactorial causes
  of hypothermia.
• Her D.D. included a CNS hemorrhage,hypoglycemia,DK
  A,myxedema coma ,sepsis,and a toxidrome.
• She was treated with antibiotics for RML
  pneumonia and 6U RI,but her serum glucose
  remained high and she remained somnolent.

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• The EP ordered heating blankets and radiant air
  warmers as well as warmed IV fluids and
  humidified O2.
• One hour after aggressive active rewarming
  brought her Temp. to 33ºC did she began
  improve.(RI fails to function below 30ºC).
• The Pt was admitted for further treatment of her
  pneumonia and diabetes,did well, and was
  discharged 1 week later.

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Pearls and Pitfalls
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1

• In order to accurately determine vital signs
  ,feel for a pulse for at least 1 min to
  distinguish bradycardia from pulselessness.

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2

• Use a thermometer that is able to detect Temp.
  below 35ºC.

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3

• Avoid using procaminide,because it increases the
  incidence of VF in hypothermia.

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4

• If a Pt fails to respond to warming
  efforts,consider the administration of steroids
  and thyroxine in those suspected of adrenal
  insufficiency or hypothyroidism.

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• Hypothermia can obscured the classic ECG findings
  hyperkalemia.RI is ineffective in Pts whose
  Temp. is below 30ºC .

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• A cold myocardium is very sensitive to iatrogenic
  induction of VF during CPR and CVP placement.If
  initial attempts at defibrillation do not convert
  VF,further defibrillation should be postponed
  until the Pt has been warmed to 28ºC to30ºC.

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• In cold climates, ET tube made of plastic can
  fractureconsider using rubber ET tubes if
  available.

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• Af doesn't necessarily require pharmacological
  intervention and will often revert to sinus
  rhythm with rewarming.Asystole is not necessarily
  a terminal rhythm,and loss of pupillary response
  does not automatically suggest brain death.

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• Patients are not dead until they are warm and
  dead.

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In mild hypothermia,the Pt may present with
initial tachycardia and transient hyperglycemia
reflecting a high catecholamine state.The Pt
will be shivering and vasoconstricted and the
basal metabolic rate will be increased.
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The End