Hypothermia Hypothermia Jacques S Lee MD MSc FRCPC Ottawa Hospital

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Hypothermia Hypothermia Jacques S Lee MD MSc FRCPC Ottawa Hospital Powered By Docstoc
					   Hypothermia



Jacques S. Lee MD, MSc, FRCPC
 Ottawa Hospital, Civic Campus
          Case Presentation:
 Patch call to Aeromedical Control
 officer of an Air Ambulance system
 Adult Male found at side of road
 partially disrobed
 Apparently   outside overnight (-22 °C)
 BLS crew on scene, asking for medical
 directives
Case Presentation: Rotary Air
  Ambulance Dispatched

 You   arrive by helicopter to a rural
  emergency clinic 20 minutes from
  tertiary care center
 Ptnt.   covered in hot blankets
       Best course of action ?

a   Call the code, prognosis from asystole
    dismal
b   Remove the hot blankets as they may
    harm the patient
c   Administer Charcoal for possible
    barbiturate overdose
d   Administer epinephrine 1:10,000 1 mg
    IV
              Hypothermia



Definition:
 Clinicalstate of subnormal temperature
 such that body is unable to generate
 enough heat to function
            Classification:

 Primary

  – Accidental
     Urban
     Recreational

       – Immersion
       – Non-Immersion
  – True Primary
    (Hypothalamic Dysfunction )
          Classification:

 Secondary   to other Disease Process:
  – CNS Dysfunction
  – Toxicologic
  – Metabolic
  – Extremes of Age
  – Dermatologic
  – Sepsis
  – Malnutrition
 Hypothermia: Classification

 Mild   < 35 °C - 32 °C

 Moderate   < 32 °C - 28 °C

 Severe   < 28 °C
  Mild Hypothermia: Findings

<   35 °C - 32 °C
 Tachycardia

 Tachypnea

 Shivering
Moderate Hypothermia: Findings

<   32 °C - 28 °C
 Altered   Mental Status (Agitated/Confused)
 Osborne    J-Waves (80% )
 Loss of   Shivering (can remain to 24 °C )
 Bradycardia

 Atrial   Dysrhythmias
Severe Hypothermia: < 28 °C
 Ventricular Dysrhythmias < 30 °C
 Coma < 27 °C
 Loss of Corneal reaction
 Loss of DTR’s
 Hypotension < 24 °C
 Flat EEG < 20 °C
 Asystole < 20 °C
 Coldest Adult Survivor: < 16 °C
Pathophysiology of Hypothermia
 Pervasive    disturbances of all systems
 Many   harmful effects: organ dysfunction
                          enzyme dysfunction
 Protective   effects vs. hypoxic damage
 Minimize     “vulnerable period” when re-
 warming
   (organ dysfunction without protection)
      Pathophysiology: Cause

   Heat Balance




          Heat Production
                            Heat Loss
 Pathophysiology: Heat Loss

 Radiation:     50%  clothing/body fat 
 Evaporation: 20% Low humidity 
    (Respiratory)
 Convection:    15% Wind chill 
 Conduction:     < 5%
                  (immersed: 25-50%!)
  Management: Pre-Hospital

 Asses   ABC’s
 Assume  C-Spine injury in
 recreational/urban hypothermia
 Severely   hypothermic ?   (<28°C)
 Need  Low-Reading thermometer
     If None: Coma/Loss of Corneal Rx
 ?
  Management: Pre-Hospital

 “On site triage of avalanche victims
 with asystole”1
>   45 min
 >32   C
 Air   pocket absent
 K+ >   10mmol/l
      Management: ABC’s
 Airway    May require Cricothiroidotomy
             (Muscular Rigidity)
 Breathing   Ventilation may be impaired
 Circulation   CPR or No CPR,
                  That is The Question
 “Gentle   Handling” (?!) to prevent V. Fib
    CPR in Severe Hypothermia ?

 Must be   positive no Pulse (60 seconds ?)
   ? Avoid CPR if sustainable rhythm but no
    pulse
 To   the degree you believe in CPR in warm
    patients
 To   the degree you believe it causes V. Fib
 AHA    and Rosen still recommend it
          Management: ACLS

 Avoid    drugs in severe hypothermia
 If   V. Fib., defibrillate once at scene
 ? Bretyllium    drug of Choice
Management: C for Celsius !!
       ongoing heat loss via 4
 Prevent
 Mechanisms:
 Radiation:   Insulate ( warming)
 Evaporation: Warmed Humidified O2

 Convection: Shelter from wind
 Conduction: Remove wet clothing
  Management: Emergency
       Department

 ABC’s   as above
C for Celsius: Determine core temp.
 with low-reading thermometer
 Re-warming   technique depends on
 Temperature
 DON’T FORGET       THE 2° SURVEY
   Re-warming Techniques

 Passive Re-warming

 Active   External Re-warming
 Active   Internal Re-warming
    Re-warming Technique:
     Passive Re-warming

 Insulation   appropriate for all categories
 Prevents   ongoing heat loss
 Promotes     self-warming
 Depends    on patients ability to generate
 own heat
      Pathophysiology: CVS

 Initially,   Active vasoconstriction
 Preserve core temp. at expense of
  extremities
 PassiveExternal Re-warming vasodilates:
     Core Temp. After-Drop
   Re-warming Technique:
  Active External Re-warming

 Hot   water bottles / blankets externally
 Risk   of Core Temp. After-Drop
 Restrict   to trunk
 Avoid   in Moderate - Severe hypotherm.
  Active Internal Re-warming

 Warmed  Humidified O2 least invasive
 form of active internal re-warming
 Effective   ?
 Canbe used alone in severe
 hypothermia if alert and oriented
  Active Internal Re-warming

 Warmed   IV Fluids: Prevent further heat
 loss, minimal effect on core temp.
 Gastric/   Bladder Lavage: ? effectiveness
 Peritoneal   Lavage: ? effectiveness
 Chest   tube Thoracostomy
 Mediastinal   Lavage
 Active Internal Re-warming:
      Thoracic Lavage

1   or 2 Chest tubes placed in Left Chest
 Allows rapid re-warming of heart: restores
 cardiac function while maintaining
 cerebral protection
 Case reportof 19 male resuscitated from
 22°C after 3.5h of CPR using only
 Thoracic Lavage2
  Active Internal Re-warming

 Femoral-Femoral   Venous Bypass:
          of 2 Fem lines, blood
 Placement
 warmer & Roll pump
 Cardiopulmonary   Bypass Tx of
 Choice in severe hypothermic arrest:
 15/32 long term survivors2
        Management: Secondary
              Survey

 All   systems potentially altered

 Metabolic               Renal

 CVS                     Respiratory

 CNS                     GI

 Heme
Pathophysiology: Metabolism


 Age old question: to correct or not
 correct ABG ?
 ALL   ABG’S WARMED TO 37 °C
       Correcting ABG’S: Pro

 Solubilityof   CO2  as Temp 
 pH   by 0.015 / °C < 37 °C
 pH   is 7.25 after ABG warmed to 37°C
 pH   Should be 7.4 in patient at 27°C
 Stop   hyperventilating ptnt. ??
      Correcting ABG’S: Con

 Enzymes   function optimally when
      [H+] = [OH-]
=   pH of Neutrality
 Optimum   pH (more basic) as Temp 
  Correcting ABG’S: No Bottom
              Line
 Endothermic/pH-stat  (corrected) vs.
 Ectothermic/alpha-stat Management
 181   Bypass patients 121 pH / 60 alpha4
 40%   V. Fib. rate in pH group
 20%   in alpha group
 RCT in   neonates favored pH Stat5
     Pathophysiology: CVS

       Dysrhythmias common: usually
 Atrial
 benign
 Conduction faster through muscle than
 His-Purkinje < 30 °C
 Pressure/Card    Out. fall (50% at 25 °C)
 Often    no pulse palpable < 30 °C
    Pathophysiology: CVS

Osborne J Wave
  – Most common II and V6
  – May be normal in Adolescents
       Pathophysiology: CVS

 Tachycardic    early
    Spontaneous depolarization 
    Bradycardia
 Pulse   1/2 normal at 28 °C
 Resistant   to Atropine
     Pathophysiology: CNS

       Agitation / Irritability / Impaired
 Initial
  judgment
 “Paradoxical   Undressing”
 Apathy  / CNS Depression
 Ataxia / Dysarthria / Hyporeflexia < 28 °C

 Metabolism  decreases 7% / °C
 Circulatory Autoregulation lost < 25°C
     Pathophysiology: Resp.

 Initial   Tachypnea: CO2 solubility as T 
 Eventual    Resp. depression centrally
 Bronchorrhea

 Ciliary   motility impaired
    Pathophysiology: Renal

 ADH   secretion inhibited:
 Cold-induced   Dieresis
 Recreationalhypothermia may be
 significantly intra-vascular volume
 depleted
          Pathophysiology:
          Gastrointestinal


 Decreased   hepatic metabolism of drugs
   GI motility: Gastric distension / ileus
                    Bibliography
1 Brugger H, Durrer B, kAdler-Kastner L. “On site triage of avalanche
   victims with asystole by the emergency doctor.” Resusc,
   1996;31(1):11-16.
2 Wineguard C. Successful treatment of severe hypothermia and
   prolonged cardiac arrest with closed thoracic cavity lavage. J Emerg
   Med, 1997.15(5):692-632.
3 Walpoth BH, Walpoty-Aslan BN, Mattle HP. Outcome of survivors of
   accidental deep hypothermia and circulatory arrest treated with
   Extracorporeal blood warming. NEJM, 1997;337(21): 1500-1505.
4 Kronke GM, “Ectothermic philosophy of Acid-Base Disturbance to
   prevent fibrillation during hypothermia” Arch surg,121;303:1986
5 duPlessisAJ, Jonas RA, Wypij D, er al. Perioperative effects of alpha-
   stat vs. pH-stat strategies for deep hypothermic cardiopulmonary
   bypass. J Thorac Card Surg, 1997;114(6):991-1000.

				
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