Accidental hypothermia

Background

Definition: Core Temp <35C (95F)

• Accidental hypothermia (unintentional core cooling <35C) is associated with significant morbidity and mortality. Roughly 1500 persons die of accidental hypothermia in the US annually. Despite the high mortality associated with pre-hospital arrest, well directed treatment can result in complete neurologic recovery in the hypothermic patient.
• 50% who die of hypothermia are >65 years old
• Risk of cardiac arrest increased w/ temp < 32C as stable cardiac rhythms can quickly degenerate into unstable rhythms. Hypothermic patient patient without a pulse must be managed differently due to physiology changes that occur at low temperatures.

Scenarios and Risk Factors

• Avalanche victims
• Homeless population
• Intoxicated patients
• Elderly patients -> particularly low income during winter months
• Submersion injuries

Clinical Features

Swiss Hypothermia Staging System

Classification	Temperature	Signs/Symptoms
I / Mild	32-35°C (90-95°F)	Shivering, awake
II / Moderate	28-32°C (82-90°F)	Shivering, depressed mental status
III / Severe	20-28°C (68-82°F)	unconscious/severely depressed mental status, shivering ceases
IV / Profound	<20°C (68°F)	unobtainable VS

Differential Diagnosis

Impaired thermoregulation

• Central failure
  • Anorexia nervosa
  • CVA
  • Head trauma
  • Hypothalamic dysfunction
  • Metabolic failure
  • Neoplasm
  • Parkinson's disease
  • Drugs-Ethanol, Sedatives-hypnotics
  • SAH
  • Toxins
• Peripheral failure
  • Acute spinal cord transection
  • Decreased heat production
  • Neuropathy
• Endocrine
  • DKA or alcoholic ketoacidosis
  • Hypothyroidism
  • Hypoadrenalism
  • Hypopituitarism
  • Lactic acidosis (Sepsis)
• Insufficient energy
  • Extreme physical exertion
  • Hypoglycemia
  • Malnutrition
• Neuromuscular compromise
  • Recent birth or advanced age
  • Impaired shivering

Increased heat loss

• Dermatologic
  • Burns
  • Exfoliative dermatitis
• Iatrogenic
  • Massive fluid or blood resuscitation
  • Emergency childbirth
  • Heat stroke treatment
• Other
  • Carcinomatosis
  • Cardiopulmonary disease
  • Multisystem Trauma
  • Shock

Diagnosis

• Use low-reading thermometer
  • Some standard thermometers record only to 34C
  • Measure core temp with esophageal probe if intubated -> most accurate
• Check blood glucose as can be very high in DM or CVA or low when metabolized to keep warm
• Potassium >10-12 mEq/L not compatible with life
• Coagulopathy: clotting factor activity and platelet function significantly reduced at temp < 34C
  • Blood is rewarmed for lab testing so results may appear normal

ECG

• Typical sequence is sinus brady > a fib with slow ventricular response > v-fib > asystole
• Other ECG findings:
  • Osborn (J) wave
  • T-wave inversions
  • PR, QRS, QT prolongation
  • Muscle tremor artifact
  • AV block
  • PVCs

General Management

Handling

• Handle pt gently
• V-fib may be induced by rough handling of pt due to irritable myocardium (anecdotal)

O2

• Hypothermia causes leftward shift of oxyhemoglobin dissociation curve
• Intubation
• Intubate gently
• if RSI is given medications may act at a slower rate

IVF

• Patients are also hypovolemic since Hypothermia > impaired renal concentrating ability > cold diuresis
• Patients are prone to rhabdomyolysis and will need hydration
• Intravascular volume is lost due to extravascular shift
• NS preferred over LR as cold liver poorly metabolizes LR

CPR

• Only perform if patient truly does not have a pulse (unnecessary CPR may lead to V-fib)
• Spend 30-45s attempting to detect respiratory activity and pulse before starting CPR

Dysrhythmias

• May occur spontaneously if temp <30C (86F)
• Rewarming is treatment of choice
• Most dysrhythmias (e.g. sinus brady, a-fib/flutter) require no other therapy
• Activity of antiarrhythmics is unpredictable in hypothermia
• Hypothermic heart is relatively resistant to atropine, pacing, and countershock
• Ventricular tachycardia or Ventricular fibrillation are most common
  • May be refractory to therapy until patient is rewarmed
  • Attempt defibrillation
  • Value of deferring repeat defibrillation until a target temperature is reached is uncertain
  • Reasonable to perform further defibrillation attempts concurrent with rewarming

Antibiotics

• Give if suspect sepsis (e.g. hypothermia fails to correct w/ rewarming measures)

Thiamine

• Consider if Wernicke disease is possible cause of hypothermia (e.g. alcoholic pt)

Hydrocortisone

• Consider if pt has history of adrenal suppression or insufficiency
  • 100mg Hydrocortisone

Thyroxine

• Consider if any suspicion for hypothyroidism/myxedema coma
• Could cause dysrhythmia or cardiac ischemia if not in myxedema coma

Rewarming

Recommendations on Rewarming Modality based on Temperature and Clinical picture

Stage of Hypothermia	Rewarming modality
I/ Mild: 32-35C (90-95F)	Passive external
II/ Moderate: 28-32C (82-90F)	Active external
III/ Severe: 20-28C (68-82F)	Active internal
IV/ Profound: <20C (68F)	As severe + modified ACLS

Passive External

• Prevent additional losses -> remove wet clothes
• Heated room
• Blankets - If patient still shivering, capable of rewarming 0.5C/hr

Active External

• Rewarm trunk BEFORE the extremities, otherwise you cause further hypotension ("core temperature afterdrop")
  • Afterdrop: warmed vasodilated peripheral tissue allows cooler blood in extremities to circulate back to core
• Options:
  • Warm water immersion (Capable of 2-4C/Hr rewarming)
  • Heating blankets
  • Radiant heat
  • Forced air - Bair hugger (Up to 1-2.5C/Hr rewarming)
  • Warm humidified air via facemask or endotracheal tube

Active Internal

• Consider alone or along with active external warming in:
  • Cardiovascular instability / life-threatening dysrhythmias
  • Severe hypothermia
  • Moderate hypothermia which fails to respond to less aggressive measures

1. Heated IV fluids: 38°C -42°C.
   • Two animal studies have showed 65°C IVF via central line warmed subjects faster without side effects, but this has not been tested in humans
   • If central line is placed avoid irritating the heart
2. GI tract lavage
3. Bladder lavage
4. Thoracic Lavage
5. Peritoneal lavage
6. Bypass/ECMO/AV Dialysis

Bladder irrigationThis method can be used if large volumes (>10L) of warmed fluids are not available

1. Insert temp sensing foley
2. Instill 100-200cc warmed fluids
3. Clamp Foley and wait for foley temp probe to begin to equilibrate 2-3 degrees celsius
4. Drain bladder and repeat

Mode	C/Hr	Comments
Warm Humidified Air (intubated)	0.5-1.2	Low heat transport capacity
Warm IV fluids (47C)	highly variable 1-3	Limited by tubing distance, requires large volumes but risk of volume overload
Intracavitary (peritoneal,bladder,thoracic) lavage	variable 1-4	6-10L/Hr with fluid heated up to 45C
Open thoracotomy lavage	Up to 8 (median 3)	Highly invasive. 71% survival in 1 study

Rewarming Rates

Various measures of rewarming cause different core body increases per hour

• IV fluids - no net change
• Shivering - 1.5°C/hr
• Warming Blanket - 2°C/hr
• Peritoneal Lavage - 3°C/hr
• Thoracic Lavage - 3-6°C/hr
• Hemodialysis 3-4°C/hr
• Cardiac Bypass 7-10°C/hr

Management of the coding hypothermic patient

Risk of cardiac arrest increased w/ temp < 32C Rhythms can quickly degenerate into unstable rhythms Be careful when inserting guidewires, persistent shocks can degenerate fib into asystole Standard ACLS guidelines may not apply: Any organized rhythm should be assumed to be perfusing the patient adequately Starting CPR may precipitate fatal ventricular rhythms Modified vs. Standard ACLS: ERC recommends up to 3 defibrillations w/ epi held until temp > 30C then epi interval of 6 min until temp >35C AHA recommends 3 defibrillations and 3 rounds of epi with further dosing guided by clinical response Recent consensus suggest only one defib and dose of ACLS meds -> rewarm 5C -> one defib/meds -> etc.

Termination of CPR

Should be considered if:

• K > 12 mmol
• Asystole persists beyond >32C
• Lactate and pH have less consistent prognostic significance in hypothermia

Complications

• Acid-base disorders
• "Afterdrop"
  • Initial drop in temp and MAP as rewarming is started due to loss of vasoconstriction/AV shunting colder peripheral tissues
• Aspiration pneumonia
• Bleeding
  • Decreased platelet function and inhibition of coagulation cascade
• Cold injuries
• Dysrhythmias
• Disseminated Intravascular Coagulation
• Pancreatitis
• Rhabdomyolysis
• Thromboembolism
  • Secondary to hemoconcentration, increased blood viscosity, and poor circulation
• Ineffective Drugs
  • Protein binding increases as body temperature drops, and most drugs become ineffective
  • Pharmacologic manipulation of the pulse and blood pressure generally should be avoided
  • Orally meds poorly absorbed because of decreased gastrointestinal motility
  • Intramuscular route avoided due to poor absorption from vasoconstricted sites

External Links

• LITFL Hypothermia
• Alaska Cold Injury Guidelines

See Also

• Therapeutic hypothermia
• Water-related injuries