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
• 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

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

Passive

Perform in all patients with hypothermia who is able to generate intrinsic heat

1. Removal from cold environment which includes removal of wet clothing
2. Insulation with warm blankets and warming devices

Active

Perform in patients with moderate to severe hypothermia or those who have failre response to passive rewarming

• 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

1. Warm water immersion
2. Heating blankets
3. Radiant heat
4. Forced air - Bair hugger
5. 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

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

Methods of Rewarming

Classes of Rewarming Modality

• Passive External
• Active External
• Active Internal
• Extracorporeal

Passive External

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

Active External

• Heated forced-air blanket -> Up to 1-2.5C/Hr rewarming
• Warm water immersion -> Capable of 2-4C/Hr rewarming

Active Internal

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

Management

Recommendations on Rewarming Modality based on Temperature and Clinical picture

Stage of Hypothermia	Rewarming modality
I/ Mild: 32-35C (90-95F)	Passive external -> Warm environment and clothing, blankets
II/ Moderate: 28-32C (82-90F)	Active External and minimally invasive active rewarming
III/ Severe: 20-28C (68-82F)	Active internal -> intraperitoneal, bladder, intrathoracic lavage Extracorporeal -> Dialysis, ECMO, Bypass
IV/ Profound: <20C (68F)	Management as with Moderate and Severe + modified ACLS

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

Pearls and Pitfalls

• Measure core temp with esophageal probe if intubated -> most accurate
• Cold patients are coagulopathic

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

Coagulopathy: clotting factor activity and platelet function significantly reduced at temp < 34C blood is rewarmed for lab testing so results may be normal If fluid warmers are not present, standard microwave can be used Caution should be taken to not heat beyond 40C Shake bag to distribute heat before administering

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