Accidental hypothermia Author(s): Philip Miller MD, CCFP(EM) Date Created: July 2012

Learning Objectives  Understand the physiology of hypothermia  Recognize predisposing factors  Have an approach to the management of accidental hypothermia  Understand the treatment of cardiac arrest scenarios

Hypothermia  Epidemiology and Definitions  Pathophysiology  Clinical features  General approach  Advanced cardiac life support  Rewarming

Key Concepts  Hypothermia simplified: Take precautions to prevent ventricular fibrillation (VF) Optimize conditions for return of spontaneous circulation (ROSC) in cardiac arrest scenarios Identification and treatment of precipitants Use of appropriate rewarming techniques

Case  2 year old, with Grandma who lost track of him by a lake  Found 2 hrs later, face down in the lake No pulse, not breathing Brought to Emergency Room  Rectal temperature 19°C  Asystole  How do you manage this patient? Should you intubate him? How long should you continue resuscitative efforts?

What is hypothermia?  Definition: core temperature less than 35ºC

Epidemiology  Actual incidence is not known and under- reported  Survival has been reported as low as 32% from avalanche victims and 70% in patients with alcohol or other drug intoxication

Pathophysiological progression  32-37ºC: vasoconstriction, shivering, and nonshivering thermogenesis (increase in basal metabolic rate)  24-32ºC: decreased basal metabolic rate, less shivering  <24º: autonomic and endocrinological mechanisms for heat generation fail

Approach to accidental hypothermia Goal: optimize heart for ROSC

Approach to accidental hypothermia Cardiac arrest (usually VF or asystole) Signs of life Post-warming care Identify and treat underlying precipitants CPR Defibrillate if indicated Rewarming techniques

Hypothermia myths  Hypothermia ‘only occurs in winter’  Hypothermia ‘only occurs in northern latitudes, and high altitude’  Although less common, hypothermia does occur in summer months, and in warm climates

Accidental hypothermia - etiology Wilderness settingUrban setting Submersion Immersion Mountain Accidents Cold exposure Trauma Alcohol and drugs of abuse Sepsis/ infection Psychiatric illness Homicide or suicide DKA Hypoglycemia Metabolic – thyroid, Addison’s

Epidemiology of predisposing factors Predisposing factors (%) Predisposing factors in those who died (%) Major medical illness 4416 Injury/ trauma Infection Submersion Overdose 68 Frostbite Danzl, Ann Emerg Med 1987

Mortality Core TemperatureMortality (%) < 32°C23 > 32°C7 Overall17 Danzl, Ann Emerg Med 1987

Factors that affect thermoregulation: Decreased heat production Increased heat loss Impaired thermoregulation

Decreased heat production  Endocrinologic failure – hypopituitarism, hypoadrenalism, hypothyroidism  Malnutrition and decreased subcutaneous fat  Neonates: less subcutaneous tissue, ineffective shivering mechanisms, lack behavioural defense mechanisms  Elderly: decreased ability to sense cold, decreased adaptive behavioural mechanisms

Increased heat loss  Exposure during resuscitation  Cold saline infusions  Loss of skin barrier (eg burns, skin conditions)  Ethanol

Impaired thermoregulation  Centrally mediated lesions (subdural hematoma, malignancies, CVAs)  Medications (antidepressants, antipsychotics, anxiolytics)

Normal physiological response  Shivering can double heat production and increase basal metabolic rate by 2-5x  However, increased heat production can only last a few hours because of fatigue and glycogen depletion

How is heat lost?  Radiation – transfer by electromagnetic waves  Conduction – transfer by direct physical contact  Convection – heat loss to air and water vapour molecules circulating around the body  Evaporation – conversion of liquid to gas (eg sweat on body)  Respiration

Hemodynamic changes  Progressive bradycardia (usually refractory to atropine)  Progressive decreased mean arterial pressure  Decreased cardiac index

ECG changes  Osborn (J) wave – may appear at any temperature under 32ºC  Increasing PR interval  Increasing QRS interval  Long QT interval  Artifact from shivering may obscure ECG Graham 2001

Dysrhythmias  Cardiac rhythm disturbances can be from many factors Acid base disturbances Hypoxia Sensitization of conduction system Decreased refractory period

Dysrhythmias  Atrial fibrillation  Ventricular fibrillation Can be related to physical jostling, autonomic dysfunction, hypoxia, acid-base disturbances Decreased threshold for ventricular dysrhythmias  Asystole can happen spontaneously below 25ºC

Mechanical trauma causing VF?  Anecdotal reports in humans but limited evidence  A 2007 study on induced hypothermia in pigs: Once below 25°C, 5/10 pigs developed VF Below 25°C, 2/10 pigs developed VF after mechanical trauma (dropping backboard from 6 and 12 inches) Grueskin 2007

Dysrhythmias Mean core temp (C) % of ECGs% died Normal sinus rhythm Sinus tachycardia Sinus bradycardia Atrial fibrillation Junctional bradycardia Graham 2001

Renal effects  Cold diuresis: Kidneys excrete dilute urine Cold water immersion may increase urine output by 3.5 times Danzl 2010

Coagulation effects  Impaired enzymatic activity of clotting cascade (from cold)  Increased fibrinolytic activity  Platelet sequestration  Also hypercoagulability and intravascular clotting Danzl 2010

Laboratory features  Arterial blood gas can give a falsely elevated pO2 and pCO2 and falsely lower pH  Falsely elevated hematocrit as a result of decreased plasma volume Danzl 2010

Lab features  Lab tests are done at 37ºC, so there may be a clinically evident coagulopathy, but normal coagulation studies  Can see leukopenia and thrombocytopenia  Lactate levels may be very high but not necessarily correlated with mortality Danzl 2010

Hypothermia  Epidemiology and Definitions  Pathophysiology  Clinical features  General approach  Advanced cardiac life support  Rewarming

What are some clinical features of hypothermia?  Confusion  Dizziness  Dyspnea  Uncoordination  Apathetic  Paradoxical undressing  Decreased level of consciousness Danzl 2010

Hypothermia Swiss Staging System  Stage 1 - Conscious, shivering Usually 32-35°C  Stage 2 - Impaired consciousness, not shivering 28-32°C  Stage 3 - Unconscious, not shivering, vital signs present 24-28°C  Stage 4 - No vital signs < 24°C Brown 2012

General Principles of Management  Prevent further cooling  Accurate temperature measurement  ABCs  Advanced cardiac life support  Rewarming techniques  Identify and treat precipitants

Prehospital initial management  Remove all wet clothing  Rewarm patient with blankets and possibly reflective foil wrapping  Accurate core temperature measurement may be difficult in the field  Be careful moving patients – cold heart is prone to VF  Insulate patient from further heat loss

When to withhold (not start) resuscitation  Obvious lethal injuries  Frozen head and mouth and blocked with ice  Frozen and CPR not possible Danzl 2010

ABCs  Intubation Theoretical risk of inducing VT - but this is not seen in prospective observational studies May be very difficult if pt is extremely cold/rigid  Pulse check for 30-60s (pulse and respirations can be difficult to detect in the hypothermic patient) If possible, give warmed humidified O2 during bag- mask-valve CPR/ defibrillation

Advanced cardiac life support  ‘The temperature at which defibrillation should occur, and the number of attempts has not been established’ Vanden Hoek 2010

Advanced cardiac life support (ACLS)  ACLS medications may not work in the hypothermic heart  Drug metabolism is theoretically decreased and may build up to toxic levels Vanden Hoek 2010

Advanced cardiac life support  Oral medications won’t work effectively because of decreased GI motility  Intramuscular medications won’t work effectively because of peripheral vasoconstriction Danzl 2010

Medications  Most dysrhythmias convert with rewarming  Defibrillation attempts are usually ineffective below 28-30ºC Danzl 2010

Dysrhythmias  Bradycardias – usually physiologic Pacing not needed unless hemodynamic compromise persists after rewarming  Atrial fibrillation usually converts with warming  Ventricular fibrillation Lidocaine and procainamide don’t work very well in hypothermia Evidence is limited for medications in VF Vanden Hoek 2010 Soar 2010

Current recommendations  For patients < 30°C, it is reasonable to shock if in VT/VF  Further shocks are ‘reasonable’ along with warming strategies  Current benefit of medications in humans under 30°C not known, although animal studies suggest a benefit Vanden Hoek 2010

Comparing different guidelines  American Heart Association Guidelines The value of more than 1 shock if < 30°C is not known May be reasonable to perform further defibrillation attempts  European Resuscitation Council Guidelines Consider 3 defibrillation attempts if < 30°C If not successful, consider withholding further until temp > 30°C Brown 2012

Overview of accidental hypothermia Cardiac arrest (usually VF or asystole) Signs of life Post-warming careIdentify and treat underlying precipitants CPR Defibrillate if indicated Rewarming techniques Goal: optimize heart for return of spontaneous circulation and normal sinus rhythm Rewarming techniques

IV fluids  Patients are usually hypovolemic and should receive warmed saline solution, heated to 40ºC  Can microwave IV bags – 2 mins on high power for 1L  There is significant loss of heat through IV tubing  Ringer’s lactate is inefficiently metabolized by the liver Danzl 2010

Measuring temperature  Continuous core temperature is important (rectal temperature can lag behind core temperature changes, and difficult if ongoing CPR)  Tympanic temperature equilibrates most rapidly with core temperature, but is less accurate, and has more variability  Esophageal probe is ideal, but rarely available in the prehospital setting or low resource setting

Core temperature afterdrop  Further drop in patient’s core temperature after removal from cold  Caused by countercooling of blood, and rewarming of extremities Danzl 2010

Rewarming definitions  Passive external rewarming Letting the patients warm themselves  Active external rewarming Applying heat to the patient externally Remove wet clothing Apply dry blankets Conscious, shivering Forced air heating systems or warm blankets Impaired consciousness, unconscious, or no vital signs Brown 2012

Warm air device – ‘Bair Hugger’

Rewarming definitions  Active internal rewarming Minimally invasive  Warmed O2  Warmed IV fluids  Bladder lavage  Gastric/ Bowel lavage Invasive – local resource-dependent  ECMO  CPB  Thoracic lavage*  Dialysis  Peritoneal lavage No vital signs Unclear when to start Impaired consciousness or unconscious Brown 2012

The cardiac arrest patient in low resource settings No pulse Thoracic lavage? Peritoneal lavage? CPR and ACLS ECMO available?Cardiopulmonary bypass available? Dialysis?

Resource poor settings  Decisions about duration of resuscitation, intubation, thoracic lavage, and other invasive modalities for rewarming should be tailored to the availability of resources, and local practice

Airway and rewarming management in resource-limited settings  On one hand, patients who arrive in cardiac arrest have poor outcomes, and intubation in certain cases may be an unjustified use of resources (in resource-limited settings)  On the other hand, hypothermia is an instance where good neurological outcomes have been documented, and aggressive treatment may be warranted

Minimally invasive internal rewarming techniques  Airway rewarming - does very little to increase core temperature (about 1.5°C/hr)  Gastric/bowel/ bladder lavage also does very little to increase core temperature because of large surface area to warm  Warmed IV solutions do nothing to warm patient, but should be used to prevent further heat loss from cold IVs Vanden Hoek 2010 Brown 2012

Cardiopulmonary bypass  Is the most rapid and efficient method  Provides simultaneous rewarming and circulatory support  Rewarming rates as high as 1–2°C every 3–5 min have been reported  Not as useful in patients with trauma or known coagulopathy as anticoagulation is needed Vanden Hoek 2010 Walpoth 1997 Brodman 2011 Brown 2012

Thoracic lavage  Rates of 3-6°C/ hr have been reported  In patient in cardiac arrest, can put 2 chest tubes bilaterally (i.e. 4 in total)  If putting chest tubes in a patient with a pulse, can put 2 chest tubes to right chest (i.e. 2 in total) Right-sided chest tubes because if pt has a pulse, there is a possibility to induce VF with left sided chest tubes Plasier 2005

Thoracic lavage method  2 large bore chest tubes to each hemithorax 1 directed anteriorly – Warm fluid flows in 1 directed posteriorly – Allows fluid to drain out  Drainage by gravity into chest tube drainage reservoir  Previous thoracic surgery/ infections and adhesions may make the procedure impossible Plasier 2005

(accessed Mar 4 th, 2013)

Thoracic lavage method  Heat saline bags via microwave or level 1 infuser (tap water use has been reported)  Monitor input and output to avoid intrathoracic hypertension  On completion, remove anterior chest tube and then remove posterior chest tube after complete drainage Plasier 2005

How to connect the tubing?? Connect anterior chest tube to warmed saline Connect posterior chest tube to regular chest tube setup One option: can use the adapter on NG tubes to connect the chest tube to the saline tubing (accessed Mar )

Dialysis/ peritoneal lavage  Dialysis – can insert a hemodialysis catheter, and dialysis machine will warm blood  Peritoneal lavage – can call General Surgery for insertion

Rewarming rates TechniqueRewarming rates Cardiopulmonary bypass 9-18°C / Hr Thoracic lavage3-6°C/Hr Peritoneal lavage2-3°C/ Hr Warmed IV solutions0°C / Hr Shivering1.5°C / Hr Blankets2°C / Hr Warmed O21.5°C/ Hr Brown 2012

Ongoing management  If intubated: Nasogastric tube Indwelling foley catheter and continous urine output measurement  Continuous cardiac monitoring  Try to avoid central venous catheters – can increase risk of dysrhythmias

Bloodwork  Complete blood count and differential  Electrolytes  Creatinine  Glucose  Serum calcium, magnesium, amylase, lipase  Coagulation studies  Toxicology screen, thyroid studies  Blood cultures

Remember the common causes...  Associated illness with accidental hypothermia: Trauma – iatrogenic or wilderness related Psychiatric – mental illness, suicide attempt Drug related – alcohol and others Infectious – many causes Metabolic: hypoglycemia, hypothyroidism, adrenal insufficiency

Failure to rewarm  May be reasonable to attempt methylprednisolone or hydrocortisone, because cold exposure can induce adrenal unresponsiveness  Empiric thyroxine should be reserved for suspected myxedema coma Danzl 2010

Empiric antibiotics?  Rewarming rates seem to be related to underlying etiology  Patients with underlying infections (HIV, sepsis, pneumonia) tend to rewarm at much slower rates than those with underlying hypoglycemia, intoxication, or immersion  It may be appropriate to administer empiric antibiotics in certain situations Delaney 2006

When to stop warming  “When they’re warm and dead”  Exact core temperature of when to stop is not known – no evidence  If you have achieved temp of 30-32°C and they remain in asystole, it is reasonable to stop* Vanden Hoek 2010 Brown 2012

Case resolution  2 year old with core temperature 19°C  Intubated, warm fluids, warm O2, warm air device  Ambient temperature of room increased  Received warm fluid peritoneal lavage  CPR ongoing for 6 hrs  Temperature reached 34°C with persistent asystole  Patient pronounced dead

Quiz Question 1  Name 6 types of active invasive internal rewarming? Cardiopulmonary bypass ECMO Dialysis Thoracic lavage Peritoneal lavage Bowel/ bladder irrigation

Quiz Question 2  Name 5 factors associated with accidental hypothermia? Sepsis/ infection/ HIV/ TB Metabolic causes (hypoglycemia, DKA) Psychiatric illness Homicide or suicide Alcohol and drug related causes Trauma/ submersion/ immersion/ avalanche

Quiz Question 3  Which of the following is false? A) It is possible to induce VF iatrogenically B) medical mercury thermometers are accurate at all temperature ranges C) Most dysrhythmias will resolve with rewarming D) Warmed O2 and warmed IV solutions are ineffective methods of rewarming E) Thoracic lavage is an effective rewarming technique in the pulseless patient

Summary  Prevent further cooling  Accurate temperature measurement  ABCs  Advanced cardiac life support  Rewarming techniques  Identify and treat precipitants

Accidental hypothermia - etiology Wilderness settingUrban hypothermia submersion immersion avalanche Cold exposure Trauma Alcohol and drugs of abuse Sepsis/ infection Psychiatric illness Homicide or suicide DKA Hypoglycemia Metabolic – thyroid, Addison’s

Overview of accidental hypothermia Cardiac arrest (usually VF or asystole) Signs of life Post-warming careIdentify and treat underlying precipitants CPR Defibrillate if indicated Rewarming techniques Goal: optimize heart for return of spontaneous circulation and normal sinus rhythm Rewarming techniques

General References  Journal Articles:  Vanden Hoek TL et al. Cardiac Arrest in Special Situations : 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010, 122:S829-S861.  Brown D et al. Accidental Hypothermia. N Engl J Med 2012; 367;20:  Danzl DF et al. Multicenter hypothermia survey. Ann Emerg Med September 1987;16:1042-l055)  Grueskin J et al. A Pilot Study of Mechanical Stimulation and Cardiac Dysrhythmias in a Porcine Model of Induced Hypothermia. Wilderness and Environmental Medicine 2007, 18:  Graham C et al. The electrocardiogram in hypothermia. Wilderness and Environmental Medicine 2001, 12:  Walpoth BH et al. Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming. N Engl J Med 1997;337:

General References  Journal Articles cont.  Brodmann MM et al. The Bernese Hypothermia Algorithm: A consensus paper on in-hospital decision-making and treatment of patients in hypothermic cardiac arrest at an alpine level 1 trauma centre Injury, Int. J. Care Injured 2011;42: 539–543.  Delaney KA et al. Rewarming Rates in Urban Patients with Hypothermia: Prediction of Underlying Infection. Academic Emergency Medicine 2006; 13:913–921.  Vretenar VF et al. Cardiopulmonary bypass resuscitation for accidental hypothermia. Ann Thorac Surg 1994;58:  Plaisier BR. Thoracic lavage in accidental hypothermia with cardiac arrest — report of a case and review of the literature. Resuscitation 2005; 66: 99–104.  Soar J et al. European Resuscitation Council Guidelines for Resuscitation 2010 Section 8. Cardiac arrest in special circumstances: Electrolyte abnormalities, poisoning, drowning, accidental hypothermia, hyperthermia, asthma, anaphylaxis, cardiac surgery, trauma, pregnancy, electrocution. Resuscitation 81 (2010) 1400–1433.  Chapters in Textbooks: Danzl DF. (2010). Accidental Hypothermia. Marx JA, Hockberger RS, Walls RM (eds). Rosen's Emergency Medicine: Concepts and Clinical Practice. (pp ). Philadelphia, PA.  Web Links: Severe Accidental Hypothermia [ hypothermia/]. Accessed July 3, 2012.