Hypothermic Arrest

Management of accidental hypothermia has seen a revolution with the use of ECLS. ECLS has substantially improved survival and is the treatment of choice in the patient with unstable circulation or CA.The crucial factor in all hypothermia cases is whether critical brain hypoxia occurs before protective brain-cooling takes place

Brain oxygen-consumption decreases by ~6 % per 1 °C fall in core temperature and reaches 16 % at 15 °C compared with normothermia. This improves the brain’s tolerance for low- or no blood-flow states. 

At 18 °C the brain tolerates CA for up to 10 times longer than at 37 °C 

Staging of Hypothermia

Factors affecting the outcome of a hypothermic arrest
(1) hypoxia (the most important single factor)
(2) patient considerations (e.g. age, co-morbidities, trauma)
(3) speed of cooling
(4) environment (air, water, snow)
(5) CA features (body temperature; whether hypoxia preceded arrest; delay before instituting CPR, and CPR quality)
(6) rescue considerations (e.g. adequate training to manage a low flow or no blood-flow state; speed of hospital transfer)
(7) proximity of appropriate hospital facilities
(8) whether hospital staff appreciate the special requirements of these cases

Effects of Hypothermia

Warming Methods

CPR and Drugs
Mechanical chest compression devices (deliver >50 % of baseline cerebral blood flow in normothermia) are likely to provide sufficient oxygen delivery to vital organs in deeply hypothermic patients. When mechanical CPR is not available and manual CPR is not feasible, intermittent >CPR has been suggested. 

International guidance differ on drug administration. ERC 2015 guidelines recommend withholding adrenaline administration in hypothermic CA (HT IV) and limiting defibrillation to three attempts until the core temperature is >30 °C. In contrast, American Heart Association guidelines allow further defibrillation attempts concurrent with rewarming strategies and state that it may be reasonable to consider adrenaline administration during CA according to the standard ALS algorithm.

The benefit of antiarrhythmic drugs in hypothermic CA is unclear. Many arrhythmias (e.g. bradycardia, atrioventricular blocks, atrial fibrillation, nodal rhythms and QRS prolongation with or without Osborn J-waves) are considered benign in accidental hypothermia, usually regress with patient rewarming and do not require further treatment provided the perfusion is deemed adequate. Most intravenous anaesthetic induction agents cause cardiovascular depression so doses should be small. Hypothermia reduces the systemic clearance of CYP450- metabolised drugs by an amount proportional to the fall in body temperature, increasing the likelihood of unanticipated toxicity.


Treatment Algorithm based on Staging and cardiopulmonary status 

Further Reading
Paal P, Gordon L, Strapazzon G, Maeder MB, Putzer G, Walpoth B, Wanscher M, Brown D, Holzer M, Broessner G, Brugger H. Accidental hypothermia–an update. Scandinavian journal of trauma, resuscitation and emergency medicine. 2016 Dec;24(1):111.

Posted by:

              

     Lakshay Chanana

     

     ST4 Trainee

     Royal Infirmary of Edinburgh

     Department of Emergency Medicine

     Edinburgh

     Scotland

     @EMDidactic

Hypothermic patient in ED

Hypothermia is defined as a temperature of <35C. It is a common presentation in the Emergency Departments esp in elderly population with ? Sepsis. Geriatric population is prone to suffer from hypothermia due to poor mobility and altered temperature perception in addition to the environmental factors. Let's look at the common causes of hypothermia: Causes Environmental (often Accidental) Hypoglycaemia (hypothalamic dysfunction secondary to glucopenia) Hypothyroidism Hypopituitarism Hypoadrenalism Hypothalamic Dysfunction (Tumor, Stroke, Infarction) Sedatives and Alcohol Sepsis Massive Blood Transfusion Burns and Exfoliative Dermatitis Systemic Effects CVS - BP and CO rise initially but later there is a phase of CVS depression and a general slow down of metabolism. This may lead to hypotension which is exacerbated by concomitant hypovolumia. Hypothermia usually causes bradyarrythmiats such as slow AF, sinus bradycardia, J waves, AV blocks, QTc prolongation on EKG. The management should focus on rewarming rather than administering anti-arrythmics. Also, hypothermic myocardium is irritable, and ventricular fibrillation may be induced by rough handling of the patient. RS - Decrease O2 utility and less CO2 production. Patients may show a respiratory alkalosis or acidosis due to CNS depression. Lactate may be elevated due to shivering and hypoxia. There is also depression of gag and cough reflex making aspiration likely. Hypothermia causes a leftward shift of the oxyhemoglobin dissociation curve and thus impairs oxygen release to tissues.  CNS - Confusion, lethargy, coma and unreactive pupils. There is decreased blood flow and cerebral protection against ischemic damages. Do not pronounce them dead until you are 100% sure. Use ECHO, ECG and Clinical judgment before you declare them dead. Renal - Cold induced diuresis which contributes to volume loss, risk of rhabdo and AKI.  Haematological - Hemoconcentration, thrombotic and embolic complications, DIC and Hypothermia induced coagulopathy. This coagulopathy may not be evident of blood tests but seen clinically.  Investigations Blood Glucose Septic Screen (including CXR, Urine) TSH Creat Kinase ECG Heat CT (Consider after a period of observation - Every elderly with hypothermia does not need a Head CT) Management ABCs Take up to 30 seconds to assess before commencing chest compressions - Use ECHO, feel for pulses and watch for respiratory movements. Handle them gently to avoid irritating the myocardium. If it is a hypothermic arrest then administer epinephrine every 6-10 minutes unless they are re-warmed and hypothermic arrhythmias may not respond to Cardioversion. Focus on warming in such a scenario Warm O2 and Warm fluids External Warming Blankets. Rapid rewarming is rarely needed. There are other rescue intensive and invasive methods such as pleura/peritoneal/GI/Bladder lasagne and ECMO.  Arrhythmias - Rewarm then and only then think about anti-arrythmics Antibiotics if concerned about Sepsis Parenteral Thiamine for critically ill/malnourished/alcoholics/unexplained lactic acidosis Steroids for septic shock refractory to one vasopressor/adrenal crisis and severe hypothyroidism Unless there is obvious evidence, death in hypothermia must be defined as a failure to revive with rewarming (at least a core T of 30C) Take Home: Think beyond sepsis and environmental causes of hypothermia, think Endocrine causes! Posted by:                     Lakshay Chanana            Speciality Doctor      Northwick Park Hospital      Department of Emergency Medicine      England      @EMDidactic