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Hypothermia and rewarming techniques

Hypothermia and rewarming techniques. Albury Wodonga Teaching Program 2013. hypothermia predisposes to a physiological state of: hypotension hypoventilation depressed mental state and bradycardia. Key points. domestic victims are generally elderly and female

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Hypothermia and rewarming techniques

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  1. Hypothermia andrewarming techniques • Albury Wodonga Teaching Program 2013

  2. hypothermia predisposes to a physiological state of:hypotensionhypoventilationdepressed mental state and bradycardia.

  3. Key points • domestic victims are generally elderly and female • non-domestic victims are male aged 13-65 • invasive techniques are for severe hypothermia with circulatory compromise • non-invasive techniques are effective

  4. Key points • Deaths from hypothermia are predominantly domestic • Co-morbid disease can precipitate hypothermia • e.g. overdose, trauma, MI, stroke • These conditions need specific treatment • Managing hypothermia may reverse physiological abnormalities

  5. Hypothermia Epidemiology of hypothermia: fatalities and hospitalisations in New Zealand Aust N Z J Med. 1994 Dec;24(6):705-10. • Incidence of death low - 0.07% of all causes • Incidence of hospitalisation 13X rate of death • Occurs at extremes of age and in young males • Domestic fatalities predominantly occur in the elderly • Non-residential fatalities occur in young males

  6. In Australia • Pathology. 2008 Jan;40(1):46-51. • Hypothermia fatalities in a temperate climate: Sydney, Australia • Case report of 24 fatalities 2001-2005 • Predominantly domestic, female and elderly

  7. Risk factors • burn injuries • extremes of age • ethanol intoxication • dehydration • major psychiatric illness • trauma • use of intoxicants • significant blood loss • sleep deprivation • malnutrition • co-existing medical conditions

  8. How cold is cold? • Mild 32o - 35o • Moderate 29o - 32o • Severe <29o • Poikilothermia - cooled to ambient temperature • Lowest recorded temperature for a survivor of accidental hypothermia is 9oC

  9. Response to cooling • metabolic rate drops 2-3X with every 10o drop • cerebral blood flow decreases 6-7% per 1o drop • shivering - down to about 34o • gluconeogenesis - via adrenaline release • peripheral vasoconstriction ➜ cold diuresis via central hypertension and ADH inhibition

  10. What happens as you cool?34-35o

  11. What happens as you cool?30-34o

  12. What happens as you cool?< 30o ‘J’ waves have no prognostic or predictive value

  13. ED Management priorities • Prevent further cooling • Establish a safe rewarming rate • Maintain cardiopulmonary stability • Provide physiological support

  14. Other factors to consider • Cardiac arrest • Acid base • Coagulopathies • Pharmacodynamics

  15. Cardiac arrest • numerous case reports of survival • optimal compression rate not known - likely to be less • duration unknown • core temp >34o • pH >6.5 • K < 10 • May consider admission to ICU for prolonged attempts

  16. Acid-base • ↓1oC ➔ • pH ↑ 0.015 • pCO2 ↓ 4.4% • pO2 ↓ 7.2% • current theories suggest not correcting for temperature • arterial pH no a prognostic guide

  17. Coagulpathies • from impaired clot formation • inhibition of thromboxane B2 (platelet function) • hypothermia induced platelet aggregation seen in surgical patients causing neurological deficit

  18. Pharmacodynamics • drug kinetics are altered • negative effects on renal and hepatic metabolism • avoid digoxin • magnesium, lignocaine and propanolol have been used • use bicarb and pressors in smaller doses

  19. ED Management priorities • Rate and method of rewarming is determined by the degree of hypothermia and severity of clinical condition

  20. Start points for treatment • core temp. >32o • Passive external rewarming • core temp. <32 • Active external rewarming • Active core rewarming

  21. Core temperature measurement • Bladder probes - available, reliable • Rectal probes - lag time, faeces • Oesophageal probes - may be influenced by warmed air • Tympanic membrane - less reliable

  22. Passive external rewarming • Remove wet clothing • Warmed blankets • Resistive heating blankets (space blanket)

  23. Active external warming • Heated air blankets • Warmed IV fluids • limited role due to reduced circulating volume • Immersion therapy • ‘afterdrop’ phenomena • not more effective than heated air blanket

  24. Warming rate oC/hr From Danzl D, Pozos RS: Multicenter hypothermia study.Ann Emerg Med 16:1042, 1987

  25. Active core rewarming • generally a treatment in the face of circulatory failure • allows more rapid increase in core temperature • some techniques are not technically possible depending on situation

  26. Active core rewarming • Heated humidified oxygen • Peritoneal lavage • Bladder irrigation • Thoracic cavity lavage • ECMO/bypass • Microwaves / total liquid ventilation(TLV) / hot IV fluids

  27. Heated Humidified Oxygen • can be performed via mask or ETT • can be used pre-hospital • needs careful monitoring of temperature and humidification • can be used routinely to complement external techniques • temperatures >50o may cause mucosal burns

  28. Warming fluid • ideal temperature 40-42o • IV fluid warmers • only certain devices are suitable for adequately warming large volumes for rapid infusion • microwaving fluids is not recommended

  29. Peritoneal lavage • can achieve rates up to 2-3o /hr • infra-umbilical incision/seldinger technique • rapid infuser device, two catheters to increase flow • theoretically less successful than thoracic lavage • wouldn’t interfere with CPR • may help in overdose

  30. Bladder irrigation • good rates of core rewarming • equipment readily available, saline or Hartmanns • smaller volumes possible - max. prob. 200mls • 1-2 minute dwell times • less risk to patient than more invasive techniques • may interfere with core temp. monitoring

  31. Thoracic cavity lavage • used in setting of cardiac arrest • closed or open • CPR can continue with either • rates of 6-7o in 20 minutes have been described • caution in coagulpathy • continue until 35o

  32. ECMO/bypass • high level of expertise/equipment/support needed • 1-2o every 3 to 5 minutes • may take some time to set up • anticoagulation required may complicate active CPR • can allow oxygenation • consider in asystole or VF

  33. Microwaves/TLV/hot IV fluids • Microwave rewarming equivalent to passive rewarming in volunteer study. Resuscitation 29:203, 1995 • TLV in animal models using warmed oxygenated perflurocarbon. Shorter rewarming times, no afterdrop phenomena and no lactate rise. Mil Med 166:853, 2001 • 60o IV fluids appear to cause little complications. Role in accidental hypothermia not defined. J Trauma 42:1112, 1997

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