Accidental Hypothermia François Dufresne McGill Emergency Medicine May 2nd 2001 The Case of Tommy • • • • • • • • 23h10 Call from MD working in James Bay Male, 27 y.o.
Download ReportTranscript Accidental Hypothermia François Dufresne McGill Emergency Medicine May 2nd 2001 The Case of Tommy • • • • • • • • 23h10 Call from MD working in James Bay Male, 27 y.o.
Accidental Hypothermia François Dufresne McGill Emergency Medicine May 2nd 2001 The Case of Tommy • • • • • • • • 23h10 Call from MD working in James Bay Male, 27 y.o. Unresponsive. Found in snow, cross-country skiing Normal Airway. Breathing. O2 sat. Femoral pulse + (35) BP. GCS=3 TR = 28C. IV. Monitor. Mask with 100% O2 The Case of Tommy… • Friend told MD: – PMH. Rx. drugs. EtOH • Major foot deformity • Looks like fell in ski and could not return home by himself… • MD has some questions for you… The Case of Tommy… • Should he intubate? Are there risks to precipitate dysrythmias? • Cold myocardium prone to arythmias? • How should he rewarm the patient? • Danger of afterdrop? • He wants an ABG but should he ask for the blood to be warmed to normal T for analysis…or it doesn’t matter? Answer: You’ll call him back… The Case of Tommy… • • • • • • MD calls you back 30 minutes later Pt in cardiac arrest : V.fib. Now 27C 3 shocks Epinephrine + re-shock Having Amiodarone prepared… How long should he do CPR and rescussitation? Answer ? Anything wrong ? Introduction • Maritime / War litterature • Hannibal experience in 218 B.C Hannibal against Rome Introduction • • • • EtOH Mental illness Homelessness Province of Quebec Cold Plan • • • • • • • Definitions Physiology Pathophysiology Labs findings : ABG, ECG Rewarming methods Afterdrop ACLS 2000 guidelines Definitions • Primary VS Secondary • Primary – Normal thermoregulation – Overwhelming cold exposure • Secondary – Abnormal thermogenesis – Multiple causes Definitions • Hypothermia : < 35C • Mild : 32-35C • Moderate : 28-32C • Severe : < 28C Physiology: Heat production • Basal metabolism (Metabolic rate) – Heart / Liver • • • • • Anterior hypothalamus Thyroid / Sympathetic Preshivering muscle tone (2x) Shivering (2-5x) Posterior hypothalamus Physiology: Heat dissipation • Radiation (55-65%) • Gradient between environement and exposed body area. • Conduction (2-3%) • Direct contact with cold substance • Convection (10-15%) • Wind… • Evaporation (20-35%) Physiology… • Above 32C: – Vasoconstriction – Shivering – Basal metabolic rate • Below 32C: – No shivering • Below 24C: – No basal metabolic rate Pathophysiology Cardiovascular – Initial tachycardia – Gradual bradycardia : HR 50% at 28C. – Not consistent ? • Hypoglycemia, intoxication, hypovolemia,…? – – – – Refractory to atropine BP CI A.fib (T < 32C) V.fib (T < 28C) Pathophysiology… CNS – Cerebral metabolism 6% / 1C – Normal autoregulation until 25C – EEG flat at 19C Renal – Cold diuresis • Peripheral vasoconstriction • Failure to reabsorb Na+ and water. Pathophysiology… Respiratory – CO2 production 50% at 30C – Decreased RR – ARDS possible Hematology – Hemostasis and coagulation impaired – Problems with CPB Mild (> 32C) • • • • • • Increase metabolic rate Maximum shivering thermogenesis Amnesia / dysarthria / ataxia Loss of coordination Tachycardic, tachypneic Normal BP Moderate (28– 32C) • • • • • Stupor No shivering Bradycardic / A.fib BP RR Pupils dilated (< 30C) Severe (<28C ) • • • • • • • • Coma No corneal or oculocephalic reflexes BP V.fib (Maximum risk: 22C) Apnea Asystole Areflexia / fixed pupils Flat EEG (19C) Lab findings : ECG • Woman, 75 y.o • Found unconscious in her apartment Osborn (J) Wave • Mr. John J. Osborn in the early ’50’s. • When T< 33C • 25%-30% of patients • Positive-negative deflection Osborn JJ: Experimental hypothermia: respiratory and blood pH changes in relation to cardiac function. Am J Physiol 1953; 175:389. Osborne (J) Wave… • Amplitude proportionnal to degree of hypothermia • Usually V3-V6 • At junction of QRS and ST segment Osborn JJ: Experimental hypothermia: respiratory and blood pH changes in relation to cardiac function. Am J Physiol 1953; 175:389. ECG in Hypothermia • Muscle tremors artifacts • Early changes – Bradycardia – T wave inversion – Prolonged PR, QRS and QT intervals • A.fib when T < 32C • V.fib when T < 28C Lab findings : ABG • • • • Man, 45 y.o,. Rectal T= 30C. LOC Intubated. Acid-base status? Technician asks you if he should warm the blood before analysis… A) Don’t warm it : 30C B) Warm it to 37C C) heu…(30+37)/2….33.5C D) Both and I’ll pick the best one. ABG in Hypothermia • 1st ABG (30C): • pH = 7.5 • pCO2 = 27 The Good One !!! • 2nd ABG (37C): • pH = 7.4 • pCO2 = 40 • Which one do you pick? • Will you try to RR or VT to pCO2 ? • Everything’s perfect, I don’t touch the ventilator ? • The answer ? …. ABG in Hypothermia… …the rationale • pH of water at any given T defines neutrality • H2O H+ + OH• As T , less free H+ and OH- are generated and pH of neutrality . • As T , CO2 content is the same but pCO2 . Delaney KA and al. Assessment of Acid-Base Disturbances in Hypothermia and their physiologic consequences. Ann Emerg Med, Jan 1989; 18:72-82. So… • 1st ABG (30C): • pH = 7.5 • pCO2 = 27 • 2nd ABG (37C): • pH = 7.4 • pCO2 = 40 ABG in Hypothermia… …the rationale • ABG machines usually warms blood to 37C. • So use the UNCORRECTED ABG for normal T . Delaney KA and al. Assessment of Acid-Base Disturbances in Hypothermia and their physiologic consequences. Ann Emerg Med, Jan 1989; 18:72-82. Rewarming methods : Passive rewarming • Endogenous heat production – Shivering, metabolic rate, TSH, sympathetic,… • Involves decreasing heat loss – Remove from cold environnement – Remove wet clothes – Provide blanket Passive rewarming… • O2 consumption can > 90% • CO2 production can by 65% • Possible anaerobic metabolism Rewarming rate : 0.5C - 2.0C /h • Method of choice for mild hypothermia • Adjunt for moderate hypothermia Rewarming methods : Active external rewarming • Heat to body surfaces – – – – – Heating blankets (fluid filled) Air blankets Radiant warmers Immersion in hot bath Water bottles / Heating pads • Less effective than internal rewarming if vasoconstricted +++ Active external rewarming… • Concern about afterdrop. • Rewarming rates : 1C – 2.5C / h • Circulatory problem may be by applying devices to trunk only. • Very few prospective controlled study comparing methods. Forced Air Blankets • ED patients • Moderate to severe hypothermia (< 32C) • Exclusion criteria – Cardiac arrest – Hypothalamic lesions • 16 patients • Randomized to passive insulation with cotton blanket or forced air blanket @ 43C . Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484. Forced Air Blanket… • • • • All patients: warm iv fluids @ 38C Warm O2 (40C) End point: T = 35C Looked at: – Rates of rewarming – Skin damage by blankets Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484. Forced Air Blanket… Results • No afterdrop in both groups • No skin erythema/damage • Rewarming rates (p=0.01) – Forced-Air: 2.4C / h – Regular blanket: 1.4C / h Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484. Forced air Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484. Electrical heating blanket • Carbon fiber-resistive blanket VS Passive rewarming • 8 patients • Induced-hypothermia (33C) • Skin thermal flux transducer • CO2 concentration production through mask • Compared: – rates of rewarming – core heat content Greif R and al, Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: a randomized controlled trial. Ann Emerg Med. April 2000; 35: 337-345. Electrical heating Results • Core heat content >> electrical heating • Rates 1.5C/h > with electical heating • No afterdrop both groups Greif R and al, Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: a randomized controlled trial. Ann Emerg Med. April 2000; 35: 337-345. Rewarming methods : Active internal (core) rewarming • • • • • • • • Warm iv fluids Warm, humid oxygen Peritoneal lavage Gastric / Esophageal lavage Bladder / Rectal lavage Pleural / Mediastinal lavage Microwaves (Diathermy) Extracorporeal circulatory rewarming Warm iv fluids • Up to 45C shown to be safe • 65C fluid studied in dogs – – – – – – Journal of Trauma 1993 (8 dogs) American Journal of Surgery 1996 (10 dogs) Through IVC Safe. No Complications 2.9C/h compared to 1.25C/h (J Trauma) 3.7C/h compared to 1.75C/h (Am J Surg) Warm iv fluids… • Saline…Not RL • Long tubulure = lost of heat • Can use microwave for saline (No D5W) – Annals of EM, 1984 and 1985 – 1L of NS to 39C : 2 minutes at high power. • No microwave rewarming for PRBC – Hemolysis – Hemoglobinuria – Transfusion reaction Warm, humidified O2 • • • • 42C-46C Prevent heat loss Negligible heat gain Very important in management of hypothermic patient: – Up to 30% of heat production lost through airway. Gastric/Oesophageal/ Bladder/Rectal lavage • Not shown to be better than external rewarming. • Limited surface area • Limited heat exchange • Limited utility (!) • Recommend as last resort when other modalities not available. Peritoneal lavage • • • • • • • Fluid at 40-45C Up to 12 L/h KCl free Hepatic rewarming Renal support when dialysate is used 2C-4C / h C.I. – Abdominal trauma – Acute abdomen – Free intra-abdominal air Peritoneal lavage… • Almost all studies before 1980 • Almost all animal studies • Critical Care Medicine 1988 – 11 dogs – Comparing peritoneal/pleural lavage and heated aerosol inhalation – Peritoneal and pleural lavage equivalent – 6C/h/m2 – Heated inhalation alone : little heat gain Pleural lavage Closed-thoracic lavage Continuous thoracic cavity lavage • Two large (38F) ipsilateral chest tubes • 1: 2nd or 3rd anterior intercostal space, midclavicular. • 2: 5th or 6th intercostal space, posterior axillary line. • NS or tap water @ 42C • Rewarms heart + greater vessels Hall KN and al. Closed thoracic cavity lavage in the treatment of severe hypothermia in human beings. Ann Emerg Med, Feb 1990;19:204-206. Mediastinal lavage • • • • • Requires certain expertise Limited clinical experience Case reports Internal cardiac massage 8C / h Douglas D. Brunette, Hypothermic cardiac arrest: An 11 year review of ED management and outcome. Am J Emerg Med 2000; 18:418-422. Extracorporeal blood rewarming techniques • • • • Hemodialysis Arteriovenous rewarming Venovenous rewarming Cardiopulmonary bypass Extracorporeal blood rewarming… - Hemodialysis : renal dysfunction AV depends on the pt’s BP CPB is the « Gold Standard ». CPB improves long term survival and neurologic outcome. - 15 of 32 long term survivors and none had neurologic deficits (7 years later). B.H. Walpoth and al. Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming, N Engl J Med, 1997;337:1500-5 Diathermy • • • • • Ultrasonic waves Microwaves Short waves Few studies Radio wave regional hyperthermia: Experience with Tx of tumors. • Not widespread because of dosages in human poorly defined. Diathermy… • Prospective • Radio Wave vs. Peritoneal lavage • 6 dogs • Rate of rewarming 3x > for Radio wave. J.D. White and al. Controlled comparison of Radio Wave regional hyperthermia and peritoneal lavage rewarming after immersion hypthermia, J Trauma, 1985; (25)10: 989-993. The Afterdrop Phenomenon • Continued fall in deep core T during the initial period of rewarming. • First described by James Currie in 1798 • Theory of Burton and Edholm (1955): – Attributed to peripheral vasodilatation – Return of cold blood to central circulation – Cooling of myocardium • Accepted theory until mid ’80’s Burton, A.C., and O.G. Edholm. Man in Cold Environment. London: Arnold, 1955, p.216. Paul Webb, An alternative explanation. J. Appl. Physiol. 1986 • Fall of T during active rewarming: – Up to 2C – 10 – 30 min • Used calorimeter, rectal, esophageal and tympanic probes. • Heat loss calculation Webb, Paul. Afterdrop of body temperature during rewarming: an alternative explanation. J.Appl.Physiol. 60(2): 385-390, 1986. 2 mecanisms for afterdrop • Convection mecanism – Return of cold blood from periphery – Minimal is any contribution • Conduction mecanism – Thermal gradient principal – Heat flow principal Webb, Paul. Afterdrop of body temperature during rewarming: an alternative explanation. J.Appl.Physiol. 60(2): 385-390, 1986. Conduction Mecanism Environement Skin/Tissues Blood vessel Heat transfer Heat transfer Afterdrop: an alternative explanation • Active external rewarming increase threat of further cooling of the heart…as much as thought before. • Correlated by many other papers •Savard, G.K., K.E. Cooper, W.L. Veale, and T.J. Malkinson. Peripheral blood flow during rewarming from mild hypothermia in humans. J. Appl. Physiol. 58(1): 4-13, 1985. •Romet, Tiit T. Mechanism of afterdrop after cold water immersion. J.Appl.Physiol. 65(4): 1535-1538, 1988. The Alcatraz/San Francisco Swim Study • • • • • • • • • San Francisco Bay…contest… Swims from Alcatraz Island to shore No wetsuits or protective clothing Water T = 12C (53F) Outside : T = 10C 3 Km 11 subjects for study 23 y.o to 70 y.o (!) Measured T after contest. Thomas J. Nuckton and al. Hypothermia and afterdrop following open water swimming: The Alcatrax/San Francisco Swim Study. Am J Emerg Med 2000; 18:703-707. Afterdrop conclusion • Rectal T lags behing esophageal T and is often > than esophageal and pulmonary T. • Think about it but you can probably not prevent it. • Issue with active external rewarming • Other concerns about external rewarming: – Acidosis – Hypotension Management: ED issues Intubation • General belief it can induce arythmias • Danzl, Multicenter Hypothermia Survey, Annals Emerg Med, Sept.87. – – – – Data from 13 ED 428 cases 117 intubation NO arythmias Management: ED issues Bretylium • Recommended for V.fib in hypothermia • Removed from new ACLS 2000: • availability and limited supply • occurrence of side effects • Still recommend in textbooks (Rosen) • Recommended by US Wilderness Emergency Medical Services Institute • Based on Dogs studies • Good for prophylaxis only Management: ED issues Drugs / Shocks • NO drugs if T < 30C – Not efficacious – Not metabolised • If > 30C, intervals between doses • If < 30C and failure of 3 shocks Management: ED issues Drugs / Shocks • NO drugs if T < 30C – Not efficacious – Not metabolised • If > 30C, intervals between doses • If < 30C and failure of 3 shocks Defer subsequent shock + Rx until T > 30C ACLS 2000 The algorithm… Conclusion • • • • • Hypothermia is rare but treatable Good outcome after prolonged arrests Include Hypothermia in your Dx Include T as a 5th vital sign… Call early to organize CPB if available if patient in cardiac arrest • Prevention is still the best…and… Play carefully… From Journal Le Soleil, february 2001 The End