HEAT STROKE. Lindsay VaughLindsay Vaughn, DVM, DACVECCDVM, DACVECC

Transcription

1 HEAT STROKE Lindsay VaughLindsay Vaughn, DVM, DACVECCDVM, DACVECC

2 Heat Stroke More Preventable Than Treatable

3 Heat Stroke A form of hyperthermia associated with a systemic inflammatory response leading to a syndrome of multi-organ dysfunction in which encephalopathy predominates (defined by human medicine)

4 Heat Stroke State of extreme hyperthermia ( F) Direct thermal damage to body tissues Heat load > Heat dissipating mechanisms Two Types of Heat Stroke Exertional Non-Exertional (classic)

5 For just a second.

6 For just a second.. From ambient temperature the window down vehicle reached 40.7 C (105 F) in 16 minutes, while the window up vehicle reached a similar temperature in 6 minutes Cars with windows up reach a temperature exceeding 205 F 2.6 times quicker than the car with windows down Interior vehicle temperature will double ambient temperature

7 Heat Dissipating Mechanisms Conduction: Transfer of heat from one substance to another Radiation: Natural process of heat release from body Convection: Transference of heat from body as air passes over it Evaporation: Fluid changing to vapor

8 Predisposing Factors INTRINSIC Obesity Thick fur coat Brachycephalic Neurologic/NM disease Laryngeal Paralysis CV disease EXTRINSIC Lack of Acclimatization Increased Environmental Temp Humidity Water Deprivation Medications Diuretics Beta Blockers

9 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

10 Pathophysiology Peripheral vasodilation and splanchnic vasoconstriction Direct cytotoxicity to multiple organs Production of both pro-inflammatory and anti-inflammatory cytokines Coagulopathy Systemic Inflammatory Response (SIRS) Multiple Organ Dysfunction (MODS)

11 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

12 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

13 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

14 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

15 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

16 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

17 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

18 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

19 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

20 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

21 CV Liver Pulmonary Kidney HEAT STROKE CNS Coagulation GI

22 Necropsy Results 11 dogs with fatal heat stroke All showed multi-organ hemorrhage with coagulative necrosis Necrosis: SI, LI, renal tubular epithelium, hepatic parenchyma, brain neural tissue Sequels of hyperthermia-induced DIC and SIRS which leads to MODS and death

23 Initial Patient Evaluation Temperature: variable, > 106 F Circulation Airway Breathing (CAB) C: mm, thoracic auscultation, pulse quality A: stridor, airway obstruction B: lung sounds Neurologic Examination Mentation, seizures

24 Diagnostics PCV/TS Hemoconcentration Anemia Glucose Hypoglycemia Electrolytes Hypernatremia Hyponatremia Blood pressure Hypotension CBC Leukocytosis/leukopeni a Anemia Thrombocytopenia nrbc Chemistry Elevated ALT Azotemia Elevated CK

25 40 client-owned dogs with naturally occurring heat stroke 90% had nrbc on presentation Cut-off point of 18 nrbc/100 leukocytes corresponded to sensitivity and specificity of 91 and 88% for death

26 Coagulation Panel (PT/PTT) Additional Diagnostics Thoracic Radiographs Electrocardiogram

27 Active Cooling Cooling by Owner Cool patient prior to transport and while in route to hospital Cool patient with water hose Place pre-soaked towel over patient Drive with A/C on or windows down AVOID submersion in cold-water bath

28 In-Hospital Cooling Active Cooling Place patient on cold metal table or wet sink Whole body cooling with tap water Increase air circulation over patient (fan) Apply cold, wet towels over thin-haired areas (ventral abdomen, axilla, and inguinal regions) Massage extremities

29 Active Cooling AVOID Immersion techniques Ice packs Pharmacologic agents to increase cooling Discontinue active cooling when patient temperature is F (prevent rebound hypothermia)

30 IV fluid therapy Goal: assist with cooling and restore circulating volume Fluid therapy guide: hemodynamic parameters (mm, CRT, heart rate, pulse quality, blood pressure) Type of fluid therapy: Balanced crystalloid solution (room temperature) Colloids

31 Volume Resuscitation Shock (tachycardia and hypotension): ¼ shock doses (dog= 20 ml/kg, cat= 12.5 ml/kg) of crystalloid over minutes until systolic BP 100 mmhg If patient has persistent symptoms of shock despite full shock dose (dogs= 80 ml/kg, cats 50 ml/kg) of crystalloids, consider colloid therapy

32 Crystalloid Therapy Dehydrated patient WITHOUT shock: Goal: replace dehydration deficit + maintenance therapy + on going losses Ex: 20 kg dog with 10% dehydration (correct over 24 hours) Dehydration: 20 kg x 0.10 x 1000= 2,000 ml dehydration deficit therefore 2,000 ml/24 hrs (83 ml/hr) Maintenance: 20 kg x 60 ml/kg/day= 1,200 ml/24 hours (50 ml/hr) Ongoing losses: based on volume of vomit/diarrhea Therefore administer fluid at 133 ml/hr (50 ml+ 83 ml)

33 Colloid Therapy Indications: hypoproteinemia or patients refractory to large-volume crystalloid therapy Dose: Administered 5 ml/kg bolus over minutes If refractory hypotension persistent despite shock dose of crystalloid and 2 doses of a colloid vasopressors may be required

34 Oxygen Therapy Supplement oxygen therapy until hypoxemia is ruled out Place ice in oxygen mask Neurologic patients should receive oxygen for minimum of 12 hours for brain support

35 GI Therapy Due to potential GI sloughing and ulceration Gastroprotectants (H2 blocker or proton pump inhibitors) Sucralfate Anti-emetics Broad spectrum antibiotics

36 Fluid therapy important Oxygen therapy Neurologic Therapy Seizure activity: benzodiazepines +/- anticonvulsant therapy Cerebral edema: mannitol or hypertonic saline Elevate patient head and avoid jugular compression

37 Glucose Supplementation Hypoglycemia may be noted at presentation or at any point during hospitalization Supplementation with 50% dextrose 0.5 ml/kg bolus diluted 1:1 with saline 2.5-5% constant IV infusion

38 Coagulopathy Coagulopathic patients may require fresh frozen plasma

39 Controversial Therapy NSAIDS and corticosteroids are not recommended Risks outweigh benefits Risks: Immunosuppression GI ulceration Altered platelet function

40 Continuous Hemofiltration

41 Continuous Hemofiltration Heat stroke induced in anesthetized dogs Rapidly reduced body temperature, normalized hemodynamics and electrolytes, improved serum enzyme concentrations and increased survival in dogs with heat stroke 5 dogs in control group died (standard treatment) vs 0% death in continuous hemofiltration group

42 Sloughing Paw Pads

43 Monitoring 24 hour supportive care and monitoring Frequent evaluation of CV and respiratory system Monitoring for kidney failure: weight q 12 hrs urine production (+/- indwelling catheter) kidney values q 24 hrs Coagulation parameters q 24hr

44 Prognosis Dependent on prior medical condition, degree and duration of heat insult, and response to therapy Overall mortality in dogs 50% Death usually occurred within 24 hours of presentation (in animals that died) All dogs that were alive 48 hours after presentation survived

45 Prognosis Duration of hospitalization 1-6 days Most non-survivors died or euthanized within hours All animals alive after 3 days survived to discharge Overall 50% mortality

46 Risk factors associated with death: Prognosis Persistent hypoglycemia despite therapy Coagulopathy Creatinine > 1.5 mg/dl after 24 hr of therapy Seizures Obesity Delayed admission to the hospital (>90 min) Response to treatment within the first hours of therapy is more indicative of prognosis

47 Fun Fact. Once a patient suffers heat stroke..they are more predisposed to heat stroke in the future

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49 CONTACT US O: F: COM