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Postanesthetic Shivering

Postanesthetic Shivering. Epidemiology, Pathophysiology, Prevention and Management. Reference. Perioperative Shivering Physiology and Pharmacology Anesthesiology 2002; 96: 467-84 Postanesthetic Shivering Epidemiology, Pathphysiology, and Approaches to Prevention and Management

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Postanesthetic Shivering

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  1. Postanesthetic Shivering Epidemiology, Pathophysiology, Prevention and Management Chih-Min Liu

  2. Reference • Perioperative Shivering • Physiology and Pharmacology • Anesthesiology 2002; 96: 467-84 • Postanesthetic Shivering • Epidemiology, Pathphysiology, and Approaches to Prevention and Management • Drugs 2001; 61 (15): 2193-2205 • Clinical Anesthesiology, third edition • Chapter 6: Patient monitors; 117-120 Chih-Min Liu

  3. Clinical Considerations • Hypothermia: < 36 oC • O2 consumption x 5; decrease saturation; myocardial ischemia and angina • Increased mortality rate • Monitoring site: • Tympanic membrane: brain temperature • Nasopharyngeal mucosa: core temperature • Rectum: slow response in change to core temp • Esophagus Chih-Min Liu

  4. Epidemiology • 40-60% after volatile anesthetics • Young male adult, rare in elder (age impairs thermoregulatory control) • Length of anesthesia or surgery • Peri-op rewarming procedure: if not • Mild hypothermia • The more serious hypothermia, the higher the probability • Anesthetic used • Less common with propofol; more with halogenated agent, pentothal Chih-Min Liu

  5. Pathophysiology • Consequence of postanesthetic shivering • Discomfort • Increased pain • IICP, IOP • O2 consumption (VO2): more 40 – 120% • Increased minute ventilation • Cardiac morbidity Chih-Min Liu

  6. Pathophysiology • Two types of postanesthetic shivering • Thermoregulated shivering • With cutaneous vasoconstriction, the response of hypothermia • Perioperative hypothermia • Non-thermoregulated shivering • Mechanism unknown • Postoperative pain related? Chih-Min Liu

  7. Pathophysiology • Origins of Postanesthetic Shivering • Perioperative hypothermia • Postoperative pain • Perioperative heat loss • Direct effect of certain anesthetics • Hypercapnia or respiratory alkalosis • The existence of pyogens • Hypoxia • Early recovery of spinal reflex activity • Sympathetic overactivity Chih-Min Liu

  8. Perioperative hypothermia • Phase I: 1st hour • Internal redistribution: from center to peripheral • Phase II: 2-4 hours • Heat loss: skin, viscera • Phase III: • Steady-state Chih-Min Liu

  9. Pathophysiology • Early recovery of spinal reflex activity • Residual effect of anesthetics on the inhibiting control exercised by supraspinal structure • Propofol in low concentration may have less effect on certain central structure such as the reticular formation, thus faster recovery of descending inhibiter control Chih-Min Liu

  10. Temperature-regulating system • Thermosensors • Skin to hypothalamus • Afferent pathway, integration area • Spinal cord • Modulate: NRM( serotonin), LS(NE) • Integration inputs: PO-AH • Efferent pathway • Central descending shivering pathway: PH • Multiple inputs>common efferent signal • Spinal αmotor neurons, axons Chih-Min Liu

  11. Pathophysiology • Human defenses to hypothermia: • Skin vasomotor activity • Nonshivering thermogenesis • Cell metabolic without mechanical work, Neonate • Shivering • Sweating • Shivering is the last-resort defense Chih-Min Liu

  12. Pathophysiology • Shivering • Several types • 4-8 Hz., waxing-and-waning pattern • Postanesthetic tremor • Thermoregulatory inhibition abruptly dissipates, thus increasing the shivering threshold toward normal • New, near-normal threshold activate shivering • Shivering like activity • Pain in post-op and labor female Chih-Min Liu

  13. Prevention & Management • Perioperative Hypothermia Prevention • Limiting the effects of internal redistribution • Skin surface rewarming with forced-air warmer for 30 minutes • Reduce heat loss • Radiation from skin surface • Room temperature > 23oC if the op field is large • Cover the patient as much as possible • Intravenous fluid rewarming Chih-Min Liu

  14. Prevention & Management • Passive prevention is not enough • Active heat transfer • Cutaneous patch is the most efficient • Forced warm air better then… • Water circulation blankets • 1/3 cover of the cutaneous surface is enough • Under GA > vasodilatation > heat loss Chih-Min Liu

  15. Prevention & Management • Physical treatment • Shivering threshold: • skin 20%, core 80% • Raise temp to inhibit postoperative shivering: • skin 4oC = core 1oC • Radiation heat system • Forced air warmer: • reduce frequency and duration of shivering Chih-Min Liu

  16. Prevention & Management • Medical treatment • Opiates • Tramadol, Ketanserin, Nefopam and Ondensetron • α2-Adrenergic Agonists • Other drugs Chih-Min Liu

  17. Opiates • Meperidine • Demoral • Κ-opioid receptor • Shivering threshold • Vasoconstriction • Sweating • Others: • Pure μ-receptor agonists • Morphine, alfentanyl, fentanyl • Sites of action • PO-AH, dorsal raphe nucleus neurons, RMN, LS, and the spinal cord Chih-Min Liu

  18. Meperidine( Demoral) • Sweating • Vasoconstriction • Shivering threshold Chih-Min Liu

  19. Tramadol, Ketanserin, Nefopam and Ondensetron • The balance of Norepinephrine and serotonin(5-HT) in the PO-AH controls the body temperature set point • 5-HT induce hyperthermia; α2-Adrenergic Agonists (clonidine) reduce core temperature • Opposite modulatory inputs from NE and serotonergic neurons shifting the shivering threshold • All 4 drugs acts on the serotonin neuromediator • Encourage the inhibiting effect of serotonin on OP-AH Chih-Min Liu

  20. Tramadol, Ketanserin, Nefopam and Ondensetron • Tramadol • Inhibits reuptake of 5-HT, NE, dopamine and facilitate 5-HT release • Site of action: Pons • Analgesic effect, non-opioid analgesic • 1 mg/kg for shivering, reduce threshold by 0.8oC • Nefopam • Inhibits reuptake of 5-HT, NE, dopamine and lower normal body temperature • Analgesic effect, 0.15mg/kg or 20mg • Ketanserin • Low efficacy • Antihypertensive effect, 5 HT2 antagonist, 10mg • Ondensetron • Antiemetic, 5 HT3 antagonist, 8mg Chih-Min Liu

  21. α2-Adrenergic Agonists • Clonidine 75μg • lower the threshold of cutaneous vasoconstriction and shivering by 0.5oC • Bolus & perfusion: • At the end of op: 1.5 or 3μg/kg • Cardiac surgery: 200 to 300μg • Mechanism: • Central • Shivering centre is under inhibiting control of the preoptic anterior hypothalamic region • α2-Adrenergic Agonists probably strengthened it • Dexmedetomidine Chih-Min Liu

  22. Other drugs • Other drugs • NMDA receptor antagonist: • Ketamine • Magnesium sulfate 30mg/kg • Methylphenidate 20mg • Analeptic agent, block reuptake of 5-HT • Physostigmine 0.04mg/kg • Central acting cholinesterase inhibitor • Doxapram 100mg or 1.5mg/kg • Respiratory stimulant, central action on pons • Recovery of the descending inhibitor control of the supraspinal effecting centers Chih-Min Liu

  23. Conclusion • Hypothermia is associated with shivering and many complications, patient should be kept normothermia • Prevention of hypothermia consists of limiting heat loss and active rewarming system • Effective treatment of shivering will reduce metabolic heat production and must be accompanied by an effective active heating system. • Skin surface rewarming is less efficient then medical treatment with meperidine, tramadol, or, in certain situations, clonidine • All antishivering drugs except ketanserin have some analgesic properties in humans, suggested that pain and thermoregulation are tightly connected • No single structure or pathway is responsible for the shivering response Chih-Min Liu

  24. Thanks for your attention Chih-Min Liu

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