Fever during Anesthesia

1. Fever during Anesthesia Speaker: Guo, Shu-LinDate: 2003-12-09

2. Thermoregulation • Thermoregulatory response:a core temperature that triggers physiological defenses against excessive heat or cold • Inter-threshold range:the difference between the sweating and vasoconstriction thresholds

3. Thermoregulation • Setpoint:the normal inter-threshold range is only a few tenths of a degree centigrade

4. Role of Fever • Pathphysiology:the pyrogenic stimulation activates hypothalamic thermoregulatory control centers • Elevation of setpoint:a synchronous elevation in the cold-response and warm-response threshold

6. Role of Fever • Kluger et al. Science. 1975 • Method: the desert iguana infected with bacteria • Result: a clear correlation between the increase in body temperature after bacterial infection and the host survival rate

7. Role of Fever • Vaughum et at. Brain Research Bulletin 1998 • Method: rabbit with fever • Result: antipyretic use reduced body temperature and significantly decreased the host survival rate

8. Role of Fever • Disadvantage: • Increasing cardiac output, oxygen consumption and energy consumption • Antipyretic use timing:the elderly or patients with poor cardiac or pulmonary function

9. Process of Fever • Thermoregulatory control • Neuron-mediated primarily • Vagal afferent pathways • Humoral mediators • The major endogenous pyrogens • Interlukin-1 • Interlukin-6 • Tumor necrosis factor (TNF-alpha) • Interferon-alpha

10. Process of Fever • Process of fever • The core temperature elevates • All thermoregulatory response thresholds also elevate • Cold-defenses are strongly augmented • The maximal temperature usually dose not exceed 42°C

11. Process of Fever • Antipyretics: • Pyrogens vs. antipyretics (cryogens) • Endogenous antipyretics: • Interleukin-10 • Glucocorticoids • Vasopression • Melanocyte-stimulating hormone (alpha-MSH) • Nitric oxide

13. Fever during Anesthesia • Thermoregulatory control during anesthesia • Volatile anesthetics, propofol, opioids and sedatives: • Slightly increase the sweating threshold • Markedly decreasing the vasoconstriction and shivering thresholds • Inter-threshold range increases to 2-4°C

14. Volatile Anesthesia And Fever • Fever is relatively rare during general anesthesia • The general anesthesia attenuates fever by the lowering of thermoregulatory threshold of cold defences

15. Volatile Anesthesia And Fever • Negishi et al. Anesthesiology 1998 • Method: desflurane and IL-2 induced fever • Result: 1.0 MAC essentially obliterating the temperature increase by IL-2

17. Volatile Anesthesia And Fever • Lenhardt et al. Anesthesiology 1999 • Methods: measure the thresholds of IL-2 induced fever and general anesthesia • Result: the combination of IL-2 administration and desflurane increased the sweating threshold and reduced the vasoconstriction threshold compared to IL-2 alone

19. Volatile Anesthesia And Fever • Peripherally mediated inhibition by desflurane anesthesia • Desflurane did not affect the plasma concentrations of the circulating cytokines induced by IL-2 • Desflurane decreases the thermoregulatory thresholds of cold defenses via central action

20. Intravenous Anesthesia And Fever • Roytblat et al. A&A 1998 • Before cardiac pulmonary bypass, ketamine (0.25mg/kg) reduces serum IL-6 concentration during and post surgery • Crozier et al. BJA 1994 • Alfentil and propofol diminishes release of IL-6 during abdominal surgery

21. Opioids And Fever • Opioids administration increases warm-response thresholds and decreases cold-response thresholds • The pattern of inhibition is similar to that produced by general anesthesia though the magnitude is somewhat low

22. Opioids And Fever • Opioids also suppress fever in a dose-dependent fashion • Opioids use in ICU or during the post-operation period need to be aware

23. Neuraxial anesthesia and Fever • Re-distribution is a major cause of core hypothermia during epidural and spinal anesthesia • The BT loss rate is determined by the inequality between heat loss and heat productions well as block level

24. Neuraxial anesthesia and Fever • With neuraxial anesthesia peripheral nerve block is a more important cause of hypothermia • Sufficient core hypothermia will trigger vasoconstriction and shivering even during neuraxial anesthesia, but only in the unblocked areas

25. Neuraxial anesthesia and Fever • Epidural analgesia is frequently associated with hyperthermia, especially during labor and post-operative period • The paradoxical hyperthermia often prompts clinical interventions such as work-up for infection and newborn sepsis

26. Neuraxial anesthesia and Fever • During epidural analgesia, the sweating threshold slightly increases • Epidural pain control vs intravenous pain control

28. Paralysis And Fever • Paralysis prevents shivering and the associated increase in metabolic heat production • Paralysis can reduce the magnitude of fever, but clinically its effect seems to be less important than anesthetic-induced inhibition of fever

29. Post-operative Fever • A positive relationship between the post-operative increase in core temperature and plasma IL-6 concentration

31. Treatment of Fever • Most febrile patients are treated with antipyretic, mainly for patients comfort • Fever should be treated in patients with cardiopulmonary dysfunction, acute brain stroke or injury, or in those whose temperature above 40°C

32. Treatment of Fever • Active cooling does not reduce core temperature, but increases the metabolic rate, activates the autonomic system, and provokes thermal discomfort

33. Treatment of Fever • Fever occurs in almost half of the patients with acute brain stroke or injury • Mild brain hyperthermia worsens the functional outcome by enhancing neurotransmitter release, exaggerating oxygen radical production, and extending blood-brain barrier breakdown

34. Any Questions?