Fever during Anesthesia Speaker: Guo, Shu-Lin Date: 2003-12-09
Dec 17, 2015
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
Thermoregulation
Setpoint:the normal inter-threshold range is only a few tenths of a degree centigrade
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
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
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
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
Process of Fever
Thermoregulatory controlNeuron-mediated primarily
Vagal afferent pathways
Humoral mediatorsThe major endogenous pyrogens
Interlukin-1Interlukin-6Tumor necrosis factor (TNF-alpha)Interferon-alpha
Process of Fever
Process of feverThe core temperature elevates
All thermoregulatory response thresholds also elevate
Cold-defenses are strongly augmented
The maximal temperature usually dose not exceed 42°C
Process of Fever
Antipyretics:Pyrogens vs. antipyretics (cryogens)Endogenous antipyretics:
Interleukin-10GlucocorticoidsVasopressionMelanocyte-stimulating hormone (alpha-MSH)Nitric oxide
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
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
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
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
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
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
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
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
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
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
Neuraxial anesthesia and Fever
Epidural analgesia is frequently associated with hyperthermia, especially during labor and post-operative periodThe paradoxical hyperthermia often prompts clinical interventions such as work-up for infection and newborn sepsis
Neuraxial anesthesia and Fever
During epidural analgesia, the sweating threshold slightly increases
Epidural pain control vs intravenous pain control
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
Post-operative Fever
A positive relationship between the post-operative increase in core temperature and plasma IL-6 concentration
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
Treatment of Fever
Active cooling does not reduce core temperature, but increases the metabolic rate, activates the autonomic system, and provokes thermal discomfort
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