Fever during Anesthesia Speaker: Guo, Shu-Lin Date: 2003-12-09.

Fever during Anesthesia

Speaker: Guo, Shu-LinDate: 2003-12-09

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

Any Questions?