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104

Chapter 8

Analgesia

A

2

-agonists have spinal and supraspinal analgesic effects. Spinal effects stimulate receptors

in the dorsal horn, which results in inhibition of the firing of nociceptive neurons and reduces

the secretion of the nociceptive neurotransmitter substance P. Supraspinal effects are

located in the locus coeruleus. Here, the α

2

-noradrenergic and the opioid system have the

same effector systems. But if only mild to moderate sedation is desired, dexmedetomidine

will not provide adequate analgesia counteracting strong and acute pain stimuli. That

means that another analgesic must to be added.

Anxiolysis

A

2

-agonists can achieve a comparable anxiolysis with benzodiazepines without respiratory

depression.

Central nervous system

Dexmedetomidine has a minor effect on the intracranial pressure. It lowers cerebral

blood flow during anaesthesia in combination with isoflurane in animal models without

inducing global ischaemia. Recent studies could even show neuroprotective properties

of dexmedetomidine. In neonatal rat models, dexmedetomidine reduces neurotoxicity

induced by isoflurane. This effect is attributed to a mechanism that is not mediated via

α

2

-receptors. The assumption is that dexmedetomidine increases the expression of growth

factors such as epidermal growth factor (EGF) and brain-derived neurotropic factors

(BDNF), which on their part cause the neuroprotective effect. At the moment, there are

no evidenced based data that dexmedetomidine should be used in acute cerebrovascular

threatening situations.