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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.