|
Receptor |
· α2 adrenoceptor agonist o Partial agonist (ceiling effect) o α2 : α1 = 200:1 o Central and peripheral o Pre- and post-synaptic · Imidazoline receptor agonist o May mediate brainstem effects |
|
Physiology |
· Locus coeruleus: o Mainly post-synaptic o ↓Activity of reticular activating system o ↓SNS outflow o ↑Descending inhibition of nociceptors · Dorsal horn: o ↓Glutamate/substance P release by nociceptors o ↓Activation of WDR projection neurons · Peripheral nerves o Pre-synaptic: ↓NAd release o Post-synaptic: similar to α1 |
|
CNS |
· Anxiolysis and sedation o Rousable and co-operative o Airway and breathing unaffected · General anaesthesia o Insufficient alone o ↓MAC / propofol Cp50 o ↓CMRO2 / ↓CBF / ↓ICP (mild) o EEG quasi NREM 3-4 · Other: o Analgesia (opioid-sparing) o Augment and prolong neuraxial blockade o Neuroprotection (↓NAd, ↓glutamate) o Anti-shivering o Anti-sialogogue |
|
CVS |
Multi-phasic effects: · At first: ± ↑SVR, ↑mAP, reflex ↓HR o Peripheral post-synaptic α2B o May occur after loading dose · Then: ↓SVR, ↓mAP, ↓HR, ↔CO o Central post-synaptic > peripheral pre-synaptic α2A o Severe if large bolus · After cessation: ± rebound hypertension, agitation o α2 receptor upregulation Use: · ↓Response to laryngoscopy and surgery · ↓Myocardial ischaemia (↑supply, ↓demand) · ↓Opioid withdrawal |
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