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Pre-emptive analgesia is an antinociceptive
treatment that prevents establishment of altered processing of afferent
input, which amplifies postoperative pain.
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Concept of preemptive analgesia was formulated by
Crile
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DEFINITION: Treatment that:
ü Starts
before surgery
ü Prevents
the establishment of central sensitization by incisional injury ( covers period
of surgery)
ü Prevents
establishment of central sensitization caused by incisional and inflammatory
injury (covers the period of surgery and the initial postoperative period).
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Strategies:
ü Local skin
infiltration-pre and post operative
ü PCM and NSAIDS:
reduces inflammation, pain , fever:
Ø Diclofenac
- used in orally, per-rectally,intramuscularly and continuous
infusion.Single dose: 1.0 - 2.0 mg/kg; maximum dose; 3mg /kg /day. Interval: 6-
8 hours.
Ø Paracetamol
- can be administered in orally, infusion and per-rectally. Single dose: 10
- 15 mg/kg; maximum dose: 60mg/kg/day. Interval: 4- 6 hours.
ü Intravenous Opioids:
Sites of action:
Ø Periaqueductal
Grey (PAG), Limbic system
Ø Caudal
brain stem (nucleus raphe magus, magnocellular reticular formation)
Ø Spinal
cord
Mechanism of action:
Ø inhibition
of neuronal activity
Ø inhibit
the release of neurotransmitters
Ø activate
descending inhibitory systems
ü Epidural
anaesthesia, Nerve blocks: Commonly practiced agents are Bupivacaine and
Lidocaine with or without Epinephrine (1:200,000 or 5 ug/ml).
ü Both
agents can be given local infiltration, intrathecal, caudal or epidural and
peripheral nerve block (llioinguinal and iliohypogastric nerve block, penile
nerve block, intercostal nerve block, brachial plexus block etc.).
ü Alpha 2 agonists:
Ø play a key
part in the descending modulation of pain.
Ø Descending
supraspinal pathways include the periaqueductal gray area of the midbrain,
stimulation of which results in widespread analgesia.
Ø In
particular, stimulation of alpha-2 receptors located in the locus ceruleus and
parabrachial nucleus of the medulla affords analgesia through G-protein
mediated potassium channel conductance
ü NMDA receptor antagonists:
Ø Magnesium, Ketamine : Combinations of ketamine and
magnesium potentiate each other.Combinations are more effective analgesics than
either alone; Superadditive
(>90%) effect of coadministration allows for reduced doses of each; thus,
less side effects.
ü Others:
Ø Dextromethorphan, Methadone
Ø Tricyclic antidepressants, Nicotine agonists
ü repeated episodes
of constant noxious input primes NMDA receptors for chronic pain state (central
sensitization)
