Local Anesthetic Adjuncts and Additives
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This document discusses common adjuncts and additives used with local anesthetics for nerve blocks and spinal anesthesia. It describes how epinephrine prolongs the duration and intensity of nerve blocks by causing vasoconstriction. Alkalinization can increase the effectiveness of local anesthetics but risks of precipitation limit its usefulness. Opioids and alpha-2 adrenergic agonists provide analgesic effects when added to local anesthetics by binding to receptors in the spinal cord. Fentanyl and morphine are commonly used opioid adjuncts. Dexamethasone may also prolong the duration of local anesthetic nerve blocks when used, though the mechanism is unknown.
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Local Anesthetic Adjuncts and Additives
- 1. L O C A L A N E S T H E T I C : C O M M O N A D J U N C T S A N D A D D I T I V E S 1 0 - M I N U T E TO P I C B Y R 1 K U L C H AYA T H I TAYA P O R N
- 2. EPINEPHRINE • Vasoconstrictor prolongs block duration & increase block intensity • Direct analgesic effects via α-2 adrenergic receptors in brain and spinal cord
- 4. EPINEPHRINE Disadvantages • Prolongs return of sacral autonomic function • Risk of urinary retention • Inappropriate for outpatient spinal anesthesia • Smallest dose due to toxic effects
- 6. ALKALINIZATION • Increases neutral form of LA • Hasten block onset • Limited clinically usefulness because precipitation occurs at pH beyond 6 – 8 especially bupivacaine and ropivacaine • Bicarbonate 1mEq/10ml of lidocaine
- 7. OPIOIDS • Spinal opioids bind to opioid receptors at substantia gelatinosa in dorsal horn • Attenuate C-fiber nociception independent of supraspinal mechanisms • Synergistic analgesia except chloroprocaine
- 8. FENTANYL • Lipophilic • Rapid onset: 5 – 10minutes • Intermediate duration: 60 – 120minutes • Augment spinal anesthesia efficacy • 20 – 25mcg in spinal anesthesia • Prolongs anesthesia duration without delaying bladder function recovery
- 9. MORPHINE • Hydrophilic • Slow onset: 30 – 60minutes • Prolonged duration: up to 24hours • Extended postoperative analgesia • 100 – 200mcg for C/S,TAH,THA, prostatectomy >>> minimal respiratory depression • 300 – 500mcg forTKA >>> side effects significantly increase
- 10. ALPHA-2 ADRENERGIC AGONISTS • Supraspinal and spinal adrenergic receptors • Direct inhibitory effects on A and C fibers • Synergistic neuraxial and peripheral analgesic effects • Additive systemic effects • Prolong analgesia duration by 2 hours regardless of LA agents • Minimal side effects Clonidine • 1 mcg/kg for peripheral nerve block • 15 – 30 mcg for spinal block
- 11. STEROIDS • Dexamethasone with extended-release LA prolongs duration of blockade • Unknown mechanism
- 12. THANK YOU FOR YOUR ATTENTION
Editor's Notes
- Decrease plasma conc of LA
- Decrease neural blood flow >>> n ischemia?
- Increase duration 70% for lidocaine
- Alkalinization = hasten onset of neural block Commercial LA pH 3.9 – 6.47 >>> acidic esp with epinephrine LA pKa 7.6 – 8.9 >>> lipid-insoluble neutral form Neutral form = penetration into neural cytoplasm Charged form = interacts with LA receptor in Na channel Increase ratio of lipid-neutral form
- Opiods have multiple central and peripheral mechanisms of analgesic action Chloroprocaine decreases epidural opioid effectiveness, unclear mechanism but not receptor antagonist
- S/E = N/V, pruritus, urinary retention
- i.e. clonidine
- Prolongs 50% after peripheral nerve block