Lidocaine Anesthetics
Dose Response study of Lidocaine 1%
Purpose:
To analyze the sensory and motor block produced by three different volumes of intrathecally lidocaine 1% and thereby determine the appropriate volume to administer for surgery of the lower limbs and perineum.
Methods Forty-eight patients scheduled for perinea or lower limb surgery were randomly assigned to receive 4, 6 or 8 ml lidocaine 1% intrathecally. The wide-spread, duration and regression of analgesia and motor block and side effects were evaluated (by a blinded observer whenever possible).
Results:
The maximum cephalic spread in the 6 ml (T8 ± 3) and 8 ml (T4 ± 1.7) groups were higher than the 4 ml group (T12 ± 2.2,P < 0.01). In the 4 ml group, six patients (33%) did not achieve analgesia to T12 and four (22%) did not have complete motor blockade. Individuals given 8 ml had longer duration of block (duration at T12: 104 ± 23vs 60 ± 24, 67 ± 14 min,P < 0.01; 8 mlvs 4, 6 ml) and slower recovery times (sensory recovery: 188 ± 27vs 142 ± 27, 157 ± 28 min,P < 0.01; 8 mlvs 4, 6 ml). Two patients (18%) from the 8 ml group and one (5%) from the 6 ml group had transient hypotension.
Conclusion:
Four milliliters intrathecally lidocaine 1% is adequate for perinea surgery but for lower limb procedures, 6 ml is more appropriate as it consistently provides sensory analgesia above L1 dermatome and complete motor block. 8 ml can effect to an unnecessarily high block with higher incidence of hypotension.
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A lidocaine anesthetic is a drug that causes reversible local anesthesia and a loss of nociception. When it is used on specific nerve pathways (nerve block), effects such as analgesia (loss of pain sensation) and paralysis (loss of muscle power) can be achieved.
Clinical local anesthetics belong to one of two classes: aminoamide and aminoester local anesthetics. Synthetic local anesthetics are structurally related to cocaine. They differ from cocaine mainly in that they have no abuse potential and do not act on the sympathoadrenergic system, i.e. they do not produce hypertension or local vasoconstriction, with the exception of Ropivacaine and Mepivacaine that do produce weak vasoconstriction.
Local anesthetics vary in their pharmacological properties and they are used in various techniques of lidocaine anesthesia such as:
- Topical anesthesia (surface)
- Infiltration
- Plexus block
- Epidural (extradural) block
- Spinal anesthesia (subarachnoid block)
The local anesthetic lidocaine (lignocaine) is also used as a Class Ib antiarrhythmic drug.
