Lidocaine 2
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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Indications
Topical lidocaine has been shown to relieve postherpetic neuralgia in some patients, though there is not enough study evidence to recommend it as a first-line treatment. It also has uses as a temporary fix for tinnitus. Although not completely curing the illness, it has been shown to reduce the effects by around two thirds.
The efficacy profile of lidocaine as a local anesthetic is characterized by a rapid onset of action and intermediate duration of efficacy. Therefore, lidocaine is suitable for infiltration, block and surface anesthesia. Longer-acting substances such as bupivacaine are sometimes given preference for spinal and peridural anesthesias; lidocaine, on the other hand, has the advantage of a rapid onset of action. Adrenaline vasoconstricts arteries and hence delays the resorption of Lidocaine, almost doubling the duration of anaesthesia. For surface anesthesia several formulations are available that can be used e.g. for endoscopies, before intubations etc.
Lidocaine is also the most important class 1B antiarrhythmic drug: it is used intravenously for the treatment of ventricular arrhythmias (for acute myocardial infarction, digitalis poisoning, cardioversion or cardiac catherization). However, a routine prophylactic administration is no longer recommended for acute cardiac infarction; the overall benefit of this measure is not convincing.
Lidocaine has also been efficient in refractory cases of status epilepticus.
Contraindications
Contraindications for the use of lidocaine include:
- Heart block, second or third degree (without pacemaker)
- Severe sinoatrial block (without pacemaker)
- Serious adverse drug reaction to lidocaine or amide local anaesthetics
- Concurrent treatment with quinidine, flecainide, disopyramide, procainamide (Class I antiarrhythmic agents)
- Prior use of Amiodarone hydrochloride
- Hypotension not due to Arrhythmia
- Bradycardia
- Accelerated idioventricular rhythm
- Pacemaker
Adverse drug reactions
Adverse drug reactions (ADRs) are rare when lidocaine is used as a local anesthetic and is administered correctly. Most ADRs associated with lidocaine for anesthesia relate to administration technique (resulting in systemic exposure) or pharmacological effects of anesthesia, but allergic reactions only rarely occur.
Systemic exposure to excessive quantities of lidocaine mainly result in central nervous system (CNS) and cardiovascular effects – CNS effects usually occur at lower blood plasma concentrations and additional cardiovascular effects present at higher concentrations, though cardiovascular collapse may also occur with low concentrations. CNS effects may include CNS excitation (nervousness, tingling around the mouth (also known as circumoral paraesthesia), tinnitus, tremor, dizziness, blurred vision, seizures) followed by depression, and with increasingly heavier exposure: drowsiness, loss of consciousness, respiratory depression and apnoea). Cardiovascular effects include hypotension, bradycardia, arrhythmias, and/or cardiac arrest – some of which may be due to hypoxemia secondary to respiratory depression.
ADRs associated with the use of intravenous lidocaine are similar to toxic effects from systemic exposure above. These are dose-related and more frequent at high infusion rates (≥3 mg/minute). Common ADRs include: headache, dizziness, drowsiness, confusion, visual disturbances, tinnitus, tremor, and/or paraesthesia. Infrequent ADRs associated with the use of lidocaine include: hypotension, bradycardia, arrhythmias, cardiac arrest, muscle twitching, seizures, coma, and/or respiratory depression.
Insensitivity to lidocaine
Relative insensitivity to lidocaine runs in families. In hypokalemic sensory overstimulation, relative insensitivity to lidocaine has been described in people who also have attention deficit hyperactivity disorder. In dental anesthesia, a relative insensitivity to lidocaine can occur for anatomical reasons due to unexpected positions of nerves. Some people with Ehlers-Danlos syndrome are insensitive to lidocaine.
Dosage forms
Lidocaine, usually in the form of lidocaine hydrochloride, is available in various forms including:
- Injected local anesthetic (sometimes combined with epinephrine to reduce bleeding)
- Dermal patch (sometimes combined with prilocaine)
- Intravenous injection (sometimes combined with epinephrine to reduce bleeding)
- Intravenous infusion
- Nasal instillation/spray (combined with phenylephrine)
- Oral gel (often referred to as “viscous lidocaine” or abbreviated “lidocaine visc” or “lidocaine hcl visc” in pharmacology; used as teething gel)
- Oral liquid
- Topical gel (as with Aloe Vera gels that include Lidocaine)
- Topical liquid
- Topical patch (Lidocaine 5% patch is marketed as “Lidoderm” in the US (since 1999) and “Versatis” in the UK (since 2007 by Grünenthal))
- Topical aerosol Spray
- Inhaled via a nebulizer
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