Lidocaine

IV Lidocaine

Lidocaine is an amide local anaesthetic and a class 1b anti-arrhythmic. The addition of lidocaine to propofol maintained TIVA will reduce requirements by 10-20%. If given as a bolus at induction it may also attenuate the pressor response to airway manipulation, although not as good as opioids. Intra- and postoperative infusions can be administered, although there have been safety concerns raised with postoperative use and this requires close supervision.
The benefits of infusions must be weighed against the risk of toxicity. Lidocaine has a narrow therapeutic index with CNS and cardiac toxicity occurring at plasma levels > 5mcg/ml.

Uses:

Adjunct to analgesia and anaesthesia. Attenuation of haemodynamic response to airway manipulation.

Preparations:

Clear colourless 1% or 2% solution. 10% is available for topical use

Actions:

• Anti-arrhythmic
• Anti-inflammatory
• Analgesia
• Anti-hyperalgesic
• Pro-peristaltic drug

Blockade of sodium channels in neural tissue leads to interruption of signal transmission. The systemic effects may exceed its plasma half-life but this is controversial and the exact mechanism is largely unknown. Alternative sites of action may be involved in addition to its effect on sodium channels. Lidocaine inhibits G-protein coupled receptors and NMDA receptors.

Benefits:

• Analgesic and anaesthetic sparing effect
• Decreased PONV (opioid sparing)
• No inhibition of intestinal motility so may have particular benefit in bowel surgery: return of normal function and lower postoperative pain scores.

Dose:

• IV loading dose 1.5 mg/kg
• +/- infusion 1-2 mg/kg/hr
• PK target controlled infusions have been described

The plasma level achieved at recommended levels is relatively low. Although, toxicity is rare patients should be monitored for toxicity.

Onset:

Rapid onset of action 1.5 minutes if given as an IV bolus

Route:

• Intravenous bolus and infusion
• Peripheral and central nerve blockade
• Topical
• Infiltration

Kinetics:

• Elimination half-life ~ 1.5-2 hours
• Plasma protein binding ~ 70-80%
• Metabolized by the liver – very high hepatic clearance
• Excreted in the urine

Caution:

• Cardiac Failure
• Heart Block
• Renal Failure
• Liver Failure

For infusions, we suggest keeping the duration less than 12 hours. Beyond this non-linear kinetics prevail making toxicity more likely. Continuing infusions one hour into the postoperative period may improve analgesia but should be done in PACU where full monitoring is available. Patients should be told about signs of toxicity such as tinnitus and circumoral paresthesia. Sedation is also a side effect.