local anaesthetic (LA) administration

local anaesthetic (LA) administration

injection of LA agent about a nerve trunk/nerve endings to achieve tissue anaesthesia (see anaesthesia; injection), or topical application of LA gel/cream to achieve superficial skin anaesthesia (see eutectic mixture of local anaesthetic)
  • administration of injected LA LA should be injected slowly, with the syringe aspirated prior to delivery of solution (see aspiration of syringe, below)

  • adverse drug reactions (ADRs) to LA agents impairment of hepatic detoxification (metabolism) of LA agent by presence of another agent, e.g. monoamine oxidase inhibitors (MAOIs, used to control acute depressive states), procarbazine (used to control lymphoma), cimetidine (used to control hyperchloridia); early signs of ADRs are masked by benzodiazepines (mask early signs of LA toxicity), diuretics (diuretic-related antihypertensive action may increase tendency to faint), and antiarrhythmics, e.g. beta-blockers and amiodarone (mask bradycardia of LA toxicity)

  • allergic reaction to LA allergic reaction to additives (e.g. pH balancers, preservatives) has been reported; true allergy to amide-type LA is very rare

  • anaphylaxis with LA see anaphylaxis

    aspiration of syringe syringe should be aspirated before depositing any LA solution, to demonstrate that needle point is not within a blood vessel; the needle should be withdrawn, and a new syringe and site selected for injection if blood shows in LA fluid; see aspiration (2); self-aspirating syringe

  • calculation of appropriate dose of LA minimum effective dose of LA should be administered; maximum safe dose is calculated in relation to specific LA agent, patient body mass (see Table 1), patient's age, physique and clinical condition and degree of vascularity of tissue at injection site

  • cessation of action see termination cessation of action of LA below

  • choice (selection) of LA dependent on depth and duration of anaesthesia required to permit proposed procedure, need for postoperative pain control; longer-acting LA agents have greater lipid affinity than shorter-acting LAs (Table 2)

  • complications of LAs patients may develop allergy (see allergic reaction to LA, above), show anaphylaxis (see anaphylaxis), or toxic reaction (see toxic reaction to LA, below) to LA agents; other complications include syncope (vasovagal attack; faint), local nerve injury, inclusion cysts, bullous reaction, intravascular injection (see aspiration, above) or failure of anaesthesia

  • contraindications to LAs in addition to the adverse reaction (see adverse drug reactions (ADRs) to LA agents, above), LAs should be used with caution in specific patient groups, e.g. compromised liver/kidney function, cardiovascular problems, epilepsy, systemic illness that may compromise healing, long-term steroid therapy, pregnancy, sepsis at injection site, likely non-compliance to postoperative care regimes

  • dosage of LAs see Table 3

  • failure of LAs includes effects of local idiosyncratic neuroanatomy, inflammation or infection at surgical site, poor LA technique, nervous patient

  • interactions of LAs with other drugs Table 4

  • maximum safe dose (MSD) of LA calculated in relation to recommended MSD of specific LA agent in relation to patient body mass; see Table 5

  • pregnancy and LA advisable to avoid use of LA during pregnancy, especially during first trimester; procedures under LA should be postponed (where possible) until pregnancy is over and lactation completed; a full medical, drug and anaesthesia history should be taken prior to the decision to administer LA during pregnancy; LA drug should be chosen with great care and certain LA drugs voided, e.g. prilocaine can cause fetal methaemoglobinaemia; long-acting LAs cross the placenta but are non-metabolized by fetal liver

  • prolonged LA long-acting LA agents, used to achieve several hours of anaesthesia, avoiding potential cumulative systemic toxicity from repeated administration of short-acting LA agents

  • selection of appropriate LA see choice (selection) of LA, above

  • systemic effects of LA; toxic effects of LA serious and potentially fatal body-wide effects due to administration of LA agents, after absorption into systemic circulation from injection site; all LA agents stabilize excitable cell membranes (e.g. brain tissue, heart muscle) and thus could induce unconsciousness and/or fit, and bradycardia

  • termination (cessation of action) of LA removal from LA agent from site of injection by local systemic circulation; patients should be monitored for 30 minutes after LA administration as rapid systemic take-up of LA can induce a toxic reaction (see toxic reaction to LA, below)

  • toxic reaction to LA induced by high plasma concentration of LA agent; both actual overdose (see Table 6) or relative overdose (i.e. accidental delivery of bolus of LA agent into blood) have the potential to depress both central nervous system (i.e. showing as initial hyperactivity/light-headedness/inebriation, leading to sedation, circumoral paraesthesia, twitching/convulsions, coma) and cardiac function (showing as increasing bradycardia, loss of consciousness, leading to cardiac collapse in extreme cases) (see systemic effects of LA, above)

  • vasoconstrictors and LA adrenalinized-LA agents (e.g. lidocaine + 1:200 000 adrenaline (epinephrine) [i.e. 5 μg/L]) may be injected in tissues proximal to the metatarsal heads; adrenalinized LAs achieve effective anaesthesia at lower drug concentration, and show slower rates of absorption (prolonged duration of anaesthesia); adrenalinized LA solutions must never be injected into a digit (risks ischaemic necrosis)

Table 1: Onset and offset times of local anaesthetics
Type of local anaestheticOnset timeOffset time
Lidocaine5 minutes30-90 minutes
Bupivacaine20 minutes6-8 hours
Prilocaine5-10 minutes2-4 hours
Mepivacaine5-10 minutes2-4 hours
Levo-bupivacaine20-30 minutes6-8 hours
Ropivacaine5-10 minutes2-4 hours
Table 2: Principal drug interactions of local anaesthetic agents and other medications
Local anaesthetic agent Proprietary name Principal drug interactionsEffect of interaction
Antiarrhythmic agents
Antibacterial agents
Ulcer-healing drugs
Increased myocardial depression
Increased risk of ventricular arrhythmias if lidocaine is given with quinpristin/dalfopristin
Increased risk of ventricular arrhythmias if lidocaine is given with any drug that prolongs the QT interval of the cardiac cycle
Plasma concentration of lidocaine increased by amprenavir, atazanavir and lopinavir
Increased myocardial depression
Increased risk of lidocaine toxicity when given with propranolol
The action of lidocaine is antagonized by the hypokalaemia caused by acetazolamide, loop diuretics or thiazide and related diuretics (i.e. a greater dose of lidocaine would be required to achieve anaesthesia)
Increased risk of ventricular arrhythmia if lidocaine is given with dolasetron
Plasma concentration of lidocaine increased when given with cimetidine; risk of lidocaine toxicity increased with cimetidine
Beta-blockersIncreased risk of bupivacaine toxicity when given with propranolol
Increased risk of myocardial depression if given with other antiarrhythmic agents
Antiarrhythmic agents
Antibacterial agents
Increased risk of myocardial depression if given with antiarrhythmic agents
Increased risk of methaemoglobinaemia if given with sulphonamide antibacterial agents
AntidepressantsMetabolism of ropivacaine is inhibited by fluvoxamine, thereby enhancing the risk of ropivacaine toxicity
Drug not listed in the British National Formulary
Table 3: Maximum safe doses of plain local anaesthetic agents (for 70Kg adult in 24 hours)
Agent (brand name)Maximum safe dose (70-kg adult)Dose per kg of body mass
Lidocaine (Xylocaine)200mg3mg/kg
Bupivacaine (Marcain)150mg2mg/kg
Levo-bupivacaine (Chirocaine)150mg2mg/kg
Mepivacaine (Scandonest)400mg6mg/kg
Prilocaine (Citanest)400mg6mg/kg
Ropivacaine (Naropin)250mg3.5mg/kg
Table 4: Calculation of the combined maximum safe doses (MSDs) of plain local anaesthetic agents
Mass of drug administeredAmount of drugs administered in relation to proportional MSDsPercentage of combined MSD
e.g. 70-kg adult
Agent 1
6mL lidocaine 2%
120mgEquivalent to (120/200) × 100% = 60% of MSD lidocaine77%
Agent 2
5mL bupivacaine 0.5%
25mgEquivalent to (25/150) × 100% = 17% of MSD bupivacaine
e.g. 40-kg child
Agent 1
4mL lidocaine 2%
80mgEquivalent to (80/120) × 100% = 77% of MSD lidocaine89.5%
Agent 2
2mL bupivacaine 0.5%
10mgEquivalent to (10/80) × 100% = 12.5% of MSD bupivacaine

Where more than one anaesthetic agent is injected in order to achieve both rapid anaesthesia and prolonged postoperative pain relief, the proportional MSD of each of the anaesthetic agents should be calculated, in order not to exceed the combined MSD.

The calculation is the product of the patient's body mass, the percentage mass of the individual anaesthetic agent and the total volume used of each local anaesthetic drug.

In the examples cited in this table, safe doses of anaesthesia would have been administered, as the combined doses of each anaesthetic does not exceed 100%.

Table 5: Maximum safe doses of plain local anaesthetic agents (for 70Kg adult in 24 hours)
Agent (brand name)Maximum safe dose (70-kg adult)Dose per kg of body mass
Lidocaine (Xylocaine)200mg3mg/kg
Bupivacaine (Marcain)150mg2mg/kg
Levo-bupivacaine (Chirocaine)150mg2mg/kg
Mepivacaine (Scandonest)400mg6mg/kg
Prilocaine (Citanest)400mg6mg/kg
Ropivacaine (Naropin)250mg3.5mg/kg
Table 6: Maximum safe doses of plain local anaesthetic agents (for 70Kg adult in 24 hours)
Agent (brand name)Maximum safe dose (70-kg adult)Dose per kg of body mass
Lidocaine (Xylocaine)200mg3mg/kg
Bupivacaine (Marcain)150mg2mg/kg
Levo-bupivacaine (Chirocaine)150mg2mg/kg
Mepivacaine (Scandonest)400mg6mg/kg
Prilocaine (Citanest)400mg6mg/kg
Ropivacaine (Naropin)250mg3.5mg/kg
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