anaesthetic toxidromes and complications

CHAPTER 2 Local anaesthetic toxidromes and complications



Local complications


Local complications are usually a result of the injection technique. Immediate complications include pain, bruising, haematoma formation, local skin reactions (dermatitis) and nerve injury. Delayed complications include infection, complicated haematomas and neurapraxias.


• Tissue irritation caused by local anaesthetics is generally related to the acidity of the infiltrated solution and there are ways to minimise this discomfort, which will be discussed later.

• Ecchymoses or haematomas are a result of the perforation of cutaneous or subcutaneous blood vessels. This may be more severe in patients with a bleeding disorder (inherent or acquired as a result of medications: aspirin, clopidogrel or other anticoagulants). If bruising occurs, the patient can simply be reassured. A significant haematoma may require drainage and a pressure dressing, but this is an extremely rare complication.

• EMLA and other topical anaesthetics can cause itching, burning, pain, pallor, erythema, oedema, and purpura. Irritant dermatitis, allergic contact dermatitis, and contact urticaria can also occur.

• Nerve injury may occur during the infiltration of a local anaesthetic. This may occur from nerve laceration by the needle or nerve contusion by intraneural injection. This complication occurs more commonly during the performance of regional blocks than local infiltration. Clinical indications of potential nerve injury include paraesthesias, ‘electric shock’ sensations and excessive pain during needle insertion, advancement or injection. Withdraw the needle and reposition it should this happen. The majority of neurapraxias resolve over a period of a few days or weeks.

• Nerve injury might also result from an excessively high concentration of local anaesthetic. For this reason, lower concentrations are preferred (bupivacaine 0.5% or lower, ropivacaine 0.5% or lower, lidocaine 2% or lower).

• Acute myotoxicity may be associated with local anaesthetics, but has only been reported following continuous peripheral nerve blocks.

• Infection is a potential complication of any injection. It occurs most commonly as a complication of haematoma formation. Maintain sterile conditions as much as possible, and ensure appropriate treatment of haematomas. Many studies have shown that these procedures are not truly sterile, but need to be as clean as possible. Extra care must be taken with patients who are immunocompromised.


Systemic complications


Systemic complications include hypersensitivity reactions, anaphylaxis and toxicity of the local anaesthetic agent.


Allergic reactions, in all forms, are idiosyncratic and can occur at any dose. They are more common with the ester local anaesthetics, but can occur with any medication. Allergic reactions can be in response to the local anaesthetic agent or to the preservative agent (e.g. methyl hydroxybenzoate). Anaphylactic reactions should be treated with intramuscular adrenaline (epinephrine) (0.5 mg in the anterolateral thigh for adults), intravenous fluids, intravenous steroids (e.g. hydrocortisone 4 mg/kg) and possibly intravenous antihistamines (e.g. promethazine 0.5 mg/kg). Resuscitation equipment should always be available in an environment where local or regional anaesthesia is practised.


Methaemoglobinaemia may be caused by any local anaesthetic agent, but prilocaine is the most common culprit, especially in children. Methaemoglobinaemia can produce clinically significant hypoxaemia and can interfere with pulse oximetry, producing an exaggeratedly low saturation figure (around 85%). Treatment is with intravenous methylene blue 1 mg/kg.


Systemic adverse effects usually occur when blood concentrations of local anaesthetic increase to toxic levels. These effects are most often encountered after inadvertent intravenous injection, systemic release of local anaesthetic after intravenous regional anaesthesia, or administration of an excessive dose of a local anaesthetic or topical agent (especially on broken skin or mucous membranes). Patients in the ED are particularly at risk since the trauma patient may get local anaesthetic for the placement of an intercostal drain, for the central venous catheter, for wound repair, topical anaesthesia of the upper airway, an intrapleural block and so on.


Patients with decreased pseudocholinesterase activity are more susceptible to toxicity from ester anaesthetics and patients who are taking medications that inhibit the cytochrome P450 system (e.g. propofol, amiodarone, ciprofloxacin, macrolides, tricyclic antidepressants, selective serotonin reuptake inhibitors, cimetidine, imidazole antifungals, antiepileptic medications, benzodiazepines, beta blockers, calcium channel blockers, statins, immunosuppressants, and antiviral agents) are more susceptible to toxicity from amide anaesthetics.


The systemic toxicity of local anaesthetic agents affects the central nervous system (CNS) and the cardiovascular system. CNS lidocaine toxicity is biphasic and as the serum levels of lidocaine increases, the effects on the CNS become more severe. The first phase of side effects occurs as a result of CNS excitation and can include irritability and seizures. The second phase causes CNS depression. The seizures stop (and not because the patient is getting better) and coma and respiratory depression or arrest may develop. This biphasic effect occurs because local anaesthetics first block inhibitory CNS pathways (resulting in stimulation) and then eventually block both inhibitory and excitatory pathways (resulting in overall CNS inhibition).


• At mildly toxic lidocaine levels, patients may experience tinnitus, light-headedness, perioral numbness, diplopia, a metallic taste in the mouth, nausea and/or vomiting, or they may become loquacious.
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Jul 4, 2016 | Posted by in ANESTHESIA | Comments Off on anaesthetic toxidromes and complications

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