Pharmacology & Poisoning
A 45 year old chef presents to the Emergency Department with a laceration to his left hand. You plan to close the wound with sutures and instil lidocaine. A few minutes later the patient complains of feeling "strange" before collapsing. Which of the following is a reversal agent for local anaesthetic toxicity?
Answer:
Intravenous lipid emulsion (Intralipid™) is a method for treating local anaesthetic systemic toxicity.Local Anaesthetic Toxicity
Pharmacology & Poisoning
Last Updated: 4th August 2021
Local anaesthetic toxicity occurs typically in the setting of regional anaesthesia as a result of excessively high plasma concentrations usually from inadvertent intravascular injection or too rapid injection. Following most regional anaesthetic procedures, maximum arterial plasma concentration of anaesthetic develops within about 10 to 25 minutes, so careful surveillance for toxic effects is necessary during the first 30 minutes after injection.
Techniques to reduce risk of toxicity
- Clear and accurate dose calculations
- Dose reduction in frail patients or those at extremes of age
- Local anaesthetic injected slowly and with regular aspiration (to avoid inadvertent intravascular injection)
- Use of adrenaline as vasoconstrictor to reduce systemic absorption
- Regional nerve blocks to anaesthetise large areas
- Use of ultrasound to facilitate nerve blocks
- Close observation and monitoring
Recognition of local anaesthetic toxicity
Local anaesthetic intoxication can present in many different ways, making it very difficult to recognise. After injection of a bolus of local anaesthetic, toxicity may develop at any time in the following hour. Techniques involving infusion of local anaesthetic through a catheter allow intoxication to develop at any time.
Early clinical features may include:
- Tinnitus
- Difficulty with visual focus
- Dizziness or lightheadedness
- Anxiety, agitation, confusion, disorientation, drowsiness
- Perioral and/or tongue numbness
- Metallic taste
Signs of severe toxicity
- Sudden alteration in mental state, severe agitation or loss of consciousness, with or without tonic-clonic convulsions
- Cardiovascular collapse: sinus bradycardia, conduction blocks, asystole, ventricular tachyarrhythmias
Management of local anaesthetic toxicity
- Immediate management
- Stop injecting the local anaesthetic
- Call for help
- Maintain the airway, and if necessary, secure it with a tracheal tube
- Give 100% oxygen and ensure adequate lung ventilation (hyperventilation may help by increasing plasma pH in the presence of metabolic acidosis)
- Confirm or establish intravenous access
- Control seizures: give a benzodiazepine, thiopental or propofol in small incremental doses
- Assess cardiovascular status throughout
- Obtain blood for analysis but do not delay definitive treatment to do this
- Further treatment without circulatory arrest
- Use conventional therapies to treat hypotension, bradycardia and tachyarrhythmia
- Consider intravenous lipid emulsion
- Further treatment with circulatory arrest
- Start cardiopulmonary resuscitation using standard protocols
- Manage arrhythmias using the same protocols
- Consider the use of cardiopulmonary bypass if available
- Give intravenous lipid emulsion
- Give an initial intravenous bolus of 1.5 ml/kg of 20% lipid emulsion over 1 minute. Give a maximum of two further boluses at 5 minute intervals IF cardiovascular stability has not been restored OR if an adequate circulation deteriorates (max. 3 bolus doses in total).
- Start an intravenous infusion of 20% lipid emulsion at 15 ml/kg/hr. Continue the infusion at the same rate, but double the rate to 30 ml/kg/hr at any time after 5 mins IF cardiovascular stability has not been restored OR if an adequate circulation deteriorates. Continue the infusion until the patient is stable or has received up to a maximum of 12 ml/kg of lipid emulsion.
- Continue CPR throughout treatment with lipid emulsion
- Recovery from local anaesthetic -induced cardiac arrest may take > 1 hour
- Follow-up
- Arrange safe transfer to a clinical area with appropriate equipment and suitable staff until sustained recovery is achieved
- Exclude pancreatitis by regular clinical review, including daily amylase or lipase assays for two days
- Report cases as follows:
- in the United Kingdom to the National Patient Safety Agency (via www.npsa.nhs.uk)
- in the Republic of Ireland to the Irish Medicines Board (via www.imb.ie)
- If Lipid has been given, please also report its use to the international registry at www.lipidregistry.org. Details may also be posted at www.lipidrescue.org.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
