Pain & Sedation
A 72 year old woman is brought to the Emergency Department after slipping on ice. She is complaining of pain in the left hip. On examination you note the left leg is shortened and externally rotated. X-ray confirms an intracapsular neck of femur fracture. You plan to administer a fascia iliaca block. Which of the following local anaesthetics is typically used for a fascia iliaca block?
Answer:
| Drug | Use | Onset | Duration | Max Dose |
|---|---|---|---|---|
| Lidocaine | Widely used for local infiltration, peripheral nerve blocks and topically | 5 - 10 mins | 1 - 2 hours (without adrenaline), 2 - 4 hours (with adrenaline) | 3 mg/kg (without adrenaline), 7 mg/kg (with adrenaline) |
| Prilocaine | Bier's block | 5 - 10 mins | 1 - 2 hours (without adrenaline), 2 - 4 hours (with adrenaline) | 6 mg/kg (without adrenaline), 9 mg/kg (with adrenaline) |
| Bupivacaine | Fascia iliaca block | 10 - 15 mins | 3 - 12 hours | 2 mg/kg |
Local Anaesthetic Pharmacology
Pain & Sedation
Last Updated: 17th September 2024
Local anesthetics (LAs) are used to block transmission of impulses in nerve fibers, to reduce or eliminate sensation.
Mechanism of action
LAs reversibly inhibit neurotransmission by binding voltage-gated sodium channels (Nav) in the nerve plasma membrane. Nav channels are integral membrane proteins, anchored in the plasma membrane. When LAs bind the sodium channel, they render it impermeable to Na, which prevents action potential initiation and propagation.
Indications for local anaesthetic
- Topical anaesthesia e.g. prior to venepuncture or venous cannulation or arterial puncture or cannulation
- Local subcutaneous and tissue infiltration e.g. cleaning, exploration and closure of wounds
- Peripheral nerve blocks e.g. femoral nerve block for femoral shaft fracture
- Intravenous regional blocks e.g. Bier's block for distal forearm fractures
- Neuraxial anaesthesia: spinal or epidural anaesthesia
Choice of agent in ED
The most commonly used local anaesthetics in ED are lidocaine, bupivacaine and prilocaine.
| Drug | Use | Onset | Duration | Max Dose |
|---|---|---|---|---|
| Lidocaine | Widely used for local infiltration, peripheral nerve blocks and topically | 5 - 10 mins | 1 - 2 hours (without adrenaline), 2 - 4 hours (with adrenaline) | 3 mg/kg (without adrenaline), 7 mg/kg (with adrenaline) |
| Prilocaine | Bier's block | 5 - 10 mins | 1 - 2 hours (without adrenaline), 2 - 4 hours (with adrenaline) | 3 mg/kg |
| Bupivacaine | Fascia iliaca block | 10 - 15 mins | 3 - 12 hours | 2 mg/kg |
Topical anaesthetics
- EMLA cream
- 50/50 mixture of 2.5% prilocaine and 2.5% lidocaine
- Must be applied for at least an hour before venepuncture to achieve anaesthesia which limits its use in ED
- Should not be applied to open wounds
- Ametop gel
- Tetracaine (amethocaine)
- Acts more quickly than EMLA and causes vasodilation aiding venous cannulation
- Should not be applied to open wounds
- LAT gel
- Lidocaine 4%, adrenaline 0.1% and tetracaine 0.5%
- Can be applied to open wounds requiring cleaning and suturing
- Reduces need to inject local anaesthetic/sedation in paediatric patients
- Should be applied for 30 mins prior to procedure and procedure should be completed within 15 minutes of removal of the gel
- Effect of local anaesthetic and vasoconstrictor reduce potential for systemic absorption and hence adverse effects
Adrenaline and local anaesthetics
Local anaesthetics cause dilatation of blood vessels. The addition of a vasoconstrictor such as adrenaline/epinephrine to the local anaesthetic preparation diminishes local blood flow, slowing the rate of absorption and thereby prolonging the anaesthetic effect and reducing the risk of systemic toxicity. It also has the advantage of reducing bleeding at the site.
Great care should be taken to avoid inadvertent intravenous administration of a preparation containing adrenaline/epinephrine, and it is not advisable to give adrenaline/epinephrine with a local anaesthetic injection in digits or appendages served by an end-artery because of the risk of ischaemic necrosis.
Adrenaline/epinephrine must be used in a low concentration when administered with a local anaesthetic. Care must also be taken to calculate a safe maximum dose of local anaesthetic when using combination products.
In patients with severe hypertension or unstable cardiac rhythm, the use of adrenaline/epinephrine with a local anaesthetic may be hazardous; for these patients an anaesthetic without adrenaline/epinephrine should be used.
Report A Problem
Is there something wrong with this question? Let us know and we’ll fix it as soon as possible.
Loading Form...
- 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 |
