Can Bupivacaine Be Used in Subtenon Blocks?
Yes, bupivacaine can be safely used for subtenon blocks in ophthalmic surgery, with typical dosing of 0.25% bupivacaine at volumes of 3-5 mL (7.5-12.5 mg total), well below the maximum safe dose of 2.5 mg/kg.
Dosing Recommendations for Subtenon Blocks
The maximum safe dose of bupivacaine 0.25% is 2.5 mg/kg (equivalent to 1 mL/kg) for peripheral nerve blocks and local infiltration, which provides a substantial safety margin for subtenon blocks 1, 2.
For a typical 70 kg adult, this translates to a maximum of 175 mg (70 mL of 0.25% solution), far exceeding the 3-5 mL typically used in subtenon anesthesia 1.
Bupivacaine 0.25% at 0.2-0.5 mL/kg is recommended for peripheral nerve blocks, and subtenon blocks fall well within this range given their small volumes 1, 3.
Clinical Advantages in Ophthalmic Surgery
Bupivacaine provides long-lasting analgesia lasting 4-8 hours or longer, making it ideal for postoperative pain control after ophthalmic procedures 1.
The slow onset of bupivacaine (typically 10-20 minutes) is not a disadvantage in subtenon blocks, as adequate time is available before surgical incision 4.
Bupivacaine's sensory-motor dissociation at lower concentrations (0.25%) provides excellent analgesia with minimal motor blockade, which is desirable for maintaining extraocular muscle function 4, 5.
Alternative Local Anesthetics
Levobupivacaine 0.25% can be used at the same 2.5 mg/kg maximum dose and offers a potentially improved safety profile with reduced cardiac toxicity compared to racemic bupivacaine 2, 4.
Ropivacaine 0.2% allows up to 3 mg/kg (1.5 mL/kg), providing a higher maximum dose than bupivacaine if larger volumes are needed, though this is rarely necessary for subtenon blocks 1, 3, 4.
Both levobupivacaine and ropivacaine are pure left-isomers with less cardiotoxic potential than racemic bupivacaine, making them preferred choices when available 4.
Safety Considerations
Always calculate total dose in mg/kg, not just volume, as concentrations vary between preparations 2, 3.
Bupivacaine has the highest cardiotoxicity among amide local anesthetics, with risk of severe cardiac effects if inadvertent intravascular injection occurs 4, 6.
The small volumes used in subtenon blocks (3-5 mL) provide an inherent safety margin, as systemic toxicity typically requires much higher doses 1, 2.
Be prepared to manage local anesthetic systemic toxicity (LAST) with lipid emulsion therapy (1.5 mL/kg of 20% lipid emulsion) for cardiovascular collapse 2.
Common Pitfalls to Avoid
Do not exceed 2.5 mg/kg total dose when using bupivacaine 0.25% for any regional block 1, 2.
Avoid using higher concentrations (0.5% or 0.75%) for subtenon blocks, as the 0.25% concentration provides adequate anesthesia with improved safety 1, 5.
In elderly patients or those with significant comorbidities, consider dose reduction to minimize systemic absorption and potential toxicity 1.