What is the appropriate bupivacaine dose for a 57‑kg HIV‑positive adult requiring a peripheral nerve block, considering likely hepatic dysfunction?

Bupivacaine Dosing for Peripheral Nerve Block in 57 kg HIV-Positive Adult

For a 57 kg HIV-positive adult requiring a peripheral nerve block, administer a maximum total dose of 171 mg (2.0 mL per nerve of 0.5% bupivacaine with epinephrine for ultrasound-guided technique, or up to 300 mg for supraclavicular brachial plexus block), with careful attention to incremental dosing and aspiration to avoid systemic toxicity.

Weight-Based Dosing Calculation

• The FDA label recommends incremental doses of 3-5 mL with sufficient time between doses to detect toxic manifestations 1
• For peripheral nerve blocks, the maximum recommended dose is approximately 2.5 mg/kg with epinephrine (1:200,000), which equals 142.5 mg for a 57 kg patient 1
• However, clinical practice supports up to 300 mg for supraclavicular brachial plexus block without evidence of systemic toxicity 2

Specific Dosing by Block Type

Ultrasound-Guided Axillary Brachial Plexus Block

• Use 1.56-2.0 mL of 0.5% bupivacaine per nerve (radial, median, ulnar, musculocutaneous) with epinephrine 1:200,000 3
• This translates to approximately 6.24-8.0 mL total volume (31.2-40 mg total dose) for four-nerve block 3
• Ultrasound guidance significantly reduces required volumes while maintaining efficacy 3

Supraclavicular Brachial Plexus Block (Non-Ultrasound)

• 300 mg (60 mL of 0.5% solution) is well-tolerated without systemic toxicity 2
• This represents 5.3 mg/kg for a 57 kg patient, which is within the safe range demonstrated in clinical studies 2

Intercostal Nerve Block

• Avoid or use extreme caution: This technique produces the highest mean arterial plasma levels 2
• If necessary, limit to maximum 171 mg (2.5 mg/kg with epinephrine) with careful incremental dosing 1, 2

Critical Safety Considerations in HIV-Positive Patients

Hepatic Dysfunction Concerns

• Bupivacaine is classified as an intermediate hepatic extraction ratio drug (E = 0.38), making it sensitive to changes in hepatic function 4
• Reduce the maximum dose by 25-30% if clinical or laboratory evidence of hepatic dysfunction exists 4
• For a 57 kg patient with suspected hepatic impairment: limit to 100-120 mg total dose 4

Protein Binding Alterations

• HIV-positive patients may have reduced plasma albumin concentrations, increasing unbound (active) bupivacaine fraction 4
• The unbound fraction can increase from 5% to 10% in patients with hypoalbuminemia 4
• Monitor for signs of systemic toxicity more vigilantly, as lower total doses may produce higher free drug concentrations 4

Administration Technique to Minimize Toxicity Risk

Incremental Dosing Protocol

• Administer in 3-5 mL increments with 3-5 minute intervals between doses 1
• Aspirate before each injection to detect intravascular placement 1
• The minimum IV dose previously associated with significant cardiotoxicity is 1.6 mg/kg (91 mg for 57 kg patient) 5

Test Dose Recommendation

• Use 3 mL of 0.5% bupivacaine with 1:200,000 epinephrine as test dose when clinical conditions permit 1
• Monitor pulse rate and cardiovascular signs for 3-5 minutes after test dose 1
• A negative test dose does not completely exclude intravascular or intrathecal injection 1

Concentration Selection

• 0.5% bupivacaine with epinephrine 1:200,000 is the preferred concentration for peripheral nerve blocks 1, 3, 2
• The 0.25% concentration provides adequate sensory blockade but may produce incomplete motor block 6
• The 0.75% concentration should not be used for peripheral nerve blocks due to increased cardiotoxicity risk without additional benefit 1

Common Pitfalls to Avoid

• Never exceed 2.5 mg/kg (142.5 mg) with epinephrine in patients with suspected hepatic dysfunction 1, 4
• Avoid rapid injection: Cardiovascular collapse has been reported with doses as low as 1.1 mg/kg when administered rapidly 5
• Do not use preservative-containing multiple-dose vials for epidural or caudal techniques 1
• Monitor for at least 30 minutes post-injection: Peak plasma levels occur 10-30 minutes after peripheral nerve block 2

Signs of Systemic Toxicity to Monitor

• Early CNS signs: circumoral numbness, metallic taste, tinnitus, dizziness 5
• Cardiovascular signs: bradycardia, hypotension, dysrhythmias, cardiac arrest 5
• Note: Cardiac toxicity may occur without preceding CNS symptoms, especially with rapid absorption 5