Anesthesia Toolbox Question:

Your hospital recently changed vendors for epidural kits, and you are taking inventory of the contents to be sure you have everything you will need. Which of the following would be MOST appropriate to use as a test dose after epidural placement?

A.5 mL 0.25% bupivacaine  X

B. 3 mL 1.5% lidocaine with 1:200K epinephrine  ✔

C. 4 mL 1% lidocaine with 1:200K phenylephrine  X

Read the discussion and key information below.

Discussion:

3 mL vial, 1.5 % lidocaine plus 1:200k epinephrine, for use as a test dose.

The purpose of the test dose after epidural placement is to test if the catheter has inadvertently been placed intravascularly (risk for local anesthetic systemic toxicity) or intrathecally (risk for a high spinal). 3 ml 1.5% or 2% Lidocaine with 1:100,000 epinephrine is used as a test dose. When giving an epinephrine containing test dose, an increase in heart rate of 10-15 beats per minute (or more) or an increase in systolic blood pressure of greater than 15 mm Hg is seen as an indicator of intravascular injection. A single dose of 45 mg Lidocaine may or may not produce signs of an intravascular injection (e.g. tinnitus, metallic taste, dizziness). Evidence of motor block after the test dose is an indication of intrathecal injection. The test dose is limited to 3 ml so that an intrathecal injection will not cause a high spinal.

Bupivacaine is usually not used as a test dose due to its higher proclivity for cardiac and other toxicity when injected intravascularly. Also, the solution mentioned as a potential answer does not contain epinephrine and would cause a profound spinal if injected intrathecally. A 1% Lidocaine with epinephrine could be used as a test dose; however, the solution listed as a possible answer contains phenylephrine and not epinephrine. The beta-agonist properties of epinephrine would add to its ability to detect an intravascular injection by producing an increase in heart rate (if the patient is not beta-blocked).

Key Information:

The purpose of the test dose after epidural placement is to test if the catheter has inadvertently been placed intravascularly or intrathecally. 3 ml 1.5% or 2% Lidocaine with 1:100,000 epinephrine is often used as a test dose. The epinephrine is to test for an intravascular injection; the local anesthetic is used to test for an intrathecal injection.

References: 

Guay J. The epidural test dose: a review. Anesth Analg. 2006;102(3):921-9. PMID 16492853

RAP Video 25 A Practical Guide to Thoracic Epidural Placement