Test Dose
A small initial dose of local anesthetic with or without epinephrine administered to detect intravascular or intrathecal catheter placement before full epidural dosing.
Full Definition
A test dose is a small, carefully calculated amount of local anesthetic solution, often containing epinephrine, administered through an epidural catheter to detect malpositioned catheters before delivering the full therapeutic dose. The standard test dose typically consists of 3 mL of local anesthetic containing epinephrine 1:200,000 (15 micrograms). If the catheter is intravascular, the epinephrine will cause maternal tachycardia and hypertension within 60-90 seconds. If the catheter is intrathecal, the local anesthetic will produce rapid onset of motor and sensory blockade. In obstetric anesthesia, test dosing is crucial for patient safety, though interpretation can be challenging due to physiological changes of pregnancy and the presence of labor contractions that may mask or mimic positive test dose responses.
Usage
Usage note: Essential safety step; interpretation may be complicated by pregnancy-related physiological changes.
In Context
- "The test dose produced transient tachycardia, suggesting possible intravascular catheter placement." — Epidural troubleshooting
- "A negative test dose confirmed proper epidural catheter position before labor analgesia initiation." — Epidural verification procedure