Ten ml bupivacaine 0.125% with 12.5 μg epinephrine is a reliable epidural test dose to detect inadvertent intravascular injection in obstetric patients. A double‐blind study

A double-blind study was designed in order to determine the specificity and sensitivity of an epidural test dose to detect inadvertent intravenous injection in obstetric patients undergoing epidural analgesia. Forty unselected obstetric patients were given an intravenous injection of 10 ml bupivacaine 0.125% with 12.5 micrograms epinephrine (test dose) or 10 ml normal physiologic saline. The maternal heart rate was monitored by the direct ECG mode of a fetal monitor and registered simultaneously with the tocogram. The primary investigator was blinded to the solution he injected into an antecubital vein. After the injection was given, he recorded his judgment of which solution he had administered. Eight other anesthesiologists made similar judgments on the basis of the recordings plus various levels of additional information (presence or absence of epidural analgesia, time of injection, subjective signs and symptoms). In contrast to the primary investigator, the blood pressure values were not given to them. For the primary investigator, the specificity of the test dose was 100% and the sensitivity 97.5%. The judgments of the 8 other anesthesiologists resulted in an excellent specificity (99.1%) and a good sensitivity (91.9% with information on time of injection and subjective signs and symptoms). The better performance of the primary investigator is probably due to the availability of blood pressure data.