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

Abstract

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.

Reduced efficacy of simulated epidural test doses in sevoflurane-anesthetized adults

“…On the other hand, Gieraerts et aL 21 showed that in labouring women sensitivity and specificity remained unchanged after lowthoracic epidural analgesia was established. These observations imply that our present results could be influenced by the extent of epidural neural blockade, especially if the block level reached high thoracic dermatomes.…”

A survey of the practice of thoracic epidural analgesia in the United Kingdom

“…Detecting intravenous placement relies on evidence from an awake patient of unusual symptoms such as peri‐oral tingling and tinnitus. The addition of adrenaline to test doses may help to indicate intravenous placement in young, fit adults [4]. However, studies in elderly patients taking antihypertensive or anti‐anginal medication have demonstrated very varying responses to similar doses of adrenaline [5] particularly if receiving a nitrous oxide and isoflurane anaesthetic [6, 7].…”

Safety in obstetric anesthesia requires more research and support

“…Extensive research resulted in the recommendation that "Every dose given in obstetric epidural analgesia can be a test dose", consisting of 10 ml of bupivacaine 0.125% + epinephrine 1;800,000, which is 12.5 mg of bupivacaine and 12.5 µg of epinephrine. This dose allows detection of intravascular injection as it produces an identifiable tachycardia for 30 s, with a slowing of the uterine contractions in such a way that one or two contractions are skipped or reduced in intensity (24)(25)(26). Aspiration is recommended before any injection via the epidural catheter but may not be entirely reliable in showing blood.…”