Epidural test dose: lidocaine 100 mg, not chloroprocaine, is a symptomatic marker of i.v. injection in labouring parturients.

The authors studied the sensitivity (SN) and specificity (SP) of an epidural test dose containing either lidocaine 100 mg or 2-chloroprocaine 100 mg as symptomatic markers of intravascular injection in labouring parturients. In a prospective, double-blind and randomized fashion 48 unmedicated and labouring parturients were equally divided into three groups. After placement of a lumbar epidural catheter the normal saline group (NS) received 5 ml normal saline i.v., the lidocaine group (LD) received lidocaine 100 mg i.v., and the 2-chloroprocaine group (CH) received 2-chloroprocaine 100 mg i.v. All injections were given during uterine diastole. Within the next one to two minutes a blinded observer recorded the patient's perception of the presence of metallic or funny taste, dizziness, and tinnitus. We then calculated SN and SP of each symptom (alone and in combination) along with their positive (+) and negative (-) predictive value (PV). In both groups no symptom alone reached clinically acceptable levels of SN (< 87%). Only in the LD group, tinnitus+taste and dizziness+taste reached a SN of 100% with a SP of 81% and 69% respectively. While the -PV was 100% for both groups of symptoms, the +PV reached 42% for tinnitus+taste and 30% for dizziness+taste. We conclude that lidocaine 100 mg is a sensitive marker of intravascular injection in labouring parturients, and that tinnitus+taste is the most reliable indicator of intravenous injection.