Lignocaine test dose to detect intravenous injection

The accidental intravascular injection of bupivacaine or etidocaine epidurally has resulted in several maternal deaths. To be effective, a test dose must allow detection of intravenous catheter placement and prevent accidental intravenous injection. This study was designed to determine the dose of lignocaine required for this purpose. Sixty healthy gynaecological patients were allocated randomly to receive an intravenous dose of normal saline (group 1), lignocaine 0.5 mg.kg-1 (group 2) or 1 mg.kg-1 (group 3) 3 min prior to induction of anaesthesia. At 1 min intervals the patients were asked about subjective symptoms produced by this 'test dose'. In group 2 only 50% of patients reported a positive test dose, whereas in the patients of group 3, a significantly greater percentage (95%) had a positive test dose (p < 0.01). This suggests that the use of 1 mg.kg-1 lignocaine as a test dose would result in a significantly higher sensitivity for detecting intravascular injection than the use of 0.5 mg.kg-1.