Ropivacaine test dose in extradural anaesthesia.

Ropivacaine test dose in extradural anaesthesia Morton and colleagues 1 have described the use of 0.75% ropiva-caine for extradural anaesthesia, and in the process have clearly demonstrated the unsuitability of this agent as a test dose. The aim of an extradural test dose is to identify inadvertent i.v. or intrathecal catheter placement. It should have high sensitivity, but produce symptoms that are safe. Morton and colleagues inadvertently administered large i.v. doses of ropivacaine to two patients, despite negative test doses of ropivacaine 22.5 mg. This is not surprising, as Scott and colleagues 2 gave 10 mg min 91 i.v. for up to 15 min before producing symptoms. We do not, however, suggest the use of a larger dose of ropivacaine as a test dose. While this may increase sensitivity in identifying vascular cannulation, dangerously high spinal anaesthesia may result in intrathecal injection. Wahedi, Nolte and Klein 3 have produced safe spinal anaesthesia with 0.75% ropivacaine 22.5 mg in non-pregnant subjects, but there are no data to clarify a safe maximum intra-thecal dose of ropivacaine in the obstetric population. The most sensitive pure local anaesthetic test dose for identifying intravascular injection of which we are aware is lignocaine 1 mg kg 91 , proposed by Michels, Lyons and Hopkins. 4 However, Richardson and Wissler 5 described abrupt and life-threatening high spinal block after intrathecal test doses of only 45 mg of lignocaine in two patients. Michels' test dose is therefore clearly potentially dangerous. In summary, we suggest that it is not possible to use a pure local anaesthetic test dose of sufficient dosage to identify the intra-vascular space without producing dangerously high spinal anaesthesia if injected intrathecally. We see no alternative but to use separate agents to identify inadvertent intravascular or intrathecal injection. Intrathecal catheter placement can be excluded easily using bupivacaine 10 mg. We remain unconvinced of the sensitivity and specificity of adding adrenaline to this test dose, and indeed have some concerns over its safety. Perhaps the addition of a potent short-acting opioid such as remifentanil warrants some investigation in this role ? The final logical but somewhat cumbersome suggestion is to follow a negative intrathecal test of bupivacaine with a second test of lignocaine 1 mg kg 91. McClure JH. Ropivacaine 0.75% for extradural anaesthesia in elective Caesarean section: an open clinical and pharmacoki-netic study in mother and neonate. Acute toxicity of ropivacaine compared to bupivacaine. Sir,—We thank …