Potentially toxic concentrations in blood of total ropivacaine after bilateral transversus abdominis plane blocks; A pharmacokinetic study

Context: Elevated blood levels of lidocaine and ropivacaine have been described after transversus abdominis plane (TAP) block. Objective: To investigate the pharmacokinetic profile of ropivacaine after bilateral TAP blocks. Design: Prospective observational pharmacokinetic study. Setting: University teaching hospital in Copenhagen, Denmark. Patients Twenty-one adult patients presenting for abdominopelvic surgery with bilateral TAP blocks were enrolled. Procedures: Ultrasound-guided TAP blocks with bilateral injections of 20 ml ropivacaine 0.5% w/v (total dose 200 mg). Blood was sampled at 0, 10, 30 and 60 min after TAP blocks. Measures: Total and free peak blood concentrations (Cmax) of ropivacaine. Results: Data were analysed from N=18 patients. The median dose of ropivacaine was 2.7mgkg ^-1 (range: 1.9-4.2mgkg ^-1). Median total ropivacaine concentrations were 1.0, 1.6 and 1.7mgml ^-1 at 10, 30 and 60 min, respectively. Six patients (33%) had Cmax values above 2.2mgml ^-1 and the highest concentration measured was 5.1mgml ^-1. One patient had a 33% drop in mean arterial blood pressure. Conclusion: TAP blocks with bilateral injections of 20 ml ropivacaine 0.5% w/v gave rise to potentially toxic peak blood concentrations of total ropivacaine in one-third of the patients.