A series of truly failed spinal anesthetics.

This report describes five patients with failed continuous spinal anesthetics with lidocaine. Lidocaine concentrations of 420 to 880 micrograms/ml were assayed in the spinal fluid despite lack of anesthesia. There was free flow of cerebrospinal fluid (CSF) through the catheter in all patients before and after the injection of lidocaine. Inactive lidocaine was not responsible for the failures, since lidocaine from the same manufacturing batch produced anesthesia in other patients. Incorrect catheter placement could not explain the failures, since bupivacaine injected through the same intraspinal catheter produced anesthesia in four of the five patients. The authors, therefore, suggest that some patients have a physiologic resistance to lidocaine.