Plasma lidocaine level during spinal or epidural anesthesia in geriatric patients

Toxicity of local anesthetics is a serious concern by anesthesiologists while performing regional anesthesia. The toxicity includes convulsion, respiratory difficulty, or sometimes cardiac arrest. Total dose of local anesthetic usually cannot predict the occurrence of toxic effects because these effects are directly correlated to the plasma concentration. The plasma concentration is dependent not only on total dose given, but also on the routes of administration, volume of distribution, plasma protein binding and the rate of local absorption. This study is to examine the plasma concentration of lidocaine during spinal or epidural anesthesia in geriatric patients. 12 ASA physical status class II-III patients, age over 65 years old, were selected in this study. They were randomly divided into two groups. Group A patients (n = 6) were anesthetized with 3 mL 2% lidocaine intrathecally and Group B patients (n = 6) were anesthetized with 15 mL 2% lidocaine epidurally. Plasma concentration of lidocaine was examined every 15 minutes after drug administration. The peak level in group A was reached at 90 minutes and group B 105 minutes after drug administration. Peak level in Group A was 1.12 +/- 0.08 micrograms/mL and the plateau was reached at 45 minutes after drug administration. In Group B, peak level was 4.70 +/- 0.74 micrograms/mL and the plateau was reached at 15 minutes. The results also indicated that the absorption of the drug in spinal is much lower than in epidural.