The effect of removal of cerebrospinal fluid on cephalad spread of spinal analgesia with 0.5% plain bupivacaine

Abstract

Increased intraabdominal pressure is well known to cause higher cephalad spread of spinal analgesia. The reason for this is believed to be a decrease in the cerebrospinal fluid (CSF) volume. If this mechanism is correct, then the cephalad spread of local anesthetic solutions should also be facilitated when the CSF volume is intentionally reduced without increasing the intraabdominal pressure. Sixty-six patients without evidence of increased intraabdominal pressure and undergoing urological procedures were randomly allocated to three groups. All received 10 mg 0.5% bupivacaine for spinal anesthesia. In Group I, the anesthetic was injected after free drops of CSF. In Groups II and III, three and five ml were removed, respectively, before injecting bupivacaine. Mean cephalad spread of analgesia 20 min after injection in the three groups was T10.2 +/- 2.0, T9.4 +/- 1.8 and T7.0 +/- 2.1, respectively. When CSF was reduced by 5 ml, the level of spread not only showed a statistically significant difference from that of the control group, but also from that of Group II (P less than 0.05). Our results show that higher cephalad spread of spinal anesthetic is possible by reducing the CSF volume without evidence of increased intraabdominal pressure.