Norepinephrine prolongs tetracaine spinal anesthesia in surgical patients: a preliminary study

We conducted a double-blinded examination of the effects of norepinephrine as a vasoconstrictor on the onset and duration of tetracaine spinal anesthesia in 80 surgical patients. The patients were randomly allocated to four groups (n = 20 in each group). Each patient received 10 mg of tetracaine in a volume of 2.0 mL which contained either 0 micrograms/mL, 5 micrograms/mL, 10 micrograms/mL, or 15 micrograms/mL of norepinephrine. The onset of spinal anesthesia was determined by the time to reach Th-10 level as well as by the time required to obtain the highest level of sensory analgesia. The time for two-segment regression and full-motor recovery were defined as the duration of spinal anesthesia. The time to reach Th-10, the highest analgesia level, and the time to obtain the highest analgesia level did not differ among the groups. Two-segment regression was prolonged significantly by 175%, 103%, and 106% as compared with the plain tetracaine group, in 5 micrograms/mL, 10 micrograms/mL, and 15 micrograms/mL of norepinephrine groups, respectively. Motor recovery also was extended significantly by 111%, 152%, and 121% as compared with the plain tetracaine group, in 5 micrograms/mL, 10 micrograms/mL, and 15 micrograms/mL of norepinephrine groups, respectively. There were no differences in the changes of arterial blood pressure and heart rate associated with the addition of norepinephrine among the groups. We conclude that norepinephrine provides a clinically meaningful prolongation of the duration of tetracaine spinal anesthesia.