Effect of volume on spinal anesthesia level with hyperbaric tetracaine

The purpose of this prospective, randomized, double-blind study was to determine if the volume of a fixed milligram dose of hyperbaric tetracaine hydrochloride injected into the subarachnoid space affected the average maximal dermatomal spread of sensory anesthesia, determined by pinprick testing. One hundred two adults received spinal hyperbaric tetracaine in a volume of 2 mL, 3 mL, or 4 mL with the dose based on the patient's height. The addition of 0.2 mg of epinephrine to the anesthetic solution was allowed at the discretion of the attending anesthesiologist. A two-way analysis of variance (ANOVA) demonstrated that neither the dose selected nor the use of epinephrine affected anesthetic spread. ANOVA showed that anesthetic volume insignificantly affects the spread of sensory anesthesia. A Tukey HSD multiple comparisons test demonstrated a mean difference greater than 1 sensory dermatome between volumes of 2 mL and 4 mL, which was clinically detectable but statistically insignificant. Increasing the volume of hyperbaric spinal tetracaine solutions to improve anesthetic spread is unjustified.