Minimal dosage of tetracaine supplemented with epinephrine for spinal anesthesia in anorectal surgery

Background: Spinal anesthesia has been widely used in clinical setting with relatively high incidences of hypotension and bradycardia. Lowering the dosage of local anesthetics is one of the methods to mitigate the side effects. This study was to evaluate the feasibility of lowering the dosage of tetracaine in spinal anesthesia for patients undergoing anorectal surgery. Methods: Thirty patients scheduled for anorectal surgery were studied. Patients were randomly divided into experiment (n = 15, 3.0 mg of tetracaine) and control groups (n = 15, 6.0 mg of tetracaine). The extent of analgesia was assessed by loss-of-sensation to pinprick. Dermatomic level of the sensory block was evaluated and recorded every minute for 10 minutes. BP and HR were recorded at 3-min interval for the 10-min in the study period. Numeric data were statistically analyzed with Student's t-test. The categorical data were compared using the chi-square test. P-value less than 0.05 was considered statistically significant. Results: Ten min after the injection, the mean peak level of sensory block reached T ₁₂ for experiment and T ₉ for control groups. A noticeable difference in frequency of hypotension between two groups was found though it was not statistically significant (P=0.08). Incidences of moderate bradycardia and severe bradycardia were similar in both groups, being 13.3% and 6.7% respectively. Conclusions: This study confirmed that lowering the dosage of tetracaine to 3.0 mg could equally provide adequate spinal anesthesia for anorectal surgery. The reduced dosage has the tendency of reducing the rate of hypotension, but apparently it does not reduce the incidence of bradycardia.