[Effects of the specific gravity on spinal anesthesia with 0.5% tetracaine]

In a double-blind study, 0.5% tetracaine 10 mg in hyperbaric or isobaric solution was administered intrathecally at random to 102 adult patients. Except the variable under study, identical technique was used for every patient enrolled. Other influential factors were also under careful control. The extent and pattern of anesthesia were compared. The time for maximal spread was short, the mean times was 7.74 min and 7.8 min for hyper-and isobaric groups respectively, there was no differences statistically. (P less than 0.05). The maximum cephalad spread was T5 (mean, range T12-T3) for the hyperbaric solution and T7 (mean, range T10-T3) for the isobaric solution. The difference was 2 dermatomes and was statistically significant (P less than 0.01). Forty three patients (86%) in the hyperbaric group and 16 patients (30%) in the isobaric group had a sensory blockade higher than T6 level. The hyperbaric group has a much higher percentage of high blockade. The isobaric group has a more predictory lower blockade, but occasionally blockade up to T3 did occur. The 2-segment regression times were also statistically significant. That of hyperbaric group was 88.9 min (mean, range 60-150 min) and 180.5 min (mean, 75-270 min) in isobaric group with a P value less than 0.01. Statistically significant differences in regard to maximum motor blockade and its onset times were found between the two groups. Maximum motor blockade assessed by modified Bromage scale was degree 2 (mean, range 1-3) for the hyperbaric group and degree 3 (mean, range 2-3) for the isobaric group.(ABSTRACT TRUNCATED AT 250 WORDS)