Forty, male or female, adult patients scheduled for lumbar laminectomy and/or discectomy were assigned randomly to two groups, one with isobaric, and the other with hypobaric tetracaine spinal anesthesia. Isobaric was prepared to 0.5% solution
with
patient's cerebrospinal fluid, and hypobaric to 0.1% solution with distilled water. Epinephrine 1:200,000 was mixed to either solutions. Dosage was determined by patient's height; ±0.1 mg per cm-height difference added to 10 mg/160 cm. Speed of
injection was fixed as the rate of 1 ml/10 sec.
The onset in hypobaric (1.70±1.43 min) was more rapid than that in isobaric (3.45±1.59 min)(p<0.05). The durations of either groups ranging 3.5 to 4 hours were similar. The mean anesthetic sensory level with hypobaric group (T6) was higher than
that
with isobaric group (T9)(p<0.05). Hypotension as major complication occurred in 50% and 60% with isobaric and hypobaric groups, respectively. However, with general managements including fluid infusion and vasopressor it was overcome.
In conclusion, both technics are useful for laminectomy in prone position, even if they had some complications including hypotension. However, further evaluations are needed for the strength and dosage, especially in hypobaric agent.
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