Women undergoing cesarean deliveries may require a smaller dose of anesthesia when administered through an intrathecal catheter, rather than a single spinal injection, according to a small study presented at the 2011 annual meeting of the Society of Obstetric Anesthesia and Perinatology.

Among a sample of 10 patients who received intrathecal catheters, the average woman required between 0.6 and 1.1 mL of 0.75% hyperbaric bupivacaine to experience a T4 to T6 block. That amount is between 25% and 50% less than published doses of the same medication delivered as a single spinal injection.

Based on these findings, study author J. Sudharma Ranasinghe, MD, associate professor of anesthesiology at the University of Miami Miller School of Medicine, recommended that clinicians opting for intrathecal catheters should use slow, incremental dosing to ensure patients do not receive excessive anesthesia.

“If an adequate block can be achieved with less local anesthetic, bolus injection of a spinal medication that was intended for single-shot spinal through a spinal catheter may lead to high spinal block with respiratory difficulty, aspiration risk and severe hypotension,” Dr. Ranasinghe told Anesthesiology News.

These findings have potentially important implications, said David Wlody, MD, professor of clinical anesthesiology at the State University of New York-Downstate Medical Center, in New York City. “I think it’s a good idea to look at this. I wouldn’t have necessarily thought that there would be a difference in dosing between an injection through a spinal needle and a catheter injection technique. I would usually use the same dose.”

However, with such few patients and a lack of a control group, modifying dosing based solely on these results would be premature, said Dr. Wlody, a member of the editorial board of Anesthesiology News. “It’s entirely possible that, when they complete the study, they’re going to get completely different results,” he said. “Let’s see what the final numbers are before we start changing practice.”