Muscle oxygenation in patients undergoing total knee arthroplasty may be positively affected by neuraxial blockade, a phenomenon that may confer s everal long-term benefits, researchers have found.
The pilot study, by a team of American and Austrian researchers, showed that muscle oxygenation decreased more in the upper than the lower extremity, which may be the result of regional sympatholysis in the areas affected by neuraxial block and a subsequent net increase in perfusion in unaffected regions.
“Numerous experimental studies have demonstrated a beneficial effect of neuraxial blockade on microcirculation,” said Ottokar Stundner, MD, a resident and research fellow at Paracelsus Medical University in Salzburg, Austria, who helped conduct the study while at the Hospital for Special Surgery, in New York City. “There is also some evidence that muscle oxygenation could be a surrogate parameter for tissue perfusion at the end-organ level.”
Clinical information on this phenomenon is scant, however, and how perfusion behaves above and below the level of sympathetic blockade is unclear, Dr. Stundner said. So, he and his colleagues compared tissue perfusion above and below the level of neuraxial blockade in the clinical setting, using noninvasive near-infrared spectroscopy.
The study involved 10 patients, aged 18 to 85 years, all of whom underwent primary total knee arthroplasty under combined spinal-epidural anesthesia. Muscle oxygenation was measured with near-infrared spectroscopy spectra at two locations above and below the level of neuraxial blockade: the deltoid and the quadriceps femoris muscles. The researchers also continuously recorded stroke volume, cardiac output, heart rate, mean arterial blood pressure (MAP) and arterial oxygen saturation.
“We found that during the course of the procedure, oxygenation decreased in both the upper and lower extremities [an average of 9.8%], but more so in the upper extremity,” Dr. Stundner said. After adjusting for covariates, muscle oxygenation in the upper extremity was consistently lower—by an average of 8.1% (95% confidence interval, 2.8%-13.5%; P=0.0031)—than in the lower extremity where the surgery was performed.
“When we looked at other cardiovascular parameters, we saw that cardiac output decreased, likely due to blood loss,” Dr. Stundner added. “Heart rate decreased slightly throughout the surgery, and arterial pressure decreased at first but reverted to baseline by the end.”
The bottom line, he said: “It would seem that despite intraoperative events such as blood loss that may explain a reduction in overall tissue oxygenation, tissue oxygenation remains more favorable in areas affected by the neuraxial blockade, likely as a result of sympatholysis.”
A possible implication, he continued, is that because increased perfusion may improve wound healing, neuraxial anesthesia might improve oxygen delivery to tissues.
Robert S. Weller, MD, head of regional anesthesia and acute pain management at Wake Forest University in Winston-Salem, N.C., said the findings are consistent with what is known about central neuraxial blockade for many years.
“Sympatholysis causes arteriolar dilation below the level of the block, with compensatory increased sympathetic tone and arteriolar constriction above. This would be expected to improve tissue perfusion below the block, particularly if mean arterial pressure and cerebral oximetry [CO] are maintained, as they were in this study,” Dr. Weller said.
“Although the authors suggest increased tissue oxygenation in the legs, it is important to note that there was an overall reduction in tissue oxygenation—arms more than legs—which the authors suggest may have been due to anemia or hemodilution,” Dr. Weller continued. “I would like to see the investigators collect data on patients having this procedure under general anesthesia, and would expect tissue oxygenation might be even more reduced in the general anesthesia group, whose CO and MAP would be likely to be lower than in these 10 patients.”
Potential advantages of improved tissue oxygenation in the surgical extremity, he added, might include improved wound healing and reduced wound infection rates. “But since the effect of the sympathetic block would only be for a period of the block itself, it is speculative that the relatively short intraoperative benefit would translate to the full period of wound healing and infection risk.”
Dr. Stundner presented the findings at the 2013 annual meeting of the American Society of Anesthesiologists (abstract 2114).
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