A study that compared epidurals placed in the L5-S1 interspace and those placed in the most clinically accessible lumbar interspace cephalad found no significant differences in efficacy. The mean number of dermatomes blocked, number of interventions required to achieve adequate analgesia, and pain scores following epidural placement and at delivery were all similar in the L5-S1 and control groups.
However, the study did demonstrate the utility of ultrasound in planning epidural trajectory and placement, according to researcher Omar Malas, MD.
“Anecdotally, we noticed that the benefit that we may be seeing from sacral sparing in the L5-S1 group may be canceled out by lumbar sparing, particularly in patients who are primigravid or who have longer labor,” said Dr. Malas, an anesthesiology resident at the University of Michigan, in Ann Arbor.
Although epidurals are widely used in patients during labor, as Dr. Malas reported at the 2016 annual meeting of the American Society of Regional Anesthesia and Pain Medicine (ASRA), studies indicate that from 0.9% to 24% of epidurals fail to adequately cover dermatomes that are in pain or give adequate analgesia (Int JObstet Anesth 2009;18:10-14).
“A common cause for this is sacral sparing, thought to be partially explained by the distance of the epidural catheter to the sacral nerve root,” Dr. Malas said, “but placing epidurals more caudally is easier said than done. Recent studies have shown that, using landmarks only, anesthesiologists are correct only 14% of the time when asked where they placed epidural catheters” (Anesth Analg 2011;113:559-564).
Prepuncture ultrasound has emerged as one of the modalities to identify definitively the location of epidural needle insertion.
Identifying Epidural Placement
In this study, Dr. Malas and his colleagues used ultrasound guidance to compare epidurals placed in the L5-S1 space with those placed in the most clinically accessible lumbar interspace cephalad to the L5-S1 interspace.
The researchers randomly assigned 96 parturients over 18 years of age with term pregnancies in the early stages of labor to the control group (n=49) or the L5-S1 group (n=47). All patients underwent paramedian longitudinal ultrasound to identify the L5-S1 space.
In the control group, patients had epidural placement ranging from L2-3 to L3-4, whereas in the L5-S1 group, all epidurals were placed in the L5-S1 space.
To achieve double blinding in the study, dermatomal coverage was assessed by a second anesthesiologist who was blinded to the location of placement, and it was assessed using ice at multiple locations, Dr. Malas reported.
Inadequate pain relief was corrected by redosing the catheter and by changing the epidural solution to a higher concentration. Any unilateral block was corrected by retracting the catheter, and if needed, the catheter was replaced.
Researchers assessed parturients’ pain using the verbal numeric rating scale (vNRS) 30 minutes after epidural placement and during delivery.
No Significant Differences
The mean number of dermatomes blocked was 10.7 in the control group and 10.4 in the L5-S1 group, a difference that was not statistically significant, Dr. Malas reported.
Interventions to optimize analgesia were required in 51% of control patients and 60% of L5-S1 patients. The type of interventions was also similar in the groups and included catheter retraction, solution changes, repeated analgesic boluses and catheter replacement.
There was no difference in the rate of catheter retraction or exchange between the groups, Dr. Malas noted. Catheters requiring removal or replacement occurred in 4% of the control group and 2% of the L5-S1 group.
In addition, researchers reported similar vNRS pain scores 30 minutes after epidural placement and at delivery in the control and L5-S1 groups.
Dr. Malas acknowledged that the single-center study limited generalizability of the findings. Furthermore, he noted, caudal dermatomes were only tested up to S2, and multiple providers performed epidural placement throughout the study.
Moderator James C. Eisenach, MD, president and CEO of the Foundation for Anesthesia Education and Research (FAER), in Schaumburg, Ill., found it “interesting that in 2016, we’re still asking which interspace to perform epidural analgesia.”
“Were the catheters placed real-time with ultrasound or was the ultrasound used for measurement purposes only?” Dr. Eisenach asked.
“It was all done prepuncture,” Dr. Malas said. “We would find the L5-S1 space before we did any puncture and then proceed with epidural placement.
“Some studies out of Germany and Canada are trying to use real-time ultrasound,” Dr. Malas added. “The issue is that it requires two users to do it accurately. Researchers are trying to develop a single-user system where the epidural needle is mounted onto the ultrasound probe, but that’s still in its infancy.”