Does Ultrasound Improve Pain Outcomes

Interventional Pain Medicine ISSUE: FEBRUARY 2012 | VOLUME: 10:02  

by Gabriel Mille 
                    
The use of ultrasound in regional anesthesia does not translate into better pain outcomes when compared with traditional techniques, according to a review of 23 randomized controlled trials published in the September 2011 issue of Anesthesia & Analgesia (113:596-604).


In fact, most studies comparing traditional localization techniques with ultrasound are not powered to look at pain outcomes, and instead define block success through surrogates like the number of needle passes or block performance time.

Of the 16 studies that evaluated pain severity, eight reported improved analgesia with ultrasound guidance, whereas the remaining eight reported no difference. Of the eight trials reporting better pain outcomes with ultrasound guidance, only a single study demonstrated a decrease in numeric pain score greater than 1. “Aside from the fact that [the decrease in pain was] statistically significant, I don’t think a decrease in numeric pain scores of less than 1 means anything to the patient,” said lead author Stephen Choi, MD, staff anesthesiologist at Sunnybrook Health Sciences Centre in Toronto, Ontario, Canada. 


The result speaks to the importance of statistically versus clinically significant results, he added, noting that previous research has shown that the minimal clinically important difference in pain is at least 1.3 units. “When you look at the outcomes that are important to patients, very few of those were actually assessed in the studies,” Dr. Choi said. Additionally, the range of designs and end points makes the studies difficult to compare. 


“The 23 trials look impressive until you look at each individual trial,” said Dr. Choi. “Because of the differing blocks, when you break it down you can’t actually compare them; no common effect was [measured]. From that perspective, there is actually very little data.” To wit, the studies included in the review had 11 unique primary end points, all of which essentially purported to characterize a better block when comparing ultrasound-guided and landmark or peripheral nerve stimulation techniques. 


Despite the limitations of these studies, “when the techniques are really put to the test (meaning one provides a better quality surgical block), the data don’t suggest that ultrasound is better, just equivalent,” said John Antonakakis, MD, anesthesiologist at Portsmouth Regional Hospital in Portsmouth, N.H. Because of this, Dr. Antonakakis said, “it’s an inefficient use of research time and resources to look at [pain outcomes] because first you have to prove that ultrasound gives you a better block. 


If we haven’t shown that ultrasound provides a better surgical block, why would we think that patients’ pain is going to be any different? “There is nothing magical about ultrasound; it doesn’t have intrinsic therapeutic benefits that we know of,” Dr. Antonakakis said. “It’s simply a tool used for nerve localization and deposition of local anesthetic. 
The outcomes that have been studied to date—that is, how easy it is to perform the block and how quickly it sets up—are important to measure [and] are the appropriate outcomes to study with ultrasound.” Whether or not there is a landmark trial demonstrating better outcomes, ultrasound has simplified regional anesthesia. 


“Ultrasound itself has revolutionized regional anesthesia; it has allowed more people to become practitioners and thus more offer it to patients,” said Dr. Choi. He said novel applications of ultrasound in the field—such as blocks that use tissue planes to deliver anesthetic further away from the nerve—will only reinforce physicians’ dependence on ultrasound. “Is it going matter if there is a major conclusive trial?” Dr. Antonakakis added. “Ultrasound has simplified regional anesthesia and given practitioners more confidence. 


Even if the literature shows that ultrasound and traditional techniques are equivalent, and it allows more practitioners to offer nerve blocks to their patients means that more patients will benefit.”