The superior trunk block provides noninferior anesthesia and analgesia for shoulder surgery compared with the interscalene block and succeeds in sparing the phrenic nerve, according to research conducted by David H. Kim, MD, and colleagues at Hospital for Special Surgery.¹

The interscalene block is one of the most commonly used nerve blocks for anesthesia and analgesia in shoulder surgery, but because it commonly results in hemidiaphragmatic paralysis, it cannot be used in patients with compromised pulmonary function.

“Hemidiaphragmatic paralysis, or HDP, is when the phrenic nerve gets blocked, preventing one side of the diaphragm from working,” Dr. Kim explained. “In a healthy patient, HDP is asymptomatic and usually patients do not notice it. However, patients with underlying pulmonary disease, such as COPD, may need both sides of their diaphragm to breathe. When we inadvertently block one side of the diaphragm, they become dyspneic, sometimes leading to difficult consequences like being on a ventilator until the diaphragm recovers.”

Recent studies have examined alternatives to the interscalene block, but none had been able to reliably show effectiveness in anesthesia and analgesia without significant risk for causing HDP.

“The interscalene block and the superior trunk block are performed along the same cluster of nerves known as the brachial plexus, but at different locations,” Dr. Kim said. “Proximally, the interscalene block (ISB) is done right when the plexus exits between the scalene muscles of the neck. The ISB is in such close proximity to the phrenic nerve that it is difficult to prevent inadvertent spread to the phrenic, even when you give extraordinarily low volumes. Distally, the superior trunk block is performed at the level where a major nerve to the shoulder (suprascapular nerve) takes off. By being further away, we prevent spread to the phrenic nerve.”

“There was a case report by a group in Toronto² that performed the superior trunk block for a patient with severe pulmonary disease. They showed that by using this technique they were able to spare the diaphragm and still provide analgesia,” Dr. Kim said.

To examine the effectiveness of the superior trunk block for anesthesia in shoulder surgery, Dr. Kim and colleagues conducted a randomized controlled trial with 126 patients who underwent arthroscopic ambulatory shoulder surgery. Half of the patients received a superior trunk block (n=63) while half received an interscalene block (n=63). The primary outcomes the researchers examined were incidence of HDP (assessed via ultrasound), and worst pain score in the recovery room. Secondary outcomes measured included noninvasively measured parameters of respiratory function, opioid consumption, handgrip strength, adverse effects, and patient satisfaction.

Dr. Kim and colleagues found that the superior trunk block had a significantly lower incidence of HDP (3 of 62 [4.8%]) compared with the interscalene block (45 of 63 [71.4%]; P <.001, adjusted odds ratio 0.02 [95% CI, 0.01, 0.07]). They also found that pain relief from the superior trunk block was noninferior to the interscalene block (worst pain scores in the recovery room: (0 [0, 2] vs 0 [0, 3]; P = .951), and that patients who received the superior trunk block had lower worst pain scores on postoperative day 1.

Patients who received the superior trunk block were also more satisfied, had unaffected respiratory parameters, and had a lower incidence of hoarseness. No difference was found between the groups in handgrip strength or opioid consumption.

“By using ultrasound, we are able to inject local anesthetic at a precise location that effectively blocks the brachial plexus but also spares the phrenic nerve,” Dr. Kim said. “This opens the possibility of improving our armamentarium of regional blocks. Goals are shifting to provide better blocks that are not only profound opioid-sparing analgesics but also spare motor strength. We are improving upon our current understanding of the anatomy and targeting the nerves we want to block.”

Dr. Kim and colleagues concluded that because the superior trunk block provided noninferior surgical anesthesia and had a much lower incidence of HDP, the superior trunk block may be an alternative to the traditional interscalene block for shoulder surgery.

“Regional anesthesia continues to evolve. With new innovations and progress, we have improved patient care and satisfaction by providing blocks that effectively provide pain relief while sparing motor function. With the superior trunk block, our patients had profound surgical anesthesia and analgesia, took minimal amounts of opioids, had sparing of the diaphragm, and was able to move their hands. This was a certain improvement on our gold standard, the interscalene block,” Dr. Kim concluded.

References

1. Kim DH, Lin Y, Beathe JC, Liu J, Oxendine JA, Haskins SC, Ho MC, Wetmore DS, Allen AA, Wilson L, Garnett C, Memtsoudis SG. Superior trunk block: A phrenic-sparing alternative to the interscalene block: a randomized controlled trial. Anesthesiology. 2019. doi: 10.1097/ALN.0000000000002841

2. Burkett-St. Laurent D, Chan V, Chin KJ. Refining the ultrasound-guided interscalene brachial plexus block: the superior trunk approach. Can J Anesth. 2014;61(12):1098-1102.