Pectoral Block Proven Effective As Motor Block, but Not Skin Sensory Block

Author: Michael Vlessides

Anesthesiology News

A team of Canadian researchers has confirmed that the PEC1 block is associated with significant motor block of the pectoral nerves, but without associated sensory block of the thoracic skin. The volunteer trial also demonstrated the ability to confirm the block’s success by measuring diminished upper limb adduction.

“The PEC1 block was first described by Blanco in 2011 [Anaesthesia 2011;66(9):847-848],” said Maxim Roy, MD, a resident at the University of Montreal. “The goal of the technique is to block the medial and lateral pectoral nerves by injecting anesthetic between the pectoralis major and pectoralis minor muscles. One year later, the same author proposed a modification of this technique, called the PEC2 block.

“Since the description of these blocks, the vast majority of literature has evaluated the PEC2 block,” he noted. “However, nobody has really proven that the PEC1 block actually blocks the lateral and medial pectoral nerves. What’s more, no standardized test exists for objectifying the presurgical success of the PEC1 block.”

To help clarify these issues, the researchers enrolled six healthy female volunteers into the randomized, double-blind, placebo-controlled trial, all of whom underwent two ultrasound-guided PEC1 blocks: one with 0.4 mL/kg of placebo (0.9% saline) and the second with 0.4 mL/kg bupivacaine (0.25% with 1:400,000 epinephrine). “So, each volunteer served as her own control,” Dr. Roy said.

Dr. Roy noted that the mean pre-block adductor strength among the six participants was 119.4±20.7 N. Forty minutes after the block was administered, this force decreased to 54.2±16.3 N under the study block (54.6% reduction), compared with 116.0±30.4 N for the placebo block.

No differences were observed between blocks for sensory testing. “That was not a big surprise for us,” Dr. Roy explained, “since we know the innervation of the thorax is mainly mediated by the intercostal nerves and these nerves are not blocked with the PEC1 block.” No complications occurred during the study.

“To our knowledge, ours is the first study to objectively assess the motor blockade obtained with the PEC1 block,” said Dr. Roy, “and confirms that it really does block the lateral and medial pectoral nerves.”

He added, “We also confirmed that the pectoral nerves don’t contribute to the sensory innervation of the external thorax. However, we still don’t know if there’s a sensitive component to the innervation of the pectoral muscle. If so, maybe this block could be useful for surgeries involving these muscles, such as breast augmentation and certain types of cancer surgeries.”

Measuring Blocks and Benefits

For session co-moderator Vishal Uppal, MD, the local anesthetic volumes used in the trial did not seem to reflect standard practice. “I really like your study, because it’s so objective,” said Dr. Uppal, an assistant professor of anesthesia, pain management and perioperative medicine at Dalhousie University, in Halifax, Nova Scotia. “However, I’m worried about the volume part of it.

“In real-world practice, we use approximately 10 mL below the pectoralis major and 20 mL below the pectoralis minor,” Dr. Uppal said. “So, although it’s a very nicely done study, it may not reflect clinical practice.”

Dr. Roy agreed. “However,” he said, “we wanted to use the same volume as Blanco first described. Moreover, with the larger volume, you can see if there’s lateral distribution of the local anesthetic to the intercostal nerves. That doesn’t seem to be the case, since we didn’t observe any sensory changes.”

Alan Macfarlane, MD, the other co-moderator and a consultant anesthetist at the Glasgow Royal Infirmary in Glasgow, Scotland, questioned the utility of the PEC1 and PEC2 blocks in patients undergoing general anesthesia.

“Certainly every operation is uncomfortable, but in the grand scheme of operation pains, breast surgery is not too uncomfortable,” he said. “I know a lot of people who have stopped using PEC blocks if the patient is going to sleep—they don’t feel there’s a huge clinical benefit.

“I think it’s another story if you’re doing the surgery awake,” Dr. Macfarlane continued. “In those cases, many anesthesiologists are using paravertebral blocks and adding in PEC blocks to get at the pectoral nerves, in case they have a sensory contribution once muscles are being cut, moved and stretched.”