• brachial plexus
• acute pain
• truncal blocks

We have read with interest the letter by Dr Altinpulluk et al1 concerning our recent publication2 in which we made an attempt to determine the mechanism of action for PECS/serratus block according to the most widely used model of sensory innervation of the chest wall.

Unfortunately, the authors do not provide any evidence to support the reason why they “believe” that the brachial plexus contributes to the sensory innervation of the chest wall. The variable good results that someone can get with PECS/serratus blocks, and other similar techniques, cannot be presented as proof that their proposed mechanism of action is correct. Indeed, it should be undisputable to any anesthesiologist that the entire trunk (chest and abdomen) receives its sensory innervation solely from spinal nerves. That is the reason for example why dermatomal maps of the trunk show sequential horizontal stripes that do not include any roots of the brachial plexus (C5-T1). That is the reason also why neuraxial anesthesia (spinal/epidural) produces a horizontal level of sensory anesthesia of the chest. If the brachial plexus contributed to the innervation of the chest wall, the line of anesthesia on the chest would necessarily be interrupted by areas of preserved sensation, reflecting the sensory contribution of different roots of the brachial plexus to the chest wall. In this scenario, the dermatomal map of the chest would resemble more a geographic map, with different patches representing individual roots of the brachial plexus. Thus, every time we determine a spinal level by using for example the nipple line to ascertain a T4 spread, we are implicitly accepting the traditional innervation model, the only one ever proposed, of the chest wall.

Our work did not dispute that PECS/serratus blocks could achieve different degrees of success. Instead, we wanted to demonstrate that such success is likely the result of spread of local anesthetic to the line of emergence of the lateral branches of upper intercostal nerves and, in that context, we proposed to move the injection site closer to it. Indeed, any technique that deposited local anesthetic close to these targets should get sensory anesthesia of the chest wall by this common mechanism.