Page 10 - CASA Bulletin of Anesthesiology 2019 Vol 6 No 5

CASA Bulletin of Anesthesiology

level of the nerve roots (C5 and C6) between the anterior and middle scalene muscles. Because
of the near proximity to take-off of the phrenic nerve, local anesthetic deposit in this region al-
most inevitably affects the ipsilateral hemidiaphragmatic function . Studies using lower volumes
in the interscalene block have shown that even amount as little as five milliliter is associated
with significant incidence of hemidaphragmatic dysfunction (up to 27-45%)(6,7).

More distal along the brachial plexus just superior to the clavicle, supraclavicular blocks
target the plexus at the level of divisions . They are thought to be associated with a lower inci-
dence of hemidiaphragmatic paralysis than interscalene blocks, by virtue of being more distant
from the phrenic nerve(9,10) . However, for these blocks, a greater volume is often necessary in

order to provide adequate analgesia to the shoulder . The reason for this is that one component of
the brachial plexus, the suprascapular nerve, which provides 70% innervation to the shoulder
and the glenohumeral joint, arises more proximally on the plexus at the superior trunk(12) . To
provide sufficient spread proximally to the suprascapular nerve, an injection volume of 20 milli-
liter or more is often needed; problematically, this can often result in phrenic nerve paralysis as
well(10,13) .

Alternatively to blocking a part of the brachial plexus, some investigations have focused
on a single or combination of nerves as they exit the plexus, with the rationale that by selec-

tively targeting individual nerves to the shoulder, there would be less unintended spread to the
phrenic nerve . For the shoulder, in addition to the suprascapular nerve, the axillary nerve pro-
vides significant innervation to the cutaneous and intra-articular surface. Results from studies
comparing blocks of the suprascapular nerve, with or without blocking the axillary nerve, were
mixed(23,24,25,26). No blocks were able to provide surgical anesthesia as reliably as intersca-
lene block, as many of these investigations were performed in conjunction with general anes-
thesia. It is unclear if this was due to complexity of the block, as they are technically difficult
and associated with high failure rates(24,25), or simply that the two nerves provided incomplete
analgesic coverage of the shoulder region . Finally, the incidence of hemidiaphragmatic paral-
ysis was often not formally assessed in many of these studies. One paper found no significant
difference in rest pain between a combined suprascapular and axillary (circumflex) nerve block

and interscalene block(26). However, PEFR (peak expiration flow rate) was reduced in both
groups, but was significantly lower in ISB. Another study reported about 8.3% incidence of dys-
pnea(25) .

A better alternative to providing analgesia noninferior to the interscalene block is the anterior
suprascapular block(27,28) . The spread of the local anesthetics is thought to cover the posterior
division of the superior trunk, thus not needing to target the axillary nerve separately(27) . The
investigators were able to demonstrate that hemidiaphragmatic excursions were unchanged;
however, about 8% of patients still noted to have dyspnea (versus about 12% in the group that

had the interscalene nerve block) .

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