Phrenic nerve blocks are indicated for treatment of persistent
hiccups. Also, it can be employed for arresting diaphragmatic action
during thoracic surgery. In cases of persistent hiccups, a bilateral
block is required.
The phrenic nerve arises from the anterior primary division of the
fourth cervical nerve, with contribution from the third and fifth cervical
segments. The three components join at the lateral border of the scalenus
anterior muscle at the level of C6 to form the main trunk of the
nerve. From there, the phrenic nerve descends obliquely across the
anterior border of the scalenus anterior muscle at its insertion on the first
rib to reach its thoracic nerve.
In the neck, this nerve is covered immediately posteriorly by the
sternocleidomastoid muscle and the internal jugular and subclavian veins and is
crossed by the transverse cervical and scapular vessels and the inferior belly
of the omohyoid muscle. One-third of its fibers are sensory, and two
thirds are motor. In the neck, it communicates with the ansa cervicalis
and the cervical sympathetic ganglia, and although its main terminal branches
are muscular to the diaphragm, the phrenic nerve gives off filaments that
supply the pleura, pericardium and diaphragmatic peritoneum and contributes
fibers to the phrenic plexus.
The patient lies supine, the head turned toward the side opposite of that
to be operated on, the arms at the side. The lateral border of the
clavicular head of the sternocleidomastoid muscle is located when the patient
raises his/her head approximately 5 cm off the table. Subcutaneous
infiltration is performed 2.5 cm above the clavicle on the lateral border of
the clavicular ear of the sternocleidomastoid muscle. Lateral anterior
muscle should be palpable. The middle and ring fingers of the operator's
non-dominant hand are placed firmly on the border of the anterior scalene
muscle, where subcutaneous infiltration is performed.
A 3.8 cm, 22 G needle attached to an extension set and a 20 ml syringe
filled with the approximate volume of local anesthetic is introduced through
the skin wheal and advanced slowly at 90 degrees to the skin. The needle
direction if caudad, pointed midway between the opposite shoulder and the
nipple. The needle should not advance more than 2.5 cm and should lie
between the sternocleidomastoid and scalenus anterior muscles. A nerve stimulator
can be attached to the needle for accurate localization. The diaphragm on
the ipsilateral side will contract with each pulse when nerve stimulation is
employed. After the phrenic nerve is localized, 1 ml local anesthetic is
initially injected as a test dose after negative aspiration for blood, air, or
CSF. This is followed by injecting up to 15 ml local anesthetic solution
to complete the nerve block.
If the block is successful, the ipsilateral diaphragm will not
function. This may be confirmed by fluoroscopy or by asking the patient
to take a deep breath and palpating the movement of the diaphragm.
Intravascular injection, epidural or subarachnoid injection, paralysis of
the recurrent laryngeal nerve, pneumothorax and Horner's syndrome are possible
complications that may arise.