A nerve block involves injecting an anesthetic agent near a nerve to temporarily interrupt signal transmission, providing localized pain relief or modulating nerve function. The phrenic nerve block is a targeted version of this technique, specifically designed to affect the nerve that controls the diaphragm. This procedure is used in specialized circumstances where temporary interruption of this nerve’s activity is medically beneficial.
The Role of the Phrenic Nerve
The phrenic nerve is a mixed nerve that originates high in the neck from the cervical spinal nerves, primarily C3, C4, and C5. It descends through the chest cavity to supply the diaphragm, the large, dome-shaped muscle separating the chest and abdomen. This nerve provides the exclusive motor control to the diaphragm, which is the body’s main muscle of respiration.
Each person has a right and a left phrenic nerve, and each controls its respective half of the diaphragm. When the nerve sends a signal, the diaphragm contracts and flattens, increasing the volume of the chest cavity and drawing air into the lungs for inspiration. The phrenic nerve also carries sensory fibers that relay information from the central part of the diaphragm and surrounding membranes like the pericardium.
Clinical Uses of the Block
The primary reason for performing a phrenic nerve block is to treat intractable hiccups, also known as singultus, which are persistent hiccups that do not respond to standard medication. Hiccups are caused by involuntary spasms of the diaphragm, and blocking the phrenic nerve can stop this uncontrolled contraction. This therapeutic use is reserved for patients whose quality of life is severely impacted by chronic hiccups, which can cause exhaustion, difficulty eating, and sleep deprivation.
Diagnostic Uses
The block also serves an important diagnostic purpose, particularly in pain management and surgical planning. Irritation of the phrenic nerve can cause referred pain felt in the shoulder or neck, and a temporary block can confirm if this nerve is transmitting pain signals from the diaphragm or structures below it.
Surgical Planning and Stabilization
If a procedure is being considered that might permanently damage the nerve, a temporary block can predict the degree of respiratory impairment a patient might experience from permanent diaphragmatic paralysis. The procedure can also be used to stabilize the diaphragm to promote lung healing after certain thoracic procedures, such as managing a persistent air leak following surgery.
The Administration Procedure
The procedure is typically performed on an outpatient basis using image guidance to ensure accuracy and safety. The patient is positioned comfortably, usually lying on their back with the neck slightly extended and turned away from the injection site. The injection site is generally in the neck, where the nerve lies close to the anterior scalene muscle.
Real-time guidance, most commonly ultrasound, allows the physician to visualize the nerve and surrounding structures, including blood vessels. The phrenic nerve appears on the ultrasound as a small, oval structure lying on top of the anterior scalene muscle. A fine needle is advanced toward the nerve, and a local anesthetic, such as bupivacaine or ropivacaine, is injected around it. Sometimes, a corticosteroid is mixed with the anesthetic to provide a longer-lasting reduction in inflammation.
Managing Expected Effects and Risks
The immediate and intended effect of the block is temporary paralysis of the hemidiaphragm on the side of the injection. This occurs because the local anesthetic temporarily prevents the phrenic nerve from transmitting motor signals to the muscle. Healthy individuals compensate for this temporary paralysis by increasing their respiratory rate and relying on other breathing muscles, such as the intercostal muscles.
A temporary feeling of breathlessness or a slight reduction in lung capacity is common, especially in patients with pre-existing lung conditions. The effect of the block lasts as long as the anesthetic is active, often a few hours, but the therapeutic benefit for hiccups may persist much longer. While rare, risks include accidental injection into a blood vessel or the nearby brachial plexus, which could temporarily affect arm movement or sensation. A serious risk is pneumothorax, or a collapsed lung, though the use of real-time ultrasound guidance significantly reduces this possibility.