Phrenic Nerve Block and Ablation
A phrenic nerve block is mainly used in the treatment of persistent and intractable hiccups. Persistent and intractable hiccups can result in depression, fatigue, impaired sleep, dehydration, weight loss, malnutrition, and aspiration syndromes. The conventional treatments for hiccups are non-pharmacological manoeuvres and pharmacological treatment. Pulsed radiofrequency lesioning (PRFL) has been proposed for the modulation of the excited nervous system pathway of pain as a safe and nondestructive treatment method. It is also useful as both a diagnostic and therapeutic manoeuvre to determine whether pain from subdiaphragmatic processes, including abscess and malignancy, is being mediated via the phrenic nerve.
The relation of the phrenic nerve to hiccup was recognized at least as early as 1833 by Shortt who recommended blistering the surface of the neck over the origin and course of the phrenic nerves for intractable hiccups. A number of reports of freezing, transecting, crushing, and injecting lidocaine into the phrenic nerve to relieve intractable hiccups were published in the 1920s and 1930s.
Each phrenic nerve controls the movement of the hemidiaphragm and provides the sensory innervation to the middle of the diaphragm, some parts of the pleura and pericardium. The phrenic nerve originates mainly from the 4th cervical nerve, but also receives contributions from the 3rd and 5th cervical nerves (C3-C5) in humans. The three nerves join at the upper lateral portion of the anterior scalene, forming the phrenic nerve. The nerve descends obliquely across the anterior scalene, through the gap between sternocleidomastoid and omohyoid muscles, and deep into the thorax. The right phrenic nerve follows the course of the vena cava to provide motor innervation to the right hemidiaphragm. The left phrenic nerve descends to provide motor innervation to the left hemidiaphragm in a course parallel to that of the vagus nerve.
The phrenic nerve is sonographically visualized as a solitary round hypoechoic structure of about 0.76 mm. However, visualization of the phrenic nerve can be considered as time-consuming even in expert hands. The transverse cervical artery that crosses superficial to the phrenic nerve in 95% cases can help the operator in identifying the phrenic nerve.
The hiccup center is located in the spinal cord between the third and fifth cervical segments. The afferent limb of the hiccup reflex consists of the vagus and phrenic nerve with contributions of the sympathetic chain arising from the 6th to the 12th thoracic segments, whereas the efferent limb consists mainly from the phrenic nerve. The proposed mechanism attributable for persistent relief from hiccups after resolution of the phrenic nerve block is a neural pathway interruption. The phrenic nerve is part of the afferent pathway and the main efferent part of the hiccup reflex.