This chapter will discuss the spinal cord, peripheral nerves, neuromuscular junction (NMJ), and their associated disorders. Focus will be placed on those disorders that potentially cause respiratory muscle weakness and hemodynamic instability. These are common findings in neurological disease that necessitate intensive care.
The spinal cord is divided longitudinally into the cervical, thoracic, lumbar, and sacral cord. The cervical cord is made up of 8 segments, the thoracic cord is made up of 12 segments, the lumbar cord is made up of 5 segments, and the sacral cord is made up of 5 segments. There is also a single coccygeal segment, for a total of 31 spinal cord segments. Each segment of the cord gives off a ventral and dorsal spinal nerve root, which ultimately become the peripheral motor and sensory fibers, respectively. The cord is surrounded along its entire length by the bony vertebral column. Each vertebral body, except for C8, corresponds to its respective spinal cord segment. There is no C8 vertebral body. From C1 to C7, each root exits above its respective vertebral body. The C8 nerve root exits between the C7 and T1 vertebrae, and each root inferior to this level exits below its respective vertebrae. The spinal cord itself extends to approximately the lower margin of the first lumbar vertebral body (L1) in adults. Below this level, the spinal canal contains the lumbar, sacral, and coccygeal spinal roots that make up the cauda equina.
DISORDERS OF THE SPINAL CORD
Spinal cord injury (SCI) is a potential cause for neurogenic shock and respiratory compromise and is therefore an important reason for admission to the intensive care unit.
Traumatic Spinal Cord Injury
Most SCIs are traumatic. In the United States in 2014, the incidence of traumatic SCI is approximately 40 cases per million people. The most common causes are motor vehicle accidents, falls, violent acts, and sports injuries.1 Acute causes of SCI lead to fractures and dislocations of the vertebrae, resulting in displaced bony fragments and disc material. The direct mechanical injury to spinal cord axons caused by these events is known as primary injury, and also includes compression and laceration. Secondary injury may continue for hours to days after the initial injury, and includes ischemia, increased intracellular calcium, extracellular glutamate, free radicals, inflammation, and apoptosis.2 In a cat model, as a result of these secondary phenomena, spinal cord edema develops within hours of injury, becomes maximal by day 3 to 6, and begins to recede by day 9.3
The severity is graded using the American Spinal Injury Association (ASIA) Impairment Scale (Fig. 17-1). Spinal cord injury is first determined to be complete or incomplete. A complete lesion is defined by the total absence of sensory and motor function in the lower sacral segments, S4 to S5. ...