THE ROLE OF NEURAXIAL ANESTHESIA IN ANESTHETIC PRACTICE
Neuraxial blocks may reduce the incidence of venous thrombosis and pulmonary embolism, cardiac complications in high-risk patients, bleeding and transfusion requirements, vascular graft occlusion, and pneumonia and respiratory depression following upper abdominal or thoracic surgery in patients with chronic lung disease. Neuraxial blocks may also allow the earlier return of gastrointestinal function following surgery. Proposed mechanisms (in addition to precluding the need for larger doses of systemic anesthetics and opioids) include reducing the hypercoagulable state associated with surgery, increasing tissue blood flow, improving oxygenation from decreased splinting, enhancing peristalsis, and suppressing the neuroendocrine stress response to surgery. Reduction of systemic opioid administration may decrease the incidence of atelectasis, hypoventilation, and aspiration pneumonia and reduce the duration of ileus. Postoperative epidural analgesia may also significantly reduce both the need for mechanical ventilation and its duration after major abdominal or thoracic surgery.
The spine is composed of the vertebral bones and intervertebral disks (Figure 32–1). There are 7 cervical (C), 12 thoracic (T), and 5 lumbar (L) vertebrae. The sacrum is a fusion of 5 sacral (S) vertebrae, and there are small rudimentary coccygeal vertebrae. The spine as a whole provides structural support for the body, protection for the spinal cord and nerves, and allows a degree of mobility in several spatial planes. At each vertebral level, paired spinal nerves exit the central nervous system.
A: Sagittal section through lumbar vertebrae. B, C: Common features of vertebrae. (Reproduced with permission from Butterworth JF, Mackey DC, Wasnick JD [eds.] Morgan & Mikhail’s Clinical Anesthesiology, 7e. New York, NY: McGraw Hill; 2022.)
The first cervical vertebra, the atlas, lacks a body and has unique articulations with the base of the skull and with the second vertebra. The second vertebra, called the axis, consequently has atypical articulating surfaces as well. All 12 thoracic vertebrae articulate with their corresponding ribs. Lumbar vertebrae have a large anterior cylindrical vertebral body. A hollow ring is defined anteriorly by the vertebral body, laterally by the pedicles and transverse processes, and posteriorly by the laminae and spinous processes. The laminae extend between the transverse processes and the spinous processes, and the pedicle extends between the vertebral body and the transverse processes. When stacked vertically, the hollow rings become the spinal canal in which the spinal cord and its coverings sit. The individual vertebral bodies are connected by the intervertebral disks. There are four small synovial joints at each vertebra, two articulating with the vertebra above it and two with the vertebra below. These are the facet joints, which are adjacent to the transverse processes. The pedicles are notched superiorly and inferiorly, and these notches form the intervertebral foramina from ...