Spinal Anesthesia: Mechanisms, Physiological Effects, Contraindications, and Complications

Abstract

Spinal anesthesia is a widely used central neuraxial technique that produces temporary sensory, motor, and sympathetic blockade through the injection of local anesthetic, with or without adjunctive drugs, into the subarachnoid space. It provides effective anesthesia and analgesia while avoiding many of the respiratory complications associated with general anesthesia and is associated with high patient satisfaction. Its effects result primarily from blockade of neural transmission at the spinal nerve roots and spinal cord through mechanisms involving sodium and calcium channels as well as modulation of neurotransmitter activity. Spinal anesthesia can be performed using midline or paramedian approaches, with the latter being particularly useful in patients with difficult spinal anatomy. Despite its clinical advantages, spinal anesthesia produces important physiological effects, particularly sympathetic blockade that may reduce systemic vascular resistance, venous return, cardiac output, and heart rate. Potential complications include hypotension, hypothermia, urinary retention, nausea and vomiting, spinal hematoma, neurological complications, failed neuraxial block, total spinal anesthesia, and post-dural puncture headache. Therefore, appropriate patient selection, careful technique, adequate monitoring, and early recognition and management of complications are essential for the safe and effective use of spinal anesthesia.