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Spinal anesthesia (also known as neuraxial anesthesia) is a regional anesthetic technique in which a local anesthetic is injected into or adjacent to the cerebrospinal fluid (CSF) to induce analgesia and motor blockade below the level of injection. Neuraxial anesthesia can be provided as a single bolus injection or via a catheter for intermittent dosing or continuous infusion. Though in common usage, spinal anesthesia and epidural anesthesia are used interchangeably, they are actually different procedures. In spinal anesthesia, anesthetic is injected into the subarachnoid space (directly into the CSF); in epidural anesthesia the anesthetic is injected into the epidural space (adjacent to the CSF). The term neuraxial anesthesia includes both techniques.

Overview

Rationale

A great variety of operations can be performed under neuraxial anesthesia with or without concomitant general anesthesia. Because major abdominal, thoracic, and laparoscopic procedures impair ventilation, tracheal intubation with general anesthesia is typically also required in these cases. Neuraxial anesthesia may be a beneficial addition to an anesthetic in that it may reduce the incidence of venous thrombosis, pulmonary embolism, By improving respiration after upper abdominal and thoracic procedures neuraxial anesthesia may reduce postoperative atelectasis and pneumonia. The reduction in postoperative opioid requirements associated with neuraxial anesthesia may also help reduce the incidence of postoperative hypoventilation.

Technique

Neuraxial anesthesia should only be performed in a facility with the required equipment available for resuscitation and intubation. Minimum monitoring requirements include blood pressure and pulse oximetry. The patient may be in the sitting or lateral decubitus position; in either case, flexion of the spine maximizes the distance between adjacent spinous processes and brings the spine closer to the skin surface, making introducing the needle easier. A spinal needle is introduced into the depression between the spinous processes above and below the level of entry. As the needle goes deeper, it penetrates first the supraspinous ligament, then the interspinal ligament, and the ligamentum flavum. From the ligamentum flavum the needle enters the epidural space. For epidural anesthesia, a catheter is threaded through the needle and into the epidural space; local anesthetic is injected through the catheter. For spinal anesthesia, the needle is advanced through the dura mater into the subarachnoid space. Entry into the subarachnoid space is confirmed with the free flow of CSF from the needle. Local anesthetic can be injected directly through the needle or a catheter can be threaded, as in the epidural technique.

Local anesthetic agents used for neuraxial anesthesia

Spinal anesthesia

• Bupivacaine
• Lidocaine
• Procaine
• Tetracaine

Epidural anesthesia

• Chloroprocaine
• Lidocaine
• Mepivacaine
• Bupivacaine
• Ropivacaine

Indications

Neuraxial anesthesia can be used alone or in conjunction with general anesthesia for a wide variety of surgical procedures. Procedures for which neuraxial anesthesia can be used as the primary anesthetic technique include lower abdominal, inguinal, urogenital, rectal, and lower extremity surgery. A common use of neuraxial anesthesia is for analgesia during labor and delivery. Neuraxial anesthesia is especially suited for the obstetric patient because it allows her to be awake and aware during the birth of her child while providing adequate analgesia.

Contraindications

Absolute contraindications

• Infection at injection site
• Patient refusal
• Coagulopathy or bleeding diathesis
• Severe hypovolemia
• Increased intracranial pressure
• Severe aortic stenosis
• Severe mitral stenosis

Relative contraindications

• Sepsis
• Uncooperative patient (may use in conjunction with general anesthesia)
• Demyelinating lesions (preexisting neurological deficits)
• Stenotic valvular heart disease
• Severe spinal deformity