Spinal and epidural anesthesia

Patient positioning and anatomical landmarks

Proper patient positioning is essential for a successful and safe puncture. The patient sits across the table, facing away from the physician, places their hands on their abdomen, and firmly presses their chin against their chest. The legs hang freely or rest on a high footstool. The main goal of this posture is to achieve maximal flexion of the spine, which significantly widens the spaces between the vertebral arches and spinous processes.

Clear anatomical lines are used to accurately determine the puncture site:

• Tuffier's line (Intercrestal line): a horizontal line connecting the highest points of the iliac crests. It reliably intersects the spinous process of the fourth lumbar vertebra.
• Line of the scapular angles: connects the inferior angles of the scapulae and projects onto the spinous process of the seventh thoracic vertebra.
• Spinous process of the seventh cervical vertebra: the most prominent process in the neck, almost always easily palpable under the skin.

Technique of spinal anesthesia

The procedure begins with local infiltration of the skin and tissues in the chosen intervertebral space (typically using 3–5 ml of a 5% procaine solution). The physician uses their left hand to fixate the spinous process and their right hand to insert a special needle with a stylet along the upper edge of the finger.

As it advances, the needle sequentially pierces several anatomical layers:

1. Skin.
2. Lumbar fascia.
3. Supraspinous ligament.
4. Interspinous ligament.
5. Ligamentum flavum.
6. Dura mater.

Usually, the puncture depth ranges from 2 to 5 cm. A reliable sign of correct needle placement in the subarachnoid space is the appearance of cerebrospinal fluid (CSF) drops after removing the stylet. A small amount of CSF is drawn into the syringe containing the anesthetic (procaine or sovCAIN), mixed with the solution, and slowly injected back. Afterward, the patient's head must be positioned higher than the level of the spine.

The choice of puncture level strictly depends on the anticipated surgical site. For perineal procedures, puncture is performed between $L_{IV}$ and $L_{V}$; for lower extremity and gynecological surgeries, between $L_{II}$ and $L_{IV}$; and for intra-abdominal procedures, between $T_{11}$ and $L_{I}$.

Features of epidural anesthesia

In epidural anesthesia, the solution is injected into the space between the outer and inner layers of the dura mater. Highly toxic drugs (tetracaine, trimecaine) are used here, requiring strict adherence to dosage guidelines. For example, when using tetracaine, it is strictly forbidden to administer more than 5 ml of a 0.3% solution in the initial dose, otherwise a severe complication such as collapse may develop.

The procedure requires a needle 6 cm long and no more than 1 mm thick. It is inserted to a depth of about 2 cm, after which the syringe containing the medication is attached. While the needle passes through the dense interspinous ligament and ligamentum flavum, the syringe plunger meets resistance, and no solution is injected. As soon as the bevel enters the epidural space, tissue resistance disappears—the needle seems to "drop into a void"—and the fluid can be injected with minimal effort. Unlike spinal anesthesia, detaching the syringe does not result in CSF leakage.

The effect of epidural drug administration develops gradually over 10–15 minutes. If anesthesia occurs immediately, it means the needle accidentally punctured the inner layer of the dura mater, and the anesthetic entered the subarachnoid space. The procedure should be stopped immediately if the patient experiences a sharp drop in blood pressure, severe headache, nausea, or vomiting.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Topographic anatomy of the spinal meninges and their spaces
• Mechanism of circulatory collapse in local anesthetic overdose
• Relationship between spinal ganglia (ganglion spinale) and sympathetic trunks (ganglion sympathicum)
• Differential diagnosis of complications in regional anesthesia techniques

Other topics in the section "General Operative Surgery. Equipment, Instruments. Anesthesia"

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