Mechanism of action and anatomical landmarks
The technique is based on injecting a local anesthetic into the epidural space. Anatomically, this area is located between the dura mater, which covers the spinal cord, and the periosteum of the vertebrae.
Unlike some other neuraxial blockade methods, the puncture level is not strictly limited to the lumbar region: access can be achieved at any level of the spine, including the cervical, thoracic, and lumbar regions. The choice of a specific level is dictated exclusively by the nature and location of the planned surgery. Once the drug enters the designated space, it bathes and temporarily blocks the sensitivity of the spinal nerve roots.
Execution technique and space identification
The procedure itself is largely similar to subarachnoid puncture; however, the critical difference is that the needle must under no circumstances puncture the dura mater.
To accurately identify the target area, the physician uses a special technique with a syringe filled with isotonic sodium chloride solution. Advancing the needle through the ligamentous apparatus is accompanied by noticeable resistance. There are three main criteria for correct needle placement:
- «Loss of resistance» sensation — as soon as the needle tip passes through the ligaments and enters the epidural space, the resistance on the syringe plunger instantly disappears, and the solution is injected with extreme ease.
- Absence of CSF — cerebrospinal fluid should not leak from the needle hub (its appearance indicates a puncture of the dura mater).
- Negative pressure — this parameter can be objectively recorded by connecting a water manometer to the needle.
The anesthetic can be administered in two ways. The first option is a single-dose injection of the entire amount directly through the needle. The second option is inserting a thin catheter through the needle lumen, which is left in place for an extended period. This allows for fractional drug administration, thereby prolonging the anesthesia as needed.
Drugs used and postoperative management
To achieve a reliable block, various local anesthetics are used in specific concentrations:
- 2% lidocaine solution;
- 0.5% bupivacaine solution;
- 0.75% ropivacaine solution.
When performing traumatic and extensive surgeries, the standard regimen is supplemented with adjuvants to enhance the effect. These agents include opioid analgesics such as morphine or fentanyl.
Placement of an epidural catheter plays a crucial role not only during the procedure itself but also in the postoperative period. Continuous epidural blockade significantly reduces the required doses of systemic opioid analgesics, thereby improving the patient's well-being.
Indications, limitations, and potential complications
The technique is widely demanded in traumatological and orthopedic procedures on the lower extremities, as well as in abdominal and pelvic surgeries.
Epidural anesthesia is of particular importance for specific patient groups. It is the method of choice for elderly and senile individuals, as well as for patients with severe comorbidities: cardiovascular and respiratory diseases, and metabolic disorders (obesity and diabetes mellitus).
Complications are rare, but may include arterial hypotension, respiratory depression, nausea, vomiting, and seizures. In approximately 5% of cases, clinicians encounter failure — a complete absence of anesthesia. The main reason for this phenomenon lies in the internal structure of the space: the presence of connective tissue partitions (septa) limits the free spread of the injected solution.
Briefly: answers to topical questions
What ligaments does the needle successively pierce during an epidural puncture via the midline approach?
During an epidural puncture via the midline approach, the needle successively pierces the supraspinous, interspinous, and yellow ligaments.
- Supraspinous ligament (lig. supraspinale) — runs along the tips of the spinous processes.
- Interspinous ligament (ligg. interspinalia) — is located between the spinous processes.
- Ligamentum flavum (ligg. flava) — connects the vertebral arches and contains elastic fibers.
Which groups of drugs are used as adjuvants to local anesthetics during epidural blockade?
Opioid analgesics — morphine and fentanyl — are used as adjuvants to local anesthetics during epidural blockade. They are employed to enhance the effect during traumatic surgeries.
What early and late complications can occur during epidural anesthesia?
Potential complications of epidural anesthesia include arterial hypotension, respiratory depression, nausea, vomiting, and seizures. The main hazard is accidental puncture of the dura mater with subarachnoid administration of the anesthetic, which can lead to severe complications, including total spinal block.
To verify correct puncture technique, remember three signs: «Loss of resistance» of the syringe plunger, absence of cerebrospinal fluid (CSF), and detection of negative pressure.
Class and exam questions
What is the main hazard when performing the puncture?
The greatest hazard is an accidental puncture of the dura mater with unintentional subarachnoid injection of the anesthetic dose. This leads to a severe complication — total spinal block.
Why does anesthesia sometimes fail despite correct technique?
In about 5% of cases, the block fails to develop due to the presence of anatomical partitions (septa) in the epidural space. They physically hinder the normal spread of the anesthetic solution around the nerve roots.
What is the advantage of space catheterization over a single needle injection?
Catheterization allows for fractional drug administration and prolongs anesthesia for an extended period. This is especially valuable in the postoperative period to reduce the need for systemic narcotic drugs.
What else to study on this topic
- Detailed pharmacokinetics of ropivacaine and bupivacaine in the epidural space
- Specifics of using adjuvants (morphine and fentanyl) in neuraxial blocks
- Pathophysiology of arterial hypotension development during root blockade
- Anatomical variations of septa in various spinal segments
- Algorithm for managing total spinal block in case of accidental dural puncture
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Other topics in the section "CHAPTER 3. ANESTHESIA"
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