Epidural anesthesia

Epidural anesthesia turns off all kinds of functional nerve activity: motor, sensory and vegetative. In contrast to the spinal, in which the local anesthetic solution is mixed and diluted with cerebrospinal fluid, with epidural anesthesia it spreads along the epidural space, part of it leaves the spinal canal through the intervertebral foramen, which makes the spread of epidural anesthesia not always predictable.

A solution of a local anesthetic injected into the epidural space spreads up and down the spinal canal, blocking the spinal nerves from the spinal cord to the corresponding intervertebral foramen. Anatomy

Localization of the epidural space can be at any level, starting from intervertebral spaces C3-C4 up to the sacral slit S4-S5. Since the spinal cord ends at the level of L1-L2, most often the puncture of the epidural space is performed in the lower lumbar region. The roots of the horse tail descend in the epidural space below the end of the dural sac S1-S2. Thus, lumbar access can ensure the blockade of all sacral segments, while the local anesthetic solution is able to reach the higher thoracic segments.

Spinal nerves innervate certain dermatomes of the human body and different levels of sensory epidural anesthesia are required for various surgical interventions. In addition, the autonomic nervous system has a significant effect on the physiological effects of blockade and the quality of anesthesia. Sympathetic preganglionic nerve fibers depart from 14 spinal segments from Th1-L2, while the sacral parasympathetic nerves are S2-S4.

Equipment for epidural anesthesia includes:

• kit for antiseptic skin treatment;
• a set of sterile diapers and napkins;
• Tuohi needles 16-18 gage in diameter, large diameter for sampling solutions from ampoules, small diameter for skin anesthesia, large diameter for puncturing the skin at the point of injection of the needle for the procedure such as epidural anesthesia;
• A syringe with a well-ground piston and having a soft stroke;
• an epidural catheter and a bacterial filter.

Epidural anesthesia is performed only if all necessary equipment is available for general anesthesia and cardiopulmonary resuscitation. Personnel involved in epidural anesthesia should be ready for diagnosis and assistance in the event of a systemic toxic reaction or total CA.

[1], [2], [3], [4], [5]

Position of the patient

Two positions of the patient are used:

1. Position on the side with reduced knees and maximum flexion of the spine.
2. The sitting position, leaning forward.

Landmarks

Epidural anesthesia in the lumbar region is performed in the intervertebral spaces L2-L3, L3-L4. Landmarks include: Vertebra prominens - protruding spinal process of the seventh cervical vertebra (C7), scapula foot (Th 3), lower angle of the scapula (Th 7), line connecting the iliac crests (L 4), posterior upper arms of the ilium (S 2 ).

How is epidural anesthesia performed?

Using a thin needle, anesthesia of the skin and subcutaneous tissue is performed at the site of the intended administration. The place of fiction of the epidural space depends on the area of operation.

Using a sharp needle of large diameter, a hole is made in the skin to facilitate its holding. Firmly holding the skin over the spinous processes between the index and middle fingers of the free hand, the needle is inserted strictly along the midline in the middle of the intervertebral space at right angles to the surface of the skin. You can not allow the skin to move, otherwise it can move too far to the side. The needle is guided through the supraspinous and interstitial ligament until the elastic resistance of the yellow ligament is felt. After that, the mandrel is extracted from it. If lumbar access is used, the distance from the skin surface to the yellow ligament is usually about 4 cm (within 3.5-6 cm). In this area, the yellow bunch along the middle line has a thickness of 5-6 mm.

It is necessary to accurately control the progress of the needle so as not to accidentally puncture the dura mater. If epidural anesthesia is performed at the thoracic level, control of its movement is even more important, since there is a danger of injuring the spinal cord.

Identification of the epidural space

The method of loss of resistance is the most widely used method. It is based on the fact that when the needle is inside the ligament, then there is a significant resistance to the introduction of fluid. This resistance drops sharply as soon as it passes through the yellow ligament and its tip reaches the epidural space. To identify the loss of resistance to the needle, attach a 5 ml syringe with a well-ground piston, containing 2-3 ml of physiological saline and air bubble (about 0.2-0.3 ml). The most difficult to master the technique of such a procedure as epidural anesthesia is to control the movement of the needle. It is essential to choose a comfortable hand position. One of the possible options: the pavilion of the needle is held between the thumb and the index roller, while the rear surface of the index finger firmly presses against the back of the patient, creating a stop that prevents accidental displacement. While it is slowly moving in the direction of the epidural space, the thumb of the other hand creates a constant moderate pressure compressing the air bubble. While the needle is in the thickness of the ligaments, elastic compression of the compressed gas is felt under the piston. When the needle passes into the epidural space, the solution begins to flow there practically without resistance, a feeling of failure occurs under the piston. The flow of fluid moves the dura mater from the tip of the needle. If the resistance to the movement of the needle is too high due to the density of the ligament apparatus, stepwise technique can be used when the needle is advanced with two hands for a minimum distance, and after every millimeter the resistance to liquid injection is evaluated.

The hanging drop method is based on the fact that the pressure in the epidural space is below atmospheric pressure. While the needle is in the thickness of the yellow ligament, a drop of physiological solution is suspended from its external opening. When the needle is inserted into the epidural space, the drop is sucked into the needle, which indicates the correct position of the needle. The presence of negative pressure in it is explained by the fact that at the moment when the needle enters there, its point pushes the dura mater from the posterior surface of the spinal canal. This facilitates the absorption of a drop of liquid suspended from the outer end of the needle. With puncture at the thoracic level, a negative pressure inside the chest, transmitted through the venous plexus, can play a role. The advantage of this method is that the needle can be held with both hands. After reaching the epidural space, the correct position of the needle is confirmed by the absence of resistance when introducing a solution or air.

Carrying out the catheter

Regardless of the method of identification, if catheterization is planned, to facilitate the conduct of the catheter, you can advance the needle by 2-3 mm. To reduce the risk of insertion of a catheter into the lumen of the vessel, a small amount of saline or air can be introduced into the epidural space prior to its placement. The catheter is inserted through the lumen of the needle. At the moment of its exit through its tip the increase in resistance is determined. This usually corresponds to a distance of about 10 cm. The needle clearance can be oriented cranially or caudally, depending on the direction of insertion of the catheter. You should not spend it too far. Usually, for anesthesia of surgical interventions, it is recommended to insert a catheter into the space to a depth of 2-3 cm, if prolonged epidural anesthesia and labor pain anesthesia is carried out - by 4-6 cm, to ensure that the catheter is fixed during patient movements. If the catheter is inserted too deeply, its displacement in the lateral or anterior space is possible, which will result in the epidural anesthesia losing its effectiveness. After insertion of the catheter, the needle is gently removed, as the catheter is gently propelled forward. After the needle is removed, the catheter is connected to the bacterial filter and the syringe attachment system, fixed to the skin with an adhesive patch.

[6], [7], [8], [9]

Epidural Anesthesia: Dose Test

Before introducing a calculated dose of a local anesthetic with epidural anesthesia, in order to prevent possible intrathecal or intravascular position of the needle or catheter, a small dose test is administered. Its magnitude should be such as to guarantee the detection of the effect when the introduction is incorrect. Usually, 4-5 ml of a local anesthetic solution is used with 0.1 ml of a 1: 1000 dilution of adrenaline, which is administered. After that, careful monitoring is carried out for 5 minutes. The pulse rate and blood pressure are monitored before and after administration. It should be remembered that a negative effect after the introduction of the test dose can not fully guarantee the correct position of the catheter, therefore, in any case, all precautions should be followed, both with the administration of the main dose, and with all repeated injections of the anesthetic.

[10], [11], [12], [13], [14]

Epidural anesthesia: the main dose

Adding some drugs to a local anesthetic solution is used to increase the duration and effectiveness of epidural anesthesia or to accelerate its development. Most often, adrenaline is used at a dilution of 1: 200,000. With it, you can increase the duration of epidural anesthesia when using anesthetics with short and medium duration of action. Phenylephrine is used with epidural anesthesia much less often than with spinal anesthesia, perhaps because it significantly reduces the peak concentration of anesthetic in the blood plasma compared to adrenaline.

[15], [16], [17], [18]

Epidural anesthesia: complications, methods of prevention and treatment

[19], [20], [21], [22], [23]

Incorrect position of catheter or needle with epidural anesthesia

An objective sign of this situation is the absence of a blockade in 15-20 minutes after the administration of the anesthetic. The most probable position of the catheter is in the thickness of the sacrospinal muscle, laterally with respect to the spinal canal.

Puncture of the dura mater during epidural anesthesia

Most often occurs in a mordant uncontrolled needle drop after passing through a yellow ligament. Diagnosed with the isolation of cerebrospinal fluid after removal of the mandrel needle. The cerebrospinal fluid should be differentiated with the solution administered during identification of the epidural space. It is distinguished by temperature, the presence of glucose, as a rule, the volume of excreted cerebrospinal fluid through a large diameter needle does not raise any doubts about its nature. One of the consequences of a puncture of the dura mater may be post-puncture headaches.

Intravascular catheter insertion

Intravascular position of the needle can be easily differentiated after the flow of blood. In this situation, the needle should be removed and tried again in the same or adjacent intervertebral space. The intravascular position of the catheter is much more difficult to diagnose. There is always the danger that the tip of the catheter, moving, can penetrate into the lumen of the vessel. In any case, before introducing the main dose of a local anesthetic, you need to make sure that this is not the case. To some extent, the aspiration test can help, but it is not reliable enough, because when creating a vacuum, the lumen of the catheter can be pressed against the wall, which blocks the movement of blood. A passive flow test is possible when the catheter drops below the puncture site. In case of the appearance of blood, it should be removed and the attempted catheterization should be repeated. In order to diagnose the intravascular position of the catheter, a dose test with the addition of epinephrine as described above is used.

Hypotension in epidural anesthesia

Epidural anesthesia causes a decrease in peripheral vascular resistance due to vasodilation. Since the capacity of the venous bed is also significantly increased, any reason for a decrease in venous return (i.e., elevated position of the compression of the inferior vena cava) will lead to a decrease in cardiac output. Hypotension can be the result of hypovolemia or compression of the inferior vena cava. In either case, a certain level of vasopressor support will be required to normalize blood pressure. A sudden decrease in pressure in a patient who is conscious, against the background of epidural anesthesia may be the result of vasovagal reflexes. This condition is accompanied by pallor, bradycardia, nausea, vomiting and hyperhidrosis, until the loss of consciousness and the transient stopping of cardiac activity. If the cause of hypotension can be related to the position or occlusion of the inferior vena cava, immediately lower the head end of the table (bed) and in case of compression of the inferior vena cava, turn on its side. Since the basis of hypotension is most often vasodilation, it is necessary to use vasopressors. They act quickly and efficiently. Pregnant women are often afraid of the negative effects of vasopressors on the placental blood flow, but the result of hypotension can be much more dangerous. Infusion load is used if there is a suspicion of hypovolemia. Otherwise, it should not be regarded as a therapeutic tool of the first line.

Epidural anesthesia can be accompanied by the emergence of a systemic toxic reaction, which is associated, first of all, with the occasional introduction of the drug into the vein. To prevent this complication, the initial dose of a local anesthetic should always be preceded by a dose test. A mandatory condition for performing epidural anesthesia is the possibility of inhalation of oxygen and artificial ventilation of the lungs, the presence of all necessary for an intubation of the trachea (laryngoscope, tube, muscle relaxants), preparations for anesthesia and anticonvulsants.

Subarachnoidal administration of the main dose of a local anesthetic can take place with insufficient attention to the conduct and evaluation of the effect of the test dose. The main problem in this situation is the timely diagnosis and treatment of effects on the part of the circulatory and respiratory system. As with any neuraxial blockade that reaches a high level, epidural anesthesia requires maintaining blood pressure and heart rate. The patient is placed in the position of Trendnerburg in order to maximize the venous return. Intravenous management of atropine and ephedrine are usually effective and give time to provide infusion of more potent catecholamines, if necessary. In addition, auxiliary ventilation is required, and if about 20-25 ml of a local anesthetic solution is injected into the cerebrospinal fluid, intubation of the trachea and artificial ventilation are indicated, since it may take at least 2 hours to restore adequate spontaneous breathing.

After the introduction of a large dose of local anesthetic into the cerebrospinal fluid, a persistent dilatation of the pupils develops, which can be interpreted as a sign of damage to the central nervous system, but if there were no reasons for this, the pupil size will return to normal as the high block resolves.

Epidural anesthesia is not characterized by the appearance of post-puncture headaches, they can occur after accidental puncture of the dura mater. However, given the large size of the needle, this complication can become quite severe and require special therapeutic measures.

Sometimes epidural anesthesia is accompanied by an infection that may be the result of a violation of asepsis rules, but in most cases, the cause of extremely rare bacterial meningitis or abscesses is the hematogenous pathway of infection.