Spinal anesthesia

Spinal anesthesia may be the method of choice for many operations below the umbilicus, such as hernia repair, gynecological and urological operations, perineal or genital interventions. Any operation on the lower limbs may be performed under spinal anesthesia. The only exception may be amputation, since the patient's presence at such an operation is regarded as a severe psychological trauma. In such a situation, a combination of spinal anesthesia and surface anesthesia is possible. Spinal anesthesia is especially beneficial in elderly patients with chronic broncho-obstructive diseases, diabetes mellitus, liver, kidney and endocrine disorders. Vasodilation accompanying anesthesia may have a favorable effect in many patients with moderate heart failure, with the exception of patients with predominant stenosis of the cardiac valves or suffering from severe arterial hypertension. Spinal anesthesia may be used in trauma patients, provided that the circulating blood volume is adequately restored. In obstetrics, it is an ideal means of anesthetic support for manual removal of placental remnants, provided there is no hypovolemia. There are certain advantages in its use for pain relief during cesarean section, both for the mother and the child.

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Spinal anesthesia: indications

Spinal anesthesia is indicated for operations below the level of the navel (for example, hernia repair), gynecological and urological operations, any interventions on the perineum, genitals and lower extremities.

Puncture level

Spinal anesthesia involves the injection of a small dose of local anesthetic directly into the cerebrospinal fluid. The puncture is performed at the level of the lumbar spine below the end of the spinal cord L2.

Landmark:

The line connecting the tops of the iliac crests corresponds to the L3-L4 border. The level of spinal anesthesia depends on the dose, specific gravity of the solution and the patient's position.

Anatomy

The spinal cord usually terminates at the level of L2 in adults and L3 in children. Puncture of the dura mater above this level is associated with a small risk of spinal cord injury. An important landmark is the line connecting the apices of the iliac crests, which passes at the level of L4 - L5. The anatomical structures through which the needle passes before obtaining cerebrospinal fluid are the skin, subcutaneous tissue, supraspinal ligament, interspinous ligament, yellow ligament, dura mater, and arachnoid mater. Local anesthetic injected into the subarachnoid space mixes with the cerebrospinal fluid and rapidly causes blockade of the nerve roots it can reach. The spread of local anesthetic within the spinal space is influenced by a number of factors - the specific gravity or baricity of the local anesthetic, the position of the patient, the concentration and volume of the injected solution, the level of puncture and the rate of injection.

Preoperative preparation. High spinal anesthesia causes significant physiological changes, primarily in the circulatory system, which makes it necessary to ensure proper monitoring and preoperative preparation. The patient should be familiarized with the technique of the upcoming spinal anesthesia in advance. It is important to explain that spinal anesthesia blocks the conduction of pain, while at the same time it is possible to maintain a certain level of tactile sensitivity in the corresponding area, which should not cause discomfort. The patient should be prepared for the manifestations of motor and sensory blockade in the lower extremities. If a feeling of pain occurs, a transition to general anesthesia is possible. The use of specific premedication is usually not necessary.

If the patient is anxious, it may be sufficient to prescribe benzodiazepine drugs (diazepam at a dose of 5-10 mg per os) on the eve of surgery. It is possible to use drugs of other pharmacological groups, in particular narcotics; there is usually no need to prescribe anticholinergics (atropine, scopolamine).

All patients undergoing spinal anaesthesia must have good intravenous access. Large-bore intravenous catheters are used to ensure that sufficient fluid is administered before induction of anaesthesia. The volume of fluid used depends on age and the extent of the block. An infusion of at least 1000 ml can be used in all patients undergoing high spinal anaesthesia. For caesarean section, approximately 1500 ml is required.

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How is spinal anesthesia performed?

It is easier to perform a lumbar puncture with maximum flexion of the lumbar spine, seating the patient on the operating table and placing a stool of the required height under his feet. Leaning his forearms on his thighs, the patient can maintain this position for a long time without straining. For additional comfort, a bolster or pillow of an appropriate size can be placed on the knees. A lumbar puncture can also be performed in the lateral lying position with maximum flexion of the legs at the knee and hip joints ("head to knees"), which ensures maximum divergence of the spinous processes and facilitates access to the puncture site. For the convenience of the patient and the anesthesiologist, the help of an assistant may be required. The sitting position is preferable for obese patients, the lying position is preferable for patients with mental disorders or deep sedation. In addition, the consequences of the rapid development of hypotension or cardiodepressive vagal reflexes in a patient in a sitting position should be taken into account. The anesthesiologist performing the blockade assumes a sitting position to ensure a stable position during the blockade.

What equipment does spinal anesthesia use?

• a set of sterile diapers and gauze napkins;
• lumbar puncture needle with a diameter of 24-29 gauge;
• 5 ml syringe for anesthetic injected into the spinal canal;
• 2 ml syringe for skin infiltration at the needle insertion site;
• a set of needles for anesthetic collection and skin infiltration;
• a set of antiseptic solutions for skin treatment (chlorhexidine, alcohol);
• sterile gauze balls for skin treatment;
• adhesive plaster to fix the bandage at the site of needle insertion;
• local anesthetic solution for intrathecal administration.

A prerequisite is that a local anesthetic solution suitable for intrathecal administration is packaged in single-dose containers. Preservatives are added to vials containing several doses, which can cause damage to the spinal cord when injected into the cerebrospinal fluid.

• a safety kit of equipment and medications for general anesthesia;
• a set of equipment and medications for performing cardiopulmonary resuscitation.

Lumbar puncture technique

The skin of the patient's back is treated with an antiseptic (ethanol). The procedure is repeated several times, changing the gauze ball, so as to treat a sufficiently large surface.

After the antiseptic has dried, a suitable interspinous space is localized. In a patient with a pronounced layer of fatty tissue, significant effort may be required for its palpation. At the site of the proposed injection, a small amount of local anesthetic is injected subcutaneously using a 2 ml syringe and a thin needle for pain relief. Then, using a needle with a stylet for anesthesia, a puncture is made in the infiltrated skin and the needle is advanced strictly along the midline between the spinous processes with a slight downward slope (5-10 °); in the midthoracic region, the angle of the needle can be 50-60 °. The needle is advanced to the yellow ligament, during the passage of which an increase in resistance is felt; after reaching the epidural space, a feeling of failure occurs, which may be repeated at the moment of passing the dura mater. If the tip of the needle is in the correct position, cerebrospinal fluid should appear after removing the stylet. If the needle rests against the bone, pull it up 1 cm, making sure it is on the midline and try to pass it by increasing the angle of inclination in the vertical plane. When using a thin needle (24-25 gauge), it is necessary to wait 20-30 seconds until the cerebrospinal fluid appears. If the cerebrospinal fluid is not obtained, insert the mandrin in its original place and pass the needle a little deeper.

After obtaining the cerebrospinal fluid, without displacing the needle, attach a syringe with a local anesthetic. It is best to fix the needle by holding its pavilion between the thumb and index finger of the free hand, firmly resting the back of the hand on the patient's back. Securely connect the needle pavilion to the syringe; the hyperbaric solution has a high viscosity and high pressure is required to inject it through a thin needle. Aspirate a small amount of cerebrospinal fluid to ensure that the needle is in the correct position, then slowly inject the local anesthetic solution. After the injection is complete, remove the needle, guidewire, and syringe as a single unit and secure a sterile bandage to the injection site using adhesive tape.

It is possible to perform a lumbar puncture from two approaches: median and paramedian.

The above-described medial approach is the technique of choice, since it involves assessing the projection of the needle in only two anatomical planes. In this case, relatively poorly vascular anatomical structures lie on its path. In cases where advancing the needle along the midline proves difficult, a possible alternative is the paramedian approach. It does not require the same level of cooperation with the patient and deep flexion of the spine in the lumbar region.

The paramedian approach involves inserting the needle at a point approximately 1 cm lateral to the midline and 1 cm below the palpable inferior margin of the apex of the spinous process of the superior vertebra. Before inserting the needle or guidewire, the skin and underlying tissues are anesthetized with infiltration. The needle is inserted at an angle of approximately 10-15° relative to the sagittal and horizontal planes as shown in Figure 17. The most common errors are inserting the needle too far from the midline and angling it excessively cranially. However, when bone is encountered, it is advisable to slightly pull the needle back and slightly increase its angulation in the cranial direction. If bone is then contacted again at a deeper level, the angle of the needle is again slightly increased so as to bypass the superior margin of the arch of the underlying vertebra.

As with the median approach, a characteristic sensation may be felt as the needle passes through the ligamentum flavum and dura mater. However, due to the oblique position of the needle, they occur at a greater depth. After obtaining cerebrospinal fluid, the spinal block is performed similarly to that with the median approach.

Choosing a Local Anesthetic

Theoretically, any local anesthetic can be used to perform a procedure such as spinal anesthesia. According to the duration of action after administration into the spinal canal, all anesthetics can be divided into two groups: with a short 1-1.5 hours (lidocaine, mepivacaine, chloroprocaine) and medium 1.5-3 hours duration of action (bupivacaine, ropivacaine). The duration of action depends on the total dose. In addition, the drugs used in spinal anesthesia are divided depending on their specific density in relation to the cerebrospinal fluid. They can be hyperbaric, i.e. have a higher specific density than the cerebrospinal fluid, isobaric or hypobaric. Since the specific density of the cerebrospinal fluid is not high - about 1.003 at 37 ° C, it is impossible to prepare a solution that would be significantly lighter than it. Therefore, in practice, iso- and hyperbaric solutions are more often used. Hyperbaric solutions are prepared by adding 5-9% glucose, which gives a specific gravity of 1.020-1.030. They are subject to gravity and mix less well with cerebrospinal fluid. Isobaric and hyperbaric solutions are capable of producing a reliable, reproducible block. The use of a hyperbaric solution followed by a change in the patient's position makes spinal anesthesia more controllable. In practice, the following drugs are most often used:

Lidocaine is available as a 5% solution, a hyperbaric solution is prepared in 7.5% glucose, its dose is 1-3 ml. A 2/4 isobaric solution in a volume of 3-6 ml is also used. The addition of 0.2 ml of adrenaline 1:1000 to lidocaine can increase its duration of action. Recently, concern has arisen regarding the safety of 5% lidocaine, in particular its neurotoxicity. Bupivacaine is used as a 0.5% hyperbaric solution in 8% glucose (dose 2-4 ml) and 0.5% isobaric solution, as well as a 0.75% hyperbaric solution in 8.25% glucose (dose 1-3 ml).

Since the anesthetic is administered only at the lumbar level during spinal anesthesia, the spread of the block is determined by the amount of solution injected, its concentration, specific gravity, and the patient's position after the injection to a greater extent than by the level of the intervertebral space at which the puncture is performed. Large volumes of concentrated anesthetic will cause a deep block over a large area. After the introduction of a small amount of hyperbaric solution, provided that the patient remains in a sitting position for some time, it is possible to obtain a classic "sciatic block" spreading only to the sacral spinal segments.

The rate of injection has little effect on the final distribution of the block. Slow injection is associated with a more predictable spread of the anesthetic, whereas rapid injection creates additional currents in the cerebrospinal fluid that may cause unpredictable results. In addition, increased intra-abdominal pressure due to any cause (pregnancy, ascites, etc.) causes distension of the epidural veins, compression of the dural sac, and a reduction in the volume of the cerebrospinal fluid, while the same amount of local anesthetic will produce a higher level of spinal anesthesia. Regardless of the patient's position at the time of puncture and the initial level of the block, the distribution of the block may change with the patient's body position during the next 20 minutes after the injection of the hyperbaric solution.

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Dynamics of the blockade

In many cases, patients cannot accurately describe their sensations, so it is reasonable to rely on objective signs. Thus, if the patient cannot lift his leg off the bed surface, the block extends to at least the middle lumbar segments. Sensitivity should not be examined with a sharp needle, leaving a series of bleeding point wounds. It is better to determine the loss of temperature sensitivity with a swab moistened with alcohol or ether. Assess the sensation of cold on the arm, chest surface, where sensitivity is not impaired. Then examine the skin surface of the leg, abdomen. Let the patient indicate the level at which he begins to feel cold from touch. If the patient finds it difficult to give a definite answer, pain sensitivity can be tested by lightly pinching the skin with a vascular clamp. This method makes it easy to assess the degree of block. Tactile sensitivity should not be assessed. The patient and surgeons should be warned that with a successful block, the feeling of touch may remain, but there will be no pain sensitivity.

If 10 minutes after the local anesthetic solution is administered, the patient still has full lower limb muscle strength and normal sensation, the block has failed, most likely because the anesthetic solution was not administered intrathecally. Try again.

In case of unilateral block or insufficient block height on one side, while using a hyperbaric solution, lay the patient on the side with insufficient block for several minutes and lower the head end of the table. If an isobaric solution was used, lay the patient on the side that should be blocked (any turn of the patient during the first 10-20 minutes after the administration of local anesthetic helps to increase the level of block).

If the block level is not high enough (when using a hypertonic solution), lay the patient on his back and lower the head end of the table so that the anesthetic solution can bypass the lumbar curve of the spine. You can make the lumbar lordosis flatter by asking the patient to bend his legs at the knees. When using an isobaric solution, turn the patient 360 degrees (on his side, then on his stomach, on the other side, and again on his back).

If the block is too high, the patient may complain of difficulty breathing and/or tingling in the hands. Do not raise the head end of the table.

If nausea or vomiting occurs, which may be one of the manifestations of high blood pressure or arterial hypotension, measure your blood pressure and act according to the result.

Respiration, pulse rate and blood pressure must be carefully monitored. Once the blockade develops, blood pressure may drop to a critical level, especially in elderly patients and those suffering from hypovolemia.

Clinical signs of hypotension are pallor, cold sweat, nausea, vomiting, anxiety, and general weakness. Mild hypotension is quite acceptable when systolic blood pressure falls to 80-90 mm Hg in young, fit people, 100 mm Hg in older people, and if the patient looks and feels well and breathes adequately. Bradycardia may also occur, especially when the surgeon is working on the intestines or uterus. If the patient feels well - blood pressure is maintained within acceptable limits, there is no need to use atropine. When the heart rate falls below 50 beats per minute or hypotension develops, give 300-600 mcg of atropine intravenously. If this is insufficient, ephedrine can be used.

In some cases, shivering may occur, in which case reassure the patient and give oxygen via mask. Oxygen inhalation via face mask at 2-4 L/min is common practice for spinal anesthesia, especially if sedation is used.

Surgery always causes a stress response in the patient, even if pain sensations are completely blocked by successful spinal anesthesia. Most patients require additional sedation. The optimal level is not easy to determine, since too deep sedation can cause hypoventilation, hypoxia, or undetected regurgitation of gastric contents. As a rule, the sedated patient should be easily aroused and retain the ability to maintain verbal communication. In cases where spinal anesthesia is inadequate, it is much better to use selectively general anesthetics and monitor the airway than to resort to high doses of benzodiazepines and opiates.

In the early postoperative period, as in the case of general anesthesia, the patient requires constant careful monitoring of vital functions. He should be transferred to a unit where monitoring is available and trained medical personnel are constantly present to provide emergency care in case of complications. This may be the recovery room or the intensive care unit. In case of hypotension, the nurse should raise the foot end of the bed, give oxygen, increase the rate of intravenous infusion and invite the responsible physician. Additional introduction of vasosprings and an increase in the volume of administered fluid may be required. The patient should be familiarized with the duration of the block and should be clearly instructed not to try to get up until his muscle strength has fully recovered.

Spinal anesthesia for cesarean section

Currently, spinal anesthesia is recognized worldwide as the method of choice for cesarean section. Spinal anesthesia has significant advantages over general anesthesia for cesarean section and combines simplicity, speed of implementation and reliability. It is devoid of such formidable complications, which are the main causes of anesthesiological mortality in obstetrics, as aspiration of gastric contents with the development of Mendelson's syndrome and difficulties in tracheal intubation accompanied by hypoxia. Such widespread use of regional anesthesia is also explained by the fact that the calculated risk ratio for fatal complications with general and regional anesthesia is 17:1. In Great Britain, against the background of an increase in the frequency of fatal outcomes from 20 cases per 1 million cesarean sections in 1979-1984 to 32 in 1985-1990, a decrease is noted among those operated on under spinal anesthesia from 8.6 to 1.9 cases. In addition, spinal anesthesia has a more favorable effect on the condition of newborns compared to general anesthesia. Children born under spinal anesthesia do not receive sedatives through the placenta and are less susceptible to respiratory depression. The assessment of the condition of newborns on the Apgar scale after cesarean section under regional anesthesia is significantly higher than after operations under general anesthesia. At the same time, there are a number of objective difficulties. Spinal anesthesia is technically more difficult to perform in a pregnant woman due to the fact that the enlarged uterus prevents flexion of the lumbar spine. If labor has already begun, the woman will not be able to sit up straight during contractions. Until spinal anesthesia began to use sufficiently thin (25 gauge) needles, the incidence of post-puncture headaches was unacceptably high. Spinal anesthesia should not be performed during cesarean section unless the anesthesiologist has sufficient experience.

In the absence of hypovolemia due to bleeding, spinal anesthesia can be a simple and safe method of pain relief for manual removal of placental remnants from the uterine cavity without causing relaxation of the uterus.

Choosing a Local Anesthetic

Although the local anesthetic lidocaine continues to be actively used in the republic, it is gradually giving way to bupivacaine and ropivacaine due to the high degree of differentiation of the block, that is, when the concentration of the latter decreases, the motor block decreases, while maintaining a high level of analgesia.

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Blockade technique

From a technical point of view, spinal anesthesia in a pregnant woman does not differ from that in general surgical practice, but it requires taking into account a number of factors. Usually, in pregnant patients, before this anesthesia, it is recommended to perform an infusion preload with crystalloid solutions in a volume of at least 1500 ml or 500-1000 ml of hydroxyethyl starch preparations. After infusion of the latter, the volume of circulating blood and cardiac output are higher, the incidence of arterial hypotension is lower, and the time for creating a preload is significantly shorter, which is important in emergency situations.

Although spinal anesthesia is not contraindicated in moderate preeclampsia, remember that preeclampsia is often associated with coagulation system insufficiency and relative hypovolemia. In addition, there is always a risk of sudden seizures, which makes it necessary to prepare a set of anticonvulsants (diazepam, thiopental) in advance.

The most preferable intervals for puncture are L2-L3. To ensure cesarean section, the block height should reach the level of Th6 (the level of the base of the sternum). In most cases, it is sufficient to administer local anesthetics in the following volumes; the use of hyperbaric solutions is preferable: 2.0-2.5 ml of 0.5% hyperbaric solution of bupivacaine, or 2.0-2.5 ml of 0.5% isobaric solution of bupivacaine, or 1.4-1.6 ml of 5% hyperbaric solution of lidocaine, or 2.0-2.5 ml of isobaric solution of lidocaine with the addition of adrenaline (0.2 ml of solution diluted 1:1000).

Mandatory monitoring of the following parameters: BPsys, BPdias, heart rate, respiratory rate, Sa02, fetal cardiac activity and uterine contractions.

Position of the pregnant patient

A pregnant patient should never be in a supine position, as the large uterus, under the force of gravity, can compress the inferior vena cava, and to a lesser extent the aorta, leading to dangerous hypotension. It is necessary to ensure sufficient lateral tilt, which can be achieved by tilting the operating table or placing a cushion under the right side. This tilts the uterus to the left and does not compress the inferior vena cava.

As in any other case, during surgery under spinal anesthesia, the patient should be given oxygen inhalation via a face mask. If hypotension develops despite the infusion preload, vasopressors can be used, among which ephedrine is the drug of choice, since it does not cause spasm of the uterine vessels. If it is not available, other vasopressors can be used, since hypotension can seriously harm the fetus. After delivery, syntocinon is preferable among oxytocin drugs, since it causes less vomiting than ergometrine.

Complications after spinal anesthesia

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Infection

It occurs extremely rarely, provided that the rules of asepsis are strictly observed.

Hypotension

It is the result of vasodilation and functional reduction of the effective volume of circulating blood. Maternal hypotension can lead to deterioration of the blood supply to the myometrium, weakening of labor activity and intrauterine hypoxia of the fetus, which requires immediate implementation of a number of measures:

1. Check the adequacy of the uterine displacement to the left (lateral tilt of the operating table to the left or a cushion under the right buttock, the minimum lateral tilt should be at least 12-15°).
2. All patients who develop hypotension should be given oxygen via a face mask until blood pressure is restored. Elevate the legs to increase venous return by raising the bottom of the operating table. Tilting the entire operating table can also increase venous return, but this will cause hyperbaric local anesthetic to spread through the spinal canal, increasing the level of the block, and worsening hypotension. If an isobaric solution was used, tilting the table will not significantly affect the height of the block.
3. Increase the rate of intravenous fluid administration to maximum until blood pressure is restored to an acceptable level.
4. If there is a sharp decrease in blood pressure and no response to the infusion load, administer ephedrine intravenously, which causes constriction of peripheral vessels and increases cardiac output due to the frequency and force of myocardial contraction, without reducing placental blood flow. Dilute the contents of the ampoule (25 mg) to 10 ml with saline and administer fractionally by 1-2 ml (2.5-5 mg), focusing on the effect on blood pressure. It can be added to a bottle with an infusion medium, while its effect is regulated by the infusion rate, or administered intramuscularly, but this slows down the development of the i-effect. Fractional administration of adrenaline (50 mcg) or infusion of norepinephrine in appropriate doses is possible. If hypotension persists, vasopressors should be used immediately; in case of bradycardia, atropine should be administered.

Headache after spinal anesthesia

One of the typical complications of spinal anesthesia is post-puncture headaches. They develop within a few hours after the operation and can last for more than a week, are usually localized in the occipital region, and may be accompanied by stiffness of the neck muscles. They are often associated with nausea, vomiting, dizziness, and photophobia. It is believed that their cause is associated with the leakage of cerebrospinal fluid through the puncture hole in the dura mater, which results in tension of the meninges and pain. It is believed that needles with a small diameter (25 or more G) and a tip shape similar to a sharpened pencil make a hole in the dura mater of a smaller diameter and are able to reduce the frequency of headaches compared to conventional needles with a cutting tip.

Patients suffering from headaches after a procedure such as spinal anesthesia prefer to remain lying down. Previously, it was believed that in order to prevent headaches, the patient should remain in bed for 24 hours after spinal anesthesia. Recently, it is believed that this is not necessary, the patient can get up if there are no surgical obstacles.

They should not be restricted in fluids, if necessary, it can be added intravenously to maintain adequate hydration. Simple analgesics such as paracetamol, aspirin or codeine can be useful, as well as all measures that increase intra-abdominal and with it epidural pressure (turning to the stomach). Migraine remedies can be effective, as well as drinks containing caffeine (coffee, cola, etc.).

Urinary retention may occur because the sacral autonomic nerve fibers are among the last to recover function after spinal anesthesia. Overfilling and painful overdistension of the bladder may require bladder catheterization.

Total block develops rapidly and can lead to death if not recognized in time and resuscitation measures are not initiated. Spinal anesthesia is complicated by this condition relatively rarely, and is more often the result of erroneous intrathecal administration of anesthetic. Clinical manifestations of total block include loss of sensation or weakness in the arms, difficulty breathing, and loss of consciousness. The algorithm for providing emergency care includes:

1. Cardiopulmonary resuscitation measures.
2. Tracheal intubation and mechanical ventilation with 100% oxygen.
3. Treatment of hypotension and bradycardia with intravenous fluid loading, atropine and vasopressors. If treatment is not timely, the combination of hypoxia, bradycardia and hypotension can quickly lead to cardiac arrest.
4. Artificial ventilation, which should be continued until the block resolves and the patient can provide the required minute ventilation volume without assistance. The time required for this will depend on which local anesthetic was administered and its dose.

Spinal anesthesia: consequences

The needle appears to be in the correct position, but no CSF appears. Wait at least 30 seconds, then try rotating the needle 90 degrees and replacing it. If no CSF appears, attach an empty 2 ml syringe and inject 0.5-1 ml of air to make sure the needle is not blocked, then slowly pull the needle back while continuously aspirating the contents with the syringe. Stop as soon as CSF appears in the syringe.

Blood is obtained from the needle. Wait a little, if the blood is diluted and cerebrospinal fluid appears - everything is fine. If pure blood is released, most likely the tip of the needle is in the epidural vein and it should be advanced a little further to reach the dura mater.

The patient complains of a sharp stabbing pain in the leg. The tip of the needle rests against the nerve root due to the needle having shifted laterally.

Pull the needle and change its direction more medially in relation to the damaged side.

Wherever the needle is directed, it hits the bone. Make sure the patient is in the correct position, their spine is maximally bent in the lumbar region, and the point of needle insertion is located in the midline. If you are unsure of the correct position of the needle, ask the patient on which side they feel the prick. If you have to deal with an elderly patient who cannot bend their back sufficiently or whose interspinous ligament is heavily calcified, the paramedian approach can be used as an alternative. To do this, insert the needle 0.5-1 cm lateral to the midline at the level of the upper border of the underlying spinous process and direct it cranially and medially. If, as you advance the needle, it hits the bone, then most likely it is the vertebral arch. Try to reach the epidural space, moving step by step along the bone, and puncture the dura mater through it. When using this technique, it is recommended to first anesthetize the muscles through which the needle is inserted.

The patient complains of pain after spinal anesthesia and during needle insertion. Most likely, the needle passes through the muscles on one side of the interspinous ligament. Pull the needle and change its direction more medially in relation to the side where the pain was felt so that the needle is in the midline, or inject a small amount of local anesthetic for pain relief.