Spinal anaesthesia technique

2021-05-15 10:45 PM

The golden ligament, this ligament is usually stiff, extending from the neck area to the lumbar spine. When poked, it creates strong resistance and that is a sign of when poked through it.

Outline

Spinal anaesthesia is a method of regional anaesthesia, which is performed by injecting a local anaesthetic into the cerebrospinal fluid, the anaesthetic will restore the conduction of nerve roots, these nerve roots are not covered. by the nerve sheath and contact with local anaesthetic in the cerebrospinal fluid.

Recall anatomy

Spine

S-shaped curvature of the spine extending from the foramen occipital to the apex. Consists of 33 vertebrae fused together (7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, 5 sacral vertebrae, 4 coccyx) forming 4 different curved segments: Neck arched forward, thoracic arch posteriorly, the waist is curved anteriorly, and the same segment is convex posteriorly (pictured).

The most curved points of the spine are also the easiest places to move, so it is easy to insert the needle during anaesthesia.

The structure of each vertebra includes vertebral body, vertebral foramen, transverse process, spinous process, vertebral arch, superior and inferior articular processes.

Between two adjacent vertebrae forming an intervertebral gap, this gap is wide or narrow depending on each segment. The spinous process is almost horizontal at the lumbar segment, so it is convenient for lumbar puncture. In other areas, the spine is inclined downward, making it difficult to poke.

 

 

Figure. Longitudinal section of the spine.The ligaments and meninges

From outside to inside include (picture):

Skin, subcutaneous organization.

Spinal ligament (usually narrow and fibrotic in the elderly).

Interspinous ligament.

The golden ligament (this ligament is usually stiff, extending from the neck area to the lumbar spine). When poked creates strong resistance and that is a tell-tale sign when poking through it.

The dura mater and arachnoid are close to the inside of the yellow ligament.

The membrane is close to the spinal cord.

 

Figure. The spine is straight, inclined.

The compartments

Epidural space:

As a virtual cavity, the anterior limit is the dura mater, behind is the yellow ligament, containing many connective tissues, fat, and blood vessels.

Subarachnoid space:

Surrounds the spinal cord, located between the arachnoid and choroidal membranes. Communicating with the superior via the ventricles. This cavity contains nerve roots and cerebrospinal fluid.

Cerebrospinal fluid

Cerebrospinal fluid is produced from the choroid plexus of the fourth ventricle. Cerebrospinal fluid flows through the foramen of Luchka to the surface of the brain and through the foramen of Magendic to the spinal cord. Cerebrospinal fluid is absorbed from the villi of the arachnoid membrane.

The amount is about 120 - 140ml or about 2ml/kg, in newborns is 4ml/kg, in which the ventricles contain about 25ml.

Density varies from 1.003 - 1.009, pH is about 7.39 - 7.5.

Ingredients: Glucose from 40 - 80mg/dl, protein from 15 - 45mg/dl, Na+ from 140 - 150mEq/l, K+ 2.8mEq/l.

In the supine position, the pressure is about 60 - 150mmH2O.

spinal cord

The spinal cord continues from the brain through the occipital foramen to the spinal canal, usually ending at L1-2.

The arterial system supplying the spinal cord is located in the anterior aspect of the spinal cord, so there are few complications during spinal anaesthesia. While in the neck there are 4 to 8 arteries supplying the spinal cord, in the thoracic region there is only one artery so there is a high risk of marrow ischemia.

Levels of pain sensation inside and outside the spinal cord

It is necessary to grasp the level of control of pain, movement and autonomic nerves to the viscera to ensure anaesthesia for a specific surgery and ensure patient safety in the true sense of "regional anaesthesia".

Sensory, motor, and autonomic control of the spinal cord depends on the level of the respective spinal vertebrae. This gives us the concept of the dominant medulla oblongata and the needlepoint. If the point of needle puncture coincides with the medullary zone that dominates the surgical area, it is easy to guarantee the success of the technique, but usually, there is a difference between the medullary zone that dominates the surgical area and the point of needle puncture. Then it requires an appropriate combination of factors such as volume, patient position, the density of anaesthetic, injection speed... to ensure the success of the technique.

Figure. The diagram that governs sensation in the skin.

The shoulder region is innervated by the brachial plexus.

The diaphragm is innervated by branches from C4.

The sternal depression of the abdomen is dominated by D8.

The navel area is dominated by D10.

The inguinal region is dominated by D12.

There are 3 types of feelings:

The sense of awareness is never completely lost

The sensation of heat and cold takes the same degree of pain relief to surgery.

The pain sensation caused by forceps is sometimes confused with the sensation of touch, so when pinching the skin it is necessary to ask the patient if there is pain.

Some other signs to know: if the patient has a slow heart rate, the inhibition level has reached D4-D5, and if the patient feels numb and cannot count with the thumb, the pain relief level has reached C8-D1.

Indications and contraindications

Point

Lower abdominal surgery: At the navel or below, eg appendectomy.

Obstetric and gynaecological surgeries: Hysterectomy, ovarian cyst removal, fallopian tube catheterization, caesarean section...

Lower limb surgeries: Orthopaedic, vascular, amputation, skin graft...

Urological surgery: Laparoscopic removal of prostate cancer through the urethra, bladder stones, ureter stones, even kidney stones.

Perineal surgery: Bartholin's cyst, anal fissure, haemorrhoids...

Contraindications

Absolute contraindication

The patient refused.

Lack of adequate circulating volume, shock.

Blood clotting disorder or taking anticoagulants.

Infection at the puncture site, bacteraemia.

Anatomical abnormalities for which a lumbar puncture cannot be performed.

Severe heart disease.

Increased intracranial pressure.

Anaesthesia allergy.

Relative contraindications

Headache and spine.

Osteoarthritis, cancer metastasis to bone.

Coronary heart disease, myocardial infarction.

Cerebral vascular sclerosis.

Severe high blood pressure or very low blood pressure.

Children are too small to do.

Mechanism of action

The time for the anaesthetic to penetrate into the nerve tissue occurs quickly and is reached quickly within the first 5 to 10 minutes after the injection (depending on the type of anaesthetic).

If 2ml of 5% lidocaine is mixed into 120-140ml of cerebrospinal fluid, it will form a solution of 1/10000, the anaesthetic will not work. But in fact, local anaesthetic is only diluted at the injection site with the highest concentration. Nerve roots arising from the spinal cord that are not covered by the nerve sheath (an epineurium) come into direct contact with the local anaesthetic in the cerebrospinal fluid. As a result, afferent and afferent nerve impulse conduction are inhibited. Local anaesthetics can also inhibit the spinal cord surface but play a minor role in spinal induction.

Some pharmacological problems

Definition of weight, specific gravity, density

Weight is the mass in grams of 1 ml of solution at a specific temperature, specific gravity is the ratio of the weight of a solution to the weight of water at the same temperature, density is the ratio of weight a solution of local anaesthetic relative to the weight of cerebrospinal fluid at the same temperature.

Local anaesthetic solution with density < 0.9998 at 370C is called low density, > 1.009 is called high density, within the upper limit is called isograft. However, this also depends on the weight of the CSF in each individual.

Local anaesthetics commonly used in spinal anaesthesia are bupivacaine, lidocaine, tetracaine..., usually, the anaesthetic is mixed with saline solution to create an isotonic and usually isotonic solution. 0.5% bupivacaine solution is a low vapour density solution, 2% lidocaine solution is a high vapour density solution. These solutions are often added with 10% dextrose to form solutions with specific gravity > 1.008. Low densities are usually produced by mixing local anaesthetics with water to produce a solution with a density < 0.9998.

Factors affecting the onset of action

The onset of action depends on pKa, solution pH, dose or concentration, nerve type, pKa as well as pH of the anaesthetic solution which determines the degree of ionization of each drug, the degree of ionization. Since drugs in the alkaline form are not charged, they are more permeable to the cell membrane than charged cations.

Myelinated nerve fibres have a slower onset of action than unmyelinated fibres, similarly, larger diameter fibres are slower. High doses have a faster onset of action than low doses.

Factors affecting the duration of anaesthesia

The duration of analgesia depends on the type of anaesthetic, the dose, and the presence of a vasoconstrictor. The duration of action of local anaesthetics depends on lipid solubility and protein binding. The higher the lipid solubility and protein binding, the longer the duration of action.

The duration of action is ranked from lowest to highest as follows: procaine < lidocaine < bupivacaine < tetracaine < dibucaine. The higher the dose, the longer the duration of action. Adding vasoconstrictors such as epinephrine and phenylephrine increases the duration of action due to vasoconstriction, slowing absorption. Ephedrine (1:1000), 200 - 500 mg or phenylephrine (1%), 2 - 5 mg are used to prolong the duration of anaesthesia.

Factors affecting the distribution of local anaesthetics

Many factors affect the distribution of local anaesthetics in the cerebrospinal fluid. Most important are the density, dose, shape of the spinal canal and the position of the patient during and immediately after the injection of an anaesthetic.

Includes the following elements:

Patient characteristics: Age, sex, weight, height, spine shape.

Technique: Placement of puncture, the direction of needle bevel, pump speed, patient position.

Cerebrospinal fluid: Composition, circulation, volume, pressure, weight.

Aesthetic solution: Density, dosage, volume.

The most important factor is the proportion of local anaesthetic. To ensure local anaesthesia in the surgical area (lower abdomen, lower extremities), it is necessary to combine position changes when using high-density drugs.

Anaesthesia technique

Prepare the patient

Morale

Spinal anaesthesia is a technique that requires good cooperation of the patient. Therefore, communicating and explaining to the patient is essential.

Infusion before anaesthesia

A systematic intravenous infusion is required prior to anaesthesia. Pre-infusion has two purposes:

Make up for the fluid that the patient lacks before surgery due to fasting, drinking or dehydration.

Preparation for volume compensation due to vasodilation after anaesthesia.

Usually, this volume is from 10 to 15 ml/kg of isotonic crystalline solution.

Prepare means and medicine

Emergency resuscitation equipment

Ambu ball, oxygen mask, intubation lamp, an endotracheal tube with numbers, canuyn Guedel, monitor, ventilator (if possible).

Prepare medicine

Emergency drugs: Atropine, ephedrine, dimedron, adrenaline, dopamine...

Anaesthesia: Anaesthesia, muscle relaxant, analgesic.

Anaesthetics: Xylocaine 5%, pethidine, Marcaine 0.5%, fentanyl...

Infusion solutions: Crystalline solution, colloidal solution.

Instruments for spinal anaesthesia

Sterile trays include Holes, syringes of all sizes, antiseptic forceps, 0.5% - 1% iodine alcohol, white alcohol or betadine, povidine...

Spinal puncture needle numbers 25G, 27G, 29G. The smaller the needle, the less damage to the organization and the loss of cerebrospinal fluid. Needles from 27G – 29G must have a guide needle.

Patient Pose

Usually, there are 2 positions:

Sitting position (Figure 6.4): Let the patient sit with his back arched, chin resting on his knees. This position may be easier to identify the vertebrae but often causes low blood pressure or discomfort for the patient, often for obese people.

Lying on the side with the arched back (Figure 6.5): The knees are pressed against the abdomen; the chin is pressed against the chest. Usually reserved for elderly and frail patients to avoid hypotension, fainting, fainting, irritability....

Figure. Sitting position and lying position.

How to determine the poke location

Usually poked in the gap between 2 vertebrae so the puncture location will depend on high or low surgery. Usually poke from L2-3 to L4-5, the line connecting the two anterior superior iliac spines of the pelvis usually passes through L4-5, then using the finger to move upwards will see the L3-4 and L2-3 slits. On the contrary, it can be determined from the top down by taking the base of the lower back, which will be equivalent to L1-2 and then determining it downwards.

Antiseptic

Use alcohol to disinfect the needle puncture area 2 to 3 times, then dry and cover the hole with a towel.

Spinal cord puncture

People who puncture the spinal cord: Wear a mask, wash your hands, wear a shirt, wear gloves. There are two punctures: the midline (Figure 9.6) and the lateral line: The puncture site is 1.5 - 2cm away from the midline, directing the needle to the midline, up and forward. Local anaesthesia of the puncture site with xylocaine 0.5 - 1%.

Using an 18G needle to guide, poke 1-2cm deep.

 

Figure. Middle line.

Using a spinal needle, insert the needle 3 - 5cm through the guide needle (the needle bevel is up when the patient is lying down, the needle is lying on the side when the patient is sitting) withdraw the needle if there is CSF leakage, it means the needle is in the lower space spider (the smaller the needle, the slower the CSF outflow). The dose of anaesthetic injected into the spinal cord depends on the dose for each patient and then the needle is closed. The injection rate is 5-10 seconds for each millilitre of anaesthetic solution.

For example, bupivacaine at a dose of 0.2 mg/kg generally does not exceed 15 mg. To reduce the dose and still be sufficient for surgery, it is recommended to add 10 mg of fentanyl to the local anaesthetic solution bupivacaine. The older the patient (65 years of age and older), the more the dose should be reduced.

When using a 25G needle for a spinal puncture, there is no need to use a guide needle.

Complications

Complications of lumbar puncture

Failure

Cannot be poked due to calcification, spinal degeneration, kyphosis, curvature. It is possible to switch to lateral puncture or switch to another method of anaesthesia.

Poking the nerve roots

When performing the puncture, the patient may feel sharp pain, jerking of the leg on one or both sides. I pulled out the needle and poked another place.

Poke into a blood vessel

If the needle has to bleed, we wait a while, if the blood becomes thinner and clear again, we inject the drug. If bleeding continues, remove the needle and puncture another site.

After lumbar puncture

Low blood pressure and slow pulse

Due to the sympathomimetic effect causing vasodilation, if inhibiting the sympathetic nerves that supply the heart, it will cause bradycardia and lower blood pressure.

Precaution: Pre-infusion 500 to 1000ml of 0.9% Nacl solution or ringer lactate solution prior to lumbar puncture.

Treatment: If blood pressure is low, elevate legs to improve return, or administer 5 - 10 mg intravenous ephedrine may be repeated if necessary.

Rehydrate crystalloids 500 - 1000ml according to blood pressure or colloid (gelofusine, HEA 6% - 10%). Atropine (0.5 - 1mg) if pulse is slow. If blood pressure is not up, adrenaline can be used.

Nausea and vomiting

Usually due to hypotension or changes in intracranial pressure or side effects of drugs (morphine family).

Treatment: raise blood pressure with fluid replacement and ephedrine or antiemetics (primperan, atropine...).

Headache

Headache occurs after 24 - 48 hours, due to a tear in the dura and loss of cerebrospinal fluid. Young people are more affected.

Precautions: Use the needle as small as possible, when making the right puncture to bevel the needle without cutting the wide dura to avoid leakage of cerebrospinal fluid.

Administer fluids first to ensure circulating volume.

Treatment: Lying motionless at the bed, avoiding stimulation, rehydration, using analgesics, caffeine 200-400mg intravenously, if no improvement can be repeated after 3 hours or taken orally.

Using the Blood-Patch method: By taking about 10-20ml of the patient's blood and then injecting it into the epidural space with the needle to close the hole to prevent the cerebrospinal fluid from escaping.

Urinary retention

Usually due to side effects of local anaesthetics and especially morphine. The drug increases the tone of the bladder neck sphincter and inhibits the plexus along with urinary retention.

Management: Apply heat, use prostigmine, catheterize and pump xylocaine into the bladder.

Back pain

Due to damage to ligaments or skin, subcutaneous tissue.

Precaution: Poke a small needle, avoid poking many times.

Treatment: Use painkillers and sedatives as above.

Neurological complications

Injury to one or more nerve roots causing dysesthesia or hyperalgesia, cauda equina syndrome, meningitis - encephalitis due to infection, possibly paralysis due to spinal cord injury or anaesthesia or compression by hematoma pressure on the nerve.

Treatment: Use pain relievers, sedation if mild. If you have an infection syndrome, you must use antibiotics, if you are pinched, you must have surgery to release the compression.

It is important to ensure absolute sterility (drugs, techniques) and respect contraindications.