Spinal Anesthesia

Generality

Spinal anesthesia is a technique of local anesthesia, characterized by the injection of anesthetics and analgesics at the level of the subarachnoid space of the spinal cord.

Its purpose is to cancel the painful sensation in the lower back and along both lower limbs.

The medical circumstances that may require performing a spinal anesthesia are some surgical procedures, such as: knee or hip orthopedic operations, inguinal hernia operations, hysterectomy, etc.

Spinal anesthesia is usually performed by a doctor who specializes in local and general anesthesia, that is, the anesthesiologist.

Spinal anesthesia is a safe, effective method that does not involve the patient falling asleep.

Brief review of the spinal cord

The spinal cord represents, together with the brain, one of the two main components that constitute the so-called central nervous system ( CNS ), the most important part of the entire nervous system of the human being.

The spinal cord resides inside the spinal column, a bone structure formed by 33-34 overlapping bones and known as vertebrae . Each vertebra has a hole, called a spinal hole or a vertebral hole ; all together, the holes of each vertebra form a long channel, the so-called spinal canal, within which the spinal cord takes place.

Interposed between the spinal cord and the internal walls of the spinal canal, there are three superimposed membranes, with a protective function, generally called meninges . The outermost meninge is the dura mater ; the central meninge is the arachnoid ; finally, the innermost meninge is the pious mother .

What is spinal anesthesia?

Spinal anesthesia is a type of local anesthesia, which involves the injection of anesthetics and analgesics at the level of the spinal canal, specifically in the subarachnoid space of the spinal cord.

The subarachnoid space of the spinal cord is the space filled with cerebrospinal fluid (or cerebrospinal fluid or CSF ), included between the meninge called arachnoid and the meninge known as dura mater.

WHO ENCOUNTERS AND WHERE HAS A SITE

Like most anesthesia techniques, spinal anesthesia is the responsibility of a specialist doctor: the anesthesiologist .

Generally, its realization takes place in a hospital setting, generally in an operating theater.

IS IT DIFFERENT FROM EPIDURAL ANESTHESIA?

Despite what many believe, spinal anesthesia and epidural (or simply epidural ) anesthesia are two different types of local anesthesia.

In the case of epidural anesthesia, the anesthesiologist injects anesthetics and analgesics into the so-called epidural space .

The epidural space is the space between the outer surface of the dura mater of the spinal cord and the internal bone wall of the spinal canal, formed by the vertebral holes.

In the epidural space there are lymphatic vessels, spinal nerve roots, loose connective tissue, adipose tissue, small arteries and a network of venous plexuses.

uses

In general, the purpose of a local anesthesia is to cancel the pain sensation in a specific anatomical area of the human body, without putting the patient to sleep.

In the specific case of spinal anesthesia, the purpose of the latter is to cancel the sensitivity to pain in the lower back and along all the lower limbs.

After this necessary premise, the medical circumstances that, for the pain they produce, generally require the use of spinal anesthesia are:

Orthopedic surgery on the hip, knee, femur and leg bones (tibia and fibula)
Hip prosthesis and knee prosthesis operations .
Surgery of inguinal hernia and epigastric hernia .
Caesarean section .
Endovascular treatment for repair of an abdominal aortic aneurysm .
Vascular surgery in the lower limbs.
Hemorrhoidectomy operations.
Surgical treatments for varicose veins .
TURP interventions (Trans-Urethral Resection of the Prostate).
Bladder and genital organs surgery.
Hysterectomy operations.

Curiosity

The annulment of the painful sensation extended to the whole body and the sleep of the patient are a prerogative of the so-called general anesthesia .

Preparation

Regarding the preparatory phase, the practice of spinal anesthesia requires that, on the day of the procedure, the patient presents himself fasting from solid foods for at least 6-8 hours and fasting from liquids for at least 2-3 hours.

Procedure

The first step in the correct execution of a spinal anesthesia is that the patient, once he has settled on a hospital bed, takes a position with his back that allows anesthetic and analgesic injection into the subarachnoid space. The positions that make it possible to reach the subarachnoid space, through the tools for pharmacological infusion, are two:

Sitting position, with the back bent forward.
Position lying on one side and with knees bent.

These two positions of the body favor the insertion of the instruments for injection, because they "open" those spaces between the vertebrae, in which the anesthesiologist will have to infuse the anesthetics and analgesics.

The phase dedicated to the placement of instruments for pharmacological infusion consists of three stages:

Injection point sterilization . The anesthesiologist will sterilize by rubbing a small cloth or piece of cotton in the area of interest, soaked in a sterilizing solution.
The insertion in the spinal canal, through the perforation of the skin, of a needle-cannula . A generic needle-cannula is a hollow needle, of discrete dimensions, which allows the passage inside it of small tubes (or catheters) for the infusion of drugs.
The introduction of a small plastic tube - the so-called spinal catheter - inside the cannula needle and its placement in the subarachnoid space. The spinal catheter is the instrument for the infusion of anesthetics and analgesics.
The anesthesiologist initiates the pharmacological injection only once he has properly placed the spinal catheter.

Generally, after a few minutes from the beginning of the pharmacological infusion, the anesthesiologist tests the effects of anesthetics on the patient, to realize if everything is proceeding correctly.

A classic test for evaluating the effects of anesthesia is to spray a cold spray solution on the anesthetized areas and to ask the patient for a description of the sensation.

When the pharmacological infusion is no longer necessary (for example at the end of the caesarean section), the anesthesiologist interrupts the anesthetic and analgesic administration and first withdraws the spinal catheter and then the needle-cannula.

IS THERE A PRECISE POINT FOR INJECTION?

During a spinal anesthesia, the insertion of the cannula needle for the introduction of the spinal catheter occurs at the level of the second lumbar vertebra or lower.

By practicing insertion in higher positions, the anesthesiologist is more likely to puncture or pinch the spinal cord with the needle-cannula, causing damage to it.

SENSATIONS AND TYPICAL EFFECTS OF A SPINAL ANESTHESIA

When the anesthesiologist inserts the needle-cannula or the spinal catheter, the patient may experience a slight discomfort, at the level of the insertion zone.

In some circumstances, it is even possible that the placement of the spinal catheter determines a sensation similar to an electroshock: this occurs when the plastic tube grazes the roots of the spinal nerves (or peripheral nerves).

Typically, shortly after the injection of anesthetics and analgesics begins, the patient begins to experience a warm numbness in the lower back and along both lower limbs. Furthermore, it warns that the legs gradually become heavier and more difficult to move.

Usually, the maximum effects of drugs used for spinal anesthesia can be appreciated as early as 5-10 minutes after administration.

It is highly probable that anesthetics cancel bladder sensitivity . From this it follows that the patient is unable to "feel" if the bladder is full and if he needs to urinate.

How important is the anesthetic dose on blocking the pain sensation?

The greater the dose of anesthetics injected to the patient, the greater the degree of insensitivity to pain.

Thus, there is a direct correlation between the administered anesthetic dose and blockage of sensory signals, which relate to pain.

DURATION OF EFFECTS

The effects of spinal anesthesia last as long as the anesthesiologist is administering anesthetic and analgesic drugs.

At the end of the administration, the sense of numbness in the lower limbs, the insensitivity to pain and the feeling of heaviness in the legs begin to fade gradually, until the complete disappearance.

In general, the patient must wait 1 to 3 hours before the situation returns to normal.

Parallel to the disappearance of the sense of numbness, insensitivity to pain and heaviness in the legs, the progressive recovery of bladder sensitivity also takes place.

Main differences between spinal anesthesia and epidural anesthesia:

Spinal anesthesia produces the same anesthetic and analgesic effects as epidural anesthesia, with lower pharmacological quantities (spinal anesthesia of 1.5-3.5 milliliters is equivalent to an epidural of 10-20 milliliters).
The effects of spinal anesthesia appear faster, compared to the effects of epidural anesthesia.
If the injection due to spinal anesthesia can only occur below the second lumbar vertebra, an epidural injection can take place in any section of the spine (cervical, thoracic, lumbar or sacral).
The procedure for placing the plastic tube, for pharmacological injection, is simpler in the case of an epidural.

AFTER A SPINAL ANESTHESIA

After a spinal anesthesia, the patient must remain at rest, in a sitting or lying position, for a short period. Generally, it is a rest of a few hours.

During this time, the medical staff offers maximum assistance to the patient and periodically monitors the vital parameters (blood pressure, heart rate, body temperature, etc.).

If the patient feels pain at the insertion point of the needle-cannula, the doctor may resort to administering painkillers, such as paracetamol.

DRUGS USED

The typical anesthetics, used for spinal anesthesia, are: bupivacaine (the most common), tetracaine, procaine, ropivacaine, levobupivacaine, lidocaine and prilocaine.

The most common analgesics, however, are: fentanyl, sufentanil.

Risks and complications

Spinal anesthesia is a technique of safe local anesthesia, which, in general, causes complications very rarely.

Among the most common adverse effects, spinal anesthesia includes:

Hypotension . Hypotension is the most frequent adverse effect of spinal anesthesia. It is caused by anesthetics, which, in addition to "blocking" the nerve endings that regulate pain, also "block" the nerve endings of the blood vessels.
Skin itching . It can result from the combination of anesthetic drugs and analgesic drugs.
Urinary retention . It is the inability to voluntarily or completely empty the bladder. This complication represents a possible effect of bladder sensitivity impairment, induced by anesthetics.
Strong headache . The headache from spinal anesthesia appears when the anesthesiologist accidentally stings the dura mater of the spinal cord, causing a small damage.
It is a complication that occurs once every 200-300 spinal anesthesia around.
Annoying pain at the time of insertion of the needle-cannula or spinal catheter.
Formation of a hematoma at the level of the spinal canal . It is a collection of blood in the spinal canal, which can, in some cases, go on to compress the spinal nerve roots located nearby. The presence of a compression of the roots of the peripheral nerves involves the onset of neurological disorders.
Development of an infection at the injection site . It is a complication that can develop several weeks after the operation that made spinal anesthesia necessary.
Spinal epidural abscess can result from such infections. Spinal epidural abscesses are dangerous because they could cause neurological damage to peripheral nerve roots.
Such neurological damage can compromise the ability to move the lower limbs (paraplegia).

As for the more unusual complications, these consist mainly of:

Allergic reactions to anesthetic drugs or analgesics used. This can lead to the onset of breathing difficulties in the patient.
Permanent damage to the nerve components of the bone marrow, whether these are the roots of the spinal nerves or otherwise. This rare complication occurs once every 50, 000 operations involving spinal anesthesia.
Cardiac arrest . The chances of cardiac arrest occurring increase, if the patient's general health conditions are precarious.

Contraindications

Doctors believe that spinal anesthesia cannot be performed when:

The patient has an infection at the level of the injection site, therefore at the lumbar level.
The patient suffers from some congenital coagulation disease, which predisposes to bleeding. One of the best known congenital coagulation disorders is haemophilia .
The patient is taking an anticoagulant drug, such as warfarin . This type of recruitment predisposes to bleeding.
The patient suffers from neurological problems due to some spinal cord malformation. One of the best known spinal cord malformations is spina bifida .
The patient has some serious spinal deformity or suffers from a severe form of arthritis in the spine .