Spinal anesthesia

Generality

Spinal anesthesia is a local anesthesia technique, characterized by the injection of anesthetics and analgesics into 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 the performance of a spinal anesthesia are some surgical interventions, such as: orthopedic operations on the knee or hip, inguinal hernia operation, hysterectomy etc.
Spinal anesthesia is usually performed by a doctor specialized in local and general anesthesia practices, ie the anesthetist.
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 make up the so-called central nervous system (CNS), the most important part of the entire nervous system of the human being.
The spinal cord resides within the spinal column, a bony structure made up of 33-34 superimposed bones known as vertebrae. Each vertebra has a hole, called the spinal hole or vertebral hole; all together, the holes in each vertebra they form a long canal, the so-called spinal canal, within which the spinal cord takes place.
Interposing between the spinal cord and the internal walls of the spinal canal, there are three overlapping membranes, with a protective function, generically called meninges. The outermost menynx is the dura mater; the central menynx is the arachnoid; finally, the innermost menynx is the pia mater.

What is spinal anesthesia?

Spinal anesthesia is a type of local anesthesia, which involves the injection of anesthetics and analgesics into the spinal canal, precisely into 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), between the menynx called the arachnoid and the menynx known as the pia mater.

WHO TAKES IT AND WHERE IT IS LOCATED

Like most anesthesia techniques, spinal anesthesia is the responsibility of a specialist doctor: the anesthetist.
Generally, its realization takes place in a hospital setting, usually in an operating room.

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 anesthetist injects the 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 inner bony wall of the spinal canal, formed by the vertebral holes.
In the epidural space reside lymphatic vessels, spinal nerve roots, loose connective tissue, fatty tissue, small arteries and a network of venous plexuses.

Uses

In general, the purpose of a "local anesthesia is to eliminate the painful sensation in a specific anatomical area of the human body, without making the patient fall asleep."
In the specific case of a "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, due to the pain they cause, generally require the use of a "spinal anesthesia are:

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

Curiosity

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

Preparation

As regards the preparatory phase, the practice of spinal anesthesia requires that, on the day of the procedure, the patient has fasted from solid food for at least 6-8 hours and fasted from liquids for at least 2-3 hours.

Procedure

The first step for the correct execution of a spinal anesthesia requires that the patient, once seated on a hospital bed, assumes a position with his back such as to allow the anesthetic and analgesic injection into the subarachnoid space. It is possible to reach the subarachnoid space, using the instruments for pharmacological infusion, there are two:

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

These two body positions favor the insertion of the injection tools, because they "open" those spaces between the vertebrae, where the anesthetist will have to infuse the anesthetics and analgesics.
The phase dedicated to the placement of the instruments for pharmacological infusion consists of three moments:

Sterilization of the injection point. The anesthetist provides for sterilization by rubbing a small cloth or piece of cotton soaked in a sterilizing solution in the area of interest.
The insertion into the spinal canal, through the perforation of the skin, of a needle-cannula. A generic needle-cannula is a hollow needle, of moderate size, which allows the passage of small tubes (or catheters) for the " infusion of drugs.
The introduction of a small plastic tube - the so-called spinal catheter - inside the needle cannula and its placement in the subarachnoid space. The spinal catheter represents the instrument for the infusion of anesthetics and analgesics.
The anesthetist starts the drug injection only once the spinal catheter has been properly placed.

Generally, after a few minutes from the beginning of the pharmacological infusion, the anesthetist tests the effects of the anesthetics on the patient, to realize if everything is proceeding correctly.
A classic test for evaluating the effects of anesthesia consists in spraying a cold spray solution on the anesthetized areas and asking 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 anesthetist interrupts the anesthetic and analgesic administration and first removes the spinal catheter and then the needle cannula.

IS THERE AN ACCURATE POINT FOR THE INJECTION?

During a spinal anesthesia, the insertion of the needle-cannula for the introduction of the spinal catheter takes place at the level of the second lumbar vertebra or lower.
By practicing insertion in higher positions, the anesthetist is more likely to prick or pinch the spinal cord with the needle-cannula, causing damage.

SENSATIONS AND TYPICAL EFFECTS OF A "SPINAL ANESTHESIA

When the anesthetist inserts the needle-cannula or the spinal catheter, the patient may feel a slight discomfort in the insertion area.
In some circumstances, it is even possible that the placement of the spinal catheter causes a sensation similar to an electric shock: this occurs when the plastic tube touches the roots of the spinal nerves (or peripheral nerves).
Typically, shortly after the injection of the anesthetics and analgesics has begun, the patient begins to feel a warm feeling of numbness in the lower back and along both lower limbs. In addition, he feels that the legs gradually become more and more heavy and difficult to move.
Usually, the maximum effects of the drugs used for a spinal anesthesia are noticeable already 5-10 minutes after administration.
Anesthetics are highly likely to nullify 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 in blocking the painful sensation?
The greater the dose of anesthetics injected to the patient, the higher the degree of insensitivity to pain.
Thus, there is a direct correlation between the anesthetic dose administered and the blocking of sensory signals, which relate to pain.

DURATION OF EFFECTS

The effects of a spinal anesthesia last as long as the anesthetist administers the 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 gradually fade, until complete disappearance.
Typically, the patient has to 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:

A "spinal anesthesia produces the same anesthetic and analgesic effects as an" epidural anesthesia, with lower drug rates (a "spinal anesthesia of 1.5-3.5 milliliters is equivalent to a" epidural of 10-20 milliliters).
The effects of a "spinal anesthesia appear faster than the effects of an" epidural anesthesia.
If the injection for a spinal anesthesia can only take place below the second lumbar vertebra, the injection for an epidural 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 rest, in a sitting or lying position, for a short period. Generally, this is a rest lasting a few hours.
During this time, the medical staff offers maximum assistance to the patient and periodically monitors his vital parameters (blood pressure, heart rate, body temperature, etc.).
If the patient feels pain at the point of insertion of the needle-cannula, the doctor may resort to the administration of painkillers, such as paracetamol.

DRUGS USED

Typical anesthetics used for spinal anesthesia are: bupivacaine (the most common), tetracaine, procaine, ropivacaine, levobupivacaine, lidocaine and prilocaine.
The most common analgesics, on the other hand, are: fentanyl, sufentanil.

Risks and complications

Spinal anesthesia is a safe local anesthesia technique which, in general, causes complications very rarely.
The most common adverse effects of a "spinal anesthesia include:

Hypotension. Hypotension is the most frequent adverse effect of spinal anesthesia. To induce it are anesthetics, which, in addition to "blocking" the nerve endings that regulate pain, also "block" the nerve endings of blood vessels.
Itchy skin. 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 anesthetic-induced impairment of bladder sensitivity.
Bad headache. The headache from spinal anesthesia appears when the anesthetist inadvertently pricks the dura mater of the spinal cord, causing little damage.
It is a complication that occurs about once every 200-300 spinal anesthesia.
Annoying pain when inserting the needle cannula or spinal catheter.
Formation of a hematoma in the spinal canal. It is a collection of blood in the spinal canal, which can, in some cases, compress the roots of the spinal nerves located nearby. The presence of a compression of the peripheral nerve roots leads to the onset of neurological disorders.
Development of an "injection site infection". It is a complication that can develop several weeks after the operation that required spinal anesthesia.
A spinal epidural abscess can result from such infections. Spinal epidural abscesses are dangerous because they could cause neurological damage to the peripheral nerve roots.
Such neurological damage can impair the movement skills of the lower limbs (paraplegia).

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

Allergic reactions to the anesthetic or analgesic drugs used. This can induce, in the patient, the appearance of breathing difficulties.
Permanent damage to the nerve components of the bone marrow, be it the spinal nerve roots or otherwise. This rare complication occurs once in every 50,000 surgeries involving spinal anesthesia.
Cardiac arrest. The chances of cardiac arrest occurring are increased if the patient's general health condition is poor.

Contraindications

Doctors consider spinal anesthesia inoperable when:

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