Spinal anesthesia: What is it?

Spinal anesthesia was first used in the late 1800s as a method of administering an anesthetic. Today, spinal anesthesia, also called a spinal block or spinal, may be combined with epidural anesthesia [link to epidural article], as they provide, long-lasting pain relief.

Why use spinal anesthesia?

Spinals provide excellent anesthesia and at the same time provide ideal operating conditions for the surgeon, since the muscles are relaxed and there is usually less blood loss than with other methods. Spinal anesthesia has been shown to be particularly beneficial for seniors, people with severe lung disease, and those who are very sensitive to the effects of general anesthetics.

When is a spinal used?

Spinal anesthesia is commonly used for surgery on the lower limbs, prostate or gynecological surgery, or hernia repair in the groin. Caesarean sections are also frequently performed under spinal anesthesia.

A spinal anesthetic is injected into the spinal space

The spinal space

Spinal anesthetic is given by a needle injected into the spinal space (see Figure 1). This is a sac-like, fluid-filled space that surrounds the brain and spinal cord. The fluid in this space is called the cerebrospinal fluid. The surrounding sac is called the dura. Medications administered into the spinal space are able to spread freely within the cerebrospinal fluid.

How far the spinal anesthetic spreads through the cerebrospinal fluid depends on the amount injected and the effect of gravity. These factors are considered by the anesthesiologist when planning to administer a spinal.

How a spinal anesthetic is done

Most spinals are placed in the lumbar (lower) region of the spine while you either sit upright or lie on your side. This position aligns the vertebrae and flexes the spine. This allows the needle to travel through the dura and into the spinal space, which contains the cerebrospinal fluid.

The anesthesiologist is able to feel when the needle has passed through the various tissues into the spinal space. A local anesthetic medication is injected into the needle and the needle is removed.

Medications such as epinephrine are often mixed with the local anesthetic to extend the length of time that the effect lasts. Epinephrine does this by constricting some of the blood vessels around the spinal tissues, which limits how rapidly the local anesthetic is removed from the spinal fluid.

Opioids such as morphine or fentanyl may also be combined with the local anesthetic to improve the quality of anesthesia and to provide pain relief once the local anesthetic wears off.

How does a spinal feel?

You will experience a warm, tingling sensation as the anesthetic freezes the nerves. This is followed by complete numbness and a lack of sensation and movement. The duration of freezing varies depending on the medication administered. Numbness usually lasts between 1 and 4 hours before it starts to disappear and you begin to feel sensations and are able to move your legs.

Spinal needle placement (middle and paramedian)

Spinal anesthetic: side effects

Headache is the most common side effect of spinal anesthesia. You may have a headache the day of the surgery or the next day, when you sit up or move around. Most headaches will gradually disappear, and are managed with bed rest, fluids, and acetaminophen. Severe headaches can be treated by performing an epidural blood patch. This involves injecting your own blood into the epidural space to patch the hole made in the dura by the spinal needle.

Varying degrees of backache have also been reported with spinal anesthesia. This may be caused by the needle piercing the tissues or, more frequently, from the stretching of the joints, ligaments, and muscles in the back that were relaxed by the local anesthetic. In addition, the position that you are placed in may put stress on your back.

Low blood pressure
You may develop low blood pressure and feel dizzy after receiving spinal anesthesia. Your doctor or nurse will monitor for this and manage it by giving you extra fluids intravenously (into a vein).

Spinal anesthesia: complications
Direct needle placement into a spinal nerve can damage the nerve fibres and cause pain and problems. However, this rarely occurs with proper technique and experience in administering spinal anesthesia. Very rarely, some people experience seizures or develop an infection (e.g., meningitis) after receiving spinal anesthesia.