Overview of Spinal Anesthesia
The history of regional anesthesia, a type of numbing technique, began with the discovery of local anesthetics like cocaine, which can numb a particular region of the body. The very first regional anesthetic method utilized was spinal anesthesia. In 1898, August Bier in Germany performed the first surgery using this type of anesthesia. Prior to this, only two types of local numbing methods were used: one that was applied to the surface of the eye, and another injected into specific areas to numb them.
The central nervous system (CNS) includes our brain and spinal cord. A type of numbing technique called ‘neuraxial anesthesia’ involves injecting an anesthetic in or around the CNS. Spinal anesthesia, which is a kind of neuraxial anesthesia, involves injecting the anesthetic directly into the space in the spine known as the subarachnoid or intrathecal space.
The subarachnoid space contains a clear liquid called cerebrospinal fluid (CSF), which surrounds and protects the brain and spinal cord. An adult human body typically contains about 130 to 140 milliliters of CSF, and about 500 milliliters of it is produced every day.
There are other neuraxial techniques like epidural and caudal anesthesia, each used for specific situations. Spinal anesthesia, however, is only done in the lower portion of the spine, known as the lumbar spine. It’s commonly used for surgeries on the lower abdomen, pelvis, and the lower parts of the body like the legs.
Anatomy and Physiology of Spinal Anesthesia
Spinal anesthesia is a procedure where an anesthetic, which is a medicine used to prevent pain during surgery, is injected into a region of your spinal cord. The main aim of this procedure is to numb the lower parts of your body to prevent you from experiencing pain during surgery. To do this correctly, the doctor needs to understand the structure of your spine and also position you properly during the procedure.
The human spine is made up of several bones: 7 in your neck area (cervical), 12 in your chest area (thoracic), 5 in your lower back (lumbar), and 5 that are fused together and form your tailbone (sacral). These bones are piled on top of each other with tiny joints and bands (ligaments) connecting them. They form a hollow space known as the spinal canal, which contains the spinal cord. Nerves from the spinal cord exit the spinal canal through small spaces between these stacked bones.
The anesthetic for spinal anesthesia is only injected in the lumbar area of your spine. This specific area is used to avoid harming your spinal cord and also to keep the anesthetic from affecting your upper chest and neck areas. Common areas used for injection are between the third and fourth lumbar bones and between the fourth and fifth lumbar bones. If these points aren’t used correctly, it can increase the chances of harming your spinal cord, especially in overweight patients. The needle goes through several layers before getting to the right spot. What it passes through will depend on the particular approach your doctor uses.
Understanding a structure called ‘dermatomes’ is very important to ensure the correct area is numbed before surgery. Dermatomes are areas of skin that are connected to specific nerves from the spinal cord. For example, if you are having a lower abdomen surgery, like a cesarean section (C-section) which involves making a cut in the lower part of your belly to deliver a baby, the incision is usually made below the “T10” dermatome, around the area of your belly button. However, to prevent you from feeling discomfort or pain during the procedure, the numbness has to extend up to the “T4” dermatome, which is around the same height as your nipples. Patients often complain about a ‘tugging’ feeling when the right level of numbness isn’t achieved. Here are examples of some important dermatomal landmarks:
* C8: Your 5th finger
* T4: Your nipple
* T7: Area of your chest where the lower part of your breastbone (xiphoid process) is located
* T10: Your belly button (umbilicus)
Why do People Need Spinal Anesthesia
Doctors can use a type of anesthesia known as neuraxial anesthesia for surgeries that take place below the neck. This type of anesthesia is commonly used for surgeries on the lower abdomen, pelvis, perineal area (the area between the genitals and the anus), and lower extremities (legs). This is especially helpful for procedures happening below the belly button.
Before you go through a procedure with spinal anesthesia, your doctor should talk to you about what it involves. They will explain why you need this type of anesthesia, what you can expect, the risks and benefits, and any alternatives available. You will be asked to give your consent for this procedure. Remember, during this procedure, you’ll be awake or slightly sedated. It’s important to know that once the anesthesia starts working, you won’t be able to move your legs until its effects wear off.
Spinal anesthesia is the best choice for short surgeries. But if your surgery will take a long time or affect your ability to breathe, your doctor will likely opt for general anesthesia instead. This helps to ensure your comfort and safety throughout the procedure.
When a Person Should Avoid Spinal Anesthesia
Sometimes, there are certain conditions that may prevent a patient from receiving a specific type of anesthesia called neuraxial anesthesia (which can be spinal or epidural).
The main reasons are if a patient does not consent to the procedure or if they have high pressure in their skull (known as elevated intracranial pressure). This can happen because of a mass in the skull or an infection at the site where the procedure is done because there’s risk of an infection of the protective membranes covering the brain and spinal cord (meningitis).
There are also other conditions which “relatively” prevent the use of neuraxial anesthesia, meaning they may not always stop the procedure but they increase the risk. These include:
- Certain nerve diseases that come and go, like multiple sclerosis
- Severe loss of body fluids (severe dehydration), because this can cause low blood pressure (hypotension). Low blood pressure is more likely in people who are older (over 40 to 50), are having emergency surgery, are overweight, drink alcohol regularly, or have long-standing high blood pressure.
- Low platelet count or a problem with blood clotting (known as thrombocytopenia or coagulopathy). This is especially risky with epidural anesthesia because it could lead to a collection of blood (hematoma) in the space around the spinal cord.
Having a severe narrowing of the heart valves (severe mitral and aortic stenosis) or obstruction of the blood flow out of the heart (left ventricular outflow obstruction), as seen with a thickened heart muscle obstructing blood flow (hypertrophic obstructive cardiomyopathy), are other reasons a patient may not receive neuraxial anesthesia.
If a patient has a problem with blood clotting, whether they can have the neuraxial block (anesthetic) should be carefully considered. The American Society of Regional Anesthesia (ASRA) provides up-to-date advice on when this type of anesthesia can be used if a patient is taking blood thinners, anti-platelet drugs, drugs to dissolve blood clots, and types of heparin (a blood thinner).
Since these procedures are not emergencies, it’s important to balance up the risks and benefits before going ahead.
Equipment used for Spinal Anesthesia
When your doctor does a procedure on your spine, called a neuraxial procedure, they need to make sure everything is super clean to prevent infections. This means they’ll be wearing a cap, mask, and sterile gloves, and they’ll also wash their hands really well. To ensure everything goes smoothly, they’ll prepare everything in advance and make sure there’s enough room for you and the medical team.
Before your procedure, monitors will be set up to keep track of your blood pressure, heart rate, and oxygen levels, as well as your body temperature. The doctor doing the procedure will know how to use and read these monitors. If they plan to give you sedation (medicine to make you sleepy and relaxed), they’ll have equipment ready to help you breathe, give you oxygen, and support your blood flow. They’ll also put in an IV (a tiny tube in your vein), which can be used to give you medicine or fluids. If you need to be fully asleep for the procedure, a specialized doctor called an anesthesiologist will be there to help.
Your doctor may use a kit specifically made for spinal anesthesia, which is a type of medicine that numbs your lower body. These kits usually include a skin cleaner called chlorhexidine with alcohol, a drape to keep things clean, and a local anesthetic (numbing medicine), usually called lidocaine. They also come with a special needle that’s used for spinal procedures, along with small syringes, and a special kind of anesthetic solution. This solution might be made from different types of medicines, like lidocaine, ropivacaine, bupivacaine, procaine, or tetracaine.
Who is needed to perform Spinal Anesthesia?
Spinal anesthesia is a type of procedure that must be done only by very skilled professionals. These are usually certified anesthesiologists or anesthesiologists being trained under the guidance of an experienced anesthesiologist. There are also other doctors specifically trained to perform spinal anesthesia. These include pain management doctors who have undergone extra studies in the physical care and recovery of patients (also known as physical medicine and rehabilitation or PM&R), brain and nervous system specialists (neurologists), and emergency medicine doctors.
Like most medical procedures, an assistant is always needed. Because the doctor performing the procedure will be at the patient’s back, another member of the medical team is usually there to help handle the equipment. This assistant also supports the patient from the front, helping them stay correctly positioned and safe throughout the procedure. This is particularly important if the patient has been given medicine to help them relax or sleep (sedation).
Preparing for Spinal Anesthesia
Before a doctor administers any kind of spinal anesthesia (a type of numbing medication injected into your spine), they will thoroughly review your medical history and do a physical exam. It’s important for them to know if you’ve ever had anesthetic medication before, if you have any allergies, and whether there have been any anesthetic problems in your family history.
In the physical exam, the doctor focuses on your back area where the spinal anesthesia will be administered. They will thoroughly check your back for any signs of skin infection or spine abnormalities such as curves in the spine (scoliosis), narrow spinal canal (spinal stenosis), previous back surgery, a genetic spine disorder (spina bifida) or history of a condition where the spinal cord attaches to the base of the spine (tethered cord). The doctor will also check how well you’re able to feel and move your legs and arms.
Before starting the procedure, the healthcare team will take a moment to confirm your identity, the planned treatment, check for any allergies and make sure you have given your permission for the procedure. They’ll also verbally discuss and confirm that your blood is capable of clotting properly.
Various drugs are used for this type of anesthesia:
* Lidocaine (5%): This drug usually starts to work within 3 to 5 minutes and can last for 60 to 90 minutes.
* Bupivacaine (0.75%): This is one of the most commonly used local anesthetics. It starts to work within 5 to 8 minutes and can last for 90 to 150 minutes.
* Other drugs that can be used include Lidocaine 5%, Tetracaine 0.5%, Mepivacaine 2%, Ropivacaine 0.75%, Levobupivacaine 0.5%, and Chloroprocaine 3%.
How is Spinal Anesthesia performed
The first step of a procedure, when a patient has been picked as the right candidate, is to make sure the patient is in the best position for the procedure. This procedure is typically done with the patient sitting or laying on their side. The patient’s comfort is of utmost importance. The aim of positioning is to make sure there’s a clear path for the needle to go between the spinal bones. The sitting position is commonly used because the spine’s shape is usually not the same on either side when a person is laying on their side. In the sitting position, the patient’s legs hang off the side of the bed, and they are asked to curve their spine to create more space between the spinal bones. This position is useful for spinal anesthesia, a type of pain relief used during surgery, with a heavier solution. Also, both left or right side laying positions can be used.
Once the patient is positioned correctly, the doctor identifies the spot they will insert the needle by feeling the patient’s back. This can sometimes be challenging with heavier patients because of the extra fat between the skin and the spinal bones. The space between two bones that the doctor can feel is usually the spot for needle insertion. To keep the area free from germs, the patient should cover their hair.
Always keeping the area clean is necessary. This can be done using a disinfectant with alcohol content, proper hand washing, and wearing a mask and cap. Cleaning starts from the chosen needle insertion site in circles and then moves away from the site. The cleaning solution has to dry first. In a spinal kit, a covering is placed on the patient’s back to keep the needle insertion area separate. Local anesthetic (usually 1% lidocaine) is used to numb the skin, and a raised area is made at the chosen site, either the middle or off to the side.
In the technique where the needle is inserted down the middle, the spinal needle goes straight into the inner part of the spine. After numbing with lidocaine, the spinal needle goes into the skin, tilted slightly upwards. The needle travels through the skin, and then through the fat under the skin. As the needle goes deeper, it comes across the ligaments which connect the spinal bones; this feels like there’s more tissue resistance. The practitioner approaches a structure called the ligamentum flavum, which feels like a “pop”. On the other side of this structure is a space called the epidural space, where medications and catheters can be placed. This is also the point where the doctor can feel a loss of resistance when injecting saline or air. For spinal anesthesia, the doctor continues to insert the needle until it crosses the membrane that covers the spinal cord, and cerebrospinal fluid (the fluid that surrounds the spinal cord) starts coming out. This is the point where the medication for spinal anesthesia is injected.
For the off-center approach, the numbed, raised area is about 2 centimeters from the middle, and the spinal needle goes in at an angle towards the middle. In this method, the ligaments that connect the bones are usually not felt. As a result, there’s little resistance felt until the needle touches the ligamentum flavum.
Possible Complications of Spinal Anesthesia
It’s essential that patients are carefully chosen and cared for to avoid common issues linked to neuraxial anesthesia, which is anesthetizing a specific region of your body. While many of these problems are unlikely to occur, it’s important to be aware of them. Serious issues are considered to be extremely rare, but their actual occurrence might be underestimated.
Some common issues can include:
* Back pain which is more common if you’ve been given an epidural, which is when anesthesia is given in the back.
* A specific type of headache known as a postdural puncture headache. This can be as high as 25% in some studies. It’s suggested that a needle that doesn’t cut through tissue should be used if a patient is at a high risk for these headaches. Moreover, the smallest needle available should be recommenced for everyone.
* Feeling sick or throwing up.
* Low blood pressure.
Some less frequent side effects can include:
* Hearing loss, typically at low sound frequencies.
* Total spinal anesthesia, which is an over-dose of anesthesia to the spine – this is feared the most.
* Damage to the nervous system.
* Spinal hematoma, which is a gathering of blood within the spinal space.
* Arachnoiditis, an inflammation of the protective layers around the brain and spine.
* Transient neurological syndrome, which refers to temporary problems with nerve function, often seen with the use of the anesthetic drug Lidocaine.
What Else Should I Know About Spinal Anesthesia?
Neuraxial anesthesia is a type of anesthesia that blocks pain from an entire region of the body. This anesthesia can let major surgeries happen while the patient is awake. This approach has proven very useful for surgeries like cesarean sections (C-sections). With neuraxial anesthesia, mothers are awake and can bond with their newborn babies right away, which might not be possible with general anesthesia.
Not only useful during surgeries, neuraxial anesthesia can also benefit patients after surgery. For instance, after chest surgery, a type of neuraxial anesthesia called thoracic epidurals can help improve a patient’s breathing. Other potential benefits are less need for pain medications, quicker return of intestinal functions, and easier participation in physical therapy. All these benefits can contribute to the patient’s smooth recovery.