Sub-topics

Local anaesthetic nerve blocks
Testing the block
What will you feel ?
During the procedure
Spinal anaesthesia
Epidural anaesthesia
Other nerve blocks

Local anaesthetic nerve blocks

top

In this website, the term ‘regional’ refers to the fact that only part of the body is anaesthetised. In some parts of the world, ‘ regional anaesthesia’ may be known as ‘ local anaesthesia’. The term ‘ nerve block’ means that the transmission of impulses in the nerve or nerves from the area of the operation is blocked by the injection of local anaesthetic drugs around the nerve(s). You will feel numb or ‘frozen’ in the area of the block. Local anaesthetics can be administered around the nerves in the spinal cord, either as a spinal or as an epidural anaesthetic. Local anaesthetics can also be injected close to other nerves, such as those in the arms or legs. Because these nerves tend to be in the body’s extremities, these nerve blocks may be called peripheral nerve blocks.

Local anaesthetics may also be used to numb certain internal membranes such as the lining of the mouth or throat, or the urethra for examination of the bladder.

The choice of which particular block to use is based in part on the anaesthetist's experience and the potential for the block to cause side-effects. The major problems that occur with nerve blocks are related to the needle and to the agent injected. The needle can cause damage to nerves and to other neighbouring structures. For example, a block of the major group of nerves to the arm, when performed at a site just above the collarbone (‘supraclavicular approach to the brachial plexus’) is associated with a 1 or 2 per cent risk of damage to the lung (pneumothorax). This is because of the nerves are close to the outer lining of the lung.

Injection of local anaesthetic agents can cause side-effects because of allergic reactions, or because of misplacement of the needle. Because an artery and vein surround each nerve, it is possible to inject local anaesthetic into either of these blood vessels. This results in a sudden increase in the concentration of local anaesthetic in the bloodstream, which can cause convulsions and cardiac arrest. To reduce the chances of these complications, nerve blocks should be performed in the Operating Room or in a specially equipped room, where monitors and resuscitation equipment are available. This equipment includes oxygen, a means of delivering the oxygen to the lungs, suction apparatus (in case of vomiting), and items for tracheal intubation. It is vital to have properly trained assistance available.

There are different types of local anaesthetics that act for different lengths of time. By choosing various drugs, your anaesthetist can tailor the length of your anaesthetic to match the length of the operation. Sometimes the anaesthetist inserts a fine plastic tube through the nerve block needle. This allows your anaesthetist to give you one or more injections of local anaesthetic, without having to re-insert the needle. This is known as giving a ‘top-up’.

Testing the block

top

Your anaesthetist then checks to see how well the block has worked, by touching your skin with an ice cube or an alcohol swab. If the block has worked, you cannot feel ‘cold’ when touched. Some anaesthetists use a very fine sterile needle and ask you if the needle feels ‘sharp’ (where the area supplied by the nerve is not blocked) or ‘blunt’ (where the nerve is blocked).

What will you feel ?

top

The aim of any nerve block is to stop you feeling any pain. However, it is important to remember that you might feel touch, pressure, or vibration, and this is considered normal for certain blocks using certain drugs.

Most anaesthetists like to remind their patients that they may feel ‘something’ but are very unlikely to feel pain. If the block does not work, there are several options:

• The block can be repeated.
• If the area of sensation is small, the surgeon might be able to inject a small amount of local anaesthetic into the area where you felt the pain.
• Your anaesthetist can give you some medication for pain, such as a low concentration of nitrous oxide or a small amount of an injected opiate or narcotic.
• A general anaesthetic may be given instead.
• Finally, in some patients, it is better to cancel the procedure and try again another day.

During the Procedure

top

After determining that your block has worked, your anaesthetist helps the nurse to set up the sterile drapes or sheets that separate you from where the surgeon is working. These drapes also prevent you from seeing what is being done. Your anaesthetist continues to monitor how you feel in general, and your vital signs (blood pressure, heart rate, and oxygen saturation). During the course of the procedure, depending on how you are feeling, your anaesthetist might choose to give you an intravenous injection of a sedative, to relax you. You will feel drowsy and might even drift off into what seems like a light sleep. At the end of the operation you will probably not remember much about the events in the Operating Room. When you are transferred to the recovery room, you feel relaxed, free of pain and quite awake.

Spinal anaesthesia

top

The most common types of nerve blocks are spinals and epidurals. The spinal cord is surrounded by fluid within a tough fibrous envelope called the ‘dura’. With a spinal, the drug is injected into the fluid. With an epidural, the drug is placed outside the dura, but still within the hollow spinal canal of the backbone.

Spinal anaesthetics are useful for surgical procedures involving the legs and lower abdomen. Typical surgical procedures include caesarean section, vaginal hysterectomy, operations on the prostate, repair of inguinal or groin hernias, repair of a fractured hip, and arthroscopic examination of the knee.

There are a few reasons why you might not be suitable for a spinal anaesthetic. It might be your choice not to have a spinal. The other major reasons have to do with an increased risk of complications from this technique. These include an infection at the site where the needle is inserted, increased pressure around the brain (from a tumour, a build-up of spinal fluid, or the presence of a blood clot) and problems with poor blood clotting. All of these are extremely rare.

If you have a spinal anaesthetic, your anaesthetist first attaches various monitors (ECG, blood pressure cuff, pulse oximeter), and starts an intravenous line. You are then positioned, either lying on one side or sitting up on the edge of the Operating Room table or trolley. If you are lying down, you are asked to curl up into a ball, with your knees drawn up to your chin (or as high as possible). If you are sitting up, you lean over a pillow placed on a small table. In either case, a nurse or the anaesthetist’s assistant helps you to get into position and to remain as still as possible. You have a sheet or blanket to cover your chest and the lower half of your body.

Then your anaesthetist feels the bones of your back to choose the level to insert the spinal needle. The site most often chosen is about 4 – 5 centimetres below your waist and right in the middle (‘midline’). After this, your anaesthetist scrubs up, and puts on sterile gloves and often a sterile gown as well. After washing a small area in the middle of your back, using antiseptic solution (which is usually cold), the anaesthetist covers the surrounding skin with sterile cloths.

The next step is insertion of the needle, during which it is extremely important for you to hold as still as possible. Your anaesthetist first gives you a small injection of some local anaesthetic into the area where the spinal needle will be inserted. This injection might feel like a small bee-sting. Then the specially designed spinal needle is inserted into the epidural space and through the covering over the spinal cord (dura). Sometimes there is a tiny ‘pop’ or ‘click’ when this happens. Once the spinal needle penetrates the dura, it sits in the spinal canal. This is a sack-like structure containing the cerebrospinal fluid, nerve roots, and the spinal cord. Local anaesthetics (and sometimes a painkiller) are injected into the spinal fluid through the needle, which is then removed.

After the needle is removed, it is safe for you to move a little bit. If you are sitting up, your anaesthetist has you lie down after about 30 seconds. If you were lying down, you continue to lie in that position, although you could straighten your legs and your neck. The local anaesthetic solution disperses in the spinal fluid and blocks the nerves. Over the next few minutes you develop profound numbness and weakness in the lower half of your body (or one side more than the other if the spinal was inserted when you were lying on one side).

The major immediate complications of spinal anaesthetics include nerve damage from the needle, a decrease in blood pressure and heart rate, and failure of the injection to produce an adequate level of anaesthesia. The chance of the block not working is about one per cent or less, depending on how frequently your anaesthetist performs spinal blocks.

The long-term complications of spinal anaesthesia include a 1 per cent chance of severe headache afterwards. Termed a post-dural puncture headache, this type of headache is unusual in that it comes on when a patient sits or stands up and is completely resolved by lying down. (The medical term for this phenomenon is ‘posturally dependent headache’.) Specific treatment may be needed for the headache.

One extremely rare complication of spinal anaesthesia includes compression of the spinal cord from a blood clot or abscess in the spinal canal. Another rare complication is ongoing nerve damage from chemical effects of the anaesthetic or other agents on the nerve roots.

A slightly more common complaint is irritation of a nerve root (radicular irritation syndrome). With this problem, patients report burning pain in the legs. The pain comes on a few days after having a spinal with certain local anaesthetic drugs. Fortunately, the pain goes away without any treatment.

Epidural anaesthesia

top

Like spinal anaesthesia, epidural anaesthesia can be used for operations on the legs and the lower part of the abdomen. Epidurals can also be inserted to help with pain management, either after an operation or during labour.

The spinal cord is surrounded by fluid within a tough fibrous envelope called the ‘dura’. With a spinal, the drug is injected into the fluid. With an epidural, the drug is placed outside the dura, but still within the hollow spinal canal of the backbone. The technique of insertion of the epidural needle is similar to that used for spinal anaesthesia. However, the needle is stopped in the epidural space and there is no attempt to penetrate the dura. Usually, epidural anaesthesia is performed using a larger needle through which a fine plastic tube (catheter) can be threaded into the epidural space. This tube is similar to fine cooked spaghetti and it is not always possible to determine where the tip of the catheter ends up. Occasionally a patient complains of a brief, shock-like sensation as the catheter is being threaded through the needle and into the back. Most anaesthetists warn their patients that this might happen and remind them not to move until the needle is withdrawn. Once the catheter is well situated, the needle is removed. The catheter is then taped up the back and secured to the hospital gown. A filter is attached to the catheter – in case the fluid to be injected contains tiny particles of glass from the drug ampoules, and to keep bacteria out.

Epidurals are often inserted to relieve the pain of labour and childbirth, as well as postoperative pain. In such cases, epidural analgesia is provided instead of epidural anaesthesia. The only difference between anaesthesia and analgesia is that analgesia uses weaker concentrations of local anaesthetic. An opiate or narcotic may also be injected into the epidural to increase pain relief. Epidurals differ from spinals in that a much larger dose of local anaesthetic is required for an epidural anaesthetic as compared to a spinal anaesthetic.

Epidurals can be inserted into the upper part of the back (the thoracic spine), and are then known as thoracic epidurals. These are particularly useful for the relief of postoperative pain after operations on the chest (thoracic surgery). In addition, the anaesthetist may use the pain relief from the epidural to reduce the amount of general anaesthetic needed during the operation.

The immediate risks from epidural anaesthesia include a decrease in blood pressure, and seizures from the accidental intravenous injection of local anaesthetic agents. In addition, effects similar to spinal anaesthesia can be seen, but because of the larger dose of local anaesthetic used with epidurals, the patient may be anaesthetised from the neck down.

The long-term complications of epidural anaesthesia include a less than 1 per cent chance the block failing to work, and a similar chance of having a post-dural puncture headache. Also possible is damage to a nerve root from the epidural needle or catheter. In extremely rare cases, an epidural blood clot ( haematoma) or abscess may occur, resulting in weakness of the legs and in loss of bowel and bladder control.

Other nerve blocks

top

Other parts or regions of the body can also be anaesthetised (‘frozen’) - for example, for operations on an eye, arm, or foot. Many different techniques have been described for such operations.

Operations on the eye can be performed under retrobulbar or peribulbar block. These blocks involve injecting local anaesthetic around the eyeball, so that the eye is pain-free and unable to move. This kind of block is used for many operations on the eye, including cataract extraction with lens insertion and repair of defects on the retina (back of the eye). Some cataract operations can also be performed under local anaesthesia, after local anaesthetic drops have been applied to the surface of the eye.

For surgery on the arm it is possible to provide satisfactory anaesthesia by blocking the major group of nerves (brachial nerve plexus) that supplies the shoulder and arm. A block may be performed at one of a number of different sites, including:

• in the neck (interscalene)
• above the collar bone (supraclavicular)
• below the collar bone (infraclavicular)
• and in the armpit (axillary).

For surgery on the leg it is possible to provide satisfactory anaesthesia by blocking the major group of nerves (sciatic nerve or femoral nerve) that supplies the hip, leg and foot. A block may be performed at one of a number of sites, including:

• in the groin (inguinal)
• under the buttocks
• at the back of the knee (popliteal fossa)
• and at the ankle.

The intravenous technique, or Bier’s block, can be used for operations on the arm, such as reduction of simple fractures of the wrist, and less commonly for procedures on the leg. With this technique, a special tourniquet with two cuffs is wrapped around the arm or leg to be anaesthetised. An intravenous cannula is inserted into a vein in the hand or foot, but no intravenous line is attached. The anaesthetist then lifts up the arm or leg and wraps a tight rubber bandage around it, to drain the blood. The tourniquet cuff closer to the head is then inflated and the rubber bandage is removed. The arm or leg is lowered and local anaesthetic is injected through the intravenous cannula. After at least five minutes, the lower tourniquet cuff is inflated. Once this has been secured, the upper cuff is released. This sequence ensures that the patient does not feel any pain from the tourniquet, which must remain inflated for at least 45 minutes. If the tourniquet is released prematurely, there would be an increased chance that the local anaesthetic will rush through the patient’s blood vessels to the heart and brain. The effect on the heart would be to decrease the heart rate and blood pressure. The effect on the brain might be to cause seizures or loss of consciousness.