This section has the following topics:
- Three phases
- General anaesthesia
- Regional anaesthesia
- Local nerve blocks
- spinal anaesthesia
- epidural anaesthesia
- Other nerve blocks
- local anaesthesia
- Keeping a record
There are three phases to any anaesthetic.
- Start or induction phase: In the case of a general anaesthetic the anaesthetist gives you the drugs that make you lose consciousness, or he or she performs the nerve block that makes part of you numb (as in a spinal or an epidural).
In some hospitals, you are taken directly into the Operating Room and then given your anaesthetic. In other hospitals, you are taken into a smaller room adjacent to the Operating Room. This smaller room is known as the Anaesthetic Induction Room, as it is where the anaesthetic is ‘induced’ or started.
In either case, you will have ‘routine monitors’ attached, which are used for virtually every patient. These include an ECG ( electrocardiograph), a pulse oximeter probe, and a blood pressure cuff. In addition, in most cases an intravenous line is started, usually in a vein in the back of one of your hands or in a vein in your forearm.
- Middle or maintenance phase: The anaesthetist ensures that you remain anaesthetised until the surgical, diagnostic or other treatment procedure is completed.
- End or emergence phase: The anaesthetist stops giving you the anaesthetic drugs, allows them to wear off, and/or gives you other drugs to reverse their effects, so that you regain consciousness or sensation.
induction (“going off to sleep”)
Your anaesthetist may start your anaesthetic or induce ‘sleep’ in one of three ways. Induction may be:
• intravenous (into the vein): the most common method
• inhalation (by breathing in) sometimes called “gas induction”: often used in children
• intramuscular< (into the muscle) injection: now used very rarely.
Before having an intravenous induction, you may have had local anaesthetic cream applied to the skin over the vein to be used for the initial injection. The location of the vein depends on the anaesthetist’s preference, the site of the operation, and the appearance of your veins. Often the veins on the back of the hand or forearm are used. The choice of hand depends on whether you are left- or right-handed, because having a bruise on the back of your dominant hand may cause discomfort afterwards. Also, if your intravenous line must remain in place for some time, you will find it easier to be able to do things, such as combing your hair or brushing your teeth, if your intravenous is not in the hand with which you normally do these things.
Having wiped away the cream and applied some cleaning alcohol to the skin, your anaesthetist inserts a cannula or fine plastic tube into the vein. This is accompanied by a sensation varying between slight pain and a feeling of light pressure. In the absence of local anaesthetic cream, you feel a short sharp pain. The cannula is secured to the skin with tape and may be attached to an intravenous ‘line’ or long clear plastic tube connected to a bag of saline or similar fluid. This fluid may feel cold when it runs into the vein (usually in your arm).
Your anaesthetist may then have you breathe oxygen from a mask. This process is known as preoxygenation. Your anaesthetist may also give you one or more drugs, before giving you the actual drug which makes you lose consciousness. For example, if you are scheduled to have your gallbladder removed, your anaesthetist might start by giving you an injection of a drug to relax you, and then a drug to decrease the chance of postoperative vomiting. You might also be given an injection of a potent painkiller (opiate or narcotic), such as fentanyl. This drug also helps minimise any marked rises in heart rate and blood pressure that can occur at a slightly later stage of the anaesthetic and operation. Sometimes anaesthetists give these additional drugs after you have lost consciousness.
The anaesthetist then injects the induction drug through the cannula into your vein. This is the time when he or she may ask you to count (often backwards, from 100). Counting is a means of distracting you and also shows when the drug has achieved its effect. The induction drug works very quickly, especially in younger patients. It takes only the time for the blood carrying the drug to return from the arm to the heart and then be pumped through the lungs, back to the heart, and then to the brain. (Anaesthetists call this the ‘arm-brain circulation time’.) In most people this time is about ten seconds, but it may be faster in children and slower in elderly or very ill patients.
Inhalation (gas) induction
This method is common in children but is also used in some adults. It involves having the anaesthetist or the patient hold a mask over the patient’s nose and mouth. The patient then breathes in a mixture of gases through the face mask until loss of consciousness occurs. Induction by mask usually takes longer than the intravenous method, and achievement of the appropriate depth of anaesthesia is often preceded by a period of restlessness. This is quite normal and the patient is already unconscious at this time.
Then the anaesthetist has an assistant (nurse, technician or another anaesthetist) hold the mask and ensures that the patient is continuing to breathe well. The anaesthetist then inserts an intravenous cannula (as above), unless one has previously been started. This is more likely to have been done in adults. From this point, the anaesthetic is similar, whether an intravenous or inhalation technique has been used.
Not just a recipe !
Individuals vary in their requirements for anaesthetic drugs. The dose of the induction drug is generally given slowly to patients who are to have an elective operation. Your anaesthetist has calculated the expected dose you should need, from your weight, your age, your sex, and your state of health. However, as the drugs are injected, the dose of each is adjusted as necessary, according to the effects produced. This is known as titrating the drugs according to their effect. In an emergency it is sometimes necessary to give the drugs quickly, and a predetermined dose is calculated.
Will you have the same anaesthetic as the patient in the bed next to you ?
Every anaesthetic given is a very individual thing and each anaesthetic depends on the patient to whom it is given. The doses of drugs that you are given are calculated according to your weight, age and state of health; the operation or examination for which it is given; and even the anaesthetist who gives them. There is no fixed recipe.
What happens once you are asleep ?
After the induction drug has caused you to lose consciousness, your anaesthetist gives you one or more other drugs (a mixture of painkillers, sedatives, and anaesthetic gases) to ensure that you remain unconscious. If these other anaesthetic agents were not given, you would regain consciousness in a few minutes, after the induction drug had worn off.
Breathing during anaesthesia
Once you are unconscious, your anaesthetist will take over the management of your breathing, while attending to any changes in your pulse, blood pressure and the amount of oxygen in the blood. This management might consist of holding the mask over your mouth and nose, ensuring that you are breathing clearly and without snoring; or holding the mask and breathing for you by squeezing a bag attached to the breathing circuit; or inserting a breathing tube into your mouth.
Throughout the operation you are given oxygen, first with the mask, and then usually through a plastic airway. There are several types of airway, each of which is a different size, depending on your age and size. The presence of an airway helps to ensure that your breathing is adequate and, in the case of an endotracheal (breathing) tube, that acid from your stomach does not pass into your lungs.
To help manage your breathing, your anaesthetist might inject a muscle relaxant, to relax or weaken your throat and abdominal muscles. Muscle relaxants have two major useful effects.
•They make it easier for your anaesthetist to insert a breathing (endotracheal) tube through your mouth or, on occasion, through your nose, into your trachea or windpipe. (This process is known as tracheal intubation.) Without muscle relaxants, your anaesthetist would have to give higher doses of other drugs so as to weaken the muscles of your mouth and throat, to make insertion of the tube ( intubation) easier.
•They actually make it possible for the surgeon to perform many operations, without causing any damage to muscle fibres. Indeed, it is difficult for a surgeon to operate inside your abdomen if the muscles are not relaxed. The same applies to other operations, such as those on the hip or in the chest, but not for those on the skin or the body surface.
If you have been given a muscle relaxant, all of your muscles will be relaxed or weakened, including the muscles that help with breathing. In that case, your anaesthetist ‘breathes for you’. This is usually done with a ventilator, which pushes gas around the anaesthetic circuit and into your lungs. Ventilation may also be done by hand, with your anaesthetist squeezing a bag attached to the anaesthetic circuit.
Airways and breathing tubes
The smallest airway is the oral airway. An average adult airway is about ten centimetres in length and one centimetre in diameter and is curved to fit over the back of the tongue. An oral airway is most often used for minor operations, such as those on a limb, particularly if the duration of the procedure is to be short. The laryngeal mask airway is longer and fits over the top of the larynx. Many anaesthetists now use the laryngeal mask for cases for that would previously have had an oral airway and for cases that may have required an endotracheal tube.
The endotracheal tube is long enough to reach from just outside your mouth or nose and down to just below your vocal cords. The decision to use an endotracheal tube is determined by your condition, the operation to be performed, and the position in which you are placed during the operation. Usually, an endotracheal tube is used if the surgeon is to operate on the brain, the head and neck region, the chest, the back, the abdomen, or the pelvis. Although the anaesthetic is started while you are lying on your back, your surgeon may need you to be in a different position for the operation. For example, if you are to have an operation on your back, the Operating Room team will turn you over onto your stomach after you are unconscious and an endotracheal tube has been inserted.
An airway is placed in your mouth after you become unconscious, although rarely an endotracheal tube must be inserted before any drugs are given and you are still conscious. This is known as ‘awake intubation’ and is only likely if you have a tumour or severe obstruction in your throat.
Before placement of an endotracheal tube while still conscious, you would be given a solution of local anaesthesia to gargle, which numbs your mouth and throat, and decreases any gagging or coughing as the tube is inserted. Your anaesthetist would explain the process beforehand.
If your anaesthetist has chosen to use a laryngeal mask or endotracheal tube, it is connected to the circuit after it has been inserted. Your anaesthetist controls and monitors the flow and concentration of gases that enter and leave the circuit and your body, so that you receive the appropriate amount of anaesthetic and breathe adequately.
How does your anaesthetist know that the tube is where it should be ?
If the anaesthetist has inserted an endotracheal tube into your trachea (windpipe), you breathe carbon dioxide out through the tube. (Carbon dioxide is the gas produced by the body as it uses oxygen to generate energy. Carbon dioxide is then excreted from the body through the lungs.) Carbon dioxide can be measured with a specific monitor, normally attached to the endotracheal tube. The presence of carbon dioxide in the endotracheal tube suggests that the tube is in your trachea.
There are other methods to help confirm the correct position of the tube, but they are less accurate than the carbon dioxide monitor. Your anaesthetist might also use a stethoscope to listen for the sounds of air moving in and out of your lungs on both sides of your chest and carefully observe how your chest moves up and down with each breath, noting whether or not this movement is symmetrical, which usually occurs when the tube is in the trachea.
Your anaesthetist might also listen to your chest to ensure that the tracheal tube has not been placed too far down into one lung. This is known as an endobronchial intubation and is sometimes done on purpose. If the surgeon wants to operate on the left lung, then the tube is intentionally placed into the right lung.
Induction of anaesthesia in children
Children vary greatly in the way they react to induction of anaesthesia. All children exhibit fear in some way, because of the strange environment, separation from their parents, and the uncertainty about what is to happen to them.
Less than six months
Infants of less than six months do not react strongly to being separated from their parents and usually respond appropriately to a parent substitute. The anaesthetist should be accustomed to caring for small children and, together with other staff, be empathetic with both child and parents.
It is uncommon for parents to accompany infants of less than six months during induction of anaesthesia. This is for two reasons: a child of this age does not suffer major separation anxiety; and everything occurs much more quickly in a baby. This includes the action of drugs and the need to act to correct problems such as breath holding. The anaesthetist must devote his or her whole attention to the child without also having to be concerned about parents.
Six months to four years
Children in this age group do not tolerate separation from their parents well and are not able to comprehend explanation. They react to the unknown with fear, withdrawal and struggling. Induction of anaesthesia is best performed either with a parent present, or premedication, or both. With a parent present, the child tends to cling. Induction of anaesthesia can be difficult in this age group. Adequately sedated, there is little problem and usually no recollection of events. However, the sedative drugs may prolong the recovery phase and delay discharge from hospitals after minor or day stay operations.
With a parent present, either an intravenous or inhalation (gas) induction may be used. For intravenous induction, the parent is asked to hold the child firmly, with the parent either sitting on a chair or leaning over the child who is in a cot or on a bed. The parent is then asked to interact with the child by talking, singing or playing with a toy. At the same time, an assistant secures an arm or a leg where local anaesthetic cream has been applied, while the anaesthetist inserts a cannula.
Inhalation induction is preferred by some anaesthetists. However, usually a mask cannot be placed over a child’s face without a struggle. Sometimes this struggle may be minimised by the anaesthetist applying a few drops of a common food flavouring, such as strawberry, orange or bubblegum, to the mask. These scents help to disguise the smell of the anaesthetic gases. Alternatively, some anaesthetists use their hand as a mask. Induction by mask takes longer than intravenous induction.
Four to six years
Children in this age group are still anxious about separation but are more accepting of explanations and reassurance. As with younger children, they benefit from having a parent present during induction, although less physical restraint is required.
Six to ten years
Children aged six to ten years have less of a problem with separation from parents and are much more amenable to reassurance. They do, however, fear anaesthesia and surgery, and particularly pain. They may have fantasies of mutilation and require reassurance about the exact nature of the operation. They will be irritable and impatient.
Intravenous induction is usually well tolerated, although the fear of needles may be so strong that even application of local anaesthetic cream is not enough to overcome the fear. Cooperation can usually be obtained for an inhalation induction with a mask. Sometimes a child indicates a preference, especially if he or she has had previous anaesthetics.
The presence of a parent or guardian can be of great assistance to the child and the anaesthetist.
This group of patients may fear loss of control and death. It is important to reassure them of the safety of modern anaesthesia and that they can be in control of their pain management after the operation.
Intravenous induction is commonly used in adolescents. However, some patients request an inhalation induction, particularly if they have undergone several (or multiple) operations.
Your role as a parent during induction of anaesthesia
You can be an enormous help during induction of your child’s anaesthetic. Your presence, in most cases, means a calmer, more cooperative patient, with less likelihood of bad memories of the hospitalisation.
There are several points to consider. Just as your child needs to be prepared for the event, so you need to learn as much as you can about what will happen.
Part of your preparation includes recognising that you, too, may be distressed by the experience. The final decision rests with the anaesthetist as to your presence. Although many anaesthetists are now used to having parents present at induction, some find their presence stressful. For the child’s safety, an anaesthetist may prefer not to have this added distraction.
Your presence may not be encouraged in every situation. This applies particularly if your child needs an emergency operation. Should something happen, such as your child vomiting, then the anaesthetist needs to focus attention on the child.
You should not feel pressured to be involved. Not everyone is comfortable with the idea of staying during induction and you are free to decline the invitation. Your child’s care will be no less professional.
You should be prepared for your child’s appearance after induction. Your child will become anaesthetised within seconds and may suddenly look lifeless, but often with the eyes still open. This is normal. At the same time the anaesthetist will be concentrating on the next step in the process of caring for your child. He or she usually cannot talk with you or to answer questions at that time.
You should go when asked to leave.
Emergency induction of general anaesthesia
Your anaesthetist might modify the induction of anaesthesia by using a technique known as a rapid sequence induction’. This is a crucial technique in patients who must undergo an emergency operation and who have a full stomach, either because they have just eaten or because their stomachs take longer than normal to empty (as a result of pain, drugs, or other conditions).
In a rapid sequence induction, you are given 100 per cent oxygen to breathe from a mask placed firmly over your mouth and nose for three to four minutes. This process is known as preoxygenation and replaces the nitrogen in your lungs (the most common gas in the air) with oxygen. As a result, the store of oxygen in your body is markedly increased and there is less chance of lack of oxygen ( hypoxia).
In the next step your anaesthetist calculates the dose of two drugs – the induction drug (usually propofol or pentothal) and a rapid-acting muscle relaxant. The dose of each drug is calculated on the basis of your weight and your general condition.
Your anaesthetist then injects the two drugs rapidly through the intravenous cannula and you quickly lose consciousness. This minimises any risk of your going through a stage during the loss of consciousness when you struggle or vomit.
As you lose consciousness, your anaesthetist instructs an assistant to apply firm pressure to the front of your neck. The assistant normally stands on your right and uses the first three fingers of the right hand to apply the pressure. (You might feel the assistant’s fingers lightly touching your neck as you lose consciousness.) The specific part where the pressure is applied, called your cricoid cartilage, is a ring of cartilage that forms part of your trachea. Pressure on the cricoid cartilage ( cricoid pressure) seals off the oesophagus and reduces the possibility of stomach contents flowing from the oesophagus into the back of the throat and then down into the lungs.
Maintenance of anaesthesia (“keeping you asleep”)
During the maintenance phase of the anaesthetic, your anaesthetist keeps you in a state of unconsciousness, using a mixture of inhaled (inhalational) and intravenous (injected) drugs. The inhalational agents are administered through the breathing circuit. They include nitrous oxide and the ‘volatile’ anaesthetic agents (because they pass easily from being a liquid to a gas). The volatile anaesthetic agents are commonly used in proportions between 0.5 and 4 per cent, although this varies according to the agent and the desired effect. They are powerful drugs and are used to keep you unconscious, as well as helping to control pain and to relax muscles. These drugs can also have side effects, such as low blood pressure, changes in heart rhythm, and difficulties with breathing.
Nitrous oxide (N2O) or (‘laughing gas’) is used in many general anaesthetics, in a mixture with oxygen of around 70 per cent nitrous oxide and 30per cent oxygen. At that concentration the nitrous oxide may make you sleepy and able to tolerate mildly painful procedures, but that is all. Nitrous oxide does, however, provide a means of giving other stronger anaesthetic gases through the breathing system.
Air, enriched with extra oxygen, is sometimes used when nitrous oxide is less desirable, such as during anaesthesia in the elderly, for some brain surgery, some major heart and lung surgery, and in some tiny premature infants.
During most anaesthetics, oxygen is added so that the usual proportion given to the patient is about 30 per cent. This extra oxygen provides some safety margin over the normal 21 per cent in room air. The critical aspect of anaesthesia care is to ensure that you continue to receive adequate oxygen, which is necessary for preservation of life and the functioning of organs.
Your anaesthetist may choose to give you other drugs through the intravenous line. Depending on the drug, your anaesthetist may do this to increase the depth of the anaesthetic (how unconscious you are). Drugs are also given to provide pain relief after the operation. If the surgeon needs your muscles to be relaxed (in order to perform the procedure), your anaesthetist may give you further doses of the muscle relaxant drug given at the time of induction, or a different drug. Intravenously administered drugs may be given in separate or discrete doses (sometimes known as ‘bolus’ doses) or by constant injection or ‘infusion’ regulated by a pump.
Sometimes your anaesthetist will not use any inhalation anaesthetics at all. When all anaesthetic drugs are given intravenously, it is referred to as Total Intravenous Anaesthesia, or TIVA. These drugs are usually given by carefully controlled infusion.
Emergence (“waking up”)
The third phase of the general anaesthetic is emergence or regaining consciousness. During this phase your anaesthetist stops giving you all inhalational anaesthetic agents (except the oxygen) and also stops any intravenous anaesthetic drugs. You gradually regain consciousness. Your anaesthetist usually needs to reverse the effects of the muscle relaxants, with the injection of two more drugs. As consciousness returns, your anaesthetist makes sure that you can breathe without help. Once you are regaining consciousness and able to breathe without any help from the anaesthetist, the breathing tube is removed. By carefully calculating the right amounts of each drug, your anaesthetist can ensure that you are completely unconscious during the operation, but awake and pain-free at the end of the procedure.
Local anaesthetic nerve blocks
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
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 ?
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
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.
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.
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
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.
Local anaesthesia sometimes refers to the administration of local anaesthetic drugs under the skin (or subcutaneously). In this technique, the local anaesthetic does not act on a specific nerve, but on a number of small nerves close to the area of skin or tissue where they provide sensation. When scheduled this way on the Operating Room schedule, this technique implies that the surgeon will give the drugs without any involvement of an anaesthetist.
Monitored (or anaesthetic) care
In many hospitals, anaesthetists provide care to patients having surgical procedures under local anaesthesia only, for example examination of the bladder (cystoscopy). The anaesthetist is available to monitor the patient and to provide intravenous or inhaled anaesthetic agents for additional sedation or pain relief. In the past, this type of care was often termed stand-by (because the anaesthetist was standing by, ready to intervene if necessary). This approach to patient care is now commonly referred to as ‘monitored anaesthetic (or anaesthesia) care’.
Because the anaesthetist is caring for the patient, the surgeon is able to focus on the operation, rather than having attention divided between the surgical field and the condition of the patient. For example, should a patient become distressed during the course of the operation, or suffer a complication from the procedure or the local anaesthetic, the anaesthetist provides necessary comfort or resuscitation and the surgeon can continue (if appropriate) with the procedure. One operation occasionally performed under ‘local by surgeon’ (or monitored anaesthetic care) is that of cataract extraction.
Keeping a record
While monitoring your anaesthetic, your anaesthetist keeps a record of your vital signs, such as your heart rate, blood pressure and oxygen saturation. Your anaesthetist also records the time, dose, and route of all drugs and fluids that you are given. A record may also be made of routine and special monitors and equipment, as well as any anaesthetic techniques. As well, your anaesthetist makes a note of any events of importance. These might include, for example, the time when your surgeon made the first incision or other important actions.
Exactly what your anaesthetist records will partly reflects local custom. For example, in Canada the Guidelines to the Practice of Anaesthesia describe the minimum amount of information that should be recorded. Similar guidelines exist in Australia, New Zealand, and other countries. These guidelines state that every patient undergoing general, regional or monitored anaesthesia care should have his or her blood pressure and heart rate measured and recorded at least every five minutes. There is one important exception to this statement, which is contained in the phrase ‘unless clinically impractical’. This phrase applies if your condition is very unstable and your anaesthetist is working hard to save your life – for example, giving you life-saving drugs and intravenous fluids. In that case, your anaesthetist might not be able to record your blood pressure or heart rate at the same time. If so, your anaesthetist would complete the anaesthetic record after the crisis was over and your condition had stabilised.