general anesthesia

What is general anesthesia

General anesthesia is treatment with certain medicines that make you are completely unconscious and unable to feel pain during medical procedures or surgery. General anesthesia is more than just being asleep; the anesthetized brain doesn’t respond to pain signals or reflexes. After you receive these medicines, you will not be aware of what is happening around you.

General anesthesia include analgesia (relief from or prevention of pain), paralysis (muscle relaxation), amnesia (loss of memory), or unconsciousness. General anesthesia usually uses a combination of intravenous drugs and inhaled gasses (anesthetics). A patient under the effects of anesthetic drugs is referred to as being anesthetized.

An anesthesiologist is a specially trained doctor who specializes in anesthesia. While you’re unconscious, the anesthesiologist monitors your body’s vital functions and manages your breathing.

In many hospitals, an anesthesiologist and a certified registered nurse anesthetist work together during your procedure.

The purpose of general anesthesia can be distilled down to three basic goals or end points:

  1. Hypnosis (a temporary loss of consciousness and with it a loss of memory). In a pharmacological context, the word hypnosis usually has this technical meaning, in contrast to its more familiar lay or psychological meaning of an altered state of consciousness not necessarily caused by drugs.
  2. Analgesia (block pain sensation which also blunts autonomic reflexes)
  3. Muscle relaxation

The ideal general anesthetic drug would provide hypnosis, amnesia, analgesia, and muscle relaxation without undesirable changes in blood pressure, pulse or breathing.

Anesthesia enables the painless performance of medical procedures that would cause severe or intolerable pain to an unanesthetized patient.

How does general anesthesia work

General anesthesia suppresses central nervous system activity and results in unconsciousness, complete muscle paralysis and total lack of sensation 1). The goal is to make and keep a person completely unconscious (or “asleep”) during the operation, with no awareness or memory of the surgery. General anesthesia can be given through an IV (which requires sticking a needle into a vein, usually in the arm) or by inhaling gases or vapors by breathing into a mask or tube. General anesthesia delivered intravenously will act quickly and disappear rapidly from the body. This allows patients to go home sooner after surgery. Inhaled anesthetics may take longer to wear off.

Surgeons use general anesthesia when they operate on internal organs and for other invasive or time-consuming procedures such as back surgery. Without general anesthesia, many major, life-saving procedures would not be possible, including open-heart surgery, brain surgery and organ transplants.

General anesthetics typically are very safe. But they can pose risks for some patients, such as the elderly or people with chronic illnesses such as diabetes. Also, side effects may linger for several days in some patients, especially the elderly and children.

Before Surgery

Although you may be able to talk to the anesthesiologist a day or two prior to the operation, you might not meet until that day. Either way, the anesthesiologist will go over your medical history and information thoroughly, so that he or she can make the right choice regarding anesthetic medications tailored to your individual needs.

To ensure your safety during the surgery, you’ll need to answer all of the anesthesiologist’s questions as honestly and thoroughly as possible. Things that may seem harmless could interact with or affect the anesthesia and how you react to it.

The anesthesiologist might order additional tests (such as X-rays or blood or laboratory tests) to help figure out the best possible personalized anesthetic plan for you.

In addition to doing a physical examination of your airways, heart, and lungs, the anesthesiologist will also want to get your medical history, which will include asking about:

  • your current and past health
  • your family’s health
  • any medications, supplements, or herbal remedies you are taking (consider bringing a list of exactly what you take, detailing how much and how often)
  • any previous reactions you or any blood relative has had to anesthesia
  • any allergies (especially to foods, medications, or latex) you may have
  • whether you smoke, drink alcohol, or take recreational drugs.

This will help your anesthesiologist choose the medications that will be the safest for you.

How you prepare for a general anesthesia

General anesthesia relaxes the muscles in your digestive tract and airway that keep food and acid from passing from your stomach into your lungs. Always follow your doctor’s instructions about avoiding food and drink before surgery.

Fasting is usually necessary starting about six hours before your surgery. You may be able to drink clear fluids until a few hours prior.

Your doctor may tell you to take some of your regular medications with a small sip of water during your fasting time. Discuss your medications with your doctor.

You may need to avoid some medications, such as aspirin and some other over-the-counter blood thinners, for at least a week before your procedure. These medications may cause complications during surgery.

Some vitamins and herbal remedies, such as ginseng, garlic, Ginkgo biloba, St. John’s wort, kava and others, may cause complications during surgery. Discuss the types of dietary supplements you take with your doctor before your surgery.

If you have diabetes, talk with your doctor about any changes to your medications during the fasting period. Usually you won’t take oral diabetes medication the morning of your surgery. If you take insulin, your doctor may recommend a reduced dose.

If you have sleep apnea, discuss your condition with your doctor. The anesthesiologist or anesthetist will need to carefully monitor your breathing during and after your surgery.

Eating and Drinking Before Anesthesia

The anesthesiologist, surgeon, or someone on the nursing staff will give you instructions about not eating or drinking before surgery. It’s important to make sure you don’t eat anything prior to surgery (usually nothing after midnight the day before the operation). You’ll get specific instructions based on your age, medical condition, and the time of day of the procedure.

Why is eating before surgery an issue? Because the body normally has reflexes that prevent food from being aspirated (or inhaled) into the lungs when it’s swallowed or regurgitated (thrown up). But anesthetic medications can suspend these reflexes, which could cause food to become inhaled into the lungs if there is vomiting or regurgitation under anesthesia.

Sometimes, though, the anesthesiologist will say it’s OK to drink clear liquids or take specific medications a few hours before surgery.

In the Operating Room

If general anesthesia is used, the anesthesiologist will start transitioning you from the normal awake state to the sleepy state of anesthesia. This is called induction, which is usually done by either injecting medicine through an IV or by inhaling gases through a mask.

If, like lots of people, you’re afraid of needles, the good news is that you may not have to get one while awake. Anesthesiologists often will begin the induction process by using a breathing mask to help you relax. The mask delivers medication to make you sleepy before and during the surgery. That way, you won’t be awake when the IV is inserted for general anesthesia or when a shot is given to numb a certain part or area of the body for local or regional anesthesia.

When using general anesthesia, the anesthesiologist will monitor your vital signs, continue to deliver anesthesia, and keep you as comfortable as possible throughout the operation.

To help you breathe and/or to help deliver general anesthesia during the operation, the anesthesiologist might use an endotracheal tube (a plastic tube that’s placed into the windpipe through the mouth or nose) or laryngeal mask airway (or LMA — a mask with a tube that fits into the back of the mouth).

During the procedure

Your anesthesiologist usually delivers the anesthesia medications through an intravenous line in your arm. Sometimes you may be given a gas that you breathe from a mask. Children may prefer to go to sleep with a mask.

Once you’re asleep, the anesthesiologist may insert a tube into your mouth and down your windpipe. The tube ensures that you get enough oxygen and protects your lungs from blood or other fluids, such as stomach fluids. You’ll be given muscle relaxants before doctors insert the tube to relax the muscles in your windpipe.

Your doctor may use other options, such as a laryngeal airway mask, to help manage your breathing during surgery.

Someone from the anesthesia care team monitors you continuously while you sleep. He or she will adjust your medications, breathing, temperature, fluids and blood pressure as needed. Any issues that occur during the surgery are corrected with additional medications, fluids and, sometimes, blood transfusions.

Blood transfusions may sometimes be necessary, such as during complex surgeries. The anesthesia care team monitors your condition and delivers blood transfusions when needed. Blood transfusions may involve risks. These risks are greater in people who are older, have low red blood cell volume or are undergoing complex heart surgeries.

After Surgery

Once the operation or procedure is over, you’ll be taken to the recovery room or PACU (post-anesthesia care unit). In the PACU, nurses and the anesthesiologist will monitor your condition very closely to make sure you are making a smooth and comfortable transition from an anesthetized state to an awakened state.

If you had general anesthesia or were sedated, don’t expect to be fully awake right away — it may take a while and you may doze off for a bit. It usually takes about 45 minutes to an hour to recover completely from general anesthesia. In some cases, this period may be a bit longer depending on medications given during or after surgery.

Although every person has a different experience, you may feel groggy, confused, chilly, nauseated, scared, alarmed, or even sad as you wake up. Depending on the procedure or surgery, you may also have some pain and discomfort afterward, which the anesthesiologist can relieve with medications. When you have recovered from the anesthesia, you’ll be evaluated to make sure you’re ready to leave the recovery room.

In many outpatient procedures, people are allowed to come home soon after the surgery is done. Before you leave the hospital, you’ll receive instructions for further recuperation at home and for a follow-up visit with the surgeon. Talk to the surgeon and/or the anesthesiologist about what to expect after the surgery and how you can stay as comfortable as possible.

Anesthesia is very safe. In today’s hospitals and surgery centers, highly trained professionals use a wide variety of modern medications and extremely capable monitoring technology to ensure that people are stable and as comfortable as possible before, during, and after their procedure.

After the procedure

When the surgery is complete, the anesthesia medications are stopped, and you slowly wake either in the operating room or the recovery room. You’ll probably feel groggy and a little confused when you first wake. You may experience common side effects such as:

  • Nausea
  • Vomiting
  • Dry mouth
  • Sore throat
  • Shivering
  • Sleepiness
  • Mild hoarseness

You may also experience other side effects after you awaken from anesthesia, such as pain. Side effects depend on your individual condition and the type of surgery. Your doctor may give you medications after your procedure to reduce pain and nausea.

During your anaesthetic

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.

Intravenous induction

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.

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.

Muscle relaxation

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.

Awake intubation

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.

Adolescents

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 hospitalization.

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.

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.

General anesthesia drugs

A general anesthetic (or anaesthetic) is a drug that can bring about a reversible loss of consciousness. Anesthesiologist (or anaesthetist) administers these drugs to induce or maintain general anesthesia to facilitate surgery. Some of these drugs are also used in lower dosages for pain management. The biological mechanisms of the action of general anesthetics are not well understood.

Mode of administration. Drugs given to induce general anesthesia can be either as gases or vapors (inhalational anesthetics) or as injections (intravenous anesthetics or even intramuscular). It is possible to deliver anesthesia solely by inhalation or injection, but most commonly the two forms are combined, with an injection given to induce anesthesia and a gas used to maintain it.

There are four main types of medications used in general anesthesia:

  1. Induction medications to produce unconsciousness
  2. Analgesics to provide pain relief
  3. Muscle relaxants to induce muscle relaxation
  4. Inhalational anesthetics to keep you unconscious.

Other medications which are given include:

  • medications that produce short-term memory loss or amnesia
  • medications that minimize nausea and vomiting (anti-emetics)
  • medications that counter-act the effect of other medications (antagonists)
  • and medications that suppress certain nervous reflexes, such as slowing of the heart.

Also, some patients may not have a general anesthetic but may remain conscious, with part of their body made numb by the use of local anesthetics.

Induction medications

These medications include thiopentone or pentothal (which was introduced in the 1930s), and propofol. When given by intravenous injection, these medications quickly make you unconscious. This rapid loss of consciousness makes the induction of anesthesia much more pleasant than previously, when patients had to breathe ether or chloroform.

Analgesics

These medications, also known as painkillers, are mostly opiates or narcotics. They are either derived from the opium poppy (such as morphine) or are synthesized in a laboratory (such as pethidine or meperidine, anileridine, fentanyl, alfentanil, sufentanil, and remifentanil).

Muscle relaxants

These medications work specifically to weaken or relax most of the (voluntary) muscles of the body. However, they do not affect the muscles of the heart, nor those of the intestines. Before muscle relaxants were introduced in the 1940s, patients had to be given large amounts of anesthetic medications to ensure that they were deeply anesthetized. This was necessary to cause their muscles to relax so that the surgeon could operate within the abdomen, or perform other delicate surgery. Now, with the use of muscle relaxants, patients do not have to receive very large amounts of anesthetic medications nor be so deeply anaesthetized. This helps to reduce the side-effects of anesthesia. Muscle relaxants include suxamethonium (or succinyl choline), pancuronium, atracurium, vecuronium, and rocuronium.

Inhalation general anesthetic

These medications keep you unconsciousness during the operation. They can also be used to induce anaesthesia, especially in small children. These medications are called inhalational agents because you inhale them or breathe them in. In the 1950s, a new inhalational agent, halothane, was introduced and rapidly replaced the older agents such as ether. Halothane has now been largely superseded by even better inhalation medications, and the commonly used agents include enflurane, isoflurane, sevoflurane, and desflurane.

Inhalational anaesthetic substances are either volatile liquids or gases, and are usually delivered using an anesthesia machine. An anesthesia machine allows composing a mixture of oxygen, anesthetics and ambient air, delivering it to the patient and monitoring patient and machine parameters. Liquid anesthetics are vaporized in the machine. All of these agents share the property of being quite hydrophobic (i.e., as liquids, they are not freely miscible—or mixable—in water, and as gases they dissolve in oils better than in water).

Many compounds have been used for inhalation anaesthesia, but only a few are still in widespread use.

  • Enflurane, desflurane, isoflurane and sevoflurane are the most widely used volatile anaesthetics today.

They are often combined with nitrous oxide. Older, less popular, volatile anaesthetics, include halothane, enflurane, and methoxyflurane. Researchers are also actively exploring the use of xenon as an anaesthetic.

Injection general anesthetic

Injectable general anesthetics are used for the induction and maintenance of a state of unconsciousness. Anaesthetists prefer to use intravenous injections, as they are faster, generally less painful and more reliable than intramuscular or subcutaneous injections.

Among the most widely used drugs are:

  • Propofol
  • Etomidate
  • Barbiturates such as methohexital and thiopentone/thiopental
  • Benzodiazepines such as midazolam
  • Ketamine is used in the UK as “field anaesthesia”, for instance at a road traffic incidents or similar situations where an operation must be conducted at the scene or when there is not enough time to move to an operating room, while preferring other anaesthetics where conditions allow their use. It is more frequently used in the operative setting in the US.

Benzodiazepines are sedatives and are used in combinations with other general anesthetics.

Anti-emetics

These medications help reduce nausea and vomiting and so are termed anti-nauseants or anti-emetics. They include droperidol, Stemetil, Gravol, and ondansetron.

Other medications

Your anaesthetist may use other medications to decrease the chance of you remembering anything that happens in the Operating Room. These medications include diazepam and midazolam, which belong to the class of medications known as benzodiazepines. Some medications are given to counteract the effects of other medications. These include naloxone, to counter the effects of an opiate or narcotic; flumazenil, to counter the effects of a benzodiazepine; and neostigmine, to reverse the actions of most of the muscle relaxants. Medications which are used to change your heart rate include atropine (to increase it) and esmolol (to decrease it). Other medications can raise your blood pressure (epinephrine or adrenaline) or lower it (nitroprusside).

Local anesthetics

Injection of a local anaesthetic around a nerve or a group of nerves temporarily blocks the transmission of the electrical impulses in the nerve. The lack of transmission causes the area of the body supplied by the nerve to become numb. This is also known as a ‘sensory block’, which may progress to muscle weakness, depending on the concentration and dose of the local anaesthetic used.

How does your anaesthetist know how much to give you ?

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.

General anesthesia risks

General anesthesia today is very safe. In very rare cases, general anesthesia can cause complications (such as strange heart rhythms, breathing problems, allergic reactions to medications, and even death). The likelihood of a complication occurring is proportional to a variety of factors related to the patient’s health, the kind of procedure (complexity of the surgery being performed) and the type of anesthesia used. Be sure to talk to your doctor, surgeon, and/or anesthesiologist about any concerns.

Most complications can be prevented by giving the anesthesiologist complete information before the surgery about things like:

  • your current and past health (including diseases or conditions such as recent or current colds, or other issues such as snoring or depression)
  • any medications (prescription and over-the-counter), supplements, or herbal remedies you are taking
  • any allergies (especially to foods, medications, or latex) you may have
  • whether you smoke, drink alcohol, or take any recreational drugs
  • any previous reactions you or any family member has had to anesthesia

To ensure your safety during the surgery or procedure, it’s extremely important to answer all of the anesthesiologist’s questions as honestly and thoroughly as possible. Things that may seem harmless could affect how you react to the anesthesia.

It’s also important that you follow the doctor’s recommendations about what not to do before the surgery. You probably won’t be able to eat or drink (usually nothing after midnight the day before) and may need to stop taking herbal supplements or other medications for a certain period of time before surgery.

You can rest assured that the safety of anesthetic procedures has improved a lot over the years, thanks to advances in technology and the extensive training anesthesiologists receive. The more informed, calm, and reassured you are about the surgery and the safety of anesthesia, the easier the experience will probably be.

General anesthesia side effects

General anesthesia is overall very safe; most people, even those with significant health conditions, are able to undergo general anesthesia itself without serious problems.

General anesthetics side effects—such as dangerously low blood pressure—are much less common than they once were. Still, as with any medical procedure, some risks exist. To minimize these risks, specialized doctors called anesthesiologists carefully monitor unconscious patients and can adjust the amount of anesthetic the patients receive.

In fact, your risk of complications is more closely related to the type of procedure you’re undergoing and your general physical health, rather than to the type of anesthesia.

Older adults, or those with serious medical problems, particularly those undergoing more extensive procedures, may be at increased risk of postoperative confusion, pneumonia, or even stroke and heart attack.

Specific conditions that can increase your risk of complications during surgery include:

  • Smoking
  • Seizures
  • Obstructive sleep apnea
  • Obesity
  • High blood pressure
  • Diabetes
  • Other medical conditions involving your heart, lungs or kidneys
  • Medications, such as aspirin, that can increase bleeding
  • History of heavy alcohol use
  • Drug allergies
  • History of adverse reactions to anesthesia

These risks are generally related to the surgery itself, not the anesthesia.

Common Side Effects of General Anesthesia

You will most likely feel disoriented, groggy, and a little confused when waking up after surgery. Some other common side effects, which should go away fairly quickly, include:

  • feeling sick and vomiting – this usually occurs immediately, although some people may continue to feel sick for up to a day
  • shivering and feeling cold – this may last a few minutes or hours
  • confusion and memory loss – this is more common in elderly people or those with existing memory problems; it’s usually temporary, but occasionally can be longer lasting
  • bladder problems – you may have difficulty passing urine
  • dizziness – you will be given fluids to treat this
  • bruising and soreness – this may develop in the area where you were injected or had a drip fitted; it usually heals without treatment
  • sore throat – during your operation, a tube may be inserted either into your mouth or down your throat to help you breathe; afterwards, this can cause a sore throat
  • damage to the mouth or teeth – a small proportion of people may have small cuts to their lips or tongue from the tube, and some may have damage to their teeth; you should tell your anaesthetist about any dental work you have had done

A number of more serious complications are associated with general anaesthetics, but these are rare.

Possible serious complications and risks include:

  • a serious allergic reaction to the anaesthetic (anaphylaxis)
  • waking up during your operation – the amount of anaesthetic given will be continuously monitored to help ensure this doesn’t happen
  • death – this is very rare, occurring in around 1 in every 100,000 cases

Serious problems are more likely to occur if you’re having major or emergency surgery, you have any other illnesses, you smoke, or you’re overweight.

Your anaesthetist will discuss the risks with you before your operation. You should try to stop smoking or drinking alcohol in the weeks before surgery, as doing so will reduce your risk of developing complications.

You may also be advised to lose weight, and if you can you should increase your activity levels in the weeks before surgery, as this is likely to reduce your risk as well.

In most cases, the benefits of being pain-free during an operation outweigh the risks.

What is Anesthesia awareness ?

Estimates vary, but about 1 or 2 people in every 10,000 may be partially awake during general anesthesia and experience what is called unintended intraoperative awareness. It is even rarer to experience pain, but this can occur as well.

Because of the muscle relaxants given before surgery, people are unable to move or speak to let doctors know that they are awake or experiencing pain. For some patients, this may cause long-term psychological problems, similar to post-traumatic stress disorder.

This phenomenon is so rare that it’s difficult to make clear connections. Some factors that may be involved include:

  • Emergency surgery
  • Cesarean delivery
  • Depression
  • Use of certain medications
  • Heart or lung problems
  • Daily alcohol use
  • Lower anesthesia doses than are necessary used during procedure
  • Errors by the anesthesiologist, such as not monitoring the patient or not measuring the amount of anesthesia in the patient’s system throughout the procedure.

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