Also called total body anesthesia, general anesthesia is basically the state of unconsciousness and unresponsiveness a patient is medically put into before a medical procedure. In other words, general anesthesia is a state of drug-induced coma. The drug(s) used to achieve this state is called an anesthetic. When in general anesthesia mode, the patient doesn’t feel pain and is motionless. And upon waking up, the patient would have no idea about things that happened when he was unconscious or motionless.

The anesthesia drug is usually administered by a specialist called anesthetist or anesthesiologist. The anesthetic could be administered as inhaling gas or injection. Besides making the patient unconscious, the anesthetic eliminates the patient’s natural pain response, causes amnesia (memory loss) and immobility, and relaxes the muscles. To maintain the anesthesia mode, a mix of inhalational agents, hypnotic agents, muscle relaxants, opioids, cardiovascular drugs, sedatives, along with thermoregulatory and ventilatory support could be required.

History

Anesthetics has been in use in the medical field since 1842. Before general anesthesia came into being, alcohol was used as analgesic. In fact, alcoholic drinks were commonly administered to armed forces personnel before surgery. However, since the anesthetic effect was often inadequate, the doctor would invariably be under pressure to complete the surgical procedure as quickly as possible. Later, more formal analgesics became available in the form of chloroform and ether. Chloroform was especially popular in England and Scotland. However, administering these drugs in the right proportion was quite a challenge since they were provided using a sponge soaked into them which was then placed onto the nose.  

Modern-day medicine resorts to a more blended approach incorporating inhalable gases’ mixtures, including nitrous oxide (also called laughing gas) and several ether derivatives such as desflurane, sevoflurane and isoflurane.

Working Mechanism

There’s not much clarity about how anesthetics work. It’s believed the drug used blocks the signals usually transported along the nerves to the brain. As a result, the brain doesn’t recognize or process any stimulation or impact to the body. There’s one more theory stating the drugs dissolve a portion of the fat found in brain cells, thereby altering the cells’ activity. The spinal cord gets affected as well, which explains why the patient goes immobile.

Furthermore, it’s believed the normal functioning of certain neurons is interrupted. The anesthetics attach to and disable many different proteins on the neurons’ surface. These proteins are required for regulating sleep, learning, memory, and attention. However, more than all of that, anesthetics impede interaction between the different areas of the brain, thereby causing unconsciousness as a whole. But neuroscientists haven’t been able to confirm those areas exactly.

General Anesthesia Stages

There are four general anesthesia stages:

  • Induction: This stage refers to the period starting from drug administration and it ends when the patient loses consciousness.
  • Excitement: This is the period starting right after loss of consciousness. During this stage, the patient’s heart rate and breathing go haywire, and pupil dilation (variation in pupil size), breath holding and nausea could occur. Due to volatile breathing and vomiting risk, choking is possible. Doctors therefore use drugs to make sure this ‘excitement’ stage is cut short as much as possible.
  • Surgical anesthesia: In this stage, the patient’s muscles relax, breathing regains normalcy and vomiting halts. Eye movements lose pace and eventually come to a standstill. This is the stage when doctors operate on the patient. The objective of the anesthetist is to keep the patient in this stage for the longest possible time during surgery.
  • Overdose: The patient enters this stage only when the dosage exceeds acceptable limits. This is a dangerous stage and could lead to cardiovascular and respiratory problems.

Before administering anesthetics, the patient could be given premedication to enter a state of sedation. The premedication practice was instituted as medications such as scopolamine and morphine made it easier for patients to tolerate highly pungent chloroform and ether vapors that were administered as anesthetics. Premedication is usually administered in a separate room so that the patient enters the operating theater calm and relaxed, ensuring zero memories attached to the room after the procedure. In case of surgeries involving major organs, a muscle relaxant could also be administered to achieve a deeper state of unconsciousness.

Dosage Levels

Appropriate anesthetic levels should be adopted for both the planned operation and interim stages. The level of anesthesia required would vary with the specific operation being performed and the various stages. In case of complex plastic surgeries, a good amount of anesthetics may be needed before surgery. Halfway into the surgery when the surgeon is preparing the patient’s skin (for example), an extremely moderate level of anesthetics would suffice. Right before the surgeon starts making the incision, a deeper anesthesia level would be needed. For effective and right anesthetic administration, the anesthesiologist should know the job well and must also have a good rapport with the surgeon.

Typically, the anesthetics administered as the operation progresses would be the minimum amount required to ensure sufficient anesthesia effect. Good judgment is needed to determine the minimum level of anesthesia. There are also machines that simplify things for the anesthesiologist. However, these equipment aren’t as widely used. Certain signs from the patient such as sweating, hypertension, capillary dilation, etc. help confirm if the patient needs more or a deeper anesthetic. Decreased blood pressure and heart rate are signs indicating deeper anesthetic levels. If the anesthetics administered are extremely deep, vital organs of the body may feel the brunt as the lymphatic system or circulatory system could get jeopardized. In extremely rare cases, the patient may even die.

Administration Form

As aforementioned, the anesthetic could be a liquid or gas. Liquid anesthetics are injected into the patient’s veins on the back of his hand via a cannula – a thin, plastic tube. The gas, on the other hand, is administered using a mask which the patient is supposed to breathe into. Since anesthetics may cause breathing troubles, a tube is usually inserted into the patient’s mouth (in the trachea) so that the airway stays open.  

The anesthetics would start working almost within seconds (not more than a minute), with the patient feeling light-headed prior to becoming unconscious. At times, especially during complex and lengthy surgeries and/or when the patient is scared of needles, the anesthetist could first administer general anesthesia through the breathing mask and then intravenously after the patient is asleep.

Role of the Anesthetist

The anesthetist would stay in the operating theater throughout the length of the surgery, so that more anesthesia can be administered if the patient shows signs of consciousness before the medical procedure is completed. Once the operation is complete, the anesthetist would stop administration. Generally, the anesthetist would use a variety of medications along with anesthetics to relieve anxiety, keep the patient asleep, reduce pain during operation and eliminate pain after surgery with the help of analgesics (painkillers), and relax muscles to help keep the patient still.

Anesthesia Drugs

The intravenous anesthetic agent could be barbiturates (methohexital, thiopental, and thiamylal). These are water-soluble and act rapidly. However, these barbiturates aren’t common anymore and have been replaced by nonbarbiturate intravenous anesthetics such as propofol. Propofol is associated with little postoperative vomiting and nausea and a much quicker and clear-headed recovery.

General anesthesia could be induced by vapor inhalation as well. The inhalation technique is quite common and works well with putting uncooperative patients (such as kids) to sleep. Sevoflurane is a nonflammable, sweet-smelling ether (chemical) used in the inhalation technique. Other analgesic gases used are meperidine, morphine, and hydromorphone, to name a few.

Pre-Surgery Assessment

Before administering anesthetics, the anesthetist would assess the patient’s condition to ascertain the drug(s) to use, and the quantity and combination. The things examined during this stage include the patient’s medical history, body mass index or BMI, age, existing medicine usage, drug/alcohol intake, head extension and neck flexibility, and mouth and airway.

Why Chose General Anesthesia?

General anesthesia is a type of anesthesia – the other kinds being local anesthesia and regional anesthesia. Doctors often have to choose between drugs that induce general or local anesthesia. At times, the patient is given the option. Drugs for general anesthesia are usually chosen when the procedure is expected to be intensive and time-consuming; significant blood loss and breathing difficulties are a possibility; and/or the patient could feel uncomfortable during the operation if awake.

Risks

General anesthesia is usually a safe state of being. However, things could go wrong if the surgery is lengthy and/or the patient is relatively old. The negative outcomes could be a heart attack, postoperative confusion, consciousness during surgery, stroke and pneumonia. Injuries to the peripheral nerves could be another concern. Patients who have certain medical issues are at a greater risk of not responding well to general anesthesia drugs. Those medical conditions include seizures, high blood pressure, smoking, alcoholism, diabetes, drug allergies, obesity, etc. Death due to general anesthesia is a possibility but it’s extremely rare, with the probability being 0.001 percent.

It’s important the details procured during pre-surgery evaluation are comprehensive and accurate. Any discrepancies could lead to major problems. For example, if the patient has a history of drug or alcohol use but that’s not mentioned on the pre-surgery assessment report, insufficient quantities of the anesthetic could be administered that could amount to unintended operative awareness or high blood pressure.   

Side Effects

There are quite a few potential side effects to general anesthesia. The anesthetist would detail the patient in brief about the possible side effects before administering the drugs. The side effects experienced would differ across patients, with some not experiencing any. The common side effects are memory loss (usually in older patients), dizziness, urine difficulties, soreness or bruising at the injection site, vomiting and nausea, and sore throat (caused by the breathing tube). The patient would likely feel disoriented and need external assistance with getting things done.

Recovery & Impact

Right after surgery, the patient is directed to a post-anesthesia care unit (PACU) for close monitoring, for at least 24 hours. Warm fluids are administered intravenously to wear away the anesthesia’s dehydration effect and shivering that were caused due to body temperature changes. Patients usually take some time to beat the general anesthesia effect, though some could wake up within an hour post-surgery. 

The impact of general anesthesia may stay for a day or two after surgery. The anesthetics could impact the patient’s concentration, memory and reflexes for a couple of days. Doctors would recommend an adult to stay with the patient for a day or two. The patient would also be advised to strictly refrain from drinking alcohol, driving, signing legal documents, or indulging in any other critical activity that require complete awareness for at least a couple of days.

What If Patient Gains Consciousness Mid-Operation?

At times, a patient could wake up (usually partially) during surgery or anesthetic administration – some patients may even feel pain. This could be if the anesthesia drug was inadequately administered, the machine(s) monitoring the patient has a malfunction, and/or the patient was not monitored properly. The awake patient is usually not able to signal or communicate to the doctor about his state of consciousness due to the anesthetic drug’s muscle-relaxing traits. Even if the patient gains consciousness during surgery, he would most likely not feel much pain since painkilling medications would have been already administered through his veins.

Fortunately, these incidences are extremely rare, with the chances of occurrence being 0.005 percent. Moreover, the consciousness is usually before surgery. Thanks to the rareness of such unintended awareness, not a lot of effort has been put in to learn what actually causes the issue. However, emergency surgery, anesthesiologist error, patient depression, lung or heart issues, etc. are, however, believed to be risk factors.