General anaesthetic

Doctors use special medicine to help you sleep. This medicine helps you stay still. You will not feel pain. You will not remember the doctor's work.

This medicine can be a gas. You breathe it in through a mask. It can also be a liquid. A doctor can put it in your vein.

Most doctors use both ways. They use a shot to help you sleep fast. Then they use gas to keep you asleep.

Doctors watch you very closely. They make sure you stay safe. It is a very helpful tool.

General anesthetics are special medicines. They make people lose consciousness. This means the person is asleep. They do not feel pain. They also do not remember what happened.

Doctors can give these medicines in two ways. One way is through a gas. A person breathes the gas through a mask. This uses an anesthesia machine. The machine mixes oxygen with the gas. Another way is through an injection. A doctor puts the liquid into a vein. This is often faster and more reliable. Most doctors use both ways together. They use an injection to start the sleep. Then they use gas to keep the person asleep.

These medicines work by changing how the brain works. They act on receptors. Receptors are tiny parts in the brain. Some drugs turn on receptors that slow the brain down. Other drugs turn off receptors that wake the brain up. This helps the person stay still and asleep. Doctors must watch the patient very closely. They check breathing and heart rate to keep the patient safe.

General anesthetics are special medicines used during surgery. They make a person lose consciousness, which means they are in a deep sleep. These drugs also help a patient stay still and not feel pain. They can even cause amnesia, so the person does not remember the procedure. Doctors use these tools to make sure surgery is safe and comfortable.

There are two main ways to give these medicines. One way is through inhalation, which means breathing in a gas or vapor. An anesthesia machine mixes oxygen with the medicine to help the patient breathe. The other way is through an injection, often into a vein. Most doctors use both ways at the same time. They use an injection to start the sleep quickly. Then, they use gas to keep the person asleep during the whole operation.

These medicines work by changing how the brain sends signals. They act on tiny parts of the brain called receptors. Some drugs, like propofol or midazolam, turn on inhibitory receptors. These receptors act like brakes to slow the brain down. Other drugs, like ketamine, work on different receptors to block signals. This helps the brain stay in a state where it does not react to pain. Scientists are still studying exactly how all these different parts work together.

Many different types of medicines are used by doctors today. For breathing in, doctors often use sevoflurane or isoflurane. For injections, they might use drugs called barbiturates or benzodiazepines. In the UK, doctors sometimes use ketamine for field anesthesia at road accidents. In the US, ketamine is often used in operating rooms. Doctors must be very careful because these drugs can change breathing or blood pressure.

Going under anesthesia happens in stages. First, a person might feel confused or lose their memory. Next, they might enter a stage of excitement where they feel delirious. Then comes surgical anesthesia, where breathing becomes regular again. Doctors check the eyes and pupils to see how deep the sleep is. Finally, they must ensure the patient does not go too deep into a dangerous state. This careful watching keeps the patient safe throughout the entire process.

General anesthetics are a diverse group of chemical compounds used in medical practice. They are designed to induce a loss of consciousness in humans or a loss of the righting reflex in animals. In a clinical setting, these drugs can also induce a coma. This state prevents a patient from being aware of painful stimuli during surgery. It is important to distinguish these from sedatives or analgesics, which serve different purposes. While analgesics focus on pain, general anesthetics aim to achieve a complete state of unresponsiveness. This state typically involves several reversible effects: immobility, analgesia, amnesia, unconsciousness, and reduced autonomic responsiveness to noxious stimuli.

To achieve these effects, doctors use different methods of administration. Inhalational anesthetics are delivered as gases or volatile liquids. These are typically managed using an anesthesia machine. This machine creates a mixture of oxygen, ambient air, and the anesthetic agent. The machine also monitors the patient and the equipment. Most liquid anesthetics are vaporized within the machine before being inhaled. Common volatile anesthetics used today include sevoflurane, isoflurane, and desflurane. These are often combined with nitrous oxide. Other older options include halothane, enflurane, and methoxyflurane. Researchers are also studying xenon for potential use.

Another method is through injection, which can be intravenous, intramuscular, or subcutaneous. Anesthetists generally prefer intravenous injections because they are faster and more reliable. They are also typically less painful for the patient. Common injectable drugs include propofol and etomidate. Doctors also use barbiturates, such as methohexital and thiopentone. Benzodiazepines, like midazolam, are often used as sedatives in combination with other drugs. In the United Kingdom, ketamine is used for "field anesthesia" during emergencies like road traffic incidents. This allows operations to occur at the scene. In the United States, ketamine is more frequently used in standard operative settings.

How these drugs actually work is a complex subject of ongoing research. It is believed that they act by targeting specific pathways in the central nervous system (CNS). One primary method is the activation of inhibitory receptors. This means the drugs turn on parts of the brain that slow down activity. Another method is the inactivation of excitatory receptors. By blocking these, the drugs prevent the brain from sending certain signals. Doctors often use a combinatorial drug approach. This means they use different drugs together to control both the state of unconsciousness and any physiological side effects.

Scientists have identified several specific biological targets for these drugs. GABAA receptor agonists are a major group. These drugs, such as propofol and benzodiazepines, act on chloride channels to hyperpolarize neurons. This action helps induce sedation or unconsciousness. Another target is the NMDA receptor. Ketamine acts as an NMDA receptor antagonist. This helps with analgesia and can alter arousal. When used alone, ketamine can cause a dissociative state involving hallucinations. Additionally, some anesthetics affect two-pore potassium channels, known as K2Ps. These channels help regulate the resting membrane potential in neurons. Activating these channels reduces neuronal excitability. Research shows that specific channels, like TREK-1 and TASK, play roles in inducing anesthesia.

Other drugs are used to support the main anesthetic state. Opioid receptor agonists, such as fentanyl or morphine, are used for their analgesic effects. While they can cause sedation, they do not cause a loss of consciousness on their own. Therefore, they are used alongside other anesthetics. Dexmedetomidine is an alpha2 adrenergic receptor agonist that produces sedation similar to non-REM sleep. Patients can be easily aroused from this state. In the past, dopamine receptor antagonists were used to create neuroleptic anesthesia. This included states of catalepsy and unresponsiveness. However, these are no longer used because patients often remained aware of the medical procedures despite being unable to move.

As a patient receives anesthesia, they pass through distinct stages known as Guedel's signs. The first stage is analgesia, where the patient may feel confusion or amnesia. The second stage is excitement, characterized by delirium, confusion, and irregular breathing. Patients may experience nausea, vomiting, or even panic during this stage. The third stage is surgical anesthesia. This is when normal breathing resumes, though it may eventually cease. Doctors monitor the depth of this stage by checking pupil size and eye movement. The final stage is medullary depression. In this stage, respiration stops and circulatory failure can occur. Without medical support for breathing and circulation, death is common at this stage.

General anesthetics also cause various physiological side effects that require careful management. They can lead to a reduction in blood pressure by dilating vasculature or reducing cardiac contractility. This drop can sometimes trigger a reflex increase in heart rate. Patients are also at risk for hypothermia. This happens because vasodilation increases heat loss through the skin. Furthermore, anesthetics affect the respiratory system by reducing tidal volume and the respiratory rate. They also dampen protective reflexes like coughing or gagging. This increases the risk of airway obstruction or asphyxiation. Because of these risks, healthcare providers must use devices like endotracheal tubes to ensure safety.