Anesthetic
An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia — in other words, to result in a temporary loss of sensation or awareness. They may be divided into two broad classes: general anesthetics, which result in a reversible loss of consciousness, and local anesthetics, which cause a reversible loss of sensation for a limited region of the body without necessarily affecting consciousness.[3][4]
Not to be confused with aesthetics or analgesic.A wide variety of drugs are used in modern anesthetic practice. Many are rarely used outside anesthesiology, but others are used commonly in various fields of healthcare. Combinations of anesthetics are sometimes used for their synergistic and additive therapeutic effects. Adverse effects, however, may also be increased.[5] Anesthetics are distinct from analgesics, which block only sensation of painful stimuli.[6][4] Analgesics are typically used in conjunction with anesthetics to control pre-, intra-, and postoperative pain.[4]
While opioids can produce unconsciousness, they do so unreliably and with significant side effects.[13][14] So, while they are rarely used to induce anesthesia, they are frequently used along with other agents such as intravenous non-opioid anesthetics or inhalational anesthetics.[11] Furthermore, they are used to relieve pain of patients before, during, or after surgery. The following opioids have short onset and duration of action and are frequently used during general anesthesia:
The following agents have longer onset and duration of action and are frequently used for post-operative pain relief:
Muscle relaxants do not render patients unconscious or relieve pain. Instead, they are sometimes used after a patient is rendered unconscious (induction of anesthesia) to facilitate intubation or surgery by paralyzing skeletal muscle.[4]These agents fall into two categories: depolarizing agents, which depolarize the motor end plate to prevent further stimulation, and non-depolarizing agents, which prevent acetylcholine receptor activation through competitive inhibition.[4]
A potential complication where neuromuscular blockade is employed is 'anesthesia awareness'.[4] In this situation, patients paralyzed may awaken during their anesthesia, due to an inappropriate decrease in the level of drugs providing sedation or pain relief. If this is missed by the anesthesia provider, the patient may be aware of their surroundings, but be incapable of moving or communicating that fact. Neurological monitors are increasingly available that may help decrease the incidence of awareness. Most of these monitors use proprietary algorithms monitoring brain activity via evoked potentials. Additionally, anesthesia providers often have steps they follow to help prevent awareness, such as ensuring all equipment is working properly, monitoring that drugs are being delivered during surgery, and asking a series of questions (the Brice questions) to help detect awareness after surgery.[4] If there is any suspicion of patient awareness, close follow-up and mental health professionals can help manage or avoid any traumatic stress associated with the awareness.[4] Certain procedures, such as endoscopies or colonoscopies, are managed a technique called conscious sedation or monitored anesthesia care. These cases are performed with regional anesthetics and a "twilight sleep" achieved through sedation with propofol and analgesics, and patients may remember perioperative events.[4] When this technique is used, patients should be advised that this is management is distinct from general anesthesia to help combat any belief or fear that they were "awake" during anesthesia.[4]