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.
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. Anesthetics are distinct from analgesics, which block only sensation of painful stimuli.
- Depolarizing muscle relaxants e.g. Suxamethonium
- Hyperkalaemia – A small rise of 0.5 mm ol/l occurs normally; this is of little consequence unless potassium is already raised such as in kidney failure
- Hyperkalaemia – Exaggerated potassium release in burn patients (occurs from 24 hours after injury, lasting for up to two years), neuromuscular disease and paralyzed (quadriplegic, paraplegic) patients. The mechanism is reported to be through up regulation of acetylcholine receptors in those patient populations with increased efflux of potassium from inside muscle cells. It may cause life-threatening arrhythmia.
- Muscle aches, commoner in young muscular patients who mobilize soon after surgery
- Bradycardia, especially if repeat doses are given
- Malignant hyperthermia, a potentially life-threatening condition in susceptible patients
- Suxamethonium apnea, a rare genetic condition leading to prolonged duration of neuromuscular blockade, which can range from 20 minutes to a number of hours. Not dangerous as long as it is recognized and the patient remains intubated and sedated, there is the potential for awareness if this does not occur.
Non-depolarizing muscle relaxants
- Histamine release e.g. Atracurium and Mivacurium
Another potentially disturbing complication where neuromuscular blockade is employed is 'anesthesia awareness'. 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. Despite the widespread marketing of these devices, many case reports exist in which awareness under anesthesia has occurred despite apparently adequate anesthesia as measured by the neurologic monitor.
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