Anesthetic

Ester local anesthetics are generally unstable in solution and fast-acting, are rapidly metabolised by cholinesterases in the blood plasma and liver,[4] and more commonly induce allergic reactions.

Amides have a slower onset and longer half-life than ester anesthetics,[4] and are usually racemic mixtures, with the exception of levobupivacaine (which is S(-) -bupivacaine)[4] and ropivacaine (S(-)-ropivacaine).

Although general rules exist for onset and duration of anesthesia between ester- or amide-based local anesthetics, these are properties are ultimately dependent on myriad factors including the lipid solubility of the agent, the concentration of the solution, and the pKa.

[4] Amides are generally used within regional and epidural or spinal techniques,[4] due to their longer duration of action, which provides adequate analgesia for surgery, labor, and symptomatic relief.

It should possess low blood gas solubility, have no end-organ (heart, liver, kidney) toxicity or side-effects, should not be metabolized, and should not irritate the respiratory pathways.

These properties allow for a less irritating and quicker induction as well as a rapid emergence from anesthesia compared to other inhaled agents.

Volatile agents are frequently compared in terms of potency, which is inversely proportional to the minimum alveolar concentration.

However, etomidate has since been shown to produce adrenocortical suppression, resulting in decreased use to avoid an increased mortality rate in severely ill patients.

[4] However, like etomidate it is frequently used in emergency settings and with sick patients because it produces fewer adverse physiological effects.

[11] Unlike the intravenous anesthetic drugs previously mentioned, ketamine produces profound pain relief, even in doses lower than those that induce general anesthesia.

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] 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.

[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.