LD261115 1PHARMACOLOGY SPRING TERM 2017 Dr LEONARDO DASSO Lecture 66 GENERAL ANESTHETICS GENERAL ANESTHESIA The state of “general anesthesia” usually includes: Analgesia Amnesia Loss of consciousness Suppression of sensory and autonomic reflexes Skeletal muscle relaxation An ideal anesthetic would: Induce anesthesia smoothly and rapidly Permit rapid recovery Possess wide margin of safety Be devoid of adverse effects BALANCED ANESTHESIA No single drug is capable of achieving all of the desired goals of anesthesia. Accordingly, in a method termed balanced anesthesia,several inhaled and/or IV drugs are used in combinationto produce the anesthetic state. 1.Anesthetic partial pressure for an inhalational agent in the brain is not attained rapidly, therefore patients are usually anesthetized with an IV agent. 2.Halogenated hydrocarbons inhaled general anesthetics often exhibit inadequate degrees of analgesia, therefore a supplemental analgesic(i.e., an opioidor N2O) is required. 3.Neuromuscular blocking agentsmust be used to provide paralysis adequate for surgical access. 4.The anesthetic plan is designed to minimize any undesirable cardiovascular and respiratory responses to these drugs. This includes using drug combinations that minimize the dose of the halogenated hydrocarbon anesthetic. For example, N2O 25-40%, which by itself produces minimal cardiovascular depression, is frequently used in combination with a halogenated hydrocarbon.
LD261115 2ANESTHESIA PROTOCOLS Vary depending on the type of intervention: Diagnostic Therapeutic Surgical For minor procedures, so-called monitored anesthesia care or conscious sedationis used, employing oral or parenteral sedatives in conjunction with local anesthetics. These techniques provide profound analgesia, but with retention of the patient's ability to maintain a patent airway and to respond to verbal commands. For more extensive surgical procedures, anesthesia frequently includes the use of preoperative benzodiazepines, induction of anesthesia withIV thiopental or propofol,and maintenance of anesthesia with a combination of inhaled and intravenous anesthetic drugs. Such protocols also often include the use of neuromuscular blocking drugs. TYPES OF GENERAL ANESTHETICS General anesthetics are administered by inhalation or by IV injection. INHALED ANESTHETICS Inhaled anesthetics can be divided into two classes based on their physical properties. Nitrous oxide(N2O) is a gas at ambient temperature. All other inhaled anesthetics are halogenated hydrocarbons.They are volatile liquids that are vaporized by the application of heat supplied by a vaporizer. Examples of halogenated hydrocarbons are halothane, enflurane, isoflurane, desflurane, sevoflurane and methoxyflurane.