Anesthesia components

Note CLapp,c apparent membrane permeability clearance for carrier-mediated transport component at lower concentrations where it is highly efficient SI, small intestine ileum for taurocholate and midgut for the others. Absorption was evaluated in our laboratory using the closed loop of the rat intestine in situ (urethane anesthesia, 1.125 g/4.5 ml/kg, i.p.) in 60 min for riboflavin and 30 min for the others. 

In surgical practice, the term general anesthesia (narcosis) presently refers to the condition of an organism with a reversible loss of consciousness at a controlled level of nervous system suppression. It includes the following components analgesia (absence of pain), amnesia (absence of memory), suppression of reflexes such as bradycardia, laryngospasm, and loss of skeletal muscle tonicity. 

Monitored anesthesia care-As an analgesic component of monitored anesthesia care. 

Among the earliest proposals to explain the mechanism of action of anesthetics is the concept that they interact physically rather than chemically with lipophilic membrane components to cause neuronal failure. However, this concept proposes that all anesthetics interact in a common way (the unitary theory of anesthesia), and it is being challenged by more recent work demonstrating that specific anesthetics exhibit selective and distinct interactions with neuronal processes and that those interactions are not easily explained by a common physical association with membrane components. Proposals for the production of anesthesia are described next. 

Anesthesia from Physicai Interactions with Lipophiiic Membrane Components... 

Anesthesia from Selective Interactions of Anesthetics with Cellular Components... 

Previously used as component of "Magic Numbing Solution" or TAC Sol (epinephrine 1 2,000, tetracaine 0.5%, cocaine 11.8%) and LET Sol (lidocaine 4%, epinephrine 0.1%, tetracaine 0.5%), which are used as topical anesthesia for repair of minor lacerations. Topical tetracain solutions no longer available... 

Both the inhaled and the intravenous anesthetics can depress spontaneous and evoked activity of neurons in many regions of the brain. Older concepts of the mechanism of anesthesia evoked nonspecific interactions of these agents with the lipid matrix of the nerve membrane (the so-called Meyer-Overton principle)—interactions that were thought to lead to secondary changes in ion flux. More recently, evidence has accumulated suggesting that the modification of ion currents by anesthetics results from more direct interactions with specific nerve membrane components. The ionic mechanisms involved for different anesthetics may vary, but at clinically relevant concentrations they appear to involve interactions with members of the ligand-gated ion channel family. 

Nelson LE et al The sedative component of anesthesia is mediated by GABAa receptors in an endogenous sleep pathway. Nat Neurosci 2002 5 979. [PMID 12195434]... 

Several other formal features of Huxley s trance condition are of interest with respect to the analogy we have drawn with REM sleep dreaming. We first consider the relaxed posture, indicating a step on the path to cataplexy. In full-blown cataplexy, the assumption of a flaccid posture is associated with the inability to move on command and is thus similar to the active motor paralysis of REM sleep dreams. Anesthesia and amnesia were both present in Huxley s trance, although they tended to be selective, and when Huxley attempted to make them global, his trance deepened. Time distortion, a distinctive component of the orientational instability of dreams, was a robust aspect of Huxley s altered state. 

Analgesic efficacy and clinical use Nalbuphine (Errick and Heel, 1983 Schmidt et al., 1985) is a medium potent opioid analgesic used for the treatment of moderate to severe pain and inter-operatively as adjunct to anesthesia. Because of its antagonistic action component, analgesia may be subject to a ceiling level. 

As a component of balanced anesthesia (intravenous administration) For control of ethanol or other sedative-hypnotic withdrawal states For muscle relaxation in specific neuromuscular disorders... 

The chemical structures of the currently available inhaled anesthetics are shown in Figure 25-1. Nitrous oxide, a gas at ambient temperature and pressure, continues to be an important component of many anesthesia regimens. Halothane, enflurane, isoflurane, desflurane, sevoflurane, and methoxyflurane are volatile liquids. 

Several drugs are used intravenously, alone or in combination with other drugs, to achieve an anesthetic state (as components of balanced anesthesia) or to sedate patients in intensive care units who must be mechanically ventilated. These drugs include the following (1) barbiturates (thiopental, methohexital) (2) benzodiazepines (midazolam, diazepam) (3) opioid analgesics (morphine, fentanyl, sufentanil, alfentanil, remifentanil) (4) propofol (5) ketamine and (6) miscellaneous drugs (droperidol, etomidate, dexmedetomidine). Figure 25-2 shows the structures of... 

Propofol (2,6-diisopropylphenol) is an extremely popular intravenous anesthetic. Its rate of onset of action is similar to that of the intravenous barbiturates recovery is more rapid and patients are able to ambulate sooner after propofol. Furthermore, patients subjectively "feel better" in the immediate postoperative period after propofol as compared with other intravenous anesthetics. Postoperative nausea and vomiting is less common because propofol has antiemetic actions. Propofol is used for both induction and maintenance of anesthesia however, cumulative effects can delay arousal following prolonged infusion. These favorable properties are responsible for the extensive use of propofol as a component of balanced anesthesia and for its great popularity as an anesthetic for use... 

Some individual components of the injury experience have been studied separately in animal experiments. Pain, fear, hemorrhage, and tissue damage can all stimulate epinephrine production (Wl). Inhalational anesthesia stimulates the adrenal medulla but in deep anesthesia with intravenous barbiturates adrenomedullary secretion may be greatly diminished. 

Propofol is being examined for its potential as a routine i.v. induction agent in the horse, as well as a component of TIVA, as an alternative to maintenance of anesthesia with inhalant agents. Propofol has not been adopted for widespread use in equine anesthesia yet and cost plays a role currently. 

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