Anesthetic drugs common

The anesthesiologist selects the anesthetic drug that will produce safe anesthesia, analgesia (absence of pain), and in some surgeries, effective skeletal muscle relaxation. General anesthesia is most commonly achieved when the anesthetic vapors are inhaled or administered intravenously (IV). Volatile liquid anesthetics produce anesthesia when their vapors are inhaled. Volatile liquids are liquids that evaporate on exposure to air. Examples of volatile liquids include halothane, desflurane, and enflurane. Gas anesthetics are combined with oxygen and administered by inhalation. Examples of gas anesthetics are nitrous oxide and cyclopropane. 

Nitrous oxide is the most commonly used anesthetic gas. It is a weak anesthetic and is usually used in combination with other anesthetic drug s. It does not cause... 

This suggests an action at receptor site 2 of the Na+ channel, a site common to local anesthetic drugs. 

Excellent and rapid anesthetization of an extremity can be obtained easily. Following insertion of an intravenous catheter in the limb of interest, a rubber bandage is used to force blood out of the limb, and a tourniquet is applied to prevent the blood from reentering a dilute solution of local anesthetic, most commonly lido-caine, is then injected intravenously. This technique fills the limb s vasculature and carries the anesthetic solution to the nerve by means of the blood supply. Because of the pain produced by a tourniquet after some time, this procedure usually is limited to less than 1 hour. The systemic blood levels of drug achieved after tourniquet release generally remain below toxic levels. 

The onset of local anesthesia can be accelerated by the addition of sodium bicarbonate (1-2 mL) to the local anesthetic solution. This maximizes the amount of drug in the more lipid-soluble (unionized) form. Repeated injections of local anesthetics can result in loss of effectiveness (ie, tachyphylaxis) due to extracellular acidosis. Local anesthetics are commonly marketed as hydrochloride salts (pH 4.0-6.0) to maximize aqueous solubility. After injection, the salts are buffered in the tissue to physiologic pH, thereby providing sufficient free base concentration for diffusion through the axonal membrane. However, repeated injections of the local anesthetic can deplete the buffering capacity of the local tissues. The ensuing acidosis increases the extracellular cationic form, which diffuses poorly and results in tachyphylaxis. Tachyphylaxis to local anesthetics is common in areas with a limited buffer capacity (eg, the cerebrospinal fluid). 

Since local anesthetics have membrane-stabilizing effects, both parenteral (eg, intravenous lidocaine) and oral (eg, mexiletine, tocainide) formulations of local anesthetics have been used to treat patients with neuropathic pain syndromes because these syndromes are thought to involve uncontrolled, rapid, sensory fiber firing. Systemic local anesthetic drugs are commonly used as adjuvants to the combination of a tricyclic antidepressant (eg, amitriptyline) and an anticonvulsant (eg, carbamazepine) in chronic pain patients who fail to respond to the combination of antidepressant and anticonvulsant. 

Halothane is a very widely used anesthetic drug, which may cause hepatic damage in some patients. It seems that there are two types of hepatic damage, however. One is a very rare reaction, idiosyncratic, resulting in serious liver damage with an incidence of about 1 in 35,000. The other form of hepatotoxicity is a mild liver dysfunction, which is more common and occurs in as many as 20% of patients receiving the drug. The two different types probably involve different mechanisms. 

Lidocaine is the most commonly used local anesthetic drug. In addition to its effectiveness for local anesthesia, it provides relief of neuropathic pain and acute migraine headache... 

A third role of natural products is their utility as prototypes or models for synthetic drugs possessing physiological activities similar to the original drug. Procaine and similar local anesthetics are commonly cited representatives of this category. 

Correct estimates of the incidence of anesthetic deaths are difficult to obtain, since many deaths are multifactorial. Mortality due to anesthetic drugs is one in 10 000-20 000 (81). The adverse effects of anesthetics have been reviewed (82). Dose-related reactions are common and carry a low mortality, whUe non-dose-related reactions are less common and carry a high mortality. 

Anaphylactoid reactions are easily misdiagnosed during anesthesia (67), since circulatory coUapse accompanied by sinus tachycardia may be the only signs (49). These are the presenting features in 70-90% of cases. Mucocutaneous manifestations (erythema, urticaria, angioedema) are reported in 60-80% of reactions, but are often only noticed much later when the acute phase is over. Bronchospasm is present in about 40% of cases. Reactions are more common in women (up to 80%), in atopic patients, and in those who have a history of asthma (who are particularly prone to develop bronchospasm) or allergy, and in patients who have had a previous reaction to anesthetic drugs (50,53) they also seem to be more common in patients under 40 years of age (54). 

FIGURE 2.4 Articaine, a common local anesthetic dentists use, and its inactive metabolite that is formed off the scene of painful action. The value for tn2 is from the reference Oertel, R. Ebert, U., Rahn, R., Kirch, W. The effect of age on pharmacokinetics of the local anesthetic drug articaine. Reg. Anesth. Pain Med. 1999, 24, 524-528. 

Local anesthesia refers to injecting anesthetic into the skin to temporarily numb a small area so that a minor procedures can be done painlessly. This type of anesthetic is normally used for stitching small lacerations or for dental procedures. Drugs commonly used as local anesthetics include lidocaine and prilocaine. 

EXAMPLE 13.6 Pressure affects a two-state equilibrium. A common anesthetic drug molecule is halothane (2-bromo-2-chloro-l,l,l-trifluoroethane). Its mode of action is presumed to involve partitioning from water (state A) into lipid bilayer membranes (state B). Figure 13.6 shows how the partitioning equilibrium depends on pressure. Putting values of (p.lnX) = (0,7.84) and (280, 7.6) into Equation (13.48) gives Av = Ubiiayer fwater ... 

Similar to alcohol (Lovinger and White 1991) and volatile anesthetics (Machu and Harris 1994), trichoroethane, trichloroethylene, and toluene enhance 5-HT3 receptor function. All three inhalants significantly and reversibly potentiated, in a dose-dependent manner, 5-HT-activated currents, mediated by mouse 5-HT3 receptors expressed in Xenopus oocytes. Another feature common to these drugs is that the acute use of inhalants, as well as alcohol and volatile anesthetics, can produce nausea and vomiting (Meredith et al. 1989). It is believed that 5-HT3 receptors located in the area postrema mediate this action of alcohol and the volatile anesthetics (Aapro 1991). 

The answer is d. (Hardman, p T36J The addition of a vasoconstrictor, such as epinephrine or phenylephrine, to certain short-acting, local anesthetics is a common practice in order to prevent the rapid systemic absorption of the local anesthetics, to prolong the local action, and to decrease the potential systemic reactions. Some local anesthetics cause vasodilation, which allows more compound to escape the tissue and enter the blood. Procaine is an ester-type local anesthetic with a short duration of action due to rather rapid biotransformation in the plasma by cholinesterases. The duration of action of the drug during infiltration anesthesia is greatly increased by the addition of epinephrine, which reduces the vasodilation caused by procaine. 

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