Anesthetic agents injectable

The onset of action is fast (within 60 seconds) for the intravenous anesthetic agents and somewhat slower for inhalation and local anesthetics. The induction time for inhalation agents is a function of the equiUbrium estabUshed between the alveolar concentration relative to the inspired concentration of the gas. Onset of anesthesia can be enhanced by increasing the inspired concentration to approximately twice the desired alveolar concentration, then reducing the concentration once induction is achieved (3). The onset of local anesthetic action is influenced by the site, route, dosage (volume and concentration), and pH at the injection site. 

The rate of removal of the local anesthetic from the site of injection also affects its profile. AH local anesthetic agents possess some vasodilatory activity at clinically useful concentrations. Agents which are more potent in this regard tend to be absorbed more rapidly by the vasculature. They are less potent anesthetics and have shorter durations than those having lower vasodilatory activity. A comparison of potency, onset, and duration as a function of physiochemical properties is presented in Table 4. 

HHMC can also be directly activated by agents injected intravenously for therapeutic (general anesthetics, protamine, etc.) or diagnostic purposes (radiocontrast media, etc.), which can cause non-IgE-mediated anaphylactic reactions in vitro [24,... 

The imidazole-containing hypnotic/injectable anesthetic agent etomidate (58) is synthesized from 1-amino-l-phenylethane starting with triethylamine mediated displacement with chloro-acetonitrile leading to secondary amine The -enantiomer... 

C. Midazolam, like all benzodiazepines given in sufficient dose, has the capacity to produce anterograde amnesia. It is also available in an injectable form and frequently is used as an anesthetic agent during short procedures. 

This involves considerable art, which must be learned in the clinic. It falls into two divisions (1) surface application to the mucous membranes, especially of the eye, nose, throat, and urethra and (2) injections about nerves, in different parts of their course and distribution, from their spinal roots to their ultimate fibrils. The advantages and disadvantages in comparison with general anesthesia and the selection of the local anesthetic agent also depend on clinical discrimination. Nervous, fearful, and excitable patients often suffer severely from apprehension, which also disposes toward accidents. They may be at least somewhat quieted by sedatives, morphine (0.015 g hypodermically) half an hour before the operation, or by barbiturates. The latter also tend to prevent convulsions. 

Clinically, 0.2 g of phenobarbital or 0.6 g of sodium barbital may be administered an hour before operation. Barbiturates do not prevent the direct circulatory collapse and depression of respiration that occur on intravenous injection of procaine, and are useless or harmful for either prophylaxis or treatment if the anesthetic agent is rapidly absorbed. However, if the symptoms develop slowly, the suppression of the convulsions is at least helpful. 

In 1958, phencyclidine (PCP) was introduced into clinical anesthesia as an injectable anesthetic agent. PCP had physiological properties that made it a useful anesthetic. The most significant of these was that it was quite effective but had no risk of cardiac or respiratory depression, as was typical of classical general anesthetic agents. 

The topical use of anesthetic agents before injection may produce superficial anesthesia. They are also of value in taking impressions or intraoral radiographs in patients with an excessive gag reflex. 

Lidocaine is the most widely used aminoamide local anesthetic agent, with a low toxic potential its effects are mostly typical for this class of drug. It can be given by injection or topically and is also combined with prilocaine in Emla for topical administration. It is also used as an antidysrhythmic drug and has occasionally been used in other conditions, such as multiple sclerosis, chronic daily headache, migraine and cluster headaches, and neuropathic pain, such as postherpetic neuralgia. 

The authors added that retinal toxicity of the local anesthetic agent did not affect the visual outcome in this patient. Scleral perforation is a well-known complication of eye blocks for ophthalmic surgery. The incidence with retrobulbar techniques is 0.075% and with peribulbar blocks 0.0002%. When recognized, ocular perforation usually requires a vitreoretinal procedure and is associated with a poor visual outcome. Risk factors include an anxious or oversedated patient, long sharp needles, superior injection, incorrect angle of needle insertion, and myopic eyes. If the intraocular pressure is increased, paracentesis may acutely reduce it, preventing retinal and optic nerve ischemia and possible permanent visual loss. 

Wadood AC, Dhillon B, Singh J. Inadvertent ocular perforation and intravitreal injection of an anesthetic agent during retrobulbar injection. J Cataract Refract Snrg 2002 28(3) 562-5. 

Comparative renal pharmacology of inhaled and injectable anesthetic agents ... 

Sodium thiopental does not alter renal blood flow although glomerular filtration rate and urine output are moderately affected [17]. The same is true for opioids such as morphine [18] and fentanyl [19, 20] and the more recently introduced I.V. agent propofol [21]. The effects of these drugs on renal function are transient. There is no evidence that injectable anesthetic agents are associated with direct nephrotoxicity. 

White K K, Hodgson D R, Hancock D et al 1989 Changes in equine carpal joint synovial fluid in response to the injection of two local anesthetic agents. Cornell Veterinarian 79 25-38... 

Spinal anesthesia is carried out by injecting the anesthetic agent into the subarachnoid. space in the spinal cord. The anesthetic acts mainly on the nerve fibers and blocks the pain regions of the body served by the sections of the spinal cord affected. 

Reportedly. the time taken for the onset of anesthesia can be reduced by the use of the hydrogen carbonate fonn of the drug. This docs not increase the toxicity of the local anesthetic agent, but it has been reported to reduce the pain associated with injection and improve the effectiveness of the block in some cases. 

A number of a-methyl-tropic esters of tropine and -tropine, together with their methiodides and decamethylene di-iodides, have been prepared (102) showing some atropine-like effect. Derivatives of a-ecgonine methyl ester have also been synthesized, e.g., benzilic and p-aminobenzoyl esters and decamethylene salts. a-Ecgonine itself, if injected, proved a potent local anesthetic agent (103), at variance with earlier findings (104). 

Anesthetics should be chosen on the basis of causing minimal stress to the animal, minimal interference effects on the analyte, and minimal hazards to the operator through accidental injection, chemical toxicity of the anesthetic agents, or injuries caused by the animal s behavior during the procedure. Anesthetic agents used for rodents include halothane, ether, barbiturate, methoxyfluorane, and carbon dioxide. Frequently repeated anesthesia can affect the analyte values. 

Some of the common local anesthetics e.g., tetracaine) are esters they are hydrolyzed and inactivated primarily by a plasma esterase, probably plasma cholinesterase. Hepatic enzymes also hydrolyze local anesthetic esters. Since spinal fluid contains little or no esterase, anesthesia produced by the intrathecal injection of an anesthetic agent will persist until the local anesthetic agent has been absorbed into the circulation. 

Local anesthetic is never intentionally injected into the nerve this would be painful and could cause nerve damage. Instead, the anesthetic agent is deposited as close to the nerve as possible. Higher concentrations of local anesthetic will provide a more rapid onset of peripheral nerve... 

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