Anesthetics, specific agents

A. Inhalation. The toxic air level is quite variable, depending on the specific agent (see Table IV-4, p 532). Freon 21 (dichlorofluoromethane TLV 10 ppm [42 m m ) is much more toxic that freons 12 and 22 (TLV 1000 ppm). In general, anesthetic or CNS-depressant doses require fairly large air concentrations, which can also displace oxygen, leading to asphyxia. The air level of dichloromonofluoromethane considered immediately dangerous to life or health (IDLH) is 5000. Other TLV and IDLH values can be found in Table IV-4 (p 532). 

An allergic reaction to specific agents is an obvious contraindication. Allergy to para-aminobenzoic acid (PABA) is a contraindication to use of ester local anesthetics due to the fact that PABA is a metabolic product of ester metabolism. Methylparaben is a common preservative chemically similar to PABA and likewise can cause an allergic reaction. Metabisulfite is a commonly used preservative that may also cause allergic reactions but more notably is neurotoxic when used intrathecally. Local anesthetics containing any preservative should not be used intrathecally. Ester local... 

Specific Local Anesthetic Agents. Clinically used local anesthetics and the methods of appHcation are summarized in Table 5. Procaine hydrochloride [51-05-8] (Novocain), introduced in 1905, is a relatively weak anesthetic having along onset and short duration of action. Its primary use is in infiltration anesthesia and differential spinal blocks. The low potency and low systemic toxicity result from rapid hydrolysis. The 4-arninobenzoic acid... 

More specifically regarding petroleum and petroleum products, the alkanes in gasoline and some other petroleum products are central nervous system depressants. In fact, gasoline was once evaluated as an anesthetic agent. However,... 

The mechanisms of action of the effects of alcohol on the nervous system remain unclear. For some time, researchers thought that the depressant effects of alcohol, like other anesthetic agents, were caused by dissolving into the cell lipid membranes and disrupting the function of various proteins. More recently, researchers have focused on specific receptors such as glutamate (excitatory) and GABA (inhibitory). Despite intensive research, the mechanism of effect of alcohol on the fetus is unknown. 

As the carbon chain length in an anesthetic series increases (for example in the family of long chain alcohols), a substance becomes more hydrophobic and should be a more potent anesthetic. This is true only until a specific size cut off when the next larger agent becomes ineffective as an anesthetic (Franks Lieb 1986). 

Contrast-enhanced MRI with Gd-DTPA has been applied to the evaluation of several compounds in man, some focusing on the hemodynamic effects of the drugs on cerebral blood volumes. Kolbtisch and others compared the anesthetic agents nitrous oxide and sevofhirane, noting them to produce compound-specific patterns of diffuse increases in cerebral blood volume (Kolbitsch et al., 2001). Intravenous cocaine, on the other hand, was observed to produce dose-dependent vasoconstriction of cerebral blood vessels (Kaufman et ul., 1998). 

First, it is clear that nearly all drugs with CNS effects act on specific receptors that modulate synaptic transmission. A very few agents such as general anesthetics and alcohol may have nonspecific actions on membranes (although these exceptions are not fully accepted), but even these non-receptor-mediated actions result in demonstrable alterations in synaptic transmission. 

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