Anesthetic Gases

It has been known for some time that anesthetists, other operating room personnel, dentists, and dental associates have higher rates of SAB and other adverse birth outcomes than control groups. I25-27 The chemicals these women are exposed to include halothane, nitric oxide, methoxy flu-rane, and other unspecified chemicals from antiseptic solutions, propellants, and adhesive solutions. Symptoms reported by these workers include headache and nausea effects that are indicative with CNS impact. These effects are consistent with those expected from anesthesia and are indicative of the impact of neurotoxins on fertility. 

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The lungs large, permeable surface makes systemic deUvery possible. For example, an inhaler deUvers 360 )Tg per dose of aerosolized ergotamine tartrate [379-79-3] for migraine (54), and inhalant systems deUver anesthetic gases. Research is under way on the systemic deUvery of proteins and peptides through the lungs (57,58). 

The toxic effect depends both on lipid and blood solubility. I his will be illustrated with an example of anesthetic gases. The solubility of dinitrous oxide (N2O) in blood is very small therefore, it very quickly saturates in the blood, and its effect on the central nervous system is quick, but because N,0 is not highly lipid soluble, it does not cause deep anesthesia. Halothane and diethyl ether, in contrast, are very lipid soluble, and their solubility in the blood is also high. Thus, their saturation in the blood takes place slowly. For the same reason, the increase of tissue concentration is a slow process. On the other hand, the depression of the central nervous system may become deep, and may even cause death. During the elimination phase, the same processes occur in reverse order. N2O is rapidly eliminated whereas the elimination of halothane and diethyl ether is slow. In addition, only a small part of halothane and diethyl ether are eliminated via the lungs. They require first biotransformation and then elimination of the metabolites through the kidneys into the... 

Drugs Central nervous system drugs - Anesthetic gases... 

Anesthetic gases Narcotic gases which when inhaled give a feeling of well-being followed by unconsciousness. 

There has been some controversy over the effect of traces of anesthehc gases in the operating room on the health of personnel working there daily Numerous animal studies usmg low levels of anestheltic gases have failed to show any effects, and several epidemiological studies show that human health is not affected by traces of anesthetic gases [20]... 

Absorption of trichloroethylene in humans is very rapid upon inhalation exposure. Trichloroethylene has a blood/gas partition coefficient that is comparable to some other anesthetic gases (i.e., chloroform, diethylether, and methoxyfluorene), but it is much more lipophilic than these gases. As a consequence of these properties, the initial rate of uptake of inhaled trichloroethylene in humans is quite high, with the rate leveling off after a few hours of exposure (Fernandez et al. 1977). The absorbed dose is proportional to the inhaled trichloroethylene concentration, duration of exposure, and alveolar ventilation rate at a given inhaled air concentration (Astrand and Ovrum 1976). Several studies indicate that 37-64% of inhaled trichloroethylene is taken up from the lungs (Astrand and Ovrum 1976 Bartonicek 1962 Monster et al. 1976). 

Most models of gas uptake in the respiratory tract have been concerned with carbon dioxide, carbon monoxide, oxygen, and anesthetic gases like chloroform, ether, nitrous oxide, benzene, and carbon disulfide (e.g., see Lin and Gumming and Papper and Kitz ). Unfortunately, there are only a few preliminary models of pollutant-gas transport and uptake in the respiratory tract. 

Gases that do not react irreversibly with epithelial tissue, such as anesthetic gases, may diffuse into the bloodstream and will ultimately be eliminated from the body. A different and earlier model developed by DuBois and Rogers estimates the rate of uptake of inhaled gas from the tracheobronchial tree in terms of diffusion through the epithelial tissue, rate of blood flow, and solubility of the gas in blood. The rate of uptake from the airway lumen is determined by the equation ... 

National Institute for Occupational Safety and Health Criteria for a Recommended Standard—Occupational Exposure to Waste Anesthetic Gases and Vapors, 255 pp. Washing-... 

The possible carcinogenicity of nitrous oxide has been studied in dentists and chairside assistants with occupational exposures. No effect was observed in male dentists, but a 2.4-fold increase in cancer of the cervix in heavily exposed female assistants was reported. Other epidemiological reports of workers exposed to waste anesthetic gases have been negative. Carcinogenic bioassays in animals have yielded negative results. Nitrous oxide was not geno-toxic in a variety of assays. ... 

Bruce DL, Bach MJ Effects of trace anesthetic gases on behavioural performance of volunteers. BrJ Anesth 48 871-876, 1976... 

Cohen EN, Brown BW, Wu ML, et al Occupational disease in dentistry and chronic exposure to trace anesthetic gases. J Am Dent Assoc 101 21-31, 1980... 

The alveolar tension-time curve always declines in an exponential manner, but the position of the curve can be greatly affected by the rate of delivery of anesthetic gases and the rate of their uptake into the pulmonary circulation. For this reason, it is important to consider factors that modify or regulate delivery and uptake. 

Tissues, including the brain, that have a high blood flow per unit mass (Fig. 25.1) equilibrate with the alveolar tension of anesthetic gases first. Tissues with lower blood flow require a longer time and continue to accumulate anesthetic gas during the maintenance phase of... 

The alveolar tension of other anesthetic gases also rises more rapidly (second gas effect) when an anesthetic such as N2O is present in high concentration. These gases are also subject to the increased inflow (pulling in of fresh gases) as N2O is taken up into the blood. 

The concentration of an inhaled anesthetic in a mixture of gases is proportional to its partial pressure (or tension). These terms are often used interchangeably in discussing the various transfer processes involving anesthetic gases within the body. Achievement of a brain concentration of an inhaled anesthetic necessary to provide an adequate depth of anesthesia requires transfer of the anesthetic from the alveolar air to the blood and from the blood to the brain. The rate at which a therapeutic concentration of the anesthetic is achieved in the brain depends primarily on the solubility properties of the anesthetic, its concentration in the inspired air, the volume of pulmonary ventilation, the pulmonary blood flow, and the partial pressure gradient between arterial and mixed venous blood anesthetic concentrations. 

Tensions of three anesthetic gases in arterial blood as a function of time after beginning inhalation. Nitrous oxide is relatively insoluble (blood gas partition coefficient = 0.47) methoxyflurane is much more soluble (coefficient = 12) and halothane is intermediate (2.3). 

Although this has been shown to occur in experimental animals after exposure of males to foreign compounds such as cyclophosphamide, there is only inconclusive evidence that this occurs in humans. Thus, studies of exposure of human males to vinyl chloride, dibromo-chloropropane, and anesthetic gases, for example, have revealed only equivocal evidence of developmental toxicity in the offspring. There now seems to be some evidence that the leukemia occurring in children, which appears to be clustered around nuclear fuel-reprocessing plants such as Sellafield in the United Kingdom, may be due to paternal exposure to radiation. 

Most inhalants have no medical use. Exceptions are the anesthetic gases and amyl nitrite. Anesthetic gases slow the heart s pumping action, resulting in a drop in blood pressure. They also deaden pain and put surgery patients into an unconscious state. Amyl nitrite, a clear, yellowish liquid, relaxes the smooth muscle in the walls of the arteries. That relaxation dilates the blood vessels, reduces blood pressure, and increases the heart rate. 

Changes in blood flow to and from the lungs influence transfer processes of the anesthetic gases. 

Four types of inhalants are abused (1) anesthetic gases (2) industrial solvents, including a variety of hydrocarbons, such as toluene (3) aerosol propellants, such as various fluorocarbons and (4) organic nitrites, such as amyl or butyl nitrite. The mode of action of the inhalant anesthetics has been discussed in Chapter 25 General Anesthetics. 

Anesthetic gases such as nitrous oxide produce difficulty in concentrating, dreaminess, euphoria, numbness and tingling, unsteadiness, and visual and auditory disturbances. Nitrous oxide is usually taken as 35% N2O mixed with oxygen administration of 100% nitrous oxide may cause asphyxia and death. Ether and chloroform are readily available, and after an initial period of exhilaration, the person often loses consciousness. 

K. Hemminki, P. Kyyrdnen and M-L. Lindbohm. Spontaneous abortions and malformations in the offspring of nurses exposed to anesthetic gases, cytostatic drugs and other potential health hazards in hospitals based on registered information of outcome. J. Epid. Comm. Health 39, 1985, 141. 

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