Hyperbaric additions

The hyperbaric addition of primary amines 167 to diester 166 leads directly to bridgehead p-aminodiesters 168 in good yields the combination of 166 and diamines 169, under the same conditions, affords the tricyclic derivatives 170 in a single step (Scheme 7.42). ... 

The so-called hyperbar vacuum filtration is a combination of vacuum and pressure filtration in a pull—push arrangement, whereby a vacuum pump of a fan generates vacuum downstream of the filter medium, while a compressor maintains higher-than-atmospheric pressure upstream. If, for example, the vacuum produced is 80 kPa, ie, absolute pressure of 20 kPa, and the absolute pressure before the filter is 150 kPa, the total pressure drop of 130 kPa is created across the filter medium. This is a new idea in principle but in practice requires three primary movers a Hquid pump to pump in the suspension, a vacuum pump to produce the vacuum, and a compressor to supply the compressed air. The cost of having to provide, install, and maintain one additional primary mover has deterred the development of hyperbar vacuum filtration only Andrit2 in Austria offers a system commercially. 

Anesthesia of the lower extremities and abdomen may be induced by the introduction of anesthetic drugs into the subarachnoid space (Figure 23.6). The drug most often used for this purpose is bupivacaine. The latency period plus the duration of the maximal cephalad level for both plain and hyperbaric bupivacaine lasts from 10 to 60 min. A bupivacaine solution is made hyperbaric by the addition of 5 to 8% glucose. The distribution of bupivacaine in the cerebrospinal fluid (CSF) is affected by gravity and is therefore influenced by the patient s position. With a dose of 15 mg of plain 0.5% bupivacaine, a half-life of about 3 h is achieved. The addition of epinephrine to bupivacaine prolongs the duration of block. 

Carbon monoxide, like cyanide, poisons by combining with the heme of both cytochrome oxidase and hemoglobin (the Fe forms). This may be treated with hyperbaric oxygen, which competes with carbon monoxide for the hemoglobin, in addition to delivering to the tissues oxygen dissolved in the plasma. 

With the introduction of 25 gauge and 27 gauge spinal needles, it was suggested that slow injection may be an additional factor predisposing to transient radicular irritation, since layering of the hyperbaric fluid in the dependent portion may lead to areas of highly concentrated local anesthetic (246). 

In addition to antidotal therapy, administration of 100% oxygen can help with cyanide detoxification, possibly by affecting the binding of cyanide to cytochrome oxidase (13). Hyperbaric therapy may be considered, but only after standard treatment has failed, or if the patient has concurrent carbon monoxide poisoning (13). 

Hyperbaric oxygenation has opened up new avenues for basic and clinical research. As more is learned about the physiological and biochemical effects of oxygen and other gases under pressure, it is certain that new uses will be found for this latest addition to the medical armamentarium (B39, G17, M2). 

The binding of CO to hemoglobin is fully dissociable, and dissociation requires ventilation. After removal from exposure to CO, administration of O reverses CO binding to hemoglobin. Utilization of 100 percent accelerates the washout of CO. Use of hyperbaric chambers with pressures up to 2 atmospheres speeds up the CO washout process even more. Addition of 5 to 7 percent CO to the O is sometimes used as a prompt to ventilatory exchange. One disadvantage of the addition of CO is the serious acidosis that results when the respiratory acidosis produced by CO inhalation is added to the metabolic acidosis produced by O deprivation in the tissues because of CO poisoning. 

In this regard, a number of specialized research centers are slated to address and participate in discussions on these issues, and include the following the Johns Hopkins Center for Cancer Complementary Medicine the Specialized Center of Research in Hyperbaric Oxygen Therapy at the University of Pennsylvania the Botanical Center for Age-Related Diseases at Purdue University and the UCLA Center for Dietary Supplement Research on Botanicals. These are in addition to other well-known cancer research and treatment centers located around the country, such as the Memorial Sloan-Kettering Cancer Center in New York City, the M.D. Anderson Cancer Center in Houston, the Fred Hutchinson Cancer Research Center in Seattle, etc. 

Treatment for the respiratory damage involves oxygen supplements, intubation, and artificial ventilation when indicated, as well as the use of a hyperbaric chamber to remove carbon monoxide, if needed. Any restriction to the chest owing to burned skin is removed surgically. The nurse must monitor arterial blood gases and oxygen saturation levels to determine the effectiveness of treatment. In addition, the nurse should monitor for signs of acidosis and related acid-base imbalances. <3 ... 

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