Millers Anesthesia - Sixth Edition_ANESTHESIA APPARATUS_18

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Miller: Miller's Anesthesia, 6th ed., Copyright 2005 Elsevier

ANESTHESIA APPARATUS

Early Delivery Systems

For the first public demonstration of ether anesthesia, Morton used a specially constructed glassbottle with an attached mouthpiece (see Chapter 9 ). In England, John Snow developed a new type ofether inhaler and took up the practice of ether anesthesia as a full-time endeavor. His apparatusprovided valves to prevent rebreathing, and although he experimented with methods for carbondioxide absorption, he did not develop it into a clinically useful technique. John Snow was aware ofthe difficulties associated with the simple mouthpiece that was used with a noseclip by Wells andMorton. In his book on ether published in 1847, [355] he states the following:

For some of the adult patients, after they lost their consciousness, made such strong

instinctive efforts to breathe by the nostrils, that the air was forced through thelachrymal ducts, and occasionally they held the breath altogether for a short time, andwere getting purple in the face, when the nostrils had to be liberated, for a short time, toallow respiration of the external air, and thus a delay was occasioned.

With the introduction of chloroform, several inhalers were developed to administer the agent.Ferdinand Junker[356] (18281901) devised a simple inhaler, consisting of a bottle to hold liquidchloroform, an inflow tube into which the anesthetist could squeeze air with a hand pump, and anoutflow tube directed into the mask. The Junker inhaler underwent several modifications to improveits safety but was rarely used in the United States. Joseph T. Clover[357][358] (18251882), the

prominent English anesthetist after John Snow, devised several devices for the administration ofnitrous oxide, ether, and chloroform. The Clover bag held more than 16 L of air, with chloroformvapor at approximately 4%. Smaller concentrations could be given by adjusting a valve on thefacemask that allowed dilution of the chloroform with air. A clever solution to avoid the problem ofhigh concentrations of chloroform was presented by Augustus Vernon Harcourt (18341919) in1912. This apparatus was one of the several "draw-over" systems that brought the inspired air over avaporizer heated by a small candle. The chloroform double-necked flask held the liquid chloroformand two beads that rose to the top or sank to the bottom, depending on the temperature of the liquid.Several draw-over chloroform delivery systems are described in Dudley Buxton's 1914 textbook.[359]The problem with these early delivery systems for longer procedures was the potential for hypoxiaand partial rebreathing of expired carbon dioxide.

Other types of anesthesia machines were developed to provide anesthesia with the insufflationmethod, whereby a small catheter was placed with its tip near the carina to deliver air and ether orchloroform. These were continuous-flow machines that did not rely on respiratory movements foroxygenation and were based on the work of Samuel Meltzer (18511920) and John Auer (18751948) demonstrating its safe use in animals.[360] It was one solution to the problem of pneumothoraxand respiratory decompensation during thoracic surgery. C. A. Elsberg's (18711948) continuous-flow machine was described in 1911 and went through several modifications.[361] The popularShipway model was used by Francis E. Shipway (18751968) to provide anesthesia to King GeorgeV of England for rib resection and drainage of empyema, a feat for which Shipway was knighted. In

retrospect, it is clear that these continuous flow machines were not capable of eliminating carbondioxide in all cases,[362] and anesthesia machines eventually were developed that allowed to-and-frorespiration through one large-bore endotracheal tube.

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Compressed Gases and Reducing Valves

Of major importance in the design of the modern anesthesia machine was the compression of gasesin metal

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cylinders. Oxygen and nitrous oxide were available under compression as early as 1885 through themanufacturers S. S. White of Philadelphia and Messrs. Coxeter of London. This allowed thedevelopment of compact machines capable of prolonged anesthetic delivery without the cumbersomefeature of low-pressure reservoirs. Frederick Hewitt's first anesthetic gas machine designed forgiving oxygen and nitrous oxide mixtures had two nitrous oxide cylinders and one oxygen cylinder

and were fed into a large breathing bag through a double cylinder yoke.[139]

Oxygen concentrationscould be adjusted at the stopcock near the mask. His preferred oxygen concentrations were 5% to8%. With the addition of oxygen, he attempted to "dispense with cyanosis, jerky and irregularbreathing, deep stertor and clonic movements of the extremities."

The invention of the reducing valve is accredited to Jay Albion Heidbrink (18571957), ananesthesiologist from Minneapolis who observed that the opening from high-pressure cylinders oftenfroze closed as the gases were released. He described a valve that reduced the high tank pressures toworking pressures and incorporated this device into his Heidbrink Anesthetizer. In Germany,Heinrich Drager (18471917) and his son Bernhard Drager (18701928) developed reducing valvesto control an even, accurate flow of carbon dioxide gas drawn from beer cylinders, and these valves

were later used in the early anesthesia machines. Further refinements to the early machines wereadded by James T. Gwathmey[363] and H. Edmund G. Boyle[364] (18751941) chiefly through theaddition of bubble-through heated water baths for estimation of gas flows. The Boyle machinepassed various amounts of oxygen through ether with a "water-sight" meter. This flowmeterestimated the flow through the vaporizer from how many of the holes were generating bubbles.Heidbrink further improved the flowmeter by using an inverted float in a tube of varying taper withcalibrations marked on the side. Rotating floats, also called rotameters, have slanted grooves cut intothe rim, causing them to rotate, and they are more accurate than the ball or nonrotating floats.Rotameters were introduced in 1908 by Karl Kuppers and first used in anesthesia in 1910.[365]




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Carbon Dioxide Absorption

Anesthesiologists from the first half of the 20th century were not privileged to visit just one hospitalduring a day's work. Visits to several institutions might take place in a single day, with thepractitioners bringing their own delivery systems and drugs with them as they traveled.Understandably, there was a priority for portability and elimination of waste, because theseanesthesiologists paid for the agents themselves. One development that conserved gases and vaporswas the use of systems that absorbed expired carbon dioxide and allowed rebreathing of expiredgases.

Several ineffectual attempts were made to introduce carbon dioxide absorption methods in the 19thcentury. John Snow and Alfred Coleman (18281902) were motivated to conserve anesthetic gasesthat escaped into the atmosphere through nonrebreathing valves. Coleman devised a system of

absorbing carbon dioxide by passing the expired gases over slaked quick lime.[366][367] The recoveredgases were then used for subsequent anesthetics ( Fig. 1-15 ). Franz Kuhn (18661929) describedsoda lime absorption of exhaled carbon dioxide in 1905, but the report did not attract attention.[368]

Dennis Jackson demonstrated the use of soda lime absorption to maintain stable levels of anesthesiafor several hours in animals with minimal ether consumption.[369] The animals were given additionaloxygen to meet metabolic needs, but the anesthetic gases were rebreathed, resulting in economy andimproved maintenance of body temperature and airway humidity. In 1923, Ralph Waters (18841979) (see Fig. 1-18B ), working then as an anesthesia practitioner in Sioux City, Iowa, contactedJackson and devised a soda lime canister for clinical use.[370] The canister was attached to a breathing

hose close to the face, and although it was cumbersome to use, the device was widely distributed.The in-line soda lime canister launched the academic career of Waters, who later became one of themost prominent figures in anesthesiology during the first half of the 20th century. In 1930, Brian C.Sword[371] altered the Waters canister by attaching it to the chassis of a movable cart with two hosesdirected to the airway, one for inspired gases and one for exhaled gases.




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Controlled Vaporizers

With the introduction of more potent volatile anesthetics such as halothane it became important tocontrol the concentration of inspired vapor carefully. To solve this problem, Lucien Morris[372]invented the copper kettle to vaporize liquid anesthetics. Its advantage rested on the

Figure 1-15 Alfred Coleman's economizing device. The anesthetic gases entered the lower bag and passed into the upperbag through a one-way valve. Gases were inhaled and exhaled through the tube (h), passing over a lime container (1, 2)held in frame (k) that eliminated carbon dioxide; (c) is gas inlet. The conserved gas in the upper bag was used during alater anesthetic administration. (From Coleman A: Mr. Coleman's economizing apparatus for re-inhaling the gas. Br JDent Sci 12:443, 1869.)

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fact that as the agent was vaporized, there was little change in the temperature of the anestheticliquid. The copper kettle could be used with any agent provided that the practitioner was cognizantof the vapor pressure of the agent and the flow rates of the inspired gases. Without the addition ofdiluent gases such as nitrous oxide or oxygen, the copper kettle could deliver lethal concentrations ofvapor. The vaporizers in common use today use bimetallic strips that bend as the temperature drops,permitting more fresh gas to enter the vaporizing chamber. Vaporizers have been designed for all theagents in use today, including halothane, enflurane, isoflurane, desflurane, and sevoflurane. Themodern anesthesia machines are also equipped with scavenging systems designed to minimizeescape of anesthetic vapors and nitrous oxide into the operating room. Although controversial, somestudies have shown that daily exposure to anesthetic vapors in low concentrations can havedeleterious side effects. [373]



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Ventilators in the Intensive Care Unit

The earliest ventilator, the Fell-O'Dwyer apparatus, was described in 1892.[374] It was used as early as1896 to provide respiratory support in cases of opium poisoning. Rudolph Matas, a surgeon in NewOrleans who contributed significantly to the early development of regional anesthesia in the UnitedStates, was one of the first to use the Fell-O'Dwyer ventilator during thoracic surgery.[375] During thepolio epidemic, thousands of afflicted patients were kept alive with the Drinker respirator,[376] oftenreferred to as the iron lung, a negative-pressure device that surrounded the patient and provided forair movement in and out of the lungs. A Swedish ventilator called the Spiropulsator was introducedin 1934 and modified in 1947 by E. Trier Moerch.[377] This ventilator used a piston pump to deliver afixed volume of gas. Ventilators today are usually an integral part of the anesthesia machine anddirect compressed air into a rigid container containing a bellows that inflates the lungs. Bjrn Ibsen[378] (1915-), a Danish anesthesiologist, initiated the concept of intensive care units in the early 1950s

to care for polio patients and guided the transition from iron lungs to modern ventilators. Intensivecare units have since become an integral part of the modern hospital, with anesthesiologists activelyinvolved in their daily operation.



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Millers Anesthesia - Sixth Edition_ANESTHESIA APPARATUS_18