Medical Gases: Storage & Supply PDF

1 Medical Gases: Storage and Supply S. NINI MALAYAMAN | GEORGE MYCHASKIW II | JAMES M. BERRY | JAN EHRENWERTH CHAPTER OUTLINE...

1 Medical Gases: Storage and Supply S. NINI MALAYAMAN | GEORGE MYCHASKIW II | JAMES M. BERRY | JAN EHRENWERTH CHAPTER OUTLINE Changes in technology and institutional organization have relieved the anesthesiologist of most of these responsibilities. Overview However, this should not excuse anesthesia providers from Medical Gas Cylinders and Their Use understanding the basic facts and safety principles associated with Oxygen Tanks the use of medical gases for anesthesia. Invariably, other health Nitrous Oxide Tanks care providers and administrators have little knowledge regarding Air Tanks these systems and look to anesthesia professionals for guidance in the use and handling of these gases in the hospital or clinic setting. Characteristics of Gas Cylinders With few exceptions, the only medical gases encountered by Size practicing anesthesiologists today are oxygen (O2), nitrous oxide Color Coding (N2O), and medical air. For safety reasons, flammable agents are Cylinder Markings rarely, if ever, used in operating rooms (ORs) today. Nitrogen Pressure Relief Valves is used almost exclusively to power gas-­ driven equipment. Connectors Helium, carbon dioxide, and premixed combinations of oxygen Gas Cylinder Safety Issues and carbon dioxide are generally no longer used. In certain Prevention of Incorrect Gas Cylinder Connections uncommon clinical situations, other gases may be used. Helium Securing Cylinders Against Damage is occasionally used as an adjunct in the ventilation of patients Transfilling undergoing laryngeal surgery because of its low density and Cylinder Hazards flow-­enhancing characteristics when flow is turbulent. Carbon Guidelines for Use of Medical Gas Cylinders dioxide is infrequently used in the management of anesthesia for Supply repair of selected congenital heart defects. Finally, nitric oxide Storage (NO) is currently available for use as a pulmonary vasodilator. Transport and Installation Anesthesiologists who use these gases should be fully versed in their characteristics and safe handling. For detailed information Medical Gas Pipeline Systems and numerous references relating to the handling and use of these Medical Gas Central Supply Systems and other unusual medical gases, along with a wealth of general Oxygen information about medical gas cylinders, the reader is directed Oxygen Concentrators to publications from the Compressed Gas Association (CGA).1,2 Medical Air Medical gas manufacturers are subject to more stringent Nitrous Oxide government and industry regulations and inspections than they Helium have been in the past. This has helped to markedly reduce the Nitric Oxide number of accidents related to medical gases. For these reasons, Nitrogen anesthesia training programs may not emphasize instruction in Central Vacuum Systems the various aspects of storing and using medical gases. Medical Gas Pipelines In addition, increased concern regarding the safety of Planning anesthetized patients has helped reduce the number of gas-­related Additions to Existing Systems injuries. Inspired oxygen monitors with lower concentration limit Installation and Testing alarms provide the anesthesia practitioner with an early warning when the oxygen supply becomes inadequate or is contaminated Hazards of Medical Gas Delivery Systems with another gas. Mixed-­gas monitoring and analysis is common Procedures and provides the practitioner with an important way to quickly detect contaminants or unusual gas mixtures before the patient is injured. If the oxygen monitor fails, pulse oximetry can alert the Overview anesthesiologist to problems with patient oxygenation related to inadequate oxygen supply. Anesthesia providers were once expected to know a great deal about the storage and supply of medical gases. In both large and small institutions, anesthesiologists often had to rely on Medical Gas Cylinders and Their Use their own knowledge and skill in this area to manage the many Medical gases are stored either in metal cylinders or in the aspects of medical gases, from purchasing to troubleshooting. reservoirs of bulk gas storage and supply systems. The cylinders 3 Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 4 PART 1 Gases and Ventilation are almost always attached to the anesthesia gas machine. Bulk the critical pressure, which must be applied at this temperature supply systems use pipelines and connections to transport to keep oxygen liquid, is 737 psia. Because room temperature is medical gases from bulk storage to the anesthesia machine. usually 20°C (far in excess of the critical temperature), oxygen Virtually all facilities in which anesthesia is administered can exist only as a gas at room temperature. are equipped with central gas supply systems. Anesthesia E-­cylinders of oxygen are filled to approximately 1900 pounds practice is currently undergoing change in this regard, and per square inch gauge (psig) pressure at room temperature: 1 many anesthetics are administered outside the OR, and even atmosphere (atm) is 760 mm Hg, which equals 0 psig or 14.7 psia. outside the hospital, where a central gas supply system may be At high pressures, psig and psia are virtually the same. When unavailable. The current emphasis on providing care away from full, the cylinders contain a fixed number of gas molecules, the the hospital—such as in dental clinics, mobile lithotripsy units, so-­called fixed mass of that gas. These gas molecules obey Boyle’s and mobile magnetic resonance imaging facilities—will only law, which states that pressure times volume equals a constant increase the demands on the anesthesia provider to ensure a safe (P1V1 = P2V2), provided temperature does not change. A full and continuous gas supply. E-­cylinders are sometimes the only E-­cylinder of oxygen with an internal volume of 5 L (V1) and source of medical gas for anesthesia machines in these settings. a pressure of 1900 psia (P1) will therefore evolve approximately If an anesthetic is being administered using only E-­cylinders, 660 L (V2) of gaseous oxygen at atmospheric pressure (P2, or then both the anesthesiologist and related support personnel 14.7 psia). Thus, Boyle’s law gives the approximate value: must first ensure that an adequate supply of reserve cylinders is V2 = P1 × V1 / P2 = 1900 × 5 / 14.7 = 660 L available. In addition, the amount of gas in the cylinders being used must be continually monitored, and the cylinders must be If the oxygen tank’s pressure gauge reads 1000 psig, the tank is replaced before they are completely emptied. The importance of approximately 50% full (1000 ÷ 1900) and contains only 330 L this cannot be overemphasized. Many anesthesia practitioners (660 × 50%) of oxygen (Fig. 1.1). If such a tank were to be used today have not been confronted with the possibility of running at an oxygen flow rate of 6 L/min, it would empty in just under out of oxygen and having to change a tank while administering an an hour (330 ÷ 6 = 55 minutes). Likewise, a full (2200 psig) anesthetic—but the evolving nature of anesthesia practice away H-­cylinder will evolve 6900 L of oxygen at atmospheric pressure. from traditional facilities is likely to make this a more common It is important to understand these principles when oxygen occurrence. If an anesthesiologist anticipates this situation, it is tanks are being used to supply the machine or a ventilator or to imperative that the anesthesia machine be equipped with two transport a patient. Because oxygen exists only as a gas at room oxygen cylinder yokes so that oxygen delivery can continue temperature, the tank’s pressure gauge can be used to determine while the empty tank is changed. how much gas remains in the cylinder. Clearly, if a machine is Anesthesia practitioners should be familiar with two sizes equipped with two E-­cylinders of oxygen, only one should ever of gas cylinders. The cylinder most often used by anesthesia be open at any time to ensure that both tanks are not emptied providers is the E-­cylinder, which is approximately 2 feet (61 cm) simultaneously. long and 4 inches (10 cm) in diameter. E-­c ylinders are also routinely used as portable oxygen sources, such as when a NITROUS OXIDE TANKS patient is transported between the OR and an intensive care unit (ICU). H-­cylinders are larger, approximately 4 feet (122 cm) Nitrous oxide has a molecular weight of 44 and a boiling point long and 9 inches (23 cm) in diameter, and are generally used as of −88°C at 760 mm Hg. Because it has a critical temperature of a source of gas for small or infrequently used pipeline systems. They may be used as an intermediate or long-­term source of gas at the patient’s bedside. Almost all hospitals store H-­cylinders of Volume oxygen in bulk as a back-­up source in case the pipeline oxygen 660 L 330 L 165 L 0L fails or is depleted. H-­cylinders of nitrogen are often used to Pressure power gas-­driven medical equipment. H-­cylinders that contain 1900 psig 950 psig 475 psig 0 psig oxygen, nitrous oxide, or air have occasionally been used in ORs and are connected to the anesthesia machine via special reducing valves and hoses. Such uncommon configurations are not only potentially hazardous, they also defeat certain safeguards. Any practitioner who uses such a system must become thoroughly familiar with it and must be certain it complies with applicable regulations and guidelines.1–5 OXYGEN TANKS Oxygen has a molecular weight of 32 and a boiling point of −183°C at an atmospheric pressure of 760 mm Hg (14.7 pounds per square inch in absolute pressure [psia]). The boiling point of a gas—that is, the temperature at which it changes from Full 50% Full 25% Full Empty liquid to gas—is related to ambient pressure in such a way that Fig. 1.1 Oxygen remains a gas under high pressure. The pressure falls as pressure increases, so does the boiling point. However, a linearly as the gas flows from the cylinder; thus, in contrast to nitrous oxide, the pressure remaining always reflects the amount of gas remain- certain critical temperature is reached, above which it boils into ing in the cylinder. (Modified from Bowie E, Huffman LM: The anesthe- its gaseous form no matter how much pressure is applied in the sia machine: essentials for understanding, 1985. With permission from liquid phase. The critical temperature for oxygen is −118°C, and GE-Datex-­Ohmeda, Madison, WI.) Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  1 Medical Gases: Storage and Supply 5 Volume L [(400 ÷ 745) × 253] of nitrous oxide gas. However, nitrous 1590 L ? ? 215 L oxide vapor does not behave like an ideal gas and does not Pressure obey Boyle’s law. In fact, the tank contains a greater fraction 745 psig 745 psig 745 psig 400 psig of nitrous oxide. This is because a vapor that is so close to its saturation point is more compressible than an ideal gas. In fact, almost one-­quarter of the full tank remains when the last drop of liquid nitrous oxide has just evaporated. Therefore, when the N2O gas pressure in the cylinder begins to fall, approximately 400 L are left to be evolved. Now, when the pressure in the tank decreases to 400 psig, there is about 215 L of nitrous oxide remaining (400 ÷ 745 × 400). N2O liquid While anesthesia is being administered, it is not practical to remove the nitrous oxide cylinder from the anesthesia machine and weigh it accurately enough to determine how much nitrous oxide is left. When the nitrous oxide is being used rapidly, the latent heat of vaporization causes the cylinder itself to become Full cold. If humidity is sufficient in the surrounding atmosphere, Fig. 1.2 At ambient temperature (20°C), nitrous oxide liquefies under some moisture (or even frost) may collect on the outside surface high pressure, and the pressure of the gas above the liquid remains of the cylinder over the portion that is filled with liquid nitrous constant independent of how much liquid remains in the cylinder. Only oxide. The moisture line, or frost line, which may drop as the gas when all the liquid has evaporated does the pressure start to fall, and is used, can provide an indication of when the nitrous oxide will then it does so rapidly as the residual gas flows from the cylinder. (From Bowie E, Huffman LM: The anesthesia machine: essentials for under- run out. A number of tapes and devices are available to mark standing, 1985. With permission from GE-Datex-­Ohmeda, Madison, WI.) the cylinders for this purpose, but their reliability has not been tested. If nitrous oxide is to be used as an anesthetic, it is best to begin with a full cylinder because the length of time the cylinder 36.5°C and critical pressure of 1054 psig, nitrous oxide can exist will last can be calculated. For example, a full E-­cylinder of as a liquid at room temperature (20°C). E-­cylinders of nitrous nitrous oxide used at a flow rate of 3 L/min will last about 9 oxide are filled to 90%–95% of their capacity with liquid nitrous hours (3 × 60 × 9 = 1620 L). oxide. Above the liquid in the tank is nitrous oxide vapor, that is, gaseous nitrous oxide. Because the liquid nitrous oxide is in AIR TANKS equilibrium with its vapor phase, the pressure exerted by the nitrous oxide vapor is its saturated vapor pressure (SVP) at the Medical air is most commonly provided in E-­size cylinders ambient temperature. which are color coded yellow. A full cylinder has a pressure of A full E-­cylinder of nitrous oxide will evolve approximately 1900 psig and contains about 625 L (Table 1.1). The air in the 1590 L of gaseous nitrous oxide at 1 atm (14.7 psia). As long cylinder exists as a gas and will obey Boyle’s law (see previous as some liquid nitrous oxide remains in the tank and the discussion of oxygen tanks). The air tank has a unique pin temperature remains constant (20°C), the pressure in the tank index and can only be installed on the air hanger yoke of the will be 745 psig, or the SVP of nitrous oxide at 20°C (Fig. 1.2). anesthesia workstation. It should be clear that, unlike oxygen, the content of a tank of nitrous oxide cannot be determined from the pressure gauge. It can, however, be determined by removing the tank, weighing Characteristics of Gas Cylinders it, and subtracting the empty weight stamped on each tank SIZE (tare weight); the difference is the weight of the contained nitrous oxide. Avogadro’s formula for volume states that 1 g Table 1.1 gives a list of the sizes, weights, and volumes of the molecular weight of any gas or vapor occupies 22.4 L at standard common cylinders that contain various medical gases. As temperature and pressure. Thus, 44 g of nitrous oxide occupies noted, the anesthesia provider will most often encounter 22.4 L at 0°C and 760 mm Hg pressure. At 20°C this volume oxygen and nitrous oxide in E-­ cylinders and a variety of increases to 24 L (22.4 × 293 ÷ 273); thus, each gram of nitrous gases in H-­cylinders. Although other gas cylinders are found oxide is equivalent to 0.55 L of gas at 20°C. in the OR—such as those used for gas-­powered equipment, Only when all the liquid nitrous oxide in the tank has been laparoscopy equipment, and lasers—these are not likely to be in used up and the tank contains only gaseous nitrous oxide, one the domain of anesthesia personnel. might expect that Boyle’s law could be applied. Thus, when the tank pressure (P1) is 745 psig from gas only and the internal COLOR CODING volume (V1) of the E-­cylinder is approximately 5 L, the volume (V2) of nitrous oxide gas that would be evolved at atmospheric Table 1.2 lists the color markings used to identify medical gas pressure (P2) is represented by the following equation: cylinders. Although the internationally accepted color for oxygen is white, green is used in the United States, primarily for reasons V2 = (P1 × V1 ) / P2 of tradition; in addition, yellow is used to identify compressed air, (745 × 5) / 14.7 = 253.4 L which represents another exception to international standards. Anesthesiologists working in countries other than the United At this point the tank appears to be 16% full (253 ÷ 1590). A States should be aware of these differences. Because nitric oxide tank showing a pressure of 400 psig at 20°C should evolve 136 cylinders are not standardized in color and are frequently supplied Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 6 PART 1 Gases and Ventilation TABLE 1.1 Typical Volume and Weight of Available Contents of Medical Gas Cylindersa MIXTURES OF OXYGEN Cylinder Style Nominal Unit of and Dimensions Volume (in3/L) Measure Air CO2 Cyclopropane He N2 N2O O2 He CO2 B 87/1.43 psig 838 75 1900 3.5 × 13 in L 370 375 200 8.89 × 33 cm lb-­oz 1–8 1–7.25 – kg 0.68 0.66 – D 176/2.88 psig 1900 838 75 1600 1900 745 1900 b b 4.25 × 17 in L 375 940 870 300 370 940 400 300 400 10.8 × 43 cm lb-­oz – 3–13 3–5.5 – – 3–13 – b b kg 1.73 1.51 – – 1.73 – b b E 293/4.80 psig 1900 838 1600 1900 745 1900 b b 4.25 × 26 in L 625 1590 500 610 1590 660 500 660 10.8 × 66 cm lb-­oz – 6–7 – – 6–7 – b b kg 2.92 – – 2.92 – b b M 1337/21.9 psig 1900 838 1600 2200 7.45 2200 b b 7 × 43 in L 2850 7570 2260 3200 7570 3450 2260 3000 17.8 × 109 cm lb-­oz – 30–10 – – 30–10 122 cu ft b b kg 13.9 – – 13.9 – b b G 2370/38.8 psig 1900 838 1600 745 b b 8.5 × 51 in L 5050 12300 4000 13800 4000 5330 17.8 × 109 cm lb-­oz – 50–0 – 56–0 b b kg 22.7 – – 25.4 b b H or K 2660/43.6 psig 2200 2200 2200 745 2200c L 6550 6000 6400 15800 6900 lb-­oz – – – 64 244 cu ft kg – – – 29.1 – aComputed contents are based on normal cylinder volumes at 70°F (21.1°C), rounded to no greater than 1% variance. bThe pressure and weight of mixed gases vary according to the composition of the mixture. c275 cu ft/7800 L cylinders at 2490 psig are available on request. Modified from Compressed Gas Association: Characteristics and safe handling of medical gases, publication P-­2, ed 7. Arlington, VA, 1989, Compressed Gas Association. TABLE 1.2 Color Marking of Compressed Gas Containers Intended for Medical Use Gas U.S. Color Canadian Color Oxygen Green Whitea Carbon dioxide Gray Gray Nitrous oxide Blue Blue Cyclopropane Orange Orange Helium Brown Brown Nitrogen Black Black Air Yellowa Black and white Mixture other than oxygen and nitrogen A combination of colors corresponding to each component gas MIXTURE OF OXYGEN AND NITROGEN Oxygen 19.5%–23.5% Yellowa Black and white All other oxygen concentrations Black and green Pink aHistorically, vacuum systems have been identified by white in the United States and yellow in Canada. Therefore it is recommended that white not be used in the United States and yellow not be used in Canada as markings to identify containers for use with any medical gas. psig, Pounds per square inch. Modified from Compressed Gas Association: Standard color marking of compressed gas containers intended for medical use, publication C-­9, ed 3. Arlington, VA, 1988, Compressed Gas Association. as bare aluminum, it is important to check the label and not solely (Fig. 1.3). The service pressure (in psig) is stamped on each rely on color coding to identify a compressed gas. cylinder and should never be exceeded. Each cylinder is also given its own serial number and commercial designation; the final code stamped on the cylinder is usually the date of the last CYLINDER MARKINGS inspection and the inspector’s mark. Medical gas cylinders must Certain codes are stamped near the neck on all medical gas be inspected at least once every 10 years, at which time they cylinders. The U.S. Department of Transportation (DOT), should also be tested for structural integrity; this is done by filling which has extensive regulations concerning the marking and the cylinder to 1.66 times the normal service pressure. The date shipping of medical gas cylinders, requires a code to indicate that of this inspection is often circled with a black marker to indicate the cylinder was manufactured according to its specifications that the cylinder has been checked by the supplier (Fig. 1.4). Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  1 Medical Gases: Storage and Supply 7 PRESSURE RELIEF VALVES All medical gas cylinders must incorporate a mechanism to vent the cylinder’s contents before explosion from excessive pressure.6 Explosion can result from exposure to extreme heat, such as in the event of a fire, or from accidental overfilling. These mechanisms are of three basic types—the fusible plug, frangible disk assembly, and safety relief valve—and are incorporated into the cylinder; as such, they cannot be inspected by the user. The fusible plug, made of a metal alloy with a low melting point, will melt in a fire and allow the gas to escape. With certain gases, such as oxygen or nitrous oxide, this can aggravate the fire because oxygen and nitrous oxide are both strong oxidizers. The frangible disk assembly contains a metal disk designed to break when a certain pressure is exceeded and thereby allow the gas to escape through a discharge vent. Finally, the safety relief valve is a spring-­loaded mechanism that closes a discharge vent. If the Fig. 1.3 Some of the cylinder markings on an E-­cylinder. DOT indi- pressure increases, the valve opens and remains open until the cates that the cylinder was manufactured according to the specifications of the United States DOT; 3AL indicates the tank is aluminum. 2015 in- pressure decreases below the valve’s opening threshold. Some dicates the maximum filling pressure of the cylinder in psig, the num- cylinders have combination devices that incorporate a fusible ber to the right is the cylinder serial number, and ALL GASS is the tank metal plug with one of the other two mechanisms. owner’s name. DOT, Department of Transportation; psig, pounds per square inch gauge. CONNECTORS Fig. 1.5 illustrates the tops of typical valves for both of the most common small (E) and large (H) cylinders. As previously mentioned, large cylinders have valve outlets that are coded and are unique to the gas content of the cylinder. The coding is based on the threads and diameter of the outlet port orifice.4 Regulators to reduce and control the pressure of the gas, also specific for each type of gas, are attached to these threaded valve ports. It is highly unsafe to use a regulator for one type of gas on a valve port of a cylinder of another type of gas. Small cylinders have cylindrical ports or holes in their valves to receive the yoke, either on an anesthesia machine or free standing, from which the gas will flow. A washer (Bodok seal), usually made of Teflon, is necessary to make this connection gas tight. Care must be taken to ensure that the retaining screw that holds the cylinder in the yoke is not placed into the safety relief device instead of in its intended location in the conical depression opposite the valve port (Fig. 1.5A). The connection between cylinder valve and yoke is made gas specific by the pin index safety system for small Fig. 1.4 An E-­cylinder of oxygen. The inspection date, August 2008, has been painted white to indicate the cylinder was checked at the time cylinder connections. it was delivered to the facility. All cylinders must be checked for leaks and structural integrity with an overpressure test at least once every 10 years. Gas Cylinder Safety Issues PREVENTION OF INCORRECT GAS CYLINDER CONNECTIONS All medical gas cylinders should come from the supplier accompanied by a tag with three perforated sections, each In the past, cylinders containing the wrong gas—for example, designating a different stage of use: empty, in use, and full. nitrous oxide instead of oxygen—were sometimes connected to The portion of the tag marked “full” should be removed anesthesia gas delivery systems, with disastrous results. This led when a cylinder is put into service. This is not usually critical, to the development of systems designed to help ensure use of however, because it is generally obvious when a cylinder is in the correct cylinder. Most of the gas tanks used for anesthesia use; making use of the tag marker becomes important when are E-­cylinders or other small cylinders, for which the pin index an empty cylinder is removed from the machine. If the tag is safety system was developed in 1952. The pin index system4 not used correctly at the outset, the problem is compounded relies on two 5-­mm stainless steel pins on the cylinder yoke with each successive stage of the cylinder’s use, and the final connector just below the fitting for the valve outlet port. Seven result is storage of an empty cylinder as a full one. Although a different pin positions are possible depending on the type of discrepancy in weight may alert a user to an incorrectly labeled gas in the cylinder (Fig. 1.6). The yoke connector for an oxygen cylinder, this error may be easily overlooked in an emergency cylinder, for example, has pins at positions 2 and 5 (Fig. 1.7). Pin situation. positions for the various gases are listed in Table 1.3. These pins Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 8 PART 1 Gases and Ventilation On/off valve spindle Packing nut Conical Outlet port depression Valve seating Safety relief Holes for device pin index system Left Right 6 1 2 5 3 7 4 A Hand wheel Nut Stem Fig. 1.6 Pin index safety system pin location is shown, looking at the Outlet port placement of holes in the tank. Pins are placed precisely complemen- tary in the tank yoke. Two pins are used to identify each type of gas. Pin Safety relief configurations are listed in Table 1.3. device roughly, the person changing the cylinder must make certain that both pins are intact. SECURING CYLINDERS AGAINST DAMAGE Gas cylinders should always be secured when placed in an upright position. If left freestanding, a cylinder can easily fall over in such a way that it would fracture at the neck (Fig. B 1.9). The cylinder’s highly pressurized gas would be suddenly Fig. 1.5 Typical cylinder valves. (A) A small cylinder packed valve, such released, and the cylinder would become an unguided missile as would be found on an E-­cylinder. Note that the female-­type port is of tremendous force; in fact, the cylinder can generate enough not unique to the gas type. (B) A large cylinder packed valve, such as force to penetrate a cinder-­block wall several feet thick. The would be seen on an H-­cylinder. Note that the male type of outlet port potential danger of such an occurrence is obvious. Therefore, has a unique diameter and threads as a safety feature intended to help ensure correct connections. (Modified from Davis PD, Parbrook EO, Par- all gas cylinders must be secured when they are upright. If that brook GD: Basic physics and measurement in anesthesia, ed 3. Oxford, is not possible, the cylinder can be laid on its side. Individual UK, 1984, Butterworth-­Heinemann.) E-­cylinders may be placed in a broad-­based wheeled carriage for support when in use. fit exactly into the corresponding holes in the cylinder valve TRANSFILLING (Fig. 1.8). This system provides an additional safety feature and, along with color coding, is designed to ensure that the correct Anesthesia personnel should never attempt to refill small gas is connected to its corresponding cylinder yoke. Obviously, cylinders from larger ones. Even if gas-­tight connections were connectors with either damaged or missing index pins are unsafe possible, the risk of explosion from the heat of compression in and should not be used under any circumstances. Because a the small cylinder would still be serious. In addition, there is pin can easily be lost or damaged when a cylinder is handled always the possibility that the wrong gas would be placed in the Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  1 Medical Gases: Storage and Supply 9 A B Fig. 1.7 (A) Cylinder yoke on the anesthesia machine. Note the two pins for the pin index system at the bottom of the yoke (bottom arrow) and the hole (top arrow; not gas specific) that aligns with the outlet port of the tank. (B) Oxygen yoke with the tank removed and the nitrous oxide tank in place. TABLE 1.3 Pin Index Safety System MIXTURES OF OXYGEN Air Cyclopropane N2 N2O O2 He CO2 Pin positions 1–5 3–6 1–4 3–5 2–5 2–4 1–6 The pin index system relies on two 5-­mm stainless steel pins on the cylinder yoke connector just below the fitting for the valve outlet port. Seven different pin positions are possible depending on the type of gas in the cylinder (the seventh pin position is for a gas not used in the United States). See Figs. 1.6 and 1.7 for pin locations. be dangerously overfilled to near-­bursting pressures, and six cylinders of compressed air were found to be contaminated with volatile hydrocarbons. Thirty cylinders were unlabeled, and the labels of many others were illegible, having been painted over. Another four cylinders were incorrectly color coded, five large cylinders were fitted with incorrect valve outlet ports (especially dangerous because an oxygen valve on an air cylinder enables air to be fed into an oxygen outlet), 14 valve assemblies were found to be loose, and four valve assemblies were inoperable. On a large number of cylinders, the current inspection date was either absent or had been painted over so as to be illegible. Numerous examples were cited of cylinders being improperly stored or secured. The results of this study serve to remind anesthesia practitioners of the danger of assuming that gas supplies are perfectly safe. All facilities should have an established system to ensure that each cylinder of medical gas is inspected and tested Fig. 1.8 Cylinder valve at the top of an E-­cylinder shows the two holes for the pin index system and the outlet port with an attached washer upon delivery to the facility. (arrow). Guidelines for Use of Medical Gas cylinder. The practice of transfilling is also forbidden. Medical Cylinders gases must be obtained only from a reputable commercial Numerous rules govern the safe handling of cylinders that supplier. contain medical gases.1,2 Summarized here are practical points that anesthesia practitioners must consider on a routine basis. CYLINDER HAZARDS SUPPLY A study of 14,500 medical gas cylinders consecutively delivered from supposedly reputable suppliers found 120 (0.83%) with As noted above, medical gases should be purchased only from potentially dangerous irregularities.7 Forty cylinders were a reputable commercial supplier. Outside metropolitan areas, delivered either empty or partially filled, three were found to the only supplier of any type of compressed gas may be the Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 10 PART 1 Gases and Ventilation A B C D Fig. 1.9 (A) Gas cylinders must never be left standing upright and unsecured. They are vulnerable to being knocked over easily, such as by opening a door. Cylinders that fall directly to the floor, and especially cylinders that fall so that the top hits a wall (B), are at great risk for breaking at the cylin- der neck. This creates a dangerous “unguided missile,” in which the high-­pressure gas escapes out the narrow neck and rockets the cylinder forward with enough force to penetrate a brick wall. (C) Lightweight aluminum oxygen cylinders are now available that are filled to a maximum pressure of 3000 psig and can evolve 1000 L of oxygen at 1 atm of pressure (Linde North America, Norcross, GA). These would present an even greater hazard if ruptured. The valve on this tank does not incorporate a pin index safety system connector because it is not designed to be placed in a hanger yoke. The tank has a nipple for delivery of O2 at 0.25–25 L/min at low pressures to an Ambu bag, nasal cannula, etc. The cylinder also incorporates a DISS oxygen connector that can be used to connect the tank to the machine’s oxygen pipeline inlet connector (see Fig. 2.6). (D) If upright, individual cylin- ders should be secured in some type of holder, such as a rolling stand for E-­sized cylinders. atm, Atmosphere; DISS, Diameter Index Safety System; psig, pounds per square inch gauge. local welding company. Purchasing medical gases from such TRANSPORT AND INSTALLATION a source can be appropriate once it has been established that this supplier meets all safety requirements and standards for Medical gas cylinders must be handled with care. As previously the manufacture and supply of medical gases. Such verification mentioned, a broken cylinder can have serious consequences, should be incorporated into a quality system to promote as can valve assemblies damaged by rough handling. Cylinders maximum safety. should undergo a final inspection just before they are used. If questions arise concerning the safety or content of a cylinder, STORAGE it should not be used; instead, an investigation should be undertaken before returning the cylinder to the supplier. Specific regulations and standards govern the storage of Before a small E-­cylinder is installed in the hanger yoke, the medical gas cylinders.2,3 For example, full cylinders and empty plastic wrapping surrounding the cylinder valve outlet must cylinders must be stored separately, each in its own “tank room” be completely removed. If this is not done, the plastic wrapper if possible. Small cylinders should be placed in nonflammable will prevent the gas from entering the inlet in the hanger yoke. racks, and large cylinders should be chained to a wall. At least Furthermore, cylinders should always be opened slowly to one anesthesiologist in each facility should be aware of these prevent dramatic heating of the suddenly pressurized piping. requirements and how they are being implemented. Anesthesia If an abnormal odor is detected when the cylinder is opened, caregivers should also assume responsibility for all aspects of gas should be collected from the tank and analyzed by gas medical gas supplies. chromatography to detect hydrocarbon contamination.8 Once Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  1 Medical Gases: Storage and Supply 11 of a medical facility is governed by standards, and the procedures required for operating a medical gas system must be followed by the plant engineering and maintenance departments. Problems in the construction of gas pipelines have led to anesthesia deaths; anesthesia providers should therefore be aware of these standards and the gas delivery system at their facility.10 The Medical Gas Professional Healthcare Organization (MGPHO) was founded in 1998 as an organization that is dedicated to advancing the safe design, manufacture, installation, maintenance, and inspection/verification of medical gas and vacuum systems through education. The organization is actively involved in identifying, understanding, and maintaining state and federal standards as well as improving the techniques used in testing and verification.11 Fig. 1.10 Proper method for attaching an E-­cylinder to the yoke of an Medical Gas Central Supply Systems anesthesia machine. The tank is first supported on the anesthesiologist’s foot while the holes on the tank are aligned with the pins in the yoke. The central supply (bulk storage) system is the source of medical The tank is then slid into place on the yoke, and the T-­handle is tight- gases distributed throughout the pipeline system. For oxygen, ened to make a gas-­tight seal. the central supply can be a series of standard cylinders connected by a manifold system or, for larger installations, pressure vessels a problem is confirmed, the cylinder in question should be of liquid oxygen with accompanying vaporizers. For medical sequestered, not returned to the supplier, and the appropriate air, the supply can be cylinders of compressed air, cylinders of local and federal authorities contacted. oxygen and nitrogen with the gases mixed by a regulator, or air Connections between gas cylinders and anesthesia machines compressors. In general, for nitrous oxide or nitrogen, a series of must be tight. Fig. 1.10 illustrates the proper method for cylinders, or liquid Dewar tanks, with a manifold system is used. balancing the tank when securing it to or removing it from the yoke. Washers (Bodok seals) are necessary for small cylinder OXYGEN yokes and occasionally need replacement; the old washer must be removed before placing a new washer. Having two washers Central supply systems that carry oxygen are both the most in place simultaneously will create a leak and may also defeat common and the most important supply systems; as such, they the pin index system. If a hissing noise is heard when a cylinder have received considerable attention. Standards for bulk systems is opened, a leak is present. Tightness can always be checked that involve the storage of oxygen as a liquid are contained in by dripping soapy water onto the connection and inspecting it NFPA Publication 55.12 Oxygen systems are extensively covered for bubbles. A connection should never be overtightened in an in NFPA Publication 9913 and in the CSA Standard Z305.1.14 attempt to compensate for a leak; doing so may damage or even Very small systems have a total storage capacity of less than crack the cylinder valve. As in all aspects of anesthesia practice, 2000 cubic feet (cu ft) of gas (a single H-­cylinder of oxygen brute force is almost never appropriate. contains 244 cu ft, or 6900 L) and have additional standards Once a new cylinder is in place, the pressure must be checked when based in nonhospital facilities. Systems in very small on the applicable gauge. Correct pressures for full cylinders are hospitals may store oxygen in a series of standard H-­cylinders listed in Table 1.1. Overpressurized cylinders are dangerous and connected by a manifold or high-­pressure header system. These must be removed at once and reported to the supplier. systems typically do not have reserve supplies. In Figs. 1.11 and 1.12, note that there are two banks of cylinders; all central Medical Gas Pipeline Systems supply systems for medical gases must be present in duplicate, with two identical sources able to provide the needed medical Medical gas pipeline systems consist of three main components: gas interchangeably. These are often referred to as the primary (1) a central supply of gas, (2) pipelines to transport gases to and secondary supplies (not to be confused with the entirely points of use, and (3) connectors at these points that connect separate reserve system). to the equipment that delivers the medical gas. Anesthesia The larger the oxygen demand of the facility, the more caregivers are primarily concerned with piped oxygen and complex the supply system. Most hospitals store their bulk nitrous oxide; however, ORs may have two other medical oxygen in liquid form (Fig. 1.13), which enables the hospital to gas supply pipelines: one for compressed air and another for maintain a large reservoir of oxygen in a relatively small space. nitrogen to power gas-­driven equipment. One cubic foot of oxygen stored at a temperature of −297°F Detailed standards and guidelines exist for the use of medical (−183°C) expands to 860 cu ft of oxygen at 70°F (21°C).15 gas delivery systems. In North America, these are published Because 1 cu ft is equal to 28.3 L, this amount of liquid oxygen by the American National Standards Institute (ANSI), the provides 24,338 L at room temperature and pressure, the American Society of Mechanical Engineers (ASME), the CGA, equivalent of 3.5 H-­cylinders of oxygen. the National Fire Protection Association (NFPA), the Canadian Liquid oxygen is stored in a special container and kept under Standards Association (CSA), and the American Hospital pressure. This container has an inner and outer layer separated Association (AHA).9 In the United States, a hospital must meet by layers of insulation and a near vacuum. This construction is the NFPA standards to be accredited by The Joint Commission similar to that of a thermos bottle and keeps the liquid oxygen (TJC) and often to obtain insurance coverage. The construction cold by inhibiting the entry of external heat (Fig. 1.14). Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 12 PART 1 Gases and Ventilation Line Relief Emergency pressure valve alarm switch regulator Vent to outside of building Piping system Main shut-off valve Vent to outside of building Relief valve Operating alarm switch Operating Operating pressure Check valve pressure regulator regulator Shut-off valve High-pressure header High-pressure header Check valve Cylinder valve Safety relief device Cylinders Cylinders (bank 1) (bank 2) Fig. 1.11 Typical cylinder (H-­size) supply system, as would be seen in a small hospital or a freestanding facility. There is no reserve supply. (From CSA Standard Z305.1-­1975, Nonflammable medical-­gas piping systems. Toronto, 1975, Canadian Standards Association.) To pipeline 2200 psig 50 psig 2200 psig Fig. 1.12 A simplified version of Fig. 1.11. The oxygen is supplied in H-­ Primary Secondary cylinders from both a primary and a sec- ondary supply. The tanks are connected by a manifold; when the tanks are full, the pressure is 2200 psig. A changeover valve automatically switches to the secondary supply once the primary supply has been exhausted. A reducing valve decreases the pressure to 50 psig before the oxygen enters the hospital pipeline. psig, Pounds per square inch gauge. (Modified from Davis PD, Parbrook EO, Parbrook GD: Ba- sic physics and measurement in anesthe- sia, ed 3. Oxford, UK, 1984, Butterworth- Changeover Heinemann.) valve Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  1 Medical Gases: Storage and Supply 13 Liquid oxygen systems must be in constant use to be cost severe burns if they come in contact with liquid oxygen or an effective. If the system goes unused for a period of time, the uninsulated pipe carrying liquid oxygen. pressure increases as some of the liquid oxygen boils. The Small hospitals typically require central supply systems that oxygen is then vented to the atmosphere. The liquid oxygen store oxygen in replaceable liquid oxygen cylinders and a reserve system contains vaporizers that heat the liquid and convert it of oxygen stored in high-­pressure H-­cylinders. The reserve to a gas before it is piped into the hospital. Environmental and system is automatically activated when the main supply, with its mechanical heat sources can be used to aid in vaporization. component primary and secondary storage, fails or is depleted Liquid oxygen can be extremely hazardous, and fires are (Fig. 1.15). Hospitals of average size may store liquid oxygen an ever-­ present danger. In addition, personnel can receive in bulk pressure vessels rather than in liquid oxygen cylinders. The storage vessel is filled from a liquid oxygen supply truck through a cryogenic hose designed to function at extremely low temperatures. In such a system, the size of the reserve system depends on the rate of oxygen use because the reserve must constitute at least an average supply for 1 day, but preferably 2–3 days. This supply may be stored in a series of high-­pressure H-­cylinders. However, large hospitals are required to have a second liquid oxygen storage vessel as the reserve system because of the impracticality of storing and connecting enough cylinders to provide an average day’s reserve supply of oxygen (Fig. 1.16). Built into all these central supply systems for oxygen are a variety of mandatory safety devices. Pressure relief valves are designed to open if pressure in the system exceeds the normal level by 50%. This prevents the rupture of vessels or pipes from the excessive pressure generated by a frozen valve or a malfunctioning pressure regulator. Alarm systems indicate when the supply in the main storage vessel is low and when the reserve supply has been accessed. An oxygen alarm should activate a rehearsed protocol within the hospital that results in contact with the oxygen supplier and subsequent verification that an oxygen delivery is on the way.16 Pressure alarms built into the main supply line sound when the line pressure varies by 20% in either direction from the normal operating pressure of approximately 55 psig. Pressure alarms should also be located in various areas in the pipeline to detect oxygen supply problems beyond the main connection (Fig. 1.17). All these alarm systems must sound in two different locations: the hospital maintenance or plant engineering department and an area occupied 24 hours a day, such as the telephone Fig. 1.13 A typical bulk-­storage vessel for liquid oxygen. switchboard. These alarms should be periodically tested as ~85 psig Safety relief valve ~50 psig Pressure regulator Fig. 1.14 Diagram of a liquid oxygen supply system. The vessel resembles a giant vacuum bottle. The liquid oxygen is at approximately To pipeline −256°F (−160°C). Pressure inside the vessel is Temperature Superheater maintained at approximately 85 psig. When approximately oxygen is used from the top of the vessel, it first 256 F passes through a superheater and then through (160 C) the pressure regulator to keep the pipeline pressure at 50 psig. During times of rapid use, the temperature in the tank may fall, along with Vacuum Control the vapor pressure. The control valve causes valve liquid oxygen to pass through the vaporizer, which adds heat and thus maintains the pres- Vaporizer sure in the tank. psig, Pounds per square inch gauge. (Modified from Davis PD, Parbrook EO, Parbrook GD: Basic physics and measure- ment in anesthesia, ed 3. Oxford, UK, 1984, Butterworth-­Heinemann.) Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 14 PART 1 Gases and Ventilation Relief Reserve supply valve operating alarm switch Vent to outside of building Piping system Operating Check Check control unit valve valve Emergency alarm switch Reserve Operating supply pressure Secondary regulator bank pressure pressure regulator regulator Shut-off Main shut-off valve Secondary supply valve Bleeder valve operating alarm switch Vent to outside Operating selector of building Shut-off valve Check valves Relief Pressure valve relief Cylinder valves device Safety relief Line pressure device regulator Primary supply Secondary supply Reserve supply (liquid cylinders) (liquid cylinders) (high-pressure cylinders) Operating supply may consist of one or more supply units on each bank. Fig. 1.15 Typical cryogenic cylinder supply system for liquid oxygen with a high-­pressure cylinder reserve supply, as would be seen in a small hospi- tal. The redundant primary and secondary liquid cylinders are intended to be the continuous oxygen source; there is an automatic switchover to the other bank when one is depleted and ready for replacement. The reserve supply is automatically activated when both banks of cylinders are depleted or fail. (From CSA Standard Z305.1–92, Nonflammable medical gas piping systems. Toronto, 1992, Canadian Standards Association.) part of a regular maintenance program because failure of such by concentrators is approximately 90%–96%, with the balance alarms has led to crisis situations. Testing the various alarms made up mostly of argon.18,19 can be difficult but is possible if the system is properly designed. Oxygen concentrators are commonly used in remote Another critical safety feature is the T-­fitting located at the locations and developing countries, but in some cases they point where the central supply system joins the hospital piping have been configured to supplement a hospital’s existing liquid system. This fitting allows delivery of an emergency supply of oxygen system as a reserve or a secondary supply.18 Oxygen oxygen from a mobile source in the event of extended failure, concentration may vary with gas flow, and concentrators are extensive repair, or modification of the hospital’s central supply. most effective at delivering oxygen at flows of less than 4 L/ The location and housing of oxygen central supply systems min to anesthesia machines.19 Accumulation of argon may are governed by strict standards.12 A bulk oxygen storage occur, however, in low-­flow conditions, so the use of an oxygen unit should be located away from public areas and flammable monitor is essential.20 As the current emphasis on cost cutting materials. in medical care continues, along with cost increases of supplied liquid and gaseous oxygen, oxygen concentrators are likely to come into wider use. OXYGEN CONCENTRATORS The use of oxygen concentrators to deliver oxygen to the MEDICAL AIR anesthesia circuit has gained attention recently. Oxygen is generated by the selective adsorption of the components of air The central supply of medical air can come from three sources: with molecular sieve technology. These sieves consist of rigid (1) cylinders of compressed air that have been cleaned to structures of silica and aluminum, with additional calcium or medical quality by filtration distillation; (2) a proportioning sodium as cations.17 Air is forced through the sieves under system (relatively uncommon) that receives oxygen and pressure, and oxygen and nitrogen are generated. The oxygen nitrogen from central sources, mixes them in a proportion of is then used clinically, and the nitrogen is vented to the 21% oxygen to 79% nitrogen, and delivers this mixture to the atmosphere. The maximum oxygen concentration produced medical air pipeline (these systems usually have compressed air Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved.  3 A B 3 24 19 20 23 2 Fig. 1.16 Typical bulk supply system for 24 oxygen, as would be seen in a large hospital. 4 Very large hospitals may require more than 23 one system of this magnitude. (A) Main liquid 1 4 oxygen reservoir; (B) reserve liquid oxygen 7 3 reservoir. 1, Connection to supply vehicle; 2, top and bottom fill lines; 3, reservoir pres- 5 5 3 sure relief valves; 4, “economizer” circuit; 5, 6 6 7 gas regulator in pressure-­building circuit; 6, pressure-­building vaporizer; 7, liquid regula- 17 tor in pressure-­building circuit; 8, cryogenic liquid-­control valves; 9, liquid vaporizers; 10, 10 downstream valves for isolation of vaporiz- ers; 11, primary line pressure regulator; 11a, 9 8 secondary line pressure regulator; 11b, valves to isolate regulators for repair; 12, pressure 18 relief valve for main pipeline; 13, reserve system liquid vaporizer; 14, reserve system 9 8 line pressure regulator; 15, gas flow check valves; 16, reserve system “economizer” line; 13 17, reserve system fill line; 18, valve control- 10 12 ling flow to reserve system from main cylin- 14 15 der; 19, low liquid level alarm; 20, reserve in use alarm; 21, main line pressure alarm; 22, 11a main shut-­ off valve and T-­ fitting; 23, liquid 11b 11b level indicators; 24, vapor or “head” pressure gauges. In normal operation, liquid oxygen 11 21 flows from the lower left of the main vessel (A) 16 via a cryogenic pipe through valves (8) and to the vaporizer (9), where the liquid becomes gaseous oxygen. It then flows through pres- sure regulators (11) and hence into the supply 22 pipeline to the hospital. (From Bancroft ML, du Moulin GC, Hedley-­Whyte J: Hazards of bulk oxygen delivery systems. Anesthesiol- To hospital ogy 1980;52:504-­510.) A B Fig. 1.17 (A) Bank of pressure gauges that monitor the gases in one zone of the operating room. These gauges are for oxygen, air, and vacuum. Note that the rooms being monitored are identified on the top of the panel. (B) A second gas monitoring panel for nitrous oxide, nitrogen, carbon dioxide, and waste gases. Note that colored lights indicate whether the line pressures are in the normal range; alarms are triggered for high or low pressures. Downloaded for Vicente Gonzalez ([email protected]) at Florida International University from ClinicalKey.com by Elsevier on September 05, 2024. For personal use only. No other uses without permission. Copyright ©2024. Elsevier Inc. All rights reserved. 16 PART 1 Gases and Ventilation cylinders or an air compressor as a reserve system); and (3) air The condensed water is then properly disposed of to eliminate compressors (Fig. 1.18), the most common source of medical air potential breeding grounds for bacteria, such as those that in hospitals. The compressor works by compressing ambient air cause Legionnaires’ disease. Valves, pressure regulators, and and then delivering the pressurized air to a reservoir or holding alarms analogous to those in oxygen supply systems are needed. tank.15 The medical air is then fed to the pressure regulator and In addition, the piping should not be exposed to subfreezing travels from there to the hospital piping system. temperatures. Air compressor systems are subject to rigorous standards.13,14 As with other systems (i.e., vacuum or electric generators), NITROUS OXIDE redundancy is important. Duplicate compressors are necessary, each with the capacity to meet the entire hospital’s medical Specific standards exist for nitrous oxide systems, and certain air needs if the other fails. The system must be used only for portions of the more general standards of the NFPA and CSA the medical air pipeline and not for the purpose of powering are applicable as well.21 A nitrous oxide central supply system equipment. If air is to be used for powering equipment, a separate may be warranted, depending