Anesthesia machines

Nitrous Oxide. Nitrous oxide, described by Priesdy in 1772, was first used to reHeve severe dental pain in the latter part of the 18th century. Sometime in the mid-1800s N2O was successfully used as an anesthetic, and its widespread usage coincided with the development of anesthesia machines. Nitrous oxide is a nonflammable, colorless, odorless, and tasteless gas that can exist as a Hquid under pressure at room temperature. It is normally stored in cylinders. However, it supports combustion. 

The inhalational anesthetics can be divided into two classes based on their physical properties. N2O and cyclopropane are gases at room temperature and are supplied in gas tanks that are regulated by the anesthesia machine. The others are liquids that are volatile following the application of low heat, which is supplied by a vaporizer attached to the anesthesia machine. The halo-genated hydrocarbons are among the most potent volatile anesthetics. 

The use of inhalational anesthetics is generally reserved for maintenance of anesthesia. The development of an anesthetic concentration in the brain occurs more slowly with inhalational anesthetics than with IV drugs. Once an anesthetic level has been achieved, however, it is easily adjusted by controlling the rate or concentration of gas delivery from the anesthesia machine. The rate of recovery from a lengthy procedure in which inhalational agents are used is reasonably rapid, since inhalational anesthetics are eliminated by the lungs and do not depend on a slow rate of metabolism for their tissue clearance. Thus, inhalational drugs meet the requirement for a relatively prompt return of the patient s psychomotor competence. 

The metabolism of enflurane and sevoflurane results in the formation of fluoride ion. However, in contrast to the rarely used volatile anesthetic methoxyflurane, renal fluoride levels do not reach toxic levels under normal circumstances. In addition, sevoflurane is degraded by contact with the carbon dioxide absorbent in anesthesia machines, yielding a vinyl ether called "compound A," which can cause renal damage if high concentrations are absorbed. (See Do We Really Need Another Inhaled Anesthetic ) Seventy percent of the absorbed methoxyflurane is metabolized by the liver, and the released fluoride ions can produce nephrotoxicity. In terms of the extent of hepatic metabolism, the rank order for the inhaled anesthetics is methoxyflurane > halothane > enflurane > sevoflurane > isoflurane > desflurane > nitrous oxide (Table 25-2). Nitrous oxide is not metabolized by human tissues. However, bacteria in the gastrointestinal tract may be able to break down the nitrous oxide molecule. 

Anesthesia is achieved rapidly and smoothly with sevoflurane, and recovery is more rapid than with isoflurane. However, sevoflurane is chemically unstable when exposed to carbon dioxide absorbents in anesthesia machines, degrading to an olefinic compound (fluoromethyl-2,2-difluoro-l-[trifluoromethyl]vinyl ether, also known as compound A) that is potentially nephrotoxic. In addition, sevoflurane is metabolized by the liver to release fluoride ions, raising concerns about potential renal damage. 

The good adsorbability of fluorocarbons can be employed for the recovery of, for example, fluorinated inhalation anesthetics from the air of anesthesia machines.18... 

When using an anesthesia machine, such as V-10 Mobile Cart System described here, ensure all carrier gas lines are securely attached and all chambers, breathing circuits, and nose cones are firmly in place (see Note 3). 

Sevoflurane undergoes degradation by soda lime and barium hydroxide lime both of which are used in modern anesthesia machines for CO2 absorption. The chief degradation product is fluoromethyl-2,2-difluoro-l(trifluoromethyl) vinylether, also called compound A... 

Sevoflurane (ULTANE Figure 13-3) is a clear, colorless, volatile liquid at room temperature and must be stored in a sealed bottle. It is nonflammable and nonexplosive in mixtures of air or oxygen. Sevoflurane can undergo an exothermic reaction with desiccated CO absorbent (BARA-lyme) to produce airway bums or spontaneous ignition, explosion, and fire. Care must be taken to ensure that sevoflurane is not used with an anesthesia machine in which the COj absorbent has been dried by prolonged gas flow through the absorbent. Sevoflurane reaction with desiccated CO absorbent also can produce CO, which can result in serious patient injury. 

Nitrous oxide (dinitrogen monoxide N2O) is a colorless, odorless gas at room temperature (Figure 13-3). It is sold in steel cylinders and must be delivered through calibrated flow meters provided on all anesthesia machines. Nitrous oxide is neither flammable nor explosive, but it does support combustion as actively as oxygen does when it is present in proper concentration with a flammable anesthetic or material. 

The analysis of the gas mixture can be carried out in the mainstream or in the sidestream. Figure 23-3 presents two examples of a circle system of an anesthesia machine with the location of the respiratory gas sensors at the Y-piece for direct measurements in the mainstream of the breathing system, or connected by a thin capillary tube or hose in the sidestream distant from the patient. (A circle system is part of the ventilation system in anesthesia machines dedicated to so-called semi-closed or closed anesthesia, which reuses the exhaled respiration gases after removing COj by an absorber.)... 

Before I was injected with carfentanil, we had carried out studies in rodents and baboons. The dose that I was to be given would be exceedingly small, but we thought it wise to have an anesthetist and an anesthesia machine present in case my breathing stopped. As it turned out, there was no effect on my breathing, but there was constriction of my pupils. We scheduled a second injection and PET imaging procedure for the next day in the nuclear medicine department. 

The primary use of air during anesthesia is as a diluent to decrease the inspired oxygen concentration. The typical primary source of medical air (there is an important distinction between air and medical air related to the quahty and the requirements for periodic testing) is a special compressor that avoids hydrocarbon-based lubricants for purposes of medical air purity. Dryers are employed to rid the compressed air of water before distribution throughout the hospital. Medical facihties with limited need for medical air may use banks of H cylinders of dry medical air. A secondary source of air may be available on the anesthesia machine as an E cylinder containing dry gas at 15.2 MPa. 

An indicator can specify a part of a process to be measured or the outcome of that process. An outcome indicator assesses the results of a process. Examples include the percentage of uncompleted, scheduled IPMs, or the number of uncompleted equipment repairs not completed within 30 days. A process indicator assesses an important and discrete activity that is carried out during the process. An example would be the number of anesthesia machines in which the scheduled IPM failed or the number of equipment repairs awaiting parts that are uncompleted within 30 days. 

When patients undergo surgery, they expect good results. When bad results occur, they may sue the physician, the hospital, and the medical device manufacturer. Modern surgery involves medical devices such as electrosurgery, anesthesia machines, and lai e imaging devices. Problems associated with such devices have resulted in serious burns, loss of limbs, and death. Because the bioengineer maybe an expert on one of these medical devices, he or she may become an expert witness in one of these cases and offer an expert opinion on the cause of the problem. 

Premature infants who require ligation of a patent ductus arteriosus (PDA) or who present with necrotizing enterocolitis (NEC) often weigh less than 1 kg and are not on conventional ventilators, thus often cannot be moved from the neonatal intensive care imit and cannot tolerate an anesthesia machine or a volatile anesthetic. 

The advantage of an electrode of this sort is that it can be used during surgical procedures in conjunction with an anesthesia machine, as long as the subject is intubulated with a tracheal tube. If the electrode is used in... 

Olds JW, Kisch AL, Eberle BJ, Wilson JN. Pseudomonas aeruginosa respiratory tract infection acquired from a contaminated anesthesia machine. Am Rev Respir Dis 1972 105 628-632. 

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