Anes Hall – Chapter 1 – Flashcards

1.(B)Orifice flow occurs when gas flows through a region of severe constriction such as described in this question.Laminar flow occurs when gas flows down parallel-sided tubes at a rate less than critical velocity. When thegas flow exceeds the critical velocity, it becomes turbulent (Miller: Anesthesia, ed 6, pp 690-691; Ehrenwerth:Anesthesia Equipment: Principles and Applications, pp 224-225).

2.(C)During orifice flow, the resistance to gas flow is directly proportional to the density of the gas mixture.Substituting helium for nitrogen will decrease the density of the gas mixture, thereby decreasing the resistanceto gas flow (as much as threefold) through the region of constriction (Ehrenwerth: Anesthesia Equipment:Principles and Applications, pp 224-225; Miller: Anesthesia, ed 6, pp 690-691, 2539).

3.(C)Modern electronic blood pressure (BP) monitors are designed to interface with electromechanical transducersystems. These systems do not require extensive technical skill on the part of the anesthesia provider for accurate usage. A static zeroing of the system is built into most modern electronic monitors. Thus, after thezeroing procedure is accomplished, the system is ready for operation. The system should be zeroed with thereference point of the transducer at the approximate level of the aortic root, eliminating the effect of the fluidcolumn of the system on arterial BP readings (Ehrenwerth: Anesthesia Equipment: Principles and Applications,pp 275-278)

4.(C)Waste gas disposal systems, also called scavenging systems, are designed to decrease pollution of the OR byanesthetic gases. These scavenging systems can be passive (waste gases flow from the anesthesia machineto a ventilation system on their own) or active (anesthesia machine connected to a vacuum system then to theventilation system). The amount of air from a venous gas embolism would not be enough to be detected in thedisposal system. Positive pressure relief valves open if there is an obstruction between the anesthesiamachine and the disposal system, which would then leak the gas into the OR. A leak in the soda limecanisters would also vent to the OR. Since most ventilator bellows are powered by oxygen, a leak in thebellows would not add air to the evacuation system. The negative pressure relief valve is used in activesystems and will entrap room air if the pressure in the system is less than -0.5 cm H2O. (Miller: Anesthesia,6th ed. pp 303-307; Stoelting: Basics of Anesthesia, ed 5, pp 198-199)

5.(D)The relationship between intra-alveolar pressure, surface tension, and the radius of alveoli is described byLaplace's law for a sphere, which states that the surface tension of the sphere is directly proportional to theradius of the sphere and pressure within the sphere. With regard to pulmonary alveoli, the mathematicalexpression of Laplace's law is as follows: T=1/2PR

6.(C)The World Health Organization requires that compressed-gas cylinders containing N2O for medical use bepainted blue. Size "E" compressed-gas cylinders completely filled with N2O contain approximately 1590 L ofgas (Stoelting: Basics of Anesthesia, ed 5, p 188).

7.(D)Many anesthesia machines have a check valve downstream from the rotameters and vaporizers but upstreamfrom the oxygen flush valve. When the oxygen flush valve button is depressed and the Y-piece (which wouldbe connected to the endotracheal tube [ETT] or the anesthesia mask) is occluded, the circuit will be filled andthe needle on the airway pressure gauge will indicate positive pressure. The positive pressure reading will notfall, however, even in the presence of a leak in the low-pressure circuit of the anesthesia machine. If a checkvalve is present on the common gas outlet, the positive-pressure leak test can be dangerous and misleading.In 1993, the United States Food and Drug Administration (FDA) established the FDA Universal NegativePressure Leak Test. With the machine master switch, the flow control valves and the vaporizers turned off, asuction bulb is attached to the common gas outlet and compressed until it is fully collapsed. If a leak ispresent the suction bulb will inflate. It was so named because it can be used to check all anesthesiamachines regardless of whether they contain a check valve in the fresh gas outlet (Miller: Anesthesia, ed 6, pp309-310).

8.(E)Check valves permit only unidirectional flow of gases. These valves prevent retrograde flow of gases from theanesthesia machine or the transfer of gas from a compressed-gas cylinder at high pressure into a container ata lower pressure. Thus, these unidirectional valves will allow an empty compressed-gas cylinder to beexchanged for a full one during operation of the anesthesia machine with minimal loss of gas. The adjustablepressure-limiting valve is a synonym for a pop-off valve. A fail-safe valve is a synonym for a pressure-sensorshutoff valve. The purpose of a fail-safe valve is to discontinue the flow of N2O if the O2 pressure within theanesthesia machine falls below 25 psi (Ehrenwerth: Anesthesia Equipment: Principles and Applications, pp46-47; Miller: Anesthesia, ed 6, p 276.)

9.(C)Boyle's law states that for a fixed mass of gas at constant temperature, the product of pressure and volume isconstant. This concept can be used to estimate the volume of gas remaining in a compressed-gas cylinder bymeasuring the pressure within the cylinder (Ehrenwerth: Anesthesia Equipment: Principles and Applications, p224)

10.(C)United States manufacturers require that all compressed-gas cylinders containing O2 for medical use bepainted green. A compressed-gas cylinder completely filled with O2 has a pressure of approximately 2000 psiand contains approximately 625 L of gas. According to Boyle's law (see explanation to question 9) the volumeof gas remaining in a closed container can be estimated by measuring the pressure within the container.Therefore, when the pressure gauge on a compressed-gas cylinder containing O2 shows a pressure of 1600psi, the cylinder contains 500 L of O2. At a gas flow of 2 L/min, O2 could be delivered from the cylinder forapproximately 250 minutes (Stoelting: Basics of Anesthesia ed 5, p 188). PICTURE OF CHART

11.(B)All of the choices listed in this question can potentially result in inadequate flow of O2 to the patient; however,given the description of the problem, no flow of O2 through the O2 rotameter is the correct choice. In anormally functioning rotameter, gas flows between the rim of the bobbin and the wall of the Thorpe tube,causing the bobbin to rotate. If the bobbin is rotating you can be certain that gas is flowing through therotameter and that the bobbin is not stuck (Ehrenwerth: Anesthesia Equipment: Principles and Applications,pp 40-42).

12.(B)Fail-safe valve is a synonym for pressure-sensor shutoff valve. The purpose of the fail-safe valve is toprevent delivery of hypoxic gas mixtures from the anesthesia machine to the patient due to failure of the O2supply. When the O2 pressure within the anesthesia machine decreases below 25 psi, this valve discontinuesthe flow of N2O or proportionally decreases the flow of all gases. It is important to realize that this valve willnot prevent delivery of hypoxic gas mixtures or pure N2O when the O2 rotameter is off, but the O2 pressurewithin the circuits of the anesthesia machine is maintained by an open O2 compressed-gas cylinder or centralsupply source. Under these circumstances, an O2 analyzer would be needed to detect delivery of a hypoxicgas mixture (Ehrenwerth: Anesthesia Equipment: Principles and Applications, pp 37-38)

13.(C)It is important to zero the electromechanical transducer system with the reference point at the approximatelevel of the heart. This will eliminate the effect of the fluid column of the transducer system on the arterial BPreading of the system. In this question, the system was zeroed at the stopcock, which was located at thepatient's wrist (approximate level of the ventricle). Blood pressure expressed by the arterial line will, therefore,be accurate, provided the distance between the patient's wrist and the stopcock remains 20 cm. Also seeexplanation to question 3 (Ehrenwerth: Anesthesia Equipment: Principles and Applications, p 276).

14.(C)O2 and N2O enter the anesthesia machine from a central supply source or compressed-gas cylinders atpressures as high as 2200 psi (oxygen) and 750 psi (N2O). First-stage pressure regulators reduce thesepressures to approximately 45 psi. Before entering the rotameters, second-stage O2 pressure regulatorsfurther reduce the pressure to approximately 14 to 16 psi (see figure with answer to question 12) (Miller:Anesthesia, ed 6, pp 274-275).

15.(C)NIOSH sets guidelines and issues recommendations concerning the control of waste anesthetic gases. NIOSHmandates that the highest trace concentration of N2O contamination of the OR atmosphere should be lessthan 25 ppm. In dental facilities where N2O is used without volatile anesthetics, NIOSH permits up to 50 ppm(Miller: Anesthesia, ed 6, pp 303-304).

16.(C)Agent-specific vaporizers, such as the Sevotec (sevoflurane) vaporizer, are designed for each volatileanesthetic. However, volatile anesthetics with identical saturated vapor pressures could be usedinterchangeably with accurate delivery of the volatile anesthetic PICTURE OF CHART

17.(A)The control mechanism of standard anesthesia ventilators, such as the Ohmeda 7000, uses compressedoxygen (100%) to compress the ventilator bellows and electrical power for the timing circuits (Miller:Anesthesia, ed 6, p 298)

18.(C)Five types of rotameter indicators are commonly used to indicate the flow of gases delivered from theanesthesia machine. As with all anesthesia equipment, proper understanding of their function is necessary forsafe and proper use. All rotameter flow indicators should be read at the upper rim except ball floats, whichshould be read in the middle (Ehrenwerth: Anesthesia Equipment: Principles and Applications, pp 40-43).

19.(B)The pressure gauge on a size "E" compressed-gas cylinder containing N2O shows 750 psi when it is full andwill continue to register 750 psi until approximately three-fourths of the gas has left the cylinder. A full cylinderof N2O contains 1590 L. Therefore, when 400 L of gas remain in the cylinder, the pressure within the cylinderwill begin to fall (Stoelting: Basics of Anesthesia, ed 5, p 188)

20.(B)In this question the reference point is the transducer, which is located 10 cm below the level of the patient'sheart. Thus, there is an approximate 10 cm H2O fluid column from the level of the patient's heart to thetransducer. This will cause the pressure reading from the transducer system to read approximately 7.5 mm Hghigher than a true arterial pressure of the patient. A 20-cm column of H2O will exert a pressure equal to 14.7mm Hg. Also see explanations to questions 3 and 13 (Ehrenwerth: Anesthesia Equipment: Principles andApplications, p 275).

21.(D)Factors that influence the rate of laminar flow of a substance through a tube is described by the Hagen-Poiseuille law of friction. The mathematical expression of the Hagen-Poiseuille law of friction is as follows: PICTURE OF THE LAW where V is the flow of the substance, r is the radius of the tube, ∆P is the pressure gradient down the tube,L is the length of the tube, and μ is the viscosity of the substance. Note that the rate of laminar flow isproportional to the radius of the tube to the fourth power. If the diameter of an intravenous catheter isdoubled, flow would increase by a factor of 2 raised to the fourth power (i.e., a factor of 16) (Ehrenwerth:Anesthesia Equipment: Principles and Applications, p 225).

22.(D)The safe storage and handling of compressed-gas cylinders is of vital importance. Compressed-gas cylindersshould not be stored in extremes of heat or cold, and they should be unwrapped when stored or when in use.Flames should not be used to detect the presence of a gas. Oily hands can lead to difficulty in handling of thecylinder, which can result in dropping the cylinder. This can cause damage to or rupture of the cylinder, whichcan lead to an explosion (Ehrenwerth: Anesthesia Equipment: Principles and Applications, pp 8-11).

23.(A)Vaporizers can be categorized into variable-bypass and measured-flow vaporizers. Measured-flow vaporizers(nonconcentration calibrated vaporizers) include the copper kettle and Vernitrol vaporizer. With measured-flowvaporizers, the flow of oxygen is selected on a separate flowmeter to pass into the vaporizing chamber fromwhich the anesthetic vapor emerges at its saturated vapor pressure. By contrast, in variable-bypassvaporizers, the total gas flow is split between a variable bypass and the vaporizer chamber containing theanesthetic agent. The ratio of these two flows is called the splitting ratio. The splitting ratio depends on theanesthetic agent, temperature, the chosen vapor concentration set to be delivered to the patient, and thesaturated vapor pressure of the anesthetic (Ehrenwerth: Anesthesia Equipment: Principles and Applications, p63).

24.(D)The contribution of the fresh gas flow from the anesthesia machine to the patient's VT should be consideredwhen setting the VT of a mechanical ventilator. Because the ventilator pressure-relief valve is closed duringinspiration, both the gas from the ventilator bellows and the fresh gas flow will be delivered to the patientbreathing circuit. In this question, the fresh gas flow is 6 L/min or 100 mL/sec (6000 mL/60). Each breath lasts6 sec (60 sec/10 breaths) with inspiration lasting 2 sec (I:E ratio = 1:2). Under these conditions, the VTdelivered to the patient by the mechanical ventilator will be augmented by approximately 200 mL. In someventilators, such as the Ohmeda 7900, VT is controlled for the fresh gas flow rate such that the delivered VT isalways the same as the dial setting (Morgan: Clinical Anesthesia ed 4, pp 82-84).

25.(C)Also see explanation to question 24. The ventilator rate is decreased from 10 to 6 breaths/min. Thus, eachbreath will last 10 seconds (60 sec/6 breaths) with inspiration lasting approximately 3.3 sec (I:E ratio = 1:2),i.e., 3.3 seconds times 100 mL/second. Under these conditions, the actual VT delivered to the patient by themechanical ventilator will be 830 mL (500 mL + 330 mL) (Morgan: Clinical Anesthesia, ed 4, pp 82-84)

26.(D)The saturated vapor pressures of halothane and isoflurane are very similar (approximately 240 mm Hg atroom temperature) and therefore could be used interchangeably in agent-specific vaporizers (see explanationand table in explanation for question 16) (Ehrenwerth: Anesthesia Equipment: Principles and Applications, pp60-63; Stoelting: Basics of Anesthesia, ed 5, p 79)

27.(D)Clinically significant concentrations of carbon monoxide can result from the interaction of desiccated absorbent,both soda lime and Baralyme. The resulting carboxyhemoglobin level can be as high as 30%. Many of thereported occurrences of carbon monoxide poisoning have been observed on Monday mornings. This isthought to be the case because the absorbent granules are the driest after disuse for two days, particularly ifthe oxygen flow has not been turned off completely. There are several factors that appear to predispose to theproduction of carbon monoxide: (1) degree of absorbent dryness (completely desiccated granules producemore carbon monoxide than hydrated granules); (2) use of Baralyme versus soda lime (provided that the watercontent is the same in both); (3) high concentrations of volatile anesthetic (more carbon monoxide isgenerated at higher volatile concentrations); (4) high temperatures (more carbon monoxide is generated athigher temperatures); and (5) type of volatile

28.(A)NIOSH mandates that the highest trace concentration of volatile anesthetic contamination of the ORatmosphere when administered in conjunction with N2O is 0.5 ppm (Miller: Anesthesia, 6 ed, pp 303-304)

29.(B)The O2 analyzer is the last line of defense against inadvertent delivery of hypoxic gas mixtures. It should belocated in the inspiratory (not expiratory) limb of the patient breathing circuit to provide maximum safety Because the O2 concentration in the fresh-gas supply line may be different from that of the patient breathingcircuit, the O2 analyzer should not be located in the fresh-gas supply line (Ehrenwerth: AnesthesiaEquipment: Principles and Applications, pp 216-220)

30.(A)The ventilator pressure-relief valve (also called the spill valve) is pressure controlled via pilot tubing thatcommunicates with the ventilator bellows chamber. As pressure within the bellows chamber increases duringthe inspiratory phase of the ventilator cycle, the pressure is transmitted via the pilot tubing to close thepressure-relief valve, thus making the patient breathing circuit "gastight." This valve should open during theexpiratory phase of the ventilator cycle to allow the release of excess gas from the patient breathing circuitinto the waste-gas scavenging circuit after the bellows has fully expanded. If the ventilator pressure-reliefvalve were to stick in the closed position, there would be a rapid buildup of pressure within the circle systemthat would be readily transmitted to the patient. Barotrauma to the patient's lungs would result if this situationwere to continue unrecognized (Eisenkraft: Potential for barotrauma or hypoventilation with the Drager AV-Eventilator. J Clin Anesth, 1:452-456, 1989; Morgan: Clinical Anesthesia, ed 4, pp 81-82).

31.(D)Vaporizer output can be affected by the composition of the carrier gas used to vaporize the volatile agent inthe vaporizing chamber, especially when nitrous oxide is either initiated or discontinued. This observation canbe explained by the solubility of nitrous oxide in the volatile agent. When nitrous oxide and oxygen enter thevaporizing chamber, a portion of the nitrous oxide dissolves in the liquid agent. Thus, the vaporizer outputtransiently decreases. Conversely, when nitrous oxide is withdrawn as part of the carrier gas, the nitrousoxide dissolved in the volatile agent comes out of solution, thereby transiently increases the vaporizer output(Miller: Anesthesia, ed 6, pp 286-288)

32.(E)The capnogram can provide a variety of information, such as verification of the presence of exhaled CO2 aftertracheal intubation, estimation of the difference in PaCO2 and PETCO2, abnormalities of ventilation, and thepresence of hypercapnia or hypocapnia. The four phases of the capnogram are inspiratory baseline, expiratoryupstroke, expiratory plateau, and inspiratory downstroke. The shape of the capnogram can be used torecognize and diagnose a variety of potentially adverse circumstances. Under normal conditions, theinspiratory baseline should be 0, indicating that there is no rebreathing of CO2 with a normal functioning circlebreathing system. If the inspiratory baseline is elevated above 0, there is rebreathing of CO2. If this occurs,the differential diagnosis should include an incompetent expiratory valve, exhausted CO2 absorbent, or gaschanneling through the CO2 absorbent. However, the inspiratory baseline may be elevated when theinspiratory valve is incompetent (e.g., there may be a slanted inspiratory downstroke). The expiratory upstrokeoccurs when the fresh gas from the anatomic dead space is quickly replaced by CO2-rich alveolar gas. Undernormal conditions the upstroke should be steep; however, it may become slanted during partial airwayobstruction, if a sidestream analyzer is sampling gas too slowly, or if the response time of the capnograph istoo slow for the patient's respiratory rate. Partial obstruction may be the result of an obstruction in thebreathing system (e.g., by a kinked endotracheal tube) or in the patient's airway (e.g., the presence of chronic obstructive pulmonary disease or acute bronchospasm). The expiratory plateau is normally characterized by aslow but shallow progressive increase in CO2 concentration. This occurs because of imperfect matching ofventilation and perfusion in all lung units. Partial obstruction of gas flow either in the breathing system or inthe patient's airways may cause a prolonged increase in the slope of the expiratory plateau, which maycontinue rising until the next inspiratory downstroke begins. The inspiratory downstroke is caused by the rapidinflux of fresh gas, which washes the CO2 away from the CO2 sensing or sampling site. Under normalconditions the inspiratory downstroke is very steep. Causes of a slanted or blunted inspiratory downstrokeinclude an incompetent inspiratory valve, slow mechanical inspiration, slow gas sampling, and partial CO2rebreathing (Ehrenwerth: Anesthesia Equipment: Principles and Applications, p 240)

33.(B)Complications of tracheal intubation can be divided into those associated with direct laryngoscopy andintubation of the trachea, tracheal tube placement, and extubation of the trachea. The most frequentcomplication associated with direct laryngoscopy and tracheal intubation is dental trauma. If a tooth isdislodged and not found, radiographs of the chest and abdomen should be taken to determine whether thetooth has passed through the glottic opening into the lungs. Should dental trauma occur, immediateconsultation with a dentist is indicated. Other complications of direct laryngoscopy and tracheal intubationinclude hypertension, tachycardia, cardiac dysrhythmias, and aspiration of gastric contents. The most commoncomplication that occurs while the ETT is in place is inadvertent endobronchial intubation. Flexion, notextension, of the neck or change from the supine to the head-down position can shift the carina upward,which may convert a mid-tracheal tube placement into a bronchial intubation. Extension of the neck can causecephalad displacement of the tube into the pharynx. Lateral rotation of the head can displace the distal end ofthe ETT approximately 0.7 cm away from the carina. Complications associated with extubation of the tracheacan be immediate or delayed. The two most serious immediate complications associated with extubation of thetrachea are laryngospasm and aspiration of gastric contents. Laryngospasm is most likely to occur in patientswho are lightly anesthetized at the time of extubation. If laryngospasm occurs, positive-pressure mask-bagventilation with 100% O2 and forward displacement of the mandible may be sufficient treatment. However, iflaryngospasm persists, succinylcholine should be administered intravenously or intramuscularly. Pharyngitis isanother frequent complication after extubation of the trachea. This complication occurs most commonly infemales, presumably because of the thinner mucosal covering over the posterior vocal cords compared withmales. This complication usually does not require treatment and spontaneously resolves in 48 to 72 hours.Delayed complications associated with extubation of the trachea include laryngeal ulcerations, tracheitis,tracheal stenosis, vocal cord paralysis, and arytenoid cartilage dislocation (Stoelting: Basics of Anesthesia, ed5, pp 231-232)

34.(B)Gas leaving a compressed-gas cylinder is directed through a pressure-reducing valve, which lowers thepressure within the metal tubing of the anesthesia machine to 45 to 55 psi (Miller: Anesthesia, ed 6, p 276).

35.(C)There is considerable controversy regarding the role of bacterial contamination of anesthesia machines andequipment in cross-infection between patients. The incidence of postoperative pulmonary infection is notreduced by the use of sterile disposable anesthetic breathing circuits (as compared with the use of reusablecircuits that are cleaned with basic hygienic techniques). Furthermore, inclusion of a bacterial filter in theanesthesia breathing circuit has no effect on the incidence of cross-infection. Clinically relevant concentrationsof volatile anesthetics have no bacteriocidal or bacteriostatic effects. Low concentrations of volatile anesthetics,however, may inhibit viral replication. Shifts in humidity and temperature in the anesthesia breathing andscavenging circuits are the most important factors responsible for killing bacteria. In addition, high O2concentration and metallic ions present in the anesthesia machine and other equipment have a significantlethal effect on bacteria. Acid-fast bacilli are the most resistant bacterial form to destruction. Nevertheless,there has been no case documenting transmission of tuberculosis via a contaminated anesthetic machine fromone patient to another. When managing patients who can potentially cause cross-infection of other patients(e.g., patients with tuberculosis, pneumonia, or known viral infections, such as acquired immune deficiencysyndrome [AIDS]) a disposable anesthetic breathing circuit should be used and nondisposable equipmentshould be disinfected with glutaraldehyde (Cidex). Sodium hypochlorite (bleach), which destroys the humanimmunodeficiency virus, should be used to disinfect nondisposable equipment, including laryngoscope blades,if patients with AIDS require anesthesia (Ehrenwerth: Anesthesia Equipment: Principles and Applications, p100).

36.(B)The diameter-index safety system prevents incorrect connections of medical gas lines. This system consists oftwo concentric and specific bores in the body of one connection, which correspond to two concentric andspecific shoulders on the nipple of the other connection (Ehrenwerth: Anesthesia Equipment: Principles andApplications, pp 21, 30, 37).

37.(C)The amount of anesthetic vapor (mL) in effluent gas from a vaporizing chamber can be calculated using thefollowing equation: PICTURE OF EQUATION where VO is the vapor output (mL) of effluent gas from the vaporizer, CG is the carrier gas flow (mL/min) intothe vaporizing chamber, SVPanes is the saturated vapor pressure (mm Hg) of the anesthetic gas at roomtemperature, and Pb is the barometric pressure (mm Hg). In this question, fresh gas flow is 100 ml/min. 100ml/min × 0.9=90 mL/min (Ehrenwerth: Anesthesia Equipment: Principles and Applications, p 61).

38.(A)The output of the vaporizer will be lower at flow rates less than 250 mL/min because there is insufficientpressure to advance the molecules of the volatile agent upward. At extremely high carrier gas flow rates (>15L/ min) there is insufficient mixing in the vaporizing chamber (Miller: Anesthesia, ed 6, p 286)

39.(C)Pulse oximeters estimate arterial hemoglobin saturation (SaO2) by measuring the amount of light transmittedthrough a pulsatile vascular tissue bed. Pulse oximeters measure the alternating current (AC) component oflight absorbance at each of two wavelengths (660 and 940 nm) and then divide this measurement by thecorresponding direct current component. Then the ratio (R) of the two absorbance measurements isdetermined by the following equation: PICTURE OF EQUATION Using an empirical calibration curve that relates arterial hemoglobin saturation to R, the actual arterialhemoglobin saturation is calculated. Based on the physical principles outlined above, the sources of error inSpO2 readings can be easily predicted. Pulse oximeters can function accurately when only two hemoglobinspecies, oxyhemoglobin and reduced hemoglobin, are present. If any light-absorbing species other thanoxyhemoglobin and reduced hemoglobin are present, the pulse oximeter measurements will be inaccurate.Fetal hemoglobin has minimal effect on the accuracy of pulse oximetry, because the extinction coefficients forfetal hemoglobin at the two wavelengths used by pulse oximetry are very similar to the corresponding valuesfor adult hemoglobin. In addition to abnormal hemoglobins, any substance present in the blood that absorbslight at either 660 or 940 nm, such as intravenous dyes used for diagnostic purposes, will affect the value ofR, making accurate measurements of the pulse oximeter impossible. These dyes include methylene blue andindigo carmine. Methylene blue has the greatest effect on SaO2 measurements because the extinctioncoefficient is so similar to that of oxyhemoglobin (Ehrenwerth: Anesthesia Equipment: Principles andApplications, pp 254-255)

40.(B)The mass spectrometer functions by separating the components of a stream of charged particles into aspectrum based on their mass-to-charge ratio. The amount of each ion at specific mass-to-charge ratios isthen determined and expressed as the fractional composition of the original gas mixture. The charged particlesare created and manipulated in a high vacuum to avoid interference by outside air and minimize randomcollisions among the ions and residual gases. An erroneous reading will be displayed by the massspectrometer when a gas that is not detected by the collector plate system is present in the gas mixture to beanalyzed. Helium, which has a mass charge ratio of 4, is not detected by standard mass spectrometers.Consequently, the standard gases (i.e., halothane, enflurane, isoflurane, oxygen, nitrous oxide, nitrogen, andcarbon dioxide) will be summed to 100% as if helium were not present. All readings would be approximatelytwice their real values in the original gas mixture in the presence of 50% helium (Ehrenwerth: AnesthesiaEquipment: Principles and Applications, pp 203-205)

41.(E)Because halothane and isoflurane have similar saturated vapor pressures, the vaporizers for these volatileanesthetics could be used interchangeably with accurate delivery of the anesthetic concentration set by thevaporizer dial. If a sevoflurane vaporizer were filled with a volatile anesthetic that has a greater saturatedvapor pressure than sevoflurane (e.g., halothane or isoflurane), a higher-than-expected concentration wouldbe delivered from the vaporizer. If a halothane or isoflurane vaporizer were filled with a volatile anesthetic thathad a lower saturated vapor pressure than halothane or isoflurane (e.g., sevoflurane, enflurane, ormethoxyflurane), a lower-than-expected concentration would be delivered from the vaporizer (Ehrenwerth:Anesthesia Equipment: Principles and Applications, pp 66-67).VAPOR PRESSURE AND MINIMUM ALVEOLAR CONCENTRATION

42.(E)Gas density decreases with increasing altitude (i.e., the density of a gas is directly proportional to atmosphericpressure). Atmospheric pressure will influence the function of rotameters because the accurate function ofrotameters is influenced by the physical properties of the gas, such as density and viscosity. The magnitude ofthis influence, however, depends on the rate of gas flow. At low gas flows, the pattern of gas flow is laminar.Atmospheric pressure will have little effect on the accurate function of rotameters at low gas flows becauselaminar gas flow is influenced by gas viscosity (which is minimally affected by atmospheric pressure) and notgas density. However, at high gas flows, the gas flow pattern is turbulent and is influenced by gas density (seeexplanation to question 2). At high altitudes (i.e., low atmospheric pressure), the gas flow through therotameter will be greater than expected at high flows but accurate at low flows (Ehrenwerth: AnesthesiaEquipment: Principles and Applications, pp 38-43, 224-225)

43.(B)Pacemakers have a three to five letter code that describes the pacemaker type and function. Since thepurpose of the pacemaker is to send electrical current to the heart, the first letter identifies the chamber(s)paced; A for atrial, V for ventricle and D for dual chamber (A+V). The second letter identifies the chamberwhere endogenous current is sensed; A,V, D, and O for none sensed. The third letter describes the responseto sensing; O for none, I for inhibited, T for triggered and D for dual (I+T). The fourth letter describesprogrammability or rate modulation; O for none and R for rate modulation (i.e., faster heart rate with exercise).The fifth letter describes multisite pacing (more important in dilated heart chambers); A, V or D (A+V) or O. AVDD pacemaker is used for patients with AV node dysfunction but intact sinus node activity. (Miller:Anesthesia, ed 6, pp 1416-1418)

44.(A)Although controversial, it is thought that chronic exposure to low concentrations of volatile anesthetics mayconstitute a health hazard to OR personnel. Therefore, removal of trace concentrations of volatile anestheticgases from the OR atmosphere with a scavenging system and steps to reduce and control gas leakage intothe environment are required. High-pressure system leakage of volatile anesthetic gases into the ORatmosphere occurs when gas escapes from compressed-gas cylinders attached to the anesthetic machine(e.g., faulty yokes) or from tubing delivering these gases to the anesthesia machine from a central supplysource. The most common cause of low-pressure leakage of anesthetic gases into the OR atmosphere is theescape of gases from sites located between the flowmeters of the anesthesia machine and the patient, suchas a poor mask seal. The use of high gas flows in a circle system will not reduce trace gas contamination ofthe OR atmosphere. In fact, this could contribute to the contamination if there is a leak in the circle system(Miller: Anesthesia, ed 6, pp 3151-3153)

45.(A)Although all of the choices in this question can contribute as sources of contamination, leakage around theanesthesia face mask poses the greatest threat (Ehrenwerth: Anesthesia Equipment: Principles andApplications, pp 128-129; Miller: Anesthesia, ed 6, pp 3151-3153)

46.(C)The amount of volatile anesthetic taken up by the patient in the first minute is equal to that amount taken upbetween the squares of any two consecutive minutes. Accordingly, 50 mL would be taken up between the16th (4 × 4) and 25th (5 × 5) minute, and another 50 mL would be taken up between the 25th and 36th (6 ×6) minute (Miller: Anesthesia, ed 5, p 87)

47.(E)In evaluating SSEPs, one looks at both the amplitude or voltage of the recorded response wave as well as thelatency (time measured from the stimulus to the onset or peak of the response wave). A decrease inamplitude (>50%) and/or an increase in latency (>10%) is usually clinically significant. These changes mayreflect hypoperfusion, neural ischemia, temperature changes, or drug effects. All of the volatile anesthetics aswell as barbiturates cause a decrease in amplitude as well as an increase in latency. Etomidate causes anincrease in latency and an increase in amplitude. Midazolam decreases the amplitude but has little effect onlatency. Opioids cause small and not clinically significant increases in latency and decrease in amplitude ofthe SSEPs. Muscle relaxants have no effect of the SSEP (Miller: Anesthesia, ed 6, pp 1525-1537; Stoelting:Basics of Anesthesia, ed 5, pp 312-314)

48.(E)Also see explanation to question 35. There is no evidence that the incidence of postoperative pulmonaryinfection is altered by the use of sterile disposable anesthesia breathing systems (compared with the use ofreusable systems that are cleaned with basic hygienic techniques) or by the inclusion of a bacterial filter in theanesthesia breathing system (Ehrenwerth: Anesthesia Equipment: Principles and Applications, p 100)

49.(D)Vaporization of a liquid requires the transfer of heat from the objects in contact with the liquid (e.g., the metalcylinder and surrounding atmosphere). For this reason, at high gas flows, atmospheric water will condense asfrost on the outside of compressed-gas cylinders (Stoelting: Basics of Anesthesia, ed 5, p 188).

50.(B)Pulmonary artery, esophageal, axillary, nasopharyngeal, and tympanic membrane temperature measurementscorrelate with central temperature in patients undergoing noncardiac surgery. Skin temperature does notreflect central temperature and does not warn adequately of malignant hyperthermia or excessive hypothermia(Miller: Anesthesia, ed 6, p 1591).

51.(D)Rotameters consist of a vertically positioned tapered tube that is smallest in diameter at the bottom (Thorpetube). Gas enters at the bottom of the Thorpe tube and elevates a bobbin or float, which comes to rest whengravity on the float is balanced by the fall in pressure across the float. The rate of gas flow through the tubedepends on the pressure drop along the length of the tube, the resistance to gas flow through the tube, andthe physical properties (density and viscosity) of the gas. Because few gases have the same density andviscosity, rotameters cannot be used interchangeably (Ehrenwerth: Anesthesia Equipment: Principles andApplications, pp 38-43)

52.(A)The critical velocity for helium is greater than that for nitrogen. For this reason, there is less work of breathingwhen helium is substituted for nitrogen (Ehrenwerth: Anesthesia Equipment: Principles and Applications, pp224-225; Miller: Anesthesia, ed 6, pp 690-691)

53.(E)The FIO2 delivered to patients from low-flow systems (e.g., nasal prongs) is determined by the size of the O2reservoir, the O2 flow, and the patient's breathing pattern. As a rule of thumb, assuming a normal breathingpattern, the FIO2 delivered by nasal prongs increases by approximately 0.04 for each L/min increase in O2flow up to a maximal FIO2 of approximately 0.45 (at an O2 flow of 6 L/min). In general, the larger the patient'sVT or faster the respiratory rate, the lower the FIO2 for a given O2 flow (Miller: Anesthesia, ed 6, pp 2812-2813)

54.(A) DIAGRAM OF CIRCUIT In a closed scavenging system interface, the reservoir bag should expand during expiration and contractduring inspiration. During the inspiratory phase of mechanical ventilation the ventilator pressure-relief valvecloses, thereby directing the gas inside the ventilator bellows into the patient breathing circuit. If the ventilatorpressure-relief valve is incompetent, there will be a direct communication between the patient breathing circuitand scavenging circuit. This would result in delivery of part of the mechanical ventilator VT directly to thescavenging circuit, causing the reservoir bag to inflate during the inspiratory phase of the ventilator cycle(Ehrenwerth: Anesthesia Equipment: Principles and Applications, p 128).

55.(C)The accurate function of dual-wavelength pulse oximeters is altered by nail polish. Because blue nail polishhas a peak absorbance similar to that of adult deoxygenated hemoglobin (near 660 nm), blue nail polish hasthe greatest effect on the SpO2 reading. Nail polish causes an artifactual and fixed decrease in the SpO2reading by these devices. Turning the finger probe 90 degrees and having the light shining sidewise throughthe finger is useful when there is nail polish on the patient's fingernails (Miller: Anesthesia, ed 6, pp 1448-1452).

56.(C) The minimum macroshock current required to elicit ventricular fibrillation is 50 to 100 mA (Brunner: Electricity,afety, and the Patient, ed 1, pp 22-23; Miller: Anesthesia, ed 6, pp 3145-3146).

57.(D)The line isolation monitor alarms when grounding occurs in the OR or when the maximum current that a shortcircuit could cause exceeds 2 to 5 mA. The line isolation monitor is purely a monitor and does interruptelectrical current. Therefore, the line isolation monitor will not prevent microshock or macroshock (Brunner:Electricity, Safety, and the Patient, ed 1, p 304; Miller: Anesthesia, ed 6, pp 3140-3141).

58.(A)A scavenging system with a closed interface is one in which there is communication with the atmospherethrough positive- and negative-pressure relief valves. The positive-pressure relief valve will preventtransmission of excessive pressure buildup to the patient breathing circuit, even if there is an obstruction distalto the interface or if the system is not connected to wall suction. However, obstruction of the transfer tubingfrom the patient breathing circuit to the scavenging circuit is proximal to the interface. This will isolate thepatient breathing circuit from the positive-pressure relief valve of the scavenging system interface. Should thisoccur, barotrauma to the patient's lungs can result (Ehrenwerth: Anesthesia Equipment: Principles andApplications, pp 127-128)

59.(B)MAC for isoflurane is 1.15% of 1 atmosphere or 8.7 mm Hg. An isoflurane vaporizer set for 1.15% will use asplitting ratio of 1:39. For purposes of illustration, imagine 100 mL of oxygen passes through the vaporizingchamber and 3900 mL through bypass chamber.100 mL × 240/(760 - 240) = 46.1 mL of isoflurane vapor (plus 100 mLoxygen)46.1/(3900 + 100) = 46.1/4000 = 1.15%1.15% × 760 mm Hg = 8.7 mm Hg (1 MAC)Consider now the same splitting ratio applied in Denver, Colo.:100 mL × 240/(630 - 240) = 61.5 mL of isoflurane vapor (plus 100 mLoxygen)61.5/(3900 + 100) = 61.5/4000 = 1.53% print1.53% × 630 mm Hg = 9.7 mm Hg (roughly 1.1 MAC

60.(A)Automated noninvasive blood pressure (ANIBP) devices provide consistent and reliable arterial BPmeasurements. Variations in the cuff pressure resulting from arterial pulsations during cuff deflation aresensed by the device and are used to calculate mean arterial pressure. Then, values for systolic and diastolicpressures are derived from formulas that use the rate of change of the arterial pressure pulsations and themean arterial pressure (oscillometric principle). This methodology provides accurate measurements of arterialBP in neonates, infants, children, and adults. The main advantage of ANIBP devices is that they free theanesthesia provider to perform other duties required for optimal anesthesia care. Additionally, these devicesprovide alarm systems to draw attention to extreme BP values and have the capacity to transfer data toautomated trending devices or recorders. Improper use of these devices can lead to erroneous measurementsand complications. The width of the BP cuff should be approximately 40% of the circumference of the patient'sarm. If the width of the BP cuff is too narrow or if the BP cuff is wrapped too loosely around the arm, the BPmeasurement by the device will be falsely elevated. Frequent BP measurements can result in edema of theextremity distal to the cuff. For this reason, cycling of these devices should not be more frequent than every 1to 3 minutes. Other complications associated with improper use of ANIBP devices include ulnar nerveparesthesia, superficial thrombophlebitis, and compartment syndrome. Fortunately, these complications arerare occurrences (Miller: Anesthesia, ed 6, pp 1269-1271; Stoelting: Basics of Anesthesia, ed 5, p 307).

61.(D)If the ventilator pressure-relief valve were to become incompetent, there would be a direct communicationbetween the patient breathing circuit and the scavenging system circuit. This would result in delivery of part ofthe VT during the inspiratory phase of the ventilator cycle directly to the scavenging system reservoir bag.Therefore, adequate positive-pressure ventilation may not be achieved and hypoventilation of the patient's lungs may result. Also see explanation to question 54 and accompanying figure (Ehrenwerth: AnesthesiaEquipment: Principles and Applications, p 120)

62.(C)A size "E" compressed-gas cylinder completely filled with air contains 625 L and would show a pressuregauge reading of 2000 psi. Therefore, a cylinder with a pressure gauge reading of 1000 psi would be half-full,containing approximately 325 L of air. A half-full size "E" compressed-gas cylinder containing air could beused for approximately 30 minutes at a flow rate of 10 L/min (see definition of Boyle's law in explanation toquestion 9 and explanation and table from question 10) (Stoelting: Basics of Anesthesia, ed 5, p 188).

63.(E)Failure to oxygenate patients adequately is the leading cause of anesthesia-related morbidity and mortality. Allof the choices listed in this question are potential causes of inadequate delivery of O2 to the patient; however,the most frequent cause is inadvertent disconnection of the O2 supply system from the patient (e.g.,disconnection of the patient breathing circuit from the endotracheal tube) (Miller: Anesthesia, ed 6, p 300)

64.(A)The esophageal detector device (EDD) is essentially a bulb that is first compressed then attached to the ETTafter the tube is inserted into the patient. The pressure generated is about negative 40 cm of water. If theETT is placed in the esophagus, then the negative pressure will collapse the esophagus and the bulb will notinflate. If the ETT is in the trachea, then the air from the lung will enable the bulb to inflate (usually in a fewseconds but at times may take more than 30 seconds). A syringe that has a negative pressure applied to ithas also been used. Although initial studies were very positive about its use, more recent studies show that upto 30% of correctly placed ETTs in adults may be removed because the EDD suggested esophagealplacement. Misleading results have been noted in patients with morbid obesity, late pregnancy, statusasthmatics and when there is copious endotracheal secretion, where the trachea tends to collapse. Its use inchildren younger than 1 year of age showed poor sensitivity as well as poor specificity. Although a cardiacoutput is needed to get CO2 to the lungs for a CO2 gas analyzer to function, a cardiac output is not neededfor an EDD (American Heart Association—Guidelines for CPR and ECC. Circulation Volume 112, Issue 24,pp IV-54, IV-150, IV-169, 2005; Miller: Anesthesia, ed 6, p 1648)

65.(D)The capnometer measures the CO2 concentration of respiratory gases. Today this is most commonlyperformed by infrared absorption using a sidestream gas sample. The sampling tube should be connected asclose to the patient's airway as possible. The difference between the end-tidal CO2 (EtCO2) and the arterialCO2 (PaCO2) is typically 5-10 mm Hg and is due to alveolar dead space ventilation. Because non-perfusedalveoli do not contribute to gas exchange, any condition that increases alveolar dead space ventilation (i.e.,reduces pulmonary blood flow such as a pulmonary embolism or cardiac arrest) will increase dead spaceventilation and the EtCO2 to PaCO2 difference. Conditions that increase pulmonary shunt result in minimalchanges in the PaCO2-ETCO2 gradient. CO2 diffuses rapidly across the capillary-alveolar membrane (Barash:Clinical Anesthesia, ed 5, pp 670-671; Miller: Anesthesia, ed 6, pp 1455-1462).

66.(E)The last gas added to a gas mixture should always be O2. This arrangement is the safest because it assuresthat leaks proximal to the O2 inflow cannot result in delivery of a hypoxic gas mixture to the patient. With thisarrangement (O2 added last), leaks distal to the O2 inflow will result in a decreased volume of gas, but theFIO2 of Anesthesia will not be reduced (Stoelting: Basics of Anesthesia, ed 5, pp 188-189)

67.(D)Most modern Datex-Ohmeda Tec or North American Dräger Vapor vaporizers (except desflurane) arevariable-bypass, flow-over vaporizers. This means that the gas that flows through the vaporizers is split intotwo parts depending upon the concentration selected. The gas either goes through the bypass chamber onthe top of the vaporizer or the vaporizing chamber on the bottom of the vaporizer. If the vaporizer is "tipped"which might happen when a filled vaporizer is "switched out" or moved from one machine to another machine,part of the anesthetic liquid in the vaporizing chamber may get into the bypass chamber. This could result ina much higher concentration of gas than dialed. With the Datex-Ohmeda Tec 4 or the North American DragerVapor 19.1 series it is recommended to flush the vaporizer at high flows with the vaporizer set at a lowconcentration until the output shows no excessive agent (this usually takes 20-30 minutes). The Drager Vapor2000 series has a transport (T) dial setting. This setting isolates the bypass from the vaporizer chamber. TheAladin cassette vaporizer does not have a bypass flow chamber and has no "tipping" hazard (Miller:Anesthesia ed 6, pp 285-288).

68.(A)Accurate delivery of volatile anesthetic concentration is dependant upon filling the agent specific vaporizer withthe appropriate (volatile) agent. Differences in anesthetic potencies further necessitate this requirement. Eachagent-specific vaporizer utilizes a splitting ratio that determines the portion of the fresh gas that is directedthrough the vaporizing chamber versus that which travels through the bypass chamber.VAPOR PRESSURE, ANESTHETIC VAPOR PRESSURE, AND SPLITTING RATIO The table above shows the calculation (fraction) that when multiplied by the quantity of fresh gas traversingthe vaporizing chamber (affluent fresh gas in mL/min) will yield the output (mL/min) of anesthetic vapor in theeffluent gas. When this fraction is multiplied by 100 it equals the splitting ratio for 1% for the given volatile.For example, when the isoflurane vaporizer is set to deliver 1% isoflurane, one part of fresh gas passedthrough the vaporizing chamber while 47 parts travel through the bypass chamber. One can determine oninspection that when a less soluble volatile like sevoflurane (or enflurane for the sake of example) is placedinto an isoflurane (or halothane) vaporizer, the output in volume percent will be less than expected. Howmuch less can be determined by simply comparing their splitting ratios 27/47 or 0.6. Halothane and enfluraneare no longer used in the United States, but old halothane and enflurane vaporizers can be (and are) usedelsewhere in the world to accurately deliver isoflurane and sevoflurane respectively (Ehrenwerth: AnesthesiaEquipment: Principles and Applications, p 67)

69.(C)Two percent of 4 L/min would be 80 mL of isoflurane per minute.VAPOR PRESSURE PER ML OF LIQUID CHART Since 1 mL of vapor produces 195 mL of gas or making the simplistic calculation of 195 × 150 mL = 29,250. Itfollows that 29,250/80 = 365 minutes or about 6 hours.Note that each mL of most volatiles will yield 200 mL vapor at 20° C. Thus 150 min × 200 mL/min = 30,000 min. Itfollows that 30,000 min/80 mL/min = 375 minutes or ≈ 6 hours. (Ehrenwerth: Anesthesia Equipment: Principles andApplications, p 60)

70.(C)The human ear can perceive sound in the range of 20 Hz to 20 kHz. Frequencies above 20 kHz, inaudible tohumans, are ultrasonic frequencies (ultra = Latin for "beyond" or "on the far side of"). In regional anesthesia,ultrasound is used for imaging in the frequency range of 2.5 to 10 MHz. Wavelength is inversely proportionalto frequency, i.e., λ = C/f (λ = wavelength, C = velocity of sound through tissue or 1540 m/sec, f = frequency).Wavelength in millimeters can be calculated by dividing 1.54 by the Doppler frequency in megahertz.Penetration into tissue is 200 to 400 times wavelength and resolution is twice the wavelength. Therefore, afrequency of 3 MHz (wavelength .51 mm) would have a resolution of 1 mm and a penetration of up to 100 -200 mm (10-20 cm) whereas 10 MHz (wavelength 0.15 mm) corresponds to a resolution of 0.3 mm, butpenetration depth of no more than 60-120 mm (6-12 cm) (Miller: Anesthesia, ed 6, p 1364)

71.(A)Microshock refers to electric shock in or near the heart. A current as low as 50 μA passing through the heartcan produce ventricular fibrillation. Use of pacemaker electrodes, central venous catheters, pulmonary arterycatheters and other devices in the heart make are necessary prerequisites for microshock. Because the lineisolation monitor has a 2 milliamps (2000 μA) threshold for alarming, it will not protect against microshock(Miller Anesthesia, ed 6, page 3145).

72.(E)Intraoperative awareness or recall during general anesthesia is rare (overall incidence is 0.2%, for obstetrics0.4%, for cardiac 1-1.5%) except for major trauma which has a reported incidence up to 43%. With the EEG,trends can be identified with changes in the depth of anesthesia, however the sensitivity and specificity of theavailable trends are such that none serve as a sole indicator of anesthesia depth. Although using the BISmonitor may reduce the risk of recall, it, like the other listed signs as well as patient movement, does not totally eliminate recall (Miller: Anesthesia, ed 6, pp 1230-1259).

73.(D)The minute ventilation is five liters (0.5 L per breath at 10 breaths per minute) and 2 liters per minute to drivethe ventilator for a total O2 consumption of 7 liters per minute. A full oxygen "E" cylinder contains 625 liters.Ninety percent of the volume of the cylinder (≈ 560 L) can be delivered before the ventilator can no longer bedriven. At a rate of 7 L/min, this supply would last about 80 minutes (Stoelting: Basics of Anesthesia, ed 5,page 188).

74.(C)After eliminating reversible causes of high peak airway pressures such as occlusion of the endotracheal tube,mainstem intubation, bronchospasm, etc., adjusting the ventilator can reduce the peak airway pressure.Increasing the inspiratory flow rate would cause the airway pressures to go up faster and would producehigher peak airway pressures. Taking the PEEP off would have no significant effect. Changing the I:E ratiofrom 1:3 to 1:2 will permit 8% (25% inspiratory time to 33% inspiratory time) more time for the VT to beadministered and would result in lower airway pressures. Decreasing the VT to 300 and increasing the rate to28 would give the same minute ventilation, but not the same alveolar ventilation. Recall that alveolarventilation equals (frequency) times (VT minus dead space); and since dead space is the same (about 2 mL/kgideal weight) alveolar ventilation would be reduced, in this case to a dangerously low level. Another option isto change from volume cycled to pressure cycled ventilation, which produces a more constant pressure overtime instead of the peaked pressures seen with fixed VT ventilation. (Barash: Clinical Anesthesia, ed 5, pp1484-1485; Miller: Anesthesia, ed 6, pp 2820-2822).

75.(D)The central hospital oxygen supply to the operating rooms is designed to give enough pressure and oxygenflow to run the three oxygen components of the anesthesia machine (patient fresh gas flow, the anesthesiaventilator and the oxygen flush valve). The oxygen flowmeter on the anesthesia machine is designed to run atan oxygen pressure of 50 psi and for emergency purposes the oxygen flush valve delivers 35 to 75 L/min ofoxygen (Stoelting: Basics of Anesthesia, ed 5, pp 187-189).

76.(B)Within the respiratory system both laminar and turbulent flows exist. At low flow rates, the respiratory flowtends to be laminar, like a series of concentric tubes that slide over one another with the center tubes flowingfaster than the more peripheral tubes. Laminar flow is usually inaudible and is dependent on gas viscosity.Turbulent flow tends to be faster flow, is audible and is dependent upon gas density. Gas density can bedecreased by using a mixture of helium with oxygen. (Barash: Clinical Anesthesia, ed 5, pp 794-795, Miller:Anesthesia, ed 6, p 2539).

77.(B)Anesthesia machines have a high, intermediate and low pressure circuits. The high pressure circuit is from theoxygen cylinder to the oxygen pressure regulator (first stage regulator) which takes the oxygen pressure froma high of 2200 psi to 45 psi. The intermediate pressure circuit consists of the pipeline pressure of about 50 to55 psi and goes to the second stage regulator, which then lowers the pressure to 14 to 26 psi (dependingupon the machine). The low pressure circuit then consists of the flow tubes, vaporizer manifold, vaporizersand vaporizer check valve to the common gas outlet. The oxygen flush valve is in the intermediate pressurecircuit and bypasses the low pressure circuit (Stoelting: Basics of Anesthesia, ed 5, p 187; Miller: Anesthesia,ed 6, pp 274-276)

78.(C)Two major problems should be noted in this case. The first obvious problem is the inspired oxygenconcentration of 4%, a concentration that is not possible if the gases going to the machine are appropriateunless the oxygen analyzer is faulty. In this case, where both the oxygen analyzer and the mass spectrometerread 4%, the pipeline gas line supplying "oxygen" most likely contains something other than oxygen. Second,the oxygen line pressure is 65 psi. The pipeline pressures are normally around 50 to 55 psi, whereas thepressure from the oxygen cylinder, if the cylinder is turned on, is reduced to 45 psi. For the oxygen tank todeliver oxygen to the patient, the pipeline pressure needs to be less than 45 psi, which in this case wouldoccur only when the pipeline is disconnected. Although we rarely think of problems with hospital gas lines, asurvey of more than 200 hospitals showed about 33% had problems with the pipelines. Most common pipelineproblems were low pressure, followed by high pressure and, very rarely, crossed gas lines. (Barash: ClinicalAnesthesia, ed 5, pp 563-564, Miller: Anesthesia, ed 6, pp 274-276).

79.(D)There are many ways to monitor the electrical activity of the heart. The five-electrode system using one leadfor each limb and the fifth lead for the precordium is commonly used in the operating suite. The precordiallead placed in the V5 position (anterior axillary line in the fifth intercostal space) gives the V5 tracing, whichcombined with the standard lead II are most common tracings used to look for myocardial ischemia (Barash:Clinical Anesthesia, ed 5, pp 889, 1539; Miller: Anesthesia, ed 6, pp 1392-1393)

80.(A)The DISS provides threaded, non-interchangeable connections for medical gas pipelines through the hospitalas well as to the anesthesia machine. The Pin Index Safety System (PISS) has two metal pins located indifferent arrangements around the yoke on the back of anesthesia machines, with each arrangement for a specific gas cylinder. Vaporizers often have keyed fillers that attach to the bottle of anesthetic and thevaporizer. Vaporizers not equipped with keyed fillers occasionally have been misfilled with the wronganesthetic liquid (Barash: Clinical Anesthesia, ed 5, p 563; Miller: Anesthesia, ed 6, pp 276 and 288).

81.(C)Calcium hydroxide lime does not contain the monovalent hydroxide bases that are present in soda lime(namely NaOH and KOH). Sevoflurane in the presence of NaOH or KOH is degraded to trace amounts ofCompound A, which is nephrotoxic to rats at high concentrations. Soda lime normally contains about 13% to15% water, but if the soda lime is desiccated (water content < 5% — which has occurred if the machine is notused for a while and the fresh gas flow is left on) and exposed to current volatile anesthetics (isoflurane,sevoflurane and especially desflurane), carbon monoxide can be produced. Neither Compound A nor carbonmonoxide are formed when calcium hydroxide lime is used. With soda lime and calcium hydroxide lime theindicator dye changes from white to purple as the granules become exhausted; however, over time, exhaustedsoda may revert back to white. With calcium hydroxide lime the dye once changed does not revert to normal.The two major disadvantages of calcium hydroxide lime are the expense and the fact that its absorptivecapacity is about half of soda lime (10.2 L of CO2/100 g of calcium hydroxide lime versus 26 L of CO2/100 gof soda lime) (Barash: Clinical Anesthesia, ed 5, pp 411-413; Miller: Anesthesia, ed 6, pp 296-298; Stoelting:Basics of Anesthesia, ed 5, pp 200-202)

82.(B)The aim of direct invasive monitoring is to give continuous arterial BPs that are similar to the intermittentnoninvasive arterial BPs from a cuff, as well as to give a port for arterial blood samples. The displayed signalreflects the actual pressure as well as distortions from the measuring system (i.e., the catheter, tubing,stopcocks, amplifier). Although most of the time the signal is accurate, at times we see an underdamped or anoverdamped signal. In an underdamped signal, as in this case, exaggerated readings are noted (widenedpulse pressure). In an overdamped signal, readings are diminished (narrowed pulse pressure). Note howeverthe mean BP tends to be accurate in both underdamped and overdamped signals (Miller: Anesthesia, ed 6, pp1272-1279)

83.(E)Rebreathing of expired gases (e.g., stuck open expiratory or inspiratory valves), faulty removal of CO2 fromthe carbon dioxide absorber (e.g., exhausted CO2 absorber, channeling through a CO2 absorber or havingthe CO2 absorber bypassed — an option in some older anesthetic machines), or adding CO2 from a gassupply (rarely done with current anesthetic machines) can all increase inspired CO2. Absorption of CO2 duringlaparoscopic surgery when CO2 is used as the abdominal distending gas would increase absorption of CO2but would not cause an increase in inspired CO2 (Miller: Anesthesia, ed 6, pp 1458-1461; Stoelting: Basics ofAnesthesia, ed 5, pp 199-201, 314)

84.(B)85. (A) 86. (D)Medical gas cylinders are color coded but may differ from one country to another. If there is a combination oftwo gases, the tank would have both corresponding colors, for example, a tank containing oxygen and heliumwould be green and brown. The only exception to the mixed gas color scheme is O2 and N2 in the proportionof 19.5% to 23.5% mixed with N2, which is solid yellow (air)

87.(A)88. (D) 89. (D) 90. (E)There are five different types of Mapleson breathing circuits (designated A through E). These circuits vary inarrangement of the fresh-gas-flow inlet, tubing, mask, reservoir bag, and unidirectional expiratory valve. Thesesystems are lightweight, portable, easy to clean, offer low resistance to breathing, and, because of high freshgas inflows, prevent rebreathing of exhaled gases. In addition, with these breathing circuits, the concentration of volatile anesthetic gases and O2 delivered to the patient can be accurately estimated. The reservoir bagenables the anesthesia provider to provide assisted or controlled ventilation of the lungs. The unidirectionalexpiratory valve functions to direct fresh gas into the patient and exhaled gases out of the circuit. In theMapleson A breathing circuit, the unidirectional expiratory valve is located near the patient and the fresh-gas-flow inlet is located proximal to the reservoir bag. This arrangement is the most efficient for elimination of CO2during spontaneous breathing. However, because the unidirectional expiratory valve must be tightened topermit production of positive airway pressure when the gas reservoir bag is manually compressed, thisbreathing circuit is less efficient in preventing rebreathing of CO2 during assisted or controlled ventilation ofthe lungs. The structure of the Mapleson D breathing circuit is similar to that of the Mapleson A breathingcircuit except that the positions of the fresh-gas-flow inlet and the unidirectional expiratory valve are reversed.The placement of the fresh-gas-flow inlet near the patient produces efficient elimination of CO2, regardless ofwhether the patient is breathing spontaneously or the patient's ventilation is controlled. The Bain anesthesiabreathing circuit is a coaxial version of the Mapleson D breathing circuit except that the fresh gas entersthrough a narrow tube within the corrugated expiratory limb of the circuit. The Jackson-Rees breathing circuitis a modification of the Mapleson E breathing circuit. In the Jackson-Rees breathing circuit, the adjustableunidirectional expiratory valve is incorporated into the reservoir bag and the fresh-gas-flow inlet is locatedclose to the patient. This arrangement offers the advantage of ease of instituting assisted or controlledventilation of the lungs, as well as monitoring ventilation by movement of the reservoir bag during spontaneousbreathing (Ehrenwerth: Anesthesia Equipment: Principles and Applications, pp 102-108; Miller: Anesthesia, ed6, pp 293-295)