Lippincott's Anesthesia Review: 1001 Questions and Answers

Chapter 3. Anesthesia Machine

Paul Sikka

    1.   Pipeline gases are supplied at pressures of about ______ psi:

          A.   25

          B.   40

          C.   50

          D.   75

    2.   Which of the following prevents delivery of hypoxic gas mixture once the oxygen pressure falls below 25 psi?

          A.   Diameter index safety system

          B.   Pin index safety system

          C.   Inspiratory check valve

          D.   Fail-safe valve

    3.   The oxygen-flush valve provides which of the following oxygen flows (L/min) to the common gas outlet?

          A.   10

          B.   25

          C.   50

          D.   90

    4.   Gas flowmeters

          A.   Are gas-specific

          B.   Have a gas flow rate which depends on viscosity at high turbulent flows

          C.   Have a gas flow rate which depends on density at low laminar flows

          D.   Are cylindrical in shape

    5.   Which of the following flowmeters is situated nearest to the gas outlet?

          A.   Nitrous oxide

          B.   Oxygen

          C.   Air

          D.   None of the above

    6.   Modern vaporizers are

          A.   Agent-specific

          B.   Temperature-compensated

          C.   Pressure-compensated

          D.   Both A and B

    7.   The Tec 6 desflurane vaporizer

          A.   Is electrically heated to 39°C

          B.   Is pressurized to 3 atm

          C.   Is pressure-compensated

          D.   All of the above

    8.   Variable bypass vaporizers should be located

          A.   Between the common gas outlet (upstream) and the flowmeters (downstream)

          B.   Between the flowmeters (upstream) and the common gas outlet (downstream)

          C.   Between the gas pipeline and the flowmeters

          D.   Inside the circle system

    9.   A standing or ascending bellow is preferred for anesthesia ventilators, as disconnection is indicated by

          A.   Collapse

          B.   Filling by gravity

          C.   Disconnection alarm

          D.   Stoppage of flowmeter gas

  10.   The National Institute for Occupational Safety and Health (NIOSH) recommends limiting operating-room concentration of nitrous oxide to ______ ppm:

          A.   10

          B.   25

          C.   50

          D.   100

  11.   The National Institute for Occupational Safety and Health (NIOSH) recommends limiting operating-room concentration of volatile inhalational agents to ______ ppm:

          A.   0.2

          B.   0.5

          C.   1

          D.   2

  12.   Capacity of an oxygen “E” cylinder is approximately ______ L:

          A.   500

          B.   600

          C.   650

          D.   750

  13.   If pressure in a full nitrous oxide “E” cylinder is 745 psi at 20°C, the pressure in a half-full cylinder will be about ______ psi:

          A.   186

          B.   248

          C.   372

          D.   745

  14.   Which of the following system prevents the wrong gas cylinder being attached to the anesthesia machine?

          A.   Diameter index safety system

          B.   Pin index safety system

          C.   Hanger yoke assembly system

          D.   Gauge-safety system

  15.   A line-isolation monitor

          A.   Warns that an electrical shock is imminent

          B.   Warns of a fault between the power line and the ground

          C.   Warns of the presence of two faults

          D.   Trips the ground leakage circuit breaker

  16.   The highest content of soda lime is

          A.   Calcium hydroxide

          B.   Potassium hydroxide

          C.   Sodium hydroxide

          D.   Silica

  17.   End products of the reaction in a soda lime CO2 canister are

          A.   Carbonates, water, heat

          B.   Carbonates, heat, sodium hydroxide

          C.   Sodium hydroxide, water, heat

          D.   Carbonates, sodium hydroxide, water, heat

           1.   CO2 + H2O → H2CO3

           2.   H2CO3 + 2 NaOH (or KOH) → Na2CO3 (or K2CO3) + 2 H2O + Energy

           3.   Na2CO3 (or K2CO3) + Ca(OH)2 → CaCO3 + 2 NaOH (or KOH)

  18.   If you notice that the CO2 absorbent is exhausted during the surgical procedure, which of the following minimal fresh gas flows (L/min) will make the CO2 absorbent unnecessary?

          A.   3

          B.   5

          C.   7

          D.   10

  19.   Compared to the Mapleson A system, the circle system

          A.   Is less bulky

          B.   Has a decreased risk of disconnection

          C.   Has decreased resistance to patient breathing

          D.   Better conserves humidity

  20.   Incorrect statement regarding the mechanisms of an Ambu bag is

          A.   It contains a nonrebreathing valve, same as the circle system

          B.   It is capable of delivery of nearly a 100% O2 concentration

          C.   It allows for positive-pressure ventilation

          D.   Patient valve has low resistance to both inspiration and expiration

  21.   You are preparing to set up for anesthesia in an off-floor location in the interventional radiology suite. The radiography equipment is consuming the limited space that is available in the suite, and therefore, the decision is made to double the extension tube length from the ventilator to the patient table. What is the impact on the dead-space ventilation that would have occurred secondary to doubling the extension tubing length?

          A.   It would double as well

          B.   It has been decreased to half the original volume

          C.   It would have increased by 4-fold

          D.   It would have not changed

  22.   Malfunction of which of the following valves within a circle system may cause rebreathing of carbon dioxide and could potentially result in hypercapnia?

          A.   Inspiratory valve

          B.   Expiratory valve

          C.   Both A and B

          D.   None of the above

  23.   Since fresh gas flow equal to minute ventilation is sufficient to prevent rebreathing, which of the following Mapleson circuit breathing/ventilation systems is the most efficient for spontaneous ventilation of the patient?

          A.   Mapleson A

          B.   Mapleson B

          C.   Mapleson C

          D.   Mapleson D

  24.   Different semi closed anesthetic ventilation/breathing systems (classically referred to as Mapleson systems and designated A to F) are pictured below. While setting up for anesthesia delivery in an “off-floor” location and planning for controlled ventilation of an asthmatic patient, which of the Mapleson systems provides for the best efficacy?

images

Figure 3-1.

          A.   D > B > C > A

          B.   A > B > C > D

          C.   D > C > B > A

          D.   C > A > D > B

  25.   Degradation of sevoflurane by soda lime results in the production of

          A.   Compound A

          B.   Compound B

          C.   Compound C

          D.   Compound D

  26.   In a CO2-absorbent canister, the greatest amount of carbon monoxide is produced by which of the following volatile agents?

          A.   Sevoflurane

          B.   Halothane

          C.   Isoflurane

          D.   Desflurane

CHAPTER 3 ANSWERS

    1.   C.   Pipeline gases are supplied at pressures between 45 and 55 psi. This is in contrast to cylinder gas pressures, which are much higher, and are reduced by pressure regulators to less than 50 psi.

    2.   D.   The fail-safe valve automatically closes nitrous oxide (and other gases) to prevent delivery of hypoxic gas mixture to the patient. The fail-safe valve is designed to be activated when oxygen pressure falls below 25 psi.

    3.   C.   The oxygen-flush valve provides gas flow at pipeline pressures of about 45 to 55 psi at 35 to 75 L/min. The high flow of oxygen is provided directly to the common gas outlet, bypassing the flowmeters and vaporizers. One should be careful when using the oxygen-flush valve, as high gas flows at high pressures can cause lung barotrauma in the patient.

    4.   A.   Gas flowmeters are calibrated for a particular gas. Gas flow rate depends on its viscosity at low laminar flows, and its density at high turbulent flows. Flowmeters are tapered in shape, with the diameter the smallest near the bottom of the tube.

    5.   B.   The oxygen flowmeter is situated nearest to the gas outlet. This is because, if a leak develops in the flowmeter tubes, a hypoxic gas mixture can be delivered to the patient. To minimize this, the oxygen flowmeter is positioned downstream and nearest to the gas outlet.

    6.   D.   Modern vaporizers are agent-specific and temperature-compensated. Also, specific fillers are available for each volatile agent, which prevent filling on the wrong agent. A constant concentration of agent is delivered, unaffected by temperature or flow rates. Temperature compensation is achieved by a metallic strip composed of two different metals, which expands/contracts to deliver a constant concentration of vapor.

    7.   A.   The Tec 6 desflurane vaporizer is electrically heated to 39°C and pressurized to 2 atm. This is done because desflurane boils at room temperature at sea level (1 atm). The heating and pressurization optimizes the delivery of desflurane.

    8.   B.   Vaporizers are located between the flowmeters (upstream) and the common gas outlet (downstream). In other words, vaporizers are located outside the circle system. This decreases the likelihood of delivery of high vapor concentrations when using the oxygen-flush valve.

    9.   A.   An ascending bellow collapses when disconnection occurs. A descending bellow, however, continues to fill by gravity when disconnection occurs. Therefore, ascending bellows are preferred for anesthesia ventilators.

  10.   B.   NIOSH recommends limiting operating-room concentration of nitrous oxide to 25 ppm. Minimizing operating-room pollution is important to prevent health-related effects in health-care providers. Waste-scavenging systems are utilized to decrease operating-room pollution.

  11.   D.   NIOSH recommends limiting operating-room concentration of volatile agents to 2 ppm. Minimizing operating-room pollution is important to prevent health-related effects in health-care providers. Waste-scavenging systems are utilized to decrease operating-room pollution.

  12.   C.   The capacity of an “E” cylinder of oxygen is about 625 to 700 L. The pressure in a full cylinder is about 1,800 psi at 20°C. Cylinders are color-coded, with oxygen being green, nitrous oxide being blue, and air being yellow.

  13.   D.   Pressure in a half-full “E” cylinder of nitrous oxide will still be 745 psi. Nitrous oxide is present in the cylinder as a liquid, and therefore, the volume remaining in the cylinder does not reflect the pressure in the cylinder. Capacity of an “E cylinder” of nitrous is about 1590 L. It is not until three-fourth of the gas is consumed (about 400 L remaining) that the pressure in the cylinder begins to fall. Therefore, the reliable way to determine the remaining nitrous oxide in the cylinder is to weigh the cylinder. The empty weight of the cylinder is stamped on the cylinder.

  14.   B.   Cylinder manufactures have adopted the pin index safety system, which prevents attachment of wrong gas cylinder to the anesthesia machine. The diameter index safety system prevents attachment of the wrong gas hose from the wall supply. Hanger yoke assembly is the method of attachment of gas cylinders to the anesthesia machine.

  15.   B.   A line-isolation monitor, when alarming, indicates that a single fault has occurred between the power line and the ground. As soon as the alarm is triggered, the equipment should be checked, especially the last equipment that was plugged in. A single fault does not cause an electrical shock, as two faults are required to produce a shock.

  16.   A.   The highest content of soda lime is calcium hydroxide (75%). Other constituents include sodium (3%) and potassium hydroxide (1%), water (20%), and silica, which is added to produce hardness. An indicator dye, such as ethyl violet, is added to indicate the degree of exhaustion.

  17.   D.   End products of the reaction occurring in a soda lime CO2 canister are carbonates, sodium hydroxide (regeneration), water, and heat. Following are the reactions:

  18.   B.   Advantages of a circle system include the use of low fresh gas flow rates because of the presence of a CO2-absorbent canister. However, if the CO2 absorbent is exhausted during a surgical procedure, the fresh gas flow rate has to be increased. A minimum fresh gas flow rate of 5 L/min will make the use of the absorbent unnecessary. Newer anesthesia machines allow changing the CO2-absorbent canister during the surgical procedure, if necessary.

  19.   D.   Advantages of the circle system include economy (low fresh gas flow rates, decreased use of volatile agents), conservation of heat and humidity, and decreased operating-room pollution. Disadvantages of circle system include greater size, decreased portability, increased risk of disconnection, and increased resistance to patient breathing.

  20.   A.   While resuscitation devices such as Ambu bags or bag-mask units have nonrebreathing valves, neither the Mapleson (only has adjustable pressure-limiting valve) nor the circle system (only has unidirectional valves and does allow rebreathing) has this component. Ambu resuscitation bags do allow for positive-pressure ventilation as the intake valve closes during bag compression. The patient valve has low resistance, but can become obstructed by exhaled moisture. Ambu bags have a reservoir system to prevent room air entrapment and are able to deliver nearly 100% oxygen.

  21.   D.   One advantage of the circle system ventilation when compared to the Mapleson system is the presence of unidirectional valves (inspiratory and expiratory valves). With the use of such valves, the volume of dead-space ventilation is limited only to that volume distal to Y-piece (including the endotracheal tube), where inspiratory and expiratory gases mix and converge, regardless of the length of tubing proximal to the Y-piece (to the anesthesia machine).

  22.   C.   Malfunction in either of the unidirectional valves within a circle system could result in the accumulation and eventual CO2 rebreathing that may result in hypercapnia.

  23.   A.   During spontaneous ventilation/breathing of the patient, the Mapleson circuit providing for the most efficacy ranges from A > D > C > B (in the order of decreasing efficiency).

  24.   A.   The efficiency of Mapleson systems drops from D > B > C > A for controlled ventilation. The Mapleson D circuit is most efficient during controlled ventilation, as its fresh gas flow drives expired air away from the patient and toward the expiratory/exhaust valve.

  25.   A.   Sevoflurane is degraded by soda lime, resulting in the production of a potentially nephrotoxic compound A. Compound A production is increased by using low fresh gas flow rates, using high concentrations of sevoflurane, and for long hours (>6 hours).

  26.   D.   Desflurane produces the highest amount of carbon monoxide in the CO2-absorbent canister, which can increase carboxyhemoglobin blood concentration. Production of carbon monoxide is increased by using low fresh gas flow rates, high concentrations of volatile agent, and a dry absorbent.