Exam 2 (Breathing system Miller's review)

Question 1

Describe the Mapleson F anesthetic breathing system.
What is another name for this anesthetic breathing system?

Answer 1

• The Mapleson F system is a T-piece arrangement with a reservoir bag and an adjustable pressure-limiting overflow valve on the distal end of the gas reservoir bag.
• Another name for this anesthetic breathing system is the Jackson-Rees circuit.

Question 2

When is the Mapleson F system commonly used?

Answer 2

For controlled ventilation during transport of endotracheally intubated patients.

Question 3

What are some advantages of the Mapleson F anesthetic breathing system?

Answer 3

• Minimal dead space and resistance.
• This makes this system ideal for pediatric anesthesia.

Question 4

What are some disadvantages of the Mapleson F anesthetic breathing system?

Answer 4

(1) The need for high fresh gas inflow to prevent rebreathing.
(2) The possibility of high airway pressure and barotrauma should the overflow valve become occluded.
(3) the lack of humidification. Lack of humidification can be offset by allowing the fresh gas to pass through an in-line heated humidifier.

Question 5

What are some advantages of the Bain circuit anesthetic breathing system?

Answer 5

(1) Warming of the fresh gas inflow by the surrounding exhaled gases in the corrugated expiratory tube.
(2) Conservation of moisture as a result of partial rebreathing.
(3) Ease of scavenging waste anesthetic gases from the overflow valve. It is lightweight, easily sterilized, reusable, and useful when access to the patient is limited, such as during head and neck surgery.

Question 6

What are some disadvantages of the Bain circuit anesthetic breathing system?

Answer 6

• Unrecognized disconnection or kinking of the inner fresh gas tube.
• The outer expiratory tube should be transparent to allow inspection of the inner tube.

Question 7

44. How does the circle system prevent rebreathing of carbon dioxide?

Answer 7

By chemical neutralization of carbon dioxide with carbon dioxide absorbents

Question 8

46. What is the most commonly used circle breathing system used in the
    United States?

Answer 8

A semiclosed system is associated with rebreathing of gases and is the most commonly used breathing system in the United States.

Question 9

47. What are some advantages of the semiclosed and closed circle systems?

Answer 9

• The semiclosed and closed circle system are both advantageous in that they allow for the rebreathing of exhaled gases.
• The rebreathing of exhaled gases results in (1) some conservation of airway moisture and body heat and (2) decreased pollution of the surrounding atmosphere with anesthetic gases when the fresh gas inflow rate is set at less than the patient’s minute ventilation.

Question 10

48. What are some disadvantages of the circle anesthetic breathing system?

Answer 10

• (1) Increased resistance to breathing because of the presence of unidirectional valves and carbon dioxide absorbent.
• (2) Bulkiness with loss of portability.
• (3) Enhanced opportunity for malfunction because of the complexity of the apparatus.

Question 11

49. What is the impact of the rebreathing of anesthetic gases in a semiclosed circle system?

Answer 11

The rebreathing of exhaled gases in a semiclosed circle system influences the inhaled anesthetic concentrations of these gases. For example, when uptake
of the anesthetic gas is high, as during induction of anesthesia, rebreathing
of exhaled gases depleted of anesthetic greatly dilutes the concentration of anesthetic in the fresh gas inflow. This dilutional effect of uptake is offset clinically by increasing the delivered concentration of anesthetic. As uptake of anesthetic diminishes, the impact of dilution on the inspired concentration produced by rebreathing of exhaled gases is lessened.

Question 12

53. What is advantageous about the corrugated tubing in the circle system?

Answer 12

• The inspiratory and expiratory corrugated tubes serve as conduits for delivery of gases to and from the patient.
• Their large bore provides minimal resistance.
• Corrugations provide flexibility, resist kinking, and promote turbulent instead of laminar flow.

Question 13

54. What is disadvantageous about the corrugated tubing in the circle system?

Answer 13

During positive-pressure ventilation, some of the delivered gas distends the corrugated tubing and some is compressed within the circuit, which leads to a smaller delivered tidal volume.

Question 14

60. What are some advantages to the closed circle anesthetic breathing system?

Answer 14

Advantages of a closed circle anesthetic breathing system over a semiclosed circle anesthetic breathing system include:
- (1) maximal humidification and warming of inhaled gases.
- (2) less pollution of the surrounding atmosphere with anesthetic gases.
- (3) economy in the use of anesthetics.

Question 15

62. What are the dangers of the closed circle anesthetic breathing system?

Answer 15

The principal dangers of a closed anesthetic breathing system are delivery of:
- (1) unpredictable and possibly insufficient concentrations of oxygen.
- (2) unknown and possibly excessive concentrations of potent anesthetic gases.

Question 16

74. What effect does tracheal intubation or the use of a laryngeal mask airway have on airway humidification?
    What are the negative consequences of this?

Answer 16

• Tracheal intubation or the use of a laryngeal mask airway bypasses the upper airway and thus leaves the tracheobronchial mucosa the burden of heating and humidifying inspired gases.
• Humidification of inspired gases by the lower respiratory tract in intubated patients can lead to:
• (1) Dehydration of the mucosa,
• (2) impaired ciliary function,
• (3) impaired surfactant function,
• (4) inspissation of secretions,
• (5) atelectasis,
• (6) a rise in the alveolar-to-arterial gradient.
• Breathing of dry and room temperature gases in intubated patients is associated with water and heat loss from the patient. Heat loss is more important than water loss, and the most important reason to provide heated humidification for intubated patients is to decrease heat loss and associated decreases in body temperature. This is especially true in infants and children, who are rendered poikilothermic by general anesthesia.

Question 17

77. Describe heat and moisture exchanger (HME) humidifiers.
    What is the difference between an HME and an HMEF?

Answer 17

• HME humidifiers are devices that, when placed between the endotracheal tube and Y-piece of the circle system, conserve some of the exhaled water and heat and return it to the inspired gases.
• They contain a porous hydrophobic or hygroscopic membrane that traps exhaled humidified gases and returns them to the patient on inspiration.
• Bacterial and viral filters can be incorporated in HME humidifiers to convert them into heat and moisture exchanging filters (HMEFs).

Question 18

78. What are the advantages of HME humidifiers over other types of humidifiers?

Answer 18

• (1) simple and easy to use,
• (2) lightweight,
• (3) not dependent on an external power source,
• (4) disposable,
• (5) low cost.

Question 19

79. What are the disadvantages of HME humidifiers?

Answer 19

• (1) are not as effective as heated water vaporizers and humidifiers in maintaining patient temperature.
• (2) add resistance and increase the work of breathing and therefore should be used with caution in spontaneously ventilating patients.
• (3) can become clogged with patient secretions or blood.
• (4) can increase dead space, which can cause significant rebreathing in pediatric patients. Special low-volume HME humidifiers are available for pediatric patients.

Question 20

80. What is the advantage of heated water vaporizers and humidifiers over HME humidifiers? When are they used most frequently?

Answer 20

• Heated water vaporizers and humidifiers are used to deliver a relative humidity higher than that delivered by HME humidifiers.
• Heated water vaporizers are more frequently used in pediatric anesthesia and intensive care unit patients.

Question 21

81. What are the risks of heated water vaporizers and humidifiers?

Answer 21

• (1) thermal injury
• (2) nosocomial infection,
• (3) increased work of breathing,
• (4) increased risk of malfunction because of the complexity of these systems.

Question 22

94. How is carbon dioxide eliminated in open and semiopen breathing systems?

Answer 22

By venting all exhaled gases to the atmosphere.

Question 23

95. How is carbon dioxide eliminated in a semiclosed or closed anesthetic breathing system?

Answer 23

By chemical neutralization.

Question 24

99. Why is the water in the soda lime carbon dioxide absorbent canister hazardous?

Answer 24

These monovalent bases can be corrosive to the skin.

Question 25

105. What is the optimal carbon dioxide absorbent granule size? How is this sizing system defined?

Answer 25

• Absorbent granule size is designated as mesh size, which refers to the number of openings per linear inch in a sieve through which the granular particles can pass.
• The granular size of carbon dioxide absorbents in anesthesia practice is between 4 and 8 mesh, a size at which absorbent efficiency is maximal with minimal resistance.
• A 4-mesh screen means that there are four quarter-inch openings per linear inch. An 8-mesh screen has eight eighth-inch openings per linear inch.

Question 26

106. What does channeling in the carbon dioxide absorbent granule-containing canister refer to?
     How does channeling in the canister affect the efficiency of carbon dioxide neutralization?

Answer 26

Channeling is the preferential passage of exhaled gases through the carbon dioxide absorber canister via pathways of low resistance such that the bulk of the carbon dioxide absorbent granules are bypassed.

Question 27

107. What is the most frequent cause of channeling in the carbon dioxide absorbent granule-containing canister?
     How can it be minimized?

Answer 27

Channeling results from loose packing of absorbent granules and can be minimized by gently shaking the canister before use to ensure firm packing of the absorbent granules.

Question 28

124. Does a manual positive-pressure leak test check the integrity of the unidirectional valves?

Answer 28

No. A positive-pressure leak check of the breathing system must be performed before every procedure. This test does not check the integrity of the unidirectional valves inasmuch as the breathing system will pass the leak check even if the unidirectional valves are incompetent or stuck shut.