Quiz 3 Flashcards
Which of the following are potential causes for discrepancies in set tidal volume and achieved tidal volume with volume-controlled ventilation? Select all that apply.
A. A breathing circuit with a compliance of 6mL/cm H20
B. Absence of leaks within a circuit
C. Fresh gas flows of 5L/min
D. Gas Compression
Correct Answer: A, C, & D
Rationale
Discrepancies in achieved and set tidal volume can be attributed to many factors when delivering volume-controlled ventilation. Gas compression losses are generally 3% of the set tidal volume and can directly decrease the achieved tidal volume (Butterworth et al., 2022, p. 70). General breathing circuit tubing has a compliance standard of 5mL/cm H20. Therefore, a breathing circuit with an even greater compliance standard will cause an even greater loss of tidal volume to expand the circuit (Butterworth et al., 2022, p. 70). Higher fresh gas flows will increase the overall achieved tidal volume as further gas flows into the circuit despite the set tidal volume (Butterworth et al., 2022, p. 68-70). An absence of leaks within a circuit will not contribute to a loss or gain in achieved tidal volume.
Which of the following is a key advantage of insufflation in anesthesia?
A) Allows for controlled ventilation
B) Prevents the need for high fresh gas flow rates
C) Avoids direct airway connection, making it useful for pediatric induction
D) Ensures a precise inspired oxygen concentration
Correct Answer:
C) Avoids direct airway connection, making it useful for pediatric induction
Rationale:
Insufflation involves blowing anesthetic gases across a patient’s face without a direct airway connection. This technique is helpful in pediatric patients who may resist face mask placement or intravenous lines. However, it does not allow for controlled ventilation, requires high fresh gas flow rates to prevent rebreathing, and contains unpredictable amounts of atmospheric air in the inspired gas mixture.
Which of the following are advantages of the circle system in anesthesia? (Select all that apply)
A. Minimal operating room and environmental pollution
B. Low resistance (less than the endotracheal tube; not as low as in nonrebreathing circuits)
C. Increased dead space (true of all respiratory apparatus)
D. Constant inspired concentrations
E. Opportunities for misconnection or disconnection
F. Conservation of respiratory tract heat and humidity
Correct Answers:
A, B, D, F
Rationale:
C is incorrect because, although the circle system has some dead space, it is not excessive compared to other systems. The dead space is primarily limited to the Y-piece to the patient’s airway, rather than the entire circuit.
E is incorrect because the risk of misconnection or disconnection is a disadvantage, not an advantage.
Which two of the following reasons would cause increased inspired CO₂ in a circle system?
a) Exhausted absorbent granules
b) Faulty unidirectional valves
c) Malfunctioning APL valve
d) Using a coaxial circuit instead of a Bain circuit
Answer:
a) and b)
Rationale:
In a circle system, CO₂ absorbent granules remove exhaled CO₂. If the absorbent becomes exhausted, CO₂ is no longer effectively removed, leading to rebreathing of CO₂ and increased inspired CO₂. Additionally, faulty unidirectional valves can cause exhaled CO₂-rich gas to bypass the absorber and mix with fresh gas, further increasing inspired CO₂. A malfunctioning APL (Adjustable Pressure-Limiting) valve affects circuit pressure regulation but does not directly cause increased inspired CO₂. A coaxial circuit is not a circle system and does not contain CO₂ absorbent granules. Instead, it relies on high fresh gas flow (FGF) to eliminate CO₂, so switching between coaxial and Bain circuits would not directly affect inspired CO₂ in a circle system.
Which of the following are factors that might increase the peak inspiratory pressure (PIP) AND the plateau pressure (PP) on a respiration waveform? (Select all that apply)
a. Pneumothorax
b. Decreased pulmonary compliance
c. surgery requiring peritoneal gas insufflation
d. Thick secretions
Answer: a, b, c
Rationale: Factors that might cause increased PIP and PP include decreased pulmonary compliance, pulmonary edema, trendelenburg position, pleural effusion, ascites, abdominal packing, peritoneal gas insufflation, tension pneumothorax, and endobronchial intubation. Increased levels of thick secretions will increase the PIP without a change to the PP (Butterworth, et al., 2022).
Where should the fresh gas inlet be positioned in the circle system, and why?
A) Between the absorber and the expiratory valve, to conserve absorption capacity
B) Between the inspiratory valve and the absorber, to prevent dilution of fresh gas
C) Between the Y-piece and the unidirectional valve, to simplify the circuit
D) Downstream from the inspiratory valve, to ensure maximum fresh gas flow
Correct Answer: B) Between the inspiratory valve and the absorber, to prevent dilution of fresh gas
Rationale: The fresh gas inlet is best placed between the absorber and the inspiratory valve to ensure fresh gas is not diluted by recirculated exhaled gas. This placement optimizes fresh gas delivery to the patient and minimizes waste. “Positioning it downstream from the inspiratory valve would allow fresh gas to bypass the patient during exhalation and be wasted. Fresh gas introduced between the expiratory valve and the absorber would be diluted by recirculating gas” (Butterworth, 2022
Which of the following factors primarily influences the transition from inspiration to expiration in a pressure-cycled ventilator?
A) A preset inspiratory pressure must be reached.
B) A fixed inspiratory time interval.
C) A predetermined tidal volume must be delivered.
D) A spontaneous breath initiated by the patient.
Correct Answer:
A) A preset inspiratory pressure must be reached.
Rationale:
In a pressure-cycled ventilator, the inspiratory phase ends when a preset inspiratory pressure is reached, regardless of the tidal volume delivered. Pressure-cycled ventilators function by delivering gas to the patient’s airway until a predetermined inspiratory pressure is reached. Once this pressure threshold is met, the ventilator terminates the inspiratory phase and transitions to expiration, regardless of how much volume (tidal volume) has been delivered to the lungs.
Which of the following is NOT a component of the circle system?
A. Fresh gas inlet inside the breathing tube
B. Y-connector
C. Reservoir bag
D. APL valve
Answer: A. Fresh gas inlet inside the breathing tube
Rationale: The components of a circle system include: A CO2 absorber containing CO2 absorbent, a fresh gas inlet, an inspiratory unidirectional valve and inspiratory breathing tube, a Y-connector, an expiratory unidirectional valve and expiratory breathing tube, an APL valve and a reservoir bag.
Fresh gas tubing is is found inside the corrugated breathing tube of a Bain circuit not a circle system. This component of the Bain circuit can lead to kinking or disconnection of the fresh gas outlet and requires period inspection of the inner tubing to avoid significant rebreathing of exhaled gas.
Which of the following conditions would increase peak inspiratory pressure without affecting plateau pressure?
A. Pulmonary edema
B. Bronchospasm
C. Increased tidal volume
D. Decreased pulmonary compliance
Answer: B. Bronchospasm
Rationale: Peak inspiratory pressure (PIP) is generated during the inspiratory cycle and provides an indication of dynamic compliance. Plateau pressure is measured during an inspiratory pause and is an indicator of static compliance. An increase in peak inspiratory pressure without an increase in plateau pressure can indicate an increase in airway resistance. Secretions, bronchospasm, a kinked endotracheal tube, and foreign body aspiration are all potential causes of increased PIP without an increase in plateau pressure.
You are providing anesthesia without complications up to this point in the procedure. Suddenly, low-pressure alarms begin to sound, and the patient’s breath sounds are absent. What should be the first course of action:
A. Check settings of fresh gas flow, scavenger, and ventilator
B. Ventilate manually using the anesthesia breathing circuit
C. Check the y-piece and other common locations for disconnections.
D. Disconnect the patient from the circuit, provide IV anesthetics, and ventilate the patient with the Ambubag
E. Troubleshoot the anesthesia machine
Correct Answer: C. Low-pressure alarms are often caused by leaks in the breathing circuit, and the most common location for disconnection is the y-piece between the breathing circuit and the endotracheal tube. When the ability to ventilate is lost due to low pressure, the anesthesia must first rapidly check for disconnections. If no disconnections are found, the provider should attempt to ventilate manually through the anesthesia machine. If unable to ventilate through the anesthesia machine, the provider should proceed to use the Ambubag. Once proper ventilation is established, check settings for fresh gas flow, scavenger, and ventilator. Do not attempt to troubleshoot the machine while the patient is under anesthesia.
In draw-over anesthesia, what happens when oxygen is supplied at 1 L/min?
A) FiO2 reaches 80-90%
B) FiO2 reaches 30-40%
C) FiO2 reaches 10-20%
D) FiO2 reaches 90-100%
Answer: B, FiO2 reaches 30-40%
Rationale: Across the clinical range of tidal volume and respiratory rate, an oxygen flow rate of 1 L/min gives a FiO2 of 30-40%. or with 4 L/min, a FiO2 of 60-80%.
When should you change your CO2 absorber canister?
A) At the first sign of color change
B) When 25%-40% of granules have changed color
C) When 50%-70% of granules have changed color
D) Once all, or nearly all, the granules have changed color
Answer: C. When 50%-70% of granules have changed color
Rationale: According to Butterworth et al. (2022), absorbent should be replaced when 50% to 70% has changed color. Although exhausted granules may revert to their original color if rested, no significant recovery of absorptive capacity returns.
Which of the following is the highest circuit pressure generated during an inspiratory cycle during mechanical ventilation?
A) Plateau pressure
B) Tidal volume
C) Peak inspiratory pressure
D) Positive end-expiratory pressure
Answer: C
Rational: Peak inspiratory pressure is the highest circuit pressure generated during an inspiratory cycle, and it provides an indication of dynamic compliance. Plateau pressure is the pressure measured during an inspiratory and mirrors static compliance. Tidal volume is the amount of air moving into and out of the lungs with each breath. An increase in tidal volume can cause in increase in both peak inspiratory pressure and plateau pressure. PEEP refers to the positive pressure maintained in the airways at the end of exhalation.
Which inhaled anesthetic agents produce the highest amount of carbon monoxide when in contact with CO₂ absorbent granules?
A) Sevoflurane
B) Isoflurane
C) Desflurane
D) Halothane
Correct Answer: C) Desflurane
Rationale: “Carbon monoxide is produced by desflurane, much more than isoflurane, when these agents are in contact with absorbent granules.”
Soda lime is a common CO2 absorbent seen on modern anesthesia machines utilizing the circle system. How much carbon dioxide is soda lime capable of absorbing?
A. 18L of CO2 per 100g of soda lime
B. 23L of CO2 per 100g of soda lime
C. 23L of CO2 per 50g of soda lime
D. 18L of CO2 per 50g of soda lime
Answer: B, 23L of CO2 per 100g of soda lime
Rationale:
Soda lime contains hydroxide salts that are capable of neutralizing the carbonic acid that forms with the reaction of carbon dioxide and water. Soda lime consists of calcium hydroxide, sodium hydroxide, and potassium hydroxide. With the use of these hydroxide salts, soda lime is capable of absorbing 23 liters of carbon dioxide per 100 grams of absorbent.
Which of the following will NOT decrease resistance within the circle system?
A. Increasing the diameter of the circuit
B. Maintaining Laminar Flow
C. Eliminating Valves
D. Using sharp bends
Correct Answer: D. Using sharp bends
Rationale: Resistance within the circle system can be reduced by decreasing the length of the circuit, increasing the diameter of the circuit, maintaining laminar flow, avoiding sharp bends, and eliminating valves (Nagelhout et al., 2023, p. 266).
Which ventilation mode is described as peak inspiratory pressure is limited and cycle is controlled by time, inspiratory flow is strongest early in inspiration and declines to flow just sufficient to maintain the set pressure later in inspiration? In this ventilation mode, tidal volume is uncontrolled and may increase if compliance increases or airway resistance falls.
A) Pressure-controlled ventilation
B) Volume controlled ventilation
C) Pressure-controlled ventilation with volume guarantee
D) synchronized intermittent mandatory ventilation
Correct answer: A) Pressure-controlled ventilation
Rational:
In pressure-controlled (PCV), the ventilator delivers breaths with a set inspiratory pressure, meaning the PIP is controlled and does not exceed the pre-set limit. PCV delivers inspiratory flow is strongest early inspiration to quickly reach the target pressure, then flow decreases to maintain the set inspiratory pressure. Unlike volume-controlled ventilation, where tidal volume is guaranteed, PCV allows the delivered tidal volume to fluctuate depending on lung compliance and airway resistance (Nagelhout et al., p.277). Volume-controlled ventilation (VCV) delivers a fixed tidal volume with each breath, and flow is constant or ramped, not decelerating. The key feature is volume guarantee, whereas the question describes variable tidal volume (Nagelhout et al., p.277). Pressure-controlled ventilation volume guaranteed (PCV-VG) combines pressure control with a guaranteed tidal volume, adjusting inspiratory pressure to ensure the set volume is delivered. The question specifies that tidal volume is uncontrolled, ruling out this option (Nagelhout et al., p.278). Synchronized intermittent mandatory ventilation (SIMV) can be either volume- or pressure-controlled, but it includes spontaneous breathing between mandatory breaths, which is not explicitly mentioned in the question (Nagelhout et al., p.278).
During a surgical case, you notice that the reservoir bag in the scavenging system is completely collapsed, and the anesthesia circuit’s fresh gas flow must be significantly increased to maintain proper ventilation in your circuit. What is the most likely cause?
A. The negative pressure relief valve is malfunctioning
B. The positive pressure relief valve is malfunctioning
C. This is an open scavenging system, and gases are entrained from excessive suction
D. The scavenging system is passive and its valve is not working properly
Answer: A. The negative pressure relief valve is malfunctioning
Rationale: An active scavenging system relies on suction to remove waste gas. A negative pressure relief valve opens to draw in room air when suction is excessive in a closed interface scavenging system. This prevents excessive suction, which could expose the breathing circuit to negative pressure and hypoxia when emptying gas from the breathing circuit. Failure in the negative pressure relief valve causes the scavenger to remove gas from the circuit system, requiring a high fresh gas flow to maintain adequate circuit volume (Nagelhout et al., p. 285).
The positive pressure relief valve, whether on an active or passive scavenging system, prevents excessive pressure buildup in the scavenging system. If this valve fails in a closed scavenging system, circuit pressure would increase, leading to possible barotrauma.
An open scavenging system has no valves and is open to the atmosphere, unlike a closed scavenging system. If suction is too high, room air may enter through the open interface, diluting gases and providing an inconsistent anesthetic gas delivery.
Passive scavenging systems do not use suction. Instead, they rely on gas being expelled passively into a ventilated area or through a gas disposal line. The passive system has a positive pressure valve. When malfunctioned, the positive pressure valve would lead to waste gas buildup, increasing pressure in the system.
