Breathing Systems — MCQs
Spontaneously breathing infant- which breathing circuit to be used?
Which of the following is NOT a rebreathing system used in anesthesia?
True about anesthesia machine – a) Cylinder is a part of high pressure system b) O2 flush delivers < 35 lit c) O2 flush delivers > 35 lit d) Pipeline is a part of low pressure system
Maximum voluntary ventilation is:
Spontaneous breathing circuit used in children is -
What is the most reliable indicator to prevent esophageal intubation?
A 20-year old spontaneous breathing patient undergoing incision and drainage under GA, which of the following is the breathing circuit of choice for spontaneous ventilation?
During intraoperative period following capnograph waveform is seen. What does it signify.
Curare notch seen in capnograph is due to
What does the image of the Capnograph depict?
Breathing Systems Indian Medical PG Practice Questions and MCQs
Question 1: Spontaneously breathing infant- which breathing circuit to be used?
- A. Bain's circuit
- B. Jackson Rees modification of Ayre's T piece (Correct Answer)
- C. Mapleson A or Magill's circuit
- D. Mapleson C or waters to & fro canister
Explanation: ***Jackson Rees modification of Ayre's T piece*** - This circuit is excellent for **spontaneously breathing infants** because it provides minimal resistance and reduces rebreathing of CO2. - Its **open design** allows for spontaneous ventilation while still enabling manual assistance if needed, making it versatile for pediatric anesthesia. *Bain's circuit* - The Bain's circuit is a **Mapleson D circuit** designed for controlled ventilation, not ideal for spontaneous breathing infants due to higher resistance. - Although it can be used for spontaneous breathing, it generally requires **higher fresh gas flows** to prevent rebreathing, which is less efficient for infants. *Mapleson A or Magill's circuit* - The Mapleson A circuit is highly efficient for **spontaneous ventilation** in adults, given adequate fresh gas flow. - However, its large, cumbersome design and relatively high resistance make it generally **unsuitable for infants**, where minimal dead space and resistance are crucial. *Mapleson C or waters to & fro canister* - The Mapleson C circuit, or Waters to & fro canister, is designed for **controlled or assisted ventilation** due to the position of its fresh gas inlet and reservoir bag. - It is **not highly efficient for spontaneous ventilation** and can lead to significant rebreathing of CO2 in a spontaneously breathing patient, especially an infant.
Question 2: Which of the following is NOT a rebreathing system used in anesthesia?
- A. Mapleson F (Correct Answer)
- B. Circle system
- C. To & fro system
- D. Water's system
Explanation: ***Mapleson F*** - This system is known as the **Jackson-Rees modification** of the Mapleson T-piece and is a **non-rebreathing system** used primarily in pediatric anesthesia. - It features an **open-ended reservoir bag** attached to the expiratory limb, allowing for manual ventilation without rebreathing of expired gases if fresh gas flow is adequate. *Circle system* - The **circle system** is a common **rebreathing system** in anesthesia characterized by unidirectional valves and a CO2 absorber, allowing rebreathing of expired gases after CO2 removal. - It utilizes a **low fresh gas flow** to conserve anesthetic agents and moisture, making it a more economical and environmentally friendly choice. *To & fro system* - The **to & fro system** is an older type of **rebreathing system** that uses a soda lime canister placed directly in the breathing circuit, allowing exhaled gases to pass back and forth through it. - While effective for CO2 absorption, it is less commonly used now due to problems with heat buildup, airway resistance, and potential for caustic dust aspiration. *Water's system* - The **Water's system**, also known as the Waters-Dale system, is a type of **closed-circuit rebreathing system** that was also used for CO2 absorption. - It features a canister of CO2 absorbent placed close to the patient, enabling rebreathing of anesthetic gases.
Question 3: True about anesthesia machine – a) Cylinder is a part of high pressure system b) O2 flush delivers < 35 lit c) O2 flush delivers > 35 lit d) Pipeline is a part of low pressure system
- A. bc
- B. a
- C. ad
- D. ac (Correct Answer)
Explanation: ***ac*** - **Cylinder** is indeed a component of the **high-pressure system** of an anesthesia machine, holding gases under high pressure before regulation. - The **O2 flush valve** bypasses the flowmeters and vaporizers, delivering a high flow of oxygen, typically **35-75 L/min**, to the common gas outlet. *bc* - This option is incorrect because while the O2 flush delivers a high flow, stating it delivers **< 35 L/min** is inaccurate; it typically delivers significantly more. - The implication that both b and c are correct cannot be true as they are contradictory (O2 flush cannot deliver both < 35 L/min and > 35 L/min simultaneously). *a* - This option is partially correct as the **cylinder** is part of the high-pressure system, but it omits the correct information about the O2 flush. - It does not account for the accurate statement regarding the flow rate of the O2 flush. *ad* - While the **cylinder** is correctly identified as part of the high-pressure system, the statement that the **pipeline** is part of the **low-pressure system** is incorrect; pipelines are part of the high-pressure system. - The low-pressure system begins after the flowmeters, encompassing components like the vaporizers and the common gas outlet.
Question 4: Maximum voluntary ventilation is:
- A. 25 L/min
- B. 50 L/min
- C. 100 L/min
- D. 150 L/min (Correct Answer)
Explanation: ***150 L/min*** - The **Maximum Voluntary Ventilation (MVV)** represents the largest volume of air that can be breathed in and out using maximal effort over a 10-15 second period. - While it varies among individuals, a typical average value for a healthy adult is approximately **150-170 L/min**. *25 L/min* - This value is significantly lower than the typical MVV; 25 L/min is closer to a normal **resting minute ventilation** (tidal volume multiplied by respiratory rate). - Resting minute ventilation reflects the volume of air exchanged at rest, not the maximum capacity. *50 L/min* - This value is still considerably lower than the average MVV and does not represent the maximum capacity of the respiratory system. - It might be seen in individuals with **severe pulmonary impairment** or at a very high resting metabolic rate. *100 L/min* - While higher than resting values, 100 L/min is generally below the average maximum voluntary ventilation for a healthy adult. - It could represent a MVV in individuals with **mild to moderate respiratory compromise** or less effort during the test.
Question 5: Spontaneous breathing circuit used in children is -
- A. Mapleson C or water's to & fro canister
- B. Bain's circuit
- C. Jackson Rees modification of Ayre's T piece (Correct Answer)
- D. Mapleson A or Magill's circuit
Explanation: ***Jackson Rees modification of Ayre's T piece*** - This circuit is particularly well-suited for **children** due to its low resistance and suitability for both spontaneous and controlled ventilation. - The **Ayre's T-piece** itself provides minimal mechanical dead space, and the Jackson Rees modification adds a reservoir bag, which improves control over ventilation and reduces gas waste. *Mapleson C or water's to & fro canister* - The **Mapleson C circuit** is inefficient for spontaneous breathing due to its high rebreathing potential and lack of a dedicated reservoir bag to mitigate CO2 accumulation. - The **Water's to & fro canister** utilizes a soda lime canister for CO2 absorption, which can be cumbersome and less effective for dynamic spontaneous breathing in children. *Bain's circuit* - The **Bain's circuit** (a modification of the Mapleson D) is primarily used for controlled ventilation and is less efficient for spontaneous breathing in children due to its high fresh gas flow requirements to prevent CO2 rebreathing. - Its design makes it more prone to heat and humidity loss, which can be detrimental in pediatric patients. *Mapleson A or Magill's circuit* - The **Mapleson A circuit** (Magill's circuit) is considered the most efficient for spontaneous breathing in adults, but its design leads to significant rebreathing of expired gases in children due to their higher respiratory rates and lower tidal volumes. - The fresh gas flow required to prevent rebreathing in children using this circuit would be excessively high, leading to increased gas consumption and potential hypothermia.
Question 6: What is the most reliable indicator to prevent esophageal intubation?
- A. Oxygen saturation on pulse oximeter
- B. Direct visualization of passing tube beneath vocal cords
- C. Auscultation over chest
- D. Measurement of CO2 in exhaled air (EtCO2). (Correct Answer)
Explanation: ***Measurement of CO2 in exhaled air (EtCO2)*** - The presence of **carbon dioxide** in exhaled air confirms tracheal intubation as the esophagus does not contain CO2. - This method provides a **real-time**, objective assessment of tube placement that is highly reliable because even small amounts of CO2 are detected. *Oxygen saturation on pulse oximeter* - This indicator measures **oxygenation**, which can remain adequate for several minutes after esophageal intubation due to pre-oxygenation. - A **delayed drop in saturation** might indicate esophageal intubation, but it's not immediate and therefore not the most reliable early indicator. *Direct visualization of passing tube beneath vocal cords* - While helpful, **direct visualization** can sometimes be misleading due to difficult airways or poor visibility, where the tube might appear to pass correctly but enter the esophagus. - This method is **operator-dependent** and its reliability can vary based on the intubator's experience and the patient's anatomy. *Auscultation over chest* - **Auscultation** can detect breath sounds; however, sounds can be transmitted from the stomach or surrounding tissues, leading to false positives. - It is also very difficult to reliably distinguish between **esophageal and tracheal sounds**, especially in noisy environments or with inexperienced personnel, making it less reliable than EtCO2.
Question 7: A 20-year old spontaneous breathing patient undergoing incision and drainage under GA, which of the following is the breathing circuit of choice for spontaneous ventilation?
- A. Mapleson C
- B. Mapleson A (Correct Answer)
- C. Mapleson D
- D. Mapleson B
Explanation: ***Mapleson A*** - The **Mapleson A circuit (Magill circuit)** is the most efficient scavenging system for **spontaneous ventilation** due to the fresh gas flow being located near the patient and the APL valve downstream. - This arrangement allows exhaled CO2 to be flushed out easily during expiration with minimal fresh gas flow, preventing rebreathing. *Mapleson C* - The Mapleson C circuit is similar in design to Mapleson B but with a shorter corrugated tube, making it **less efficient for spontaneous ventilation** due to increased rebreathing. - It is often used for **transport** or in resuscitation kits but is not the circuit of choice for routine spontaneous breathing under general anesthesia. *Mapleson D* - Mapleson D circuits, particularly the **Bain circuit** (a coaxial modification), are efficient for both **controlled and spontaneous ventilation**, but they are **most efficient for controlled ventilation**, which is not the primary mode described in the question. - For spontaneous ventilation, it requires a higher fresh gas flow rate (2-3 times minute ventilation) to prevent CO2 rebreathing compared to Mapleson A. *Mapleson B* - The Mapleson B circuit is **less efficient for spontaneous ventilation** due to the fresh gas inlet and APL valve being close to the patient, leading to significant rebreathing of CO2 unless very high fresh gas flows are used. - It is generally considered **inefficient** for both spontaneous and controlled ventilation compared to other Mapleson circuits.
Question 8: During intraoperative period following capnograph waveform is seen. What does it signify.
- A. Airway obstruction
- B. Oesophageal intubation
- C. Return of spontaneous ventilation (Correct Answer)
- D. Hyperventilation
Explanation: ***Return of spontaneous ventilation*** - The capnogram shows a gradual increase in **tidal volume** and then a drop with a notch towards the end, which is characteristic of the patient taking an occasional **spontaneous breath**. - This pattern, where the patient's own respiratory effort adds to or takes over mechanical ventilation, signifies the **return of spontaneous ventilation**. *Airway obstruction* - Airway obstruction typically manifests as a **sharper upstroke** (phase II) and a **prolonged expiratory phase** (phase III) with a sloped plateau, sometimes with a 'shark fin' appearance if severe. - The waveform in the image does not demonstrate these specific characteristics of obstructed airflow. *Oesophageal intubation* - **Esophageal intubation** would show either **no CO2 waveform** (flat line) or very small, sporadic waveforms due to gastric CO2, which quickly disappear as gastric CO2 depletes. - The sustained CO2 levels and clear respiratory pattern seen in the image rule out esophageal intubation. *Hyperventilation* - **Hyperventilation** would lead to a **decrease in end-tidal CO2 (ETCO2)** values as more CO2 is exhaled. The waveform morphology itself would typically remain normal, just shifted to lower CO2 levels. - While the patient might be breathing more, the specific notch pattern is not indicative of simple hyperventilation but rather spontaneous efforts.
Question 9: Curare notch seen in capnograph is due to
- A. Spontaneous breathing (Correct Answer)
- B. Carbon dioxide rebreathing
- C. Valve malfunction
- D. Bronchospasm
Explanation: ***Spontaneous breathing*** - The "Curare notch" a dip in the expiratory plateau of the **capnograph waveform**, occurs when a patient begins to initiate **spontaneous breaths** against the ventilator. - This signifies that the **neuromuscular blockade** from paralytic agents (like curare derivatives) is wearing off. *Carbon dioxide rebreathing* - **CO2 rebreathing** would typically elevate the baseline of the capnogram and potentially prolong the expiratory plateau, but it would not create a characteristic notch. - This is usually caused by insufficient fresh gas flow or a faulty absorbent, leading to the patient inhaling previously exhaled CO2. *Valve malfunction* - A **valve malfunction**, such as a stuck expiratory valve, would typically cause a persistent elevation of the expiratory CO2 plateau or an inability to exhale, rather than a transient notch. - This would indicate a problem with the mechanical ventilation circuit. *Bronchospasm* - **Bronchospasm** typically results in a **sloping or shark fin-shaped expiratory plateau** on the capnogram due to prolonged expiration and uneven gas emptying from the lungs. - It does not produce a distinct "notch" as seen with the return of spontaneous breathing.
Question 10: What does the image of the Capnograph depict?
- A. Capnograph during inspiration
- B. Capnograph showing inspiration with cardiac oscillations
- C. Capnograph during expiration
- D. Capnograph indicating spontaneous respiration (Correct Answer)
Explanation: ***Capnograph indicating spontaneous respiration*** - The characteristic dip in the **EtCO2 waveform** during the plateau phase (phaselll) is indicative of a breath taken by the individual which is a classic finding of **spontaneous respiration**. This dip is because when a patient takes a breath in, fresh gas with no CO2 is pulled into the sampling line momentarily decreasing the measured CO2. - This pattern is often referred to as a "**curare cleft**" or "**respiratory indentation**," and it signifies incomplete paralysis or return of spontaneous breathing. *Capnograph during inspiration* - During normal inspiration, there is no CO2 in the inhaled air, so the capnograph reading would theoretically drop to **zero** or near-zero, not exhibit a waveform with a plateau. - The baseline of the capnograph reflects inspiration, which should be flat (zero CO2). *Capnograph showing inspiration with cardiac oscillations* - Cardiac oscillations typically appear as **small rhythmic fluctuations** on the baseline or the expiratory plateau, synchronized with the heartbeat. - These oscillations are usually much smaller and do not present as distinct, sharp dips within the expiratory plateau as seen in the image. *Capnograph during expiration* - During a normal expiration, the capnograph waveform rises from a baseline of zero (phase I, **dead space ventilation**) to a plateau (phase III, **alveolar gas emptying**) with a peak value, before returning to baseline during inspiration. - While the image shows expiration with a plateau, the key feature of the dip during the plateau is more specific to spontaneous respiration than just general expiration.
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