Anesthesia Machine Components — MCQs
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?
If an anesthetist at high altitude uses plenum vaporizers, what will be the delivered vapor concentration?
Which of the following is NOT a rebreathing system used in anesthesia?
True about anaesthesia breathing circuit is
A sevoflurane vaporizer can accurately deliver the dose of an anesthetic agent. This accuracy depends on which of the following properties of the anesthetic agent?
Gas cylinder with single pin index ?
What is the most reliable indicator to prevent esophageal intubation?
All of the following are used to maintain proper oxygen flow to the patient except:
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 40–year female has to undergo incisional hernia surgery under general anaesthesia. She complains of awareness during her past cesarean section. Which of the following monitoring techniques can be used to prevent such awareness ?
Anesthesia Machine Components Indian Medical PG Practice Questions and MCQs
Question 1: 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 2: If an anesthetist at high altitude uses plenum vaporizers, what will be the delivered vapor concentration?
- A. Lower than concentration at same partial pressure
- B. Higher than the concentration at same partial pressure (Correct Answer)
- C. Lower than the concentration at lower partial pressure
- D. Higher than the original concentration at high partial pressure
Explanation: ***Higher than the concentration at same partial pressure*** - Plenum vaporizers are calibrated at **sea level** and deliver a constant *volume percent* of volatile anesthetic. At high altitude, ambient pressure is lower, meaning a given volume percent represents a **higher partial pressure** of anesthetic. - While the *anesthetic partial pressure* might be what the anesthetist aims for, the *delivered concentration* (volume percent) will be higher than the concentration that would achieve the same partial pressure at sea level because the total pressure is lower. *Lower than concentration at same partial pressure* - This statement is incorrect because a plenum vaporizer will deliver a **higher partial pressure** at altitude for a given dial setting, due to the reduced ambient pressure. - A lower partial pressure for the same set concentration would only occur if the ambient pressure were higher than calibration. *Lower than the concentration at lower partial pressure* - This option is vaguely worded and does not accurately describe the behavior of plenum vaporizers at altitude. When total pressure drops, the *partial pressure* delivered by a plenum vaporizer at a given dial setting will increase, not decrease. - A lower vapor concentration leading to a lower partial pressure is generally true, but it doesn't address the specific issue of a plenum vaporizer's performance at high altitude. *Higher than the original concentration at high partial pressure* - This option is confusing as it refers to "original concentration at high partial pressure" which isn't a standard comparison. The key is that a plenum vaporizer's *delivered volume % remains constant*, regardless of altitude. - However, this constant volume % translates to a higher *partial pressure* when the **ambient atmospheric pressure is lower**, as is the case at high altitude.
Question 3: 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 4: True about anaesthesia breathing circuit is
- A. Oxygen flush delivers more than 135 litres
- B. Pipelines is a part of low pressure system
- C. Cylinder is a part of high pressure system (Correct Answer)
- D. Oxygen flush delivers less than 35 litres
Explanation: ***Cylinder is a part of high pressure system*** - The **cylinders** containing medical gases (e.g., oxygen, nitrous oxide) are stored under very high pressure, typically **2000 psi** (pounds per square inch) or more, classifying them as part of the high-pressure system. - The high-pressure system also includes components like the cylinder **pressure gauge** and the **pressure regulator**, which reduce the gas pressure to a safer, more manageable level before entering the low-pressure system. *Oxygen flush delivers more than 135 litres* - The **oxygen flush mechanism** typically delivers oxygen at a rate of 35-75 L/min (liters per minute), which is significantly less than 135 L/min. - This function bypasses the flowmeters and vaporizer, providing a rapid surge of **unvaporized oxygen** directly to the breathing circuit. *Pipelines is a part of low pressure system* - **Medical gas pipelines** (e.g., oxygen, nitrous oxide, air) deliver gases from a central supply (like a bank of cylinders or a liquid oxygen tank) at an intermediate pressure, typically around **50-55 psi**, to wall outlets in the operating room. - This intermediate pressure is then further reduced by pressure regulators at the anesthesia machine to enter the low-pressure system, making pipelines an **intermediate pressure system** rather than a low-pressure one. *Oxygen flush delivers less than 35 litres* - The **oxygen flush valve** delivers oxygen at a rate of approximately **35-75 L/min**, not less than 35 L/min. - This high flow rate is used for rapidly filling the breathing bag or diluting anesthetic gases.
Question 5: A sevoflurane vaporizer can accurately deliver the dose of an anesthetic agent. This accuracy depends on which of the following properties of the anesthetic agent?
- A. Vapor pressure (Correct Answer)
- B. Blood gas partition coefficient
- C. Molecular weight
- D. Oil gas partition coefficient
Explanation: ***Vapor pressure*** - Sevoflurane vaporizers are designed to deliver a specific concentration of anesthetic gas by controlling the amount of carrier gas (**oxygen** or **air**) that flows over or through a liquid anesthetic. - The precise control relies on the **vapor pressure** of the liquid anesthetic, which determines how much vapor is formed at a given temperature. *Blood gas partition coefficient* - The **blood gas partition coefficient** describes the solubility of an anesthetic in blood relative to inspired gas, influencing the **speed of onset** and **recovery**. - It does not directly affect the vaporizer's ability to accurately deliver a set concentration of anesthetic from the liquid state. *Molecular weight* - **Molecular weight** is important for the physical properties of the anesthetic, but it does not directly determine the accuracy of vapor delivery by the vaporizer. - While it plays a role in diffusion, the vaporizer's function is primarily driven by vapor pressure and flow dynamics. *Oil gas partition coefficient* - The **oil gas partition coefficient** indicates the solubility of an anesthetic in fat, reflecting its **potency** and distribution into fatty tissues. - This coefficient influences the **pharmacodynamics** and tissue distribution of the anesthetic but has no direct bearing on the accuracy of the vaporizer's output of a specific vapor concentration.
Question 6: Gas cylinder with single pin index ?
- A. Nitrogen
- B. Oxygen
- C. Entonox (Correct Answer)
- D. Air
Explanation: **Entonox** - Entonox cylinders have a unique **single pin index** safety system to prevent accidental connection to incorrect gas lines. - This distinct pin configuration ensures the delivery of the correct 50% nitrous oxide and 50% oxygen mixture. *Nitrogen* - Nitrogen cylinders typically use a **double pin index** system (7-2 configuration) for connection. - This gas is primarily used for powering surgical equipment and is not a breathing gas. *Oxygen* - Oxygen cylinders are easily identifiable by their **white colour** and use a **double pin index** system (2-5 configuration) for connection. - This prevents interchangeability with other medical gases that have different pin configurations. *Air* - Medical air cylinders are grey and white and use a **double pin index** safety system (1-5 configuration). - This ensures only medical air is connected and used for patient ventilation or nebulization.
Question 7: 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 8: All of the following are used to maintain proper oxygen flow to the patient except:
- A. Different pin index for nitrogen and oxygen (Correct Answer)
- B. A proportioner between N₂ and O₂ control valves
- C. Calibrated oxygen concentration analyzers
- D. Placement of oxygen flowmeter downstream of the nitrogen flowmeter
Explanation: ***Different pin index for nitrogen and oxygen*** - Oxygen and nitrogen *do not* use pin index safety systems; the **Pin Index Safety System (PISS)** is used for small gas cylinders to prevent wrong gas connection, but nitrogen is a non-medical gas. - While medical gases have specific pin index patterns, this system is for preventing inadvertent connection of gas cylinders to the wrong yoke, not for *maintaining proper oxygen flow to the patient* from the anesthesia machine's internal system. *A proportioner between N₂ and O₂ control valves* - This device, such as the **Ohio proportioner** or **Link 25 system**, mechanically or pneumatically links the **nitrous oxide (N₂O)** and **oxygen (O₂)** flow controls. - It ensures that the inspired oxygen concentration never falls below a preset safe level, typically 25%, thereby **preventing hypoxic gas mixtures**. *Calibrated oxygen concentration analyzers* - **Oxygen analyzers** continuously monitor the inspired oxygen concentration and provide an audible and visual alarm if the level deviates from the set range. - This serves as a critical safety measure to detect and alert anesthesia providers to **hypoxic gas delivery** or machine malfunctions. *Placement of oxygen flowmeter downstream of the nitrogen flowmeter* - Positioning the **oxygen flowmeter downstream** (closest to the patient) of all other gas flowmeters (e.g., nitrous oxide, air) is a crucial safety feature. - This design ensures that **any leak occurring upstream** of the oxygen flow tube will primarily affect other gases, reducing the risk of an **undetected hypoxic mixture** reaching the patient.
Question 9: 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 10: A 40–year female has to undergo incisional hernia surgery under general anaesthesia. She complains of awareness during her past cesarean section. Which of the following monitoring techniques can be used to prevent such awareness ?
- A. Color doppler
- B. Transesophageal echocardiography
- C. Bispectral index monitoring (Correct Answer)
- D. Pulse plethysmography
Explanation: ***Bispectral index monitoring*** - **Bispectral Index (BIS) monitoring** is a technology that processes electroencephalogram (EEG) signals to provide a numerical value (0-100) indicating the patient's **level of consciousness or depth of anesthesia**. - A lower BIS value (typically 40-60) indicates a suitable depth of anesthesia for surgery, helping to prevent **intraoperative awareness**, especially in patients with a history of it. *Color doppler* - **Color Doppler** is an imaging technique used to visualize blood flow in vessels and assess the speed and direction of flow. - It is primarily used to diagnose conditions like **deep venous thrombosis**, *arterial stenosis*, or to evaluate blood flow to organs, and has no direct role in monitoring depth of anesthesia. *Transesophageal echocardiography* - **Transesophageal echocardiography (TEE)** is an invasive imaging technique that uses ultrasound from a probe inserted into the esophagus to provide detailed images of the heart. - TEE is critical for assessing **cardiac function**, *valvular heart disease*, or *aortic dissection* during surgery, but it does not monitor brain activity or the depth of anesthesia. *Pulse plethysmography* - **Pulse plethysmography** is a non-invasive method that measures changes in blood volume in a part of the body, often used to determine **heart rate** and assess peripheral perfusion. - While it is a component of pulse oximetry, it does not provide information about the **depth of anesthesia** or brain activity.
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