Anesthesia Ventilators — 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?
Which of the following statements given below is incorrect regarding CPR?
Which among the following modes of ventilation has the highest risk of a patient developing respiratory alkalosis?
Which of the following parameters is most critical for maintaining optimal oxygenation?
Circuit of choice for controlled ventilation ?
Which of the following is most associated with respiratory alkalosis?
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 ?
During intraoperative period following capnograph waveform is seen. What does it signify.
The most appropriate circuit for ventilating a spontaneously breathing infant during anaesthesia?
Curare notch seen in capnograph is due to
Anesthesia Ventilators 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: Which of the following statements given below is incorrect regarding CPR?
- A. Chest compression rate 100-120/min
- B. Depth of chest compression up to 5-6 cm
- C. Ventilation 22-25/ min (Correct Answer)
- D. Allow adequate chest recoil
Explanation: ***Ventilation 22-25/ min*** - A ventilation rate of 22-25 breaths/min is **too high** for CPR, which typically recommends 10-12 breaths/min, corresponding to 2 breaths after every 30 compressions. - Excessive ventilation can lead to **hyperventilation**, increasing intrathoracic pressure and reducing venous return, thus decreasing cardiac output. *Chest compression rate 100-120/min* - The recommended chest compression rate for adults in CPR is **100-120 compressions per minute**, ensuring adequate blood flow to vital organs. - Maintaining this rate is crucial for maximizing the effectiveness of chest compressions by providing sufficient circulation. *Depth of chest compression up to 5-6 cm* - The recommended depth for adult chest compressions is at least 5 cm (2 inches), but no more than **6 cm (2.4 inches)** to prevent injury. - This depth ensures that enough pressure is exerted to circulate blood effectively without causing excessive trauma. *Allow adequate chest recoil* - Complete chest recoil is essential to allow the heart to **fully refill with blood** between compressions. - Leaning on the chest between compressions prevents adequate recoil, which can reduce pulmonary and coronary perfusion and **decrease the effectiveness of CPR**.
Question 3: Which among the following modes of ventilation has the highest risk of a patient developing respiratory alkalosis?
- A. Assist Control Mode (AC) (Correct Answer)
- B. Controlled Mandatory Ventilation (CMV)
- C. Synchronous Intermittent Mandatory Ventilation (SIMV)
- D. Pressure Control Mode (PCM)
Explanation: ***Assist Control Mode (AC)*** - In AC mode, every patient-initiated breath triggers a **full mandatory breath** from the ventilator, delivering a preset tidal volume or pressure. - If the patient has a high respiratory drive, this can lead to excessive ventilation and a significant decrease in **partial pressure of carbon dioxide (PaCO2)**, causing respiratory alkalosis. *Controlled Mandatory Ventilation (CMV)* - In CMV, the ventilator delivers breaths at a **preset rate and tidal volume**, independent of patient effort. - While it can cause alkalosis if the set rate and volume are too high, it doesn't amplify patient's own respiratory efforts to the same extent as AC mode. *Synchronous Intermittent Mandatory Ventilation (SIMV)* - SIMV delivers **mandatory breaths** at a set rate, but also allows the patient to breathe spontaneously between these breaths. - The patient's spontaneous breaths are *not* assisted by additional ventilator-delivered mandatory breaths, making it less likely to cause hyperventilation compared to AC mode. *Pressure Control Mode (PCM)* - In PCM, the ventilator delivers breaths to a **preset pressure target**, which may be either patient-triggered or time-triggered. - While it offers consistent pressure support, the total minute ventilation is more variable than in AC mode and less likely to consistently lead to excessive minute ventilation unless the pressure settings are extremely high.
Question 4: Which of the following parameters is most critical for maintaining optimal oxygenation?
- A. FiO2
- B. Respiratory rate
- C. PEEP (Correct Answer)
- D. Tidal volume
Explanation: ***PEEP*** - **Positive End-Expiratory Pressure (PEEP)** is crucial for maintaining optimal oxygenation because it prevents **alveolar collapse** at the end of expiration, thereby increasing the **functional residual capacity** and improving gas exchange. - By keeping alveoli open, PEEP increases the number of available alveoli for ventilation, preventing **atelectasis** and optimizing the **venous admixture** from non-ventilated lung units. *FiO2* - While **Fraction of Inspired Oxygen (FiO2)** is essential for providing sufficient oxygen, simply increasing FiO2 without proper alveolar recruitment and patency (often achieved with PEEP) can be less effective and potentially harmful due to **oxygen toxicity**. - High FiO2 can improve oxygenation in cases of **hypoxemia**, but it doesn't address underlying problems like **alveolar collapse** or **ventilation-perfusion mismatch** as directly as PEEP does. *Respiratory rate* - **Respiratory rate** primarily affects **carbon dioxide elimination** (PaCO2) and, to some extent, alveolar ventilation. - While an adequate respiratory rate is necessary for overall gas exchange, it is not the most direct or critical parameter for optimizing **oxygenation** compared to PEEP's role in maintaining alveolar patency. *Tidal volume* - **Tidal volume** also primarily affects **carbon dioxide elimination** and plays a role in overall minute ventilation. - Excessive tidal volume can lead to **ventilator-induced lung injury (VILI)**, while insufficient tidal volume can reduce minute ventilation, but it does not directly optimize oxygenation by preventing **alveolar collapse** in the same way PEEP does.
Question 5: Circuit of choice for controlled ventilation ?
- A. Magill circuit
- B. Type C
- C. Type E
- D. Type D (Correct Answer)
Explanation: **Type D** - The **Type D circuit** (also known as the **Bain circuit** or a modified Mapleson D circuit) is highly efficient for **controlled ventilation** due to its fresh gas flow entering near the patient, effectively sweeping away exhaled gases. - Its design maintains a relatively constant **expiratory resistance**, making it suitable for precise control of ventilation parameters. *Magill circuit* - The **Magill circuit** (Mapleson A) is efficient for **spontaneous ventilation** but requires a high fresh gas flow to prevent rebreathing during controlled ventilation. - During controlled ventilation, a high minute volume is required to flush out expired gases efficiently, which can be wasteful of anesthetic agents. *Type C* - The **Type C circuit** (Mapleson C circuit) is a simple system useful for **resuscitation** and short procedures but is inefficient for prolonged controlled ventilation. - It has a high resistance to gas flow and a tendency for significant rebreathing during both spontaneous and controlled breathing, leading to high CO2 levels. *Type E* - The **Type E circuit** (Mapleson E circuit) is a basic T-piece system, primarily used for **spontaneous breathing in infants and children**. - It lacks a reservoir bag and adjustable pressure limiting valve, making it unsuitable for controlling ventilation effectively in adults.
Question 6: Which of the following is most associated with respiratory alkalosis?
- A. SIMV
- B. Non invasive ventilation
- C. Pressure controlled
- D. Assisted control mode ventilation (Correct Answer)
Explanation: ***Assisted control mode ventilation*** - In **assisted control mode**, every patient effort above a set sensitivity triggers a fully supported breath at the set tidal volume or pressure, leading to the potential for **excessive ventilation** and respiratory alkalosis if the patient's respiratory drive is high. - This mode ensures a **minimum number of breaths** per minute, but also delivers full mechanical breaths for any additional patient-initiated breaths, which can result in **hyperventilation**. *SIMV* - **Synchronized intermittent mandatory ventilation (SIMV)** delivers a set number of mandatory breaths, but patient-initiated breaths between these mandatory breaths are either unsupported or supported at a lower level, making it less prone to causing excessive ventilation and alkalosis compared to AC. - SIMV allows for more patient participation in breathing and is often used to **wean patients off ventilation**, whereas AC prioritizes full ventilatory support. *Non invasive ventilation* - While **non-invasive ventilation (NIV)** can cause respiratory alkalosis if settings are too aggressive, it is generally used to avoid intubation and often allows for more patient control over their breathing pattern than AC, especially in modes like BiPAP where inspiratory and expiratory pressures are set. - The goal of NIV is to provide ventilatory support without an artificial airway, and it can be titrated to prevent both hypoventilation and hyperventilation more easily than the full support of AC. *Pressure controlled* - **Pressure-controlled ventilation** delivers breaths until a set inspiratory pressure is reached, with tidal volume varying based on lung compliance and resistance. While it can cause respiratory alkalosis if the set pressure or respiratory rate is too high, it is a *mode* of ventilation rather than a specific *type* of ventilatory support that inherently overventilates. - It focuses on limiting peak inspiratory pressures to protect the lungs, and can be used in either AC or SIMV modes, making its association with alkalosis dependent on specific settings and patient interaction.
Question 7: 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.
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: The most appropriate circuit for ventilating a spontaneously breathing infant during anaesthesia?
- A. Mapleson A or Magill's circuit
- B. Mapleson C or Waters to and fro canister
- C. Bains circuit
- D. Jackson Rees modification of Ayre's T piece (Correct Answer)
Explanation: ***Jackson Rees modification of Ayre's T piece*** - This circuit is excellent for spontaneously breathing infants due to its **low resistance**, preventing patient fatigue and allowing for easy visualization of respirations. - The Jackson Rees modification adds a **reservoir bag** at the expiratory limb, enabling assisted ventilation and PEEP while still maintaining low dead space. *Mapleson A or Magill's circuit* - The Magill circuit is efficient for **spontaneous ventilation** in adults, but its design leads to significant **dead space** and resistance in infants, making it unsuitable. - In infants, this circuit would lead to **rebreathing of CO2** and increased work of breathing due to the long expiratory limb and dead space. *Mapleson C or Waters to and fro canister* - The Mapleson C circuit has a compact design with a CO2 absorber, but it also has **high resistance** and **high dead space volume** for infants, making it impractical for spontaneous breathing. - The Waters system is a **closed system** primarily used for controlled ventilation and poses a risk of rebreathing CO2 due to its design, which is not ideal for spontaneous breathing. *Bains circuit* - The Bain circuit is a **Mapleson D modification**, which is highly efficient for both spontaneous and controlled ventilation in adults and larger children due to its coaxial design. - While it has low resistance, its **larger internal volume** and potential for rebreathing if fresh gas flow is inadequate make it less ideal than a Jackson Rees for very small infants.
Question 10: 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.
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