Respiratory and Airway Management Practice Questions

Q: Which statement best describes high air flow oxygen enriched (HiAFOE) devices?

They deliver constant concentrations of oxygen.. ### Explanation **High Air Flow Oxygen Enriched (HiAFOE)** devices, most commonly represented by the **Venturi mask**, are classified as **fixed performance devices**. **1. Why Option B is Correct:** The core principle of HiAFOE devices is that they provide a **total gas flow** (oxygen + entrained room air) that meets or exceeds the patient’s peak inspiratory flow rate (typically >30 L/min). Because the device provides the entire inspired atmosphere, the fraction of inspired oxygen (**FiO₂**) remains **constant and predictable**, regardless of the patient’s respiratory rate, tidal volume, or inspiratory flow pattern. **2. Why the Other Options are Incorrect:** * **Option A:** Variable performance devices (e.g., nasal cannulas, simple face masks) deliver FiO₂ that fluctuates based on the patient's breathing pattern. HiAFOE devices are the opposite; they are **fixed performance**. * **Option C:** These devices utilize **air entrainment** (Bernoulli’s principle/Venturi effect) where high-velocity oxygen draws in room air. They do not "entrain oxygen"; they entrain air to dilute a pure oxygen source to a specific concentration. * **Option D:** They require **open (loose-fitting) masks** with large exhalation ports. Since the device provides the total flow required, a tight seal is unnecessary and would interfere with the washout of expired CO₂. **High-Yield Clinical Pearls for NEET-PG:** * **Bernoulli Principle:** The pressure drop across a narrowing allows for air entrainment. * **COPD Patients:** HiAFOE/Venturi masks are the **gold standard** for patients with Type 2 Respiratory Failure (COPD) because they prevent the delivery of excessive oxygen, which could otherwise abolish the hypoxic respiratory drive. * **Color Coding:** Venturi valves are color-coded for specific FiO₂ (e.g., Blue = 24%, White = 28%, Yellow = 35%, Red = 40%, Green = 60%).

Q: What combination of gases is used to prevent combustion during anesthesia?

O2 25% & He 75%. **Explanation:** The risk of airway fires is a critical concern in anesthesiology, particularly during laser surgeries of the airway (e.g., vocal cord procedures). Combustion requires three elements: an ignition source (laser), fuel (endotracheal tube), and an oxidizer. **Why Option C is Correct:** Helium (He) is an inert, non-flammable gas. When mixed with Oxygen (O2), it creates **Heliox**. A mixture of **25% O2 and 75% Helium** is used because it significantly reduces the concentration of the oxidizer (Oxygen) below the threshold required to support combustion. Furthermore, Helium has high thermal conductivity, which helps dissipate heat from the laser, and low density, which improves laminar flow through narrowed airways. **Why Other Options are Incorrect:** * **Options A, B, and D:** These involve **Nitrous Oxide (N2O)**. While N2O is not flammable itself, it is a potent **oxidizer** that supports combustion just as vigorously as oxygen. In the presence of an ignition source, N2O breaks down to release oxygen, intensifying any fire. Therefore, N2O must be strictly avoided during laser airway surgery. **High-Yield Clinical Pearls for NEET-PG:** * **FiO2 Management:** During laser surgery, the Fraction of Inspired Oxygen (FiO2) should be kept at the lowest possible level (usually **<30%**) to prevent ignition. * **Laser-Safe Tubes:** Use specially wrapped or metallic endotracheal tubes (e.g., Mallinckrodt Laser-Flex). * **Cuff Protection:** Fill the ET tube cuff with **saline dyed with methylene blue**. The saline acts as a heat sink, and the blue dye serves as an immediate visual indicator if the cuff is punctured by the laser. * **Initial Step in Airway Fire:** Immediately stop ventilation, disconnect the circuit, and remove the endotracheal tube.

Q: Which of the following describes a time-sparing method of preoxygenation?

Four vital capacity breaths in 30 seconds.. **Explanation:** Preoxygenation (denitrogenation) aims to replace the nitrogen in the functional residual capacity (FRC) with oxygen, creating an oxygen reservoir to delay desaturation during apnea. **Why Option A is Correct:** The standard method of preoxygenation is tidal volume breathing (TVB) of 100% oxygen for 3 minutes. However, in emergency or "time-sparing" scenarios, the **Four Vital Capacity (VC) breaths over 30 seconds** technique is used. This method utilizes deep, maximal inspirations to rapidly wash out nitrogen. Studies show that 4 VC breaths provide an arterial oxygen tension ($PaO_2$) comparable to 3 minutes of TVB, making it the gold-standard rapid technique for clinical practice. **Why Other Options are Incorrect:** * **Option B:** While eight VC breaths over 60 seconds provide a slightly higher margin of safety (longer time to desaturation) than four breaths, it is not the classic "time-sparing" definition taught for exams. Four breaths is the minimum threshold for rapid effectiveness. * **Option C:** Two VC breaths are insufficient to achieve adequate denitrogenation of the FRC, leaving the patient at risk for rapid desaturation during induction. **High-Yield Clinical Pearls for NEET-PG:** * **Goal:** To increase the "Duration of Apnea without Desaturation" (DAWD). * **The Reservoir:** The FRC acts as the primary oxygen store (approx. 2500 mL in adults). * **Efficacy:** 3 minutes of TVB is still superior to 4 VC breaths in terms of the duration of the "safety margin" before the $SpO_2$ drops below 90%. * **Special Populations:** In obese patients or pregnant women, FRC is decreased; therefore, preoxygenation is less effective and desaturation occurs much faster.

Q: What is the appropriate size of a tracheal tube for a newborn weighing 2.5 kg?

3.0. The selection of an endotracheal tube (ETT) in neonates is primarily based on **gestational age and birth weight**, as the subglottic region (the narrowest part of the pediatric airway) must be protected from trauma while ensuring adequate ventilation. ### **Explanation of the Correct Answer** For a newborn weighing **2.5 kg**, the standard recommendation is a **3.0 mm ID (Internal Diameter)** uncuffed tube. * **The Rule of Thumb:** * 2 kg: 3.0 to 3.5 mm Since 2.5 kg falls into the healthy term/near-term category, 3.0 mm is the most appropriate starting size to avoid mucosal ischemia and post-extubation stridor. ### **Analysis of Incorrect Options** * **A. 2.0:** This size is too small for a 2.5 kg infant. It would significantly increase airway resistance and work of breathing. It is typically reserved for extremely premature neonates ( 1 year):** * Uncuffed: $(Age / 4) + 4$ * Cuffed: $(Age / 4) + 3.5$ 2. **Depth of Insertion (Lip to Tip):** A quick bedside guide for neonates is **6 + weight in kg**. For this 2.5 kg baby, the depth would be ~8.5 cm. 3. **Narrowest Part of Airway:** In children, it is the **Cricoid Cartilage** (funnel-shaped airway), whereas in adults, it is the **Glottis/Vocal Cords** (cylindrical). 4. **Straight Blades (Miller):** Preferred in neonates because the epiglottis is long, stiff, and U-shaped (omega-shaped).

Q: Which of the following parameters are adjusted to maintain optimum oxygenation?

PEEP and FiO2. In mechanical ventilation, it is crucial to distinguish between parameters that affect **oxygenation** (getting $O_2$ into the blood) and those that affect **ventilation** (removing $CO_2$ from the blood). ### Why PEEP and $FiO_2$ are Correct Oxygenation is primarily determined by the **Mean Airway Pressure (mPaw)** and the **Fraction of Inspired Oxygen ($FiO_2$)**. * **$FiO_2$:** Increasing the concentration of oxygen in the inspired gas directly increases the partial pressure of oxygen in the alveoli. * **PEEP (Positive End-Expiratory Pressure):** PEEP prevents alveolar collapse at the end of expiration (recruitment). This increases the functional residual capacity (FRC) and the surface area available for gas exchange, thereby improving oxygenation and reducing shunting. ### Why Other Options are Incorrect * **Tidal Volume (TV) and Respiratory Rate (RR):** These are the primary determinants of **Minute Ventilation** ($MV = TV \times RR$). Adjusting these parameters primarily affects the elimination of $CO_2$. Increasing them will lower $PaCO_2$ (causing respiratory alkalosis), but has a negligible direct effect on $PaO_2$. * **Options A, C, and D** are incorrect because they include at least one "ventilation" parameter (TV or RR) rather than focusing purely on "oxygenation" parameters. ### High-Yield Clinical Pearls for NEET-PG * **The "Oxygenation" Rule:** To improve $PaO_2$, increase $FiO_2$ or PEEP. * **The "Ventilation" Rule:** To decrease $PaCO_2$, increase Tidal Volume or Respiratory Rate. * **I:E Ratio:** Increasing the Inspiratory time (Inversed Ratio Ventilation) can also improve oxygenation by increasing the mean airway pressure. * **Toxicity Limit:** While increasing $FiO_2$ is the fastest way to improve oxygenation, $FiO_2 > 0.6$ for prolonged periods can lead to absorption atelectasis and free radical oxygen toxicity. Therefore, PEEP is often increased to allow for a reduction in $FiO_2$.

Question 1

With a fixed performance mask such as a Venturi mask, which of the following is true?

Accepted Answer

Total gas flow is higher than the patient’s peak inspiratory flow.

Answer

Rebreathing is possible.

Answer

Plugging the side holes increases the oxygen concentration.

Answer

There is high equipment dead space.

Question 2

Blind nasal intubation is not indicated in which of the following conditions?

Accepted Answer

Basilar skull fracture

Answer

Temporomandibular joint ankylosis

Answer

Impossible laryngoscopy

Answer

Cerebrospinal fluid otorrhea

Question 3

Which statement best describes high air flow oxygen enriched (HiAFOE) devices?

Accepted Answer

They deliver constant concentrations of oxygen.

Answer

They are variable performance devices.

Answer

They require oxygen entrainment.

Answer

They require closed face masks.

Question 4

What combination of gases is used to prevent combustion during anesthesia?

Accepted Answer

O2 25% & He 75%

Answer

O2 25% & N2O 75%

Answer

O2 50% & N2O 50%

Answer

O2 75% & N2O 25%

Question 5

During rapid induction of anesthesia, which of the following is true?

Accepted Answer

Pre-oxygenation is mandatory

Answer

Sellick's maneuver is not required

Answer

Suxamethonium is contraindicated

Answer

The patient is mechanically ventilated before endotracheal intubation

Question 6

Sustained high inspiratory pressures during positive-pressure ventilation increase the risk of?

Accepted Answer

Barotrauma

Answer

Hypoventilation

Answer

Hypoxia

Answer

Hyperventilation

Question 7

Atropine should never be administered when the patient is cyanosed due to the danger of:

Accepted Answer

Respiratory arrest

Answer

Cerebral edema

Answer

Ventricular fibrillation

Answer

None of the above

Question 8

Which of the following describes a time-sparing method of preoxygenation?

Accepted Answer

Four vital capacity breaths in 30 seconds.

Answer

Eight vital capacity breaths in 1 minute.

Answer

Two vital capacity breaths.

Answer

None of the above.

Question 9

What is the appropriate size of a tracheal tube for a newborn weighing 2.5 kg?

Accepted Answer

3.0

Answer

2.0

Answer

4.0

Answer

5.0

Question 10

Which of the following parameters are adjusted to maintain optimum oxygenation?

Accepted Answer

PEEP and FiO2

Answer

Tidal volume and PEEP

Answer

FiO2 and respiratory rate

Answer

Respiratory rate and tidal volume

Respiratory and Airway Management — MCQs

Respiratory and Airway Management — MCQs

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