Respiratory and Airway Management — MCQs

A 79-year-old ventilator-dependent male with encephalopathy undergoes an uneventful tracheotomy. After several spontaneous breaths, the patient stops breathing. The anesthesiologist assists ventilation for several minutes, after which the patient again breathes spontaneously. What is the most likely cause of the apnea?

Respiratory and Airway Management Indian Medical PG Practice Questions and MCQs

Question 71: The Heimlich maneuver is indicated for which of the following conditions?

A. Near drowning
B. Wet drowning
C. Choking (Correct Answer)
D. Gagging

Explanation: **Explanation:** The **Heimlich maneuver** (abdominal thrusts) is the standard emergency procedure used to relieve **Choking** caused by a foreign body airway obstruction (FBAO). **Why Choking is Correct:** The physiological basis of the Heimlich maneuver is the **artificial cough**. By applying quick, upward thrusts to the abdomen (between the umbilicus and xiphoid process), the diaphragm is elevated. This increases intrathoracic pressure and compresses the lungs, forcing the residual volume of air out through the trachea. This sudden bolus of air acts like a piston to dislodge and expel the obstructing object. **Why Other Options are Incorrect:** * **Near Drowning/Wet Drowning:** Current ILCOR and AHA guidelines strictly contraindicate the Heimlich maneuver for drowning. It does not remove aspirated water (which is quickly absorbed into the circulation) and significantly increases the risk of vomiting and aspiration of gastric contents, which can worsen the prognosis. * **Gagging:** This is a protective reflex (Gag reflex) mediated by the glossopharyngeal (afferent) and vagus (efferent) nerves. As long as the patient can cough or gag effectively, the airway is only partially obstructed, and manual maneuvers are not indicated as they may shift the object into a total obstruction. **Clinical Pearls for NEET-PG:** * **Universal Sign of Choking:** The victim clutching their neck with both hands. * **Special Populations:** For **pregnant women** or **morbidly obese** patients, perform **chest thrusts** instead of abdominal thrusts. * **Infants (<1 year):** Abdominal thrusts are contraindicated due to the risk of liver injury. Use a combination of **5 back blows and 5 chest thrusts**. * **Unconscious Patient:** If a choking victim becomes unconscious, start **CPR** immediately; do not continue abdominal thrusts.

Question 72: What is the approximate oxygen concentration provided by mouth-to-mouth respiration?

A. 16% (Correct Answer)
B. 20%
C. 22%
D. 24%

Explanation: **Explanation:** The correct answer is **16%**. This question tests the understanding of the composition of exhaled air during basic life support (BLS). **1. Why 16% is correct:** Atmospheric air contains approximately **21% oxygen**. When a healthy person inhales, the body utilizes only a fraction of this oxygen. Under normal physiological conditions, the body extracts about 4–5% of the inspired oxygen for metabolic processes. Consequently, the air exhaled by the rescuer during mouth-to-mouth ventilation contains approximately **16–17% oxygen** and about 4% carbon dioxide. This concentration is sufficient to maintain life and provide adequate oxygenation to the victim's tissues during emergency resuscitation until advanced equipment arrives. **2. Why the other options are incorrect:** * **20% & 22%:** These values are too high. 21% is the concentration of ambient (room) air. Since the rescuer’s body consumes oxygen, the exhaled air cannot have a concentration nearly equal to or higher than room air. * **24%:** This is the typical FiO₂ provided by a Venturi mask at a low flow rate (2L/min). It is impossible to achieve this via expired air without supplemental oxygen. **Clinical Pearls for NEET-PG:** * **FiO₂ of Room Air:** 21% (0.21). * **Mouth-to-Mask Ventilation:** If the rescuer uses a pocket mask with supplemental oxygen at 10–15 L/min, the FiO₂ can increase to approximately **50%**. * **Ambu Bag (Self-inflating bag):** Provides **21%** (room air), **40%** (with oxygen but no reservoir), and **90–100%** (with oxygen at 15 L/min and a reservoir bag). * **Expired Air CO₂:** Exhaled air contains roughly **4% CO₂**, which is why capnography is the gold standard for confirming tracheal intubation.

Question 73: All of the following are criteria for weaning a patient from mechanical ventilation, except?

A. Vital capacity: >10 mL/kg
B. Tidal volume: 4-6 mL/kg
C. Minute ventilation: <10 L/min
D. Rapid shallow breathing index: <120 (Correct Answer)

Explanation: **Explanation:** The goal of weaning is to transition a patient from mechanical support to spontaneous breathing. The correct answer is **D** because the threshold for the **Rapid Shallow Breathing Index (RSBI)** is typically **<105**, not <120. **1. Why Option D is the correct answer (The Exception):** The RSBI (calculated as Respiratory Rate / Tidal Volume in Liters) is the most predictive index for weaning success. A value **<105** indicates that the patient can sustain spontaneous ventilation without fatigue. A value of 120 is too high and is often associated with weaning failure due to rapid, inefficient breathing. **2. Analysis of Incorrect Options (Standard Weaning Criteria):** * **Option A (Vital Capacity >10 mL/kg):** This measures the patient's reserve and ability to take a deep breath (important for coughing and clearing secretions). A value >10-15 mL/kg is a standard positive predictor. * **Option B (Tidal Volume 4-6 mL/kg):** An adequate spontaneous tidal volume ensures sufficient alveolar ventilation. Values in this range indicate the patient is not taking dangerously shallow breaths. * **Option C (Minute Ventilation <10 L/min):** If a patient requires >10 L/min to maintain normal CO2 levels, they are likely to fatigue quickly once disconnected from the ventilator. **High-Yield Clinical Pearls for NEET-PG:** * **RSBI (Yang and Tobin Index):** The most reliable predictor. Formula: $f / V_T$. * **Maximum Inspiratory Pressure (MIP/NIF):** Should be more negative than **-20 to -30 cm H2O**. * **PaO2/FiO2 Ratio:** Should be **>150–200** with PEEP ≤ 5–8 cm H2O. * **Spontaneous Breathing Trial (SBT):** The "gold standard" diagnostic test for weaning, usually performed via T-piece or low-level Pressure Support (PSV).

Question 74: Pre-oxygenation is done to achieve what physiological goal?

A. Increase the oxygen content of the functional residual capacity (FRC)
B. Decrease the nitrogen content of the functional residual capacity (FRC)
C. Both of the above (Correct Answer)
D. None of the above

Explanation: **Explanation:** Pre-oxygenation (also known as denitrogenation) is a critical step before the induction of anesthesia to provide a safety buffer during periods of apnea (e.g., during intubation). **Why Option C is Correct:** The primary physiological goal of pre-oxygenation is to maximize the oxygen reservoir in the lungs. This reservoir is located in the **Functional Residual Capacity (FRC)**. 1. **Denitrogenation:** Room air consists of approximately 78% nitrogen. By breathing 100% oxygen, the nitrogen in the FRC is "washed out" and replaced by oxygen. 2. **Oxygen Enrichment:** This process increases the fraction of alveolar oxygen ($FiO_2$) from 0.21 to nearly 1.0. By simultaneously **decreasing nitrogen** and **increasing oxygen content** in the FRC, the duration of "safe apnea time" (the time until hemoglobin saturation falls below 90%) is significantly extended—from about 1–2 minutes to up to 8 minutes in a healthy adult. **Why Other Options are Incorrect:** * **Options A and B** are individually correct but incomplete. Pre-oxygenation is a dual process; you cannot increase the partial pressure of oxygen in a fixed volume (FRC) without displacement of the existing nitrogen. Therefore, "Both of the above" is the most accurate physiological description. **High-Yield Clinical Pearls for NEET-PG:** * **Standard Technique:** Breathing 100% $O_2$ for 3 minutes at normal tidal volume or taking 4–8 deep vital capacity breaths over 30–60 seconds. * **The Reservoir:** The FRC is the most important oxygen store in the body (approx. 2500 mL in adults). * **Reduced Safe Apnea Time:** Expect faster desaturation in obese patients, pregnant women, and children due to a **decreased FRC** and/or increased metabolic rate. * **End-point:** Pre-oxygenation is considered adequate when the **End-Tidal Oxygen ($EtO_2$)** reaches approximately 90% or the **End-Tidal Nitrogen ($EtN_2$)** is less than 5%.

Question 75: All are true about the dosing of succinylcholine EXCEPT:

A. In adults, a dose of 1.0 mg/kg body weight can yield intubating conditions.
B. Children are resistant to succinylcholine, so between 1 to 2 mg/kg is required.
C. In infants, the dose is between 2-3 mg/kg.
D. In obese patients, the dose is calculated according to lean body weight. (Correct Answer)

Explanation: **Explanation:** Succinylcholine (Suxamethonium) is a depolarizing neuromuscular blocker characterized by its rapid onset and short duration. The dosing of succinylcholine is unique because it is primarily metabolized by **pseudocholinesterase (plasma cholinesterase)**. **1. Why Option D is the Correct Answer (The False Statement):** In obese patients, the dose of succinylcholine should be calculated based on **Total Body Weight (TBW)**, not lean body weight. This is because both the extracellular fluid volume and, more importantly, the **pseudocholinesterase activity** increase in proportion to total body weight. Using lean body weight in obese patients would lead to under-dosing and suboptimal intubating conditions. **2. Analysis of Other Options:** * **Option A:** In adults, the standard intubating dose is **1.0–1.5 mg/kg**, which typically provides excellent relaxation within 60 seconds. * **Options B & C:** Infants and children have a **larger volume of distribution** for water-soluble drugs like succinylcholine (due to a higher percentage of extracellular fluid). Consequently, they require higher weight-based doses. Infants typically require **2–3 mg/kg**, while children require **1–2 mg/kg**. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Still considered the gold standard for **Rapid Sequence Induction (RSI)** due to its unmatched speed of onset. * **Pre-treatment:** To prevent fasciculations, a small dose of a non-depolarizing agent (1/10th dose) can be used, but this necessitates increasing the succinylcholine dose to ~1.5 mg/kg. * **Black Box Warning:** Avoid in children for routine intubation due to the risk of undiagnosed myopathies (e.g., Duchenne) leading to **hyperkalemic cardiac arrest**. * **Storage:** Should be stored at **2–8°C** to maintain potency.

Question 76: A 33-year-old woman is brought to the emergency room following a severe motor vehicle accident. She is combative, confused, uncooperative, and appears dusky and dyspneic. Which of the following is the most appropriate management of her airway?

A. Awake endotracheal intubation is indicated in patients with penetrating ocular injury.
B. Steroids have been shown to be of value in the treatment of aspiration of acidic gastric secretions.
C. The stomach may be assumed to be empty only if a history is obtained indicating no ingestion of food or liquid during the prior 8 hours.
D. Intubation should be performed as soon as possible (in the emergency room) if the patient is unstable. (Correct Answer)

Explanation: **Explanation:** The patient presents with signs of **impending respiratory failure** (duskiness, dyspnea) and **altered mental status** (combative, confused) following trauma. In the setting of hemodynamic or respiratory instability, securing the airway is the absolute priority. **1. Why Option D is Correct:** In an unstable trauma patient, the "ABC" (Airway, Breathing, Circulation) protocol dictates immediate airway stabilization. A combative, dusky patient likely has hypoxia or hypercapnia, and delay in intubation increases the risk of cardiac arrest. Intubation should be performed in the ER using **Rapid Sequence Induction (RSI)** to secure the airway quickly while minimizing the risk of aspiration. **2. Why the other options are incorrect:** * **Option A:** Awake intubation is generally **contraindicated** in penetrating ocular injuries because the associated coughing, gagging, and struggling can acutely increase intraocular pressure, leading to extrusion of vitreous humor. * **Option B:** While once common, clinical evidence shows that **steroids are not beneficial** in treating aspiration pneumonitis (Mendelson’s syndrome). Management is primarily supportive (suctioning, oxygenation, and PEEP). * **Option C:** In trauma, the stomach is **always assumed to be full**, regardless of the last meal. Pain, anxiety, and opioids significantly delay gastric emptying. The "8-hour rule" does not apply to emergency trauma management. **Clinical Pearls for NEET-PG:** * **Mendelson’s Syndrome:** Aspiration of gastric contents with pH <2.5 and volume >0.4 mL/kg (25 mL). * **RSI Components:** Pre-oxygenation, cricoid pressure (Sellick’s maneuver), and a rapid-acting induction agent plus a neuromuscular blocker (usually Succinylcholine or Rocuronium). * **Airway Priority:** In trauma, assume a cervical spine injury; use **Manual In-Line Stabilization (MILS)** during intubation.

Question 77: Which manuever helps to improve laryngoscopic view?

A. Decrease risk of aspiration
B. Improve laryngoscopic view (Correct Answer)
C. Open the airway
D. Stabilize ET tube position

Explanation: The question refers to the **BURP maneuver** (Backward, Upward, Rightward Pressure) or **OELM** (Optimal External Laryngeal Manipulation). These maneuvers are specifically designed to bring the glottic opening into the line of sight during direct laryngoscopy. ### **Explanation of Options** * **B. Improve laryngoscopic view (Correct):** By applying external pressure on the thyroid cartilage, the larynx is displaced posteriorly and superiorly. This aligns the oral, pharyngeal, and laryngeal axes more effectively, moving the vocal cords into the laryngoscopist's field of vision (improving the Cormack-Lehane grade). * **A. Decrease risk of aspiration:** This describes **Sellick’s Maneuver** (Cricoid Pressure). While it also involves external pressure, it specifically targets the cricoid cartilage to occlude the esophagus. It is used in Rapid Sequence Induction (RSI) but can actually worsen the laryngoscopic view. * **C. Open the airway:** Basic maneuvers like the **Head Tilt-Chin Lift** or **Jaw Thrust** are used to relieve functional airway obstruction (tongue falling back) in a spontaneous breathing patient, but they do not specifically "improve the view" during the act of laryngoscopy. * **D. Stabilize ET tube position:** This is typically achieved through taping, commercial tube holders, or inflammatory cuff inflation, not by laryngeal manipulation maneuvers. ### **High-Yield Clinical Pearls for NEET-PG** * **BURP Maneuver:** Backward, Upward, Rightward Pressure on the **thyroid cartilage**. * **Cormack-Lehane Classification:** Used to grade the laryngoscopic view (Grade I: Full view of glottis; Grade IV: Neither glottis nor epiglottis seen). * **Sniffing Position:** Achieved by flexion of the neck and extension at the atlanto-occipital joint; it is the optimal position for laryngoscopy as it aligns the three axes. * **Difference:** Remember, **Sellick's** is for safety (aspiration), while **BURP** is for visibility (intubation).

Question 78: Which neuromuscular blocking agent has a duration of onset of action less than 2 minutes?

A. D-tubocurarine
B. Succinylcholine (Correct Answer)
C. Pancuronium
D. Gallamine

Explanation: **Explanation:** The duration of onset of a neuromuscular blocking agent (NMBA) is the time from drug administration to maximum suppression of neuromuscular transmission. **1. Why Succinylcholine is correct:** Succinylcholine is the only **depolarizing** neuromuscular blocker used clinically. It has the fastest onset of action among all NMBAs, typically occurring within **30–60 seconds**. This rapid onset is due to its mechanism of mimicking acetylcholine at the nicotinic receptors and its high bioavailability at the motor endplate. It is the gold standard for **Rapid Sequence Induction (RSI)** where securing the airway quickly is critical. **2. Why the other options are incorrect:** * **D-tubocurarine:** A long-acting non-depolarizing NMBA with a slow onset of action (3–5 minutes). It is largely obsolete in modern anesthesia due to significant histamine release. * **Pancuronium:** A long-acting non-depolarizing steroid-based NMBA. It has an onset of action of approximately 3–5 minutes. * **Gallamine:** A long-acting non-depolarizing agent with an onset of 3–5 minutes. It is rarely used today due to its potent vagolytic (tachycardic) effects. **Clinical Pearls for NEET-PG:** * **Rocuronium** is the non-depolarizing NMBA with the fastest onset (60–90 seconds), making it the alternative to Succinylcholine for RSI when the latter is contraindicated. * **Metabolism:** Succinylcholine is metabolized by **pseudocholinesterase** (plasma cholinesterase). * **Key Side Effects of Succinylcholine:** Fasciculations, hyperkalemia (avoid in burns/trauma), muscle ache, and it is a known trigger for **Malignant Hyperthermia**.

Question 79: Which of the following endotracheal tubes features a high-pressure, low-volume cuff?

A. Red rubber tube
B. RAE tube
C. Laser tube (Correct Answer)
D. Microlaryngeal tube

Explanation: **Explanation:** The correct answer is **C. Laser tube**. **Understanding the Concept:** Endotracheal tube (ETT) cuffs are generally classified into two types: High-Volume Low-Pressure (HVLP) and **Low-Volume High-Pressure (LVHP)**. * **HVLP cuffs** (standard PVC tubes) have a large surface area, minimizing pressure on the tracheal mucosa to prevent ischemia. * **LVHP cuffs** have a small surface area and require high internal pressure to create a seal. **Laser-resistant tubes** (e.g., stainless steel or specialized foil-wrapped tubes) utilize LVHP cuffs because they are typically made of thicker, less compliant materials designed to withstand laser strikes. A smaller, high-pressure cuff reduces the "target area" for the laser and is often filled with saline (plus methylene blue) to act as a heat sink and provide a visual cue if the cuff is punctured. **Analysis of Incorrect Options:** * **Red rubber tube:** These are reusable tubes that traditionally featured low-volume, high-pressure cuffs. However, in modern practice and standard NEET-PG contexts, the **Laser tube** is the classic example cited for this cuff profile due to its specific design requirements. * **RAE tube (Ring-Adair-Elwyn):** These are pre-formed tubes used in oral/nasal surgeries. They are made of PVC and feature standard **HVLP** cuffs. * **Microlaryngeal tube (MLT):** These are used for laryngeal surgeries. They have a small external diameter but a **large-diameter HVLP cuff** to ensure a seal in an adult trachea despite the narrow tube. **High-Yield Facts for NEET-PG:** * **Ideal Cuff Pressure:** 20–30 cm H₂O. Pressures >30 cm H₂O compromise tracheal capillary perfusion, leading to mucosal ischemia and stenosis. * **Laser Safety:** If a laser tube cuff is punctured, the methylene blue-tinted saline alerts the surgeon immediately. * **Most common ETT material:** Polyvinyl chloride (PVC).

Question 80: A 79-year-old ventilator-dependent male with encephalopathy undergoes an uneventful tracheotomy. After several spontaneous breaths, the patient stops breathing. The anesthesiologist assists ventilation for several minutes, after which the patient again breathes spontaneously. What is the most likely cause of the apnea?

A. A mucus plug blocked the tracheotomy tube.
B. Bleeding in the trachea.
C. Preoperative respiration was driven by hypoxia. (Correct Answer)
D. The patient was allergic to latex.

Explanation: **Explanation:** The correct answer is **C: Preoperative respiration was driven by hypoxia.** **Mechanism:** In patients with chronic respiratory failure or prolonged ventilator dependence (as seen in this 79-year-old patient), the central chemoreceptors often become desensitized to high levels of carbon dioxide ($CO_2$). Consequently, the primary stimulus for breathing shifts from hypercapnia to **hypoxemia** (low $O_2$), sensed by peripheral chemoreceptors. This is known as the **Hypoxic Drive**. When a tracheotomy is performed, the anatomical dead space is reduced, and the efficiency of oxygenation and ventilation increases significantly. The sudden rise in arterial oxygen tension ($PaO_2$) and the rapid washout of $CO_2$ remove the patient’s only remaining stimulus to breathe, leading to **apnea**. Once the anesthesiologist assists ventilation and $O_2$ levels stabilize or $CO_2$ slightly rises again, the drive may return. **Analysis of Incorrect Options:** * **A & B (Mucus plug/Bleeding):** While these are common tracheotomy complications, they typically cause **respiratory distress, stridor, or high airway pressures**, rather than sudden apnea followed by a return to spontaneous breathing after assisted ventilation. * **D (Latex Allergy):** Anaphylaxis would present with bronchospasm, hypotension, and rashes, not isolated transient apnea. **NEET-PG High-Yield Pearls:** * **Dead Space:** Tracheostomy reduces anatomical dead space by approximately **30–50%**. * **Chemoreceptors:** Central chemoreceptors (medulla) respond to $pH/CO_2$; Peripheral chemoreceptors (carotid/aortic bodies) respond primarily to $PO_2 < 60\ mmHg$. * **Clinical Tip:** Always oxygenate cautiously in "CO2 retainers" to avoid suppressing their hypoxic drive. Post-tracheotomy apnea is a classic board-exam scenario for this physiological shift.

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Respiratory Physiology

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Airway Anatomy

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Preoxygenation Techniques

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Mask Ventilation

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Supraglottic Airway Devices

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Direct Laryngoscopy

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Video Laryngoscopy

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Fiberoptic Intubation

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Surgical Airway Management

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One-Lung Ventilation Techniques

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Ventilation Strategies During Anesthesia

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Extubation Criteria and Techniques

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