Respiratory and Airway Management — MCQs

Respiratory and Airway Management Indian Medical PG Practice Questions and MCQs

Question 131: Which of the following anesthetic agents is known to cause tachypnoea?

A. Ether
B. Halothane
C. Trichloroethylene (Correct Answer)
D. Cyclopropane

Explanation: **Explanation:** The correct answer is **Trichloroethylene (Trilene)**. **1. Why Trichloroethylene is correct:** Trichloroethylene is unique among older volatile anesthetics for its tendency to cause **tachypnoea** (rapid, shallow breathing). This occurs because it sensitizes the **stretch receptors** in the lungs (Hering-Breuer reflex). As the respiratory rate increases, the tidal volume decreases, which can lead to inadequate alveolar ventilation and hypercapnia if not monitored. Additionally, Trichloroethylene is known for its potent analgesic properties but is no longer used due to its potential to react with soda lime to produce toxic **dichloroacetylene**, which can cause cranial nerve palsies (especially the trigeminal nerve). **2. Analysis of Incorrect Options:** * **Ether:** Diethyl ether typically maintains or slightly increases respiratory rate due to sympathetic stimulation and respiratory tract irritation, but it does not characteristically cause the rapid tachypnoea seen with Trichloroethylene. * **Halothane:** Halothane is a potent respiratory depressant. It decreases tidal volume and increases respiratory rate slightly, but its overall effect is a reduction in minute ventilation and a blunting of the response to CO2. * **Cyclopropane:** This agent generally maintains respiration well but can cause a shift toward respiratory depression at deeper planes of anesthesia. It is more famously associated with "cyclopropane shock" and cardiac arrhythmias due to catecholamine sensitization. **3. High-Yield Clinical Pearls for NEET-PG:** * **Trichloroethylene + Soda Lime:** Never use Trilene in a closed circuit; it reacts with soda lime to form **Dichloroacetylene** (neurotoxic) and **Phosgene** (pulmonary toxic). * **Halothane:** Known for "Halothane Hepatitis" and sensitizing the myocardium to catecholamines (arrhythmogenic). * **Ether:** The "safest" for beginners due to its wide therapeutic index, but highly inflammable/explosive.

Question 132: In volume-cycled ventilation, what is the typical inspiratory flow rate set at?

A. 140–160 L/min
B. 110–130 L/min
C. 60–100 L/min (Correct Answer)
D. 30–50 L/min

Explanation: In volume-cycled ventilation (VCV), the **Inspiratory Flow Rate** determines how quickly the preset tidal volume is delivered to the patient. ### **Explanation of the Correct Answer** **Option C (60–100 L/min)** is the standard clinical range for adults. This rate is chosen to balance two critical factors: 1. **Patient Comfort:** A flow rate of 60–100 L/min typically meets or exceeds the peak inspiratory demand of a resting adult, preventing "flow starvation" and reducing the work of breathing. 2. **Gas Distribution:** It allows for a sufficiently short inspiratory time ($T_i$), ensuring an adequate expiratory time ($T_e$) to prevent air trapping (Auto-PEEP), while not being so fast that it causes excessive peak airway pressures. ### **Analysis of Incorrect Options** * **Options A & B (110–160 L/min):** These rates are excessively high. High flow rates increase turbulence and peak inspiratory pressure (PIP), which can lead to barotrauma and uneven gas distribution (Pendelluft phenomenon). * **Option D (30–50 L/min):** These rates are generally too low for adults. Low flow rates prolong the inspiratory phase, which may lead to patient-ventilator asynchrony and inadequate time for exhalation, increasing the risk of CO2 retention. ### **High-Yield Clinical Pearls for NEET-PG** * **Flow Waveform:** In VCV, the flow is usually **constant (square wave)**, whereas in Pressure-Controlled Ventilation (PCV), the flow is **decelerating**. * **I:E Ratio:** The standard ratio is **1:2**. Increasing the flow rate shortens the inspiratory time, thereby increasing the expiratory time. * **Obstructive Airway Disease (COPD/Asthma):** Higher flow rates (closer to 100 L/min) are often preferred to allow for a longer expiratory phase to prevent "stacking" of breaths. * **Peak vs. Plateau Pressure:** High flow rates increase **Peak Pressure** (resistance) but do not affect **Plateau Pressure** (compliance).

Question 133: What is true about endotracheal intubation?

A. It reduces normal anatomical dead space. (Correct Answer)
B. It produces a decrease in resistance to respiration.
C. Subglottic edema is the most common complication.
D. All of the above.

Explanation: **Explanation:** **1. Why Option A is Correct:** Endotracheal intubation involves placing a tube directly into the trachea, bypassing the upper airway structures (nose, mouth, and pharynx). These structures normally constitute a significant portion of the **anatomical dead space** (the volume of air that does not participate in gas exchange). By bypassing these areas, an endotracheal tube (ETT) effectively **reduces anatomical dead space by approximately 30-50%**. This is a high-yield physiological change associated with airway management. **2. Why the Other Options are Incorrect:** * **Option B:** Intubation actually **increases resistance** to respiration. Resistance is inversely proportional to the fourth power of the radius (Poiseuille’s Law). Because an ETT has a smaller internal diameter than the natural human trachea and is longer, it significantly increases the work of breathing compared to natural ventilation. * **Option C:** While subglottic edema is a serious concern (especially in pediatrics), the **most common** complications of intubation are minor traumatic injuries, such as **sore throat**, hoarseness, or minor mucosal trauma. In the long term, tracheal stenosis is a more common structural complication than acute subglottic edema in adults. **Clinical Pearls for NEET-PG:** * **Dead Space:** Tracheostomy reduces anatomical dead space even more than an ETT because the tube is shorter. * **Resistance:** To minimize resistance, always use the largest appropriate ETT size for the patient. * **Murphy’s Eye:** The small hole at the distal end of the ETT is designed to prevent complete airway obstruction if the main tip is occluded by the tracheal wall. * **Confirmation:** The "Gold Standard" for confirming ETT placement is **persistent end-tidal CO2 (Capnography)**.

Question 134: What is the name of the test performed before drawing an arterial blood gas sample?

A. Virchow test
B. Water hammer test
C. Allen test (Correct Answer)
D. Trendelenburg test

Explanation: **Explanation:** The **Allen test** (or Modified Allen test) is a mandatory clinical assessment performed before radial artery cannulation or arterial blood gas (ABG) sampling. **1. Why Allen Test is Correct:** The primary objective is to assess the **patency of the ulnar artery** and the adequacy of **collateral circulation** to the hand via the palmar arch. During the test, both radial and ulnar arteries are compressed while the patient clenches their fist to blanch the palm. Pressure on the ulnar artery is then released. If the palm flushes (reperfuses) within 5–15 seconds, the test is positive, indicating sufficient collateral flow. This ensures that if the radial artery is damaged or thrombosed during the ABG procedure, the hand will not suffer ischemic injury. **2. Analysis of Incorrect Options:** * **Virchow test:** There is no "Virchow test"; however, *Virchow’s Triad* describes the three factors contributing to venous thrombosis (stasis, hypercoagulability, and endothelial injury). * **Water hammer test:** This refers to the assessment of a "Corrigan pulse," a bounding pulse characteristic of **Aortic Regurgitation**. * **Trendelenburg test:** Used in surgery/orthopedics to assess the competency of venous valves in varicose veins or the stability of the hip (gluteus medius strength). **Clinical Pearls for NEET-PG:** * **Gold Standard:** While the Allen test is standard, **Doppler ultrasound** is the most objective method to assess collateral flow. * **Alternative Site:** If the Allen test is negative (inadequate flow), the other arm should be tested or the **brachial/femoral artery** considered. * **Complication:** The most common complication of radial artery puncture is **hematoma**; the most serious is **digital ischemia**.

Question 135: Which of the following is contraindicated during this procedure?

A. Neck flexion at atlanto-occipital joint (Correct Answer)
B. Introduction of blade towards the right side of oropharynx
C. Head elevation
D. Preoxygenation with 100% oxygen

Explanation: ***Neck flexion at atlanto-occipital joint*** - **Atlanto-occipital flexion** is contraindicated during direct laryngoscopy as it worsens visualization of the vocal cords and glottis. - The correct position requires **atlanto-occipital extension** combined with **cervical flexion** (sniffing position) to align the oral, pharyngeal, and laryngeal axes. *Introduction of blade towards the right side of oropharynx* - This is the **correct technique** for laryngoscope insertion to avoid trauma to teeth and soft tissues. - The blade is inserted from the **right corner of the mouth** and then advanced towards the **midline** to reach the vallecula. *Head elevation* - **Head elevation** (ramping) is beneficial and recommended, especially in obese patients to improve laryngoscopic view. - It helps achieve optimal **sniffing position** and reduces the risk of **aspiration** by elevating the head above the level of the stomach. *Preoxygenation with 100% oxygen* - **Preoxygenation** is a standard and essential step before laryngoscopy to maximize oxygen reserves. - It provides a **safety margin** of 3-5 minutes during apnea and prevents **hypoxemia** during intubation attempts.

Question 136: Which anesthetic induction agent is contraindicated in a patient with asthma?

A. Ketamine
B. Thiopentone
C. Propofol
D. Althesin (Correct Answer)

Explanation: **Explanation:** The correct answer is **Althesin**. **Why Althesin is contraindicated:** Althesin is a steroid-based anesthetic induction agent (a mixture of alphaxalone and alphadolone). It was withdrawn from clinical use primarily because of its high propensity to cause **Type 1 hypersensitivity reactions** and massive **histamine release**. In patients with asthma, histamine release triggers potent bronchoconstriction, which can lead to life-threatening status asthmaticus. **Analysis of Incorrect Options:** * **Ketamine:** This is the **induction agent of choice** for asthmatic patients. It has potent bronchodilatory properties mediated by sympathomimetic effects (release of endogenous catecholamines) and direct relaxation of bronchial smooth muscle. * **Thiopentone:** While Thiopentone does not directly cause bronchodilation and can occasionally cause histamine release, it is not strictly contraindicated. However, it should be used with caution as it may not sufficiently suppress airway reflexes, potentially leading to laryngospasm or bronchospasm during intubation. * **Propofol:** It is generally considered safe and even beneficial in asthmatics because it effectively suppresses airway reflexes and has mild bronchodilatory effects. **NEET-PG High-Yield Pearls:** * **Drug of Choice for Induction in Asthma:** Ketamine. * **Inhalational Agent of Choice in Asthma:** Sevoflurane (least pungent, potent bronchodilator). * **Avoid in Asthma:** Althesin (due to histamine), d-Tubocurarine (muscle relaxant causing high histamine release), and Beta-blockers. * **Althesin Composition:** Alphaxalone + Alphadolone in **Cremophor EL** (the solvent responsible for most anaphylactic reactions).

Question 137: What is the gold standard for confirming the placement of an endotracheal tube?

A. Capnography (Correct Answer)
B. Visualization of chest excursion
C. Auscultation
D. Ultrasound

Explanation: **Explanation:** The **gold standard** for confirming endotracheal tube (ETT) placement is **Capnography (EtCO2 monitoring)**. This is based on the physiological principle that carbon dioxide is produced by cellular metabolism and transported to the lungs for excretion. The detection of a persistent CO2 waveform (capnogram) over several breaths confirms that the tube is within the trachea and that ventilation is occurring. **Analysis of Options:** * **A. Capnography:** It is the most reliable method. A sustained CO2 waveform distinguishes tracheal intubation from esophageal intubation (where CO2 is absent or rapidly disappears). * **B. Visualization of chest excursion:** This is a subjective clinical sign. It can be misleading in cases of esophageal intubation (gastric distension) or in patients with high airway resistance/low lung compliance. * **C. Auscultation:** While a standard clinical step (checking bilateral breath sounds and the epigastrium), it is not definitive. Breath sounds can be transmitted from the stomach or the opposite lung, leading to false positives. * **D. Ultrasound:** Point-of-care ultrasound (POCUS) is an emerging, highly accurate tool for "real-time" confirmation, but it has not yet replaced capnography as the universal gold standard in clinical guidelines. **High-Yield NEET-PG Pearls:** * **Direct Visualization:** Seeing the tube pass through the vocal cords is the most reliable *visual* confirmation during the procedure. * **Colorimetric Capnography:** Uses pH-sensitive paper (turns **purple to yellow** in the presence of CO2). * **False Negatives in Capnography:** May occur during **Cardiac Arrest** or massive Pulmonary Embolism due to lack of pulmonary blood flow (no CO2 reaching the lungs). * **False Positives:** May occur briefly if the patient recently consumed carbonated beverages (CO2 in the stomach), but the waveform will disappear after 5–6 breaths.

Question 138: In anesthetizing the lower anteriors, all of the following techniques are indicated except?

A. Fischer 123 technique
B. Classical inferior alveolar block
C. Mental nerve block (Correct Answer)
D. Incisive block

Explanation: To anesthetize the **lower anterior teeth** (incisors and canines), the anesthetic agent must reach the **Incisive nerve**, which is a terminal branch of the Inferior Alveolar Nerve (IAN) that remains within the mandibular canal to supply the pulp of the anterior teeth. ### Why Mental Nerve Block is the Correct Answer The **Mental nerve block** is the correct answer because it is **ineffective** for pulpal anesthesia. The mental nerve exits the mental foramen to supply only the skin of the chin and the mucous membrane of the lower lip. It does not provide any innervation to the teeth themselves. Therefore, it cannot be used for procedures involving the lower anteriors. ### Explanation of Other Options * **Fischer 123 Technique & Classical IAN Block:** Both are variations of the Inferior Alveolar Nerve Block. By depositing local anesthetic near the mandibular foramen, the entire IAN (including its incisive branch) is anesthetized, providing profound pulpal anesthesia to all teeth in that quadrant, including the anteriors. * **Incisive Block:** This technique involves depositing anesthetic at the mental foramen and applying pressure to force the solution into the foramen. This anesthetizes the **Incisive nerve**, providing pulpal anesthesia to the premolars, canines, and incisors without requiring a full IAN block. ### High-Yield Clinical Pearls for NEET-PG * **Mental vs. Incisive Block:** The injection site is the same (mental foramen), but the **Incisive block** requires post-injection pressure to ensure the fluid enters the canal to reach the dental nerves. * **Cross-innervation:** For lower anterior procedures, a "cross-over" from the contralateral incisive nerve may occur at the midline. Supplemental infiltration on the opposite side of the midline is often required. * **Nerve sequence:** IAN → Mandibular Canal → Divides into **Mental nerve** (sensory to lip/chin) and **Incisive nerve** (sensory to anterior teeth).

Question 139: Which intravenous anesthetic agent should be avoided in a patient with bronchoconstriction?

A. Thiopentone (Correct Answer)
B. Propofol
C. Etomidate
D. Ketamine

Explanation: **Explanation:** The correct answer is **Thiopentone (Option A)**. **Why Thiopentone is avoided:** Thiopentone is a barbiturate that triggers the release of **histamine** from mast cells. Histamine causes smooth muscle contraction in the airways, leading to **bronchospasm**. Additionally, thiopentone does not sufficiently suppress laryngeal and cough reflexes; if the airway is manipulated (e.g., intubation) under light planes of thiopentone anesthesia, it can precipitate severe reflex bronchospasm. Therefore, it is strictly avoided in patients with active asthma or reactive airway disease. **Analysis of Incorrect Options:** * **Ketamine (Option D):** This is the **drug of choice** for induction in patients with bronchoconstriction. It has potent bronchodilatory properties due to its sympathomimetic effects (catecholamine release) and direct relaxant effect on bronchial smooth muscle. * **Propofol (Option B):** It is a safe and frequently used agent in asthmatics. It effectively suppresses airway reflexes and has mild bronchodilatory properties, making it superior to thiopentone for laryngeal mask airway (LMA) insertion. * **Etomidate (Option C):** It is "respiratorily neutral." It does not cause histamine release and has minimal effects on airway resistance, making it safer than thiopentone for hemodynamically unstable asthmatic patients. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for Induction in Asthma:** Ketamine. * **Inhalational Agent of Choice for Bronchodilation:** Sevoflurane (least pungent, potent bronchodilator). * **Avoid:** Thiopentone (histamine release) and Desflurane (pungent, can cause airway irritation/coughing). * **Pre-medication:** Hydrocortisone and nebulized β2-agonists are often used pre-operatively to optimize airway status.

Question 140: What is a contraindication for nasotracheal intubation?

A. Anterior cranial fossa fracture (Correct Answer)
B. Middle cranial fossa fracture
C. Posterior cranial fossa fracture
D. GCS < 8

Explanation: ### Explanation **1. Why Anterior Cranial Fossa (ACF) Fracture is the Correct Answer:** Nasotracheal intubation is strictly contraindicated in patients with suspected or confirmed **Anterior Cranial Fossa fractures** (often clinically indicated by CSF rhinorrhea, Raccoon eyes, or Battle’s sign). The anatomical basis is the potential disruption of the **cribriform plate of the ethmoid bone**. If the cribriform plate is fractured, a blindly inserted nasogastric or nasotracheal tube can inadvertently pass through the fracture site and enter the **intracranial space**, causing direct brain parenchyma injury or introducing infection (meningitis). **2. Analysis of Incorrect Options:** * **B & C (Middle and Posterior Cranial Fossa Fractures):** While these are serious injuries, they do not involve the cribriform plate. The risk of intracranial tube entry is specific to the ACF. However, in clinical practice, any basilar skull fracture generally warrants extreme caution or avoidance of the nasal route. * **D (GCS < 8):** A GCS score of less than 8 is an **indication** for intubation (to protect the airway), not a contraindication. While orotracheal intubation is usually the preferred rapid method, a low GCS does not specifically prohibit the nasal route if otherwise indicated. **3. High-Yield Clinical Pearls for NEET-PG:** * **Absolute Contraindications for Nasal Intubation:** ACF fracture, mid-face fractures (Le Fort II and III), coagulopathy/bleeding disorders, and severe nasal obstruction (e.g., polyps). * **Preferred Route:** Orotracheal intubation is the "Gold Standard" for emergency airway management. * **Tube Size:** A nasotracheal tube is typically **0.5–1.0 mm smaller** in internal diameter than an orotracheal tube for the same patient. * **Vasoconstriction:** Always use a topical vasoconstrictor (e.g., Oxymetazoline or Xylometazoline) to prevent epistaxis, the most common complication of nasal intubation.

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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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