Respiratory and Thoracic Anesthesia Flashcards

During one-lung ventilation (OLV) in a patient with severe COPD, hypoxic pulmonary vasoconstriction (HPV) is blunted. Which pharmacological agent, if administered, would MOST significantly impair HPV and worsen intraoperative hypoxemia?

Answer: Intravenous nitroglycerin 1 mcg/kg/min

Intravenous vasodilators such as nitroglycerin cause systemic vasodilation and directly inhibit HPV by increasing pulmonary blood flow to the non-ventilated (collapsed) lung, worsening shunt and hypoxemia. Inhaled nitric oxide selectively vasodilates ventilated lung regions, improving V/Q matching. Almitrine potentiates HPV and improves oxygenation during OLV. Ipratropium has minimal direct effect on pulmonary vasomotor tone.

A 58-year-old patient undergoing right pneumonectomy develops sudden cardiovascular collapse 90 minutes post-extubation. Transthoracic echocardiography reveals a hyperdynamic left ventricle with near-obliteration of the left ventricular cavity in systole. The MOST likely underlying mechanism is:

Answer: Dynamic left ventricular outflow tract obstruction due to intravascular volume depletion and catecholamine surge

Post-pneumonectomy patients are at risk for dynamic LVOTO due to the combination of a hyperdynamic state (catecholamines, pain, fever) and relative hypovolemia. This results in systolic anterior motion of the mitral valve and functional outflow obstruction, presenting as obstructive shock with a hyperdynamic, underfilled ventricle on echo. Treatment requires volume resuscitation, beta-blockade, and avoidance of vasodilators. Acute RV failure would show a dilated, hypokinetic RV, not a hyperdynamic LV.

When performing high-frequency jet ventilation (HFJV) for rigid bronchoscopy and subglottic tracheal stenosis resection, which physiological principle BEST explains adequate CO2 elimination despite tidal volumes smaller than anatomical dead space?

Answer: Asymmetric velocity profiles and augmented molecular diffusion (Taylor dispersion)

CO2 elimination during HFJV occurs through multiple mechanisms, but the most important at high frequencies with sub-dead-space tidal volumes is Taylor dispersion (augmented axial diffusion). Asymmetric turbulent velocity profiles create radial mixing, dramatically enhancing the effective diffusion coefficient for CO2 far beyond simple Fickian diffusion. Entrainment does occur with open-circuit HFJV and contributes, but it does not fully explain CO2 clearance at all frequencies. Mass convection (bulk flow) is the dominant mechanism only at lower HFJV frequencies.

In a patient with a large right-sided bronchopleural fistula (BPF) requiring general anesthesia, which sequence of induction and airway management is MOST appropriate to prevent tension pneumothorax and ensure lung isolation BEFORE positive pressure ventilation?

Answer: Inhalational induction with sevoflurane maintaining spontaneous ventilation, followed by left-sided DLT with bronchoscopic confirmation

With a large BPF, positive pressure ventilation before lung isolation risks converting a communicating fistula into a tension pneumothorax. Inhalational induction maintaining spontaneous respiration preserves the patient's own airway pressures (which are lower) until the DLT is placed and the fistula side is isolated. Awake FOI with a DLT is also acceptable but technically demanding with a large DLT in an awake patient. RSI before isolation risks immediate barotrauma. A chest drain alone does not prevent ventilatory loss through the fistula. The left-sided DLT is chosen because right-sided DLTs have poor endobronchial fit variability and a BPF is already on the right.

A patient with a known mediastinal mass causing 60% tracheal compression at the carina is scheduled for tissue biopsy under general anesthesia. After induction and tracheal intubation, complete airway obstruction occurs despite the ETT tip being above the carina. The MOST effective immediate maneuver is:

Answer: Advance the ETT past the carina into the right main bronchus

Mediastinal masses can cause dynamic airway compression at or below the carina. When extrinsic compression occludes the distal trachea or mainstem bronchi after induction (due to loss of muscle tone and negative intrathoracic pressure), advancing the ETT past the obstruction into the right or left main bronchus can re-establish a patent airway lumen distal to the mass. Changing to lateral decubitus may help in some cases by shifting the mass, but is a slower maneuver. Prone positioning has no established benefit for acute tracheal obstruction. Withdrawing the ETT would worsen obstruction if the carina is the level of compression.

During thoracic epidural analgesia (TEA) at T4–T5 for a right thoracotomy, the patient develops unexpected bradycardia and hypotension. Cardiac accelerator fibers (T1–T4) are likely blocked. Which additional reflex mechanism, specific to thoracic surgery and TEA, MOST likely contributes to the hemodynamic compromise in this setting?

Answer: Cardiac vagal (parasympathetic) predominance unopposed by blocked sympathetic accelerator fibers, exaggerated by surgical manipulation triggering carinal and pulmonary stretch receptors

With high thoracic sympathetic blockade abolishing cardiac accelerator input (T1–T4), the cardiac vagus (CN X) is unopposed. During thoracic surgery, surgical manipulation — particularly traction near the carina, hilum, or lung parenchyma — activates stretch receptors innervated by the vagus nerve, triggering reflex bradycardia and vasodilation. This vagally-mediated reflex (Bezold-Jarisch-like) is potentiated by the absence of compensatory sympathetic tone under TEA. Phrenic nerve palsy is not a feature of mid-thoracic epidural. Intercostal paralysis does not significantly reduce preload. Splanchnic vasodilation contributes to hypotension but does not explain the bradycardia component.