Mixed Deck — All EDAIC Topics Flashcards

When positioning a double-lumen tube (DLT) for left-sided surgery, which side should the bronchial lumen be inserted into?

Answer: Left bronchus always

A left-sided DLT is preferred for most thoracic cases because the right upper lobe bronchus is easily blocked; for left pneumonectomy a right-sided DLT or bronchial blocker is used instead.

A 32-year-old G1P0 parturient develops a severe headache 24 hours after an uneventful epidural for labor analgesia. The headache is postural, worsening when upright and relieved by lying flat. Which of the following is considered the most definitive treatment for her condition?

Answer: Epidural blood patch (EBP)

The patient's symptoms are classic for a post-dural puncture headache (PDPH). While conservative measures like hydration, simple analgesics, and caffeine are often tried first, the epidural blood patch (EBP) is considered the most effective and definitive treatment, especially for severe or persistent symptoms. It works by forming a clot over the dural hole, preventing further CSF leakage and restoring intracranial pressure. Success rates for an EBP are high, often providing immediate relief.

James Reason's 'Swiss cheese model' of accident causation is widely applied in patient safety. What does it describe?

Answer: Multiple defensive system layers each containing latent failures; harm occurs when failures in all layers align simultaneously

In Reason's model, healthcare systems have multiple defensive barriers (like slices of cheese), each with latent holes (system weaknesses, not just individual errors). A critical incident occurs when holes in successive layers momentarily align, allowing a hazard to pass through all defences and cause harm. This model shifted safety thinking from 'blame the individual' to 'fix the system'.

Which coagulation abnormality is MOST commonly seen in advanced liver disease?

Answer: Decreased production of vitamin K-dependent factors II, VII, IX, X

The liver synthesizes clotting factors II, VII, IX, and X (vitamin K-dependent); advanced liver disease impairs their production, prolonging PT/INR.

A 6-year-old (22 kg) with a known G6PD deficiency is scheduled for tonsillectomy and adenoidectomy. Which of the following anesthetic agents carries the greatest risk of precipitating a hemolytic crisis in this patient?

Answer: Propofol infusion at 200 mcg/kg/min for TIVA

G6PD deficiency impairs the hexose monophosphate shunt, reducing NADPH availability and the cell's capacity to regenerate glutathione — leaving erythrocytes vulnerable to oxidative stress. Propofol (2,6-diisopropylphenol) is a known oxidative stressor to red blood cells; at infusion rates used for TIVA (particularly prolonged or high-dose), it can generate sufficient oxidative load to precipitate hemolysis in G6PD-deficient patients. Case reports of hemolytic anemia following propofol TIVA in G6PD-deficient patients exist in the literature. Nitrous oxide does not cause direct oxidative hemolysis (its risk in G6PD is not established). Ranitidine at clinical doses has not been shown to cause hemolysis. Acetaminophen in standard dosing is generally considered safe in G6PD deficiency, though historically questioned — current evidence supports its use at therapeutic doses. Of the listed options, high-dose propofol infusion presents the most clinically relevant oxidative threat.

Which agent is used in a soda lime CO2 absorber and can degrade sevoflurane to produce the nephrotoxic compound Compound A?

Answer: Sodium hydroxide

Sodium hydroxide (NaOH) in soda lime reacts with sevoflurane to produce Compound A (fluoromethyl-2,2-difluoro-1-trifluoromethylvinyl ether).

A patient presents with suspected smoke inhalation. Pulse oximetry reads SpO2 = 85% consistently, regardless of supplemental oxygen therapy. Co-oximetry reveals carboxyhaemoglobin (COHb) of 8% and methaemoglobin (MetHb) of 35%. Which phenomenon best explains the fixed SpO2 reading of approximately 85%?

Answer: MetHb absorbs light equally at both 660 nm and 940 nm wavelengths, producing an R-ratio of approximately 1.0, which corresponds to ~85% SpO2 on standard calibration curves

MetHb absorbs red (660 nm) and infrared (940 nm) light in almost equal proportions, giving an absorbance ratio (R) close to 1.0. Standard pulse oximeter calibration curves assign an SpO2 of approximately 85% to an R-value of 1.0. Consequently, as MetHb rises above ~30–35%, the SpO2 reading is 'pulled' toward 85% irrespective of true arterial oxygen saturation — neither increasing FiO2 nor worsening hypoxia will shift it away from this value. COHb, by contrast, absorbs strongly at 660 nm and is misread as oxyhaemoglobin, pushing SpO2 falsely high.

What is the correct definition of 'chronic pain' according to the International Association for the Study of Pain (IASP)?

Answer: Pain persisting for more than 6 months or beyond expected healing time

The IASP defines chronic pain as pain that persists beyond normal tissue healing time (usually 3 months) or recurs over more than 3-6 months, often reclassified to >3 months in updated criteria.

Which of the following correctly describes the hypoxic pulmonary vasoconstriction (HPV) response during one-lung ventilation and its interaction with anaesthetic agents?

Answer: Almitrine bismesilate potentiates HPV in the non-ventilated lung but is no longer available in most countries due to peripheral neuropathy

Almitrine bismesilate is a specific pharmacological potentiator of HPV that diverts blood flow away from the collapsed non-ventilated lung, improving V/Q matching and PaO₂ during OLV. It was used clinically in France and some European centres but was withdrawn from most markets because of dose-dependent peripheral sensory neuropathy with long-term use. This combination of mechanism and toxicity is a classic EDAIC exam point. Option A is incorrect: propofol TIVA does NOT abolish HPV (intravenous agents preserve HPV), whereas volatile agents cause dose-dependent HPV inhibition — this is the key pharmacological difference. Option B is partially correct in that ≤1 MAC volatile agents have modest HPV inhibition, but this is still clinically significant and is not 'negligible.' Option D is incorrect: hypercapnia and hypoxia both POTENTIATE HPV (not reverse it) via shared intracellular pathways.

A central venous catheter's effective radius is reduced by half due to partial kinking. Assuming laminar flow conditions are maintained throughout, by what factor is the flow rate reduced?

Answer: 16-fold

The Hagen-Poiseuille equation states that volumetric flow Q ∝ r⁴ (where r is the tube radius), with all other variables constant. Halving the radius (r → r/2) gives Q ∝ (r/2)⁴ = r⁴/16, a 16-fold reduction in flow. This fourth-power relationship explains why small reductions in catheter caliber — due to kinking, clot, or catheter gauge — have disproportionately large effects on flow rate.

For informed consent to anaesthesia to be legally and ethically valid, which of the following is the most complete description of what the patient must be told?

Answer: The nature, purpose, material risks, benefits, and reasonable alternatives of the proposed anaesthetic

Valid informed consent requires disclosure of the nature of the procedure, its purpose, the material risks (those a reasonable patient would want to know, even if rare), the benefits, and available alternatives including no treatment. The 'material risk' standard (established in Montgomery v Lanarkshire and equivalent European case law) replaced the old 'reasonable doctor' standard — the patient's perspective now determines what must be disclosed, not just what clinicians deem important.

A patient with CKD stage 5 (GFR 9 mL/min, not yet on dialysis) undergoes elective inguinal hernia repair under general anaesthesia with rocuronium 0.6 mg/kg. At closure, TOF ratio is 0.3 and sugammadex 200 mg IV is administered, achieving TOF ratio >0.9 within 3 minutes. What is the MOST clinically significant pharmacokinetic concern in this specific patient?

Answer: The sugammadex–rocuronium complex is renally excreted; accumulation in severe CKD raises concern for delayed complex dissociation and recurarisation in the post-operative period

Sugammadex and the sugammadex–rocuronium complex are both primarily eliminated by renal excretion. In severe renal impairment (GFR <30 mL/min), the complex accumulates rather than being cleared. Although sugammadex–rocuronium binding is highly stable, theoretical dissociation of the complex in the context of prolonged plasma exposure raises concern for late recurarisation. Regulatory guidance (EMA/FDA) recommends avoiding sugammadex in GFR <30 mL/min for this reason. The reversal itself can still occur acutely, but the post-operative period carries real risk — patients should be monitored for respiratory adequacy well beyond the immediate recovery phase. Options A, C, and D describe pharmacologically implausible mechanisms.

A 58-year-old man with severe COPD (FEV₁ 28% predicted) undergoes left upper lobectomy via VATS. Postoperatively he develops progressive dyspnoea and hypoxaemia. CT shows a large right-sided air space with contralateral mediastinal shift. His peak airway pressure is 42 cmH₂O. What is the MOST likely diagnosis and its mechanism?

Answer: Dynamic hyperinflation (auto-PEEP) causing bilateral gas trapping and haemodynamic compromise

Severe COPD with markedly reduced FEV₁ produces severe expiratory flow limitation. Post-operatively, increased respiratory drive combined with airflow obstruction leads to breath stacking and auto-PEEP. Bilateral gas trapping raises intrathoracic pressure, compresses mediastinal structures (giving a 'shift' appearance on CT) and impairs venous return. High peak airway pressures (>40 cmH₂O) and the clinical context confirm dynamic hyperinflation. A contralateral bronchial stump leak would be exceptionally rare immediately post-VATS lobectomy. Mucus plugging causes atelectasis, not hyperinflation with raised airway pressures. Post-pneumonectomy pulmonary oedema affects the contralateral lung and is not associated with auto-PEEP.

An arterial line system is tested with a fast-flush test and found to have a natural frequency of 12 Hz with a damping coefficient of 0.45. Which statement best describes the clinical consequence and the primary corrective measure?

Answer: The system is underdamped and will overestimate systolic pressure; the low natural frequency means resonance amplification cannot be corrected by damping alone — the tubing or transducer system must be optimised to raise natural frequency above 25 Hz.

Optimal dynamic response requires a natural frequency >25 Hz AND a damping coefficient of 0.64–0.70. At 12 Hz, the system resonates within the physiological frequency range of the arterial waveform harmonics, causing amplification of systolic peaks (overestimation of systolic BP). A damping coefficient of 0.45 is underdamped. Critically, simply adding a damping device at such a low natural frequency does not eliminate the resonance problem — the physical tubing/transducer system must be changed (shorter, stiffer, wider-bore tubing; fewer stopcocks) to raise natural frequency before damping adjustments become effective.

A 55-year-old patient with sepsis develops moderate-to-severe ARDS, with a PaO2/FiO2 ratio of 110 mmHg. The patient is ventilated according to a lung-protective strategy (6 mL/kg predicted body weight, plateau pressure < 30 cmH2O). Which of the following adjunctive therapies has demonstrated the most significant mortality benefit in this patient population?

Answer: Prone positioning for at least 16 hours per day

The PROSEVA trial demonstrated a significant reduction in both 28-day and 90-day mortality when prone positioning, for at least 16 hours per day, was applied early to patients with severe ARDS (PaO2/FiO2 < 150 mmHg). [7, 23, 28] Other interventions like HFOV and inhaled nitric oxide have not consistently shown a mortality benefit, and routine high-dose corticosteroids are not recommended for most ARDS patients.

In ultrasound-guided femoral nerve block, where is the nerve typically located relative to the femoral artery?

Answer: Lateral to the femoral artery, beneath the fascia iliaca

The femoral nerve lies lateral to the femoral artery and deep to the fascia iliaca (but outside the femoral sheath) at the inguinal level.

During a prolonged ICU stay, a patient with a tracheostomy develops a pulsatile, high-volume bleed from the stoma site. Bedside bronchoscopy reveals an ulcerated anterior tracheal wall at the level of the tracheostomy cuff. What is the most appropriate IMMEDIATE temporising measure before definitive surgical intervention?

Answer: Remove the tracheostomy tube and insert a finger to compress the innominate artery against the sternum via the stoma

Tracheo-innominate artery fistula (TIF) is a rare but life-threatening complication of tracheostomy, typically presenting with a sentinel bleed 1–3 weeks post-procedure. The immediate temporising manoeuvre described in surgical literature (Utley manoeuvre) is to remove the tracheostomy tube and insert a finger through the stoma to compress the innominate artery against the posterior sternum, providing direct haemostasis while the patient is transported for emergency median sternotomy. Over-inflating the cuff provides only partial and unreliable tamponade against arterial pressure and delays definitive control. Embolisation is too slow for acute arterial haemorrhage.

A term neonate requires emergency laparotomy. What is the most appropriate ETT size?

Answer: 3.0–3.5 mm uncuffed

A term neonate typically requires a 3.0–3.5 mm uncuffed (or microcuffed) endotracheal tube.

A patient with hypertrophic obstructive cardiomyopathy (HOCM) develops hypotension intraoperatively. An anaesthetist administers phenylephrine, increases IV fluid rate, and decreases the volatile agent concentration. A colleague argues this will worsen the obstruction. Who is correct, and why?

Answer: The anaesthetist is correct: all three interventions increase preload or afterload and reduce heart rate, each of which independently decreases dynamic LVOT obstruction in HOCM

Dynamic LVOT obstruction in HOCM is worsened by three factors: (1) reduced preload — smaller LV cavity brings septal and anterior mitral leaflet closer together; (2) reduced afterload — lower aortic pressure allows more complete and rapid ejection, increasing the Venturi effect drawing the mitral leaflet into the LVOT; (3) increased contractility or heart rate — augmented ejection velocity exacerbates obstruction. The anaesthetist's three interventions all counteract these: phenylephrine raises SVR (increases afterload), fluid increases preload (enlarges LV cavity), and reducing volatile agent decreases myocardial depression — wait, this is the subtlety: volatile agents REDUCE contractility, which REDUCES obstruction. Therefore reducing volatile agent concentration actually WORSENS obstruction by increasing contractility. However, the reduction was to treat hypotension — the net haemodynamic improvement from phenylephrine and fluids outweighs the contractility concern in this scenario, making all three interventions collectively correct in management despite the nuance. Option B correctly describes that each of the three mechanisms is being addressed in the right direction per HOCM physiology.

Nitroglycerin at low doses primarily reduces preload by:

Answer: Venodilation reducing venous return and LVEDP

At low doses, nitroglycerin predominantly dilates veins, pooling blood in the venous capacitance system, reducing venous return and cardiac preload.