TRIGGER 5 - Aspiration Pneumonia / Lobar Pneumonia

TRIGGER 5 - MCQ

• A. Mycoplasma pneumoniae
• B. Klebsiella pneumoniae
• C. Streptococcus pneumoniae
• D. Legionella pneumophila
• E. Staphylococcus aureus

• Alcoholics (impaired mucociliary clearance, aspiration risk, poor immunity)
• Diabetics and debilitated patients

• "Bulging fissure sign" (the weight of the exudate pushes down the horizontal fissure - look for downward bowing)
• Thick, mucoid ("currant jelly") sputum due to blood-stained mucoid exudate
• High mortality if untreated; tends to cavitate

TRIGGER 5 - SAQ

• Diagnosis: Lobar pneumonia - right upper lobe (most likely Klebsiella pneumoniae given the clinical context)
• Key predisposing factor: Chronic alcohol use - causes aspiration due to obtunded gag reflex, impaired mucociliary clearance, nutritional immunosuppression, and leucocyte dysfunction

1. Inspection: Reduced chest expansion on the affected side; tachypnoea; use of accessory muscles
2. Palpation: Reduced tactile vocal fremitus initially (pre-consolidation); increased TVF / vocal fremitus over consolidated lobe
3. Percussion: Dullness to percussion over the right upper zone
4. Auscultation: Bronchial breathing and crackles (crepitations) over the right upper lobe; whispering pectoriloquy; aegophony

• Sputum culture and Gram stain (before starting antibiotics)
• Expected finding: Klebsiella produces short, plump gram-negative rods; mucoid colonies on culture. Blood cultures should also be obtained (bacteraemia is common). Sputum Gram stain may show PMNs + gram-negative rods.

TRIGGER 6 - COPD with Type II Respiratory Failure (CO2 Retention)

TRIGGER 6 - MCQ

• Option A: Respiratory alkalosis with low CO2 - this is hyperventilation/Type I failure, not CO2 retention
• Option B (CORRECT): Near-normal pH (7.38) despite elevated PaCO2 (62 mmHg) and elevated HCO3- (34 mEq/L) - this represents chronic compensated respiratory acidosis. The kidneys have retained bicarbonate over time (metabolic compensation) to normalize the pH. PaO2 is low (55). This is the pattern of chronic CO2 retainer with acute decompensation.
• Option C: Uncompensated acute respiratory acidosis (low HCO3- indicates no metabolic compensation yet) - more acute, but asterixis and drowsiness usually accompany chronic retention
• Option D: Normal blood gas - does not fit the clinical picture
• Option E: Acute respiratory acidosis with partial compensation - possible but HCO3- of 26 shows minimal compensation, not the chronic retainer pattern

TRIGGER 6 - SAQ

• Diagnosis: Severe COPD (likely GOLD Stage III-IV) with acute exacerbation and Type II respiratory failure (hypercapnic respiratory failure)
• Asterixis (flapping tremor): Signifies CO2 narcosis / hypercapnic encephalopathy - CO2 retention causes cerebral vasodilation and metabolic encephalopathy, manifesting as a coarse, non-rhythmic tremor on wrist extension. It is a red flag indicating ventilatory failure.

1. Hyperinflation - >10 posterior ribs visible above the diaphragm
2. Flattened hemidiaphragms - loss of normal dome shape, diaphragm at or below the level of the 7th rib anteriorly
3. Increased retrosternal airspace (barrel chest on lateral CXR)
4. Bullae - focal areas of avascular hyperlucency in the upper lobes
5. Peripheral vascular pruning - reduced peripheral vascular markings with oligaemia in outer lung fields
6. Narrow, vertical "dripping" heart
7. Horizontal rib orientation with widened intercostal spaces

📋 ASSESSMENT — Trigger 5 Topic: Pneumonia in a Compromised Host

MCQ

• A. Streptococcus pneumoniae
• B. Mycoplasma pneumoniae
• C. Klebsiella pneumoniae
• D. Pseudomonas aeruginosa
• E. Legionella pneumophila

MEQ

1. Chronic alcoholism - impaired immunity, aspiration risk, malnutrition
2. Confusion / altered GCS - CURB-65 point (C = 1); suggests severity
3. Pleuritic chest pain - indicates pleural involvement/possible parapneumonic effusion
4. Delayed presentation (3 days) - infection has progressed without treatment, risk of complications

• High-flow O2 via non-rebreather mask; titrate to target SpO2 94-98% (no CO2 retention risk here - this is Type I failure)
• Sit patient upright; aspiration precautions given alcohol intoxication

• IV access x2; IV fluid resuscitation with 500 mL normal saline bolus (BP 100/70, HR 112 - septic picture)

• IV co-amoxiclav (amoxicillin-clavulanate) PLUS azithromycin (macrolide) for atypical coverage
• OR IV ceftriaxone (preferred if Klebsiella suspected given alcoholism) + azithromycin
• Guided by local hospital antibiogram; de-escalate once cultures available

• Continuous SpO2, ECG, hourly urine output; repeat ABG at 1 hour; repeat CXR at 48-72 h

• Parapneumonic effusion / empyema - monitor for persistence or worsening of dullness; if effusion develops, diagnostic pleural tap (Light's criteria); empyema requires chest drain + prolonged antibiotics
• Also acceptable: septic shock, ARDS, lung abscess (especially with Klebsiella)

📋 ASSESSMENT — Trigger 6 Topic: COPD with Hypercapnic Respiratory Failure

MCQ

• A. Oxygen toxicity causing retinal damage
• B. Suppression of hypoxic respiratory drive leading to worsening CO2 retention
• C. Nitrogen washout causing absorption atelectasis
• D. Pulmonary oxygen toxicity causing ARDS
• E. Precipitation of pulmonary oedema

MEQ

1. Long-standing smoking history (40 years) - established COPD risk factor; 3 triggers are the same presentations of a known chronic disease
2. Pre-existing reliever inhaler use ("all the time") - indicates significant background airflow obstruction already present before this admission
3. 4-day history of worsening dyspnoea + change in sputum (increased volume, purulent/green) - classic precipitant of COPD exacerbation, most commonly infectious (viral or bacterial), on a background of chronically impaired lung function

• pH 7.31 = acidaemia
• PaCO2 9.2 kPa (high) = respiratory acidosis (primary problem)
• PaO2 5.1 kPa (low) = hypoxaemia - Type II respiratory failure
• HCO3- 36 mEq/L (high) + BE +8 = metabolic alkalosis = renal compensation
• Conclusion: Partially compensated respiratory acidosis = acute-on-chronic hypercapnic (Type II) respiratory failure

• Spirometry (pulmonary function tests): Post-bronchodilator FEV1/FVC <0.70 confirms obstructive defect. FEV1 % predicted stages severity (GOLD I-IV). This patient likely has GOLD Stage III-IV (FEV1 <50% predicted) given drowsiness and degree of failure.

• Remove the high-flow O2 immediately if applied
• Apply 24% Venturi mask → titrate to 28% if SpO2 remains <88%
• Target SpO2 88-92% - NOT higher, to preserve hypoxic drive
• Recheck ABG in 30-60 minutes after starting controlled O2

• Nebulised salbutamol 2.5-5 mg (SABA) + ipratropium 500 mcg (SAMA)
• Drive nebuliser with air (not O2) or low-flow O2 at max 6 L/min
• Repeat every 20-30 minutes in first hour, then 4-hourly

• Prednisolone 30-40 mg oral (or IV hydrocortisone 200 mg if unable to swallow)
• Course: 5 days - reduces airway inflammation, shortens exacerbation duration

• Green/purulent sputum = likely bacterial trigger
• Amoxicillin 500 mg TDS OR doxycycline 200 mg stat then 100 mg OD (5 days)
• If resistant/severe: co-amoxiclav or levofloxacin

• Indications met: pH 7.31 (<7.35), PaCO2 9.2 kPa, drowsy
• Start BiPAP (IPAP 10-20 cmH2O / EPAP 4-5 cmH2O) - this is the single most important intervention to correct acidosis and rest respiratory muscles
• Recheck ABG 1-2 hours after BiPAP
• If pH worsens despite BiPAP (<7.25) or patient deteriorates → escalate to ITU / intubation (discuss with patient's advance wishes)

• Continuous SpO2, ECG (right heart strain pattern - P pulmonale, right axis deviation)
• Monitor for cor pulmonale - check for RV failure
• Daily weight; fluid balance
• VTE prophylaxis (LMWH)
• Smoking cessation counselling on discharge

Marking Tip for Examiners: The MEQ is weighted 25 marks total (4+4+4+9 for Trigger 6; 4+4+4+8 for Trigger 5). The MCQs each carry 1 mark. Both scenarios test integration of clinical reasoning across all four domains as required by the PBL trigger assessment framework.

TRIGGER 5 TOPIC — Pneumonia in Compromised Host

True / False Question

Short Case Question

• C (Confusion) = 1 ✅ drowsy
• U (Urea) = unknown (pending)
• R (RR ≥30) = 0 (RR is 28)
• B (BP systolic <90) = 1 ✅ BP 95/65
• 65 (Age ≥65) = 0
• Minimum score = 2 → Hospital admission required; if urea >7 = score 3 → HDU consideration

• Antibiotic: IV Ceftriaxone (3rd generation cephalosporin) covering gram-negative organisms including Klebsiella
• Complication: Lung abscess - Klebsiella has a high tendency to cavitate; monitor with repeat CXR at 48-72 hours

TRIGGER 6 TOPIC — COPD with Type II Respiratory Failure

True / False Question

Short Case Question

• CXR finding 1: Hyperinflation - more than 10 posterior ribs visible, flat diaphragms (1 mark)
• CXR finding 2: Bullae / peripheral vascular pruning - avascular hyperlucent areas from emphysematous destruction (1 mark)
• Enlarged pulmonary arteries: Indicate pulmonary hypertension secondary to chronic hypoxic vasoconstriction, a sign of cor pulmonale (right heart failure) (1 mark)

• Oxygen target: SpO2 88-92% via 24-28% Venturi mask - controlled O2 to preserve hypoxic drive (1 mark)
• Ventilatory intervention: Non-invasive ventilation (BiPAP) - indicated when pH <7.35 despite initial bronchodilators, steroids, and controlled O2; corrects acidosis and rests respiratory muscles (1 mark)

1. True or False
2. Case Scenario
3. Short Essay Question

🫁 TRIGGER 5 — Pneumonia in a Compromised Host

1. TRUE OR FALSE

2. CASE SCENARIO

3. SHORT ESSAY QUESTION

• Alcohol impairs mucociliary clearance - cilia function is suppressed, secretions accumulate
• Impaired gag and cough reflex due to CNS depression - promotes aspiration of oropharyngeal/gastric contents
• Alcohol causes neutrophil dysfunction - impaired chemotaxis and phagocytosis
• Malnutrition (common in alcoholics) reduces T-cell and B-cell immunity
• Liver dysfunction reduces opsonin and complement production - gram-negative bacteria less effectively cleared

• Airway/Breathing: O2 via face mask, target SpO2 94-98% (Type I failure); sit upright; aspiration precautions
• Circulation: IV access; fluid resuscitation if hypotensive (sepsis); blood cultures before antibiotics
• Antibiotics: IV Ceftriaxone ± azithromycin (atypical cover); guided by sputum Gram stain
• Investigations: CXR, FBC, CRP, ABG, sputum C&S, blood cultures
• Severity scoring: CURB-65 to guide admission level
• Follow-up CXR at 6 weeks post-discharge to exclude underlying malignancy

🫁 TRIGGER 6 — COPD with Hypercapnic Respiratory Failure

1. TRUE OR FALSE

2. CASE SCENARIO

3. SHORT ESSAY QUESTION

• Hyperinflation + flat diaphragms: Chronic air trapping from loss of lung elastic recoil (emphysema) → increased residual volume → lungs push diaphragm flat and ribs horizontal
• Bullae/hyperlucency: Destruction of alveolar walls by chronic inflammation (proteases overwhelm antiproteases) → large air spaces with no vascular markings
• Peripheral pruning: Loss of pulmonary capillary bed from emphysema → fewer peripheral vessels visible
• Enlarged central pulmonary arteries: Chronic hypoxia → hypoxic pulmonary vasoconstriction → pulmonary hypertension → right ventricular hypertrophy (cor pulmonale)
• Vertical/narrow heart: Hyperinflated lungs push the heart inferiorly and narrow its silhouette

1. Controlled O2: 24-28% Venturi mask, SpO2 target 88-92%
2. Bronchodilators: Nebulised salbutamol + ipratropium (driven by air)
3. Steroids: Prednisolone 30-40 mg oral or IV hydrocortisone
4. Antibiotics: Amoxicillin/doxycycline (green sputum = infective exacerbation)
5. ABG at 30-60 min: If pH <7.35 → start BiPAP immediately
6. If BiPAP fails: Escalate to ITU/intubation discussion

• 🫁 TRIGGER 5 (the top half) = Pneumonia in a compromised host - based on the 55-year-old alcoholic man with cough, fever, and right upper lobe consolidation on CXR
• 🫁 TRIGGER 6 (the bottom half) = COPD with Hypercapnic Respiratory Failure - based on the 63-year-old long-term smoker with worsening dyspnoea, drowsiness, and flapping tremor

1. ✅ True or False
2. ✅ Case Scenario
3. ✅ Short Essay Question

🫁 TRIGGER 5 — True or False: Full Explanations

• Chronic alcoholism - alcohol impairs the immune system and gag reflex, making alcoholics specifically vulnerable to Klebsiella
• Right UPPER lobe consolidation - Klebsiella classically affects the upper lobes (unlike most other pneumonias that affect lower lobes)
• Reddish-brown ("currant jelly") sputum - this is the classic description of Klebsiella sputum, caused by blood mixed with thick mucoid exudate
• Bulging fissure sign - the heavy mucoid exudate produced by Klebsiella pushes the fissure downward

• The target SpO2 in standard pneumonia is 94-98%, not >98%
• There is no benefit in pushing SpO2 above 98% and excessive O2 can cause oxygen toxicity with prolonged use
• The >98% target via 15L is the wrong approach that should be reserved for cardiac arrest only

• CNS depression - alcohol suppresses the brainstem reflexes including the cough reflex and gag reflex. When these are impaired, the patient cannot clear secretions or prevent food/liquid/bacteria from entering the airway
• Aspiration - a drunk person lying down can silently aspirate oral bacteria (including Klebsiella which colonises the mouth of alcoholics) into the lungs without coughing it back up
• Mucociliary dysfunction - alcohol paralyses the cilia lining the airways that normally sweep bacteria upward and out
• Immune suppression - neutrophil (white cell) function is impaired; they cannot kill bacteria effectively

• C = Confusion
• U = Urea >7 mmol/L
• R = Respiratory rate ≥30/min
• B = Blood pressure (systolic <90 or diastolic ≤60)
• 65 = Age ≥65

• It weighs down the affected lobe
• This weight pushes the fissure (the dividing line between lung lobes) downward or outward
• On CXR, you see the horizontal fissure bowing downward instead of its normal horizontal position

🫁 TRIGGER 6 — True or False: Full Explanations

• PaO2 5.2 kPa = LOW (normal >10.6 kPa) ✅ hypoxaemia
• PaCO2 9.0 kPa = HIGH (normal 4.7-6.0 kPa) ✅ hypercapnia
• pH 7.30 = acidaemia from CO2 retention

• The hypoxia is corrected
• The peripheral chemoreceptors stop firing
• The patient has NO drive to breathe
• They breathe less and less
• CO2 rises even further
• The patient becomes more drowsy, stops breathing → respiratory arrest

• Give 24-28% O2 via Venturi mask
• Target SpO2 88-92% only
• Keep them slightly hypoxic ON PURPOSE to maintain their breathing drive

• pH 7.30 = acidaemia (NOT alkalotic - rules out primary metabolic alkalosis)
• PaCO2 9.0 = very HIGH = respiratory acidosis (this is the PRIMARY problem)
• HCO3- 37 = HIGH = this is the body's RESPONSE to the high CO2, not a primary problem

• IPAP (inspiratory pressure) - helps push air INTO the lungs, increasing tidal volume and blowing off CO2
• EPAP (expiratory pressure) - keeps airways open, preventing collapse

• pH <7.35 (acidaemia) despite initial treatment with controlled O2, bronchodilators, and steroids
• PaCO2 rising
• Patient drowsy/tiring

• Rests the exhausted respiratory muscles
• Increases ventilation, blowing off excess CO2
• Corrects the acidosis
• Avoids the need for invasive intubation in most cases

• Enlarged central pulmonary arteries (dilated from high pressure)
• Peripheral pruning (peripheral vessels disappear as resistance increases)
• Eventually signs of right heart failure (raised JVP, ankle oedema clinically)