🫁 Chapter 32: Disease-Specific Ventilation

Tailoring ventilation for: normal lungs, airway obstruction (asthma/bronchiolitis), hypoxemic failure (ARDS/pneumonia), acute-on-chronic CLD, restrictive lung/chest wall disease. Time constant-based strategies · Permissive hypercapnia · PEEP titration · Lung protection

🔍 Core Concepts: Disease-Specific Ventilation

📌 Normal lungs (shock, post-op, cerebral oedema)
Goal: airway protection, normal gas exchange. Use normal-for-age settings (TV 6-8 mL/kg). Avoid hypotension from induction agents. PPV may decrease preload in cardiogenic shock.
🌬️ Severe airway obstruction (asthma, bronchiolitis)
↑ resistance → ↑ time constants. Strategy: low rate (10-12), long expiratory time (I:E 1:3-1:4), low TV (5-7 mL/kg), permissive hypercapnia (pH ≥7.2), limit Pplat <35. Set external PEEP ~2/3 auto-PEEP.
🫀 Acute hypoxemic failure (ARDS, pneumonia)
↓ compliance → ↓ time constants. Strategy: low tidal volume (6 mL/kg), limit Pplat <30, optimal PEEP, permissive hypercapnia, conservative fluids, prone positioning, HFOV if refractory.
📈 Acute-on-chronic respiratory failure
Goal: return to baseline PaCO2, not normal. Low rate, long expiration, PEEP 0-5 (if auto-PEEP, set external PEEP ~2/3). NPPV first line. Treat infection aggressively.
🦴 Restrictive lung/chest wall disease (neuromuscular, deformities)
Normal lung but respiratory pump failure. NIV preferred if airway reflexes intact. Respiratory muscle conditioning. Consider tracheostomy for prolonged weaning.
⚙️ Key questions while on ventilator
Why ventilated? Underlying physiology (↑resistance vs ↓compliance)? Patient triggering? Auto-PEEP? Graphics interpretation? Dual control?

🩺 Stepwise Approach: Disease-Specific Ventilation

1
Identify predominant pathophysiology
Measure compliance, resistance, time constant. Obstructive (asthma) → long TC, need low rate, long expiration. Restrictive (ARDS) → short TC, higher rate, decelerating flow. Mixed pattern may exist.
2
ARDS / hypoxemic failure strategy
Low tidal volume (6 mL/kg IBW), limit Pplat <30, optimal PEEP (PV loop or compliance-guided), permissive hypercapnia (pH ≥7.2). If refractory, consider HFOV, prone positioning, iNO, ECMO.
3
Asthma / airway obstruction strategy
Low rate (10-14), prolonged expiratory time (I:E 1:3-1:4), low TV (5-7 mL/kg), set PEEP at 2/3 of measured auto-PEEP (if present). Avoid hyperinflation. Permissive hypercapnia.
4
Acute-on-chronic lung disease
Target baseline PaCO2 (not normal). Low rate, long expiration, PEEP 0-5. Use NPPV first. If intubated, wean to baseline CO2. Treat infection, pulmonary hypertension.
5
Restrictive / neuromuscular disease
NIV (BiPAP) with backup rate if intact airway reflexes. Respiratory muscle conditioning. Avoid disuse atrophy. Tracheostomy if prolonged weaning (>2 weeks).
6
Monitor & adjust
Use ventilator graphics, ABGs, compliance trends. Adjust PEEP, rate, I:E ratio based on disease evolution. Wean when underlying process resolves.