Master ventilator modes, initial settings, troubleshooting, weaning, and complications.
120 min estimated
The two fundamental ventilation strategies are volume control (VC) and pressure control (PC). In volume control, a set tidal volume is delivered regardless of the pressure required — the pressure varies with lung compliance and resistance. In pressure control, a set inspiratory pressure is applied and tidal volume varies with lung mechanics.
Volume control guarantees minute ventilation — critical when oxygenation or CO2 removal cannot be compromised. Pressure control limits peak airway pressure — important in ARDS or at risk of barotrauma. PRVC (Pressure-Regulated Volume Control) combines both: it targets a set volume while using the lowest pressure possible, adjusting breath to breath.
Clinical Tip
When transitioning from PC to VC in an improving ARDS patient, set the target Vt to what was being delivered in PC mode to avoid sudden overdistension.
Starting a patient on mechanical ventilation requires setting mode, tidal volume, rate, FiO2, PEEP, and flow/I:E ratio.
For most adults: AC/VC mode, Vt 6–8 mL/kg IBW, RR 12–16, FiO2 1.0 initially then titrate to SpO2 92–96%, PEEP 5 cmH2O, flow 40–60 L/min (I:E ~1:2).
In ARDS: use lung-protective ventilation — Vt 4–6 mL/kg IBW, Plateau pressure <30 cmH2O, driving pressure <15 cmH2O, higher PEEP per ARDSNet table, permissive hypercapnia acceptable.
For COPD: avoid auto-PEEP by prolonging expiration (low RR 10–12, extended expiratory time, I:E 1:3 to 1:4).
Clinical Tip
IBW for males: 50 + 2.3 × (height in inches - 60). For females: 45.5 + 2.3 × (height in inches - 60). Never use actual body weight for Vt calculation.
Weaning is the process of gradually reducing ventilatory support. The daily spontaneous breathing trial (SBT) is the cornerstone of weaning assessment.
Pre-SBT readiness criteria (ABCDEF bundle): Alert and cooperative, adequate Breathing (FiO2 ≤0.4, PEEP ≤5–8), hemodynamically stable, cause of respiratory failure improving.
SBT: Place patient on PS 5–8 cmH2O + PEEP 5 x 30–120 min. Pass criteria: RR <35, SpO2 >90%, HR and BP stable, no distress, RSBI (f/Vt) <105.
Extubation criteria: patent airway, adequate cough and secretion clearance, intact mental status, hemodynamically stable. Post-extubation stridor: racemic epinephrine and dexamethasone.
Clinical Tip
RSBI is calculated with the patient breathing spontaneously — turn off all pressure support briefly, measure RR and Vt over 1 minute, divide.
Ventilator-associated complications include: barotrauma (pneumothorax, pneumomediastinum), volutrauma (alveolar overdistension), VAP, oxygen toxicity, and auto-PEEP.
Auto-PEEP (intrinsic PEEP) occurs when expiration is incomplete — air trapping. Suspect in obstructive disease (COPD, asthma). Diagnose: occlude expiratory port at end-expiration, read pressure gauge. Treat: increase expiratory time, reduce RR, bronchodilators.
High peak pressure with normal plateau = increased resistance (secretions, bronchospasm, kinked tube). High peak AND plateau = decreased compliance (pneumothorax, ARDS, pulmonary edema, mainstem intubation).
For sudden deterioration on vent: DOPE — Displacement, Obstruction, Pneumothorax, Equipment failure.
Clinical Tip
When a vented patient suddenly deteriorates, manually ventilate with a bag first — this immediately separates patient from equipment as a cause.
Sudden Rise in Peak Airway Pressure
A 55-year-old intubated for ARDS is on AC/VC: Vt 450 mL, RR 18, FiO2 0.5, PEEP 10. Ppeak suddenly rises from 32 to 52 cmH2O. Pplat is 28 cmH2O.
What is the most likely cause, and what is your first intervention?
High Ppeak with normal Pplat indicates increased airway resistance. Most likely cause: secretions, bronchospasm, or kinked ET tube. First intervention: suction.
Ppeak reflects both resistance AND compliance, while Pplat reflects only compliance. When Ppeak rises but Pplat stays normal, resistance is the problem. Suction first; if unchanged, auscultate for bronchospasm and administer bronchodilator. Check tube position and rule out kinked circuit.
Weaning Assessment
A 45-year-old is being evaluated for extubation after 5 days of ventilation for pneumonia. FiO2 0.35, PEEP 5, awake and following commands. During SBT on PS 5/PEEP 5, RR = 24, Vt = 380 mL.
Calculate the RSBI and determine if extubation is appropriate.
RSBI = 24 ÷ 0.38 = 63. RSBI <105 indicates readiness for extubation.
RSBI (Rapid Shallow Breathing Index) = RR ÷ Vt in liters. A value <105 predicts successful extubation. This patient also meets other criteria: low FiO2/PEEP, awake, cooperative. Proceed with extubation and monitor closely.
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