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Ventilator Settings: Complete Reference with Clinical Significance

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Core Ventilator Parameters

1. Fraction of Inspired Oxygen (FiO2)

• Directly increases alveolar partial pressure of oxygen, improving arterial oxygenation
• Initial setting: Start at 1.0 (100%) for any unstable intubated patient, then titrate down
• Target: SpO2 92-96% (or PaO2 55-80 mmHg) using the lowest effective FiO2
• FiO2 >0.5-0.6 for prolonged periods can cause oxygen toxicity (absorptive atelectasis, free radical injury)

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2. Tidal Volume (VT)

• Too large = volutrauma (alveolar overdistention) and VILI (ventilator-induced lung injury)
• Too small = atelectasis and inadequate ventilation
• Standard default: 6-8 mL/kg IBW for most patients (based on predicted/ideal body weight, NOT actual weight)

The ARMA trial showed that low VT (6 mL/kg) vs. conventional (12 mL/kg) ventilation in ARDS reduced mortality from 40% to 31%. - Harrison's Principles of Internal Medicine, 22E

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3. Respiratory Rate (RR)

• Together with VT, determines minute ventilation (MV = RR x VT)
• Increasing RR increases CO2 elimination (reduces PaCO2, raises pH)
• Decreasing RR retains CO2 (useful in permissive hypercapnia strategies)
• Standard default: 12-16 breaths/min (AC mode), 10-14 (volume control)

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4. Positive End-Expiratory Pressure (PEEP)

• Keeps alveoli open throughout the respiratory cycle (combats atelectrauma)
• Increases mean airway pressure, improving oxygenation
• Reduces work of breathing (by counterbalancing intrinsic PEEP in COPD)
• Can reduce cardiac preload at high levels (compresses great veins)
• Standard default: 5 cmH2O (baseline physiologic PEEP)

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5. Peak Inspiratory Pressure (PIP) / Peak Airway Pressure

• Reflects airway resistance (elevated by secretions, bronchospasm, kinked ETT)
• High PIP + normal plateau = airway resistance problem
• High PIP + high plateau = compliance problem (stiff lungs)
• Should generally be kept <40-45 cmH2O

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6. Plateau Pressure (Pplat)

• The most important pressure target in lung-protective ventilation
• Reflects true alveolar distending pressure (not just airway)
• Target: ≤30 cmH2O (ARDSNet); in ECMO settings ≤24-25 cmH2O
• Plateau pressure - PEEP = Driving Pressure (see below)

• Reduce VT
• Consider increasing PEEP (may improve compliance by keeping alveoli open)
• Identify and treat underlying cause (pneumothorax, bronchospasm, effusion)

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7. Driving Pressure (ΔP)

• Represents the stress applied to the lung parenchyma per breath
• Target: <15 cmH2O (studies show >15 cmH2O associated with increased VILI and mortality)
• Growing evidence suggests driving pressure is the most important predictor of ARDS mortality
• In ECMO, target driving pressure <15 cmH2O, keeping inspiratory Pplat <25 cmH2O

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8. Inspiratory Flow Rate

• In volume-control ventilation (VCV): clinician sets flow rate (typically 40-80 L/min)
• Higher flow = shorter inspiratory time = longer expiratory time (beneficial in COPD/asthma)
• Higher flow = higher PIP (but not plateau pressure)
• Two waveforms available:
  • Decelerating (ramp): More physiologic, better distribution of ventilation, preferred in most patients
  • Square wave (constant): Faster delivery, useful when short inspiratory time is needed

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9. Inspiratory Time (Ti) and I:E Ratio

• I:E ratio 1:2 is physiologic baseline
• Prolonging I time (inverse ratio ventilation, e.g., 1:1 or 2:1): increases mean airway pressure, improves oxygenation in refractory ARDS (rarely used now)
• Prolonging E time (e.g., 1:3 to 1:4): essential in COPD and asthma to allow full exhalation and prevent auto-PEEP

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10. Trigger Sensitivity

• Flow trigger: Ventilator detects a drop in baseline flow (typically 1-3 L/min below baseline). More sensitive and responsive.
• Pressure trigger: Patient must drop airway pressure below PEEP by a set amount (typically -0.5 to -2 cmH2O)
• Too sensitive: Auto-triggering (ventilator fires without patient effort) - causes hyperventilation
• Too insensitive: Increased work of breathing, patient-ventilator dyssynchrony
• In COPD with auto-PEEP: Sensitivity effectively increased by the auto-PEEP, requiring greater patient effort to trigger - apply extrinsic PEEP to counteract this

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Ventilation Modes Summary

Volume Control Ventilation (VCV / AC-VC)

• Guarantees a minimum minute ventilation
• Does NOT guarantee safe pressures - plateau must be monitored
• Best for: unstable/sedated patients, ARDS (gold standard for lung-protective ventilation)

Pressure Control Ventilation (PCV / AC-PC)

• Guarantees airway pressure will not exceed set level
• VT varies with changing compliance (must monitor closely)
• Best for: ARDS after thoracic surgery, patients where pressure limitation is key

Synchronized Intermittent Mandatory Ventilation (SIMV)

• Delivers set mandatory breaths synchronized to patient effort, patient can breathe spontaneously between
• Add pressure support (PSV) if using SIMV to reduce work of spontaneous breaths
• Less preferred as primary mode (increases work of breathing, prolongs weaning)

Pressure Support Ventilation (PSV)

• Every breath is patient-triggered and patient-cycled
• Used for weaning trials and spontaneous breathing trials (SBT)
• Spontaneous breathing trial: PSV at 5-7 cmH2O (or T-piece) for 30-120 min to assess readiness for extubation
• Backup apnea rate usually set

CPAP (Continuous Positive Airway Pressure)

• Single continuous pressure level throughout the respiratory cycle
• Provides no active inspiratory support
• Used in: OSA, mild COPD exacerbation, cardiogenic pulmonary edema (NIV)

BiPAP (Bilevel Positive Airway Pressure) / NIV

• IPAP provides inspiratory assistance (like pressure support)
• EPAP acts as PEEP (improves oxygenation, prevents atelectasis)
• Initial settings: IPAP 10 cmH2O, EPAP 5 cmH2O; titrate in 1-2 cmH2O increments
• IPAP >20 cmH2O: avoid (discomfort, gastric insufflation)
• IPAP - EPAP = effective pressure support level

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Condition-Specific Settings at a Glance

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Liberation Criteria (Extubation Readiness)

• Underlying condition improved
• Patient awake, off/minimal sedation
• FiO2 ≤0.5, PEEP <8 cmH2O, SpO2 >88%
• Hemodynamically stable
• Adequate cough and manageable secretions

• RR <35, SpO2 >90%, systolic BP 90-180 mmHg, HR stable (<20% change)
• No significant anxiety or dyspnoea

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Key Numbers to Remember

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• Harrison's Principles of Internal Medicine, 22E (2025) - Chapter 313: Mechanical Ventilation
• Roberts & Hedges' Clinical Procedures in Emergency Medicine - Chapter 8: Ventilation Modes
• Current Surgical Therapy, 14e - Mechanical Ventilation in ARDS
• Murray & Nadel's Textbook of Respiratory Medicine - Lung-Protective Strategies