Ventilator Settings Calculator

ARDS (ARDSnet Protocol)

COPD / Obstructive Disease

Normal Lungs

Why use ideal body weight instead of actual weight?

Tidal volume should be based on lung size, which correlates better with ideal body weight (IBW) than actual weight. Using actual weight in obese patients leads to excessive tidal volumes and ventilator-induced lung injury (VILI). IBW-based calculations prevent volutrauma and barotrauma.

What is the ARDSnet protocol?

The ARDSnet protocol is a lung-protective ventilation strategy from the landmark ARMA trial (2000). It uses low tidal volumes (6 mL/kg IBW), limits plateau pressure to ≤30 cm H₂O, and accepts permissive hypercapnia. This approach significantly reduced mortality in ARDS patients compared to traditional high tidal volume ventilation.

What is driving pressure and why does it matter?

Driving pressure (ΔP) is the difference between plateau pressure and PEEP (ΔP = Pplat - PEEP). It represents the pressure needed to deliver the tidal volume and reflects lung compliance. Driving pressure <15 cm H₂O is associated with better outcomes. Higher driving pressures indicate either stiff lungs or excessive tidal volumes.

How do I measure plateau pressure?

Plateau pressure (Pplat) is measured by performing an inspiratory hold maneuver (0.5-1 second pause at end-inspiration). This allows pressure to equilibrate across the lung and reflects alveolar pressure. Always measure Pplat when adjusting tidal volume or PEEP in ARDS patients. Ensure patient is not actively breathing during the maneuver.

What is auto-PEEP and how do I manage it?

Auto-PEEP (intrinsic PEEP) occurs when expiratory time is inadequate, trapping air in the lungs. Common in COPD and asthma. Measure with expiratory hold maneuver. Manage by: reducing respiratory rate, decreasing tidal volume, shortening inspiratory time, treating bronchospasm, and sometimes adding external PEEP (to ~80% of auto-PEEP).

When should I use pressure vs. volume control?

Volume control (VAC) guarantees minute ventilation and is useful in ARDS for precise tidal volume. Pressure control (PAC) limits peak pressures and may improve distribution in heterogeneous lung disease. PRVC combines benefits of both. Choice often depends on institutional practice and clinical scenario. Both can achieve lung-protective ventilation.

How do I approach difficult oxygenation?

Stepwise approach: 1) Increase FiO₂ to 100%, 2) Optimize PEEP (use PEEP/FiO₂ table or recruitment maneuvers), 3) Ensure adequate minute ventilation, 4) Consider prone positioning (P/F <150), 5) Paralytics if patient-ventilator dyssynchrony, 6) Inhaled pulmonary vasodilators (epoprostenol, NO), 7) ECMO for refractory hypoxemia.

When can I start weaning from the ventilator?

Consider daily spontaneous breathing trials (SBT) when: underlying cause improving, hemodynamically stable, adequate oxygenation (FiO₂ ≤40%, PEEP ≤8), awake and able to protect airway, minimal secretions, and no escalating vasopressor requirements. Use PSV 5-8 or T-piece for 30-120 minutes. Successful SBT + appropriate mental status = consider extubation.