Respiratory

Ventilator Rate for a Target PaCO₂ Calculator

The rate that should reach a target PaCO₂ if tidal volume, dead space and CO₂ production stay the same.

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

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Formula

New rate = current rate × current PaCO₂ ÷ target PaCO₂
From the alveolar ventilation equation: PaCO₂ = 0.863 × V̇CO₂ ÷ V̇A, with V̇A = (tidal volume − dead space) × rate; with the same tidal volume, dead space and CO₂ production, PaCO₂ × rate stays constant

How it is used

• Aim for the pH, not a normal PaCO₂: in ARDS the ARDS Network protocol raised the rate to no more than 35/min for a pH of 7.30–7.45 and otherwise accepted hypercapnia (ARDS Network 2000).
• Faster rates shorten expiratory time; with airflow obstruction the lungs do not empty, and the trapped gas (auto-PEEP) lowers venous return and blood pressure (Pepe & Marini 1982).
• Raising the set rate only adds breaths if it is above the patient’s own rate, and fever, agitation or changing dead space move the PaCO₂ on their own (alveolar ventilation equation).

Key points

• After raising the rate, check the flow waveform and an end-expiratory hold for auto-PEEP; in asthma or COPD it can appear at modest rates.
• Hypotension after a rate increase suggests auto-PEEP: briefly disconnecting the ventilator to let the patient exhale is the bedside test and treatment.

Same formula as the app. Open it in the web app.

Related one-pagers

• Ventilator Modes and Settings
• ABG Interpretation in 6 Steps

Related calculators

• A-a Gradient
• Alveolar Gas Equation (PAO₂)
• Arterial Oxygen Content (CaO₂)
• Minute Ventilation
• P/F Ratio (PaO₂/FiO₂)
• Predicted Body Weight (PBW)
• SpO₂/FiO₂ Ratio

For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Verify results independently and follow your local protocols and medical direction. Not a substitute for clinical judgment.