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.
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.
Related one-pagers
Related calculators
- A-a Gradient
- Alveolar Gas Equation (PAO₂)
- Arterial Oxygen Content (CaO₂)
- Dead Space Fraction (Bohr)
- Driving Pressure
- Dynamic Compliance
- Minute Ventilation
- O₂ Extraction Ratio
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For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Verify results independently and follow your institution’s protocols. Not a substitute for clinical judgment.