Desired Ve / PaCO₂ Calculator

Leave exactly one field blank and we’ll calculate it.

Current PaCO₂ (mmHg)

Desired PaCO₂ (mmHg)

Current Minute Ve (L/min)

Desired Minute Ve (L/min)

How this works

PaCO₂ varies inversely with minute ventilation (Ve). Holding CO₂ production and dead space constant, Ve↑ → PaCO₂↓ and Ve↓ → PaCO₂↑. This tool uses that proportionality to solve for the missing variable.

Rate vs Tidal Volume — which to adjust?

Because PaCO₂ ∝ 1/Ve, you can reach a target PaCO₂ by increasing respiratory rate or tidal volume (Ve = Vt × f). Clinically, we often prefer small Vt with higher rates to protect lungs from over‑distension. Use the calculator’s Suggested Rate to see a safe, rounded whole‑number rate for your current Vt.

If Vt already meets lung‑protective goals (≈6–8 mL/kg IBW), favor rate adjustments first.
If auto‑PEEP or breath stacking occurs at higher rates, consider a modest Vt change instead.
For obstructive disease, avoid excessive rates; allow adequate expiratory time.

Keywords: minute ventilation, tidal volume, respiratory rate, PaCO₂ reduction, lung‑protective ventilation

Typical ranges & quick checks

Protective Vt

~4–6 mL/kg (lung‑protective), ~6–8 mL/kg typical adult

Common rates (adult)

12–24 breaths/min

Always reassess gases and the patient’s work of breathing after any change. Verify plateau pressures and dynamic hyperinflation before increasing rate further.

Keywords: target PaCO₂, ventilator settings, protective ventilation, plateau pressure, dynamic hyperinflation

Dead space, metabolic CO₂, and why this is an estimate

This tool assumes relative stability in dead‑space fraction (V_D/V_T) and CO₂ production. Shock states, fever, sepsis, and equipment dead space can alter the PaCO₂–Ve relationship.

Rising PaCO₂ despite higher Ve suggests increased dead space or fatigue.
Consider ventilator graphics, ETCO₂ versus PaCO₂ gap, and hemodynamics.

Keywords: dead space fraction, Vd/Vt, hypercapnia, end‑tidal CO₂, PaCO₂–Ve relationship

FAQ

Should I use permissive hypercapnia?

Permissive hypercapnia can be acceptable in ARDS or severe obstructive disease to maintain protective Vt and avoid barotrauma. Target pH and clinical context should guide decisions.

What if the suggested rate is very high?

Re‑check Vt (mL), dead space, and auto‑PEEP. You may need small Vt adjustments, sedation optimization, or to accept a higher PaCO₂ temporarily.

Does mode matter (AC/VC, PC, PRVC)?

The PaCO₂–Ve relationship holds across modes, but delivered Vt and patient effort vary. Confirm measured Ve on the ventilator and trend ABGs.

Keywords: permissive hypercapnia, ARDS, barotrauma, ventilator mode, arterial blood gas