Alveolar Ventilation Calculator
VA = (VT − VD) × RR · Dead space physiology · ATS/ERS 2022 aligned
VA = (VT − VD) × RR · Normal: 4 – 6 L/minVE = VT × RR · Dead space fraction: VD/VT (normal ≤ 0.35)VD/VT = (PaCO₂ − PēCO₂) / PaCO₂ · Requires mixed expired CO₂| State | VA (L/min) | PaCO₂ trend | Clinical causes | Key actions |
|---|---|---|---|---|
| Severe hypoventilation | < 2.0 | ↑↑ Marked hypercapnia | Central apnoea, opioid toxicity, neuromuscular failure | Urgent airway; mechanical ventilation; reverse precipitant |
| Hypoventilation | 2.0 – 3.9 | ↑ Hypercapnia | COPD exacerbation, OHS, airway obstruction, sedation excess | NIV/CPAP; bronchodilators; adjust ventilator settings; optimise analgosedation |
| Normal | 4.0 – 6.0 | ↔ 35–45 mmHg | Healthy spontaneous breathing | Maintain; reassess if clinical change |
| Hyperventilation | 6.1 – 10.0 | ↓ Hypocapnia | Anxiety, pain, PE, metabolic acidosis compensation, fever | Identify and treat cause; rebreathing not recommended; anxiolytic if appropriate |
| Excessive hyperventilation | > 10.0 | ↓↓ Marked hypocapnia | Mechanical over-ventilation, neurogenic hyperventilation, severe metabolic acidosis | Reduce RR or VT on ventilator; treat underlying metabolic cause; monitor ABG |
VA = (VT − VD) × RR · ATS/ERS Pulmonary Function Guidelines 2022 · Bohr equation for physiological dead space · No patient data stored
- 1.Graham BL, Brusasco V, Burgos F, et al. 2017 ERS/ATS standards for single-breath carbon monoxide uptake in the lung. Eur Respir J. 2017;49(1):1600016. (ATS/ERS pulmonary function standards)
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- 3.Bohr C. Über die Lungenatmung (On pulmonary respiration). Skand Arch Physiol. 1891;2:236–268. (Original Bohr dead space equation derivation)
- 4.Enghoff H. Volumen inefficax. Bemerkungen zur frage des schädlichen raumes. Uppsala Läkarefören Förhandl. 1938;44:191–218. (Enghoff modification for physiological dead space)
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- 6.Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for ARDS. N Engl J Med. 2000;342(18):1301–1308. (ARDSNet — VT 6 mL/kg IBW)
- 7.Lumb A. Nunn's Applied Respiratory Physiology. 9th ed. Elsevier; 2020. (Comprehensive respiratory physiology reference — dead space, VA, and gas exchange)
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- 9.Beydon L, Uttman L, Rawal R, Jonson B. Effects of positive end-expiratory pressure on dead space and its partitions in acute lung injury. Intensive Care Med. 2002;28(9):1239–1245. (PEEP effects on dead space in ICU)
For educational and professional reference only. This Alveolar Ventilation Calculator is intended to assist qualified clinicians — intensivists, pulmonologists, anaesthesiologists, respiratory therapists, and medical educators. It is not a substitute for direct patient assessment, arterial blood gas interpretation, or clinical judgment.
The alveolar ventilation formula (VA = [VT − VD] × RR) uses anatomical dead space as a fixed estimate. In critically ill patients, physiological dead space (including alveolar dead space from V/Q mismatch and intrapulmonary shunting) is substantially larger — as quantified by the Bohr-Enghoff equation using mixed expired PCO₂ from ABG. The calculated VA from this tool represents a simplified estimate.
Dead space increases substantially in ARDS (VD/VT may reach 0.60–0.70), pulmonary embolism (underperfused alveoli), and mechanical ventilation with PEEP (overdistension). Estimating dead space from anatomical values alone significantly overestimates effective alveolar ventilation in these conditions.
PaCO₂ predictions shown are approximations based on the alveolar gas equation (VA × PaCO₂ ≈ constant). Actual PaCO₂ requires arterial blood gas measurement. This tool does not store or transmit patient data.
Last reviewed: January 2026 · ATS/ERS pulmonary function standards 2022 · ARDSNet · West's Pulmonary Pathophysiology · Nunn's Applied Respiratory Physiology 9th ed.
