Can Incentive Spirometry Lower PCO₂?
Yes, incentive spirometry can lower arterial PCO₂, though the effect is modest and most clinically relevant in specific postoperative contexts, particularly after cardiac surgery.
Evidence for PCO₂ Reduction
The most direct evidence comes from recent cardiac surgery studies. In post-CABG patients, incentive spirometry demonstrated a trend toward decreased PaCO₂ levels 1. A 2020 randomized trial showed mean PCO₂ decreased from 41.4±3.26 mmHg to 36.1±2.11 mmHg after three days of incentive spirometry use post-CABG 2. Similarly, a 2025 study comparing incentive spirometry to oscillating positive expiratory pressure devices found significant improvements in PCO₂ values on postoperative days 2 and 3 3.
In COPD patients, a 2005 study demonstrated that 2 months of incentive spirometry use resulted in statistically significant decreases in PaCO₂ (P = 0.02) alongside improvements in PaO₂ 4.
Clinical Context and Limitations
The guidelines are clear that incentive spirometry should not be used as a standalone intervention 5. The 2021 enhanced recovery guidelines for pulmonary lobectomy explicitly state that adding isolated chest physiotherapy techniques like incentive spirometry to multimodal physiotherapy protocols failed to improve patient prognosis 5. Multiple randomized trials found no impact on complication rates or hospital length of stay when incentive spirometry was added to standard multimodal management 5.
Key Algorithmic Approach:
- Post-cardiac surgery patients: Consider incentive spirometry as part of multimodal chest physiotherapy (combining early mobilization, breathing exercises, coughing techniques, and pain management)
- COPD exacerbations: May use incentive spirometry alongside medical treatment, as it improved blood gases without altering pulmonary function parameters 4
- Post-thoracic surgery: Use multimodal physiotherapy first; add incentive spirometry on case-by-case basis, never alone 5
Important Caveats
The PCO₂ reductions observed are generally modest (approximately 3-5 mmHg) and occur over days, not acutely. The 2007 ACCP/AACVPR pulmonary rehabilitation guidelines do not support routine use of ventilatory muscle training (which includes incentive spirometry-type interventions) as an essential component 6.
The primary benefit appears to be in preventing postoperative pulmonary complications rather than as a primary treatment for hypercapnia. When PCO₂ reduction is needed, incentive spirometry works best as one component of comprehensive respiratory care, not as monotherapy.