Calculates a simplified stress index from three airway-pressure measurements during constant-flow inflation.
Overview
Calculates a simplified stress index from three airway-pressure measurements during constant-flow inflation.
Clinical Significance
A value near 1 suggests approximately linear pressure rise; values above or below 1 may suggest upward or downward concavity. This simplified bedside surrogate is not identical to nonlinear curve fitting.
How It Is Calculated
- Simplified curvature ratio = (P75 − P50)/(P50 − P25).
Interpretation
- A value near 1 suggests approximately linear pressure rise; values above or below 1 may suggest upward or downward concavity. This simplified bedside surrogate is not identical to nonlinear curve fitting.
Worked Example
Enter a clinically consistent set of values in the displayed units. MedicalC applies: Simplified curvature ratio = (P75 − P50)/(P50 − P25).
Limitations
- This tool does not establish a diagnosis or mandate treatment.
- Published cut-offs may vary between cohorts and measurement methods.
- Calculation precision cannot compensate for poor source data.
Clinical Pearls
- Trend the result over time where clinically appropriate.
- Record the source values and units alongside the calculated result.
Common Mistakes
- Using the wrong unit.
- Combining measurements obtained at different times.
- Applying a research-derived threshold as a universal treatment trigger.
Frequently Asked Questions
What does this calculator provide?
Calculates a simplified stress index from three airway-pressure measurements during constant-flow inflation.
Can this result be used alone?
No. It must be interpreted with clinical context and appropriate investigations.
What equation is used?
Simplified curvature ratio = (P75 − P50)/(P50 − P25).
What is the main limitation?
The result depends on valid inputs and may not be calibrated for every population or setting.
References
- Ranieri VM et al. Effect of mechanical ventilation on inflammatory mediators in patients with ARDS. JAMA. 1999. — Formula, physiological or validation reference.
Reviewed by: MedicalC Clinical Editorial Team
Last reviewed: July 2026