Airway Resistance Calculator
Calculate airway resistance using peak inspiratory pressure, plateau pressure, and inspiratory flow. This calculator can accept flow in L/min or L/sec and will convert as needed.
Calculator
Calculate Airway Resistance
Formula: Raw = (PIP − Pplat) ÷ Flow. Flow must be in L/sec, but this calculator can convert from L/min.
Airway Resistance
—
cmH₂O/L/sec
Enter PIP, Pplat, and flow to calculate airway resistance.
Formula
Airway Resistance Formula
Raw = (PIP − Pplat) ÷ Flow
Example: PIP 35, Pplat 25, Flow 60 L/min
60 L/min ÷ 60 = 1 L/sec
(35 − 25) ÷ 1 = 10 cmH₂O/L/sec
Example: PIP 35, Pplat 25, Flow 60 L/min
60 L/min ÷ 60 = 1 L/sec
(35 − 25) ÷ 1 = 10 cmH₂O/L/sec
RT Memory Trick
Use the Units When You Forget the Formula
Airway resistance is reported as:
cmH₂O/L/sec
Pressure is on top, and flow is on the bottom. The pressure difference that represents resistance is PIP − Pplat because plateau pressure removes the resistive pressure component.
That tells you:
Airway Resistance = (PIP − Pplat) ÷ Flow
Airway Resistance = (PIP − Pplat) ÷ Flow
Interpretation
How to Interpret Airway Resistance
| Airway Resistance | Interpretation | Possible Clinical Meaning |
|---|---|---|
| < 5 cmH₂O/L/sec | Low resistance | Less resistance to flow than expected. |
| 5–10 cmH₂O/L/sec | Normal range | Typical adult airway resistance range. |
| 11–15 cmH₂O/L/sec | Mildly elevated | Early bronchospasm, secretions, or flow-related resistance. |
| 16–20 cmH₂O/L/sec | Moderately elevated | Bronchospasm, mucus, tubing issue, or ET tube resistance. |
| > 20 cmH₂O/L/sec | Severely elevated | Significant obstruction or resistance problem. |
Clinical Pearl
What Increases Airway Resistance?
Patient causes
Bronchospasm, asthma, COPD exacerbation, mucus plugging, secretions.
Bronchospasm, asthma, COPD exacerbation, mucus plugging, secretions.
Artificial airway causes
Small ET tube, kinked ET tube, biting the tube, partial obstruction.
Small ET tube, kinked ET tube, biting the tube, partial obstruction.
Circuit causes
Water in tubing, kinked tubing, obstructed HME or filter.
Water in tubing, kinked tubing, obstructed HME or filter.
Ventilator clue
High PIP with normal Pplat usually points toward a resistance problem.
High PIP with normal Pplat usually points toward a resistance problem.
Pressure Pattern Troubleshooting
Compare PIP and Plateau Pressure
| Pattern | Think | Examples |
|---|---|---|
| High PIP + normal Pplat | Resistance problem | Bronchospasm, secretions, kinked tube, water in tubing. |
| High PIP + high Pplat | Compliance problem | ARDS, pneumonia, pulmonary edema, atelectasis. |
| Both resistance and compliance concerns | Combined problem | COPD with pneumonia, ARDS with secretions, severe asthma with air trapping. |
Common Student Mistakes
Avoid These Errors
Using L/min without converting
The formula requires L/sec. The calculator converts L/min automatically.
The formula requires L/sec. The calculator converts L/min automatically.
Using PIP alone
Resistance pressure is PIP − Pplat, not PIP by itself.
Resistance pressure is PIP − Pplat, not PIP by itself.
Confusing resistance with compliance
A high PIP alone does not tell you the cause. Compare PIP and Pplat.
A high PIP alone does not tell you the cause. Compare PIP and Pplat.
Ignoring flow
Resistance is pressure difference divided by flow, so flow matters.
Resistance is pressure difference divided by flow, so flow matters.
Continue Learning
Connect Resistance, Compliance, and Ventilator Troubleshooting
Use static compliance, dynamic compliance, and airway resistance together to understand whether the problem is stiffness, resistance, or both.