Desired Respiratory Rate Calculator
Breaths per minute
Partial pressure of CO₂ in mmHg
Target range is usually 35-45 mmHg
Target Setting
How to Calculate Desired Respiratory Rate
In mechanical ventilation management, adjusting the respiratory rate (frequency) is a primary method for correcting ventilation abnormalities, specifically regarding carbon dioxide (CO₂) removal. The Desired Respiratory Rate formula is used to correct respiratory acidosis (high PaCO₂) or respiratory alkalosis (low PaCO₂).
Assuming the tidal volume (VT) and CO₂ production (VCO₂) remain constant, the relationship between alveolar ventilation and arterial PCO₂ is inversely proportional.
The Formula
The standard formula used in critical care and respiratory therapy is:
New RR = (Current RR × Current PaCO₂) / Desired PaCO₂
Variables Explained
| Variable | Definition | Typical Unit |
|---|---|---|
| Current RR | The actual set rate on the ventilator. | breaths/min |
| Current PaCO₂ | Arterial Carbon Dioxide tension obtained from an Arterial Blood Gas (ABG). | mmHg |
| Desired PaCO₂ | The target level for the patient, typically the physiological norm. | 35-45 mmHg |
Clinical Application & Examples
This calculation is vital when a patient's ABG results indicate inadequate ventilation. Before adjusting Tidal Volume (which risks barotrauma or volutrauma), clinicians often adjust the respiratory rate.
Example 1: Correcting Respiratory Acidosis
A patient on a ventilator has a respiratory rate of 10 bpm. Their latest ABG shows a PaCO₂ of 60 mmHg (high). The goal is to bring the PaCO₂ down to 40 mmHg.
- Calculation: (10 × 60) / 40
- Result: 600 / 40 = 15 bpm
The clinician should increase the rate to 15 breaths per minute to wash out excess CO₂.
Example 2: Correcting Respiratory Alkalosis
A patient is hyperventilating with a rate of 20 bpm and a PaCO₂ of 25 mmHg (low). The target is 40 mmHg.
- Calculation: (20 × 25) / 40
- Result: 500 / 40 = 12.5 bpm
The clinician should decrease the rate to roughly 12-13 breaths per minute to retain CO₂.
Important Considerations
While this formula provides a mathematical target, clinical judgment is essential:
- Auto-PEEP: Setting a respiratory rate too high can decrease expiratory time, potentially leading to air trapping (Auto-PEEP), especially in patients with obstructive lung disease (COPD/Asthma).
- Dead Space: If the tidal volume is significantly lower than dead space volume, simply increasing the rate may not effectively lower PaCO₂.
- Patient Comfort: Significant changes in rate may require adjustments to sedation or synchrony settings.