Ventilatory ratio: a simple bedside measure of ventilation

Area of Science:

• Respiratory Physiology
• Critical Care Medicine
• Pulmonary Function Testing

Background:

• Traditional monitoring of ventilated patients focuses on oxygenation, often overlooking carbon dioxide elimination.
• Carbon dioxide elimination is influenced by production and alveolar ventilation, impacting Pa(CO2) levels.
• Assessing ventilatory efficiency through comparisons of actual and predicted measurements is underutilized.

Purpose of the Study:

• To introduce and validate the ventilatory ratio (VR) as a novel measure of ventilatory efficiency.
• To provide clinicians with a simple tool for monitoring carbon dioxide elimination in ventilated patients.

Main Methods:

• Developed the ventilatory ratio (VR) as a unitless ratio: VR = (V(E measured) x Pa(CO2 measured))/(V(E predicted) x Pa(CO2 predicted)).
• Established predicted values: V(E predicted) = 100 (ml kg(-1) min(-1)) and Pa(CO2 predicted) = 5 kPa.
• Designed VR for easy bedside calculation.

Main Results:

• The VR is intuitively linked to carbon dioxide production and ventilatory efficiency.
• A VR close to 1 is expected in normal individuals.
• An increasing VR indicates worsening ventilation, increased CO2 production, or both.

Conclusions:

• The ventilatory ratio (VR) is a novel and practical tool for clinicians.
• VR provides valuable supplementary information for managing ventilated patients.
• This ratio aids in assessing changes in ventilatory efficiency and CO2 elimination.