Table 3 A proof-of-concept classification of VR on the mortality according to the P/F ratio in a mechanically ventilated population

Relationship of VR and ICU mortality

J-shaped dose–response association

Positive correlation

Cutoff of VR

0.9

1.3

Pathophysiology meaning of VR

When VR < 0.9, a decreased VR may indicate hyperventilation under excessive mechanical ventilation support. Moreover, the value of VR was impacted by hypocapnia. Hence, a low VR might be related to a poor outcome

When VR > 0.9, the VR was positively related to mortality

An increase in VR might reflect an increased dead space level. Hence, a high VR indicates severe lung injury and a poor outcome