Table 2 Characteristics of tests and indices assessing preload responsiveness based on heart–lung interactions
Test/index | Advantages | Limitations | Confounding factors | Criterion of judgement | Diagnostic threshold | Level of evidence |
|---|---|---|---|---|---|---|
PPV | →Automatically measured →Widely available (invasive or non-invasive arterial pressure curve) →Requires no manoeuvre →Very well validated | →Impossible to use in many patients because of confounding factors | →False positives in case of cardiac arrhythmias, spontaneous breathing activity and possibly right ventricular failure →False negatives in case of low Vt, low lung compliance and IAH | Absolute value itself | ≥ 15% | ++++ |
SVV | →Automatically measured →Requires no manoeuvre →Well validated | →Impossible to use in many patients because of confounding factors →Requires a device for pulse contour analysis | →Those of PPV →An arterial pressure of poor quality may provide wrong values | Absolute value itself | ≥ 15% | +++ |
EEO test | →Easy to perform →Works regardless of breathing activity, cardiac rhythm, Vt, lung compliance →Well validated | →Requires a direct estimation of CO/SV →Requires mechanical ventilation →Cannot be used if the patient interrupts the 15-s EEO | →Interruption of the test before its end by breathing efforts of the patient | ↗ CO | ≥ 5% | +++ |
↗ VTI (better with additional EIO) | EEO alone: ≥ 5% EEO + EIO: ≥ 13% | + | ||||
↗ perfusion index | ≥ 2.5% | + | ||||
Vt challenge | →Requires no measurement in CO/SV (just an invasive or non-invasive arterial pressure curve) →Reliable in prone position and in spontaneously breathing patients | →Requires mechanical ventilation →Different diagnostic thresholds reported →Requires more validation | →Cardiac arrhythmias? →Intra-abdominal hypertension? | ↗ PPV | ≥ 1 to 3.5% | ++ |
Vena cava distensibility | →Requires no measurement in CO/SV | →False positives in case of spontaneous breathing activity and possibly right ventricular failure →False negatives in case of low Vt, low lung compliance →Quite low reliability →Not reliable in case of IAH →For SVC: requires TOE | →Those of PPV (except cardiac arrhythmia) | Absolute value itself | IVC: ≥ 12% SVC: ≥ 12 to 36% | + |