The purpose of the study was to evaluate the efficacy of using the respiratory variation in inferior vena cava diameters as an index of fluid responsiveness after tidal volume challenge in mechanically ventilated patients after cardiac surgery.

The "tidal volume challenge" is a novel test to predict fluid responsiveness in patents in shock, ventilated using low tidal volume without spontaneous breathing activity. The test involves transiently increasing tidal volume from 8 ml/kg PBW to 12 ml/kg PBW for one minute and observing the change in PPV or SVV. The aim of this study was to evaluate whether the respiratory variation in inferior vena cava diameter after tidal volume challenge can predict fluid responsiveness in cardiac surgical patients with mechanical ventilation

Inclusion Criteria:

• acute circulatory failure (low blood pressure or urine output, tachycardia, or mottling)
• clinical signs of organ hypoperfusion (renal dysfunction or hyperlactatemia)

Exclusion Criteria:

• a contraindication to elevation of tidal volume
• evidence of cardiac arrhythmia
• left ventricular ejection fraction less than 50%
• echocardiographic examination that showed the existence of severe tricuspid or mitral regurgitation or right heart dysfunction
• intracardiac shunt
• pulmonary hypertension
• severe chronic obstructive pulmonary disease
• a contraindication to the passive leg raising (PLR) test
• air leakage through chest drains
• abdominal compartment syndrome
• portal hypertension
• pregnancy
• inability to perform ultrasonography

Patients after cardiac surgery