Fluid status assessment in mechanically ventilated septic patients

Background

Early optimization of fluid status is of major importance in the treatment of critically ill patients. It is unclear whether sonographic measurement of the inferior vena cava (IVC) diameter is valuable in the evaluation of fluid status in mechanically ventilated septic patients.

Methods

Thirty mechanically ventilated patients with severe sepsis or septic shock (age 59.9 ± 15.4 years; APACHE II score 30.6 ± 7.7; 18 males) requiring advanced invasive hemodynamic monitoring due to cardiovascular instability were included in a prospective observational study in a university hospital setting with a 24-bed medical ICU and a 14-bed anaesthesiological ICU. Volume-based hemodynamic parameters were determined using the thermal-dye transpulmonary dilution technique. Simultaneously, the IVC diameter was measured throughout the respiratory cycle by trans-abdominal ultrasonography.

Results

We found a statistically significant correlation of both inspiratory and expiratory IVC diameter with central venous pressure (P = 0.004 and P = 0.001), extravascular lung water index (P = 0.001 and P < 0.001), intrathoracic blood volume index (P = 0.026 and P = 0.05), the intrathoracic thermal volume (both P < 0.001), and the paO₂/FiO₂ oxygenation index (P = 0.007 and P = 0.008, respectively).

Conclusion

Sonographic determination of the IVC diameter is useful in the assessment of volume status in mechanically ventilated septic patients. This approach is rapidly available, noninvasive, inexpensive, easy to learn and applicable in almost any clinical situation without doing harm. IVC sonography may contribute to a faster, more goal-oriented optimization of fluid status and may help to identify patients in whom deleterious volume expansion should be avoided. It remains to be elucidated whether this approach influences the outcome of septic patients.