PEEP titration and variability in renal venous congestion metrics in mechanically ventilated patients

Fluid overload contributes to extubation failure in mechanically ventilated patients. Point-of-care ultrasonography, particularly the Venous Excess Ultrasound Score (VExUS), enables noninvasive assessment of venous congestion. The effect of positive end-expiratory pressure (PEEP) on renal venous congestion is unclear. We aimed to explore the effect of PEEP titration on renal venous congestion metrics assessed by ultrasonography in mechanically ventilated patients.

We conducted a non-randomized crossover study in the ICU of a tertiary hospital, enrolling adults immediately prior to ventilator liberation. Each patient underwent renal Doppler ultrasonography at PEEP 5 and 10 cmH₂O, with crossover to the alternate setting separated by a one-hour interval. Intrarenal venous flow (IRVF) patterns, venous impedance index (VII), and renal resistive index (RRI) were assessed. IRVF was analyzed descriptively, while mixed-effects regression accounted for crossover design and cumulative fluid balance.

Thirty-five patients (median age, 68 years; 62.9% male) were analyzed. IRVF patterns were stable across PEEP levels; however, three patients (8.6%) transitioned to a different IRVF pattern. VII increased significantly with higher PEEP (difference, 0.08; 95% CI, 0.01-0.14). RRI did not change significantly (difference, 0.005; 95% CI, -0.012 to 0.022).

In this exploratory study, increasing PEEP from 5 to 10 cmH₂O was associated with a higher VII, while IRVF patterns and RRI showed minimal change. PEEP titration may contribute to variability in sonographic assessment of renal congestion. For patients approaching ventilator liberation, serial ultrasonography is best interpreted at the same or similar PEEP levels to ensure accurate fluid evaluation and VExUS scoring.