Impact of mild hypoxemia on renal function and renal resistive index during mechanical ventilation

Abstract

Rationale Short-term hypoxemia affects diuresis and natriuresis in healthy individuals. No data are available on the impact of the mild hypoxemia levels usually tolerated in critically ill patients receiving mechanical ventilation. Objectives To assess the renal effects of mild hypoxemia during mechanical ventilation for acute lung injury (ALI). Methods Prospective, physiological study in 12 mechanically ventilated patients with ALI. Patients were studied at baseline with an arterial saturation (SaO₂) of 96% [94–98] then a comparison was performed between SaO₂ values of 88–90% (mild hypoxemia) and 98–99% (high oxygenation). Main results FiO₂ was set at 0.25 [0.23–0.32] and 0.7 [0.63–0.8], respectively, to obtain SaO₂ of 89 [89–90] and 99% [98–99]. Hemodynamic or respiratory parameters were not significantly affected by FiO₂ levels. Compared with high oxygenation level, mild hypoxemia using low FiO₂ was associated with increase in diuresis (median [interquartile range], 67 [55–105] vs. 55 [45–60] ml/h; P = 0.003) and in doppler-based renal resistive index (RI) (0.78 [0.66–0.85] vs. 0.72 [0.60–0.78]; P = 0.003). The 2-h calculated creatinine clearance also increased (63 [46–103] vs. 35 [30–85] ml/min; P = 0.005) without change in urinary creatinine (P = 0.13). No significant change in natriuresis was observed. Half of the patients were under norepinephrine infusion and the renal response did not differ according to the presence of vasopressors. Conclusion In patients with ALI, mild hypoxemia related to short-term low FiO₂ induce increases in diuresis and in renal RI. This latter point suggests intra-renal mechanisms that need to be further investigated.