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. © 2009 Springer-Verlag.