Renal arterial resistance in septic shock: effects of increasing mean arterial pressure with norepinephrine on the renal resistive index assessed with Doppler ultrasonography

Objective: To determine the effects of increasing mean arterial pressure ( MAP) on renal resistances assessed by Doppler ultrasonography in septic shock. Design and setting: Prospective, single- center, nonrandomized, open- label trial in the surgical intensive care unit in a university teaching hospital. Patients and participants: 11 patients with septic shock who required fluid resuscitation and norepinephrine to increase and maintain MAP at or above 65 mmHg. Interventions: Norepinephrine was titrated in 11 patients in septic shock during three consecutive not randomized periods of 2 h to achieve a MAP at successively 65, 75, and 85 mmHg. Measurements and results: At the end of each period hemodynamic parameters and renal function variables ( urinary output, creatinine, clearance) were measured, and Doppler ultrasonography was performed on interlobar arteries to assess the renal resistive index. When increasing MAP from 65 to 75 mmHg, urinary output increased significantly from 76 +/- 64 to 93 +/- 68 ml/h and the resistive index significantly decreased from 0.75 +/- 0.07 to 0.71 +/- 0.06. No difference was found between 75 and 85 mmHg. Conclusions: Doppler ultrasonography and resistive index measurements may help determine in each patient the optimal MAP for renal blood flow and may be a relevant end- point to titrate the hemodynamic treatment in septic shock.