Increasing mean arterial pressure in patients with septic shock: Effects on oxygen variables and renal function

Bourgoin A, et al. Crit Care Med 2005;33:780-786

Introduction

Septic shock is a form of distributive shock characterized by vasodilatation and changes in cardiac function and organ perfusion. Current treatment is frequently aimed at increasing mean arterial pressure (MAP) to at least 60 mm Hg, because this is believed to be the autoregulatory threshold for organ blood flow. The current study investigates the effects of increasing MAP from 65 to 85 mm Hg with norepinephrine on oxygen and renal variables.

Study

This is a prospective, randomised controlled unblinded single centre study. A total of 28 patients with severe septic shock were included if they needed both fluid resuscitation and norepinephrine to raise MAP. All patients received broad-spectrum antibiotic and mechanical ventilation. A pulmonary artery catheter and an arterial catheter were in place. Norepinephrine was the only vasopressor or inotropic agent allowed in this study. The patients were randomized into two groups. Both were first treated with fluid resuscitation until no further rise in cardiac index (CI) or signs of pulmonary overperfusion occurred and than kept at a constant pulmonary artery occlusion pressure. Norepinephrine was titrated to a MAP of 65 mm Hg. After an equilibration period of 60 minutes and an additional 4-h period of hemodynamic stability, hemodynamic and metabolic variables were collected [MAP, MPAP, CI, DO2, SVRI, PVRI, LVSWI, RVSWI, VO2 (by indirect calorimetry), SvO2, serum lactate, urine flow (UF), serum creatinine, urine creatinine clearance (CrCl) and norepinephrine dose]. In group 2 norepinephrine was than titrated up to a MAP of 85 mm Hg, whereas MAP was maintained at 65 mm Hg in group 1. After a 45-minute equilibration period and an additional 4-h period of hemodynamic stability the same variables were collected.

In increase in MAP to 85 mmHg in group 2 in the second 4-h period resulted in a significant increase of CI, SVRI, LVSWI, RVSWI, DO2 and SvO2 compared to group 1. No changes were found in VO2, lactate, blood gases, haemoglobin levels, UF, serum creatinine and CrCl were observed between groups. The oxygen extraction ratio significantly decreased.

Discussion

This study is properly conducted and shows no beneficial effects of increasing MAP from 65 to 85 mm Hg in a group of septic shock patients. On the other hand increased vasoconstriction did not adversely affect systemic tissue perfusion or renal function either. The authors suggest that this was partly because the patients were optimally fluid loaded and because SVRI and MAP were kept within the normal range. Unfortunately, patients with hypertension or atherosclerosis may benefit from a higher MAP because organ perfusion may be pressure dependent over a wider pressure range. In selected cases a brief period of increased MAP may be safely tried. For most patients with septic shock however, a MAP of 65 mm Hg appears to be appropriate.

J. van Dijk, fellow Intensive Care
J.G. van der Hoeven, Internist-intensivist