Influence of arterial pressure on tissue perfusion in septic shock

Introduction

The aim of this study was to measure the effects of increasing mean arterial pressure (MAP) on systemic oxygen metabolism and regional tissue perfusion in septic shock.

Methods

Twenty patients with the diagnosis of septic shock who required pressor agents to maintain a MAP ≥ 65 mmHg after fluid resuscitation to a pulmonary artery occlusion pressure (PAOP) ≥ 12 mmHg were included. Norepinephrine was titrated to MAPs of 65 mmHg, 75 mmHg and 85 mmHg in 20 patients with septic shock.

Results

At each level of MAP, hemodynamic parameters (heart rate, PAOP, cardiac index, left ventricular stroke work index, and systemic vascular resistance index), metabolic parameters (oxygen delivery, oxygen consumption, blood lactate), and regional perfusion parameters (gastric mucosal PCO₂, skin capillary blood flow and red blood cell velocity, urine output) were measured. Increasing the MAP from 65 to 85 mmHg with norepinephrine resulted in increases in cardiac index from 3.5 ± 0.4 l/min/m² to 5.0 ± 0.5 l/min/m² (P < 0.03). Blood lactate was 3.5 ± 0.8 mEq/l at a MAP of 65 mmHg and 3.0 ± 0.8 mEq/l at 85 mmHg (P = NS). The gradient between arterial PCO₂ and gastric intramucosal PCO₂ was 11 ± 3 mmHg (1.5 ± 0.3 kPa) at a MAP of 65 mmHg and 15 ± 3 mmHg at 85 mmHg (2.0 ± 0.3 kPa, P = NS). Urine output at 65 mmHg was 40 ± 10 ml/hour and was 45 ± 12 ml/hour at 85 mmHg (P = NS). As the MAP was raised, there were no significant changes in skin capillary blood flow or red blood cell velocity.

Conclusion

Increasing the MAP from 65 mmHg to 85 mmHg with norepinephrine does not significantly affect systemic oxygen metabolism, skin microcirculatory blood flow, urine output, or splanchnic perfusion.