Effects of perfusion pressure on tissue perfusion in septic shock

Objective: To measure the effects of increasing mean arterial pressure (MAP ) on systemic oxygen metabolism and regional tissue perfusion in septic sho ck. Design:Prospective study. Setting: Medical and surgical intensive care units of a tertiary care teach ing hospital. Patients: Ten patients with the diagnosis of septic shock who required pres ser agents to maintain a MAP greater than or equal to 60 mm Hg after fluid resuscitation to a pulmonary artery occlusion pressure (PAOP) greater than or equal to 12 mm Hg. Interventions: Norepinephrine was titrated to MAPs of 65, 75, and 85 mm Hg in 10 patients with septic shock. Measurements and Main Results:At each level of MAP, hemodynamic parameters (heart rate, PAOP, cardiac index, left ventricular stroke work index, and s ystemic vascular resistance index), metabolic parameters (oxygen delivery, oxygen consumption, arterial lactate), and regional perfusion parameters (g astric mucosal Pco(2), skin capillary blood flow and red blood cell velocit y, rine output) were measured. Increasing the MAP from 65 to 85 mm Hg with norepinephrine resulted in incr eases in cardiac index from 4.7 +/- 0.5 L/min/m(2) to 5.5 +/- 0.6 L/min/m(2 ) (p < 0.03). Arterial lactate was 3.1 +/- 0.9 mEq/L at a MAP of 65 mm Hg a nd 3.0 +/- 0.9 mEq/L at 65 mm Hg (NS). The gradient between arterial Pco(2) and gastric intramucosal Pco(2) was 13 +/- 3 mm Hg (1.7 +/- 0.4 kPa) at a MAP of 65 mm Hg and 16 +/- 3 at 85 mm Hg (2.1 +/- 0.4 kPa) (NS). Urine outp ut at 65 mm Hg was 49 +/- 18 mL/hr and was 43 +/- 13 mL/hr at 85 mm Hg (NS) . As the MAP was raised, there were no significant changes in skin capillar y blood flow or red blood cell velocity. Conclusions: Increasing the MAP from 65 mm Hg to 85 mm Hg with norepinephri ne does not significantly affect systemic oxygen metabolism, skin microcirc ulatory blood flow, urine output, or splanchnic perfusion. (Crit Care Med 2 000; 28:2729-2732).