Discordance between microcirculatory alterations and arterial pressure in patients with hemodynamic instability

Purpose: Recent studies reported that microcirculatory blood flow alterations occur in patients with circulatory shock independent of arterial pressure but typically lack baseline microcirculatory data before the insult and after recovery. We selected cardiopulmonary bypass (CPB) patients with expected and rapidly reversible hemodynamic instability to test the hypothesis that microcirculatory alterations can occur independent of mean arterial pressure (MAP). Methods: Prospective observational study using sidestream darkfield videomicroscopy to measure sublingual microcirculatory flow preoperative (PRE), postoperatively after CPB (POST), and after recovery (REC). We determined the microcirculatory flow index (MFI) at each time point, blinded to all clinical data and compared change in MFI and MAP across time points using analysis of variance adjusted for multiple comparisons. Results: We enrolled 20 subjects, 17 of 20 required inotrope/vasopressor agents at CPB discontinuation, 7 of 20 were on inotrope/vasopressor agents at the time of imaging, 20 of 20 were receiving continuous nitroglycerin. We observed an increase in post-CPB MFI (PRE, 2.16 ± 0.29; POST, 2.45 ± 0.62; REC, 2.26 ± 0.25; P < .01) without a concomitant increase in MAP. Conclusion: In this cohort of patients with hemodynamic instability, we observed discordance between microcirculatory blood flow and arterial pressure. These data support the concept that microcirculatory blood flow indices can yield physiologic information distinct from macrocirculatory hemodynamic parameters.