Perfusion index for assessing microvascular reactivity in septic shock after fluid resuscitation

Microcirculation disturbances are implicated in the prognosis of septic shock. Microvascular hyporesponsiveness can be assessed by an oximetry-derived perfusion index and reactive hyperemia. Using this perfusion index, we investigated reactive hyperemia and its relationship with peripheral perfusion and clinical-hemodynamic parameters in septic shock.

Eighty-two patients were evaluated: 47 with septic shock and 35 controls. Tests were performed within 24 hours after admission. The perfusion index was evaluated before and after a 3-min blood flow occlusion using a time-response analysis for 5 min. The perfusion index was also evaluated in the hyperemic phases and was mainly derived by mechanosensitive (ΔPI0-60) and metabolic mechanisms (ΔPI60-120). Correlation tests were performed between reactive hyperemia and clinical-hemodynamic data.

Reactive hyperemia measured by the perfusion index was significantly lower in patients with septic shock, but this was only observed for the first 45 seconds after cuff-deflation. In the remaining period, there were no statistical differences between the groups. The peaks in the perfusion index were similar between groups, although the peak was reached more slowly in the septic group. Values of ΔPI0-60 were lower in shock [01% (-19% - -40%) versus 39% (6% - 75%); p = 0.001]. However, ΔPI60-120 was similar between the groups [43% (18% - 93%) versus 48% (18% - 98%); p = 0.58]. The time-to-peak of the perfusion index was correlated positively with the SOFA scores and negatively with C-reactive protein; the peak of the perfusion index was positively correlated with vasopressor doses; and the ΔPI60-120 values were positively correlated with C-reactive protein and vasopressor doses. No other significant correlations occurred.

This perfusion index-based study suggests that septic shock promotes initial peripheral vascular hyporesponsiveness and preserves posterior vascular reactivity to a considerable degree. These results demonstrate a time-dependent peripheral hyperemic response and a significant ischemic reserve in septic shock.