Correlation between Perfusion Index and Lactate Level in Critically Ill Patients

Background: During shock resuscitation, early detection of tissue hypoperfusion would guide physician to actively manage for the better outcome. Serum lactate is commonly used but it needs blood sampling and obtains intermittent data. Perfusion index (PI) analyzed from pulse-oximetry signal is a non-invasive and continuous monitoring for peripheral tissue perfusion. Previous studies have shown correlations between PI and microcirculation parameters in critically ill patients; however, limited data is available.

Objective: To investigate the correlation between PI and lactate level in critically ill patients.

Materials and Methods: The present study was a prospective observational study at the surgical intensive care unit of King Chulalongkorn Memorial Hospital (KCMH). All critically ill patients having tissue hypoperfusion and serum lactate of 2 mmol/L or greater were enrolled. PI was measured by MasimoRadical-7®PulseCO-Oximeter® and recorded values simultaneously with serum lactate at 0, 2, 6, and 24-hours during resuscitation.

Results: Of the 42 patients, the authors found a significant correlation between PI and lactate level at 0 and 2-hours (r=–0.397, p=0.009 and r=–0.311, p=0.045, respectively). The change in PI also significantly correlated with lactate clearance at first 6-hours of resuscitation (r=0.444, p=0.003 at 0 to 2-hour and r=0.370, p=0.017 at 2 to 6-hours). Twenty-four patients or 57% had lactate clearance of 10% or more within 2-hours, whereas 18 patients (42.8%) did not. The cut-off value of increasing in PI of less than 0.86 predicted patients who were not lactate clearance at 2-hours, (sensitivity 88.9%, specificity 54.2%, AUC 0.699, 95% CI 0.54 to 0.86, p=0.029).

Conclusion: PI may have value to adjunct continuous monitoring for peripheral perfusion during early resuscitation by using concurrently with serum lactate. Increase in PI of less than 0.86 within 2-hours should prompt the physician to manage it further.

Keywords: Lactate; Perfusion index; PI; Peripheral tissue perfusion; Microcirculatory monitoring