Alteration of skin perfusion in mottling area during septic shock

Background: Mottling score has been reported to be a strong predictive factor during septic shock. However, the pathophysiology of mottling remains unclear. Methods: In patients admitted in ICU for septic shock, we measured on the same area the mean skin perfusion by laser Doppler, the mottling score, and variations of both indices between T1 (6 hours after vasopressors were started) and T2 (24 hours later). Results: Fourteen patients were included, SAPS II was 56 [37-71] and SOFA score at T1 was 10 [7-12]. The mean skin surface area analyzed was 4108 +/- 740 mm(2); 1184 +/- 141 measurements were performed over each defined skin surface area. Skin perfusion was significantly different according to mottling score and decreased from 37 [31-42] perfusion units (PUs) for a mottling score of [0-1] to 22 [20-32] PUs for a mottling score of [2-3] and 23 [16-28] for a score of [4-5] (Kruskal-Wallis test, P = 0.05). We analyzed skin perfusion changes during resuscitation in each patient and together with mottling score variations between T1 and T2 using a Wilcoxon signed-rank test. Among the 14 patients included, mottling score increased (worsened) in 5 patients, decreased (improved) in 5 patients, and remained stable in 4 patients. Baseline skin perfusion at T1 was arbitrarily scored 100%. Mean skin perfusion significantly decreased in all the patients whose mottling score worsened from 100% baseline to 63.2 +/- 10.7% (P = 0.001), mean skin perfusion significantly increased in all patients whose mottling score improved from 100% baseline to 172.6 +/- 46.8% (P = 0.001), and remained stable in patients whose mottling score did not change (100.5 +/- 6.8%, P = 0.95). Conclusions: We have shown that mottling score variations and skin perfusion changes during septic shock resuscitation were correlated, providing additional evidence that mottling reflects skin hypoperfusion.