Knee area tissue oxygen saturation is predictive of 14-day mortality in septic shock

Thenar eminence tissue oxygen saturation (StO(2)) was developed to assess organ perfusion. However, mottling, a strong predictor of mortality in septic shock, develops preferentially around the knee. We aimed to evaluate the prognostic value of StO(2) measured around the knee in septic shock patients and compare it to thenar StO(2).

This was a prospective observational study in a tertiary teaching hospital. All consecutive patients with septic shock were included. Parameters were recorded when vasopressors were started (H0) and every 6 h during 24 h. Their predictive value was assessed on 14-day mortality.

Fifty-two patients were included. SOFA score was 11 (9-15) and SAPS II was 56 (40-72). At 6 h after ICU admission (H6), mean arterial pressure, cardiac index, and central venous pressure were not different between non-survivors and survivors; but non-survivors had higher arterial lactate level (8.8 ± 5.0 vs. 2.2 ± 1.5 mmol/l, P < 0.001), lower urinary output (0.22 ± 0.45 vs. 0.70 ± 0.50 ml/kg/h, P < 0.001) and ScvO(2) (62 ± 20 vs. 72 ± 9 %, P = 0.03). At H6, StO(2) was lower in non-survivors; this difference was not significant for thenar StO(2) (70 ± 15 vs. 77 ± 12 %, P = 0.10) but was very pronounced for knee StO(2) (39 ± 23 vs. 71 ± 12 %, P < 0.001). At H6, a low knee StO(2) was associated with a higher mottling score (P < 0.01), a higher lactate level (P < 0.002, R (2) = 0.2), and a lower urinary output (P = 0.02, R (2) = 0.12).

After initial septic shock resuscitation, StO(2) measured around the knee is a strong predictive factor of 14-day mortality.