Objective: To investigate the correlation of transcutaneous oxygen challenge test (OCT) [the degree of PtcO2 response to increased fractional inspired oxygen concentration (FiO2) of 1.0 is identified as transcutaneous OCT] and central venous oxygen saturation (ScvO2) in septic shock patients after resuscitation.
Methods: A total of 49 septic shock patients were prospectively studied. They underwent PtcO2 monitoring and OCT (a temporary increase of FiO2 for 10 min). Baseline central venous blood gases, baseline arterial blood gases and post-OCT arterial blood gases were examined. The parameters of PtcO2 index (baseline PtcO2/PaO2), tissue oxygen index (baseline PtcO2/FiO2), 10 min OCT value [(PtcO2 after 10 min on FiO2 of 1.0) minus (baseline PtcO2)], oxygen challenge index [(10 min OCT value)/(PaO2 on FiO2 1.0 minus baseline PaO2)] were calculated during OCT. The patients were divided into 2 groups according to ScvO2 values: normal ScvO2 group (ScvO2 ≥ 70%) versus low ScvO2 group (ScvO2 < 70%). The parametric differences of transcutaneous OCT were compared between two groups.
Results: (1) There was a significant correlation between baseline PtcO2 (r = 0.382, P = 0.007), tissue oxygen index (r = 0.355, P = 0.012), 10 min OCT value (r = 0.427, P = 0.002), oxygen challenge index (r = 0.5, P < 0.001) and ScvO2, but not with arterial blood lactate concentration; (2) there were 27 patients in the low ScvO2 group and 22 patients in the normal ScvO2 group. ScvO2 was significantly lower in the low ScvO2 group than in the normal ScvO2 group (61 ± 8 vs 77 ± 6, P < 0.05). No differences in age, severity score, vital signs, arterial blood lactate concentration, vasoactive drugs, PtcO2, PtcO2 index and tissue oxygen index were observed between these groups. Compared with those in the normal ScvO2 group, the patients in the low ScvO2 group had a lower 10 min OCT value and oxygen challenge index (P < 0.05); (3) the area under the receiver operating characteristic curve (ROC) for detecting the lower ScvO2 values was 0.621, 0.560, 0.589, 0.721 and 0.763 respectively according to baseline PtcO2, PtcO2 index, tissue oxygen index, 10 min OCT value and oxygen challenge index. The cutoff of 10 min OCT value was ≤ 57 mm Hg (1 mm Hg = 0.133 kPa) for detecting ScvO2 values under 70%, resulting in a sensitivity of 51.9% and a specificity of 95.5%.
Conclusion: OCT may improve the diagnostic accuracy of PtcO2 in assessing the low ScvO2 values in septic shock patients after resuscitation.