Comparing point of care midline vs central line venous blood gas oxygen saturations: a novel pilot study

SESSION TITLE: Blood and Drugs in the ICU SESSION TYPE: Rapid Fire Original Inv PRESENTED ON: 10/10/2023 12:00 pm - 12:45 pm PURPOSE: Midlines (ML) are long peripheral intravenous catheters inserted above the antecubital space via the basilic, cephalic, or brachial veins terminating within or below the axilla. These catheters provide safe and comfortable mid-term vascular access for critically-ill patients. Central venous oxygen saturations (ScvO2) obtained from central venous catheters (CVCs) are often used to approximate cardiac oxygen delivery. Given the proximity of MLs to the axillary vein, we aimed to compare the equivalence of midline oxygen (MO2) saturation and ScvO2. If correlated, MO2 could provide additional physiologic information, while potentially decreasing the need for invasive CVCs. METHODS: Critically ill adult patients who had simultaneously a internal jugular or subclavian CVC and ML inserted as part of their standard care were included in this prospective study conducted at a single academic tertiary care center. Blood samples were drawn simultaneously from the CVCs and MLs and analyzed for venous oxygen saturation using the Abbott Point of Care i-STAT blood analyzer within a 15 minute period. RESULTS: A total of forty-eight patients (n=48) were enrolled. The data was analyzed using the Student’s t test for parametric data and Wilcoxon analysis for non-parametric data. Bland and Altman analysis was also used to compare midline and non-femoral oxygen saturation. The mean age was 60.7 +/- 13.8 years. The mean APACHE II and SOFA scores were 19.8 +/- 7.9 and 9.3 +/- 4.5 respectively. The mean ScvO2 and MvO2 were 65.5% +/- 11.2% and 62.7 +/- 17.6% respectively [p = 0.1197]. In the Bland-Altman analysis, the mean bias is 2.8% +/- 12.3% [95% limits of agreement: -21.3% to 26.9%]. More than 60% of the ScvO2 and MvO2 values diverged by ≥ 5%. Patients with a right upper extremity midline location had a mean ScvO2 and MvO2 of 64.8% +/- 11.8% and 63.0% +/- 16.8% respectively [p = 0.3744]. Patients on vasopressors had a mean ScvO2 and MvO2 of 63.6% +/- 12.3% and 62.6% +/- 18.3% [p = 0.67]. Patients with an APACHE II score > 25 had a mean ScvO2 and MvO2 of 64.9% +/- 10.0% and 65.5% +/- 16.0% [p = 0.91]. CONCLUSIONS: MO2 as a potential correlate of ScvO2 is an intriguing concept and its clinical utility remains to be seen. Our findings showed an approximate aggregate 2.8% difference in mean MO2 vs ScvO2. However, these were found to have a significant divergence of ≥ 5% in >60% of subjects. In a subgroup analysis, patients with right sided MLs, vasopressor use, and high APACHE II scores were independent variables associated with a closer relationship between the ScvO2 and MvO2. Nevertheless, the large variability presents a challenge for the bedside clinician. CLINICAL IMPLICATIONS: As of now, clinicians should not rely on the MO2 in lieu of the ScVO2 to guide resuscitation in critically-ill patients. While these values remain close, the relationship is inconsistent and unclear. Further large scale studies with robust prospective data are required. DISCLOSURES: No relevant relationships by Rishika Bheem No relevant relationships by Danielle Davison No relevant relationships by Philip Dela Cruz No relevant relationships by Sasa Ivanovic No relevant relationships by Justin Kim No relevant relationships by Dora Lin No relevant relationships by Robert Markie No relevant relationships by Eduard Shaykhinurov No relevant relationships by Maria Wu No relevant relationships by david yamane