The Role of Carbon Dioxide Gap and Oxygen Extraction Ratio with Lactate Clearance in Predicting Mortality in Septic Shock Patients

INTRODUCTION: Sepsis is a life-threatening condition and a global disease burden. Today, the heterogeneous syndrome is defined as severe organ dysfunction caused by a dysregulated host response to infection. The scores are SOFA, qSOFA, APACHE, MPM, SAPS etc, among them SOFA score is used to predict the multi organ dysfunction and it is a sequential measurement throughout the ICU stay. Basal lactate rate is ineffective for determining treatment for individuals who are septic, despite being useful for assessing the severity of these patients. Lactate clearance is more important than static and basal lactate levels in predicting mortality in septic shock patients. Persistence of such a large pCO2gap after 24 h of treatment was predictive of higher mortality. PvaCO2/CavO2 ratio variations are faster than lactate kinetics, which make it an attractive variable to monitor. In this prospective study is to evaluate predictors of mortality in septic shock patients by considering the lactate clearance, PCO2 gap, CvaO2, PvaCo2/CavO2 ratio and O2 ER ratio during early hours of resuscitation. OBJECTIVES: To compare the effectiveness of predicting mortality using PvaCO2 Gap, CavO2, PvaCo2/CavO2 ratio, oxygen extraction ratio and lactate clearance in septic shock patients. To predict the need of renal replacement therapy. Duration of ICU stay in days. MATERIAL AND METHODS: This is a prospective observational study done on ICU adult patients age > 18 years between July 2023 and June 2024. APACHE II and SOFA score will be calculated at the time of admission. Resuscitation will be started with crystalloids and nor epinephrine is started to maintain MAP > 65 mm Hg. Both central and arterial catheterizations will be done. Oxygenation and ventilation parameters will be measured and compared at the start of resuscitation (T0) and after 6 hours (T6). CavO2, oxygen extraction ratio (O2ER), PcvCO2 gap, and PcvCO2/CavO2 were calculated: CaO2 = (1.34 x SaO2 x Hb) + (0.003 x PaO2) CvO2 = (1.34 x ScvO2 x Hb) + (0.003 x PcvO2) CavO2 = CaO2-CvO2 PcvCO2gap = PcvCO2-PaCO2 PcvCO2/ CavO2 ratio = PcvCO2gap/CavO2 O2ER = CavO2/CaO2 Lactate levels were measured at 3 points i.e. before (T0), after 6 hours (T6) and after 12 hours (T12). Lactate clearance and delta changes were calculated from the difference between the second or the third and the first reading divided by first reading. SOFA score was calculated after 48hours of admission. Most our values of delta changes were measured from T6 lactate levels. ROC curve will be used to detect cutoff values, sensitivity, specificity of different variables. P value of <0.05 was considered as statistically significant. RESULTS: Development of AKI and requirement of Dialysis was higher in expired group and both of them were statistically significant (P value = 0.001). All studied parameters except lactate were not correlating with requirement of dialysis. P value was 0.043. Lactate mean value at T0 and T6 were 5.5 and 6.7 respectively. The lactate clearance i.e., delta change has P value of <0.001. PvaCO2 gap mean value after resuscitation at T6 has significant than T0. P value was 0.058 at T6. Delta change P value was 0.848. CavO2 mean value in survived was 3.21 and 3.38 at T0 and T6. This has significant p value. Static measurements have significance than delta change. We couldn't find any significance of PvaCo2/CavO2 ratio in predicting the mortality. Oxygen extraction ratio at T0 and T6 were significant in predicting the mortality. P value was 0.001. Delta changes no significance. Sensitivity and specificity of CavO2 were 68.8% and 58.8% respectively. PPV was 51.2% and NPV was 75%. Oxygen extraction ratio's sensitivity was 43.8% and specificity was 88.2%. PPV and NPV were 70.0% and 71.4% respectively. PvaCO2 gap's sensitivity and specificity were 43.8% and 74.5% respectively. PPV was 51.9% and NPV was 67.9%. Sensitivity and specificity were 56.3% and 86.3% respectively after cross tabulation for lactate clearance. PPV was 72.0% and NPV was 75.9%. In this study, we observed that Lactate, ER O2, CavO2, CvO2, ScvO2 and PvaCO2 were statistically significant when comparing with duration of ICU stay. CONCLUSION: Lactate clearance was more significant than static lactate levels in predicting the mortality. Gradual increase in lactate level is associated with mortality. PvaCO2/CavO2 ratio has no significance in the study. Decrease in PvaCO2 Gap after resuscitation is associated with survival rate. CavO2 and ER O2 at initiation and after resuscitation, both were significant in predicting mortality. Delta change of all ABG indices except lactate has no role in predicting the mortality. All these indices were significantly correlated with duration of ICU stay and no relation with requirement of Dialysis.