Ratio Requiem: Shedding the Shroud of Septic Shock

BACKGROUND: Assessing the adequacy of resuscitation in septic shock patients is challenging. Both under and over-resuscitation have been associated with mortality. Markers like lactate have their limitations. v-aCO2 gap and pv-aCO2/ca-vO2 ratio reflect the adequacy of cardiac output and anaerobiosis, respectively. This study was undertaken to ascertain the accuracy of the v-aCO2 gap and pv-aCO2/ca-vO2 ratio in predicting mortality in septic shock patients. METHODS: In this single-centre, prospective observational study, successive adult patients with septic shock were recruited. Arterial and venous blood gas were simultaneously taken at recruitment, 3-h, 6-h and 12-h after recruitment. We compared its accuracy of mortality prediction with APACHE-II and lactate. RESULTS: High median (IQR) v-aCO2 gap [6.0(6.0,12.75)] and pv-aCO2/ca-vO2 ratio [2.16(1.88,3.6)] at 12-h predicted mortality with 80% sensitivity [positive likelihood ratio 2.67, negative predictive value 88%, area under the ROC 0.76 (Standard error 0.09)]. In predicting mortality, these were also non-inferior to lactate [ROC 0.91] and APACHE-II [ROC 0.92]. There was a good linear correlation between the v-aCO2 gap and the pv- aCO2/ca-vO2 ratio [correlation coefficient 0.75, p<0.01(56% of the variance in the pv- aCO2/ca-vO2 ratio values were due to the v-aCO2 gap values)]. CONCLUSION: High v-aCO2 gap and pv-aCO2/ca-vO2 ratio are associated with poor outcomes in patients with septic shock.