Veno-arterial carbon dioxide and pH gradients and survival in critical illness

Recent studies have shown that the veno-arterial gradient for carbon dioxide (dVApCO2) is increased in the case of low cardiac index (CI). In order to further investigate this matter 220 haemodynamic measurements from 34 patients with septic shock and from 28 patients in the post-operative state without sepsis were evaluated. The arteriovenous gradient for pH (dAVpH) was also evaluated. CI was found to be inversely correlated to both dVApCO2 and dAVpH when the two groups of patients were analysed separately (r = -0.76 and r = -0.78, P < 0.001 for the relationship between CI and dVApCO2, r = -0.58 and r = -0.69, P < 0.001 for the relationship between CI and dAVpH). When volume loading over 2h was used to increase CI, 58-66% of the patients in the two groups showed a decline in dVApCO2 > 10% when CI was increased by > 10%. The corresponding values for a reduction in dAVpH > 10% during volume loading was 36-52%. While dAVpH was found to be increased in non-survivors (n = 27) when compared to survivors (0.32 +/- 0.01 vs. 0.24 +/- 0.1, P < 0.05) at the second day in the IUC, dVApCO2 was not a significant predictor of mortality despite the fact that CI was found to be decreased in the non-survivors (3.5 +/- 0.94 vs. 4.3 +/- 1.0 L min-1 m-2, P < 0.01). In conclusion, the veno-arterial carbon dioxide gradient was found to be inversely correlated to cardiac performance in patients both in patients with septic shock and in non-septic post-operative patients.(ABSTRACT TRUNCATED AT 250 WORDS)