Correlation of lactate, pHi and oxygen extraction ratio with cardiac index in ICU patients after aortic surgery

Introduction

Investigation of the relationship among Lac acid, pHi and O₂ER with cardiac index (CI) and determination of the early indicator of hemodynamic compromise in patients undergoing aortic surgery during the first 24 hours of their stay in a multidisciplinary ICU.

Methods

Our prospective study included 17 patients after aortic aneurysm surgery. They were all men of mean age 70.5 ± 5.56 with admission mean APACHE II score 16.2 ± 3.96. In all cases the duration of cross-clamping was 2–3 hours. The following parameters were recorded: CI, PCWP, Hb, DO₂, VO₂, SaO₂, SvO₂, O₂ER, Lac acid and sigmoid pHi. The pHi was monitored continuously with the TONOCAP-™ monitor for regional tonometry. All the other parameters were recorded at the admission in the ICU and every 4 hours for 24 hours. Regression analysis and curve estimation were performed among CI and pHi, Lac and estimated O₂ER every 4 hours. Level of significance was P < 0.05.

Results

At admission in ICU there was correlation between CI and Lac (r²= 0.6, P < 0.05). At the first 8 hours there was a statistically significant inverse correlation between CI and levels of Lac (r² = 0.68, P < 0.008). After the 8 hours until the end, pHi was then statistically correlated to CI (r² = 0.65, P < 0.01). It is noticeable that O₂ER was strongly inversely correlated to CI (r² = 0.91, P < 0.008) during the whole study at any phase of the study.

Conclusions

According to our data until now, it seems that the levels of Lac during the first 8 hours reflect early hemodynamic instability while the sigmoid pHi, indicating local microcirculation and reperfusion phenomena, is correlated with CI at later stages during the cardiovascular and metabolic stabilisation. Finally, O₂ER is the most powerful indicator of the hemodynamic status.