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


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.


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.


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.


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.


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Kiparissi, E., Andoniadou, E., Vassiliagou, S. et al. Correlation of lactate, pHi and oxygen extraction ratio with cardiac index in ICU patients after aortic surgery. Crit Care 7, P206 (2003).

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  • Cardiac Index
  • Aortic Aneurysm
  • Hemodynamic Instability
  • Extraction Ratio
  • Hemodynamic Status