Evaluation of gastric intramucosal pH measurements with tissue oxygenation indices in patients with severe sepsis

Author： ESEN F TELCI L ÇAKAR N TÜTÜNCÜ A KESECIOGLU J AKPIR K

ISSN： 0956-3075

Source： Clinical Intensive Care, Vol.7, Iss.4, 1996-08, pp. : 180-180

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Abstract

In this study tonometric measurements of gastric intramucosal pH (pHi) were compared with oxygen delivery (DO₂), oxygen consumption (VO₂) and arterial lactate as systemic indices of tissue oxygenation in patients with severe sepsis. Dobutamine was infused at increasing doses of 5-10 μg/kg/min at 60-minute intervals in 24 patients. DO₂ was calculated as the product of cardiac index (CI) and arterial oxygen content. VO₂ was determined directly from expired gas analysis (mVO₂) and, indirectly, by calculating the product of cardiac index (CI) and arteriovenous oxygen content difference (cVO₂). pHi was obtained by gastric tonometry. After each dose administration of dobutamine mVO₂, cVO₂, DO₂, lactate levels and pHi were determined. The phenomenon of oxygen supply dependency (OSD), as characterised by a linear relationship, was found when the pooled data of both measured and calculated oxygen consumption were plotted against the corresponding level of oxygen delivery (DO₂ to cVO₂: y=0.34x-106.4, r=0.05 (p<0.05); DO₂ to mVO₂: y=80.9+0.10x, r=0.31 (p<0.0001). When the individual measurements were evaluated, 15 out of 24 patients showed OSD with calculated measures of VO₂; however, this was only found in seven of the 24 patients using directly measured values of VO₂. When these results were related to survival, neither the individual data nor the pooled data of the relationships between oxygen delivery and consumption could separate survivors from non-survivors. Separating the patients according to their lactate levels, no significant relationship between DO₂ and mVO₂ was observed in the pooled data of six patients with normal lactate levels (DO₂ to mVO₂: y=152+0.01x, r=0.005, p=0.76). These patients also showed higher pHi values than those with elevated lactate levels. However, pHi values of six patients in the normal lactate group were still abnormal (pHi<7.32), implying the existence of regional tissue hypoxia. Gastric pHi increased significantly in both groups with increasing levels of oxygen delivery, but reached normal values only in the group with normal lactate levels. Comparing survivors and non-survivors, both arterial lactate levels and pHi measurements were closely associated with a poor prognosis. In conclusion, the relationship between DO₂ and VO₂ is complex and the existence of a pathological relationship between these two variables cannot be used as a predictor of outcome. In contrast, blood lactate levels have a strong relationship with outcome; however, a normal lactate level does not necessarily reflect adequate regional oxygenation. Measurement of pHi as a non-invasive procedure is a valuable adjunct to lactate measurement as both a prognostic indicator and a reliable guide to therapy in patients with severe sepsis.