Cross-correlation analysis of blood and microdialysis-assessed tissue lactate monitoring: a study in critically ill septic patients
© Ilias et al.; licensee BioMed Central Ltd. 2012
Published: 20 March 2012
In the critical care setting, blood lactate (BL) concentration is measured to assess - albeit indirectly - tissue oxygenation. In addition, serial BL measurements are clinically useful since a drop in BL is a good prognostic finding, whereas persistent BL elevation portends poor outcome. Microdialysis (MD) enables direct monitoring of tissue metabolic changes. This study aimed to describe the dynamics of MD-assessed tissue lactate (TL) vis-à-vis BL in septic patients with and without shock.
We measured BL and thigh adipose tissue TL serially every 4 hours for 6 days in 88 patients with septic shock and 45 patients at various sepsis stages hospitalized in a tertiary-care hospital ICU. Analysis was done with measurement of the area under the curve (AUC) of lactate*hours, cross-approximate entropy (X-ApEn) and cross-correlation. Comparisons of septic shock versus nonseptic shock patients' results were done with t tests and z statistics.
BL and TL were higher in septic shock patients compared to nonseptic shock patients (AUCs of 276 vs. 176 and 355 vs. 273 mmol/l*hours, respectively; Welch's t test: P < 0.0001). X-ApEn for MDL/BL was lower in septic shock patients compared to those without septic shock (mean ± SD: 0.79 ± 0.12 vs. 1.14 ± 0.13, respectively; t test: P < 0.0001). Cross-correlation of TL versus BL was stronger in septic shock patients, with TL leading BL by 4 hours compared to TL versus BL with no lag time (r = +0.85, P < 0.0001 and r = +0.66, P < 0.0001, respectively) than in nonseptic shock patients (r = +0.58, P = 0.0003 with TL leading BL by 4 hours and r = +0.66, P < 0.0001 with no lag time; z statistic = 2.41 and P = 0.016 for leading BL compared to z statistic = 0.036, P = 0.971 for no lag time).
In septic shock patients, tissue lactate levels - measured by MD - are higher compared to nonseptic shock patients. Furthermore, TL is better correlated with and precedes - within 4 hours - BL in septic shock patients compared to nonseptic shock patients. Further studies are warranted to assess the clinical value of serial TL monitoring.
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