Interrelationship between blood and tissue lactate in a general intensive care unit: A subcutaneous adipose tissue microdialysis study on 162 critically ill patients

Purpose: The aim of the study was to study the interrelationship between blood and tissue lactate in critically ill patients with or without shock admitted in a general intensive care unit. Materials and Methods: We studied 162 mechanically ventilated patients: 106 with shock (septic shock, 97; cardiogenic shock, 9) and 56 without shock (severe sepsis, 38; systemic inflammatory response syndrome, 18). A microdialysis catheter was inserted in the subcutaneous adipose tissue of the upper thigh, and interstitial fluid was collected every 4 hours for a maximum of 6 days. We assessed the relationship between tissue and blood lactate using cross-approximate entropy and cross-correlation analysis. Results: Patients with shock had higher area under the curve for blood (261 vs 175 mmol/L^*hours, P < .0001) and tissue lactate (386 vs 281 mmol/L^*hours, P < .0001) compared with patients without shock. The interrelationship of tissue-blood lactate, as assessed with cross-approximate entropy, was more regular in patients with shock compared with patients without shock. Cross-correlation of tissue vs blood lactate yielded higher correlation coefficients in patients with shock compared with those without shock, being higher when tissue lactate preceded blood lactate by 4 hours compared with tissue vs blood lactate with no lag time. Conclusions: In critical illness, the detailed dynamics between blood and tissue lactate are affected by the presence of shock. In patients with shock, microdialysis-assessed tissue lactate is higher compared with those without shock and may detect metabolic disturbances before these become evident in the systemic circulation.