The association of bioimpedance analysis parameters with the outcomes of critically ill patients.

Abstract

The association between bioimpedance analysis (BIA) parameters and the outcomes of critically ill patients was explored through a retrospective investigation. The study enrolled patients in the intensive care units of our hospital who had a record of BIA measurements as well as disease severity scores assessed by Acute Physiology and Chronic Health Evaluation II (APACHE II), Simplified Acute Physiology Score II (SAPS II) and Sequential Organ Failure Assessment (SOFA). The associations between clinical conditions, outcomes and BIA parameters were analysed. The relationship between individual bioimpedance values and the current frequencies fit well to a natural logarithmic function, providing a regression coefficient S value. Other parameters obtained from the BIA measurements included phase angle (PA), the ratio of bioimpedance at high and low frequencies (IR), extracellular water (ECW), intracellular water (ICW) and total body water (TBW). Among 201 enrolled patients, the 90-day in-hospital mortality was 35.8%. Compared to the survivors at 7-days, for the non-survivors, the IR, S value, ratio of ECW/weight and ratio of ECW/TBW were higher, and the PA was lower (P<0.05). Compared to the survivors at 90-days, for the non-survivors, the IR, S value and ratio of ECW/weight were higher, and the PA was lower (P<0.05). Multinomial logistic regression analysis results showed that only SAPS II and S value were independent risk factors for 7-day and 90-day death (P<0.01). When analysed by ROC, the AUC of the S value for predicting 7-day and 90-day death was non-significantly lower than SAPS II (S vs. SAPS II, 0.729 vs. 0.747 (7-day); 0.701 vs. 0.779 (90-day), P>0.05). Importantly, both the 7-day and the 90-day mortality in patients with S values ≤-25.5 were 0; for the others, the mortality increased with the rise of S value. For patients with SAPS II ≤33, the mortality varied minimally; and for patients with SAPS II >55, the mortality was 100%. The S value and SAPS II are independent risk factors for 7-day and 90-day death in critically ill patients; the former may have a greater negative predictive value, while the latter may have a greater positive predictive value.