Bioelectrical impedance analysis to assess body water status during fluid infusion in a rat model of extracorporeal membrane oxygenation

Fluid monitoring is vital in patients receiving extracorporeal membrane oxygenation (ECMO), but research on the value of bioelectrical impedance analysis (BIA) for such patients is rare. This study aimed to assess the effectiveness of BIA in monitoring body water changes during fluid therapy with ECMO support. Using a rat model of venoarterial and venovenous ECMO (n = 13 each), fluid was administered before and after initiation, every 30 min during the 120-min ECMO support, and after ECMO termination. Tetrapolar electrodes for BIA were attached to rats’ upper and lower trunks, with measurements performed every minute. Three rats died and were excluded. Among the 23 rats analyzed, all BIA parameters changed significantly across eight time points: resistance at infinite frequency (R_inf, χ² = 50.146), resistance at zero frequency (R₀,χ² = 82.464), Intracellular resistance (R_i, χ² = 39.536), and phase angle (χ² = 22.679) (P < 0.01). R_inf (inversely proportional to total body fluid) significantly decreased irrespective of ECMO type (P < 0.01). Similarly, R₀ and R_i (inversely proportional to extracellular and intracellular water content, respectively) decreased during ECMO when fluid was administered. A linear mixed-effects model analysis indicated that R_inf changes were dependent on the duration of fluid accumulation. Linear mixed-effects model analysis revealed that each 30-min increment of fluid accumulation significantly reduced R_inf (T = − 5.438, P < 0.001) and increased phase angle (T = 2.436, P = 0.023), independently of ECMO mode. The phase angle, indicative of cell membrane integrity, steadily increased throughout the ECMO support with fluid infusion. BIA utilization may be helpful for monitoring body water changes during the early phase of ECMO support, particularly in terms of fluid infusion. Further research is required to confirm its clinical effectiveness.