# Fluid removal improves muscle performance and weakness in critically ill patients: a pilot study

## TL;DR

Removing excess fluid in critically ill patients may improve muscle quality and strength, according to a small study using ultrasound and strength assessments.

## Contribution

This pilot study is the first to show that ultrafiltration reduces muscle edema and improves muscle strength in critically ill patients.

## Key findings

- Ultrafiltration reduced muscle thickness and echogenicity, suggesting decreased edema.
- Muscle strength scores improved in patients undergoing ultrafiltration.
- Higher ultrafiltration volumes correlated with better muscle strength outcomes.

## Abstract

Fluid overload in critically ill patients has been associated with muscle edema, decreased tissue quality, and the development of intensive care unit-acquired weakness (ICU-AW). Continuous renal replacement therapy (CRRT) with ultrafiltration (UF) contributes to removing excess extracellular fluid. This study aimed to evaluate whether UF is associated with changes in muscle ultrasound parameters and strength in critically ill patients.

Critically ill patients with resolved hypoperfusion undergoing CRRT with fluid removal via UF were prospectively enrolled and compared with a control group without UF. Muscle ultrasound assessments included rectus femoris and vastus intermedius thickness, echogenicity, and subcutaneous tissue. Global muscle strength was assessed using the Medical Research Council Sum Score (MRC-SS). Assessments were performed at CRRT initiation (T1) and again 36 h later (T2).

Twenty-eight patients were enrolled, 18 in the UF group and 10 patients in the control group. All ultrasonographic variables measured were different between the UF and control groups. In the UF group, median rectus femoris thickness decreased from 1.74 to 1.57 cm (p = 0.03), vastus intermedius from 1.14 to 0.95 cm (p < 0.01), echogenicity from 91.7 to 78.3 grayscale units (p < 0.01), and subcutaneous tissue thickness from 1.98 to 1.79 cm (p < 0.01). MRC-SS increased from 45.0 to 49.0 points (p = 0.05). A positive correlation was found between UF volume (mL/kg) and MRC-SS at T2 (ρ = 0.71, p < 0.01), and a negative correlation between UF volume and change in muscle echogenicity (ρ = − 0.49, p = 0.039). ROC curve analysis identified that a UF volume ≥ 82 mL/kg was associated with MRC-SS > 48 points obtaining an AUC of 0.982 (95% CI: 0.928–1.000), sensitivity 92.9%, and specificity 100%.

Ultrafiltration was associated with changes in muscle echogenicity and subcutaneous tissue as well as an increase in MRC scoring at follow-up. These results suggest a potential relationship between fluid balance and muscle ultrasound parameters. No causal inferences can be drawn; therefore, further studies are needed.