Volume removal intolerance during net ultrafiltration in patients with acute kidney injury in the intensive care unit: protocol for a prospective multicentre observational study (VINKO).

INTRODUCTION: Fluid overload in critically ill patients with acute kidney injury (AKI) is independently associated with increased mortality, prolonged mechanical ventilation and impaired renal recovery. Net ultrafiltration (UFNET) during continuous renal replacement therapy (CRRT) is a cornerstone de-resuscitation strategy; however, tolerance to fluid removal is highly variable and difficult to predict. Ultrafiltration intolerance, encompassing haemodynamic instability, peripheral perfusion deterioration and tissue hypoperfusion during UFNET, lacks a standardised definition and has not been prospectively evaluated using a comprehensive multiparametric monitoring strategy. The Volume removal Intolerance during Net ultrafiltration in acute Kidney injury patients, an Observational study (VINKO) aims to identify clinical, haemodynamic, ultrasound-based, perfusion-related and biochemical factors associated with the development of ultrafiltration intolerance in critically ill patients with AKI undergoing CRRT. METHODS AND ANALYSIS: VINKO is a prospective, multicentre, observational analytical case-control study enrolling adult intensive care unit patients with AKI requiring CRRT with prescribed UFNET. Cases are defined as patients who develop ultrafiltration intolerance during the 24-hour observation period, whereas controls are patients who tolerate UFNET without meeting intolerance criteria. Serial assessments include macrohaemodynamic variables, dynamic functional tests (passive leg raising and sitting manoeuvre), focused echocardiography, venous congestion assessment using the Venous Excess Ultrasound protocol, peripheral perfusion markers (capillary refill time, mottling score and peripheral perfusion index) and biochemical markers including lactate, albumin, ionised calcium and B-type natriuretic peptide/N-terminal pro-B-type natriuretic peptide when available. Measurements are obtained at predefined time points from UFNET initiation through 24 hours, with additional off-schedule assessments triggered by intolerance events. The primary objective is to identify independent predictors of ultrafiltration intolerance. A total of 128 patients (64 cases and 64 controls) will be enrolled based on a predefined sample size calculation. ETHICS AND DISSEMINATION: The study has been approved by the Scientific Ethics Committee of the Talcahuano Health Service (Act No. 15, 14 April 2026) and will be conducted in accordance with the Declaration of Helsinki, Council for International Organizations of Medical Sciences (CIOMS) guidelines and current Chilean regulations. Results will be disseminated through presentations at scientific meetings and publication in peer-reviewed journals. TRIAL REGISTRATION NUMBER: NCT07643597.