Portal vein Doppler in peri-operative and critical care medicine

Portal vein Doppler ultrasound has emerged as a promising tool for haemodynamic assessment in critical care and peri-operative medicine. This educational narrative review integrates fundamental cardiovascular physiology concepts, including Guyton's venous return model and the hepatic arterial buffer response, with practical clinical applications of portal vein assessment at the bedside. The portal vein's position at the intersection of splanchnic circulation and hepatic perfusion makes it relevant in evaluating venous haemodynamics. We describe the technical aspects of portal vein Doppler measurement, including probe positioning, anatomical landmarks and measurement standardisation. Portal vein Doppler ultrasound characteristics (diameters, flows, pulsatility) are primarily determined by backward right ventricular pressure wave transmission through the hepatic venous system, modulated by right ventricular function and systemic venous compliance. We present portal flow patterns across different haemodynamic conditions and discuss their clinical interpretation in three settings: cardiac surgery, general intensive care and peri-operative medicine. The relationship between portal vein Doppler and other venous congestion assessment tools, including the venous excess ultrasound score, is discussed. While portal vein pulsatility provides valuable information to guide clinical strategies regarding volume status and venous congestion, the current evidence is predominantly observational. Prospective multicentre validation studies are needed before portal vein Doppler-guided algorithms can be recommended for routine clinical use.