# Invisible Active Bleeding Due to the Watershed Phenomenon

## TL;DR

This paper discusses a case where active bleeding was suspected but not visible on a CT scan due to altered blood flow patterns.

## Contribution

Highlights the importance of recognizing the vascular watershed phenomenon in VA-ECMO patients during CT angiography.

## Key findings

- Active bleeding was suspected in a patient on VA-ECMO but not visible on initial CT scans.
- The vascular watershed phenomenon can cause flow-related artefacts that obscure bleeding in CT angiography.

## Abstract

A case is presented of an 83-year-old female patient with a strong suspicion of active bleeding, but no diagnostic contrast blush could be seen on the original computed tomography (CT) scan.

Teaching point: When performing CT angiography in veno-arterial extracorporeal membrane oxygenation (VA-ECMO), it is important to understand the altered haemodynamics, as flow-related artefacts such as the vascular watershed phenomenon can obscure bleeding.