Purpose: To investigate whether the use of viscous fluids, such as concentrated contrast, to inflate endovascular balloons is responsible for incomplete expansion, accounting for differences in catheter length, delivery system size and contrast-to-saline ratios. Background: In our tertiary trauma centre, the vascular surgeon in an emergency case was handed a more viscous fluid than expected for inflation and subsequently noted the balloon-mounted stent was undersized and had shifted position. We hypothesise the surgeon was mistakenly given pure Visipaque contrast, triple the expected viscosity, as typically used mixes are 1/3 or 1/2 contrast in saline for inflation. Contrast is eleven times more viscous than saline. This raised questions about whether using a viscous fluid significantly prolonged inflation time, leading to stent under-expansion. Per the Hagen-Poiseuille law, the flow rate through a balloon catheter decreases and time for expansion increases with more viscous fluid and with longer or narrower catheters. Current FDA and ISO guidelines allow water, with a viscosity 9% that of contrast, to be used as the inflation fluid in testing, and there is a paucity of literature on whether the use of viscous fluids significantly increases balloon expansion time. Methodology: An experimental study will use increasing percentages of room-temperature contrast (Visipaque 320) in 0.9% saline to inflate 9mm balloons of differing lengths (90, 130cm) and wire delivery sizes (0.18”, 0.35”). The time taken for balloon inflation and the percentage expansion at 1 minute will be measured for each combination of contrast concentration, length and delivery system size using a stopwatch and a digital calliper. Results: We hypothesise that high contrast concentrations significantly increase the time to full expansion of balloon catheters, with clinical consequences potentially witnessed at our site, though this will be investigated in the experiment. Conclusion: To be determined.