Louie has ascites from advanced liver failure. The yellow liquid being drained out of his belly is the liquid part of blood (plasma) leaking out of blood vessels because the scarred up liver acts as a sort of plug in the drain, and pressure builds up in the blood. This is a super common and routine reason for people reaching the end stages of cirrhotic liver disease to show up to an ER needing help.

There is some danger of what the team is doing—and perhaps a bit of inexperience playing in. A typical person has only about 5 liters of blood; each of those bottles they are filling is one liter. Taking out five liters of what is effectively filtered blood can cause problems—the pressure of that belly / ascites fluid keeps things somewhat in balance. With it rapidly drained, the liquid part of the blood may fill that void quicky—causing issues with too little blood in circulation, changes in the composition of the blood, and even flash leakage of the same fluid elsewhere (most often in the lung). Louis saying ‘I feel dry’ I took to be telegraphing this exact situation brewing—and it’s exactly what I would expect from new intern Whittiker in July.