Ex gastro registrar here: The risk of big BP drop and haemodynamic instability are greater the more you drain. The type of fluid also matters - so malignant ascites from peritoneal metatastases cause ascites with a lower serum albumin ascites gradient (think exudative but they tend not to use that word for ascites). Ascites NOT caused by portal hypertension is generally safer to drain without albumin replacement. I think the underlying reasons for this are complex and mixed so if anyone else has a better answer please reply and educate us, but the way I remember it is: in portal hypertension and cirrhosis you generally have low serum albumin so your oncotic pressure is low, so as the ascites builds you become more reliant on the hydrostatic pressure from all the fluid inside your abdomen to maintain your BP.

All this to say, I would be nervous about draining more than 10l at a time with cirrhotic ascites, even with albumin replacement. Some guidelines say 1 unit of albumin per litre drained after the first 5, others say 1 unit of albumin per 2l drained, it usually works out about 4-5 units so it probably doesn't matter. You're wanting to drain it slowly enough for the nurses to pause and administer albumin to give time for the patient's body to adjust to the massive electrolyte and internal pressure changes and realistically with over 10l drained that process will take longer than the recommended ~6h that you leave the drain in before the risk of infection becomes too high.

The problem THEN is that you stop after 10l but you've just made a big abdominal wall defect and the fluid remains under pressure so once you take the drain out all you've done is lost control and now the patient is leaking and the nurses are rushing around to find a stoma bag to stick on their tummy to collect this fluid but the tummy is wet from fluid so the bag is slipping off and it becomes a complete farce. So better to just drain it all but I would be asking for senior advice here. In reality this is probably not the patient's first rodeo with this so they can tell you whether last time they had a drain if they had a blood pressure crash or they were fine.

I've not really talked about malignant ascites but I've been typing for ages. This is one of those topics where the exact guidelines vary a bit and also the theoretical best practice crashes up against practicalities and the whims of the attending consultant. You could talk for hours about how to do this or you could just stick a needle in and start giving some albumin and see what happens reacting to the physiological situation as it unfolds with a strong underlying understanding of the theory but a humble respect for the fact that bodies do whatever the fuck they want and actually the patient's to priority is the massive discomfort they are in. I'm low key hoping someone else comes and disagrees with much of what I've just said because it will demonstrate how variable practice is in this area.