Why PCV isn’t the first indicator of blood loss — and better signs to watch for

Speaking after his lecture at the Fetch dvm360 Long Beach conference in California, Gianluca Bini, DVM, MRCVS, DACVAA, describes a common error veterinarians make in assessing surgical bleeding, including a frequent misconception about lab values. He outlines, instead, more telling signals that can help veterinarians gauge low blood volume in patients.

Below is the transcript, lightly edited for clarity and cohesion

Bini: I'm Dr Gianluca Bini. I'm the cofounder and CEO of Safe Pet Anesthesia. I'm also an assistant professor at Oklahoma State University. I originally got my DVM in Italy. I did a rotating internship and an anesthesia internship in England, and then I did my residency in anesthesia at [North Carolina State University]. Then, I worked as a professor at Ohio State [University] for 3 years. I am now currently at Oklahoma State [University] — I moved here in 2024.

Unfortunately, the most common thing that people do [when a patient starts bleeding] is run a [packed cell volume] (PCV) and total solids. PCV looks at the percentage of red blood cells in the blood, and [total solids] looks at...the concentration of proteins in the blood. Unfortunately, those tests may kind of lie to you at the beginning — it takes a few hours for [PCV and total solids values] to actually be affected.

A common misconception is that people [should] try to look at PCV first. In reality, total solids is usually affected first, it actually takes a longer time for PCV to be affected.

If there is significant bleeding, you can also see it on your monitor. You’ll see the heart rate spike and the blood pressure come down afterward. Usually those are more telltale signs of lack of volume. And of course, if there is active bleeding, you're going to have less blood volume, so those are the signs we look at the most.

Visualization of the bleeding is, of course, the easiest thing, but sometimes it's hard to quantify. A lot of people doing surgery use suction. You can technically look at your suction canister, but if you've been flushing with saline, it's diluted, so it’s kind of hard to tell how much of that is actual pure blood [versus] how much has been diluted. There are some tests you can run to figure that out...you can run a PCV/[total protein] on your suction canister [to estimate] how much of it is actual blood.

You can look at your sponges that have been soaking up blood, and there are some numbers you can use to estimate how much blood is in them. Ideally, you should weigh your sponges first and then do surgery. In reality nobody does that, it's very time-consuming, and you don’t want to do it for every single surgery. You would spend half a day doing that.

Sometimes it can be hard to quantify [blood loss].... Sometimes it’s very apparent, and sometimes it can be tricky.