POTD: How to measure Hounsfield Units?

Adam Ranginwala · September 25, 2020 · Radiology, Trauma

Today we will show you how to actually measure HU on our radiology software, Medview/ PACS.

First open the CT and find the slice where you would like to measure the HU of a particular area. In the first image below, we see some free fluid around the liver which we would like to know whether it is blood or ascites.

Follow the steps in the images below and your HU measurement is on the second line. In this case, the free fluid in this patient's abdomen had a HU of 19.5 which is consistent with ascites.

Stay well,

TR Adam

Right click on the image to open the following menu bar

Go to "Annotation Tools" on the menu bar and find and click on "ROI- Rectangle:"

Now create a small box (drag your mouse) over the area you would like the measure the HU. Make sure not to overlap over another area of the slice or it will distort your measurement. You may want to magnify the area you would like to measure

POTD: Free Fluid in the Belly (Trauma Tuesday!)

Adam Ranginwala · September 23, 2020 · Radiology, Trauma

This POTD was inspired by a morning report I was present for in Shock Trauma. The case was a 40ish male involved in an MVA. Patient was "shan scanned" for blunt traumatic mechanism. Surgeons saw a ton of free fluid on the scan and took patient directly to the OR. No intra abdominal injuries nor hemoperitoneum were found in the OR. It was later discovered, the patient had a drinking history w/ a cirrhotic liver and the free fluid initially assumed to be blood was actually acetic fluid.

PODT: Free Fluid in the Belly

So you have a trauma patient with a history of alcoholic cirrhosis. Your FAST is positive but your are unsure whether the free fluid you are seeing is blood from the trauma or the patient's chronic ascites.

You Pan-CT the patient and again all you see is free fluid, unable to tell if what you're seeing is blood or ascites. Your vitals, labs may help guide you. You can also potentially do a diagnosis parenthesis if there is a big enough fluid pocket but this is a very invasive procedure.

What you should do, is look at the Hounsfield Units (HU)!

HU are built into most imaging software and can be used to measure the radiodensity of the material on CT to help distinguish various structures.

Uncoagulated blood typically measures 30 to 45 HU

Clotted blood measures higher at 60 to 100 HU

Ascites/ Plasma measures around 0 to 20HU

So there you have it. You can use HU while looking at your CT images to help you determine whether your trauma patient is bleeding into their belly or what your seeing is more chronic.

TR Adam

TXA in Trauma

David Elkin · August 5, 2020 · Trauma

Going to take a quick break from the PSA for #traumatuesday

What is TXA and how does it work?

Tranexamic Acid is a medication used to treat or prevent excessive bleeding.

It works by reversibly binding receptor sites on plasminogen, which reduces conversion of plasminogen to plasmin, further preventing fibrin degradation making up the clot's framework.

Here's a cute animated video showing the mechanism of TXA: https://www.youtube.com/watch?v=emAHFC-Aidg

What role does TXA play in trauma?

CRASH-2 Trial (Clinical Randomization of an Antifibrinolytic in Significant Hemorrhage-2)

Double-blinded RCT published in 2010
20,211 patients with traumatic hemorrhage (SBP < 100 and/or HR > 110) or at risk of significant hemorrhage, within 8 hours of injury
Dose used was 1g TXA over 10 minutes + 1g over 8 hours
All-cause mortality significantly reduced with TXA
Risk of death due to bleeding on day of presentation significantly reduced with TXA
No significant difference in vascular occlusive events
No significant reduction in blood transfusion requirements
Greatest benefit seen with early administration (< 1 hour after injury but also < 3 hours). Increased risk of death due to bleeding if administered after 3 hours.

MATTERs (Military Application of TXA in Trauma Emergent Resuscitation)

Retrospective observational cohort study published in 2012
896 military personnel who received at least 1 Unit of PRBCs within 24 hours of admission following a combat-related injury
Dose used was 1g TXA IV bolus, repeated as deemed necessary by provider
All-cause mortality significantly reduced at 48 hours and 30 days especially in patients requiring massive blood transfusion due to their injury

CRASH-3 Trial (Clinical Randomization of an Antifibrinolytic in Significant Hemorrhage-3)

Double-blinded RCT published in 2019
12,639 patients with traumatic brain injury (< 3 hours after injury, GCS < 13 or ICH on CT). Patients excluded had major extracranial bleeding, GCS of 3, bilateral unreactive pupils.
Dose used was 1g TXA over 10 minutes + 1g over 8 hours
Death due to head injury significantly reduced at 24 hours but not at 28 days
No significant difference in disability or vascular occlusive events

Bottom Line (based on the literature above):

In adult trauma patients in severe hemorrhagic shock for which you are transfusing blood, administer TXA 1g IV over 10 minutes, followed by 1g infused over 8 hours.
Reasonable to try TXA for TBI patients with GCS 9-15 and ICH on CT within 3 hours of injury but need more evidence

CRASH-2: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(10)60835-5/fulltext

MATTERs: https://jamanetwork.com/journals/jamasurgery/fullarticle/1107351

CRASH-3: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(19)32233-0/fulltext

Reviews from FOAMed sources:

https://emcrit.org/pulmcrit/crash3/

https://www.thebottomline.org.uk/summaries/icm/crash-2/

https://rebelem.com/crash-3-txa-for-ich/

https://first10em.com/the-crash-2-trial/

https://first10em.com/crash-3/

https://emcrit.org/wp-content/uploads/2012/02/TXA-in-trauma-How-should-we-use-it.pdf