All posts by TheTraumaPro

The July 2021 Trauma MedEd Newsletter Is Live! Yet More Potpourri

I’ve put together another issue of miscellaneous, interesting stuff!

In this issue, learn about:

  • The effect of ambulance deceleration on ICP in head injury patients
  • An interesting technique for sealing vacuum systems applied around external fixators
  • An analysis of thrombotic events following TXA administration
  • The utility of a second head CT in patients taking DOACs

To download the current issue, just click here!

Or copy this link into your browser: https://www.traumameded.com/courses/more-potpourri-july-21/

This newsletter was released to subscribers over a week ago. If you would like to be the first to get your hands on future newsletters, just click here to subscribe!

 

Liver Laceration And Liver Function Tests

Over the years I’ve seen a number of trauma professionals, both surgeons and emergency physicians, order liver transaminases (SGOT, SGPT) and bilirubin in patients with liver laceration. I’ve never been clear on why, so I decided to check it out. As it turns out, this is another one of those “old habits die hard” phenomena.

Liver lacerations, by definition, are disruptions of the liver parenchyma. Liver tissue and bile ducts of various size are both injured. Is it reasonable to expect that liver function tests would be elevated? A review of the literature follows the typical pattern. Old studies with very few patients.

From personal hands-on observations, the liver tissue itself tears easily, but the ducts are a lot tougher. It is fairly common to see small, intact ducts bridging small tears in the substance of the liver. However, larger injuries can certainly disrupt major ducts, leading to major problems. But I’ve never seen obstructive problems develop from this injury.

A number of papers (very small, retrospective series) have shown that transaminases can rise with liver laceration. However, they do not rise reliably enough to be a good predictor of either having an injury, or the degree of injury. Similarly, bilirubin can be elevated, but usually not as a direct result of the injury. The most common causes are breakdown of transfused or extravasated blood, or from critical care issues like sepsis, infection, and shock.

Bottom line: Don’t bother to get liver function tests in patients with known or suspected injury. Only a CT scan can help you find and/or grade the injury. And never blame an elevated bilirubin on the injury. Start searching for other causes, because they will end up being much more clinically significant.

References:

  • Evaluation of liver function tests in screening for intra-abdominal injuries. Ann Emerg Med 20(8):838-841, 1991.
  • Markers for occult liver injury in cases of physical abuse in children. Pediatrics 89(2):274-278.
  • Combination of white blood cell count with liver enzymes in the diagnosis of blunt liver laceration. Am J Emerg Med 28(9):1024-1029, 2010.

Upcoming Trauma Meeting: 8th Annual Excellence In Trauma Care Conference

I’m excited to be a part of the upcoming 8th Annual Excellence in Trauma Care Conference, sponsored by Intermountain Healthcare in Salt Lake City! I was a speaker last year, virtually.

This will be my first in-person conference since before the pandemic! I’m very excited to attend and give not one, but two talks this year.  It is being held physically at the Zermatt Utah Resort & Spa in Midway, Utah. It will also be live online for those who are unable to travel.

This is a fun conference with lots of interesting talks and speakers. You can download the full brochure by clicking here.  I will be giving two talks:

  • World class trauma care – a team sport. I will be talking about best practices for the numerous “teams” that take care of trauma patients.
  • Trauma Mythbusters  Part Deux – yet more myths to be busted!

I hop to see you there, or at least in the online audience. Check it out!

8th Annual Excellence in Trauma Care Conference
click here for meeting info

Uber / Lyft For Medical Transport???

In this day and age of ride sharing apps like Uber and Lyft, it is possible to get a cheap ride virtually anywhere there is car service and a smart phone. And of course, some people have used these services for transportation to the hospital in lieu of an ambulance ride. What might the impact be of ride services on patient transport, for both patient and EMS?

Ambulance rides are expensive. Depending on region, they may range from $500-$5000. And although insurance may reduce the out of pocket cost, it can still be expensive. So what are the pros vs the cons of using Uber or Lyft for medical transport?

Pros:

  • Ride shares are inexpensive compared to an ambulance ride
  • They may arrive more quickly because they tend to circulate around an area, as opposed to using a fixed base
  • Riders may select their preferred hospital without being overridden by EMS (although it may be an incorrect choice)
  • May reduce EMS usage for low acuity patients

Cons:

  • No professional medical care available during the ride
  • May end up being slower due to lack of lights and siren
  • Damage fees of $250+ for messing up the car

A very interesting paper suggests that ambulance service calls decreased by 7% after the introduction of UberX rides.  The authors mapped out areas where UberX rides were launching, and examined emergency response data in these areas. They used a complex algorithm to examine trends over time in over 700 cities in the US, and used several techniques to try to account for other factors. Here is a chart of the very fascinating results:

Bottom line: Uber and Lyft are just another version of the “arrival by private vehicle” paradigm. Use of these services relies on the customer/patient having very good judgment and insight into their medical conditions and care needs. And from personal experience, this is not always the case. I would not encourage the general public to use these services for medical transport, and neither do the companies themselves!

Reference: Did UberX Reduce Ambulance Volume? Health Econ 28(7)L817-829, 2019.

Rapid Infusers: How Fast Can They Go?

The rapid infusion pump is a mainstay of high volume trauma resuscitation. According to the manufacturers, these devices can now deliver fluids at up to 1000 ml/minute. Or can they?

Here is a chart from the manufacturer of the Belmont rapid infuser. This shows the (theoretical) flow rates achievable for each of their two devices (max flow rate of 750 ml/min and 1000 ml/min models). The charts show the maximum flow rates for crystalloid or blood for various sizes of IV catheters that are 2″ long.

Notice two things:

  • The flow rate decreases exponentially as the size of the IV catheter decreases
  • The difference in flow rate between blood and crystalloid diminishes as the catheter size increases

These observations can be explained by something I’m sure you haven’t thought about since high school physics: Pouiseulle’s Equation. Of course you remember, right?

The equation states that the flow of a fluid (F) is proportional to the fourth power of the radius of the catheter and the pressure gradient across the two ends of it (delta P), and inversely proportional to the viscosity of the fluid (greek letter eta) and the length of the catheter (L).

What does this mean in practical terms?

  • The pressure gradient is fixed at about 300 mm Hg (the pressure bag or pump) so you can essentially ignore this factor
  • The viscosity (measured in centipoise) is based on the fluid begin given. Crystalloid (water) has a viscosity of 1. Whole blood has a viscosity of about 2.7, and packed cells are about 10. This means that our typical infusion of PRBC flows 10 times more slowly than saline.
  • The length and diameter of the IV catheter are controlled by the trauma professional who inserts it, and it has a massive impact on flow. This is particularly true for the diameter (gauge), which varies directly as the fourth power.

So let’s put all these numbers together. Let’s assume that we are using balanced resuscitation and are infusing lots of blood, not crystalloid. The choice of IV catheter is the most important factor for a successful volume resuscitation! Here’s a table I constructed that lists the approximate relative flow rates for several catheter types. I use a 9 Fr introducer as the gold standard and have defined the flow rate for that device as 1.

IV Catheter Internal Radius Length Relative flow
9 Fr Introducer 1.5 mm 10 cm 1
14 Ga IV 0.8 mm 5 cm 1/6 x
Triple lumen cath 0.3 mm 20 cm 1/1265 x

Bottom line: High-speed volume resuscitation forces us to squeeze a thick (and hopefully warm) liquid through a small straw into our patient’s vein. The smaller and longer the straw, the harder it is to do that. I think that people underestimate how much of an impact the choice of catheter makes.

Always use the largest and shortest possible access for rapid infusion. Ideally, this should be a large, straight introducer. Some have a side port (e.g. Cordis) at a right angle to the catheter, but this introduces some extra resistance and will slow the infusion rate. A large bore (14 Ga) short (2 inch) IV catheter is good, but will only flow at one sixth the rate of an introducer.

And never use anything with more than one lumen! The typical triple lumen catheter has three lines that are either 20 or 21 Ga. They are tiny and very long. Looking at the table above, you will be lucky to infuse a few cc’s per minute through one of these, compared to hundreds of cc’s via a straight introducer.

References: