Category Archives: Equipment

The Rise And Fall Of MAST Trousers

Remember MAST Trousers (Military Anti-Shock Trousers)? They were a staple of prehospital care starting in the 1970s and lasting through the turn of the century. But what happened after that? They seem to have disappeared. I recently received a question on the topic recently and wanted to share the real story with you readers.

The basic MAST trouser consists of three inflatable compartments: two legs and one covering the abdomen and pelvis. Each can be inflated or deflated separately. The basic concept was first described by a surgeon who wanted to increase blood pressure during neurosurgical procedures in the early 1900s. The US military embraced the concept during the Vietnam war, using it to augment systolic pressure in servicemen in shock.

Military surgeons migrated this device into civilian prehospital care during the mid-1970s, and the American College of Surgeons Committee on Trauma listed this device as essential on all ambulances in 1977. MAST trousers then came into widespread use throughout the 1980s and 1990s.

Early research in the 1970s suggested that this device could provide up to a 20% boost in volume to the upper part of the body when applied. But as occurs with so many new toys, additional research demonstrated that this auto-transfusion effect was actually only about 5% of blood volume. Some significant complications also came to light as lower extremity ischemia and compartment syndromes were described. Ben Taub Hospital published a study in 1987 which showed no improvement in mortality in patients with penetrating injury.

At the end of the century, support for MAST started to dry up. The NAEMSP published a position paper limiting use to ruptured abdominal aortic aneurysms and pelvic fractures with hypotension. The final straw was a review by the Cochrane Collaboration in 2000 that confirmed no reduction in mortality with MAST use.

Although a few older textbooks may still mention MAST trousers, they are no longer the standard of care. There are no longer any accepted indications for their use, and the few trousers that remain are gathering cobwebs in some corner of the trauma basement.

Reference: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan.

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Cool EMS Stuff: The Backboard Washer!

Backboards are made to get messy. And every time your friendly EMS provider brings you a patient, they invariably have to swab it down to give the next patient a reasonably sanitary surface to lie on. But sometimes the boards get downright nasty and the cleanup job is a major production.

Enter… the backboard washer. I recently saw one of these for the first time at a Level III hospital in Ohio. Fascinating! Pop the board inside and seven minutes later it’s clean. And I mean really squeaky clean. You may think it looks clean and a good hand wash, but just take a look at the effluent water coming out of this washer!

These units use standard 100V 20A power and only require a hot water hookup and a drain. They can wash two boards at once.

Hospitals in the know need to locate one of these next to a work area for completing paperwork and some free food. What could be better?

Reference: Aqua Phase A-8000 spec sheet. Click to download.

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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.


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So You Want Your Own Hybrid Room?!

You’re hooked! You are thinking back to a number of cases that you think might have done better with a hybrid room. And now let’s assume you already have one in your OR suite. Now what do you do? Here’s my final post in this series to give you some things to think about.

The key is to avoid jumping right in and sending your next eligible patient straight to that room. You absolutely must take some time to develop policies and guidelines to make sure things go smoothly.

Here are some important things to think about:

  • Identify which specific patients are eligible so you don’t squander this resource
  • Who calls the OR to secure the room (surgeon, resident, other)?
  • Who calls the interventional radiologist?
  • What if another case (TEVAR, etc) is already on the table?
  • What if another case is getting ready to use the OR? How are conflicts resolved?
  • Develop an initial in-room report process so all the teams know the game plan
  • Assign an extra circulator to the room. You’ll need them!
  • Make sure all retractor and positioning systems (abdomen, crani) fit the table! Remember that little asterisk in the previous section? Some retraction systems may need adaptors to work with your table. Don’t find this out at the last minute!
  • What about lithotomy position? How will this work with your hybrid table? Most don’t have sections that break away, so this will not be available to you.
  • Ensure radiation protection for all, including thyroid shields.
  • Bag the bottom x-ray detector, otherwise it will get very, very gross!
  • Create an external fixator equipment cart that can be moved into the hybrid room. This will save time over having someone go pick individual items from the central core.
  • Create an embolization cart with appropriate wires, catheters, coils, etc. This stuff may not be stocked normally in the hybrid room.
  • If embolization is needed, be sure to have a “gopher” to fetch any equipment that’s not already on the cart or in the room.

And I’m sure there are more details that I haven’t thought of. If you have some helpful suggestions, policies, or protocols, please share them with me!

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Is The Hybrid OR For Trauma Useful? Part 2

In my last post I reviewed several older papers that showed some positive associations with the use of a hybrid room for trauma patients. However, these rooms were not dedicated to the trauma patient. This means that they may not be staffed at all hours, or other elective cases could be scheduled in them. In either case, there were periods of time where the hybrid room might not be available for trauma procedures.

A study of the experience of one trauma center (University of Florida, Gainsville) with a truly dedicated, always available hybrid room for trauma patients was published just last month. Three and a half years of experience with the room was compared with historical controls from a similar period of time before implementation.  Patients younger than 18 were excluded, as were patients operated for reasons other than bleeding control (i.e. emergent trach). The room itself was a repurposed and remodeled angiography suite located one floor above the emergency department trauma bays.

Here are the factoids:

  • Overall patient demographics, including mechanism, severity of injury, prehospital intubation, and initial blood pressure.
  • Median Injury Severity Score (ISS) was 18 pre-hybrid and 22 post (not statistically significant but probably clinically so)
  • There was greater use of REBOA in the post-hybrid group (8%) vs pre-hybrid OR (1%)
  • The hybrid group achieved earlier hemorrhage control (49 vs 60 minutes); this is both statistically and clinically significant!
  • Blood and plasma transfusions given between 0 and 4 hours of arrival were the same pre- vs post-hybrid (3 vs 2.5 units PRBC and 2 vs 1.5 units plasma)
  • Although the authors claim significantly fewer transfusions of both products between 4 and 24 hours, the numbers  are clinically the same (1 vs 0 units of each)
  • The number of infectious complications was significantly less (27% pre- vs 15% post), but was entirely driven by pneumonia reduction from 12% to 4%. All other infections (bloodstream, surgical site, UTI, C. Diff, graft infection) were the same.
  • The number of days on the ventilator decreased from 3 to 2, which was statistically significant but clinically questionable

Bottom line: This paper was a bit problematic for me. I want to believe that a hybrid room is valuable because I’ve been involved with a handful of cases where I believe it made a big difference. And if you read only the abstract or the conclusions of the paper, it sounds great!

Always be careful of papers that go along with your confirmation bias. Read them even more carefully than you normally would. I have a few comments / questions:

  • First, the good news. The time to hemorrhage control decreased from 60 to 49 minutes using the hybrid room. Eleven minutes. Doesn’t seem like a lot, but this is probably the most important conclusion. Ongoing bleeding rapidly decreases survival, and literally, every minute counts.
  • Why was so little blood and plasma given? I can’t recall a hybrid room case where we have given less than 10 units of blood and other products. The volumes given in this study were just a couple of units, and the decrease of half a unit was statistically significant. In my opinion, this is not clinically relevant in these sick patients. But this fact is touted in the abstract and conclusion. And you can’t chalk it up to REBOA, because they only used it in 8% of the hybrid room patients.
  • The decrease in pneumonia was indeed clinically significant, dropping from 27% to 15%. However, all other infectious complications remained the same. But once again, the fact that infections (generically) were significantly decreased was called out in the abstract and conclusions. Just focus on pneumonia because that’s all it was.
  • Ventilator days decreased from 3 to 2 days, which may or may not be clinically significant even though statistical significance was achieved. This, too, is emphasized in the abstract and conclusions.

I really wanted this to paper to soundly demonstrate how great a dedicated hybrid room is. But what I see is a single-center experience that only shows that it clinically significantly decreases time to hemorrhage control and the incidence of pneumonia and not much more. The authors hit the nail on the head with their last sentence:

Association between time to hemorrhage control and clinical outcomes require further investigation, ideally using granular, standardized electronic health record data from multiple institutions.

I will keep waiting for the next paper and hope it really answers these questions! This one left me wanting a lot more.

Reference: Clinical impact of a dedicated trauma hybrid operating room. JACS 232(4):560-571, 2021.

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