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Philosophy

Serial Lab Testing: Worthwhile or Worthless? Part 2

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Yesterday, I posted a series of sodium levels that were drawn daily. There was no change in clinical status as the levels varied from 131 to 125 and back up.

Now let me give you a bit more information. The patient was actually getting serial checks every 6 hours (or more)! Here’s the updated chart:

Day/Time Na Treatment NaCl per day
Day 1 18:30 131
Day 1 22:54 132 0.9% NS @ 125/hr 3G
Day 2 05:59 133 continues 3G
Day 2 12:19 129 continues
Day 2 17:50 129 continues
Day 3 07:18 127 continues
Day 3 12:09 127 continues
Day 3 17:58 126 continues
Day 3 23:53 126 continues
Day 4 07:45 125 continues
Day 4 11:38 122 2% NS @ 25/hr 6G
Day 4 15:25 125 continues
Day 4 19:31 125 continues
Day 5 00:06 122 continues 6G
Day 5 04:04 126 continues
Day 5 08:01 122 continues
Day 5 11:50 132 stop
Day 5 16:14 126
Day 5 19:26 127
Day 6 00:20 129 9.2G
Day 6 04:42 127 2% NS @ 40/hr
Day 6 08:30 124 continues
Day 6 12:29 127 stop
Day 6 16:16 127 Salt tabs 2G tid
Day 6 20:28 132 continues
Day 7 05:22 134 Salt tabs 2G qid 8G
Day 7 12:33 135 continues
Day 8 07:02 131 stop None
Day 8 13:33 136

Confused? Me, too! This poor person had 30 blood draws in 8 days, with 6 per day for two of those days. Carefully look at the amount of salt given in each 24 hour period, and look at the sodium levels for that day.

See the variability, even when getting high doses of sodium chloride? What does this tell you? Was the salt administration helpful? Was seeing the lab value every 4-6 hours valuable?

Tell me what you think. Leave comments or tweet your opinions. Next, I’ll discuss the known variability of the serum sodium assay, and give you my opinion on the value of serial testing.

Philosophy

Serial Lab Testing: Worthwhile or Worthless?

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We’ve all done it at some point. Serial hemoglobin. Serial sodium. Serial serum porcelain levels. What does serial mean to you? And what does it tell us about or patient?

Today and tomorrow, I’d like to present an example from real life. For today, have a look at the daily sodium tests done for a patient with a head injury. The concern was for cerebral salt wasting, which is probably grounds for its own blog post.

So have a look at this series of sodium determinations. It represents serial values based on daily testing.

Day/time Na
Day 1 18:30 131
Day 2 05:59 133
Day 3 07:18 127
Day 4 07:45 125
Day 5 04:04 126
Day 6 04:42 127
Day 7 05:22 134

At what point, if any, would you be concerned with significant hyponatremia, and begin some type of supplementation?

Tomorrow, I’ll provide a little more info on levels and treatment

Technique

2 Ways To Perform A Pericardial Window For Trauma: Part 2 With Video!

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In my last post, I reviewed the classic, “old-timey” subxyphoid approach to the pericardial window procedure for trauma. Today, I’ll describe the operative approach if you are already in the abdomen managing injuries there.

The same considerations apply to these patients in deciding to perform the window. Either there is a suspicion of actual pericardial tamponade based on physiology or diagnostic imaging, or an injury has been noted in proximity to the heart that raises that suspicion.

If you are already exploring the abdomen, the procedure is much simpler. The instruments required are already in your laparotomy setup:

  • Two toothed forceps
  • Tissue (Metzenbaum) scissors

First, and most importantly, the upper abdomen must be evacuated of all blood. This is critically important since a positive window is solely determined by the presence of blood in the pericardial fluid. If it is contaminated with blood as it flows into the peritoneal cavity, a false positive may result leading to an unneeded thoracotomy or sternotomy.

The midline incision must extend to the xiphoid process in order to get adequate exposure of the diaphragm. The left lobe of the liver is retracted downwards by your assistant, and the two of you can then grasp an area of the pericardial portion of the diaphragm with the toothed forceps. As it is tented away from the heart, the scissors are used to dissect through both the diaphragm and pericardium. Although some use cautery for this, I’m a weenie using electricity near the heart.

The diaphragm is thick, so expect to cut through several mm of tissue before you see pericardial fluid. Watch the color of the fluid carefully. If it is the least bit blood tinged, the result is positive. And be sure to watch for 15-30 seconds. Sometimes the initial fluid is amber, but it becomes bloody as more is drained.

Bloody fluid equals positive result. This means that a thoracic procedure is indicated to evaluate the heart and repair the injury. The choice of sternotomy vs thoracotomy is determined by mechanism, foreign body trajectory, and suspected area of injury on the heart.

If the result is negative, you may close the hole with your suture of choice. If the abdomen is contaminated from a bowel injury, I recommend you use the traditional subxiphoid approach separate from the laparotomy incision to avoid contaminating the pericardial sac.

Here’s a YouTube video of a transdiaphragmatic window created laparoscopically. Since abdominal explorations for major trauma seldom lend themselves to laparoscopy, don’t get any ideas from watching this!

YouTube player
Technique

2 Ways To Perform A Pericardial Window For Trauma: Part 1 with Video!

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In this two-part post, I’ll describe two ways to perform a pericardial window for trauma. The pericardial window should be considered in any trauma patient who has one of the following:

  • A suspected diagnosis of pericardial tamponade. These patients do not yet have classic signs and symptoms. If they did, a thoracotomy or sternotomy is in order, not a window.  But they do have a mechanism that could produce bleeding into the pericardial sac, and a positive imaging study. Typically, this study is a FAST exam of the heart. Occasionally, pericardial fluid may be seen on chest CT. This is uncommon but significant when detected.
  • An injury in proximity to the heart that is of concern for cardiac injury with a negative or indeterminant FAST. These are typically penetrating injuries so close to the heart that it’s hard to believe it wasn’t injured. If the FAST is not helpful, a window will make the definitive diagnosis.

Pericardial window is a very invasive procedure. For trauma, it is usually performed in the operating room and requires general anesthesia. It could be performed in the ED if the patient is already intubated and sedated.

There are two ways to perform this procedure. Today, I’ll discuss the old-timey subxiphoid approach.  The equipment required is minimal:

  • Scalpel
  • Tissue (Metzenbaum) scissors
  • Once or two toothed forceps
  • Your finger
  • Good lighting

A 4-8 cm incision is made extending from the top of the xiphoid, extending about 4 cm down onto the abdominal midline. Enter the retrosternal space with your finger, and head to the heart. Usually, some fatty tissue must be bluntly dissected out of the way. Note: the heart is frequently further away than you think!

Sweep the fat out of the way, exposing the pericardium. Grasp the pericardium with the toothed forceps and tent it away from the heart. Use the Metzenbaum scissors to incise the pericardium immediately adjacent to the forceps. If this is difficult, then have an assistant grasp the pericardium with another pair so a short line of pericardium is elevated. (Note: sometimes having a second set of forceps in the incision makes it too difficult to see, which is why I prefer the single forceps technique).

Make sure that the wound is bloodless when you incise the pericardium! There is always at least a small amount of pericardial fluid that will squirt out, and you are looking at its color. If it is anything but amber, you have a positive result. If you have a bloody field that contaminates the fluid, a false positive diagnosis could occur leading to an unnecessary thoracotomy.

If the window is positive, cover the wound and head immediately to the OR if your’re not already there. Your patient has a cardiac injury until proven otherwise. If negative, then close the skin wound with your sutures / staples of choice. Do not attempt to close the tiny pericardial hole!

Here’s a video that shows the basic technique. The procedure depicted is being performed for non-trauma, so the operator takes his time. He has the luxury of dissecting and exposing the field well. But in trauma, we don’t usually have time to resect the xiphoid or take 10 minutes to dissect out the field.

YouTube player

In my next post, I’ll discuss the technique that is used if you already find yourself in the abdomen when a cardiac injury is suspected.

Abstracts

Best Of EAST #10: MTP With Whole Blood

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Here’s one last abstract to consider before the EAST meeting kicks off this afternoon. Every trauma center must have a massive transfusion protocol (MTP). But not every one has access to whole blood. And whole blood is all the rage now for transfusion in the trauma world.

Believe it or not, we must still ask the question “is using whole blood safe?” More than 50 years ago, all we had was whole blood. But we didn’t use it in trauma the way we do today. And we didn’t have the tools then to determine whether there were any adverse effects from its use. Now we do, and we are slowly rediscovering the nuances of using it. Some work has shown that small volumes of whole blood appear to be safe. But there is little information on the safety of using large volumes in MTP.

The group at Oregon Health Sciences University in Portland attempted to do this with a quick shot paper to be presented tomorrow morning. They reviewed their experience over a two year period. For the first 18 months, they used standard component therapy (PRBC + plasma + platelets) in their MTP. For the final six months, they used cold-stored uncrossmatched, low-titer group O blood. Any patient who had MTP activated and received even a single unit of blood was included in the study. 

Here are the factoids:

  • 83 patients received component therapy and 42 received whole blood; demographics were the same
  • The component therapy patients received an average of 6 PRBC, 5 plasma, and 0 platelets; the whole blood group received 6.5 units (4 PRBC, 4 plasma, and 1 platelets based on the usual composition of a unit)
  • Plasma:RBC ratio was 0.8:1 for the component group and 0.94:1 in the whole blood group (statistically significant, but not clinically significant, see below)
  • The authors described a component-equivalent unit of product which is not defined. It was 12 for component therapy and 27 for whole blood.
  • There were no differences in 24-hour or 30-day mortality, and no transfusion reactions

The authors concluded that MTP using whole blood is feasible, and that it appeared to be safe and effective. They also commented that it may lead to more balanced resuscitation.

My comment: Alright, this is the last time I’ll mention study power (for a while). If a study does not have the statistical power to show a difference between groups, then seeing no difference means nothing. The absence of a difference does not mean that the two groups are equivalent. And this study of 125 patients is small potatoes for showing any difference in a crude outcome like mortality.

Besides having a small number of subjects, the average number of units given was low for an MTP. For most trauma centers, this was just over one cooler of products. Although ISS was 29, the patients don’t sound like they had huge blood replacement requirements, so it’s no wonder that mortality was the same between the two groups.

And finally, the statement about more balanced resuscitation is open to debate. The difference between 0.8 units of plasma and 0.94 units is 35cc per unit of red cells given, a little over 1 tablespoon. It’s hard to believe that this would ever make a difference clinically.

To those who read only the title or the conclusion of an abstract (or paper for that matter), beware. The devil is in the details. This study is a good start toward addressing the question posed, but needs several hundred more subjects (and a lot more blood products given) to close in on an answer.

Reference: Massive transfusion with whole blood is safe compared to component therapy. EAST Annual Assembly Quick Shot #8, 2020.