All posts by TheTraumaPro

What Is: A Passy-Muir Valve?

Some critically injured patients undergo tracheostomy due to prolonged ventilatory failure. As they recover, the trach tube is usually downsized over time until it can be permanently removed. Unfortunately, this process may take a month or more, and the patient is generally unable to speak during this time. Writing and other forms of communication are both slow and frustrating, so a Passy-Muir valve may be attached to the trach to allow (nearly) normal speech during the recovery process.

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The Passy-Muir is a one way valve that allows air to be inhaled through the trach tube, but not exhaled through it. Instead, the air must circulate around the tube and up through the trachea to the pharynx. This particular brand has features that help keep the tube from collecting secretions during speech. See the brief video from the manufacturer below.

The downside to this device is that it increases the work of breathing during exhalation because air must flow around the entire trach tube, which is narrowing the available tracheal lumen. Note: if the trach tube has a balloon, it must be deflated or the patient will not be able to breathe! Some patients do not have enough strength to overcome this narrowing initially, and may not be able to speak or say more than a few words at a time. This improves with practice, and helps speed up tube removal.

Use of a fenestrated tracheostomy tube with the Passy-Muir is helpful, because it has a strategically placed (but small) hole that allows air flow through a portion of the tube. When this type of tube is used, the balloon must also be deflated, since it is subject to mucus plugging which would completely obstruct the airway. Work of breathing is still increased because this hole is small relative to the diameter of the trachea.

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Note: I have no financial interest in Passy-Muir Inc or any other tracheostomy product manufacturers.

Flying After Pneumothorax

Patients who have sustained a traumatic pneumothorax occasionally ask how soon they can fly in an airplane after they are discharged. What’s the right answer?

The basic problem has to do with Boyle’s Law (remember that from high school?). The volume of a gas varies inversely with the barometric pressure. So the lower the pressure, the larger a volume of gas becomes. Most of us hang out pretty close to sea level, so this is not an issue.

However, flying in a commercial airliner is different. Even though the aircraft may cruise at 30,000+ feet, the inside of the cabin remains considerably lower though not at sea level. Typically, the cabin altitude goes up to about 8,000 to 9,000 feet.Using Boyle’s law, any volume of gas (say, a pneumothorax in your chest), will increase by about a third on a commercial flight. 

The physiologic effect of this increase depends upon the patient. If they are young and fit, they may never know anything is happening. But if they are elderly and/or have a limited pulmonary reserve, it may compromise enough lung function to make them symptomatic.

Commercial guidelines for travel after pneumothorax range from 2-6 weeks. The Aerospace Medical Association published guidelines that state that 2-3 weeks is acceptable. The Orlando Regional Medical Center reviewed the literature and devised a practice guideline that has a single Level 2 recommendation that commercial air travel is safe 2 weeks after resolution of the pneumothorax, and that a chest xray should be obtained immediately prior to travel to confirm resolution.

Bottom line: Patients can safely travel on commercial aircraft 2 weeks after resolution of pneumothorax. Ideally, a chest xray should be obtained shortly before travel to confirm that it is gone. Helicopter travel is okay at any time, since they typically fly at 1,500 feet or less.

Related post:

References:

  • Practice Guideline, Orlando Regional Medical Center. Air travel following traumatic pneumothorax. October 2009.
  • Medical Guidelines for Airline Travel, 2nd edition. Aerospace Medical Association. Aviation, Space, and Environmental Medicine 74(5) Section II Supplement, May 2003.

Why People Don’t Change Their Minds Despite The Data

Has this happened to you?

Your (emergency physician / neurosurgeon / orthopaedic surgeon) colleague wants to (get rib detail xrays / administer steroids / wait a few days before doing a femur ORIF). You question it based on your interpretation of the literature. You even provide a stack of papers to them to prove your point. Do they buy it? Even in the presence of randomized, double-blinded, placebo-controlled studies with thousands of patients (good luck finding those)?

The answer is generally NO! Why not? It’s science. It’s objective data. WTF?

Sociologists and psychologists have shown that there is a concept that they call the Backfire Effect. Essentially, once you come to believe something, you do your best to protect it from harm. You become more skeptical of facts that refute your beliefs, and less skeptical of the items that support them. Having one’s beliefs challenged, even with objective and authoritative data, causes us to hold them even more deeply. There are plenty of examples of this in everyday life. The absence of weapons of mass destruction in Iraq. The number of shooters in the JFK assassination. President Obama’s citizenship.

Bottom line: It’s human nature to try to pick apart a scientific article that challenges your biases, looking for every possible fault. It’s the Backfire Effect. Be aware of this built in flaw (protective mechanism?) in our psyche. And always ask yourself, “what if?” Look at the issue through the eyes of someone not familiar with the concepts. If someone challenges your beliefs, welcome it! Be skeptical of both them AND yourself. You might just learn something new!

The Pan-Scan For Trauma

Diagnostic imaging is a mainstay in diagnosing injuries in major trauma patients. But the big questions are, how much is enough and how much is too much? X-radiation is invisible but not inocuous. Trauma professionals tend to pay little attention to radiation that they can’t see in order to diagnose things they can’t otherwise see. And which may not even be there.

There are two major camps working in emergency departments: scan selectively and scan everything. It all boils down to a balance between irradiating enough to be satisfied that nothing has been missed, and irradiating too much and causing harm later. 

A very enlightening study was published last year from the group at the University of New South Wales. They prospectively looked at their experience while moving from selective scanning to pan-scanning.They studied over 600 patients in each cohort, looking at radiation exposure, missed injuries, and patient injury and discharge disposition variables.

Here are the interesting findings:

  • Absolute risk of receiving a higher radiation dose increased from 12% to 20%. This translates to 1 extra person of every 13 evaluated receiving a higher dose.
  • The incidence of receiving >20 mSv radiation dose nearly doubled after pan-scanning. This is the threshold at which we believe that cancer risk changes from low (<1:1000) to moderate (>1:1000).
  • The risk of receiving >20 mSv was lower in less severely injured patients (sigh of relief)
  • There were 6 missed injuries with selective scanning and 4 with pan-scanning (not significant). All were relatively minor.

Bottom line: Granted, the study groups are relatively small, and the science behind radiation risk is not very exact. But this study is very provocative because it shows that radiation dose increases significantly when pan-scan is used, but there was no benefit in terms of decreased missed injury. If we look at the likelihood of being helped vs harmed, patients are 26 times more likely to be harmed in the long term as they are to be helped in the short term. The defensive medicine naysayers will always argue about “that one catastrophic case” that will be missed, but I’m concerned that we’re creating some problems for our patients in the distant future that we are not worrying enough about right now.

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Reference: Comparison of radiation exposure of trauma patients from diagnostic radiology procedures before and after the introduction of a panscan protocol. Emerg Med Australasia 24(1):43-51, 2012.

If A Tree Falls In A Forest…

Time for a little philosophy today. There seem to be two camps in the world of initial diagnostic testing for trauma: selective scanning vs scan everything. I admit that I am one of the former. Yes, the more tests you do, the more things you will find. Some will be red herrings. Some may be true positives, but are they important? Here’s the key question:

“If a tree falls in a forest and no one is around, does it make a sound?”

There is a clinical corollary to this question in the field of trauma:

“If an injury exists but no one diagnoses it, does it make a difference (if there would be no change in treatment)?”

Here’s an example. On occasion, my colleagues want to order diagnostic studies that won’t make any clinical difference, in my opinion. A prime example is getting a chest CT after a simple blunt assault. A plain chest xray is routine, and if injuries are seen or the physical exam points to certain diagnoses, appropriate interventions should be taken. But adding a chest CT does not help. Nothing more than the usual pain management, pulmonary toilet, and an occasional chest tube will be needed, and those can be determined without the CT.

Trauma professionals need to realize that we don’t need to know absolutely every diagnosis that a patient has. Ones that need no treatment are of academic interest only, and can lead to accidental injury if we look for them too hard (radiation exposure, contrast reaction, extravasation into soft tissues to name a few). This is how we get started on the path to “defensive medicine.”

Bottom line: Think hard about every test you order. Consider what you are looking for, what you might find, and if it will change your management in any way. If it could, go ahead. But always consider the benefits versus the potential risks, or what I call the “juice to squeeze ratio.”

Tomorrow I’ll look at some of the “scan all” vs “scan selectively” literature. Which camp are you in?

References:

  • George Berkeley, A Treatise Concerning the Principles of Human Knowledge, 1734, section 45.
  • paraphrased by William Fossett, Natural States, 1754.