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A Blurb From Bruce

Bruce is a critical care registered nurse and paramedic who has worked in Connecticut, Massachusetts and Maryland.  His clinical background includes the ICU, ER, Trauma, Cardiology and Flight.  His graduate degree is in Education.  He is happily married to Stephanie, after meeting her while working at the Johns Hopkins Hospital in ...Baltimore, MD.  They currently live in Connecticut with their daughter Ava Mae and their 160 lb. English Mastiff, Maggie.  In addition to being an active volunteer and officer with the Ellington Volunteer Ambulance Corps, Inc., Bruce enjoys professional gigs in clinical and distance medical education, advocacy, leadership, consultation and blogging. @BruceEHoffman | bruce.hoffman@flightbridgeed.com More
MAR
28

Mixed up About Venous Oxygen Saturations? Go Central or Go Home!

Red Blood Cell

Mixed venous oxygen saturations can help to establish the relationship between oxygen consumption and oxygen delivery.  Understanding the difference between the amount of oxygen being delivered and the amount of oxygen being consumed by the body can lead the clinician to early detection of a soon-to-be-deteriorating patient.  The mixed venous oxygen saturation is a key monitoring parameter for both the in-hospital and pre-hospital critical care provider.  Average mixed venous oxygen saturation in a healthy adult patient is approximately 70%.

When learning about mixed venous oxygen saturations, there are often two variables that are discussed – SvO2 and ScvO2; the difference being the addition of the letter “c” in the name.  The SvO2 is typically the oxygen saturation of mixed venous blood as it is found in the pulmonary artery.  Remember that this blood is a mixture of different sources of venous blood – the inferior and superior vena cava and the coronary sinus; whereas the ScvO2 is primarily just a sample of the vena cava blood.  Knowing this, we can clearly understand why the ScvO2 is slightly higher (3-5%) than the SvO2.  Mixing the vena caval blood with the coronary sinus (used blood from the myocardium) causes a further reduction in the saturation of oxygen on the hemoglobin.

If the body is consuming increased levels of oxygen, the amount of oxygen returning to the heart would be low.  This is typically seen in situations where the body’s cells are hyperactive and demanding more oxygen.  On the contrary, if the SvO2 comes back high, the body is typically being blocked from extracting oxygen from the blood into the tissues.  Situations like drug-induced paralysis or infiltrative microbial disease could be a cause of such.

Overall, the efficacy of circulation can be best measured by a mixed venous oxygen saturation.  The more central you obtain the sample, the more accurate the result.  Remember, the difference between oxygen consumption and oxygen demand, lies in the value of the mixed venous oxygen saturation.

 Peer Review #1:

While many of you may dismiss this blog under the premise that SvO2 (and certainly the more invasive ScvO2) are going the way of the Swan-Ganz catheter, replaced by newer metrics such as lactate and end-tidal CO2. However, even if your daily practice does not require interpretation of central oxygen saturation values, the concept of shock as a mismatch of supply and demand is always worth reviewing, and several new devices are about to hit the airwaves that will play off this theme.

In the world of resuscitation, the sole purpose of the human body is to deliver oxygenated blood to tissues. While oxygenation status is definitely a contributor, the most clinically relevant factor that limits this delivery is a decrease in tissue perfusion via limited blood volume, pump failure, and/or shunting away from the microcirculation. This explains why we generally get away with focusing on the oxygen content of blood returning to the heart, whether through measurement of blood samples taken from the vena cava or coronary sinus or via an oxygen saturation-measuring central venous catheter, rather than always comparing these values to measurements taken from the arterial side of the circulation.

The point is well made that a true systemic sample - either SvO2 or ScvO2 - is necessary to gain insight into the perfusion status of the entire body rather than a single limb (as with oxygenation measurements taken from a peripheral catheter) or specifically from the brain (as with a jugular venous sample). However, new devices are available for noninvasive tissue measurements, requiring careful site selection and understanding of the specific perfusion patterns for that tissue under pathophysiological conditions. Examples include near-infrared measurement of cerebral lactate-to-pyruvate ratios (again, reflecting the delicate balance between supply and demand), gastric pH, rectal mucosal perfusion (surprisingly, not as popular to study!), and skeletal muscle oxygen saturation (SmO2). It is clear that we will need to gain experience with some of these indirect and/or organ-specific devices before we can use them most effectively to care for our patients. In the meantime, keep the SvO2/ScvO2 lessons in mind and understand the basic paradigm of shock as a mismatch of supply and demand.

Dr. Dan Davis, MD

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FEB
12

Inequality in FDPAC Port Utility is Totally Appropriate

cateter swan ganz

Yes, this is a medical article; yes, it is relevant to the critical care transport provider and finally, yes, it is definitely worth reading.  Suffice it to say that you’ve already passed the most difficult piece of this article – the title.  With that said, let’s cut to the point.  The ports on a flow-directed pulmonary artery catheter (FDPAC) are to be used with extreme prejudice.  They are NOT innocuous; and careless utility can absolutely be the cause of patient death.  Not knowing is a crappy reason to put a patient at risk.  Learn with me, as we explore which ports we can use and those that we should avoid.

I’ll start with a short but impactful phrase that stuck with me from the first moment I heard it.  “RED and YELLOW will KILL a fellow”.  This phrase traditionally references the color patterns on specific types of snakes; helping to identify a poisonous snake from a non-poisonous snake.  If we were to compare the coral snake (venomous) with the king snake (harmless) by simply looking at them, they look very similar – a mixture of red, yellow and black stripes.  One might ask themselves – to touch or not to touch?!  I can assure you that my answer would be the latter regardless of the color, size, shape or type.  However, for the more curious folk, a closer look reveals a distinct difference.  On the coral snake (the venomous one), the red and yellow stripes are touching each other.  On the king snake (the non-venomous one) red and yellow never touch, but are separated by a black stripe – hence, the catchy phrase - “RED and YELLOW will KILL a fellow”.  If you see a snake and the red stripes and yellow stripes are touching each other – take the subtle hint, and steer clear.  We can apply this same simplicity to the various, color-coded ports on the flow-directed pulmonary artery catheter.

As you can gather, the two ports that should be avoided when working with a Swan-Ganz catheter are the red port, and the yellow port.  Regardless of the manufacturer, these two colors have been reserved for the two ports that should be avoided.  The red port is typically the balloon port.  The provider may notice that this port is typically shorter than the others and will also have a locking device built into it.  The locking device ensures that in the event the control syringe becomes separated from this port, no air will be pulled into the patient’s body.  When air is pushed through this port, it ends up at the distal portion of the catheter and fills a balloon.  The appropriate capacity for this balloon is 1.5 milliliters; and is only accessed with a control syringe (only allows the provider to draw up a max volume of air equaling 1.5 milliliters).  Using this port to infuse anything other than the aforementioned air is not appropriate and could cause significant harm to your patient – as in balloon rupture followed by a downstream shower of foreign emboli.

The second port to avoid is the yellow, also known as the distal port.  The termination of this port is at the very tip of the catheter; exactly where the pressure transducer is located.  During transport of a critically ill patient who has a Swan-Ganz catheter, the provider should be transducing pulmonary artery waveform, to assure that the catheter does not migrate.  For this reason, any infusion through this port can significantly alter the pressure being transduced – providing a false representation of the patient’s current hemodynamics.  It is important to understand that many Swan-Ganz catheters are colored yellow, creating further confusion when identifying this port.  At the very proximal portion of the port, the provider will notice that this port will be labeled as PA or distal – further making it clear that it should not be used for continuous or intravascular push medications.  The critical care provider may see other healthcare specialists which do infuse fluid through this port; these situations are usually related to procedure areas such as the cardiac catheterization laboratory, etc.  The provider may also notice that during the initial set-up and placement of a flow-directed pulmonary artery catheter, the distal or PA port, may be flushed with a heparin-infused saline solution.  Note, that this is typically only done while the catheter is OUTSIDE of the patient’s body.  To reiterate, during transport of critically ill patient who have this catheter, the distal port is NOT to be used for infusion purposes.

So, let’s recap – discriminatory use of the ports on a Swan-Ganz catheter is imperative.  For purposes of critical care transport, use of the red and yellow ports for any type of fluid infusion is never appropriate – and like the snake, steer clear.  Remember “RED and YELLOW will KILL a fellow”!!

Peer Review #1:

Excellent article! As Bruce brings up, one of the most important things a provider can do when transferring a patient with a FDPAC, is monitoring for migration. The ways I remember what to look for on the wave form is by thinking about Dub Step music. Right after the bass drops the song gets crazy! Well if you notice the PA waveform base drop you have migrated to the RV and....!!  Could get crazy! 

Right Heart Pressures
When Physicians are passing these lines the goal is to spend as little time in the RV as possible to avoid arrhythmias. So watch out for that base drop!! The quickest way to terminate a invasive line induced arrhythmia is to withdraw the line. However make sure you have deflated the balloon first.
Tyler Christifulli, FP-C
 
Peer Review #2:

As the indications for Swan-Ganz catheterization decrease, familiarity with their safe use becomes problematic.  Rather than applying the old adage “See one, do one, teach one…” or relying upon frequent use to maintain competency, we have to develop unique strategies to avoid complications when one of these patients is encountered.  The author of this blog applies the concept of “disconjugate imagery”, in which a completely unrelated but memorable image is introduced.  Rather than being more difficult to recall under stress, you will find that the mental image of a coral snake will pop into your brain the next time you see a Swan-Ganz catheter.  Just remember that, like our blog author, both red and yellow may “kill a fellow”.

Dr. Dan Davis, MD

Peer Review #3:

The Swan-Ganz catheter has slowly lost its use in many patients. The evidence suggests no improvement in 30-day discharge when used in sepsis or other hemodynamically unstable patients. Although the use is still widely acceptable in the thoracic surgery or cardiac ICU setting, these catheters are removed as soon as possible due to the infection risk associated.  With than being said, the critical care paramedic or nurse may encounter these catheters or see questions on exams related to their use and applicability. Using teaching tips such as mental imagery will allow the provider quick recall abilities.  I truly believe we remember pictures much easier and can relate images to things we like or dislike.

The saying “Red Touch Yellow” Kill a Fellow was coined for purposes of Coral vs. King snake identification. Dr. Swan happened upon this literature as he and Dr. Ganz were developing this catheter. As they attempted to color code these ports he identified and related this saying to the color-coding system now used with the Swan-Ganz catheter. The balloon port “Red” and distal port “Yellow” are not by accident. We should always remember the potentially lethal consequence associated with the improper use of these two ports.  Remember, the coral snake is the deadliest snake in the US, although docile, the coral snake will get you if your not paying attention.  Remember this the next time you grab the ports off the Swan-Ganz catheter! “Red and Yellow” Will Kill a Fellow!

Eric Bauer, MBA, FP-C, CCP-C, C-NPT

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