Count Backwards From 10

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We aim to teach you Anesthesia with FREE, memorable and quick digital "chalk talks" on a wide variety of topics in Anesthesia and Critical Care to all interested in learning!

I cannot tell you how many times I have been told the equation, "Coronary perfusion pressure = Aortic diastolic pressure...
02/28/2023

I cannot tell you how many times I have been told the equation, "Coronary perfusion pressure = Aortic diastolic pressure - Left ventricular end diastolic pressure," and boy is that only part of the story. So today, I wanted to address coronary perfusion pressure and what gets perfused when and why!

The perfusion pressure through a coronary artery, or anywhere for that matter, is a function of the pressure gradient between where flow starts and where the flow is going. In the case of the coronary arteries: we can measure the starting pressures since blood flow through the coronaries originates in the aorta, and a simple blood pressure measurement estimates our aortic pressure during systole and diastole, 120/80 mmHg in a normal patient. 

We can estimate the pressure in the coronary arteries by assuming that the pressure within them is equal to the pressure in the ventricle that they are feeding as they run along the chamber. Therefore, we have a general idea of pressure in the coronaries, and as a result, the coronary perfusion pressure throughout the cardiac cycle! 

🫀Left Coronary Artery: In systole, aortic pressure = 120 mmHg, while the LV systolic pressure is also 120 mmHg making the delta 0, resulting in NO coronary perfusion!

🫀Left Coronary Artery: In diastole, aortic pressure = 80 mmHg, while the LV diastolic pressure is somewhere closer to 8 to 10 mmHg, leading to a delta of roughly 70 to 72 mmHg!

🫀Right Coronary Artery: In systole, aortic pressure = 120 mmHg, while the RV systolic pressure is roughly 25 mmHg, making the delta 95 mmHg and contributing to RCA perfusion during systole (unlike the LCA)

🫀Right Coronary Artery: In diastole, aortic pressure = 80 mmHg, while the RV diastolic pressure is somewhere closer to 5 mmHg, leading to a delta of roughly 75 mmHg!
(Continued in comments)

We'll be heading back to some basic cardiac physiology as we move through our next section, mechanical circulatory suppo...
02/06/2023

We'll be heading back to some basic cardiac physiology as we move through our next section, mechanical circulatory support. Without a firm understanding of the basics, MCS can be very difficult. First to cover is mixed and central venous oxygen saturation! 

Central and mixed venous oxygen saturations are a way of evaluating oxygen delivery by the heart 🫀and extraction by the tissue 💪🏻. The central venous oxygen (CvO2) is drawn from the CVP port and samples roughly from the SVC (the central vein), which reflects oxygen extraction from the upper extremity and head! Normal value is roughly 70%. 

The mixed venous O2, (MvO2), is drawn from the PA tip of the swan, sampling a MIXTURE of blood from the SVC, IVC, and coronary sinus. Because of the high oxygen extraction by the heart, the mixed venous is usually about 5% less than a central venous O2. 

I think of venous O2 as a train 🚂 analogy! In this analogy, the passengers are oxygen, the RBCs are the train cars, the blood vessels the track, the organs are the destinations, the lungs are the loading stations for the passengers, the left heart is the train engine propelling the train cars, and the right heart is the weigh station where the passengers are counted! 

As a result, anything that alters the amount of train cars, the passengers on the train, the passengers getting off at destinations, the train tracks, or the train engine will result in changes to the mixed venous oxygen saturation! We will go over this in more detail in the next post!

Have you ever thought of the mixed venous like this? Let me know if this helped clarify in the comments below 👇🏻 ! 

*For educational purposes only.
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In light of completing our discussion on pericardial tamponade, I would be remiss if we did not talk briefly about the p...
12/22/2022

In light of completing our discussion on pericardial tamponade, I would be remiss if we did not talk briefly about the pericardiocentesis. Pericardiocentesis is a procedure, done either electively or emergently, in which a needle is placed percutaneously into the pericardial sac to drain fluid (many times blood) as treatment of a worsening effusion or tamponade. 

The procedure is performed by placing a long needle, usually 20g or larger through the skin and advancing under ultrasound guidance into the pericardial sac, withdrawing as you go. Once you hit blood, aspirate, and eject blood via a 3 way stopcock until the patient experiences symptom relief.

A guidewire and catheter may be placed in order to leave an ongoing drain that can be utilized should fluid re-accumulate or as a bridge to a pericardial window. 

An alligator clip can be attached to the needle and an ECG monitor during advancement into the sac, which will produce a normal ECG waveform. If you enter the myocardium, the ECG will demonstrate ST elevations, telling you you have gone too far! 

While blind procedures can be performed, it is not recommended due to the increased risk of morbidity and mortality as you can perforate the heart!

What has your experience been with pericardiocentesis? Let me know in the comments below!👇🏻

*For educational purposes only.
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📧: [email protected]
💻: www.countbackwardsfrom10.com
📱: instagram.com/countbackwardsfrom10
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Hemodynamic considerations during tamponade are critical to consider due to the risk of cardiovascular collapse. Just re...
12/07/2022

Hemodynamic considerations during tamponade are critical to consider due to the risk of cardiovascular collapse. Just remember these patients need to be FAST! FULL! And TIGHT!

1️⃣ FAST: in order to maintain adequate cardiac output due to the inability to fill the heart as well and increase stroke volume, heart rate must remain fast.

2️⃣ FULL: give them volume wide open through large bore access! This keeps the heart full increasing pressure within the chamber helping to prevent collapse

3️⃣ TIGHT they need tone to ensure organ perfusion! Pressors are crucial.

❕Epinephrine❕ is your friend as it accomplishes multiple goals between pressure and heart rate.

You also want to ‼️avoid positive pressure ventilation‼️ as this can result in increase pressure on the heart and pulmonary vasculature decreasing both LV and RV filling further. Many will opt for ketamine and volatile anesthetic for induction rather than paralysis because of this physiology!

Let me know below if this helped you understand the hemodynamic management of tamponade in the comments below!

*For educational purposes only.
-----
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‼️OH S@¥&‼️Tamponade!! Nobody panic! Cardiac tamponade is the pathology in which the pressure (usually within the perica...
11/23/2022

‼️OH S@¥&‼️Tamponade!! Nobody panic! Cardiac tamponade is the pathology in which the pressure (usually within the pericardial sac) increases and puts pressure on the heart enough to cause hemodynamic instability. This is most often caused by fluid within that space from bleeding, effusion, and more. But understand, tamponade can be caused by other scenarios such as the surgeon pushing on the heart in the OR!

This can be either acute where an accumulation as little as 150 to 200cc can cause symptoms, or over time, up to 2 liters chronically.

The pressure on the heart reduces ⬇️ venous return to the right heart, and thus decreases ⬇️ to the left as well leading to obstructive shock.

Some high yield findings include things like:
1️⃣ JVD, as a result of volume building back up into the SVC and jugular veins
2️⃣ distant heart sounds, because the sounds don’t travel through the fluid as well
3️⃣ electrical alternans, as the heart swings back and forth in the fluid
4️⃣ narrow pulse pressure
5️⃣ and some more!

Stay tuned for the next post where I explain PULSES PARADOXUS! An important finding in tamponade.

Did this help you understand tamponade a little better? Let me know in the comments below 👇🏻!

*For educational purposes only.
-----
📧: [email protected]
💻: www.countbackwardsfrom10.com
📱: instagram.com/countbackwardsfrom10
🎥: youtube.com/c/countbackwardsfrom10
🐦: twitter.com/anesthesiacbf10

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