Thread by @FSotoMD

[1] #Hemodynamics Tweetorial #2

Heart failure pt in ICU is -3.5L after 2d of aggressive diuresis. On day 3, urine output is ⬇️and BUN/Cr is ⬆️

You personally wedge #PAC at bedside and obtain a mean wedge 17 mmHg (a normal mean wedge is 6-10 mmHg). Admission wedge was 24

[2]
Question 1. Based on wedge 17 mm Hg (good waveform; no trick), you:

[3]
Before you use the pulmonary artery catheter #PAC information, you should know its pitfalls

Given the potential impact of #PAC-related decisions, consider learning as much (or more) as the ICU nurse/cath lab tech about #PAC setup and troubleshooting

[4]
🔹”Zeroing”
🔹”Leveling”
🔹”Damping”

[5]
🔹”Zeroing”

-Device is “zeroed” to open the air-fluid interface to atmospheric pressure (AP)

-AP is the reference standard against which other pressures are measured

-“Re-zeroing” is done often since transducer and atmospheric pressure drift away from calibration point

[6]
Transducer components and directions of the components 👇🏻

[7]
To zero:

-Point the 3-way stopcock “off” towards the patient (points up on the transducer)

-This now allows the vent port to be “opened” to atmospheric pressure

-If vent port cap is not fenestrated, it has to be temporarily removed
(port cap in video 👇🏻 is fenestrated)

[8]
🔹”Leveling”

Question 2. For #PAC, you place the transducer to match the level of:

[9]
🔹”Leveling”

-Selection of a point of interest (R atrium for #PAC) at which the ref standard (zero) is set

-RA is considered the phlebostatic axis (RA is also used as the ref point for CVP assessm)

*REMEMBER:
Pressure changes 7.4mmHg for every 10 cm transd is ⬆️ or ⬇️ RA

[10]

To level:
Identify the point at which the:
🔹mid-axillary line intersects with the
🔹4th intercostal space

That point should be at the same level of the transducer’s diaphragm

Consider using an accurate leveling system (e.g., laser) to match transducer ht with RA ht

[11]
Leveling is 🔑

🔷IN RELATIONSHIP TO TRANSDUCER:

🔹For every 10cm that RA “rises” above transducer, pressure falsely “rises” 7.4 mmHg

🔹For every 10cm that RA is “lowered” below transducer, pressure falsely “lowers” 7.4 mmHg

—

RA ⬆️ = pressure ⬆️

RA ⬇️= pressure ⬇️

[12]
Answer to Question 1 is: “Can I trust that wedge?”

In our case, when wedge 17 mmHg was obtained, transducer wasn’t leveled and pt’s RA was about 11 cm above the transducer.

Therefore, real wedge was <10 mmHg.

Diuresis was held for a few hrs and restarted at home dose

BONUS:

If you see pressure tracings that become negative (below Zero), consider an unaddressed LEVELING issue before you interpret and use that #PAC info

See 👇🏻 RAP tracing: transducer was higher than RA level, causing sub-Zero values (RA level is ⬇️ = pressure is “falsely” ⬇️)

[13]
🔹”Damping”

Damping is the “shock absorber” effect on the pressure line (like a car suspension)

Overdamping:
Sluggish oscillations

Underdamping:
Oscillations are too pronounced

Causes of Over and Under-Damping 👇🏻

[14]
Which answer is FALSE regarding an OVERDAMPED waveform

[15]
🔹OVER-damping

🔸Slurred upstroke
🔸ABSENT Dicrotic Notch
🔸Systolic is Underestimated
🔸Diastolic is Overestimated
🔸MAP is usually preserved
🔸Pulse pressure is underestimated (affects PAPi calc)
🔸The waveform gets “squished” (think letter “O” for “O”verdamped)

[16]

How to address an OVERDAMPED #PAC (and arterial) waveform
👇🏻

[17]
Which answer is FALSE regarding an UNDERDAMPED waveform:

[18]
🔹UNDER-damping

🔸Non-physiologic oscillations during Diast phase
🔸Deep dicrotic notch
🔸Systolic is Overestimated
🔸Diastolic is Underestimated
🔸Pulse pressure overestimation
🔸MAP is usually preserved
🔸Waveform gets “stretched out” (inverted “U” for “U”nderdamped”

[19]

How to address an UNDERDAMPED #PAC waveform
👇🏻

[20]

Besides looking at the waveforms, consider FAST-FLUSH test (square wave test) to assess for waveform damping characteristics

🔸Hold fast-flush device for <1 sec
🔸Assess the square wave and characteristics of the wave (s) that follow

See image 👇🏻

[21]

TAKE-HOME Messages (applies to ICU and outpt cardiac/PH pts)

🔷Before you interpret/use #PAC info, verify:
🔸Zeroing (atmosp pressure)

🔸Leveling (match transducer level to RA, AKA phlebostatic axis)

🔸Waveforms (to exclude OVER or UNDER damping affecting actual values)

TAKE-HOME Messages 2

🔸If you see -ve (below Zero) pressures, especially in non-ill pts, consider leveling error

🔸Over and Underdamping affect Syst and Diast pressures; MAP is usually preserved

🔸Verify line flushing/waveform every time a MVsat is drawn from distal #PAC port

Additional relevant reading:
-NEJM Art Line Pressure Transducer
nejm.org/doi/full/10.10…

-Deranged physiology
derangedphysiology.com/main/cicm-prim…

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