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RHC Flashcards

1
Q

Formula for Fick-derived cardiac output

A

Fick CO = Estimated O2 consumption / [10 x A-VO2 difference]

A-V O2 difference = 1.34 x [Hb] x (SaO2 - SvO2)

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2
Q

At what part of the respiratory cycle should wedge be taken?

A

End-expiration to minimize effect of intrathoracic pressure
-want all measurements taken at FRC (functional residual capacity)- end exhalation of tidal breathing

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3
Q

Direct vs. indirect Fick equation

A

Direct Fick- measure inspired and expired O2, mixed venous from PA, arterial O2 from ABG

Indirect Fick- one or any of these are estimated
ex: oxygen consumption based on nomogram, arterial O2 from sat

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4
Q

If concern for intracardiac shunt- where to take oximetry measurements from?

A

IVC, SVC, high RA, low RA, RV, PA

But of course this only detects L to R shunt

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5
Q

Cutoff for step-up in oxygenation expected in

(a) L to R atrial shunt
(b) Shunt at level of RV or PA

A

(a) 7% or greater increase from IVC/SVC to RA indicative of L to R atrial shunt

(b) O2 increase of 5% or greater raises suspicion for shunt at level of RV or PA

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6
Q

What to measure during RHC to get Fick cardiac output

A

Technically mixed venous sat (sat from PA) and arterial sat from ABG (often use room air SpO2)

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7
Q

Why measure at end exhalation

A

At end expiration (functional residual capacity) intra and extra-thoracic pressures are equal, so minimizing the effect of intrathroacic pressure on wedge/pressures

-Can also take average of 3 values, questionable if better to take average over respiratory cycles

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8
Q

Typical length and size of PA catheter

A

110cm

5-8F, Roxana likes 7F (2.3mm) Edwards

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9
Q

In what circumstances would RA pressure not correctly estimate RVEDP

A

Some tricuspid valve disease
ex: TR

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10
Q

Line up CVP tracing with EKG lead

(a) a
(b) c
(c) v

A

(a) a (atrial contraction) with P-wave

(b) c (cusp) of TV protruding backwards into RA as RV begins to contract- correlates with end of QRS

(c) v-wave = RA filling (against tricuspid valve), just after EKG’s T-wave

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11
Q

What is the c stand for in ‘a/c/v’ of a CVP tracing

A

C for cusp of the tricuspid valve protruding backwards into the RA as the RV begins to contract

(if on A-line then is closure of mitral valve)

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12
Q

Change in CVP expected in AFib

A

Afib- no organized atrial contraction => no A-wave

Can just look like disorganized activity b/c contraction is so disorganized that it may not produce pressure waves

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13
Q

Line up CVP tracing with EKG lead

(a) x-descent
(b) y-descent

A

(a) X-descent = downward movement of RV as RV contracts. Just before T-wave on EKG (atrial relaxation)

(b) Y-descent = opening of tricuspid valve right just before atria contracts, time of passive RV filling, occurs just before p-wave (early ventricular filling)

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14
Q

What part of the CVP tracing can tell you about tricuspid competence?

(a) CVP tracing in TR

A

V-wave: as blood fills the RA it hits the TV and produces this back-pressure wave

(a) Expect huge V-wave in TR, representing blood flowing back out of the contracting RV
In severe TR could expect V-wave to reach RVSP

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15
Q

What happens to y-descent in tamponade?

A

Y-descent = tricuspid valve opening to allow passive RV filling (just before atrial contraction)

Loss of y-descent suggests restriction to RV filling = tamponade

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16
Q

Explain how thermodilution estimates cardiac output

A

Mean decrease in temperature of blood (blood is warmer than room temp or cold injectate) inversely correlated to cardiac output

If flow is slower, takes longer time to equilibrate temperature

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17
Q

Thermodilution curve in low cardiac output state

A

Blood temperature will take a longer time to equilibrate with colder (cold or room temp) injectate, blunted initial spike because not moving as quickly

So shorter y-axis spike and longer x-axis time

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18
Q

Margin of error for thermodilution cardiac output measurements

A

Cardiac output measured by thermodilution can vary by 10% measurement to measurement without change in patient hemodynamics

Change in 15% accepted as different

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19
Q

Why use 10cc vs. 5cc during thermodilution measurement

A

5cc shown to underestimate cardiac output- smaller AUC = more error prone

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20
Q

Explain why want PA catheter in West Zone 3 of the lung for optimal CO measurement

A

Want uninhibited flow through vessel.

If in dead space (no blood flow) than there is no flow past the thermister
-So closer to zone 2/1 can underestimate cardiac output

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21
Q

List 3 tests that suggest appropriate PA catheter positioning in West Zone 3

A
  1. Catheter tip below level of LA on lateral Xray
  2. Minimal changes in PAWP with applied PEEP or changes in alveolar pressure
  3. PAWP < PADP
    -O2 sat in wedge > O2 sat unwedged
  4. PAWP should have recognizable a and v waves, while could be unnaturally smooth if in zones 1/2 (b/c not pulsatile)
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22
Q

Differentiate thermodilution abnormality seen in

(a) R to L shunt
(b) L to R shunt

A

Thermodilution abnormality

(a) R to L shunt: spuriously elevated cardiac output b/c cold injectate rapidly escapes to the L w/o getting measured, giving false impression of faster pulmonary blood flow
(b) L to R shunt: confuses thermistor, potential second peak in temperature as cold injectate circulates back into R heart, increased area under curve

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23
Q

How erratic respiration can mess up thermodilution cardiac output measurements

A

Erratic changes in preload => erratic CO measurements

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24
Q

List 2 conditions where PAWP will read higher than LVEDP

A

PAWP > LVEDP

-Mitral stenosis, MR
-Catheter not in zone 3 placement
-L to R shunt
-PEEP or invasive positive pressure ventilation

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25
Q

What abnormality is this RA pressure indicating?

A

Prominent v-waves

v-wave = RA filling just after T-wave (atrial diastole/ventricular systole)

26
Q

Name 3 abnormalities seen in CVP tracing of patient with severe TR?

A
  1. Prominent (large) V-wave
  2. V-wave so large that can merge with c-wave = c-v wave
  3. Disappearance of x-descent (b/c during ventricular systole blood rushing into RA)
27
Q

Aside from number how to differentiate RV and PAP waveform

A

During diastole RV is filling (pressure upsloping) while PA is not (downslope)

28
Q

Overwedging

A

-Can suspect overwedging if PAWP > dPAP

29
Q

Differentiate PAP tracing (vs. art-line) in RBBB and LBBB

A

RBBB- PA perfused after so arterial upstroke precedes the PA upstroke

LBBB- PA perfused before LV so PA upstroke will come before the arterial upstroke

30
Q

Differentiate CVP tracing findings in pericardial construction vs. tamponade

A

Both have impaired filling, both have tall A and V-waves

31
Q

Why does the diastolic pressure step up from the RV to the PA?

A

RVDP = RA pressure (assuming normal tricuspid valve) b/c tricuspid valve is open during diastole (so pressures equilibrate)

Once in PA during diastole pulmonic valve shuts and there is flow resistance in the pulmonary arterial network

32
Q

PA catheter troubleshooting-

3 possible etiologies of trouble floating catheter from SVC into RA or RA into RV

A
  1. TR
  2. Left SVC if went through the Left IJ- try going through right or fem
  3. Persistent chiari network = fibrous strands attached to eustachian and/or thebesian valves abnormally persisting into adulthood Chiari network = fenestrated, net-like embryonic remnants of valves of sinus venosus lying near the IVC and coronary sinus
33
Q

What is a Chiari network?

(a) How may make floating PA catheter difficult?

A

Chiari network = filamentous, weblike structure in the RA resulting from incomplete resorption of the embyronic sinus venosus
-uncommon anatomical variant

(a) Difficulty passing PA catheter from SVC into RA

34
Q

Maneuvers to try if having difficulty passing PA catheter from SVC into RA or RV

A

TR, persistent chiari network, or left IVC

-for TR: can try filling balloon with 1.5ml of NS and lying patient on L side- use gravity to guide heavier balloon into the RV

35
Q

In what situations may PA catheter have difficulty advancing from RV into PA

A

PA catheter can get coiled in a big RV or if having high afteroad

-RV dilation
-Elevated PA pressures
-Poor RV contractility

36
Q

Maneuvers to try if having difficulty passing PA catheter from RV into PA

A

-To help pass the pulmonic valve: head up, R side down

37
Q

Explain:

PA catheter giving arterial waveform but only 30cm deep

A

Cannulated the coronary sinus! Withdraw catheter and try again, very low chance of happening again

38
Q

Why it matters for catheter to be below the LA when measuring wedge

A

Measuring wedge requires column of blood between pressure transducer and LA- if balloon is above the LA => no column of blood

39
Q

What to do if during RHC

(a) arrhythmia
(b) complete heart block

A

(a) Move the catheter, likely ticked the endocardium
(b) Irritated endocardium in a way that disrupted AV nodal conduction. Pacer pads and pace!

40
Q

Why will PA catheter most typically end up in West Zone 3 on its own?

A

Normally Wests Zone 3 enjoys highest blood flow

41
Q

Positioning that may help get PA catheter to wedge L instead of R

A

Most catheters easily float towards the R PA, to selectively catheterize L PA position with R side down

42
Q

What RVP tracing can tell you about RV compliance

A

Flattness of the diastolic portion can tell you about compliance- in normally compliant RV as the RV fills (diastole) pressure should not drastically rise, so RV curve during diastole is generally pretty flat with a small upslope

43
Q

How far in should PA catheter be to hit the main chambers

A

RA around 20cm, RV 30-35, PA 40-45, wedge at 50cm

44
Q

Correlate a, c, v with EKG tracing

A

A-wave (RA contraction) just after P-wave

c-wave (cusp, tricuspid valve closure) at beginning of RV systole just after R-wave

v-wave (systolic filling of RA) just following ECG’s T-wave

45
Q

At which part of the curve should CVP technically be measured

A

Measure CVP at base of C-wave = final pressure in RV before onset of systole

46
Q

Normal

(a) RV pressure tracing appearance
(b) RVSP
(c) RVDP

A

Normal

(a) RV- big upstroke for systolic pressure (15-28) with relatively flat diastolic (slightly uptrending) curve b/c RV filling during diastole
(b) RVSP 15-28
(c) RVDP same as normal CVP, 0-5

47
Q

Normal difference btwn

(a) CVP and RA tracing
(b) RVSP and PASP

A

(a) CVP and RA tracing are generally identical
(b) RVSP = PASP in most cases (if normal pulmonic valve basically)

48
Q

Describe the parts of a PA pressure tracing

A

PA tracing
-big upstroke from RV contraction (RVSP generally = PASP)
-dicrotic notch from closure of pulmonic valve
-then diastolic run-off

49
Q

Explain how PAWP reflects LA pressure

A

No flow = no pressure differential

wedge position stops all distal flow => static fluid column btwn catheter tip and junction of pulmonary veins with the LA

50
Q

The pressure at the tip of the PA catheter reflects what (instead of wedge) if PA catheter is in West zone 1

A

In West zone 1 (Palv > Part > Pvein), pressure at the tip of the PA catheter when in wedge position will reflect alveolar pressure instead of pulmonary venous pressure

51
Q

Why measure all values at end expiration

A

End-expiration is when pleural pressure is closest to atmospheric pressure so will have smallest effect on measurements

52
Q

PEEP > 10 will cause over or undestimation of CVP and PAWP

A

Possible overestimation of PAWP due to PEEP due to increase in pericardial pressure/ intra-alveolar pressure directly transmitted to central circulation

53
Q

Air bubble in catheter or tubing may cause

(a) What kind of dampening
(b) Falsely high or low systolic pressure?

A

Air bubble in PA cath or tubing (or art line)

(a) Cause overdampening (<1.5 oscillations during fast flush test)
(b) False underestimation of PASP or SBP (falsely low systolic pressure)

54
Q

Differentiate overdampening and underdampening

(a) Appearance of waveform during fast flush test
(b) Impact of systolic blood pressure

A

Flash fush test- look at oscillations during the diastolic pressure run-off on a PA catheter

Overdampening
(a) < 1.5 oscillations during fast-flush test
(b) Cause falsely low systolic blood pressure (underestimate SBP)
ex: bubble in the tubing can cause falsely low PASP

Underdampening
(a) > 2 oscillations during fast-flush test
(b) Can falsely elevate/overestimate SBP or PASP and underestimate DBP, also cause amplification of waveform artifacts

MAP more reliable in these cases :-)

55
Q

Change in CVP tracing seen in severe TR

A

Early systolic large v-wave (blood leaking into RA during ventricular systole)

56
Q

Change in PAWP tracing seen in MR

A

Elevated V-wave due to elevated LA pressure

57
Q

Explain maneuver of occluding AV fistula

A

Goal is to complete loss of palpable thrill for ~1 minute, measure pressures (mPAP and CO) before and after.

If upper arm (brachio-cephalic) occlude manually, if forearm (radial-cephalic) inflate BP cuff above elbow.

58
Q

Explain purpose of temporary AV dialysis access exclusion

A

Indicate fistula’s contribution to high CO heart failure and mPAP

Basically see occluding the fistula raises the SVR enough that CO (and therefore mPAP) declines

59
Q

At what fistula flow rate is there an increased risk of high output heart failure

A

AV access flow > 1.5 or 2 L/min, or when fistula flow / cardiac ouptut is > 20%

Generally flow in forearm fistulas are lower than upper arm so lower risk of high output failure

60
Q

Diastolic pressure gradient

(a) Formula

A

DPG = dPAP - wedge

significance to see if any precapillary component of group II PH (higher the dPAP, more likely a pre-caipllary component)

PH (9 decks)

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