RHC Flashcards
Formula for Fick-derived cardiac output
Fick CO = Estimated O2 consumption / [10 x A-VO2 difference]
A-V O2 difference = 1.34 x [Hb] x (SaO2 - SvO2)
At what part of the respiratory cycle should wedge be taken?
End-expiration to minimize effect of intrathoracic pressure
-want all measurements taken at FRC (functional residual capacity)- end exhalation of tidal breathing
Direct vs. indirect Fick equation
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
If concern for intracardiac shunt- where to take oximetry measurements from?
IVC, SVC, high RA, low RA, RV, PA
But of course this only detects L to R shunt
Cutoff for step-up in oxygenation expected in
(a) L to R atrial shunt
(b) Shunt at level of RV or PA
(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
What to measure during RHC to get Fick cardiac output
Technically mixed venous sat (sat from PA) and arterial sat from ABG (often use room air SpO2)
Why measure at end exhalation
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
Typical length and size of PA catheter
110cm
5-8F, Roxana likes 7F (2.3mm) Edwards
In what circumstances would RA pressure not correctly estimate RVEDP
Some tricuspid valve disease
ex: TR
Line up CVP tracing with EKG lead
(a) a
(b) c
(c) v
(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
What is the c stand for in ‘a/c/v’ of a CVP tracing
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)
Change in CVP expected in AFib
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
Line up CVP tracing with EKG lead
(a) x-descent
(b) y-descent
(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)
What part of the CVP tracing can tell you about tricuspid competence?
(a) CVP tracing in TR
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
What happens to y-descent in tamponade?
Y-descent = tricuspid valve opening to allow passive RV filling (just before atrial contraction)
Loss of y-descent suggests restriction to RV filling = tamponade
Explain how thermodilution estimates cardiac output
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
Thermodilution curve in low cardiac output state
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
Margin of error for thermodilution cardiac output measurements
Cardiac output measured by thermodilution can vary by 10% measurement to measurement without change in patient hemodynamics
Change in 15% accepted as different
Why use 10cc vs. 5cc during thermodilution measurement
5cc shown to underestimate cardiac output- smaller AUC = more error prone
Explain why want PA catheter in West Zone 3 of the lung for optimal CO measurement
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
List 3 tests that suggest appropriate PA catheter positioning in West Zone 3
- Catheter tip below level of LA on lateral Xray
- Minimal changes in PAWP with applied PEEP or changes in alveolar pressure
- PAWP < PADP
-O2 sat in wedge > O2 sat unwedged - PAWP should have recognizable a and v waves, while could be unnaturally smooth if in zones 1/2 (b/c not pulsatile)
Differentiate thermodilution abnormality seen in
(a) R to L shunt
(b) L to R shunt
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
How erratic respiration can mess up thermodilution cardiac output measurements
Erratic changes in preload => erratic CO measurements
List 2 conditions where PAWP will read higher than LVEDP
PAWP > LVEDP
-Mitral stenosis, MR
-Catheter not in zone 3 placement
-L to R shunt
-PEEP or invasive positive pressure ventilation
What abnormality is this RA pressure indicating?
Prominent v-waves
v-wave = RA filling just after T-wave (atrial diastole/ventricular systole)
Name 3 abnormalities seen in CVP tracing of patient with severe TR?
- Prominent (large) V-wave
- V-wave so large that can merge with c-wave = c-v wave
- Disappearance of x-descent (b/c during ventricular systole blood rushing into RA)
Aside from number how to differentiate RV and PAP waveform
During diastole RV is filling (pressure upsloping) while PA is not (downslope)
Overwedging
-Can suspect overwedging if PAWP > dPAP
Differentiate PAP tracing (vs. art-line) in RBBB and LBBB
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
Differentiate CVP tracing findings in pericardial construction vs. tamponade
Both have impaired filling, both have tall A and V-waves
Why does the diastolic pressure step up from the RV to the PA?
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
PA catheter troubleshooting-
3 possible etiologies of trouble floating catheter from SVC into RA or RA into RV
- TR
- Left SVC if went through the Left IJ- try going through right or fem
- 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
What is a Chiari network?
(a) How may make floating PA catheter difficult?
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
Maneuvers to try if having difficulty passing PA catheter from SVC into RA or RV
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
In what situations may PA catheter have difficulty advancing from RV into PA
PA catheter can get coiled in a big RV or if having high afteroad
-RV dilation
-Elevated PA pressures
-Poor RV contractility
Maneuvers to try if having difficulty passing PA catheter from RV into PA
-To help pass the pulmonic valve: head up, R side down
Explain:
PA catheter giving arterial waveform but only 30cm deep
Cannulated the coronary sinus! Withdraw catheter and try again, very low chance of happening again
Why it matters for catheter to be below the LA when measuring wedge
Measuring wedge requires column of blood between pressure transducer and LA- if balloon is above the LA => no column of blood
What to do if during RHC
(a) arrhythmia
(b) complete heart block
(a) Move the catheter, likely ticked the endocardium
(b) Irritated endocardium in a way that disrupted AV nodal conduction. Pacer pads and pace!
Why will PA catheter most typically end up in West Zone 3 on its own?
Normally Wests Zone 3 enjoys highest blood flow
Positioning that may help get PA catheter to wedge L instead of R
Most catheters easily float towards the R PA, to selectively catheterize L PA position with R side down
What RVP tracing can tell you about RV compliance
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
How far in should PA catheter be to hit the main chambers
RA around 20cm, RV 30-35, PA 40-45, wedge at 50cm
Correlate a, c, v with EKG tracing
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
At which part of the curve should CVP technically be measured
Measure CVP at base of C-wave = final pressure in RV before onset of systole
Normal
(a) RV pressure tracing appearance
(b) RVSP
(c) RVDP
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
Normal difference btwn
(a) CVP and RA tracing
(b) RVSP and PASP
(a) CVP and RA tracing are generally identical
(b) RVSP = PASP in most cases (if normal pulmonic valve basically)
Describe the parts of a PA pressure tracing
PA tracing
-big upstroke from RV contraction (RVSP generally = PASP)
-dicrotic notch from closure of pulmonic valve
-then diastolic run-off
Explain how PAWP reflects LA pressure
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
The pressure at the tip of the PA catheter reflects what (instead of wedge) if PA catheter is in West zone 1
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
Why measure all values at end expiration
End-expiration is when pleural pressure is closest to atmospheric pressure so will have smallest effect on measurements
PEEP > 10 will cause over or undestimation of CVP and PAWP
Possible overestimation of PAWP due to PEEP due to increase in pericardial pressure/ intra-alveolar pressure directly transmitted to central circulation
Air bubble in catheter or tubing may cause
(a) What kind of dampening
(b) Falsely high or low systolic pressure?
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)
Differentiate overdampening and underdampening
(a) Appearance of waveform during fast flush test
(b) Impact of systolic blood pressure
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 :-)
Change in CVP tracing seen in severe TR
Early systolic large v-wave (blood leaking into RA during ventricular systole)
Change in PAWP tracing seen in MR
Elevated V-wave due to elevated LA pressure
Explain maneuver of occluding AV fistula
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.
Explain purpose of temporary AV dialysis access exclusion
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
At what fistula flow rate is there an increased risk of high output heart failure
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
Diastolic pressure gradient
(a) Formula
DPG = dPAP - wedge
significance to see if any precapillary component of group II PH (higher the dPAP, more likely a pre-caipllary component)
