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RV failure after Cardiopulmonary
Bypass
S Magder
Department of Critical Care,
McGill University Health Centre
BP = Cardiac Output x SVR (+k)
BP = Cardiac Output x SVR
First Question to ask:
Is the cardiac output decreased
Or
Is the cardiac output normal or increased
Measured variable
Part = Q x SVR (+K)
ReturnStressed volume
Compliance
Resistance
Pra
Sepsis
Drugs
SpinalHeartHeart Rate
Afterload
Contractility
Preload
Cardiac Output
Return Function
Stressed volume
Compliance
Resistance
Pra
Cardiac Function
Heart Rate
Afterload
Contractility
Preload
Clinical Scenario
• Patient comes back from aorto-coronary bypass
surgery. The initial hemodynamics are:
– Q = 2.2 l/min/m2 , Pra = 12 mmHg,
Pw = 8 mmHg, Part = 110/70 mmHg
• One hour later
– Q = 1.8 l/min/m2, Pra = 6 mmHg,
Pw = 7 mmHg, Part = 90/70 mmHg
What would you do?
Clinical Scenario
• Patient comes back from aorto-coronary bypass
surgery. The initial hemodynamics are:
– Q = 2.2 l/min/m2 , Pra = 8 mmHg,
Pw = 6 mmHg, Part = 110/70 mmHg
• One hour later
– Q = 1.8 l/min/m2, Pra = 12 mmHg,
Pw = 8 mmHg, Part = 80/70 mmHg
What would you do?
What would you do?
• Wedge is only 8 mmHg - give volume?
• You do an echo and the LV is hyper-dynamic
and under-filled
–Give volume?
Concept:
No left sided success
without right sided
success
This is an example of RV limitation with
RV dysfunction
• RV limitation because Q and BP went down
with rise in CVP/Pra
• Q is less than <2.2 with high CVP/Pra
• BP is depressed
Review of physiological basics and
definitions
What does the right heart do?
• Lowers right atrial pressure and allows
venous blood to return to the heart
• The LV only can pump out what the RV
gives it.
Stressed Volume
Cv x RvQ =
Heart has a
“restorative”
function
Volume stretches the veins and creates the “recoil”
pressure that drives flow back to the heart
The RV has a
“permissive”
function. It lowers
the outflow
pressure and
allows veins to
empty
which refills the veins
Determinants of flow
Volume
Pre
ssu
reLV RV
SV
SV
• Sharper break to passive filling curve
• Flatter slope to ESPV (Es)
• Much lower Syst-P• Same Stroke Volume
Comparison of LV and RV P-V curves
120 mmHg
18 mmHg Maximum P-sytolicFor RV (~50-60 mmHg)
Sharp break is due to the pericardium, but also by the cardiac cytoskeleton in the absence of a pericardium
Holt 1960
Pericardial P-V
Volume
Pre
ssu
re
1
23
SV 123
• On the flatter part of the passive filling curve, SV can be maintained when afterload increases by increasing preload
• When the steep part is reached, SV must fall with an increase in afterload (unless HR or contractility, ie slope of Es, change) = RV LIMITATION
Es, gives maximum possible pressure for given volume
Increase in PAP
This does not mean that there is RV dysfunction
P
V
1 23
4
Pra
Q
1
2
3
4
Pressure-Volume of RV Cardiac Function Curve“Starling Curve”
“Starling Curve”
0-
10-5
5
Is RV necessary?• If PVR is low – No!
• Eg Fontan patients–Can even exercise to > 80% of predicted
aerobic power
• Bad RV can actually limit flow
• Problem is “pulsatility”–Limits the time for RV fillin
–Also TR
Definitions of RV “dysfunction”
and RV limitation
How do you assess RV limitation?
• Best is change in flow with change in Pra
• = Same as fluid responsive - thus any test of
fluid responsiveness can be used
Does not equal dysfunction
How do you determine if there is
a cardiac limitation?
1 Assess the value of Pra
(note NOT the wedge).
2 Give fluid challenge to
raise Pra by ~2mmHg
and observe Q.
• Of more limited value – cannot tell if volume is limited
• Leftward bowing of septum is late
• Changes in TR can help
• Respiratory variations IVC (not as good as SVC)
• Variations in Doppler flows across valves
• Echo help asses RV dysfunction based on the wall motion and ejection
Echo for assessment of RV limitation
‘a’0-
‘c’
20-
‘y’
‘v’
Prominent ‘y’
13 mmHg
Unlikely to respond to fluids when ‘y’ ≥ 4 mmHg
Differentiate RV limitation,
dysfunction, and failure
• Limitation is what counts clinically
• Dysfunction predicts potential problem with increase
flow demand or increased PAP
– Only a problem when there is limitation
• Failure = dysfunction plus limitation OR
Increased load ie Pulmonary hypertension
- Leads to limitation!
Volume
Pre
ssu
re
1
23
VolumeP
ress
ure
1
23
SV 123
SV123
Primary issue in RV dysfunction is depression of Es--- or too high a load, ie PAP, for the RV
Es
Depressed RV
• Sx pt do not have the congestive signs of chronic patient
• RV may not be very big acutely • Could even have normal output
• KEY is higher filling pressure for normal output • Lower cardiac ouput• Lower plateau to cardiac function curve
How do you distinguish RV dysfunction from limitation in post-op cardiac surgery ?
• Limitation and dysfunction could be present with higher than normal resting cardiac output because the values are still low compared to maximum and thus should not be limiting
• This is seen with hyperdynamic “septic” like picture.
Reasons for RV dysfunction post cardiac
surgery
1. It is more difficult to protect RV with cardioplegia
2. Rapid filling and distention coming off pump
3. Increased in pulmonary artery pressure
4. Long pump and bypass time
5. Excessive volume infusion especially if significant bleeding overdistends RF
– Limitation refers to a maximally filled RV – ie non-responsive to flow – occurs likely in 40 to 50% of cases
• Treatment may not be different for each• If signs of hypoperfusion – rising lactate, low mixed venous,
decreased sensorium - inotropes are needed• Could use Dobutamine, Epinephrine, Milrinone – especially
if Pulmonary pressure elevated• Fluids are not of help• If PVR elevated - reduce it• Avoid high Driving Pressure on ventilator- use low Tv
(6ml/kg)
Treatment of dysfunction and limitation
Conclusion• Distinguish RV “limited” from dysfunction
– Limitation is what counts and is easier to assess
• Dysfunction means depression of Es (or failure to increase it)
• Clinicaly this is seen as
– higher CVP/Pra for cardiac output
– Enlarged RV (if not volume depleted!)
– Lower plateau of cardiac function curve
• Inadequate cardiac output for tissue needs
Background
• Distinguish cardiac limitation from right failure
• True failure is not common
• More often the problem is Limitation
P
V
1 23
4
Pra
Q
1
2
3
4
Pressure-Volume of RV Cardiac Function Curve“Starling Curve”
“Starling Curve”
0-
10-5
5
= RV limitation
With enough volume, the limit can be reached even
when the heart is normal
“A commonly used definition for RVF does
not exist, while a recent statement defined
ARHS as a rapidly progressive syndrome
with systemic congestion resulting from
impaired RV filling and/or reduced RV flow
output”
“A commonly used definition for RVF does
not exist, while a recent statement defined
ARHS as a rapidly progressive syndrome
with systemic congestion resulting from
impaired RV filling and/or reduced RV flow
output”
RV dysfunctionCan be because the muscle is not functioning well
(Injured, myopathy)
Or
Because the load is too high(PE, PHT)
Key clinical point
Patients need adequate volume to
compensate
• Stressed volume reserves (rapid)
• Interstitial volume (slower)
• Volume infusion (clinician)
A
a b c d
Pra
Q
Pra
B
a
b
Q
When filling is limited only a change
in cardiac function will increase Q