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