Left
Heart Bypass
Benefits of vortex pumps for left heart bypass
Cannulation sites for left heart bypass
Significance of Patent Foramen Ovale
Pressure monitoring in left heart circuit
Partial left heart bypass for surgery to the aorta
Transfer of circulation from cardiopulmonary
bypass to left heart circulation
1.
Indications in left ventricular failure
a)
CI < 1.8 - 2.0 l/m2/min
b)
PCWP (left ventricular
filling pressure) > 18 - 25 mmHg
c)
MAP < 70 mmHg despite
inotropes & IABP
d)
But reasonably
functioning right side
2.
Post cardiotomy cardiogenic shock (PCCS) —
Short term ventricular assistance
a)
PCCS occurs in 2% — 6% of
all patients undergoing CABG or valvular surgery
b)
Used to resuscitate
stunned myocardium and maintain adequate systemic and pulmonary function
c)
If myocardial recovery
does occur; occurs within a week
d)
Preoperative predictors
of need for circulatory assistance:
i)
Prior myocardial
infarction with depressed ventricular function
ii)
Severe valvular dx with
endstage myocardial involvement
iii)
Coronary artery
grafting that is only partially amenable to grafting with poor LV function
iv)
Anticipated long CPB
time
e)
Preoperative predictors
of need for circulatory assistance:
i)
Inadequate myocardial
protection
ii)
Reperfusion injury
iii)
Prolonged CPB
iv)
Air or particulate
emboli in coronary artery
v)
Large ventriculotomy or
aneurysm resection
f)
Contraindicated:
i)
Patients who have had
incomplete revascularisation or imperfect operation as are not likely to recover
ii)
Patients sustaining
very large perioperative infarct
iii)
Right ventricular
failure
3.
Ventricular failure after MI
a)
Role of VAD not
evaluated
b)
Greater role for IABP
4.
Bridge to transplantation — Long term ventricular assistance
a)
Used for patients with no
likely hood of myocardial recovery ie end stage cardiomyopathy
b)
Circulatory support is
required until heart transplantation
c)
Up to 1/3 die before
receiving new heart
5.
Descending aorta surgery
a)
Left atrium to femoral
artery
1.
Pressure sensitive
a)
Increases flow when
preload increases or afterload decreases
b)
Decreases flow when
preload decreases or afterload increases
c)
As are sensitive to
afterload pressure
i)
Catastrophic pressure
buildup in arterial line (eg kinked tubing) cannot happen as flow decreases as
pressure increases
2.
Tendency to not pump
accidentally introduced air
a)
Bubbles tend to remain
at the low pressure inlet point
b)
Massive introduction of
air unprimes pump, stopping flow
3.
Better blood handling
characteristics
a)
Less haemolysis,
complement activation, white cell activation & platelet activation
[controversial]
4.
Absence of tubing
trauma prevents spallation & associated particulate embolisation
5.
Not suitable for long
term use due to heat produced in the bearing housing predisposing to thrombus
formation in this area
1.
Post cardiotomy cardiogenic
shock (PCCS) — Short term ventricular assistance
a)
Outflow
i)
ascending aorta
ii)
femoral artery
b)
Inflow
i)
left atrium via a tube
attached to venous line via a 1/2 1/2 3/8 connector
ii)
Clamp off the RA cannula
2.
Bridge to
transplantation — Long term ventricular
assistance
a)
Outflow
i)
ascending aorta
b)
Inflow
i)
left ventricle; aids in
ventricular decompression
3.
Descending aorta surgery
a)
Outflow
i)
Femoral artery
b)
Inflow
i)
Left atrium
4.
Tubing length
a)
Centrifugal pump or
roller pump
i)
pump mounted away from
patient; longer tubing required
b)
LVAD
i)
pump mounted on
patient; shorter tubing required
1.
Dangers of diastolic
vacuum
a)
Patent Foramen Ovale
i)
Occurs in 25% of
general population
ii)
Can cause severe R®L intracardiac
shunting if left atrial pressure is reduced below right atrial pressures
iii)
Should always be
diagnosed (TOE; visual) and surgically closed prior to insertion of LV CPB
cannula
b)
Open Chest
i)
Diastolic vacuum may
draw air into the circulation prior to closure of the chest
ii)
Negative inflow
pressures generated by centrifugal pumps or excessive venous drainage has the
potential to draw air into the circulation at suture lines or central venous catheters
iii)
Use soft shell
reservoir; try not to direct draw
a)
Minimise cavitation
b)
Able to add volume more
effectively
c)
Normally (without PFO)
CVP: keep >10 to prevent cavitation
i)
control by adding
volume; no partial clamp
ii)
If underfilled, unable
to flow
a)
(using a soft shell
reservoir + bimedicus pump) -> unable to maintain systemic blood pressure
b)
Rollerpump: potential
for cavitation also if no soft shell reservoir
iii)
PA to be zero: resting
left side of heart; do not want to eject
1.
Short term VAD
a)
Continuous IV heparin
b)
ACT: 200-250 seconds
2.
Long term VAD
a)
Initially continuous IV
heparin; dextran
b)
Long term maintenance
with Warfarin ±
dipyridamole
c)
Balance between haemorrhaging
and thromboembolism
3.
Carmeda
a)
ACT: 150-200 [assuming
flows > 2l/min]
b)
Boluses heparin
c)
Monitor from circuit
(not patient)
1.
Centrifugal pumps
during left heart assist
a)
Pump rate is adjusted
so that the pump maintains adequate pressure on its outflow side while
effecting adequate decompression on its inflow or venous side
b)
Left atrial pressures
kept below an acceptable maximum value to rest left side
i)
>0 but < 5 mmHg
ii)
But not too low: danger
of air entrainment
c)
MAP kept at an
acceptable minimum value
d)
CVP keep filled
2.
Centrifugal pumps
during right heart assist
a)
RA -> PA
b)
CVP kept at a
reasonable safe maximum
i)
>0 but < 5
ii)
To rest right side
c)
MeanPA or LAP kept at a
reasonable minimum
3.
Accomplished by
adjusting pump speed & blood volume
4.
Note that the
centrifugal pump needs continuous vigilence as its output is affected by
changes in afterload
5.
Note prior to RVAD or
LVAD should assess whilst using CPB to determine suitability for long term LVAD
-RVAD(eg 1 hour) looking for ventricular failure of the opposite side of the
heart
1.
Surgical approaches to
repair descending & thoracoabdominal aortic disease
a)
Simple cross-clamp
b)
Left atrium to left
femoral artery bypass
c)
Left ventricle to left
femoral artery shunt
d)
Partial CPB (femoral
vein to femoral artery)
e)
Total CPB (femoral vein
to femoral artery)
f)
Passive shunt (Gott
shunt) (Proximal aorta to distal aorta)
2.
Left atrial to left
femoral artery partial CPB
a)
Centrifugal pump
b)
No oxygenator to reduce
haemodilution & cost (One lung should be oxygenating - but advantage of
using an oxygenator is the use of a heat exchanger and to cover any oxygenator
problems)
c)
Minimum heparinisation
(especially if Carmeda)
d)
Possible add heat
exchanger
e)
Soft shell reservoir -
avoid direct suction unto a vessel, reducing cavitation, shearing, difficult to
add volume, mechanical shut down if run out of volume
f)
Drainage to the pump
comes from the preload chamber of the left ventricle
i)
Increasing pump flow
decreases ventricular filling, cardiac output, & proximal systemic pressure
ii)
Must monitor upper
& lower body pressures simultaneously
iii)
Improper drainage of
the left atrium may lead to upper-body hypotension leading to cerebral &
cardiac ischaemia
g)
Not recommended for
routine use
h)
Recommended for
patients with poor ventricular &/or renal function
3.
Femoral vein to femoral
artery
a)
Oxygenator
b)
Full heparinisation
c)
Hypothermia
d)
±
Circulatory arrest
e)
Indicated for extensive
thoracoabdominal aneurysms
i)
Allows prolonged
intercostal and visceral ischaemia with reduced post operative paraplegia and
bowel infarcts
f)
Associated with
increased incidence of coagulopathies & post op bleeding
LVAD
1.
Insert cannula standard
single stage [30 F] cannula into left atrium and attach via 3/8” to a
1/2-1/2-3/8 connector attached to venous line - clamp off right atrial line on
normal CPB
2.
Assess patient’s
suitability for LVAD by staying at this state for at least an hour and observe
for failure of right side; if patient doesn’t get any worse continue LVAD
3.
Set up centrifugal +
soft shell circuit, hand 3/8 line to table, both ends of line handed back to be
inserted into reservoir & pump head
[no oxygenator or arterial filter] and primed - pump off & cannulated
RVAD
1.
RA -> PA
2.
See above
3.
Ideal left atrial line
for monitoring
4.
Need to have enough left
sided filling for ejection