54 / 56
66
Chapter 2
•
Cardiovascular Care
A Closer Look at VADs
There are three types of VADs.
1.
A right VAD provides pulmonary support by diverting blood from the
failing right ventricle to the VAD, which then pumps the blood to the
pulmonary circulation via the VAD connection to the left pulmonary
artery.
2.
With a left VAD, blood flows from the left ventricle to the VAD, which
then pumps blood back to the body via the VAD connection to the aorta.
3.
When a right and a left VAD are used, it is referred to as a
biventricular
VAD (BiVAD).
VAD
VAD
L E F T VA D
R I G H T VAD
•
It may pump regardless of the
patient’s cardiac cycle.
•
Nonpercutaneous centrifugal
pumps, which are used for
cardiopulmonary bypass.
They are used primarily for
cardiopulmonary bypass during
open heart cases and thus are not
placed percutaneously. They cause
too much hemolysis to permit
long-term use. There are presently
two centrifugal pumps available
for very short-term use (less than
six hours).
•
the Bio-Medicus
•
Sarns
•
Extracorporeal membrane
oxygenator pumps
While each device has a different
design and operation, the following
parameters of circulatory function
are improved by all devices; however
the degree of improvement varies
between devices and patients.
•
End-organ perfusion
•
Reduction in intracardiac filling
pressures
•
Reduction in left ventricular
volumes, wall stress, and
myocardial oxygen consumption
•
Augmentation of coronary
perfusion
As a result of treatment with these
devices the following clinical
parameters may be improved:
•
Prevention or amelioration of
cardiogenic shock
•
Reduction in pulmonary
congestion
•
Reduction in manifestations of
myocardial ischemia
•
Reduction in infarct size
Extracorporeal Membrane
Oxygenation
(ECMO) is part
of a larger term identified as
extracorporeal life support (ECLS)
which is a cardiopulmonary support
system that. ECMO moves blood
forward, removes carbon dioxide
and adds oxygen to venous blood
using an artificial membrane
lung. The pulmonary circulation
is bypassed and oxygenated blood
returns to the patient via an arterial
or venous route. With venovenous
bypass, ECMO is effective primarily
as a therapeutic option for patients
with severe respiratory failure.
With venoarterial bypass, an
extracorporeal pump is utilized to
support systemic perfusion, thus
providing a hemodynamic support
option in patients with circulatory
and respiratory failure.
The ECMO systems involve
placement in the central arterial and
venous circulation using a large bore
catheters that allow positioning of a
cannula in the aorta and right atrium.
Blood from the venous catheter is
pumped through a heat exchanger
and oxygenator and then returned
to the systemic arterial circulation
via the arterial cannula. The ECMO
systems can be used for support for
up to 30 days.
Indications for Use of ECMO
•
Hypoxemic respiratory failure.
•
Hypercapnic respiratory failure
with an arterial pH less than 7.20.
•
Ventilatory support as a bridge to
lung transplantation.
•
Cardiac/circulatory failure/
refractory cardiogenic shock.
•
Massive pulmonary embolism.
•
Cardiac arrest
•
Failure to wean from
cardiopulmonary bypass after
cardiac surgery.
•
As a bridge to either cardiac
transplantation or placement
of a VAD.