1.
Right heart
a)
Normally
vented by venous cannula
b)
See ‘heart rotation’.
for relative effectiveness of various venous cannula in decompressing right
heart
c)
If bicaval
cannulation + tourniquet are used, venting of right heart does not occur—>
therefore require venting [opening; cannula; cardiotomy]
2.
Purpose of Venting
a)
Prevent
distension
a)
Decrease
myocardial oxygen consumption
(1)
Minimise
myofibril overstretch; reduce wall tension
(2)
Decreased
myocardial work
b)
Promote
subendocardial blood flow
c)
Promote
subendocardial flow of cardioplegia
d)
Reduce pulmonary
hypertension (causing pulm HT/oedema)
b)
Reduce
myocardial rewarming
c)
Minimise
risk of air ejection; means to evacuate surgical air
d)
Improve
surgical exposure
e)
Create a
dry surgical field especially during distal coronary anastomosis
f)
Venting is
very important in the early postischaemic reperfusion period when elevated
intraventricular pressure may reduce subendocardial perfusion and increase
metabolic needs of heart
3.
Sources of Blood entering Left Ventricle
a)
Normal
i)
Bronchial
a)
Bronchial
blood flow to periphery of lungs drains into the pulmonary veins; can be a
substantial amount on CPB and is influenced by perfusion pressures
b)
Increased
bronchial flows in CAL & cyanotic congenital heart dx
ii)
Thebesian
iii)
From right
ventricle via lungs
a)
Coronary
sinus blood flow should diminish upon X-clamping the aorta
b)
Abnormal
i)
Left superior pulmonary vein draining into
coronary sinus (RA)
ii)
Patent
ductus arteriosus
iii)
Aortic
regurgitation (may occur 2° to manipulation of heart; aortic root cardioplegia)
iv)
Malpositioned
X-clamp
4.
Methods of Venting
a)
Active
application of suction
i)
Aortic root
a)
Unable to
plege & vent at same time: if left ventricle distends, may have to
interrupt pleging and vent
ii)
Direct left
ventricular
a)
venting via
right superior pulmonary vein
b)
directly
into LV apex
iii)
Left atrium
iv)
Pulmonary
artery
b)
Passive
i)
Amputation
tip of left atrial appendage with subsequent repair
ii)
Holes in
the aortic root for proximal anastomosis during X-clamping
5.
Complications of venting Left Ventricle
a)
All active
venting techniques that involve suction on a cardiac chamber may introduce
intracardiac air
b)
Introduction
of air into left ventricle —> air embolisation
i)
Danger
during time of insertion or removal of vent if left heart volume is low (fill
heart during these times)
ii)
Excessive
suction —> air entrapment
iii)
Reversal of
roller pump
c)
Bleeding
d)
Damage to
heart
i)
eg left
vent aneurysms
e)
Excessive
vent return (eg due to bronchial or aortic regurgitation) steal systemic flow:
must compensate by increasing pump flow accordingly
6.
Venting during Cardiac procedures
a)
CABG
i)
Aortic root
b)
AVR
i)
None;
relying on good venous drainage with a reduced flow rate to keep the heart cold
and empty
ii)
Right
superior pulmonary vein
iii)
Need to
increase the vent flow as heart is opened (clamp chimney)
c)
MVR (Left
atrial approach)
i)
Aortic root
a)
Gentle
suctioning upon removal of X-Clamp
b)
Do not vent
when X-clamp is on and heart is opened
d)
Ascending
aorta
i)
Right
superior pulmonary vein
7.
Monitoring of adequacy of venting
a)
X-clamp on
i)
LAP or PAP
(>15 mmHg cause for concern)
b)
X-clamp off
i)
Pulse pressures
on pulmonary artery or radial trace
KCPotgerã