VENTING

A) RIGHT HEART

· Normally vented by venous cannula

· See ‘Venous Cannulation’ for relative effectiveness of various venous cannula in decompressing right heart

· If bicaval cannulation + tourniquet are used, venting of right heart does not occur—> therefore require venting [opening; cannula; cardiotomy]

B)LEFT HEART

i) Purpose of Venting

· Prevent distension

a) Increased myocardial work

b) Reduced subendocardial blood flow

c) Myofibril overstretch

d) Pulmonary hypertension (causing pulm HT/oedema)

· Reduce myocardial rewarming

· Minimise risk of air ejection

· Improve surgical exposure

ii) Sources of Blood entering Left Ventricle

1. Normal

a) Bronchial

i) 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

ii) Increased bronchial flows in CAL & cyanotic congenital heart dx

b) Thebesian

c) From right ventricle via lungs

i) Coronary sinus blood flow should diminish upon X-clamping the aorta

2. Abnormal

a) Left superior pulmonary vein draining into coronary sinus (RA)

b) Patent ductus arteriosus

c) Aortic regurgitation (may occur 2° to manipulation of heart; aortic root cardioplegia)

iii)Methods of Venting

1. Aortic root

a) Unable to plege & vent at same time: if left ventricle distends, may have to interrupt pleging and vent

2. Direct left ventricular

a) venting via right superior pulmonary vein

3. Left atrium

4. Pulmonary artery

iv) Complications of venting Left Ventricle

1. Introduction of air into left ventricle —> air embolisation

a) Danger during time of insertion or removal of vent if left heart volume is low (fill heart during these times)

b) Excessive suction —> air entrapment

c) Reversal of roller pump

2. Bleeding

3. Damage to heart

a) eg left vent aneurysms

4. Excessive vent return (eg due to bronchial or aortic regurgitation) steal systemic flow: must compensate by increasing pump flow accordingly

v) Venting during Cardiac procedures

1. CABG

a) Aortic root

2. AVR

a) None; relying on good venous drainage with a reduced flow rate to keep the heart cold and empty

b) Right superior pulmonary vein

c) Need to increase the vent flow as heart is opened (clamp chimney)

3. MVR (Left atrial approach)

a) Aortic root

i) Gentle suctioning upon removal of X-Clamp

ii) Do not vent when X-clamp is on and heart is opened

4. Ascending aorta

a) Right superior pulmonary vein

KCPotger©