Surgical methods of eradication of blood from anastomosis site

Cardiac surgery: heart rotation for circumflex artery anastomosis; surgical manipulation of venous cannula

Application of elective electrical fibrillation in coronary surgery

Surgical methods of eradication of blood from anastomosis site

1. Distal anastomosis

a) Aortic root venting to create a dry surgical field

b) CO₂ gas jet

c) Locally applied sucker

d) Reduce pressures

e) Hypothermia to tolerate lower flows

2. Proximal anastomosis

a) clamp in situ

i) Suction on aortic root vent

b) X-clamp removed

i) Use of ‘side-biter’ to isolate section of aortic root

3. Sources of Blood entering coronary arteries

a) Via cardiac chambers to aortic root

i) Normal

a) Bronchial

(1) Bronchial blood flow to periphery of lungs drains into the pulmonary veins into left heart or azygous vein into right heart; can be a substantial amount on CPB and is influenced by perfusion pressures

(2) Increased bronchial flows in CAL & cyanotic congenital heart dx

b) Thebesian

c) From right ventricle via lungs

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

ii) 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)

d) Malpositioned X-clamp

b) Directly into coronary arteries

i) From right atrium via coronary sinus thereby reaching coronary arteries retrogradely

ii) Non coronary collateral return (NCCR)

a) NCCR reaches the myocardium via collateral vessels from the mediastinal vessels

b) They approach the heart via the walls of the great vessels and through the pericardial reflections

c) NCCR is greatest during cardiac arrest and is particularly high with left ventricular hypertrophy and coronary artery disease

d) Even with the aorta X-clamped, this NCCR blood flow is implicated in flushing out the cardioplegia within the coronaries

iii) Turn cardioplegia off; ensure X-clamp on properly

Cardiac surgery: heart rotation for circumflex artery anastomosis; surgical manipulation of venous cannula

Surgical manipulation/insertion of venous cannula

a) Atrial arrhythmias

i) Ensure aorta is already cannulated

ii) May be only transient during manipulation

b) Air embolisation

i) Especially if atrial pressure is low which could cause systemic embolisation with right to left shunts

c) Laceration of venae cavae & atrium

i) IVC especially prone

ii) Ensure aorta if already cannulated

iii) Replace volume lost via aortic cannula

iv) Commence emergency CPB using cardiotomy suckers for venous return

d) Reduced venous drainage 2° malpositioning of tip

i) Atrial approach

a) Azygous, hepatic, innominate, across ASD

b) 2-stage inserted too far into IVC (distended SVC)

ii) Femoral

a) Too far in: SVC

b) Not far enough in: IVC

e) Impaired cardiac output during insertion

i) Lifting of heart to insert IVC cannula

Heart rotation for circumflex artery anastomosis

a) Circumflex position

i) When lifting the heart to make an anastomosis to the posterior branches of the circumflex coronary arteries

b) Issues

i) Rotation of heart may impair venous blood return to atrium thereby engorging SVC

ii) Raised SVC pressures

a) Reduced cerebral perfusion pressures

iii) Reduced venous return

a) Reduced flows

b) Reduced CPP

iv) Attempt to maximise venous drainage/ emptying of heart

a) Reduced flows

b) Reduced CPP

v) Attempt to raise venous reservoir level by adding fluid

a) Severely impaired venous return

b) Exacerbate raised SVC pressures

c) Reduced CPP

vi) Increase level of venous gravity drainage

vii) Rearrange venous cannula

viii) Changing surgical traction on heart

ix) Increase vent flow

c) Clinical approach

i) Drop flows to minimal flow rate (determined by SvO2)

a) Minimise SVC pressures

ii) Use Aramine to maintain blood pressure

a) Maximise CPP

d) Choice of venous cannula

	*Bicaval*		*Single*
	*Tourniquet*	*No Tourniquet*	*Atrial*	*Cavoatrial*
Atrial incisions	2	2	1	1
Right heart exclusion	Complete	Incomplete	No	No
Right heart decompression	None	Fair	Good	Best
Right heart decompression with heart lifted up	Bad	Bad	Bad; very sensitive to position	Good
Caval drainage	Best	Good	Moderate; less good for IVC	Good
Caval drainage with heart lifted up “Circumflex position”	Good	Good	Bad; very sensitive to positioning	Good drainage of IVC; potentially poor drainage of SVC
Indication	Entry into right heart	Mitral valve surgery; due to retraction distorts cavoatrial junctions

Myocardial temperature monitoring

i. Cardioplegic solutions are usually cooled prior to myocardial delivery. An in-line thermistor distal to the heat exchanger validates the temperature of the cardioplegia prior to infusion

ii. The effectiveness of the solution in cooling the myocardium is best monitored through the use of myocardial temperature probes

iii. Typically, thermocouple probes are used, as they are easily made into a needle design, but thermister needle probes are also available albeit slightly larger

iv. In addition to validating initial cooling by the cardioplegia, the myocardial temperature probe alerts the perfusionist to rewarming and identify the need for additional cardioplegic cooling

v. Needle is inserted into interventricular septum (do not want to enter cavity)

vi. Should be < 15°C during cold cardioplegia (normally 12°C myocardial temperature)

vii. Should be used for severe left main dx, retrograde pleging

viii.Warming of the right heart, intraventricular septum and even the left heart by systemic CPB venous blood not being diverted to the heart-lung machine is a real cause of right ventriula failure following ischaemic aortic cross clamping

ix. Use of single atrial cannulation or cavoatrial cannula warrants constant monitoring of myocardial temperature and cardiac decompression (PA pressures) during aortic cross clamping

x. It is important to monitor myocardial temperatures & cardiac decompression when cavoatrial cannulating without ventricular venting during aortic X-clamping

Application of elective electrical fibrillation in coronary surgery

1. Technique

a) Applying low voltage AC (5 V) to surface of heart induces VF

b) Hypothermia

2. Physiology

a)

Spont VF & vented

Myocardial oxygen consumption at 37°C

a) Continuous VF impedes coronary blood flow to myocardium causing ischaemia, therefore a use of a vent is essential during prolonged VF

b) Moderate hypothermia (32°C) has a salutary effect on oxygen consumption if a vent is used

c) Important to maintain adequate coronary perfusion pressures

2. Advantages

a) Produces relatively quiet heart without interrupting coronary perfusion allowing the surgeon to proceed without need for X-clamping

b) Avoids risk of air embolism that is associated with surgery on a beating heart

3. Disadvantages

a) Increased myocardial oxygen consumption

b) Higher risk of ischaemic injury in the hypertrophied heart

4. Practical technique

a) Adequate venting

i) Left ventricular vent

ii) Intracavitary press < 5 mmHg

b) Moderate systemic hypothermia

i) 20°C — 25°C

c) ± Pericardial cooling

d) Adequate coronary perfusion pressures

i) Systemic pressure 80 — 100 mmHg

5. Technique prior to sophisticated pacemaker for fibrillating a asystolic heart prior to defibrillating (AC 5 V )

Surgical methods of eradication of blood from anastomosis site

4. Distal anastomosis

a) Aortic root venting to create a dry surgical field

b) CO₂ gas jet

c) Locally applied sucker

d) Reduce pressures

e) Hypothermia to tolerate lower flows

5. Proximal anastomosis

a) clamp in situ

i) Suction on aortic root vent

b) X-clamp removed

i) Use of ‘side-biter’ to isolate section of aortic root

6. Sources of Blood entering coronary arteries

a) Via cardiac chambers to aortic root

i) Normal

a) Bronchial

(2) Increased bronchial flows in CAL & cyanotic congenital heart dx

b) Thebesian

c) From right ventricle via lungs

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

ii) 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)

d) Malpositioned X-clamp

b) Directly into coronary arteries

i) From right atrium via coronary sinus thereby reaching coronary arteries retrogradely

ii) Non coronary collateral return (NCCR)

a) NCCR reaches the myocardium via collateral vessels from the mediastinal vessels

b) They approach the heart via the walls of the great vessels and through the pericardial reflections

c) NCCR is greatest during cardiac arrest and is particularly high with left ventricular hypertrophy and coronary artery disease

d) Even with the aorta X-clamped, this NCCR blood flow is implicated in flushing out the cardioplegia within the coronaries

iii) Turn cardioplegia off; ensure X-clamp on properly

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