Differences to bypass in patients with aortic incompetence and aortic stenosis

Advantages & disadvantages of bicaval and single caval cannulation for valve surgery

Removal of intracardiac air for Valve Surgery

Arterial Line Air upon cessation of CPB

Differences to bypass in patients with aortic incompetence and aortic stenosis

	Aortic Incompetence	Aortic Stenosis
Perioperative goals:	1. Maintain LV preload i) Due to increased LV volumes ii) Dependent on adequate preload b) Avoid preload reducers i) GTN ii) Platelet sequestration 2. Heart rate: High [90 bpm] i) Reduce LVEDV: minimise time for regurgitant flow back into heart; maintain forward output ii) Maintain DBP iii) Increased subendocardial flows iv) Atrial contribution not so important, AF common 3. Maintain constant Contractility a) Use of inotropes 4. Maintain reduced SVR a) See dilation of peripheral arterioles in chronic AR b) Use afterload reducers to augment forward output	1. Maintain LV preload a) Due to decreased LV compliance b) Dependent on adequate preload to maintain adequate SV: ‘fixed SV’ c) Avoid preload reducers i) GTN ii) Platelet sequestration 2. Heart rate: Low [50-70 bpm] i) > 70; reduced Coronary perfusion (hypertrophic heart) ii) < 50; Reduced CO with ‘fixed SV’ iii) Importance of atrial contraction to augment filling of ventricle 3. Maintain constant Contractility a) Beta blockade poorly tolerated 4. Maintain raised SVR a) Require elevated DBP to perfuse coronaries b) Attempts to decrease afterload have little effect on heart as most of afterload is due to stenotic valve
Pre CPB	1. During induction: a) Avoid dilation of capacitance vessels; reducing preload b) Maintain reduced afterload, contractility and higher heart rates	1. During induction: a) Use alpha-adrenergic to maintain DBP i) To maintain CPP ii) As most of impedance to heart is due to aortic valve, raising SVR has little effect on afterload b) Dysrhythmias must be avoided; loss of atrial contraction can lead to spiralling deterioration in haemodynamics c) Impossible to maintain adequate CO by external massage: i) Ensure perfusionist on standby to initiate CPB
Initiation CPB [prior to X-clamp]	PRE LV VENT 1. Danger of VF prior to insertion of LV vent; due to: a) distension of LV 2° regurgitant flow of blood into LV via AI 2. reduce risk by: a) Warm primes (cold primes may ppt VF) b) Lignocaine c) Avoid raised SVR/afterload [vasopressors] 3. If VF occurs prior to venting a) Cool b) Reduce flows to reduce ventricular distension c) Maintain CPP with alpha agonists d) Apply X-clamp and cardioplege 4. Due to chronic low SVR state to augment SV; expect low mean BP; requirement for alpha agonists 5. Maintain mean BP prior to X-clamp £ 50 mmHg to prevent distention of LV 2° regurgitant flow via AR a) Avoid raising SVR; ie avoid a-agonists 6. Observe PAD for Ý 2° LV distention POST LV VENT · Reduced danger distension · Able to cool · Can raise SVR	1. Ensure maintenance of adequate mean BP to maintain CPP in hypertrophic heart 2. Ensure adequately drained LV to optimise CPP
Pleging	1. Unable to plege via aortic root: a) Coronary sinus or Ostial b) If minor AI may be able to plege via AR by manually massaging LV 2. Note: usually also have a degree of hypertrophy, therefore vigilance with cardioplegia: a) Adequate flows, pressures & times b) Ensure high retrograde flows (250 ml/min +) with max sinus pressures (40 mmHg) - low sinus pressures may result in hypoperfused/shunted myocardium c) Role of topical cooling devices d) Role of systemic hypothermia	1. In presence of ventricular hypertrophy; extreme vigilance to adequate pleging to avoid ‘stone heart’ caused by myocardial ischaemia 2. Role of retrograde & continuous cardioplegia 3. Role of topical cooling devices 4. Note: usually also have a degree of hypertrophy, therefore vigilance with cardioplegia: a) Adequate flows, pressures & times 5. Ensure high retrograde flows (250 ml/min +) with max sinus pressures (40 mmHg) - low sinus pressures may result in hypoperfused/shunted myocardium 6. Role of systemic hypothermia

Weaning CPB & early post CPB	‘Sicker Heart’ 1. Meticulous deairing 2. See immediate reduced LVEDV & LVEDP but hypertrophy & dilatation persists a) Maintain LVEDV by adequate preload 3. A declined in LV function may require inotropes or IABP 4. Ensure adequate Hct as may have some degree of hypertrophy	‘Healthier heart’ 1. Meticulous deairing 2. In absence of any associated ventricular dysfunction or coronary artery disease; inotropic support not required as the patient now has reduced afterload 3. Ensure adequate Hct 4. SNP may be required
Pacing	Heart Blocks common due to damage to AVnode	Heart Blocks common due to damage to AVnode

Advantages & disadvantages of bicaval and single caval cannulation for valve surgery

	Atrial				Femoral-iliac
	Bicaval		Single
	Tourniquet	No Tourniquet	Atrial	Cavoatrial
Atrial incisions	2	2	1	1
Cannulation speed	Slowest	Slow	Fast	Fast	Slow
Technical difficulty	Very	Moderate	Easiest	Easy	Difficult
Right heart exclusion	Complete	Incomplete	No	No	No
Coronary sinus return	Excluded; a real concern during direct coronary plegia as right heart will fill	Partial	Included	Included	Included
Right heart decompression	None Note: are usually venting right heart by surgical opening RA	Fair Note: are usually venting right heart by surgical opening RA	Good	Best	Fair -positional
Right heart decompression with heart lifted up	Bad	Bad	Bad; very sensitive to position	Good	Fair -positional
Caval drainage	Best	Good	Moderate; less good for IVC	Good	Fair -positional
Caval drainage with heart lifted up	Good	Good	Bad	IVC OK; SVC often compromised	Fair -positional
Potential rewarming of heart by venous return	No	Yes	Yes	Yes	Yes
Myocardial preservation	Best; due to reduced rewarming	Good	Suboptimal	Excellent; due to superior heart decompression	Suboptimal
Indication	Entry into right heart Note: tapes must be released during weaning to allow filling of heart	Mitral valve surgery; due to retraction distorts cavoatrial junctions	Paediatrics - used during procedures where CPB is used simply to cool & rewarm patient (circulatory arrest - temporaily remove cannula))	CABG, AVR, Ascending & transverse aorta, some MVR	Reoperations, Descending aorta repair, tamponade, circulatory assist - during single CABG
	· For operations requiring isolation of the right atrium · eg ASD, Tricuspid valve, · And entry into LA via RA · eg MVR & LA Myxoma · Used for complete bypass (all of venous return exits into CPB machine — none enters heart) · Creates a bloodless operative field · Reduces rewarming of heart by VR a) Open heart procedures b) Severe Rca dx (avoid rewarming right heart		Contraindicated in MVR & ASD: see air entrainment (MVR: going via atrial septum into LA)

Removal of intracardiac air for Valve Surgery

Aortic Surgery

a) Initiation of CPB

b) Fill heart & insertion of LV vent via right superior pulmonary vein

c) Insertion of retrograde cannula (may have already been inserted prior to venous cannula if no AI)

· Importance of early insertion of vent in AI

d) Application of X-clamp

e) Plegia (ostial or retrograde) & opening of aortic root

f) Valve replaced

g)