Venous & arterial connections for right & left congenital heart surgery
Aetiology of operative field blood from shunts
Bypass complications of patent ductus arteriosus
Application of hypothermic arrest
1.
Venous
a) Right heart procedures
i) SVC & IVC are cannulated separately, and external caval tourniquet are applied to completely divert systemic venous return to the extracorporeal circuit and maintain a clear surgical field
ii) Note that increased proportion of venous blood returns from SVC
b) Left heart procedures
i) Single venous cannula
c) Deep hypothermic arrest
i) Single venous cannula in right atrium
d) Procedures involving intraatrial manipulation
i) Directly cannulate vena cavae using right angled catheters for improved access and visibility of heart
ii) Eg: Mustard or Senning repair; Fontan procedure
e) Persistent left SVC
i) May require cannulation or division prior to cannulation
f) Glenn shunt
i) May require to cannulate SVC at innominate junction
g) Anomalous systemic venous return
i) Direct cannulation of anomalous veins
ii) In small infants with complex anomalous venous return, single atrial cannulation with systemic hypothermic arrest
h) Senning repair
i) Right atrial cannula is transfered to the left atrium once the superior & inferior caval pathways are constructed
2.
Arterial
a) Most cases
i) Aorta cannulated just proximal to innominate
b) Hypoplastic left heart syndrome
i) Pulmonary artery may be cannulated alone
c) Discontinuity (or near discontinuity) of the ascending & descending aorta (Repair of interrupted aortic arch)
i) arterial cannula to adequately perfuse whole body
ii) the arterial line into 2 cannula allowing separate perfusion of upper & lower systemic circulation
iii) Eg: ascending aorta & pulmonary artery, descending aorta or femoral artery
d) Aneurysm, pseudoaneurysm of right ventricle
i) Poor access to ascending aorta: use femoral or iliac artery
3.
General concerns
a) Cannulation can be difficult in the neonate
i) Small hearts & hypoplastic vessels can make the size and type of cannula used critical in minimising the morbidity associated with CPB
ii) Arterial line pressures must be carefully monitored to diagnose malpositioned or improperly sized cannulas
iii) When multiple arterial cannula are used, the flow rates are dependent on the diameters of the cannula
4. Sizing of cannula
a) Arterial
i) Determined by:
a) Actual cannula internal diameter
b) Pressure drop across cannula
c) Circuit configuration
d) Size of aorta
e) Existence of shunts or collaterals
b) Venous
i) Choosing proper size is more difficult and more subjective than one-size-fits-all approach in adults
1.
Venting
a) Venting of left ventricle carries increased significance in the infant as a greater proportion of paediatric procedures are intracardiac and cyanotic patients have greater bronchial arterial collateral flows
b) Left ventricle is generally vented from the right atrium through a ASD or PFO
c) Left ventricle may be vented through the left superior pulmonary vein, left atrium or left ventricle
d) Must minimise vent & sucker tubing as up to 30% of a neonates circulating blood volume may be held within their tubing
2.
Abnormal sources of
blood returning to left ventricle
a) Left superior pulmonary vein that drains into coronary sinus & right heart
b) Left SVC draining into left atria
c) Patent ductus arteriosus (blood returning via pulmonary veins)
i) Systemic to pulmonary artery shunts
1. Usually accomplished via left thoracotomy not using CPB
2. Ligation and division of the PDA may be required in older children because recanalisation can occur with ligation alone
3. A calcified ductus complicates repair and may require CPB
4. Intraoperative complications
a) Shunting of perfused aortic blood into pulmonary circulation; adequacy of peripheral perfusion?
b) Excessive shunted blood returning the left ventricle via pulmonary veins
i) concerns of adequacy of LV decompression
ii) Concern of adequacy of cardioplegia; excessive pulmonary blood return may enter aortic root & flush out plegia
c) A large systemic to pulmonary artery anastomosis must be dissected before commencement CPB and should be closed before cooling at the onset of CPB to avoid distension of heart & over-perfusion of lungs
d) Impaired systemic perfusion?
e) Deep hypothermic arrest
i) Even a small PDA must be closed
ii) If persistent PDA; risk of cerebral air embolism when heart is open
5. Post operative complications
a) LV dysfunction due to elevation in afterload caused by removal of low resistance pulmonary circuit
b) Because vessel diameters are similar, the left PA or descending aorta may be mistakenly ligated, causing hypoxaemia or systemic hypoperfusion respectively
c) Recurrent laryngeal nerve damage
d) Ductal recanalisation
1. Application
a) Most intracardiac repairs in paediatric cardiac surgery are performed under moderate to profound hypothermia (<25°C)
b) Mild to moderate hypothermia (25->32°C) used for short procedures
c) Deep hypothermic circulatory arrest (DHCA) used for
i) Infants <1 year (< 10 kg)
ii) Repair of specific abnormalities (eg aortic arch repair)
2. Advantages of DHCA
a) Bloodless operating field to permit precise repair
b) Enhanced myocardial protection by reducing non coronary blood flow
c) Decreased blood trauma due to reduced CPB times
3. Technique
a) Cooling commenced with 25°C perfusate
b) Surface cooling is commenced in some small infants prior to sternotomy
i) Ice bags (head, axillae, groin)
c) Water blanket used to facilitate cooling & rewarming
d) minutes may be required to cool to a core of 18 °C (augmented by vasodilator)
e) Once reached target temperature
i) Stop CPB
ii) Body exsanguinated via single atrial cannula prior to its removal
f) Resumption of CPB
i) Reinsertion of arterial & venous cannula
ii) Deairing of cannula
iii) Deairing of heart
g) Rewarming
i) Gradient between water and arterial blood < 12°C
ii) Perfusate temp does not exceed 39°C
iii) Water temperature does not exceed 42°C