Discussion:
CPB is a standard procedure in paediatric cardiac surgery.[3]The
general principles of CPB are same for neonates and adults. It requires
aortic and bicaval cannulations, andsome modifications are necessary to
accommodate the multiple anatomical variations that may be encountered
in congenital defects i.e. two aortic and three cava cannulas in
associated interrupted aortic arch and a persistent left superior vena
cava (LSVC) for adequate drainage during the CPB.[4] The aortic
cannulation is primarily done at the distal ascending aorta, positioning
the cannula close to the origin of the brachiocephalic trunk.[5]The
appropriate arterial cannula size depends upon the required CPB flow,
calculated using the formula ;CPB blood flow rate (litre/ min)=Body
surface area (BSA)(m2)×Cardiac index (CI),(L m−2/min). Flows of 1.8 to
2.5 L/min/m2 are commonly used for infants, children,
and adults during mildtomoderate systemic hypothermia.The pump flow for
this patient was calculated as Weight in KG x 150 ml/min= 750ml/min and
accordinglyrecommended aortic cannula of 12 Fr for 700 ml – 1000 ml
flow was used.If a cannula is too large, it can obstruct native heart
output, particularly in the ascending aortic position as this output is
critical during cannulation and the initiation and weaning phases of
bypass, also too large of a cannula may require an aortotomy that is
difficult to close in a standard fashion. Therefore, aortic cannula size
should be selected in conjunction with the perfusionist team to utilize
the appropriate cannula for adequate flow during CPB.Table below shows
general sizes of cannulas used for initiating CPB.