Preparing for bypass

Before the operation

• Ensure cross-matched blood available for perfusionist, to prime pump if needed, for cardioplegia, for blood loss.
• Check imaging, planned procedure for anatomy that could complicate cannulation.
• Aortic: e.g. calcification/plaques, porcelain aorta, aneurysms, number of proximal graft anastomoses, aortic aneurysm/dissection surgery,
• Venous: type of venous cannulation (bicaval or atrial)
• Ensure patient is weighed for heparin dosing, and height measured for CPB settings.

During sternotomy

• As chest is being opened, the perfusionist would hand off the sterile lines to the scrub nurse/assistant who secures the CPB lines on the sterile field using towel clips. It is usually secured on the assistant side (CPB side) at the level of the abdomen.
• ‘Dividing the lines’ – the venous inflow and the arterial outflow lines are connected together in a circuit as they come out of the pack. They need to be flushed with the clear perfusate to clear the air in the lines.
• Inform the perfusionist & scrub nurse: Divide the lines
• The perfusionist circulates perfusate to fill the sterile circuit and clamps it to prevent air entry during line division. informs the surgeon: Clamping
• Only after the CPB-end is clamped does the surgeon clamp it at the venous end and then the arterial end, and informs the perfusionist: Clamping
• If the surgical end is clamped first, then high pressures will develop in the circuit, causing connectors to burst.
• Now that the line clamps are placed on either side of the built-in connector, the arterial and venous lines are cut with heavy scissors. Clamp at a suitable length for allowing the lines to be secured in the field AND be connected to the caval/aortic cannulae, not too long that it kinks/twists.

Checks before bypass

Heparin – dose calculated by weight (300-400 units / kg), ACT checked to be above 400 seconds.

Order of cannulation – Aortic, Atrial, Antegrade cardioplegia, Retrograde cardioplegia.

Aortic cannulation

Preparing the aorta

• The aorta is palpated for abnormalities – calcification, plaques, etc, and a suitable site identified for cannulation. This is usually in the anterior portion of the distal ascending aorta close to the pericardial reflection.
• The aorta may be dissected free from the pulmonary trunk to pass a tape around the aorta using curved haemostat.
• To prevent dissection and haematoma formation, pressures are controlled by the anaesthetist to less than 100mmHg systolic and 65-70mmHg mean.

Purse-strings

• At the desired site of cannulation, aortic adventitia may be dissected away using scissors.
• Double-pursestrings are placed in the aorta in two concentric diamonds shapes, as viewed by the operator.
  • If using a single-ended suture, the initial bite is forehand, starting at the diamond corner opposite, and coming out anti-clockwise in the superior portion of the aorta. The second bite starts there and comes on the diamond corner nearest the operator. At this point the diamond may be completed with backhand bites with the same needle. This will place the inner purse-string ends on the assistant side. The next purse-string starts concentrically outside the initial box in the opposite manner on the operator side, bringing the purse-string on the operator side.
  • If using a double-ended suture, start on the operator side with a back-hand to bring the ends to the assistant side, and vice versa.
• The needle bites are taken into the media, but not into the lumen.
• Purse-strings are secured using snuggers, clipped using small artery forceps, and hung loose.
• Ensure the aortic cannula is closed (with a cap or clamp) before inserting it.

Aortotomy

• Size-11 scalpel blade is used to make a stab incision within the purse-string and insert the aortic cannula. This can be done in two ways.
  • Either with the scalpel blade in the left hand making the incision followed by immediately inserting the cannula held in in the right.
  • Or the incision made with the right hand, the left hand placed over the incision to stop bleeding whilst the scalpel is handed back to the scrub nurse and exchanged for the aortic cannula.
  • Or a semi-circular flap of adventitia is taken with the forceps in the left hand and cut with the knife in the right hand, followed by aortotomy. The flap is used to cover the aortotomy whilst the right hand places the aortic cannula.
• It is important to make a deep incision with the scalpel through all the layers of the aortic wall into the lumen. If not, the aorta is at risk of acute dissection when the cannula is inserted.
• While the cannula is held up, the snuggers are tightened by the surgeon (and assistant) in turn. A heavy silk tie is then placed around the snuggers and cannula near the base. This tie is crucial for securing the cannula.

Connecting to arterial line

• The aortic cannula, now filled with blood, is tapped and clamped so that its cap can be removed. The clamp is slowly released to allow blood to flush any air out of the cannula, and the cannula is filled to the brim, and the clamp secured again. The flushed blood is directed into the surgical field where it can be sucked back into the CPB machine.
• The cannula is held in the left hand and the arterial line in the right hand. Instruct the perfusionist to flush the arterial line very slowly: ‘Bring up the arterial line’.
• Both lumen are held vertically side-by-side and connected from bottom to top to allow air to escape.  The bottom of the lumina are approximated first, but the top is free so air can escape as the perfusate spills over into the arterial line. When the line is connected, the perfusionist stops the flow, the surgeon cleans the line to visualise any bubbles of air, and observes the column of blood exhibiting an arterial swing into the line.
• If TOE is available, the anaesthetist may check for bubbles.
• The surgeon checks for ventricular distension, arterial trace dampening, or is informed by the perfusionist about high CPB line pressures – they are indicative of obstruction of the aorta or the line and requires adjustment of the cannula or repositioning.
• If all is well, at this point, the surgeon informs the perfusionist the line is connected properly: ‘Over to you’

Venous cannulation

• The scrub nurse ensures internal cardioversion paddles are ready for use before venous cannulation due to haemodynamically-unstable arrythmias from handling the RA/SVC.
• Purse-strings are placed (snugged and clipped) in the RA appendage and/or IVC (and SVC depending on the type of cannulation).
• When placing IVC pursestrings especially, the surgeon informs the anaesthetist about the manipulation of the heart to get exposure: ‘Pressing on the heart.’
• Cardiotomy suction devices (clear, blue) should be placed in the field to be used if necessary, the surgeon informs the perfusionist: ‘Take back what you get’. In an emergency situation, CPB may be instituted with sucker bypass.
• With forceps controlling the incision, a size-11 scalpel is used to make a stab incision and scissors used to dilate the opening. The forceps can be used to stem bleeding by approximating one side against other (with an assistant’s help if required).
• The venous cannula is inserted unclamped and open. It is directed superiorly or inferiorly (depending on the type of cannulation) ensuring it is freely moving. The snuggers are tightened and heavy tie used to secure the cannula. The cannula is allowed to fill either by bringing the level of the tip to the level of the heart, or by injecting saline into the lines. The venous line is unclamped after connecting the cannula.
• If bicaval cannulation, snares (umbilical tapes) are placed around the SVC and IVC and snugged, or alternatively with two pairs of Cooley venacava clamps.
• Venous drainage may be either by siphon effect or suction. If siphoned, the venous reservoir must be below the level of the patient. Air bubbles can cause an air lock and disruption of flow.

Cardioplegia

• The scrub nurse requests the perfusionist to flush the cardioplegia line and taps any air out, ready for the surgeon to connect when the cardioplegia cannula is inserted.
• A single purse-string is placed on the proximal ascending aorta, snugged and clipped.
• The cardioplegia cannula (which has a large-gauge needle) is inserted within the purse-string. The suture is loosened and guided around the rungs on its base,  tightened and snugged.
• The cannula fills up with blood, flushing air out. The cardioplegia line is also trickled: ‘Trickle the cardioplegia’ to flush the air – keep the lumen facing up during trickling, to allow air to escape.  Whilst trickling, connect the cardioplegia and inform the perfusionist to stop trickling: ‘Stop trickling’