Tips, Tricks, and Pitfalls for Cardiopulmonary Bypass
This video describes the set up and pitfalls for cardiopulmonary bypass, including common types of arterial and venous access, as well as cardioplegia routes and venting strategies.
For arterial access, aortic cannulation is the most common. First, epiaortic ultrasound is used to assess for aortic calcifications that would affect cross clamp and cannulation sites. Next, either the distal ascending aorta or the aortic arch is cannulated with initial placement of double purse string sutures, followed by aortotomy with an 11 or 15 blade scalpel.
After the cannula is in the aorta, it will fill retrograde with blood. Then it is connected to the arterial line, where the perfusionist checks for pulsatility and matching pressures. The perfusionist then gives some volume through the cannula to test for any resistance. Any problems in these steps could mean there is a kink in the cannula or, more concerningly, an aortic dissection.
Next, the first purse string suture is placed. This suture is placed with partial thickness through the aortic wall, usually done forehand, forehand, backhand, then either forehand or backhand. It is snared and the square configuration is noted.
The next purse string inversely mirrors the first one, where any place that the first suture is outside of the aorta, the second suture is within the aorta. This maximizes hemostasis and is often performed with both arms of the suture, using all forehand bites. The adventitia can hinder cannula placement, so clearing it from the aorta makes for smoother insertion.
Next, the aortotomy is created and the cannula and snare are inserted, ensuring that the snares are below any cannula markers. Other options for aortic cannulation include using the Seldinger technique, which is helpful during aortic dissections, and the “stab and go” technique.
For “stab and go,” assistance is crucial since it is performed when the patient is crashing and no purse strings are used, so the cannulae can easily dislodge. Quickly, an aortotomy is created and a cannula is placed and connected to the lines. A right atriotomy and venous cannula are placed, connected, and bypass is initiated.
Pitfalls in aortic cannulation include difficulty with cannula insertion, which is usually due to the aortic adventitia obstructing the aortotomy, or the aortotomy being too small. Prior to connecting the lines, deairing is critical to prevent air emboli. A calcified aorta may result in stroke during cannulation, so epiaortic ultrasound can help guide cannula placement.
Lastly, iatrogenic aortic dissection occurs uncommonly, but must always be considered a possibility during cannulation due to its repercussions. Besides the earlier mentioned checklist, prevention includes cannulating the aorta when SBP is under 110 mmHg.
Axillary artery cannulation is most commonly used during circulatory arrest operations due to the ability to provide antegrade cerebral perfusion and avoidance of the aorta. With this technique, blood pressure monitoring is needed in both the right and left arms to assess for hyper and hypoperfusion.
The two options for cannulation are direct insertion or anastomosing a side graft, usually 8 or 10mm in diameter. First, the anatomical borders are marked: deltoid, mid third of the clavicle, and lateral edge of the sternum. A 4 cm incision is made infraclavicularly at the mid third of the clavicle, then dissected and spread with retractors.
The pectoralis major is divided, but the pectoralis minor can often be retracted inferiorly. Surgeons then palpate for the arterial pulse and use sharp and blunt dissection to locate the subclavian vein, in which a vessel loop is then used to retract inferiorly. Afterwards, the artery is noted, and vessel loops are placed for proximal and distal control.
For the direct insertion technique, a double purse string is placed in a similar fashion to the aortic cannulation using partial thickness bites, then the adventitia is cleared. Pitfalls for axillary cannulation include brachial plexus injury, axillary artery dissection, and postoperative seroma formation.
Femoral artery cannulation is useful for redo sternotomy cases, as well as for obtaining emergent arterial access. Direct insertion via groin cutdown or percutaneous Seldinger technique is most commonly performed. Anastomosis of a side arm graft is an option, but more frequently performed for ECMO.
Pitfalls include femoral artery dissection, a slightly higher stroke risk than aortic cannulation, and groin cutdown infections. Peripheral arterial disease is a particular concern with femoral cannulation. Whether there are severe femoral calcifications, stenotic lesions, or aneurysmal disease, they can all be very problematic with femoral bypass due to ischemia, stroke risk, or aneurysmal rupture.
Transapical cannulation is often a last resort when the aorta is not an option, such as during a Type A dissection with rupture. A ventriculotomy is created, watching out for the LAD, and the cannula is inserted into the ventricle then through the aortic valve. Another option in this situation could be the Samurai technique, in which the aorta is transected, the cannula is directly placed, and a cross clamp is applied. This results in a brief period of warm circulatory arrest.
For venous cannulation, right atrial cannulation with a double or triple stage cannula is most commonly used. The cannula can be placed in two locations: the right atrial appendage, which is easier to close during decannulation, but the pectinate muscles here may hinder initial cannula insertion; and the free wall of the right atrium, which has thinner pectinate muscle, making cannula insertion easier. However, the thinner wall makes bleeding more likely during decannulation.
For either approach, a single purse string is placed followed by atriotomy with an 11 blade, dilated with a tonsil, and a cannula is inserted with the distal tip sitting in the IVC, just past the hepatic vein. The purse string is placed with a double loaded suture, usually forehand for a few bites, followed by another few bites forehand or sometimes backhand. The atriotomy is created, dilated, and the cannula is inserted.
The cannula has two marking lines to help assess depth during placement. A simplified guide, based on average height, is to place the cannula to the first marker for females and to the second marker for males. The cannula is snared and connected to the venous line and the patient is ready to initiate bypass.
Pitfalls for atrial cannulation include difficulty inserting the cannula, which is usually due to the pectinate muscles. Poor venous drainage can be due to a number of factors, such as hypovolemia and cannula depth. A cannula that is too superficially placed can cause poor IVC drainage and if it is placed too deep, can cause poor SVC drainage. Hepatic congestion can occur when the distal tip of the cannula is lodged in the hepatic vein. Echocardiogram guidance can help prevent this complication.
Lastly, injury can occur to the SA node if the purse string is placed too close to the cavoatrial junction, and right coronary artery injury can occur if the purse string is placed too close to the atrioventricular junction.
Bicaval cannulation is used commonly for right-sided surgeries such as tricuspid, pulmonic, and atrial septal and ventricular septal surgery, but is also helpful in mitral valve surgery. The cannulae can be placed directly into the SVC and IVC, or it can be placed in the right atrium and guided into the SVC and IVC. For direct placement into the SVC and IVC, taking down the pericardial reflections here can help with exposure, but be aware that this will also weaken the walls of the cava, making tears more likely.
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