Cardiopulmonary bypass

Parts of the CPB machine

1

What is the name of the cannula that delivers blood from the pump to the systemic circulation?What is the name of the cannula responsible for delivering blood from the pump to the systemic vessels?

Aortic cannula

2

What is the name of the cannula used to withdraw blood from the body to the CPB machine?

Venous cannula

3

What is the name of the cannula used for administering high-potassium solutions?

Cardioplegia cannula

4

These cannulas are used to retrieve blood from the body back to the pump via suction.

“Pump suckers” and “vents”

5

What is the difference between ECMO and cardiopulmonary bypass?

The reservoir

• The reservoir allows the perfusionist to regulate the volume of blood in the heart, depending on how much is drained 
• This can also result in periods of blood stagnation, which may require a higher dose of heparin. 

Medications

1

What medications are used for anticoagulation during bypass, and what are their mechanisms of action?

• Heparin: Heparin works by enhancing the activity of antithrombin III, which inactivates thrombin and factor Xa, preventing the formation of fibrin clots. 

• Bivalirudin: Bivalirudin is a direct thrombin inhibitor that binds to both the active site and exosite of thrombin, preventing thrombin from converting fibrinogen to fibrin. 

2

We use this medication to reverse the anticoagulant effects of heparin. What is its mechanism of action?

• Polypeptide composed primarily of arginine
• The primary commercial source of protamine is salmon sperm.
• Positively charged arginine residues on protamine form ionic bonds with the negatively charged sulfate groups on heparin, neutralizing its anticoagulant effect.
• Patients with fish allergies may have an allergic reaction to protamine.
• After injection, free heparin is immediately and irreversibly bound to protamine.
• The dose is variable: typically 1 mg of protamine for every 100 to 300 units of heparin.
• ALWAYS INFORM THE PERFUSIONIST WHEN 1/3 OF THE PROTAMINE HAS BEEN ADMINISTERED, AS PROTAMINE CAN CAUSE CLOT FORMATION IN THE CPB PUMP.

3

Name two components of the cardioplegia solution.

• Potassium: Used to induce cardiac arrest by depolarizing the myocardial cells, stopping the heart.
• Bicarbonate: Helps to buffer the solution and maintain the pH balance, preventing acidosis during the period of cardiac arrest.
• Glucose: Provides an energy source for the myocardial cells during the period of cardiac arrest. While the heart is stopped, glucose can help prevent cellular injury by supporting anaerobic metabolism and reducing the accumulation of harmful metabolites.
• Low-dose Calcium: Helps to stabilize the myocardial cell membrane and maintain cellular function when the heart is re-warmed or after the arrest phase.
• Magnesium: Often included to reduce myocardial irritability and prevent arrhythmias during and after reperfusion.

4

What are the two antifibrinolytics commonly used in cardiac surgery?

• Tranexamic Acid: It inhibits plasminogen activation, reducing the breakdown of fibrin clots and minimizing bleeding during and after surgery.

• Aminocaproic Acid: Similar to tranexamic acid, it also works by inhibiting plasminogen activation and preventing excessive fibrinolysis, helping to control bleeding during surgery.

5

How many types of reactions can Protamine adversely cause?

• Allergic reactions: These can range from mild symptoms, such as rash or fever, to severe reactions like anaphylaxis. Patients with fish allergies, particularly to salmon, are at higher risk.

• Anaphylactoid reaction: A common reaction due to the release of histamine and other vasoactive substances when protamine is administered.

• Pulmonary hypertension: Protamine may cause a transient increase in pulmonary vascular resistance, which can affect the cardiovascular system, especially in patients with pre-existing pulmonary conditions.

How to go on bypass

1

Which cannula goes in first?

The first step is to place the aortic cannula.

When inserting any device into the aorta, it is VERY IMPORTANT to ensure that the systolic blood pressure is not too high (ideally below 110 mmHg).

This is critical, as elevated pressure increases the risk of aortic dissection.

2

When the surgeon asks the perfusionist, 'Are you going to RAP?', what does that mean?

Retrograde Autologous Priming (RAP): RAP is a technique used to minimize hemodilution during the initiation of cardiopulmonary bypass (CPB).

This process involves replacing the crystalloid used to prime the CPB circuit with the patient's own blood, achieved through passive exsanguination from the arterial and venous cannulation sites.

3

In this image, explain the blood flow during cardiopulmonary bypass

 

Once on bypass, the venous cannula drains blood from the heart into the venous reservoir, which then passes through an oxygenator before being returned to the patient via the aortic cannula."

When the perfusionist says 'FULL FLOW,' that is the time to turn off the lungs.

4

How is cardioplegia delivered during bypass?

A cannula is placed for antegrade cardioplegia, allowing the high-potassium solution to flow forward through the coronary arteries. This cannula is positioned below the aortic cannula, so it can be clamped in between.

Another cannula may be placed in the coronary sinus for retrograde cardioplegia, where the solution flows backward from the coronary sinus into the capillaries and then the coronary arteries.

5

What is the purpose of the aortic cross clamp?

• Once the cross-clamp is applied, cardioplegia is used to stop the heart, and the actual surgery begins."

• Clamp time represents the ischemic time for the heart. During this phase, the surgeon is typically in 'go mode,' so it’s not the best time to talk or ask questions."

• Ideal clamp time: <1 hour."

• The duration of the clamp affects the extent of myocardial injury and is an independent risk factor for morbidity and mortality."

• The lowest myocardial pH recorded during cross-clamping is associated with higher mortality rates.

How to come off bypass

1

What happens after "Rewarming"

• Once the surgery is nearly complete, you'll hear 'rewarming'.

• When ready, the clamp is removed, and the heart's functions gradually returns until it's prepared to separate from bypass.

• Some surgeons may ask you to position the patient in Trendelenburg and administer a deep breath before releasing the clamp, to avoid any residual air from reaching the systemic circulation- The air will go to the apex of the heart and will be removed by the LV vent.

2

Ideally, when do you start the infusions after the clamp is released?

You can start the infusions at any time, but ideally, there should be a consistent, regular rhythm before doing so.

3

What are the risks of administering calcium during bypass?

Risk of stone heart

Stone heart refers to myocardial stiffness caused by excessive calcium administration during bypass. This can make it difficult to restart the heart or maintain normal heart function after the procedure.

Too much calcium can cause the myocardium to contract too forcefully, leading to reduced compliance (stiffness) of the heart muscle. This can make it harder for the heart to relax and properly fill with blood.

Increased calcium levels can also affect coronary perfusion, further contributing to myocardial injury.

4

What lab values do we need to check before coming off bypass?

ABG: Lactate and Hb

TEG/Quantra

Platelets

Fibrinogen

5

Where are the epicardial wires typically placed? How do we check for proper placement?

Epicardial Wires

• A = Atrium
• V = Ventricle

Procedure Steps:

• The surgical team will inform you when they have placed A's (atrial) or V's (ventricular).
• Set the pacemaker to DDD mode at a higher rate than the patient's native HR.
• Check the threshold: Apply a small electrical current to the wires and observe for appropriate capture on the ECG (Spikes on EKG). The threshold is the minimum energy required for capture.
  • Safety margin: Set the pacemaker 5-8 mA above the threshold.
• Call your attending if they are not in the room by the time the wires go in.

Possible Causes for Failure to Capture:

• Hyperkalemia
• Alkalosis
• Acidosis
• Myocardial ischemia
• Abnormal antiarrhythmic levels

CABG

1

Which arteries are responsible for perfusing the heart, and what regions of the heart do they supply?

• Left Main Coronary Artery (LMCA):

  • Left Anterior Descending (LAD) artery: Supplies blood to the anterior wall of the left ventricle, the interventricular septum, and parts of the apex of the heart.
  • Left Circumflex (LCx) artery: Supplies blood to the lateral and posterior walls of the left ventricle and parts of the left atrium.

• Right Coronary Artery (RCA):

  • Right Marginal artery: Supplies the right ventricle.
  • Posterior Descending Artery (PDA): Supplies the posterior wall of the left ventricle, the interventricular septum, and parts of the right ventricle.
  • In some individuals, the RCA also provides blood to the sinus node and atrioventricular (AV) node.

2

What is a Left Main Equivalent?

Left main equivalent is defined as >70% stenoses of the proximal LAD AND circumflex coronary arteries.

3

What are the differences between stunned, hibernating, and necrotic myocardium?

Stunned Myocardium:

• Occurs after brief ischemia, causing temporary dysfunction.
• Myocardium remains viable, but with impaired contractility.
• Responds well to inotropes.
• Dobutamine echo: Improves with low doses, worsens with high doses.

Hibernating Myocardium:

• Chronic, reversible contractile dysfunction.
• Adequate blood flow for viability but not full contractility.
• Function can be restored with reperfusion, taking weeks to months.
• Dobutamine echo: Improves with low doses, worsens with high doses.
• Best treated with revascularization.

Necrotic Myocardium:

• Occurs after prolonged ischemia, leading to tissue death.
• No viable tissue, even with revascularization.
• Can cause mechanical complications (e.g., papillary muscle rupture, LV wall rupture).

4

Contraindications for PCI

•Diffuse >2cm in length

•Tortuosity

•Angulated segments over 90 degrees

•Total occlusions > 3 mo

•Old vein grafts with friable lesions

•Inability to protect major side branches

5

Name a change on the postop EKG demonstrate perioperative acute MI

•New persistent Q-waves of at least 0.03 seconds

•Broadening of existing Q-waves

•New QS deflections