Coronary Artery Bypass Graft Surgery

Overview

Procedure Summary

• CABG surgery is used to treat CAD by restoring adequate blood flow to the heart. Autologous arteries or veins are selected, harvested, and then used as grafts to bypass the obstructed coronary artery.¹
• Most patients undergoing CABG use a multiple graft strategy. Common graft conduits include the left internal mammary artery, radial arteries, and saphenous vein.
• Most CABG procedures are performed through a median sternotomy, utilizing to arrest the heart. A sternotomy provides optimal exposure and creates favorable surgical conditions. The chest is then wired shut after the procedure.¹

Preoperative Evaluation

Risk Assessment

• The Society of Thoracic Surgeons risk score is commonly used for risk stratification of patients considered for CABG.^2,4
• Risk factors include:
  • Patient demographics
  • Cardiac status: ejection fraction, unstable angina, recent heart attack, arrhythmias, need for mechanical support.
  • Comorbidities: diabetes, hypertension, peripheral artery disease, cerebrovascular disease, lung disease, renal failure/dysfunction, liver disease.
  • Preoperative status: obesity, mechanical ventilation, and functional status.
  • Surgical factors: prior cardiac surgery, number of diseased vessels.

Intraoperative Management

• Monitors and equipment^3,4,5
  • Standard American Society of Anesthesiologists monitors, including pulse oximetry, electrocardiogram, end-tidal carbon dioxide, and core temperature.
  • Defibrillation pads
  • Invasive arterial blood pressure
  • Central vascular access
  • Transesophageal echocardiography (TEE): associated with measurable outcome benefits.
  • Pulmonary artery catheter remains controversial. The decision to include is made by the care team.
• Induction
  • There is no single approach; each induction should be individualized to the patient.
  • The goal is a smooth, controlled induction maintaining stable hemodynamics and preventing ischemia.^5,6,7
  • Induction should balance enough anesthetic depth to allow intubation without a marked hypertensive response, while also avoiding excessive amounts leading to hypotension.^1,5
• Intubation
  • Endotracheal intubation with single lumen tube is used most often.³
  • Institutions may have standardized protocols that differ.
• Maintenance of general anesthesia
  • A hemodynamically stable maintenance strategy is critical.
  • The goal is to maintain tissue perfusion and oxygen delivery to prevent end-organ dysfunction by recognizing and treating myocardial ischemia.¹
  • There is no difference in outcome with any particular technique.^1,5
  • Inhaled anesthetics have recognized cardioprotective properties.^1,7

Cardiopulmonary Bypass

Prebypass Period

• There is an initial period of minimal stimulation with frequent hypotension during skin preparation and draping.
• This is followed by periods of intense stimulation associated with hypertension and tachycardia at incision, sternotomy/retraction, and pericardium opening.^5,6
  • A vagal response may be seen during sternal retraction with marked bradycardia and hypotension.⁵
• Anticoagulation
  • It must be established to avoid clot formation in the CPB pump.
  • Heparin is the most commonly used anticoagulant.
  • Bivalirudin or argatroban may also be considered in select patients as indicated (e.g., history of heparin-induced thrombocytopenia).⁵
  • Coagulation status should be measured and confirmed by activated clotting time (ACT). 400-480 is considered adequate.⁵
• Bleeding prophylaxis
  • Bleeding prophylaxis with antifibrinolytic agents (ε-aminocaproic acid or tranexamic acid) may be initiated before or after anticoagulation.
• Cannulation
  • Aortic cannulation:
    • After heparinization, the aorta is cannulated first to avoid hemodynamic instability from venous cannulation. This also allows for rapid transfusion if necessary.
    • Usually placed in the ascending aorta.
    • Risk of aortic dissection
  • Systolic pressure is typically lowered to 90-100 mmHg to reduce risk.⁵
    • Risk of cerebral or coronary air emboli
  • Air is removed from the arterial line.
  • Some use Trendelenburg positioning to reduce risk.⁵
  • Venous cannulation
    • A two-stage single cannula through the right atrial appendage is sufficient for most cases. Separate superior vena cava and inferior vena cava cannulas can be used for more complex operations (bicaval).⁵
    • Manipulation of the vena cava and heart may cause hypotension or arrhythmia.^4,5
    • Brief supraventricular tachyarrhythmias usually need no treatment.
    • Sustained arrhythmias may require drugs, cardioversion, or prompt initiation of bypass once anticoagulation is verified.⁵

Bypass Period

• Initiation
  • CPB may be initiated once cannulas are placed and secured, ACT is acceptable, and the perfusionist is ready.
  • The arterial pump is started first, and the venous lines are then unclamped.
  • The heart should empty with effective CPB.
  • Poor venous return requires reduced pump flow until the issue resolves.
    • This may be due to mispositioned cannulas, forgotten clamps, kinks or air locks.
  • Severe aortic insufficiency compromising perfusion may require immediate aortic cross-clamping and cardioplegia.⁵
• Flow and pressure
  • Typical mean arterial pressure (MAP) goal is 60-65 mmHg as pump flows increase to 2-2.5 L/min/m2.⁵
  • It is common for MAP to fall abruptly at initiation due to hemodilution, lowering blood viscosity, and decreased systemic vascular resistance.⁵
  • Persistent hypotension warrants evaluation for possible aortic dissection and assessment for inadequate venous return, pump malfunction, or transducer error.
  • MAP greater than 110 mmHg increases the risk of aortic dissection or cerebral hemorrhage.
    • This is treated by reducing pump flow, increasing volatile anesthetic, or administering vasodilators such as clevidipine, nicardipine, or nitroprusside.
• Monitoring
  • Serial ACT and arterial blood gas
  • Particular attention should be paid to hematocrit, potassium, and blood glucose.
• Hypothermia
  • Moderate hypothermia is commonly used because it helps maintain normal cellular integrity by reducing basal metabolic oxygen consumption and energy expenditure.⁵
  • Lower temperatures also permit lower flow rates but require more time for cooling and rewarming.
• Cardioplegia
  • Potassium-rich cardioplegic solution is delivered via the coronary circulation after aortic cross-clamping, arresting the heart in diastole. This it typically done either:
    • Antegrade through the catheter in the proximal aorta.
    • Retrograde through the right atrium into the coronary sinus.
• Ventilation
  • Lung ventilation is usually discontinued once adequate pump flow is achieved and the heart stops ejecting blood.
  • Volatile anesthetics are administered through the CPB pump at approximately 1 mean alveolar concentration to maintain an appropriate anesthetic depth.⁵
• Readiness for termination of bypass⁵
  • Core body temperature is more than 37°C
  • Stable rhythm and adequate heart rate (80-100 bpm)
  • Pacing is often used
  • Lab values within acceptable limits⁵
  • Acidosis corrected
  • Hematocrit ideally more than 22%
  • Ventilation resumed with 100% oxygen
  • A TEE is often done at this stage to assess cardiac function.

Postbypass Period

• Bleeding is controlled, bypass cannulas are removed, anticoagulation is reversed and chest is closed.
  • The surgeon may lift the heart to check for bleeding posteriorly, which may cause transient hypotension.
  • Heparin is reversed with protamine.
  • Rare protamine reactions may occur.
  • ACT should be done every 3-5 minutes after protamine administration to verify adequate reversal.⁵
• Patients generally fall into 4 groups in the early postbypass period.⁵

Postoperative Care

• This is variable depending on the patient population and institutional preferences.
• The patient may be extubated in the operating room at the conclusion of the procedure or sedated for transport to the ICU.
  • The ICU goal is typically fast-track weaning and early extubation.
• Unless contraindicated, enhanced recovery after cardiac surgery (ERAS) protocols should be adopted to improve outcomes and expedite recovery.⁴
• ERAS guidelines for CABG include:
  • Smoking cessation prior to surgery.
  • Perioperative glycemic control with a goal blood glucose of 81-180 mg/dL.¹
  • Surgical care bundle to reduce surgical site infections.
  • Lung protective mechanical ventilation.
  • Antifibrinolytic therapy (e.g., TXA) while on pump.
  • Goal-directed fluid therapy
  • Normothermia after CPB (greater than 36.0°C), avoiding hyperthermia (greater than 37.9°C) during rewarming.
  • Multimodal opioid sparing pain management
  • Early mobilization and enteral feeding

Complications and Prevention