What are the key considerations for anesthesia management in cardiac surgery, including blood management, anticoagulation, and bypass initiation and weaning?

Cardiac Surgery Anesthesia Management

Anesthetic management in cardiac surgery should be directed toward early postoperative extubation and accelerated recovery in low to medium-risk patients undergoing uncomplicated cardiac surgery. 1

Preoperative Considerations

• A careful preoperative evaluation and treatment of modifiable risk factors is essential before cardiac surgery 1
• Proper handling of preoperative medications is critical, particularly regarding cardiovascular medications such as beta-blockers, ACE inhibitors, and ARBs which may cause hemodynamic alterations 1
• Establish central venous access and implement careful cardiovascular monitoring before induction 1

Anesthetic Technique

• Volatile anesthetic-based regimens are useful for facilitating early extubation and reducing patient recall 1
• In the United States, most patients receive general anesthesia with endotracheal intubation using volatile halogenated anesthetics with opioid supplementation 1
• Intravenous benzodiazepines are commonly given as premedication or for induction, along with agents such as propofol or etomidate 1
• Nondepolarizing neuromuscular-blocking agents with intermediate duration of action are preferred over longer-acting agents like pancuronium 1
• Short-acting neuromuscular blocking agents should be considered in cardiac anesthesia 1

Blood Management

• Transfuse packed red blood cells if hemoglobin is <6.0 g/dL or if hematocrit is between 21-24% when oxygen delivery falls below 273 mL/min/m² 1, 2
• Monitor venous saturation (<68%) and oxygen extraction ratio (>39%) to guide transfusion decisions 1, 2
• Fresh frozen plasma during CPB should only be used for supplementing antithrombin in patients with poor heparin responsiveness 1
• Antithrombin concentrate is more effective than FFP in restoring heparin responsivity 1

Anticoagulation for Cardiopulmonary Bypass

• For cardiopulmonary bypass, administer an initial dose of not less than 150 units of heparin sodium per kilogram of body weight 3
• For procedures estimated to last less than 60 minutes, a dose of 300 units/kg is commonly used; for procedures lasting longer than 60 minutes, 400 units/kg is recommended 3
• Monitor activated partial thromboplastin time (aPTT) or activated clotting time (ACT) to ensure adequate anticoagulation 3
• After CPB, neutralize heparin with protamine sulfate, but be vigilant for hyperheparinemia or bleeding that can occur 30 minutes to 18 hours after cardiac surgery despite initial complete neutralization 4

Initiation and Management of Bypass

• During on-pump CABG, particular care is required during vascular cannulation and weaning from CPB 1
• Administer low concentrations of volatile anesthetic via the venous oxygenator during CPB to facilitate amnesia and reduce systemic vascular resistance 1
• Monitor oxygenator exhaust concentrations of volatile agents during CPB 1
• The oxygenator exhaust concentration of volatile anesthetic agents during CPB should be at least the same as that before CPB, except during rewarming when it should be increased 1

Cardioplegia

• Protection of myocardial function from ischemic damage during CPB is achieved through cardioplegia techniques 1
• Standard technique includes delivery of high potassium concentration (8-20 mEq/L) by either crystalloid or blood carrier solutions 1
• Blood cardioplegia may be preferable in high-risk patients to reduce hematocrit dilution 2

Weaning from Bypass

• Close interaction between the anesthesiologist and surgeon is required, particularly when manipulation of the heart or great vessels is likely to induce hemodynamic instability 1
• Monitor and manage hemodynamic alterations, including changes in heart rate, cardiac output, and systemic vascular resistance 1
• Emergency use of perioperative transesophageal echocardiogram is reasonable in patients with hemodynamic instability to determine the cause when it persists despite attempted corrective therapy 1

Achieving Hemostasis

• After CPB, additional doses of protamine sulfate should be administered if indicated by coagulation studies, such as the heparin titration test with protamine and plasma thrombin time 4
• Administer protamine slowly to avoid severe hypotensive and anaphylactoid reactions 4
• Maintain normothermia to potentially reduce perioperative cardiac events 1

Intraoperative Problems After Bypass

• Monitor for hyperheparinemia or bleeding that can occur 30 minutes to 18 hours after cardiac surgery despite initial complete neutralization with protamine 4
• Be vigilant for hemodilution effects, which include reduced plasma protein concentrations affecting drug pharmacokinetics and pharmacodynamics 2
• Implement strategies to mitigate hemodilution effects, such as miniaturized CPB circuits, ultrafiltration techniques, and retrograde autologous priming 2
• Use balanced crystalloid solutions rather than normal saline for priming and maintenance fluids to prevent hyperchloremic metabolic acidosis 2

Common Pitfalls and Caveats

• Avoid cyclooxygenase-2 inhibitors for CABG as they are not recommended 1
• Routine use of early extubation strategies in facilities with limited backup for advanced airway respiratory support is potentially harmful 1
• Too-rapid administration of protamine can cause severe hypotensive and anaphylactoid reactions 4
• Routine use of pulmonary artery catheterization is not recommended 1
• Prophylactic intravenous nitroglycerin is not effective in reducing myocardial ischemia in patients undergoing cardiac surgery 1