Basics
Description
Cardiac surgery presents unique challenges due to cardiopulmonary bypass (CPB), surgical trauma, anesthesia, and pre-existing cardiac comorbidities. Prompt recognition and treatment are essential to minimizing early postoperative morbidity and mortality.
Pathophysiology
Pathophysiologic effects of CPB:
- Fluid and electrolyte disturbances: Increased fluid and rapid shifts increase exchangeable sodium, decrease exchangeable potassium, deplete phosphate, and cause hyperglycemia.
- Inflammatory response: Precipitated by blood contact with bypass equipment, operative trauma, and anesthesia. Inflammation results in platelet-endothelial cell interaction, coronary vasospasm, capillary leak, and the "post-pump syndrome" characterized by fever, leukocytosis, coagulopathy, hypoxemia, pulmonary capillary leak, renal dysfunction, and cognitive dysfunction.
- Transient depression of ventricular function: Secondary to ischemia and reperfusion-induced free radicals. LV function is generally, worst 4-5 hr post-CPB, significantly recovered by 8-10 hr, and fully recovered by 24-48 hr. Off-pump surgery is associated with less dysfunction.
- Hypothermia: Predisposes to dysrhythmias, increases systemic vascular resistance (SVR), impairs coagulation, and causes shivering, which increases O2 consumption and CO2 production.
- NOTE: SVR drops during re-warming, requiring volume/vasopressor support.
- Respiratory insufficiency: Results from V/Q mismatch (atelectasis), decreased respiratory drive (anesthetics), and mechanical effects of sternotomy. Resultant hypercarbia precipitates/exacerbates catecholamine surge.
- Bleeding: Results from residual heparin effects, incomplete surgical hemostasis, HTN, hypothermia, platelet dysfunction, thrombocytopenia (hemodilution), and clotting factor depletion (consumption or hemodilution), HTN
Treatment
Medication
- Reinstitute medications for comorbid diseases
- Anticoagulation for valves, atrial fibrillation/flutter, and other conditions and in patients with high thromboembolic risk
- Aspirin, lipid-lowering agents for CABG patients (clopidogrel commonly used as well)
- Endocarditis prophylaxis; mechanical valves
- β-Blockers for atrial fibrillation prophylaxis; amiodarone in high-risk patients.
- Diltiazem (1 mo) to prevent spasm if radial artery graft used
- Vasoactive medications for hypotension:
- Dobutamine and dopamine when low-output
- Norepinephrine 1st-line in vasodilatory states
- IV fluids for volume support
- Short-acting IV antihypertensives:
- Nitroprusside for rapid onset/offset
- Esmolol when β-blocker indicated
- Diuretics transiently, if volume overloaded
- DVT prophylaxis
- Insulin infusion if hyperglycemic
- Opiates, acetaminophen for pain control
Additional Treatment
General Measures
- Postoperative Complications
- HTN:
- Present in most patients without LV dysfunction. PVR increased due to catecholamine surge/RAS activation from CPB and hypothermia. Resolution of capillary leak expands intravascular volume.
- Treatment minimizes graft/anastomosis damage, pulmonary edema, and bleeding
- Treatment goal: G 10% above upper limit of normal MAP. Nitroprusside and esmolol commonly used
- Hypotension:
- Potential etiologies: Vasodilation from rewarming; inflammatory reaction to CPB; diastolic dysfunction; low-output syndrome
- Treatment is volume expansion and vasoactive drugs.
- Low-output syndrome:
- Most common among patients with preoperative LV dysfunction, long CPB run, perioperative MI. Clinical features include:
- Cold extremities, systolic BP (SBP) <90 mm Hg, but may be >100 if SVR elevated
- Urine output <30 mL/h
- Cardiac index <2.0 L/min/m2
- Low early postoperative cardiac index associated with increased mortality
- Mixed venous O2 <50% (except in sepsis)
- Acidosis generally present
- Define etiology; use Swan-Ganz catheter, echo to identify decreased preload, LV contractility, or RV function, tamponade, sepsis, or arrhythmia:
- Nonuniform compression from clot can complicate distinction between tamponade and LV dysfunction. Echo is essential.
- Vasoactive medications: Dopamine and dobutamine 1st choices for low output; norepinephrine if low SVR.
- If severe/persistent, intraaortic balloon counterpulsation, ECMO, other devices
- RV failure:
- Can precipitate LV failure
- Fluid administration to ensure preload
- Minimize airway pressures
- Pulmonary vasodilators may be useful
- Perioperative MI:
- Symptoms unreliable
- Risk factors: Age, long CPB run, elevated LVEDP, left main disease.
- Diagnose by ECG, cardiac biomarkers; echo may be confirmatory.
- No routine postoperative biomarkers unless intraoperative hemodynamic instability or new ECG changes.
- Arrhythmias:
- Supraventricular: Atrial tachyarrhythmias particularly common in valvular procedures
- Sinus tachycardia: Can be normal response to catecholamines, but evaluate for other precipitants (hypovolemia, infection, low-output syndrome).
- Atrial fibrillation (AF):
- 10-30% occurrence postoperatively
- Risk factors: Advanced age, history of AF, DM, and long CPB/cross-clamp time
- Commonly occurs around post-op day 2. Prophylactic β-blocker, amiodarone if high-risk
- 80% return to sinus rhythm within 1-3 days following digoxin or β-blocker.
- IV diltiazem, esmolol for rate control; cardioversion for hemodynamic compromise (required in about 10%)
- Atrial flutter may convert to sinus rhythm using atrial epicardial pacing. Burst pace 15-30 sec @ 300-600 bpm
- Ibutilide most effective at converting new atrial flutter (but can cause torsade de pointes); cardiovert if unstable.
- Ventricular:
- Frequent ectopy (>6 bpm) in 1st 12 hr postop suggests ischemia.
- Ectopy common postoperative days 3-5.
- Variable use of pharmacotherapy (procainamide, lidocaine) to suppress.
- Ventricular tachycardia: Re-entrant circuits often from revascularizing nonviable myocardium; sustained VT usually requires amiodarone. Cardiovert if unstable.
- Note: Wide complex tachycardia with rates 250-300 bpm suggests accessory pathway. Procainamide is drug of choice, but cardioversion more widely used. Avoid lidocaine and verapamil.
- Bradyarrhythmias/conduction defects:
- Conduction defects in up to 45% of patients
- Prevalent in aortic valve replacement (AVR)
- Majority transient, particularly hemiblocks; some related to incomplete washout of cardioplegia or operative trauma
- AV nodal transection during AVR a well-known cause of permanent AV block
- Right bundle branch block the most common conduction defect; AF with slow ventricular response, sinus bradycardia, and junctional rhythm are less common
- Bradycardia: Temporary atrial pacing
- Dyssynchrony: AV sequential pacing
- High-grade block: Epicardial pacing
- Interrogate/reactivate ICDs and pacemakers
- Pulmonary:
- Pulmonary complications the most significant cause of morbidity and major cause of mortality after CPB.
- Atelectasis (70% of patients): Primarily left lower lobe (intraoperative compression).
- Altered mechanics contribute to atelectasis and result in V/Q mismatch and hypoxemia:
- Decreased chest wall movement due to incisional pain or decreased compliance post-sternotomy
- Phrenic nerve damage may require up to 6 wk for recovery; may be permanent.
- Decreased respiratory drive (medications)
- Exacerbation of obstructive lung disease:
- CPB can induce bronchospasm.
- Pleural effusions:
- Often resolve spontaneously or with diuresis
- Repeat thoracentesis if large or persistent
- Adult respiratory distress syndrome (ARDS) (<2% occurrence; 80% mortality):
- Early clues: Decreased pulmonary compliance (high airway pressures) and difficulty maintaining oxygenation
- Management: Low tidal volume ventilation (permissive hypercapnia), and euvolemia.
- Mortality: Primarily multisystem organ failure
- Pneumonia:
- Increased risk with prolonged intubation.
- Peak incidence ~4 days after surgery.
- Diagnosis and appropriate antibiotics critical.
- Ventilator management:
- Tidal volumes (Vt) 8-10 mL/kg typically used to prevent atelectasis; low Vt in ARDS.
- Goal PaO2> 65; wean FiO2 aggressively
- Early (fast-track) extubation often possible, particularly for off-pump cases.
- Infection:
- Noninfectious postop fever common (atelectasis, phlebitis, pleuropericarditis, post-pump syndrome); suspect infection if temperature >38.5 C.
- Incisional:
- Leg: Occurs in 1% of patients; common in obese women, thigh incisions
- Sternal/mediastinitis: Occurs in 0.4-5% of patients; diabetics with bilateral IMA grafts at greatest risk.
- Infective endocarditis:
- Perioperative antibiotic prophylaxis in appropriate patients.
- CABG: No increased risk for native valves
- Prosthetic valve: Rare, but serious disease.
- Neurologic:
- Cerebral injury: Likely microembolic (air, thrombus, atheromatous debris)
- Delirium/encephalopathy: Up to 2/3 of patients; generally resolves.
- Some have mild long-term cognitive disorder
- Major cerebrovascular accident incidence ~2% (3% have minor/transient deficits)
- Peripheral nerve injury:
- Brachial plexus, ulnar and median nerves; usually temporary, may require up to 6 mo for recovery.
- Phrenic and recurrent laryngeal nerve injury; can cause respiratory failure from diaphragmatic/vocal cord palsy
- Visual symptoms common: Floaters, decreased acuity, spots, and stripes
- Incisional pain: Thoracotomy generally more than sternotomy; secondary to muscle incision.
- Persistent pain: Evaluate for fracture, subluxation, infection
- Leg incisions often require pain control
- Hematologic:
- Blood loss and hemodilution:
- Transfuse as needed; target HCT often >30, but sparse evidence for this goal.
- Aminocaproic acid, aprotinin, DDAVP, platelets, fresh-frozen plasma, and cryoprecipitate all can be helpful.
- Recombinant factor VIIa for severe refractory bleeding
- Monitor for heparin-induced thrombocytopenia
- Anticoagulation (AC): Warfarin indications:
- High risk for thromboembolism; presence of atrial fibrillation; presence of intracardial thrombi
- Valve replacement: Risk with mechanical valve > bioprosthetic valve; mitral > aortic; duration of AC for bioprosthetic valves by patient risk factors
- At least 3 mo if no contraindication
- INR target/longer duration based on valve position/risk factors; lifelong AC with mechanical valves
- Increased INR (2.5-3.5) in 1st 3 mo, in MVR, and high-risk patients; adjunctive aspirin therapy based on valve site and patient risk factors
- Endocrine/Metabolic:
- Electrolyte disturbances: Hyperkalemia, hypomagnesemia, hypophosphatemia essential to correct. Hypocalcemia rarely requires correction unless hypotensive
- Hyperglycemia: Surgical trauma and CPB induce catecholamine and cortisol:
- Tight control (typically with insulin infusion) improves mortality, wound healing
- Insulin requirements may be significant in immediate postoperative period
- Renal:
- Incidence of postop renal dysfunction up to 30%, but rarely requires dialysis.
- Etiology: CPB (loss of pulsatile perfusion), hypotension, vasoconstriction
- Greatest incidence (and morbidity/mortality) in older patients, long CPB runs and cross-clamp times, preoperative renal dysfunction
- Mannitol, furosemide, and dopamine may reduce ischemic insults intraoperatively.
- Gastrointestinal: Serious complications rare, often ischemic
Surgery
Reexploration for persistent, uncontrolled bleeding or if tamponade suspected secondary to thrombus. Reexploration can, in some cases, be done in ICU.
In-Patient Considerations
Discharge Criteria
Hemodynamic stability, normal sinus rhythm or rate-controlled atrial fibrillation, ability to ambulate and eat, and presence of adequate family support to provide basic needs for convalescence.
Ongoing Care
Follow-Up Recommendations
Patient Monitoring
In the 1st weeks to months after discharge, patients should be seen by cardiac surgeon, cardiologist, and primary care provider. Patients monitored for:
- Emotional/mental well-being, attitude
- Healing at sternal, extremity wound sites
- Activity level/reconditioning/return to work
- Return of CBC indices to baseline
- Proper medication regimen
- Risk factor control
Patient Education
- Modification of cardiac risk factors
- Proper diet, activity, and coping with stress
- Education regarding AC, other medications
Prognosis
6 wk to several months generally to regain or improve exercise tolerance if postoperative course uncomplicated. Patients should not drive or lift >20 lbs for 4-6 wk after sternotomy.
Additional Reading
1
Eagle KA. ACC/AHA 2004 guideline update for coronary artery bypass graft surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1999 Guidelines for Coronary Artery Bypass Graft Surgery). Circulation. 2004;110(14):e340-437. [View Abstract] 2
Gray RJ, Sethna DH.
Medical management of the patient undergoing cardiac surgery. In: Libby PBraunwald's Heart disease: A Textbook of Cardiovascular Medicine, 8th ed.Philadelphia: WB Saunders, 2008;1993-2009. 3
Morris DC, Clements SD, Pepper J.
Management of the patient after cardiac surgery. In: Fuster V et al., Hurst's the Heart, 12th ed.New York: McGraw-Hill, 2008;1519-1528. 4
Morris DC, St.
Claire D Jr. Management of patients after cardiac surgery. Curr Probl Cardiol. 1999;24:161-228. [View Abstract] 5
Weissman C.
Pulmonary complications after cardiac surgery. Semin Cardiothorac Vasc Anesth 2004;8:185-211. [View Abstract]
Clinical Pearls
- Preoperative status the most important predictor of postop morbidity and mortality.
- Ascertaining etiology of postop hypotension can be difficult given many potential causes, but is essential to proper management.
- Pulmonary complications represent the major cause of postop morbidity and a major source of mortality in cardiac surgery patients.