Why do liver enzymes get elevated post Coronary Artery Bypass Grafting (CABG)?

Causes of Liver Enzyme Elevation After CABG

Liver enzymes are commonly elevated after CABG due to multiple factors including inadequate intraoperative cardiac protection, global or regional ischemia, reperfusion injury, oxygen free radical generation, and decreased hepatic blood flow during cardiopulmonary bypass. 1, 2

Mechanisms of Liver Enzyme Elevation Post-CABG

• During CABG, cardiopulmonary bypass can cause systemic effects on multiple organs, including the liver, leading to transient alterations in hepatic enzymes 2
• Decreased hepatic blood flow during surgery, hypoxia, and pump-induced inflammation are primary contributors to post-CABG liver enzyme elevation 2
• Global or regional ischemia related to inadequate intra-operative cardiac protection can affect liver perfusion and function 1
• Microvascular events related to reperfusion and oxygen free radical generation during CABG can cause hepatocellular damage 1
• Hypotension during surgery has been significantly associated with changes in alkaline phosphatase and aspartate aminotransferase levels 2

Pattern and Timing of Liver Enzyme Elevation

• A significant increase in total bilirubin, aspartate aminotransferase (AST), and alkaline phosphatase (ALP) is typically observed by the third postoperative day 2
• Approximately 2% of patients show elevated liver enzymes (alanine and aspartate transaminases) in the weeks to months after surgery 1
• The elevation pattern is predominantly hepatocellular, reflecting disturbance of hepatocellular integrity 3
• Cardiac biomarker release is considerably higher after valve replacement with CABG than with bypass surgery alone, and with on-pump CABG compared to off-pump CABG 1

Clinical Significance

• Most post-CABG liver enzyme elevations are transient and not associated with permanent hepatotoxicity or increased risk of hepatitis 1
• No data are available to suggest that these elevations are associated with permanent liver damage 1
• The presence of active or chronic liver disease is a contraindication to statin use, which is commonly prescribed after CABG 1
• Patients with pre-existing liver disease are at higher risk for complications and require more intensive monitoring 4

Management Approach

• Monitor vital signs and hemodynamic parameters closely in patients with elevated liver enzymes 4
• Repeat liver enzyme tests in 2-5 days to establish trend (increasing, stable, or decreasing) 4
• Review medication list and consider discontinuing potentially hepatotoxic medications if clinically appropriate 4
• Maintain adequate blood glucose control with continuous intravenous insulin to achieve and maintain postoperative blood glucose concentration ≤180 mg/dL, as hyperglycemia can worsen outcomes and potentially affect liver function 1
• Resume statin therapy when the patient is able to take oral medications, unless contraindicated by liver enzyme elevations suggesting hepatotoxicity 1

Special Considerations

• Avoid unnecessary discontinuation of essential cardiac medications without clear evidence of drug-induced liver injury 4
• Consider hepatology consultation in cases of progressive or severe enzyme elevation 4
• Patients with elevated baseline liver enzymes may experience higher levels post-CABG and require closer monitoring 1
• Pump time has a significant relationship with pre- and post-operative bilirubin changes 2

In conclusion, liver enzyme elevations after CABG are common and typically transient phenomena related to the physiological stress of surgery and cardiopulmonary bypass. Most cases resolve spontaneously without specific intervention, but monitoring is important to detect the rare cases of significant liver injury.