Hyperlactatemia and Cardiac Surgery.

Area of Science:

• Biochemistry
• Critical Care Medicine
• Physiology

Background:

• Normal blood lactate levels range from 0-2 mmol/L; hyperlactatemia is variably defined as >3-5 mmol/L.
• In cardiac surgery, hyperlactatemia has both hypoxic and non-hypoxic origins.
• Lactate acts as a strong anion, influencing blood's acid-base balance.

Purpose of the Study:

• To differentiate mechanisms and clinical significance of early- and late-onset hyperlactatemia in cardiac surgery patients.
• To explore the role of lactate/pyruvate ratio in distinguishing causes of hyperlactatemia.
• To highlight the importance of investigating underlying causes of hyperlactatemia despite normal global oxygen delivery indices.

Main Methods:

• Analysis of lactate and lactate/pyruvate ratios in cardiac surgery patients.
• Categorization of hyperlactatemia into early-onset (in OR or early ICU) and late-onset (6-12 hours post-ICU admission).
• Correlation of hyperlactatemia onset with clinical outcomes and potential underlying mechanisms (hypoxic vs. non-hypoxic).

Main Results:

• Early-onset hyperlactatemia is linked to adverse outcomes, arising from hypoxic and non-hypoxic (accelerated aerobic metabolism) causes.
• Late-onset hyperlactatemia is a benign, self-limiting condition resolving within 24 hours, with an unclear mechanism.
• Elevated lactate/pyruvate ratio (>20) suggests impaired oxygen delivery, while a normal ratio (<20) points to accelerated aerobic metabolism.
• Epinephrine treatment can cause hyperlactatemia via accelerated aerobic metabolism, requiring no intervention.

Conclusions:

• Hyperlactatemia in cardiac surgery is multifactorial, with distinct clinical implications for early- and late-onset presentations.
• Investigating hyperlactatemia necessitates a search for underlying tissue hypoperfusion, even with normal global oxygen delivery.
• Understanding lactate dynamics is crucial for managing critically ill cardiac surgery patients.