From the Guidelines
Lactic acid is a crucial laboratory marker that indicates tissue hypoxia and anaerobic metabolism, with elevated levels suggesting inadequate oxygen delivery to tissues. Elevated lactic acid levels (normal range typically 0.5-2.2 mmol/L) are associated with increased mortality in critically ill patients, particularly those with sepsis 1. The significance of lactic acid levels can be understood by considering the following points:
- Elevated lactic acid levels are a marker of tissue hypoxia and anaerobic metabolism, which can occur in conditions like shock, severe infections, cardiac arrest, and tissue ischemia.
- Persistent elevation of lactic acid levels (>4 mmol/L) correlates with increased mortality in critically ill patients, particularly those with sepsis 1.
- Serial measurements of lactic acid levels are more valuable than single readings, as trending lactate levels helps assess response to treatment.
- Lactate clearance, or the percentage decrease in levels over time, is a useful prognostic indicator 1.
- When interpreting lactic acid results, clinicians should consider potential confounders such as liver dysfunction (which impairs lactate clearance), certain medications (metformin, propofol), seizures, and vigorous exercise.
- Rapid lactate measurement is essential in emergency settings to guide resuscitation efforts and evaluate tissue perfusion. It is essential to note that lactate-guided resuscitation has been shown to reduce mortality in patients with septic shock, with a significant reduction in mortality seen in lactate-guided resuscitation compared to resuscitation without lactate monitoring 1. Therefore, lactic acid levels should be monitored closely in critically ill patients, and lactate-guided resuscitation should be considered to improve outcomes.
From the Research
Laboratory Significance of Lactic Acid
- Lactic acid is a crucial intermediate in carbohydrate and nonessential amino acid metabolism, and its presence in elevated levels in critically ill patients has important implications for morbidity and mortality 2.
- Elevated blood lactate concentrations are associated with increased mortality in patients with sepsis and septic shock, and lactate measurements have gained a prominent role in sepsis definitions, screening protocols, management guidelines, and quality measures 3, 4.
- However, lactate is not specific to infection, and its use for sepsis screening and diagnosis may trigger unnecessary broad-spectrum antibiotic use in some patients 4.
- Lactate clearance and vasopressor use have been identified as predictors of mortality in severe sepsis patients with lactic acidosis 5.
Pathophysiology of Lactic Acidosis
- Lactic acidosis is not entirely related to tissue hypoxia or reversible by increasing oxygen delivery, and lactate formation during sepsis is a complex process involving multiple factors 3, 6.
- Aerobic glycolysis in skeletal muscle secondary to epinephrine-stimulated Na+,K+-ATPase activity may contribute to increased blood lactate levels, rather than anaerobic glycolysis due to hypoperfusion 6.
- The traditional paradigm that hyperlactatemia reflects tissue hypoxia is overly simplistic and incomplete, and lactate metabolism is influenced by various cellular interactions and metabolic processes 4, 2.
Clinical Implications of Lactate Measurement
- Lactate measurements have been used as a diagnostic, prognostic, and therapeutic tool in sepsis management, but the evidence behind its use is not always clear-cut 4.
- Serial lactate levels and lactate clearance may be useful prognostic indicators, but their role in guiding resuscitation strategies is still debated 3, 5, 4.
- The use of lactate monitoring in sepsis management requires careful consideration of its limitations and potential pitfalls, including the risk of unnecessary fluid and volume overload 4.