Is lactate (lactic acid) useful in diagnosing or managing shock?

From the Guidelines

Lactate is useful in shock as both a diagnostic marker and a therapeutic target, with current guidelines suggesting guiding resuscitation to normalize lactate in patients with elevated lactate levels as a marker of tissue hypoperfusion 1.

Key Points

• Elevated lactate levels (>2 mmol/L) indicate tissue hypoperfusion and can help identify shock even before hypotension develops.
• Serial lactate measurements are valuable for monitoring treatment response, with decreasing levels suggesting improvement.
• Lactate-guided resuscitation protocols that focus on normalizing lactate levels through fluid administration, vasopressors, and addressing the underlying cause have been associated with improved outcomes in septic shock and other shock states.
• The physiological basis for lactate elevation in shock involves tissue hypoxia leading to anaerobic metabolism, though other mechanisms like catecholamine-driven aerobic glycolysis also contribute.

Recommendations

• Measure lactate levels at baseline and every 2-4 hours until normalization during shock management.
• Target lactate clearance of at least 10-20% within the first 6 hours of resuscitation.
• Use fluid administration, vasopressors (like norepinephrine starting at 0.05-0.1 mcg/kg/min), and addressing the underlying cause to normalize lactate levels.

Evidence

• Five randomized controlled trials (647 patients) have evaluated lactate-guided resuscitation of patients with septic shock, showing a significant reduction in mortality compared to resuscitation without lactate monitoring 1.
• Current guidelines recommend guiding resuscitation to normalize lactate in patients with elevated lactate levels as a marker of tissue hypoperfusion 1.

From the Research

Lactate as a Diagnostic Tool

• Lactate levels are commonly evaluated in acutely ill patients, particularly in the context of shock 2
• However, lactate levels can be elevated for many reasons, and clinicians need to be aware of the various potential causes of lactate level elevation 2
• Lactate is a reliable indicator of sepsis severity and a marker of resuscitation, but it is an unreliable marker of tissue hypoxia/hypoperfusion 3

Lactate Kinetics and Prognosis

• Blood lactate concentration and lactate kinetics over time may be helpful markers of shock severity 4
• The initial lactate level and the 6-hour lactate kinetic were significantly associated with outcome, and a higher initial lactate level and lower lactate kinetic were associated with a higher risk of mortality 4
• A relation between the initial lactate level/lactate kinetic and the required therapy was found, and the optimal cut-off for the 6-hour lactate kinetic to predict mortality was 38.1% 4

Utility of Measuring Lactate Levels

• Elevations in blood lactate concentrations are associated with increased mortality, and serial lactate levels have prognostic accuracy 5
• However, lactate measurements have limitations, and the traditional paradigm that hyperlactatemia reflects tissue hypoxia is overly simplistic and incomplete 5
• There is a lack of high-quality evidence demonstrating that initial and serial lactate monitoring leads to better patient-centered outcomes 5

Lactate as a Beneficial Energy Source

• Blood lactate concentration predicts mortality in critically ill patients and is clinically used in the diagnosis, grading of severity, and monitoring response to therapy of septic shock 6
• Lactate turnover reflects lactate release primarily from muscle, gut, adipose, and erythrocytes and uptake by the liver and kidney, primarily for the purpose of energy production 6
• The conventional concept of tissue hypoxia can account for most blood lactate findings, and there is no need to implicate a purposeful production of lactate for export to other organs 6