What is the significance of elevated lactic acid in arterial blood?

From the Guidelines

Elevated lactic acid in arterial blood is a significant indicator of tissue hypoperfusion or hypoxia, and guiding resuscitation to normalize lactate levels is a crucial step in managing patients with septic shock, as suggested by the 2016 Surviving Sepsis Campaign guidelines 1. The significance of elevated lactic acid in arterial blood can be understood by considering the following points:

• Elevated lactic acid levels (>4 mmol/L) may indicate tissue hypoperfusion or hypoxia, which can lead to increased morbidity and mortality if left unaddressed.
• The 2016 Surviving Sepsis Campaign guidelines suggest guiding resuscitation to normalize lactate in patients with elevated lactate levels as a marker of tissue hypoperfusion, although this is a weak recommendation based on low-quality evidence 1.
• Normalizing lactate levels can help evaluate the effectiveness of interventions in shock states and guide further resuscitation efforts. Some key considerations for measuring arterial lactic acid levels include:
• Collecting an arterial blood sample, typically from the radial artery, using a heparinized syringe to prevent clotting.
• Immediately placing the sample on ice to prevent ongoing metabolism.
• Analyzing the sample within 15-30 minutes using a blood gas analyzer with lactic acid measurement capability.
• Interpreting the results in the context of the patient's clinical condition, with normal arterial lactic acid levels typically less than 2 mmol/L. The use of dynamic over static variables to predict fluid responsiveness, as suggested by the guidelines, can also help inform resuscitation efforts in patients with septic shock 1. Overall, elevated lactic acid in arterial blood is a critical indicator of tissue hypoperfusion or hypoxia, and guiding resuscitation to normalize lactate levels is an essential step in managing patients with septic shock, with the goal of improving morbidity, mortality, and quality of life outcomes.

From the FDA Drug Label

Metformin associated lactic acidosis was characterized by elevated blood lactate concentrations (>5 mmol/L), anion gap acidosis (without evidence of ketonuria or ketonemia), and an increased lactate: pyruvate ratio; Elevated lactic acid in arterial blood is a sign of lactic acidosis, a potentially fatal condition. The significance of elevated lactic acid is that it may indicate metformin-associated lactic acidosis, particularly in patients with risk factors such as renal impairment, age 65 or greater, or those who have undergone radiologic studies with contrast.

• Key risk factors for metformin-associated lactic acidosis include: + Renal impairment + Age 65 or greater + Radiologic studies with contrast + Hepatic impairment + Alcoholism + Heart failure
• Clinical recommendations for managing metformin-associated lactic acidosis include: + Discontinuing metformin hydrochloride tablets + Prompt hemodialysis to correct the acidosis and remove accumulated metformin + General supportive measures in a hospital setting 2

From the Research

Significance of Elevated Lactic Acid in Arterial Blood

Elevated lactic acid in arterial blood is a significant indicator of various underlying conditions. The following points highlight the importance of lactic acid levels:

• Lactate levels are commonly evaluated in acutely ill patients to assess the severity of their condition 3.
• Elevated lactate levels can be caused by various factors, including tissue hypoperfusion, sepsis, cardiac arrest, trauma, seizure, ischemia, diabetic ketoacidosis, thiamine deficiency, malignancy, liver disease, toxins, overdose, and medication 3.
• In patients with severe sepsis or septic shock, increased blood lactate concentration is associated with significant morbidity and mortality 4.
• Lactic acidosis, defined as an increase in arterial lactate with an indicator of more than five mmol/L and an arterial blood pH of less than 7.35, can occur in patients with chronic kidney disease (CKD) taking metformin 5.

Clinical Implications

The clinical implications of elevated lactic acid in arterial blood are:

• Elevated lactate levels can be used as a diagnostic and prognostic tool in patients with sepsis and septic shock 4, 6.
• Lactate measurements can help guide resuscitation strategies, but their use as a therapeutic target is still debated 6, 7.
• Long-term β-blocker therapy can decrease blood lactate concentration in severely septic patients, which may affect the use of lactate as a triage tool 7.
• Metformin can increase lactate levels in CKD patients, but the risk of lactic acidosis is still considered low 5.

Key Findings

Key findings related to elevated lactic acid in arterial blood include:

• The traditional paradigm that hyperlactatemia reflects tissue hypoxia is overly simplistic and incomplete 6.
• Lactate formation during sepsis is not entirely related to tissue hypoxia or reversible by increasing oxygen delivery 4.
• The use of lactate monitoring as a diagnostic and prognostic tool is still evolving, and its clinical utility is being reevaluated 6.