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Lactic acid is the normal endpoint of the anaerobic breakdown of glucose in the tissues.

It can be either

• L-lactate

  • Commonly measured level in the laboratory & by product of human metabolism.

  • Represents increased anaerobic metabolism due to tissue hypoperfusion.
    
    
    

• D-lactate

  •  Byproduct of bacterial metabolism

  • Short-gut syndrome or in those with a history of gastric bypass or small-bowel resection
    
    

Normal value

0.5 – 1.0 mmol/L
Critical illness : < 2.0 mmol/L

Hyperlactatemia V/S Lactic Acidosis

Hyperlactatemia is defined as a persistent, mild to moderate (2-4 mmol/L) increase in blood lactate concentration without metabolic acidosis.

Lactic acidosis is characterized by persistently increased blood lactate levels (usually >5 mmol/L) in association with metabolic acidosis.

Cohen & Woods Classification

ETIOLOGY

• Circulatory shock

  • Increase in lactate level indicates impaired oxygenation status.

  • Blood lactate levels are directly proportional to mortality rate.
    

• Sepsis : They can lead to either
  
  

1. Stress hyperlactemia : It characterized by Lactate levels of 2 – 5 mEq/L;Normal lactate to pyruvate ratio & normal blood pH. It is due to hypermetabolism without impaired oxygen utilization.
   
   

2. Cytopathic hypoxia : It is characterized by elevated levels of lactate, increased lactate pyruvate ratio ,reduced blood pH, Impaired oxygen utilization.

• Thiamine deficiency

  • Co factor for pyruvate dehydrogenase enzyme that initiates pyruvate oxidation in the mitochondria.
    
    
    

• Drugs

  • Drugs like nucleoside reverse transcriptase inhibitor, acetominophen, epinephrine, metformin, propofol & nitroprusside.
    
    
    

• Propylene Glycol

  • It is an alcohol agent used to enhance the water solubility of many hydrophobic I.V. Medication.

  • Lorazepam, diazepam, esmolol, nitroglycerin & phenytoin.

  • Agitation, coma, seizures, tachycardia, hypotension & hyperlactemia.

  • Suspect : Unexplained hyperlactatemia

  • More common in persons receiving infusion of lorazepam & diazepam.

  • Midazolam doesnot have propylene glycol.
    
    
    
    

• Seizures:Increased lactate production

• Hepatic insufficiency:Reduced lactate  clearance

• Acute asthma: enhanced production by respiratory muscles.
  
  

Clinical Signs

• Hypotension

• Alteration in sensorium

• Peripheral vasoconstriction

• Oliguria

• Kussmaul hyperventilation

• Fever or hypothermia

Diagnosis

• Blood lactate levels

• High anion gap acidosis
  
  

MANAGEMENT

GENERAL PRINCIPLES

• CAB

• Secure an IV line

• Early goal directed therapy in sepsis

• Fluid resuscitation if signs of shock.

• Antibiotics

• Drainage

• 
  
  

Bicarbonate Therapy

• It is the standard buffer used for lactic acidosis . But has limited success. It is used in setting of severe metabolic acidosis (pH <7.1). HCO3 deficit = 0.6 * wt * (Desired HCO3 – Measured HCO3). One half of the estimated deficit is corrected.
  
  ADVERSE EFFECTS
  
  

  • Paradoxical worsening of intracellular acidosis.

  • It can create extracellular alkalosis that will shift the oxyhemoglobin saturation curve and inhibit oxygen release.

  • Hypernatremia and hyperosmolarity

  • Hypocalcemia
    
    

• It can be over come by giving slow infusions ,increasing minute volume in patients on ventilator ,correcting hypocalcemia
  
  

Carbicarb

• It is a buffer solution 1:1 sodium bicarbonate & disodium bicarbonate. Produces less bicarbonate and a much lower PCO2. Has some theoretical advantage but lacks evidence.
  
  

Dichloro Acetate

• Potent stimulus of pyruvate dehydrogenase. It is a rate limiting enzyme for aerobic oxidation of glucose, pyruvate & lactic acid. Inhibits glycolysis & has positive inotropic effects.
  
  

Dialysis

Dialysis may be done in severe lactic acidosis; occurs in combination with renal failure and cardiac failure.

Thiamine

• Thiamine deficiency may be associated with cardiovascular compromise and lactic acidosis. Thiamine repletion given as 50-100 mg intravenously [IV] followed by 50 mg/d orally [PO] for 1-2 wk.
  
  

Tris Hydroxymethyl Aminomethane (THAM)

• It is a weak alkali and theoretical has the advantage over bicarbonate as it produces less carbon dioxide.Clinical trials do not prove THAM to be more effective.
  
  
  

Other agents : Coenzyme Q, l-carnitine, and riboflavin have been used to treat lactic acidosis due to antiretroviral therapy. These agents has no definitive demonstration of efficacy.

Updated on : 15/1/2015

Reference

• Tinitinalli

• The ICU; Paul marino

• Early lactate clearance is associated with improved outcome in severe sepsis and septic shock. By Bryant Ngyuen et al. Critical Care Medicine 2004.

• Lactate Clerance vs Central Venous Oxygen Saturation as Goals of Early Sepsis Therapy. A Randomized Clinical Trial. By Alan E Jones. JAMA. 2010