Metabolic acidosis in patients with sepsis: epiphenomenon or part of the pathophysiology?

OBJECTIVE: To review the mechanisms of metabolic acidosis in sepsis. DATA SOURCES: Articles and published reviews on metabolic acidosis in sepsis. SUMMARY OF REVIEW: Sepsis affects millions of patients each year and efforts to limit mortality have been limited. It is associated with many features one of which is acidosis which may be a result of the underlying pathophysiology (e.g. respiratory failure, shock, renal failure) or may also result from the way in which we manage critically ill patients. Lactic acidosis identifies septic patients at risk and aggressive fluid resuscitation (along with inotropes and blood in some patients) to reverse acidosis and improve venous oxygen saturation will improve mortality. However, most patients with severe sepsis or septic shock receive 0.9% saline and therefore may develop hyperchloraemic acidosis as a consequence of their resuscitation. Therefore alterations in acid-base balance are almost always in the background in the management of patients with sepsis. What is unknown is whether acidosis is in the causal pathway for organ dysfunction or whether it is simply an epiphenomenon. Changes in acid-base balance, of the type and magnitude commonly encountered in patients with sepsis, significantly alter the release of inflammatory mediators. Less significant changes in the immune response have already been implicated in influencing outcome for patients with sepsis and a reduction in acidosis in septic patients may have the same effect.
CONCLUSIONS: Understanding the effects of acid-base on the inflammatory response is relevant as all forms of metabolic acidosis appear to be associated with prolonged hospital and ICU length of stay. Since metabolic acidosis is both commonly caused and treated by clinicians, understanding of the physiologic consequences of altered blood pH is imperative.