Lactic versus nonlactic metabolic acidosis: outcomes in critically ill patients

Introduction

Critical care physicians associate lactic acidosis (LA) with higher morbidity and mortality. Other forms of metabolic acidosis are generally regarded as less dangerous and any association with adverse outcomes in critically ill patients is poorly understood. We sought to compare differences in mortality and length of stay (LOS) between LA and other forms of metabolic acidoses.

Methods

In this observational pilot study, we reviewed records of 9799 patients admitted to the ICUs at our institution between 1 January 2001 and 30 June 2002. This cohort of patients had an inpatient mortality of 14%, a hospital LOS of 12 days and an ICU LOS of 5.8 days. We selected cases on the following criteria: 1) clinicians caring for each patient suspected the presence of LA; 2) arterial blood gas (ABG) and lactate were measured; 3) Na⁺, K⁺, Cl^-, and CO₂^- were drawn within 4 hours of the referenced ABG, Ca, Mg, Phos within 24 hours, and albumin any time during the hospitalization. When multiple data sets were available, the set with the highest lactate was used. We classified patients into four groups: A) no metabolic acidosis, standard base excess (SBE) ≥ -2; B) lactic acidosis, lactate accounted for > 50% of SBE; C) strong ion gap (SIG) acidosis, SIG accounted for > 50% of SBE (and not LA); D) hyperchloremic acidosis, absence of A, B, or C.

Results

We identified 862 patients (8.9% of ICU admissions). Of these, 546 patients (63.3%) had a metabolic acidosis. LA occurred in 43% of acidemic patients and was associated with a 57% mortality. Table 1 presents the unadjusted relative mortality and LOS. Other forms of acidosis were collectively associated with a 37% mortality. There was no difference in ICU or hospital LOS between all groups.

Table 1

Conclusions

In patients suspected of having LA, LA was more commonly associated with hospital mortality than non-LA. However, all forms of metabolic acidosis, even hyperchloremic, appear to be associated with high mortality and increased ICU and hospital LOS.