Early metabolic acidosis in critically ill patients: a binational multicentre study

Abstract

Objective: We aimed to measure the incidence, prevalence, characteristics and outcomes of intensive care unit (ICU) patients with early (first 24 hours) metabolic acidosis (MA) according to two different levels of severity with a focus on recent data. Design: We retrospectively applied two diagnostic criteria to our analysis based on literature for early MA: i) severe MA criteria (pH ≤ 7.20 and Paco₂ ≤ 45 mmHg and HCO₃^- ≤ 20 mmol/L with total Sequential Organ Failure Assessment [SOFA] score ≥ 4 or lactate ≥ 2 mmol/L), and ii) moderate MA criteria (pH < 7.30 and base excess < -4 mmol/L and Paco₂ ≤ 45 mmHg). Setting: ICUs in the Australian and New Zealand Intensive Care Society Adult Patient Database program. Participants: Adult patients registered to the database from 2008 to 2018. Main outcome measures: Incidence, prevalence, and hospital mortality of patients with MA by the two criteria. Results: We screened 1 076 087 patients. Given the Australian and New Zealand population during the study period, we estimated the incidence of severe MA at 39.5 per million per year versus 349.2-411.5 per million per year for moderate MA. In the most recent 2 years, we observed early severe MA in 1.5% (1350/87 110) of patients compared with 8.4% (20 679/244 740) for moderate MA. Overall, hospital mortality for patients with early severe MA was 48.3% (652/1350) compared with 21.5% (4444/20 679) for moderate MA. Conclusions: Early severe MA is uncommon in Australian and New Zealand ICUs and carries a very high mortality. Moderate MA is over seven-fold more common and still carries a high mortality.

Figure 1

Study flowchart ANZICS-APD = Australian and New Zealand Intensive Care Society Adult Patient Database; BE = base excess; BICAR-ICU = Sodium Bicarbonate to Treat Severe Acidosis in the Critically Ill: a multiple centre randomised clinical trial; HCO₃^- = bicarbonate; ICU = intensive care unit; MA = metabolic acidosis; MMA = moderate metabolic acidosis; Paco₂ = arterial partial pressure of carbon dioxide. The numbers of patients are indicated in each box.

Figure 2

Change of annual incidence and prevalence of moderate metabolic acidosis Annual incidence and prevalence of moderate metabolic acidosis were indicated as line graphs.

Figure 3

Annual crude hospital mortality of patients with and without moderate metabolic acidosis as well as adjusted annual odds ratio for the hospital mortality ICU = intensive care unit; MA = metabolic acidosis. Numbers of patients and hospital deaths were indicated by with and without moderate metabolic acidosis. The parentheses show the crude mortality rate.