Renal tubular acidosis is highly prevalent in critically ill patients.

INTRODUCTION: Hyperchloremic acidosis is frequent in critically ill patients. Renal tubular acidosis (RTA) may contribute to acidemia in the state of hyperchloremic acidosis, but the prevalence of RTA has never been studied in critically ill patients. Therefore, we aimed to investigate the prevalence, type, and possible risk factors of RTA in critically ill patients using a physical-chemical approach.

METHODS: This prospective, observational trial was conducted in a medical ICU of a university hospital. One hundred consecutive critically ill patients at the age ≥18, expected to stay in the ICU for ≥24 h, with the clinical necessity for a urinary catheter and the absence of anuria were included. Base excess (BE) subset calculation based on a physical-chemical approach on the first 7 days after ICU admission was used to compare the effects of free water, chloride, albumin, and unmeasured anions on the standard base excess. Calculation of the urine osmolal gap (UOG)--as an approximate measure of the unmeasured urine cation NH4(+)--served as determinate between renal and extrarenal bicarbonate loss in the state of hyperchloremic acidosis.

RESULTS: During the first week of ICU stay 43 of the patients presented with hyperchloremic acidosis on one or more days represented as pronounced negative BEChloride. In 31 patients hyperchloremic acidosis was associated with RTA characterized by a UOG ≤150 mosmol/kg in combination with preserved renal function. However, in 26 of the 31 patients with RTA metabolic acidosis was neutralized by other acid-base disturbances leading to a normal arterial pH.

CONCLUSIONS: RTA is highly prevalent in critically ill patients with hyperchloremic acidosis, whereas it is often neutralized by the simultaneous occurrence of other acid-base disturbances.

TRIAL REGISTRATION: Clinicaltrials.gov NCT02392091. Registered 17 March 2015.