title: Alterations in urinary strong ion difference in critically ill patients with metabolic acidosis: a prospective observational study.
abstract: OBJECTIVE
  The correct renal response to metabolic acidosis should be a negative shift in the urinary strong ion difference ([SID](urinary) = [Na(+)](urinary) + [K(+)](urinary) - [Cl(-)](urinary)). Our hypothesis was that the failure to decrease the [SID](urinary) is frequently present and leads to a more severe metabolic acidosis.
  
  
  METHODS
  Prospective observational study conducted in the medical/surgical intensive care unit of a teaching hospital between 1 January 2006 and 30 April 2007. Participants were 98 patients with metabolic acidosis on ICU admission and 10 healthy volunteers.
  
  
  METHODS
  None.
  
  
  METHODS
  Severity of metabolic acidosis; behaviour of acid-base variables according to positive or negative [SID](urinary).
  
  
  RESULTS
  Twelve patients (12%) had negative [SID](urinary) and 86 (88%) had positive [SID](urinary). Compared with patients with positive [SID](urinary), those with negative [SID](urinary) had higher [HCO(3) (-)] (20 ±2 v 18 ±3 mmol/L), base excess ([BE]) (-5 ±2 v -7 ±2 mmol/L), anion gap ([AG]) (21 ±5 v 17 ±4 mmol/L), Δ[AG] - Δ[HCO(3)(-)] (1 ±5 v -3 ±3 mmol/L) and lower [Cl(-)] (105 ±5 v 111 ±3 mmol/L).
  
  
  CONCLUSIONS
  Most of the critically ill patients with metabolic acidosis showed inappropriate renal compensation, as evidenced by positive [SID](urinary) and higher plasma [Cl(-)]. These patients had more severe metabolic acidosis. On the other hand, patients with adequate renal response and negative [SID](urinary) had positive Δ[AG] - Δ[HCO(3)(-)]. These findings, usually considered as a diagnosis of associated metabolic alkalosis, might be interpreted as the proper renal response to metabolic acidosis.
authors.affiliation: Servicio de Terapia Intensiva, Sanatorio Otamendi y Miroli, Buenos Aires, Argentina.
authors.forename: Fabio D
authors.initials: FD
authors.lastname: Masevicius
authors.forename: Graciela
authors.initials: G
authors.lastname: Tuhay
authors.forename: María C
authors.initials: MC
authors.lastname: Pein
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Ventrice
authors.forename: Arnaldo
authors.initials: A
authors.lastname: Dubin
mesh_terms: D000138:Acidosis / Q000150:complications / Q000628:therapy / Q000652:urine*; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002712:Chlorides / Q000652:urine*; D003422:Critical Care; D016638:Critical Illness; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011188:Potassium / Q000652:urine*; D011446:Prospective Studies; D012964:Sodium / Q000652:urine*
chemical_list: D002712:Chlorides; D012964:Sodium; D011188:Potassium