title: Real-time urinary electrolyte monitoring after furosemide administration in surgical ICU patients with normal renal function.
abstract: BACKGROUND
  Although the loop-diuretic furosemide is widely employed in critically ill patients with known long-term effects on plasma electrolytes, accurate data describing its acute effects on renal electrolyte handling and the generation of plasma electrolyte alterations are lacking. We hypothesized that the long-term effects of furosemide on plasma electrolytes and acid-base depend on its immediate effects on electrolyte excretion rate and patient clinical baseline characteristics. By monitoring urinary electrolytes quasi-continuously, we aimed to verify this hypothesis in a cohort of surgical ICU patients with normal renal function.
  
  
  METHODS
  We retrospectively enrolled 39 consecutive patients admitted to a postoperative ICU after major surgery, and receiving single low-dose intravenous administration of furosemide. Urinary output, pH, sodium [Na(+)], potassium [K(+)], chloride [Cl(-)] and ammonium [NH4 (+)] concentrations were measured every 10 min for three to 8 h. Urinary anion gap (AG), electrolyte excretion rate, fractional excretion (Fe) and time constant of urinary [Na(+)] variation (τNa(+)) were calculated.
  
  
  RESULTS
  Ten minutes after furosemide administration (12 ± 5 mg), urinary [Na(+)] and [Cl(-)], and their excretion rates, increased to similar levels (P < 0.001). After the first hour, urinary [Cl(-)] decreased less rapidly than [Na(+)], leading to a reduction in urinary AG and pH and an increment in urinary [NH4 (+)] (P < 0.001). Median urinary [Cl(-)] over the first 3-h period was higher than baseline urinary and plasmatic [Cl(-)] (P < 0.001). During the first 2 h, difference between FeCl(-) and FeNa(+) increased (P < 0.05). Baseline higher values of central venous pressure and FeNa(+) were associated with greater increases in FeNa(+) after furosemide (P = 0.03 and P = 0.007), whereas higher values of mean arterial and central venous pressures were associated with a longer τNa(+) (P < 0.05). In patients receiving multiple administrations (n = 11), arterial pH, base excess and strong ion difference increased, due to a decrease in plasmatic [Cl(-)].
  
  
  CONCLUSIONS
  Low-dose furosemide administration immediately modifies urinary electrolyte excretion rates, likely in relation to the ongoing proximal tubular activity, unveiled by its inhibitory action on Henle's loop. Such effects, when cumulative, found the bases for the long-term alterations observed. Real-time urinary electrolyte monitoring may help in tailoring patient diuretic and hemodynamic therapies.
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Università degli Studi di Milano, Via F. Sforza 35, 20122, Milan, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Zazzeron
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Università degli Studi di Milano, Via F. Sforza 35, 20122, Milan, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Ottolina
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Università degli Studi di Milano, Via F. Sforza 35, 20122, Milan, Italy.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Scotti
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Università degli Studi di Milano, Via F. Sforza 35, 20122, Milan, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Ferrari
authors.affiliation: Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Bruzzone
authors.affiliation: Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Silvio
authors.initials: S
authors.lastname: Sibilla
authors.affiliation: Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Marenghi
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, Georg-August-University Göttingen, Göttingen, Germany.
authors.forename: Luciano
authors.initials: L
authors.lastname: Gattinoni
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Università degli Studi di Milano, Via F. Sforza 35, 20122, Milan, Italy. pietro.caironi@unimi.it.|Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Milan, Italy. pietro.caironi@unimi.it.
authors.forename: Pietro
authors.initials: P
authors.lastname: Caironi
keywords: Furosemide; Loop-diuretics; Metabolic alkalosis; Urinary chloride; Urinary sodium