title: Electrolyte shifts across the artificial lung in patients on extracorporeal membrane oxygenation: interdependence between partial pressure of carbon dioxide and strong ion difference.
abstract: OBJECTIVE
  Partial pressure of carbon dioxide (PCO2), strong ion difference (SID), and total amount of weak acids independently regulate pH. When blood passes through an extracorporeal membrane lung, PCO2 decreases. Furthermore, changes in electrolytes, potentially affecting SID, were reported. We analyzed these phenomena according to Stewart's approach.
  
  
  METHODS
  Couples of measurements of blood entering (venous) and leaving (arterial) the extracorporeal membrane lung were analyzed in 20 patients. Changes in SID, PCO2, and pH were computed and pH variations in the absence of measured SID variations calculated.
  
  
  RESULTS
  Passing from venous to arterial blood, PCO2 was reduced (46.5 ± 7.7 vs 34.8 ± 7.4 mm Hg, P < .001), and hemoglobin saturation increased (78 ± 8 vs 100% ± 2%, P < .001). Chloride increased, and sodium decreased causing a reduction in SID (38.7 ± 5.0 vs 36.4 ± 5.1 mEq/L, P < .001). Analysis of quartiles of ∆PCO2 revealed progressive increases in chloride (P < .001), reductions in sodium (P < .001), and decreases in SID (P < .001), at constant hemoglobin saturation variation (P = .12). Actual pH variation was lower than pH variations in the absence of measured SID variations (0.09 ± 0.03 vs 0.12 ± 0.04, P < .001).
  
  
  CONCLUSIONS
  When PCO2 is reduced and oxygen added, several changes in electrolytes occur. These changes cause a PCO2-dependent SID reduction that, by acidifying plasma, limits pH correction caused by carbon dioxide removal. In this particular setting, PCO2 and SID are interdependent.
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy; Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milano, Italy. Electronic address: tom.langer@hotmail.it.
authors.forename: Thomas
authors.initials: T
authors.lastname: Langer
authors.affiliation: Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milano, Italy.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Scotti
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Carlesso
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy; Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milano, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Protti
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy.
authors.forename: Loredana
authors.initials: L
authors.lastname: Zani
authors.affiliation: Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milano, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Chierichetti
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy; Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milano, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Caironi
authors.affiliation: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milano, Italy; Dipartimento di Anestesia, Rianimazione ed Emergenza Urgenza, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milano, Italy.
authors.forename: Luciano
authors.initials: L
authors.lastname: Gattinoni
mesh_terms: D000136:Acid-Base Equilibrium; D000328:Adult; D000838:Anions / Q000097:blood; D002245:Carbon Dioxide / Q000097:blood*; D002712:Chlorides / Q000097:blood; D004573:Electrolytes; D015199:Extracorporeal Membrane Oxygenation; D005260:Female; D006441:Hemoglobin A / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D012964:Sodium / Q000097:blood
chemical_list: D000838:Anions; D002712:Chlorides; D004573:Electrolytes; D002245:Carbon Dioxide; D006441:Hemoglobin A; D012964:Sodium; D010100:Oxygen
keywords: Acid-base equilibrium; Electrolyte shift; Extracorporeal membrane oxygenation; Gas exchange; Respiratory failure; Stewart approach