title: [Influence of the method used to obtain pleural fluid on the determination of the Acid-base balance].
abstract: OBJECTIVE
  To analyze the methods used in our hospital for obtaining pleural fluid to determine the acid-base balance and to evaluate the clinical repercussions of each method.
  
  
  METHODS
  Initially we studied the methods used by physicians in our hospital to collect pleural fluid for determination of the acid-base balance. In a second phase, we performed a prospective, descriptive, comparative study with the participation of 71 patients with pleural effusions in order to compare the acid-base balance according to the technique used to obtain the fluid.
  
  
  RESULTS
  Pleural fluid was obtained using 3 methods: a) direct extraction using a heparinized syringe (group 1); b) extraction using a 20 mL syringe with subsequent aspiration from this syringe into a heparinized syringe (group 2); and c) filling a heparinized syringe from the 20 mL syringe (group 3). The only significant differences between group 1 and groups 2 and 3 were an increase in the pleural PO2 and oxygen saturation. The difference in the mean pH between groups 1 and 2 was 0.009 (95% confidence interval: -0.39 to 0.02; P=.5) and between groups 1 and 3 was 0.007 (95% confidence interval: -0.38 to 0.023; P=.6). The correlations between findings for PO2, pH, and PCO2 obtained in the different groups were statistically significant, with values superior to .95 in the last 2 variables.
  
  
  CONCLUSIONS
  Physicians who perform thoracentesis in our hospital use different methods for obtaining fluid to determine the pleural acid-base balance. The 3 methods analyzed show no significant differences with regard to pH or PCO2. Pleural fluid may be obtained by a single puncture with a large-volume syringe, subsequently transferring the fluid to a heparinized syringe without this significantly affecting the pH or PCO2, thus reducing the number of manipulations and the risk of complications.
authors.affiliation: Servicio de Neumología, Hospital Universitario de Girona Dr. Josep Trueta, Girona, España. mip.mharo@htrueta.scs.es
authors.forename: Manuel
authors.initials: M
authors.lastname: Haro-Estarriol
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Calderón-López
authors.forename: Gladis
authors.initials: G
authors.lastname: Sabater-Talaverano
authors.forename: Núria
authors.initials: N
authors.lastname: Font Vall-Llobera
authors.forename: Luis Alberto
authors.initials: LA
authors.lastname: Alvarez-Castillo
authors.forename: Salvi
authors.initials: S
authors.lastname: Sendra-Salillas
mesh_terms: D000136:Acid-Base Equilibrium; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D010996:Pleural Effusion / Q000737:chemistry*; D011446:Prospective Studies; D013048:Specimen Handling / Q000379:methods