title: Does pleural fluid pH change significantly at room temperature during the first hour following thoracentesis?
abstract: BACKGROUND
  Usually, pleural fluid (PF) pH is measured immediately following thoracentesis, and if there is any delay in the measurement, the PF sample is preserved on ice.
  
  
  OBJECTIVE
  To determine if PF pH changes significantly at room temperature during the first hour following thoracentesis.
  
  
  METHODS
  Prospective, self-controlled.
  
  
  METHODS
  Tertiary care center.
  
  
  METHODS
  All patients undergoing thoracentesis.
  
  
  METHODS
  The PF pH of a sample collected in an arterial blood gas syringe was measured immediately following thoracentesis by an arterial blood pH/gas analyzer. Additional measurements were made at 5, 15, 30, 45, and 60 min from the first pH measurement (pH0), maintained at room temperature.
  
  
  RESULTS
  For 28 PF samples, pH0 (mean +/- SD) was 7.351 +/- 0.158, and the 60-min pH (pH60) was 7.359 +/- 0.161. The mean difference between pH60 and pH0 was 0.008 +/- 0.026, which was not significant, either clinically or statistically (p = 0.13). Similarly, the interim pH values (for measures at 5, 15, 30, 45 min after pH0) were not significantly different from pH0 (mean differences, 0.002, 0.003, 0.005, and 0.004, respectively; p values, 0.51, 0.21, 0.06, and 0.22, respectively).
  
  
  CONCLUSIONS
  The pleural fluid pH of a sample preserved at room temperature does not change significantly during the first hour following thoracentesis. Hence, contrary to the common medical practice, there is no need to perform the pH measurement within minutes after thoracentesis and to preserve a pleural fluid sample on ice.
authors.affiliation: Department of Pulmonary and Critical Care Medicine, Cleveland Clinic Foundation, Cleveland, OH 44195, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Sarodia
authors.forename: L S
authors.initials: LS
authors.lastname: Goldstein
authors.forename: D M
authors.initials: DM
authors.lastname: Laskowski
authors.forename: A C
authors.initials: AC
authors.lastname: Mehta
authors.forename: A C
authors.initials: AC
authors.lastname: Arroliga
mesh_terms: D000046:Academic Medical Centers; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001826:Body Fluids / Q000166:cytology / Q000378:metabolism*; D002452:Cell Count; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007297:Inpatients; D008297:Male; D008875:Middle Aged; D010045:Outpatients; D019152:Paracentesis; D010996:Pleural Effusion / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D011184:Postoperative Period; D011379:Prognosis; D011446:Prospective Studies; D013696:Temperature