title: Diagnostically significant variations in pleural fluid pH in loculated parapneumonic effusions.
abstract: OBJECTIVE
  Parapneumonic effusions are common, and measurement of pleural pH is one of the most useful measurements in assessing the need for tube drainage. Use of pleural pH assumes that a single measurement conveys a representative picture of pH throughout the effusion. Often effusions are multiloculated, and varying concentrations of nondiffusible acids such as lactic acid, if present in different concentrations, could mean clinically significant variations in pH between locules. If these differences were large, a single pH measurement could misrepresent the "stage" that the parapneumonic effusion had reached. We therefore set out to test the hypothesis that pH varies significantly between locules in complicated parapneumonic effusions.
  
  
  METHODS
  The study was performed in seven consecutive patients presenting to our institution with complicated parapneumonic effusions.
  
  
  METHODS
  In each case, pleural pH was measured in several separate pleural fluid locules, using ultrasound-guided pleural fluid sampling.
  
  
  RESULTS
  Significant variations were found in pleural fluid visual appearance, pH, and lactate dehydrogenase between locules in four of seven patients. Three of seven patients had variations, resulting in pH levels both above and below 7.2, which is the threshold used in our institution to indicate the need for tube drainage.
  
  
  CONCLUSIONS
  This is the first reported series of variation in pleural pH between different locules in complicated parapneumonic effusions. These variations are clinically important and cast light on the mechanisms responsible for the acidosis seen in infected effusions. Physicians should be aware of this when making drainage decisions in these patients using the clinical picture and a single pH result alone.
authors.affiliation: Oxford Centre for Respiratory Medicine, Churchill Hospital, John Radcliffe NHS Trust, Oxford, Oxfordshire, UK. nickmaskell@doctors.org.uk
authors.forename: Nick A
authors.initials: NA
authors.lastname: Maskell
authors.forename: Fergus V
authors.initials: FV
authors.lastname: Gleeson
authors.forename: Mike
authors.initials: M
authors.lastname: Darby
authors.forename: Robert J O
authors.initials: RJ
authors.lastname: Davies
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000032:analysis; D015505:Chest Tubes; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008297:Male; D008875:Middle Aged; D010996:Pleural Effusion / Q000737:chemistry / Q000175:diagnosis* / Q000209:etiology / Q000628:therapy; D018410:Pneumonia, Bacterial / Q000150:complications*
chemical_list: D015415:Biomarkers; D007770:L-Lactate Dehydrogenase