title: Effect of bladder volume on measured intravesical pressure: a prospective cohort study.
abstract: BACKGROUND
  Correct bedside measurement of intra-abdominal pressure (IAP) is important. The bladder method is considered as the gold standard for indirect IAP measurement, but the instillation volumes reported in the literature vary substantially. The aim of this study was to evaluate the effect of instillation volume on intra-bladder pressure (IBP) as an estimation for IAP in critically ill patients.
  
  
  METHODS
  In this prospective cohort study in 13 sedated and mechanically ventilated patients, we used a revised closed system repeated measurement technique for measurement of IBP. After the system was flushed, IBP was measured with 25 ml increments up to 300 ml. The absolute bias for each volume was calculated as IBP at a given volume minus IBP at zero volume.
  
  
  RESULTS
  In total, 30 measurement sets were performed (mean 2.3 per patient). The median IBP at 25 ml was already significantly higher than IBP at zero volume (7.5 versus 6 mmHg). There was no correlation between IBP at zero volume and absolute IBP bias at any bladder volume. Median absolute IBP bias was 1.5 mmHg at 50 ml; 2.5 mmHg at 100 ml; 5.5 mmHg at 150 ml; and up to 11 mmHg at 300 ml.
  
  
  CONCLUSIONS
  Larger instillation volumes than the usually recommended 50 ml to estimate IAP by bladder pressure may cause clinically relevant overestimation of IAP. Small volumes to a maximum of 25 ml, enough to create a fluid column and to remove air, may be sufficient.
authors.affiliation: Intensive Care Unit, Ziekenhuisnetwerk Antwerpen Campus Stuivenberg, Lange Beeldekensstraat, B-2060 Antwerp, Belgium. manu.malbrain@skynet.be
authors.forename: Manu L N G
authors.initials: ML
authors.lastname: Malbrain
authors.forename: Dries H
authors.initials: DH
authors.lastname: Deeren
mesh_terms: D000283:Administration, Intravesical; D000368:Aged; D015331:Cohort Studies; D005260:Female; D006801:Humans; D006973:Hypertension / Q000175:diagnosis / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009929:Organ Size / Q000502:physiology; D011312:Pressure; D011446:Prospective Studies; D012121:Respiration, Artificial; D012965:Sodium Chloride; D001743:Urinary Bladder / Q000502:physiology* / Q000503:physiopathology*
chemical_list: D012965:Sodium Chloride