title: Use of bladder pressure to correct for the effect of expiratory muscle activity on central venous pressure.
abstract: OBJECTIVE
  To assess whether subtracting the expiratory change in intra-abdominal (bladder) pressure (Delta IAP) from central venous pressure (CVP) provides a reliable estimate of transmural CVP in spontaneously breathing patients with expiratory muscle activity.
  
  
  METHODS
  Prospective observational study in a medical ICU.
  
  
  METHODS
  Twenty-four spontaneously breathing patients with central venous and bladder catheters: 18 with no clinical evidence of active expiration (group 1) and 6 with active expiration (group 2).
  
  
  METHODS
  Patients in group 1 were coached to change their breathing pattern to one of active expiration for several breaths; those in group 2 were asked to sip water through a straw to briefly interrupt active expiration.
  
  
  RESULTS
  During active expiration end-expiratory CVP (uncorrected CVP) and Delta IAP were measured; Delta IAP was subtracted from uncorrected CVP to obtain corrected CVP. End-expiratory CVP during relaxed breathing (best CVP) was assumed to represent the best estimate of transmural CVP. The absolute difference between corrected CVP and best CVP was much less than the difference between uncorrected CVP and best CVP (2.3+/-2.0 vs. 12.5+/-4.7 mmHg).
  
  
  CONCLUSIONS
  In patients with active expiration, subtracting Delta IAP from end-expiratory CVP yields a more reliable (and lower) estimate of transmural CVP than does the uncorrected CVP value.
authors.affiliation: University of Minnesota, Division of Pulmonary and Critical Care Medicine, Hennepin County Medical Center, Minneapolis, MN 55415, USA.
authors.forename: Ahmad S
authors.initials: AS
authors.lastname: Qureshi
authors.forename: Robert S
authors.initials: RS
authors.lastname: Shapiro
authors.forename: James W
authors.initials: JW
authors.lastname: Leatherman
mesh_terms: D000005:Abdomen / Q000502:physiology; D002404:Catheterization; D002496:Central Venous Pressure; D003422:Critical Care; D045853:Exhalation / Q000502:physiology*; D006801:Humans; D007362:Intensive Care Units; D008910:Minnesota; D008991:Monitoring, Physiologic; D011446:Prospective Studies; D012119:Respiration; D001743:Urinary Bladder