title: How central obesity influences intra-abdominal pressure: a prospective, observational study in cardiothoracic surgical patients.
abstract: BACKGROUND
  Intra-abdominal hypertension (IAH) is frequently present in critically ill patients and is an independent predictor for mortality. Better recognition of clinically important thresholds is necessary. Increased intra-abdominal pressure (IAP) is associated with renal dysfunction, and renal failure is one of the most consistently described organ dysfunctions associated with IAH. Obesity is also associated with kidney injury. The underlying mechanisms are not yet fully understood. Increased IAP may be a link in this association. The aim of this study was firstly to find the range in values of intra-abdominal pressure (IAP) in cardiothoracic surgery patients a secondly to investigate the relationship between central obesity, body mass index (BMI) and IAP and thirdly to investigate the relationship between IAP, inflammation and renal function in this population.
  
  
  METHODS
  Consecutive adult patients admitted to the cardiothoracic unit of the intensive care unit (ICU) after undergoing elective cardiothoracic surgery were included in this prospective, observational study. C-reactive protein (CRP) as a marker of inflammation and serum creatinine as a marker of renal function were measured pre- and postoperatively. Estimated glomerular filtration rates were calculated pre- and postoperatively. BMI was calculated. Waist circumference (WC), hip circumference (HC) and transvesical IAP were measured once directly after admission to the ICU postoperatively. Waist/hip ratio (WHR) was calculated (WC divided by HC). Three definitions of central obesity were used. Central obesity was defined according to WC, WHR or median WHR.
  
  
  RESULTS
  In total, 186 patients undergoing cardiothoracic surgery were included. Mean IAP was 9.1 mmHg (SD 4.4). IAP ≥ 12 mmHg was observed in 50 patients (26.9 %). IAP > 20 mmHg was measured in 4 patients (2.2 %). There was a positive correlation between IAP and BMI (r2= 0.05, p = 0.003). Correlations between IAP and WC (r2= 0.02, p = 0.054) and between IAP and WHR (r2= 0.01, p = 0.173) were not significant. There were no correlations between pre- or postoperative CRP and IAP (r2= 2.3 × 10-4, p = 0.839 and r2= 0.013, p = 0.117, respectively). In obese patients postoperative CRP was significantly higher than in non-obese patients (p = 0.034). There were no correlations between pre-operative serum creatinine and IAP (r2= 3.3 × 10-5, p = 0.938) or postoperative serum creatinine and IAP (r2= 0.003, p = 0.491).
  
  
  CONCLUSIONS
  The range in IAP in patients undergoing cardiothoracic surgery was wide. There was a positive correlation between IAP and BMI. Correlations between IAP and indices for central obesity were not significant. In a multiple regression model BMI was a better predictor of IAP than WHR in this population. There were no correlations between pre- or postoperative CRP and IAP. Furthermore, this study did not find evidence for a relation between IAP and pre- and postoperative serum creatinine.
authors.affiliation: Department of Critical Care (BA 49), University Medical Center Groningen, University of Groningen, PO Box 30001, 9700 RB, Groningen, The Netherlands. m.smit@umcg.nl.
authors.forename: Marije
authors.identifier: http://orcid.org/0000-0002-4658-7287
authors.initials: M
authors.lastname: Smit
authors.affiliation: Department of Critical Care (BA 49), University Medical Center Groningen, University of Groningen, PO Box 30001, 9700 RB, Groningen, The Netherlands.
authors.forename: Maureen J M
authors.initials: MJM
authors.lastname: Werner
authors.affiliation: Department of Critical Care (BA 49), University Medical Center Groningen, University of Groningen, PO Box 30001, 9700 RB, Groningen, The Netherlands.
authors.forename: Annemieke Oude
authors.initials: AO
authors.lastname: Lansink-Hartgring
authors.affiliation: Department of Critical Care (BA 49), University Medical Center Groningen, University of Groningen, PO Box 30001, 9700 RB, Groningen, The Netherlands.
authors.forename: Willem
authors.initials: W
authors.lastname: Dieperink
authors.affiliation: Department of Critical Care (BA 49), University Medical Center Groningen, University of Groningen, PO Box 30001, 9700 RB, Groningen, The Netherlands.
authors.forename: Jan G
authors.initials: JG
authors.lastname: Zijlstra
authors.affiliation: Department of Critical Care (BA 49), University Medical Center Groningen, University of Groningen, PO Box 30001, 9700 RB, Groningen, The Netherlands.
authors.forename: Matijs
authors.initials: M
authors.lastname: van Meurs
keywords: Acute kidney injury; Body mass index; Central obesity; Intra-abdominal pressure; Renal failure; Waist circumference; Waist/hip ratio