title: Commonly applied positive end-expiratory pressures do not prevent functional residual capacity decline in the setting of intra-abdominal hypertension: a pig model.
abstract: BACKGROUND
  Intra-abdominal hypertension is common in critically ill patients and is associated with increased morbidity and mortality. The optimal ventilation strategy remains unclear in these patients. We examined the effect of positive end-expiratory pressures (PEEP) on functional residual capacity (FRC) and oxygen delivery in a pig model of intra-abdominal hypertension.
  
  
  METHODS
  Thirteen adult pigs received standardised anaesthesia and ventilation. We randomised three levels of intra-abdominal pressure (3 mmHg (baseline), 18 mmHg, and 26 mmHg) and four commonly applied levels of PEEP (5, 8, 12 and 15 cmH2O). Intra-abdominal pressures were generated by inflating an intra-abdominal balloon. We measured intra-abdominal (bladder) pressure, functional residual capacity, cardiac output, haemoglobin and oxygen saturation, and calculated oxygen delivery.
  
  
  RESULTS
  Raised intra-abdominal pressure decreased FRC but did not change cardiac output. PEEP increased FRC at baseline intra-abdominal pressure. The decline in FRC with raised intra-abdominal pressure was partly reversed by PEEP at 18 mmHg intra-abdominal pressure and not at all at 26 mmHg intra-abdominal pressure. PEEP significantly decreased cardiac output and oxygen delivery at baseline and at 26 mmHg intra-abdominal pressure but not at 18 mmHg intra-abdominal pressure.
  
  
  CONCLUSIONS
  In a pig model of intra-abdominal hypertension, PEEP up to 15 cmH2O did not prevent the FRC decline caused by intra-abdominal hypertension and was associated with reduced oxygen delivery as a consequence of reduced cardiac output. This implies that PEEP levels inferior to the corresponding intra-abdominal pressures cannot be recommended to prevent FRC decline in the setting of intra-abdominal hypertension.
authors.affiliation: Intensive Care Unit, Sir Charles Gairdner Hospital, Hospital Avenue, Nedlands, Perth, WA 6009, Australia. adrian.regli@gmail.com
authors.forename: Adrian
authors.initials: A
authors.lastname: Regli
authors.forename: Lisen E
authors.initials: LE
authors.lastname: Hockings
authors.forename: Gabrielle C
authors.initials: GC
authors.lastname: Musk
authors.forename: Brigit
authors.initials: B
authors.lastname: Roberts
authors.forename: Bill
authors.initials: B
authors.lastname: Noffsinger
authors.forename: Bhajan
authors.initials: B
authors.lastname: Singh
authors.forename: Peter V
authors.initials: PV
authors.lastname: van Heerden
mesh_terms: D000005:Abdomen; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output / Q000502:physiology; D004195:Disease Models, Animal; D005652:Functional Residual Capacity / Q000502:physiology*; D006973:Hypertension / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood; D011175:Positive-Pressure Respiration; D013552:Swine
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen