title: Effects of positive end-expiratory pressure on intestinal circulation during graded mesenteric artery occlusion.
abstract: BACKGROUND
  Reduced gut perfusion is associated with multiple organ failure. Positive end-expiratory pressure (PEEP) reduces cardiac output (CO) and portal blood flow, and might be detrimental in a situation of already compromised intestinal circulation. The aim of this study was to investigate regional circulatory and metabolic effects of PEEP during graded regional hypoperfusion.
  
  
  METHODS
  In 12 barbiturate-anesthetized pigs, we measured systemic and regional blood flows (superior mesenteric arterial, QSMA and portal venous, QPORT), jejunal mucosal perfusion (LDF), tissue oxygenation (PO2TISSUE) and metabolic parameters at PEEP (0, 4, 8 and 12 cm H2O) in a randomized order. Measurements were performed at unrestricted intestinal perfusion pressures (IPP) and at IPP levels of 50 and 30 mmHg.
  
  
  RESULTS
  During unrestricted IPP, PEEP decreased MAP, CO, QSMA and QPORT, while systemic, and preportal (RPORT) vascular resistances and jejunal mucosal perfusion were not significantly changed. Preportal tissue oxygen delivery and PO2TISSUE decreased, while preportal tissue oxygen uptake was unaltered. During restricted IPP, PEEP produced the same pattern of hemodynamic alterations as when IPP was not restricted. QPORT and QSMA were lowered by the reductions in IPP, and QPORT was further reduced during PEEP. At an IPP of 30 mmHg, this reduction in QPORT decreased preportal tissue oxygen uptake. Consequently, intestinal ischemia, as indicated by increased net lactate production, occurred. Simultaneously, jejunal mucosal perfusion and PO2TISSUE declined.
  
  
  CONCLUSIONS
  At IPP levels below 50 mmHg, even moderate levels of PEEP impaired local blood flow enough to cause intestinal ischemia. Our data underscore the importance of considering regional circulatory adaptations during PEEP ventilation.
authors.affiliation: Department of Surgical and Perioperative Sciences, Anesthesiology and Intensive Care and Surgery, Umeå University Hospital, Umeå, Sweden. stefan.lehtipalo.us@vll.se
authors.forename: S
authors.initials: S
authors.lastname: Lehtipalo
authors.forename: B
authors.initials: B
authors.lastname: Biber
authors.forename: R
authors.initials: R
authors.lastname: Fröjse
authors.forename: C
authors.initials: C
authors.lastname: Arnerlöv
authors.forename: G
authors.initials: G
authors.lastname: Johansson
authors.forename: O
authors.initials: O
authors.lastname: Winsö
mesh_terms: D000758:Anesthesia; D000818:Animals; D001784:Blood Gas Analysis; D005260:Female; D006439:Hemodynamics; D007413:Intestinal Mucosa / Q000098:blood supply / Q000378:metabolism; D007422:Intestines / Q000098:blood supply*; D019344:Lactic Acid / Q000097:blood; D008638:Mesenteric Arteries / Q000502:physiology*; D008641:Mesenteric Vascular Occlusion / Q000378:metabolism / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D011175:Positive-Pressure Respiration; D012039:Regional Blood Flow / Q000502:physiology; D013552:Swine; D014655:Vascular Resistance / Q000502:physiology
chemical_list: D019344:Lactic Acid; D010100:Oxygen