title: Improved ventilation-perfusion matching with increasing abdominal pressure during CO(2) -pneumoperitoneum in pigs.
abstract: BACKGROUND
  CO(2) -pneumoperitoneum (PP) is performed at varying abdominal pressures. We studied in an animal preparation the effect of increasing abdominal pressures on gas exchange during PP.
  
  
  METHODS
  Eighteen anaesthetized pigs were studied. Three abdominal pressures (8, 12 and 16 mmHg) were randomly selected in each animal. In six pigs, single-photon emission computed tomography (SPECT) was used for the analysis of V/Q distributions; in another six pigs, multiple inert gas elimination technique (MIGET) was used for assessing V/Q matching. In further six pigs, computed tomography (CT) was performed for the analysis of regional aeration. MIGET, CT and central haemodynamics and pulmonary gas exchange were recorded during anaesthesia and after 60 min on each of the three abdominal pressures. SPECT was performed three times, corresponding to each PP level.
  
  
  RESULTS
  Atelectasis, as assessed by CT, increased during PP and in proportion to abdominal pressure [from 9 ± 2% (mean ± standard deviation) at 8 mmHg to 15 ± 2% at 16 mmHg, P<0.05]. SPECT during increasing abdominal CO(2) pressures showed a shift of blood flow towards better ventilated areas. V/Q analysis by MIGET showed no change in shunt during 8 mmHg PP (9 ± 1.9% compared with baseline 9 ± 1.2%) but a decrease during 12 mmHg PP (7 ± 0.9%, P<0.05) and 16 mmHg PP (5 ± 1%, P<0.01). PaO(2) increased from 39 ± 10 to 52 ± 9 kPa (baseline to 16 mmHg PP, P<0.01). Arterial carbon dioxide (PCO(2) ) increased during PP and increased further with increasing abdominal pressures.
  
  
  CONCLUSIONS
  With increasing abdominal pressure during PP perfusion was redistributed more than ventilation away from dorsal, collapsed lung regions. This resulted in a better V/Q match. A possible mechanism is enhanced hypoxic pulmonary vasoconstriction mediated by increasing PCO(2) .
authors.affiliation: Department of Medical Sciences, Clinical Physiology, University of Uppsala, Uppsala, Sweden.
authors.forename: C M
authors.initials: CM
authors.lastname: Strang
authors.forename: F
authors.initials: F
authors.lastname: Freden
authors.forename: E
authors.initials: E
authors.lastname: Maripuu
authors.forename: U
authors.initials: U
authors.lastname: Ebmeyer
authors.forename: T
authors.initials: T
authors.lastname: Hachenberg
authors.forename: Göran
authors.initials: G
authors.lastname: Hedenstierna
mesh_terms: D000005:Abdomen / Q000000981:diagnostic imaging / Q000502:physiology*; D000758:Anesthesia; D000818:Animals; D002245:Carbon Dioxide; D015902:Gamma Cameras; D006439:Hemodynamics / Q000502:physiology; D008991:Monitoring, Physiologic; D011028:Pneumoperitoneum, Artificial / Q000379:methods*; D011312:Pressure; D001261:Pulmonary Atelectasis / Q000503:physiopathology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D013552:Swine; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed; D014692:Ventilation-Perfusion Ratio
chemical_list: D002245:Carbon Dioxide