title: Improved ventilation-perfusion matching by abdominal insufflation (pneumoperitoneum) with CO2 but not with air.
abstract: BACKGROUND
  Pneumoperitoneum (PP) by CO2-insufflation causes atelectasis however with maintained or even improved oxygenation. We studied the effect of abdominal insufflation by carbon dioxide (CO2) and air on gas exchange during PP.
  
  
  METHODS
  Twenty-seven anesthetized pigs were studied during PP with insufflations to 12 mmHg by either 1/CO2, 2/ air or 3/CO2 during intravenous nitroprusside infusion (SNP) (N.=9 in each group). In 3 pigs in each group, gamma camera technique (SPECT) was used to study ventilation and perfusion distributions, in another 6 pigs an inert-gas technique (MIGET) was used for assessing ventilation-perfusion matching (VA/Q). Measurements were made during anesthesia before and after 60 minutes of PP.
  
  
  RESULTS
  CO2-PP caused a shift of blood flow away from dependent, non-ventilated (atelectatic) to ventilated regions. Air-PP caused smaller, and SNP-PP even less shift of lung blood flow. Shunt decreased during CO2-PP (6 ± 1% compared to baseline 9 ± 2%, P<0.05), did not change during Air-PP (10 ± 2%) and increased during SNP-PP (16 ± 2%, P<0.05). PaO2 increased from baseline 35 ± 2 to 41 ± 3 kPa during CO2-PP and decreased to 32 ± 3 kPa during Air-PP and to 27 ± 3 kPa during SNP-PP (P<0.05 for all three comparisons). PaCO2 increased during CO2- and SNP-PP.
  
  
  CONCLUSIONS
  CO2-PP enhanced the shift of blood flow towards better ventilated areas of the lung compared to Air-PP and SNP blunted the effects seen with CO2-PP. SNP may thus have blunted and CO2 potentiated vasoconstriction, by hypoxic pulmonary vasoconstriction or another mechanism.
authors.affiliation: Department of Medical Sciences, Clinical Physiology, Uppsala University, Sweden. christof.strang@med.ovgu.de
authors.forename: C M
authors.initials: CM
authors.lastname: Strang
authors.forename: U
authors.initials: U
authors.lastname: Ebmeyer
authors.forename: E
authors.initials: E
authors.lastname: Maripuu
authors.forename: T
authors.initials: T
authors.lastname: Hachenberg
authors.forename: G
authors.initials: G
authors.lastname: Hedenstierna
mesh_terms: D000388:Air; D000758:Anesthesia; D000769:Anesthesia, Inhalation / Q000379:methods*; D000818:Animals; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000494:pharmacology*; D006439:Hemodynamics / Q000502:physiology; D008168:Lung / Q000000981:diagnostic imaging; D008991:Monitoring, Physiologic; D011028:Pneumoperitoneum, Artificial / Q000379:methods*; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology; D013552:Swine; D015899:Tomography, Emission-Computed, Single-Photon; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide