title: Development of atelectasis and arterial to end-tidal PCO2-difference in a porcine model of pneumoperitoneum.
abstract: BACKGROUND
  Intraperitoneal insufflation of carbon dioxide (CO2) may promote collapse of dependent lung regions. The present study was undertaken to study the effects of CO2-pneumoperitoneum (CO2-PP) on atelectasis formation, arterial oxygenation, and arterial to end-tidal PCO2-gradient (Pa-E'(CO2)).
  
  
  METHODS
  Fifteen anaesthetized pigs [mean body weight 28 (SD 2) kg] were studied. Spiral computed tomography (CT) scans were obtained for analysis of lung tissue density. In Group 1 (n=5) mechanical ventilation (V(T)=10 ml kg (-1), FI(O2)=0.5) was applied, in Group 2 (n=5) FI(O2) was increased for 30 min to 1.0 and in Group 3 (n=5) negative airway pressure was applied for 20 s in order to enhance development of atelectasis. Cardiopulmonary and CT data were obtained before, 10, and 90 min after induction of CO2-PP at an abdominal pressure of 12 mmHg.
  
  
  RESULTS
  Before CO2-PP, in Group 1 non-aerated tissue on CT scans was 1 (1)%, in Group 2 3 (2)% (P<0.05, compared with Group 1), and in Group 3 7 (3)% (P<0.05, compared with Group 1 and Group 2). CO2-PP significantly increased atelectasis in all groups. PaO2/FI(O2) fell and venous admixture ('shunt') increased in proportion to atelectasis during anaesthesia but CO2-PP had a varying effect on PaO2/FI(O2) and shunt. Thus, no correlation was seen between atelectasis and PaO2/FI(O2) or shunt when all data before and during CO2-PP were pooled. Pa-E'(CO2), on the other hand correlated strongly with the amount of atelectasis (r2=0.92).
  
  
  CONCLUSIONS
  Development of atelectasis during anaesthesia and PP may be estimated by an increased Pa-E'(CO2).
authors.affiliation: Department of Medical Sciences, Clinical Physiology, Uppsala University, Uppsala, Sweden.
authors.forename: C M
authors.initials: CM
authors.lastname: Strang
authors.forename: T
authors.initials: T
authors.lastname: Hachenberg
authors.forename: F
authors.initials: F
authors.lastname: Fredén
authors.forename: G
authors.initials: G
authors.lastname: Hedenstierna
mesh_terms: D000768:Anesthesia, General / Q000379:methods; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood*; D004195:Disease Models, Animal; D005260:Female; D010535:Laparoscopy; D008297:Male; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D011028:Pneumoperitoneum, Artificial / Q000009:adverse effects*; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging / Q000209:etiology*; D012121:Respiration, Artificial / Q000379:methods; D034421:Sus scrofa; D014057:Tomography, X-Ray Computed
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen