title: Modelling of hypoxaemia after gynaecological laparotomy.
abstract: BACKGROUND
  Late postoperative arterial hypoxaemia is common after major surgery, and may contribute to cardiovascular, cerebral or wound complications. This study investigates the time course of hypoxaemia following gynaecological laparotomy, and estimates parameters of mathematical models of pulmonary gas exchange to describe hypoxaemia.
  
  
  METHODS
  Twelve patients were studied on four occasions; preoperatively, 2, 8 and 48 h after surgery. On each occasion inspired oxygen fraction (FIO2) was varied, changing end-expired oxygen fraction (FEO2) to achieve arterial oxygen saturations (SaO2) ranging from 90% to 100%. Measurements of ventilation and blood gases were taken. Oxygenation was characterized plotting FEO2 against SaO2. The shape and position of the FEO2/SaO2 curve was described using two mathematical models including parameters describing gas exchange: either shunt and resistance to oxygen diffusion (Rdiff); or shunt and asymmetry of ventilation-perfusion (fA2).
  
  
  RESULTS
  Two hours after surgery SaO2 was reduced from 97.5%+/-1.2% (mean+/-SD) to 93.8%+/-2.7% (mean+/-SD) (P<0.001). Values of shunt, Rdiff and fA2 were significantly changed at 2 and 8 h postoperatively. Forty-eight hours postoperatively Rdiff and fA2 were still significantly changed.
  
  
  CONCLUSIONS
  Oxygenation in 12 patients preoperatively, 2, 8 and 48 h after gynaecological laparotomy is described. Two patients were hypoxaemic (SaO2 <92%) 48 h postoperatively. When two different models of oxygen transport are fitted to patient data, high values of Rdiff or low values of fA2 describe the right shift in the FEO2/SaO2 curve seen in patients with oxygenation problems. These models fit patient data identically, and may be useful in quantifying postoperative hypoxaemia.
authors.affiliation: Department of Anaesthesiology, Aalborg Hospital, Denmark. sck@dadlnet.dk
authors.forename: S
authors.initials: S
authors.lastname: Kjaergaard
authors.forename: S E
authors.initials: SE
authors.lastname: Rees
authors.forename: J A
authors.initials: JA
authors.lastname: Nielsen
authors.forename: M
authors.initials: M
authors.lastname: Freundlich
authors.forename: P
authors.initials: P
authors.lastname: Thorgaard
authors.forename: S
authors.initials: S
authors.lastname: Andreassen
mesh_terms: D000328:Adult; D005260:Female; D013509:Gynecologic Surgical Procedures; D006801:Humans; D000860:Hypoxia / Q000209:etiology*; D007813:Laparotomy / Q000009:adverse effects*; D008433:Mathematics; D008875:Middle Aged; D008954:Models, Biological; D011183:Postoperative Complications / Q000209:etiology*; D011659:Pulmonary Gas Exchange