title: A simplified method for deriving shunt and reduced VA/Q in infants.
abstract: BACKGROUND
  Right to left shunt and regional hypoventilation (reduced ventilation/perfusion ratio (V(A)/Q)) have different effects on the curve relating inspired oxygen (P(I)O(2)) to oxygen saturation measured by pulse oximetry (SpO(2)) and can be derived non-invasively from measurements of SpO(2) and inspired oxygen pressure (P(I)O(2)) using complex models of gas exchange. We developed a simpler computerised "slide-rule" method of making these derivations.
  
  
  OBJECTIVE
  To describe the slide-rule method and determine agreement between measurements derived with this and a more complex algorithm.
  
  
  METHODS
  Series of P(I)O(2) versus SpO(2) data points obtained during 43 studies in 16 preterm infants with bronchopulmonary dysplasia were analysed. Percentage shunt and the degree of right shift (kPa) of the P(I)O(2) versus SpO(2) curve compared with the oxyhaemoglobin dissociation curve (a measure of V(A)/Q) were determined for each dataset with both methods, and the results were compared using the method of Bland and Altman.
  
  
  RESULTS
  The computer slide-rule method produced results for all 43 datasets. The more complex model could derive results for 40/43 datasets. The mean differences (95% limits of agreement) between the two methods for measurements of shunt were -1.7% (-6.5 to +3.5%) and for measurements of right shift were 0.3 kPa (-2.9 to +3.6 kPa).
  
  
  CONCLUSIONS
  The slide-rule method was reliable for deriving shunt and right shift (reduced V(A)/Q) of the P(I)O(2) versus SpO(2) curve when compared with the more complex algorithm. The new method should enable wider clinical application of these measurements of oxygen exchange.
authors.affiliation: Department of Anaesthetics, Norfolk and Norwich University Hospital, Norwich, UK.
authors.forename: L
authors.initials: L
authors.lastname: Rowe
authors.forename: J G
authors.initials: JG
authors.lastname: Jones
authors.forename: D
authors.initials: D
authors.lastname: Quine
authors.forename: S S
authors.initials: SS
authors.lastname: Bhushan
authors.forename: B J
authors.initials: BJ
authors.lastname: Stenson
mesh_terms: D000465:Algorithms; D001997:Bronchopulmonary Dysplasia / Q000175:diagnosis / Q000503:physiopathology*; D003198:Computer Simulation; D005260:Female; D005865:Gestational Age; D006801:Humans; D007040:Hypoventilation / Q000503:physiopathology; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D008954:Models, Biological; D008991:Monitoring, Physiologic / Q000379:methods; D010092:Oximetry / Q000379:methods; D010100:Oxygen / Q000097:blood; D011650:Pulmonary Alveoli / Q000502:physiology; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*
chemical_list: D010100:Oxygen