title: Ventilation/perfusion ratios measured by multiple inert gas elimination during experimental cardiopulmonary resuscitation.
abstract: BACKGROUND
  During cardiopulmonary resuscitation (CPR) the ventilation/perfusion distribution (VA /Q) within the lung is difficult to assess. This experimental study examines the capability of multiple inert gas elimination (MIGET) to determine VA /Q under CPR conditions in a pig model.
  
  
  METHODS
  Twenty-one anaesthetised pigs were randomised to three fractions of inspired oxygen (1.0, 0.7 or 0.21). VA/ Q by micropore membrane inlet mass spectrometry-derived MIGET was determined at baseline and during CPR following induction of ventricular fibrillation. Haemodynamics, blood gases, ventilation distribution by electrical impedance tomography and return of spontaneous circulation were assessed. Intergroup differences were analysed by non-parametric testing.
  
  
  RESULTS
  MIGET measurements were feasible in all animals with an excellent correlation of measured and predicted arterial oxygen partial pressure (R(2)  = 0.96, n = 21 for baseline; R(2)  = 0.82, n = 21 for CPR). CPR induces a significant shift from normal VA /Q ratios to the high VA /Q range. Electrical impedance tomography indicates a dorsal to ventral shift of the ventilation distribution. Diverging pulmonary shunt fractions induced by the three inspired oxygen levels considerably increased during CPR and were traceable by MIGET, while 100% oxygen most negatively influenced the VA /Q. Return of spontaneous circulation were achieved in 52% of the animals.
  
  
  CONCLUSIONS
  VA /Q assessment by MIGET is feasible during CPR and provides a novel tool for experimental purposes. Changes in VA /Q caused by different oxygen fractions are traceable during CPR. Beyond pulmonary perfusion deficits, these data imply an influence of the inspired oxygen level on VA /Q. Higher oxygen levels significantly increase shunt fractions and impair the normal VA /Q ratio.
authors: Department of Anaesthesiology, Medical Centre of the Johannes Gutenberg-University, Mainz, Germany.
authors: E K
authors: EK
authors: Hartmann
authors: B
authors: B
authors: Duenges
authors: S
authors: S
authors: Boehme
authors: M
authors: M
authors: Szczyrba
authors: T
authors: T
authors: Liu
authors: K U
authors: KU
authors: Klein
authors: J E
authors: JE
authors: Baumgardner
authors: K
authors: K
authors: Markstaller
authors: M
authors: M
authors: David
mesh_terms: D000096:Acetone / Q000493:pharmacokinetics; D000818:Animals; D001775:Blood Circulation; D002304:Cardiac Pacing, Artificial; D016887:Cardiopulmonary Resuscitation; D000077335:Desflurane; D017097:Electric Impedance; D004737:Enflurane / Q000493:pharmacokinetics; D004986:Ether / Q000493:pharmacokinetics; D005240:Feasibility Studies; D006439:Hemodynamics; D007530:Isoflurane / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D007726:Krypton / Q000493:pharmacokinetics; D013058:Mass Spectrometry / Q000379:methods*; D005741:Noble Gases / Q000493:pharmacokinetics; D010100:Oxygen / Q000097:blood; D011897:Random Allocation; D013459:Sulfur Hexafluoride / Q000493:pharmacokinetics; D034421:Sus scrofa; D013552:Swine; D014692:Ventilation-Perfusion Ratio; D014693:Ventricular Fibrillation / Q000097:blood / Q000503:physiopathology / Q000628:therapy*
chemical_list: D005741:Noble Gases; D004986:Ether; D000096:Acetone; D007726:Krypton; D004737:Enflurane; D000077335:Desflurane; D007530:Isoflurane; D010100:Oxygen; D013459:Sulfur Hexafluoride