title: Relief of hypoxemia contributes to a reduction in cardiac index related to the use of positive end-expiratory pressure.
abstract: OBJECTIVE
  We have investigated the role that improvement in arterial oxygenation has, consequent on positive end-expiratory pressure (PEEP), in the reduction of cardiac index (CI) determined by applying PEEP.
  
  
  METHODS
  2 x 2 factorial trial.
  
  
  METHODS
  Department of intensive care medicine at a university hospital.
  
  
  METHODS
  13 patients on mechanical ventilation for acute lung injury.
  
  
  METHODS
  Four experimental conditions, each one characterized by one level of PEEP and one level of PaO2: LOLP = Low PaO2 (approximately 50 mmHg) Low PEEP (approximately 1 cmH2O) LOHP = Low PaO2 (approximately 50 mm Hg) High PEEP (approximately 10 cmH2O) HOLP = High PaO2 (approximately 80 mmHg) Low PEEP (approximately 1 cmH2O) HOHP = High PaO2 (approximately 80 mmHg) High PEEP (approximately 10 cmH2O) MEASUREMENTS AND RESULTS: Hemodynamic and gas exchange data were collected for each experimental condition. CI showed a 13% decline from LOLP (7.0 +/- 1.71/min per m2) to HOHP (6.1 +/- 1.31/min per m2). Both the direct effect of PEEP on the CI (LOLP + HOLP vs LOHP + HOHP, p < 0.01) and the indirect effect related to the improvement in oxygenation (LOLP + LOHP vs HOLP + HOHP, p < 0.01) contributed to the reduction in CI.
  
  
  CONCLUSIONS
  In evaluating CI changes induced by PEEP we should take into account the indirect effect of arterial oxygenation upon CI. This should be considered, at least in part, as a physiological adjustment rather than as impaired cardiovascular performance.
authors.affiliation: University of Milan, Department of Anaesthesia and Intensive Care, S. Gerardo Hospital, Monza (MI), Italy.
authors.forename: M
authors.initials: M
authors.lastname: Borelli
authors.forename: R
authors.initials: R
authors.lastname: Fumagalli
authors.forename: F
authors.initials: F
authors.lastname: Bernasconi
authors.forename: M
authors.initials: M
authors.lastname: Cereda
authors.forename: L
authors.initials: L
authors.lastname: Gattinoni
authors.forename: A
authors.initials: A
authors.lastname: Pesenti
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001784:Blood Gas Analysis; D002302:Cardiac Output; D006801:Humans; D000860:Hypoxia / Q000097:blood / Q000503:physiopathology* / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D011175:Positive-Pressure Respiration / Q000009:adverse effects / Q000379:methods*; D011659:Pulmonary Gas Exchange
chemical_list: D010100:Oxygen