Time required for equilibration of arterial oxygen pressure after setting optimal positive end-expiratory pressure in acute respiratory distress syndrome

Crit Care Med. 2005 May;33(5):995-1000. doi: 10.1097/01.ccm.0000163402.29767.7b.


Objective: To evaluate the time course of Pao2 change following the setting of optimal positive end-expiratory pressure (PEEP) in patients with acute respiratory distress syndrome (ARDS).

Design: Prospective clinical study.

Setting: Multidisciplinary intensive care unit of a university hospital.

Patients: Twenty-five consecutive patients with ARDS.

Interventions: ARDS was diagnosed during pressure-regulated volume control ventilation with tidal volume of 7 mL/kg actual body weight, respiratory rate of 12 breaths/min, inspiratory/expiratory ratio of 1:2, Fio2 of 1, and PEEP of 5 cm H2O. A critical care attending physician obtained pressure volume curves and determined the lower inflection point. Following a rest period of 30 mins with initial ventilation variables, PEEP was set at 2 cm H2O above the lower inflection point, and serial blood samples were collected during 1-hr ventilation with optimal PEEP. Arterial blood gas analyses were performed at 1, 3, 5, 7, 9, 11, 15, 20, 30, 45, and 60 mins.

Measurements and main results: Twenty-five patients were found eligible for the study. Three patients were excluded due to deterioration of oxygen saturation and hemodynamic instability following the initiation of optimal PEEP. Eight cases (36%) were considered to be of pulmonary origin and 14 cases (64%) of extrapulmonary origin. Optimal PEEP levels were 14 +/- 3 cm H2O and 14 +/- 4 cm H2O in pulmonary and extrapulmonary ARDS, respectively. Pao2 demonstrated a 130 +/- 101% increase at the end of 1-hr period in total study population. This improvement did not differ significantly between pulmonary and extrapulmonary forms of ARDS (135 +/- 118% vs. 127 +/- 95%, p = .8). Mean 90% oxygenation time was found to be 20 +/- 19 mins. In the subset of patients with ARDS of pulmonary origin, 90% oxygenation time was 25 +/- 26 mins, whereas it was 17 +/- 15 mins in patients with ARDS of extrapulmonary origin (p = .8).

Conclusions: Our data showed that 20 mins would be adequate for obtaining a blood gas sample in ARDS patients with pulmonary and extrapulmonary origin after application of optimal PEEP 2 cm H2O above the lower inflection point.

Publication types

  • Clinical Trial

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Female
  • Humans
  • Intensive Care Units
  • Male
  • Middle Aged
  • Oxygen / blood*
  • Positive-Pressure Respiration / methods*
  • Prospective Studies
  • Respiratory Distress Syndrome / therapy*
  • Time Factors


  • Oxygen