Venous admixture (Qva/Q) and true shunt (Qs/Qt) in ARF patients: Effects of PEEP at constant FIO2

A. Pesenti, A. Riboni, R. Marcolin, L. Gattinoni

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Venous admixture (Qva/Q) in ARF patients is due to both true right to left shunt (Qs/Qt: perfusion of truly unventilated areas) and to maldistribution ((Qva-Qs)/Qt: effects of unevenness of ventilation/perfusion ratio). Using the retention rate of sulphur hexafluoride we determined the effects of PEEP on Qs/Qt and (Qva-Qs)/Qt at a constant FIO2 for each patient (0.57±0.19 SD, range 0.4-0.95). Eleven patients with ARF (treated either by CPPV or CPAP) were studied on 16 occasions. Each measurement was repeated at two levels of PEEP, 5 cm H2O below and 5 cm H2O above the patient's clinically determined PEEP level. The increase in PEEP resulted in: - a decrease in Qva/Q (from 0.37±0.13 to 0.27±0.12, pIO2: (Qva-Qs)/Qva=0.75-0.86 FIO2 (r=0.74, pIO2 (0.4-0.6).

Original languageEnglish
Pages (from-to)307-311
Number of pages5
JournalIntensive Care Medicine
Issue number6
Publication statusPublished - 1983


  • Acute respiratory failure
  • Inert gas retention
  • Lung arteriovenous shunt
  • Lung ventilation perfusion ratio
  • Positive end expiratory pressure
  • Sulphur hexafluoride

ASJC Scopus subject areas

  • Critical Care and Intensive Care Medicine


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