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Establishing a gradient between partial pressure of arterial carbon dioxide and end-tidal carbon dioxide in patients with acute respiratory distress syndrome
  1. Tariq Yousuf1,
  2. Taylor Brinton1,
  3. Ghulam Murtaza1,
  4. Daniel Wozniczka1,
  5. Khansa Ahmad1,
  6. Joy Iskandar1,
  7. Raju Mehta1,
  8. Hesam Keshmiri2,
  9. Tabassum Hanif1
  1. 1Department of Medicine, Advocate Christ Medical Center, Oak Lawn, Illinois, USA
  2. 2Department of Cardiology, Illinois Masonic Medical Center, Chicago, Illinois, USA
  1. Correspondence to Dr Tariq Yousuf, Department of Medicine, Advocate Christ Medical Center, 4440 W. 95th St., Oak Lawn, IL 60453, USA; tmyousuf614{at}


End-tidal carbon dioxide (ETCO2) monitoring is useful in many situations. However, ETCO2 monitoring is unreliable in patients with acute respiratory distress syndrome (ARDS) due to widespread lung inflammation. In our study, we attempt to establish the gradient between the arterial pressure of carbon dioxide (PaCO2) and ETCO2 in patients with ARDS, which we defined as the PaETCO2 gradient. The main objective of the study was to establish a PaETCO2 gradient in each severity of ARDS. We analyzed 35 patients with ARDS and a total of 88 arterial blood gases were included. PaCO2, PaO2/FiO2 and ETCO2 were measured. Patients were stratified into mild, moderate and severe ARDS as classified by the Berlin ARDS criteria. PaCO2 and ETCO2 were compared at each severity stratification. The mean PaCO2 was 50.0, the mean ETCO2 was 26.6 and the gradient among all samples was 23.24 (±12.02). The mean gradient for each severity is as follows: mild: 19.3 (±9.9), moderate: 27.9 (±13.2) and severe: 23.9 (±7.8). The difference between the PaETCO2 gradient of the mild to moderate (p=0.001) and mild to severe groups (p=0.01) reached statistical significance. However, the difference between the moderate to severe groups did not reach statistical significance (p=0.48). We found the gradient between PaCO2 and ETCO2 in patients with ARDS is vast and tends to worsen with increasing severity of ARDS. This indicates that the gradient between the 2 may be used as an indicator of increasing severity of ARDS.

  • Respiratory Distress Syndrome, Adult
  • Intensive Care Units
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  • Competing interests None declared.

  • Ethics approval IRB.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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