Recruitment to Lung Inflation Ratio or R/I ratio

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This article focuses on the quantitative assessment of the potential for lung recruitment, the implementation of new mechanics based index to directly quantify the potential for lung recruitment, also known as Recruitment to Inflation Ratio or R/I ratio. It is used to estimate the increase in end expiratory lung volume induced by the PEEP and how much of this increase is distributed between the recruitment lung and the inflation of the baby lung.

Detailed SummaryΒ 

The range of R/I ratio is from 0 – 2.0.

The higher the ratio, the higher is the potential for lung recruitment.

R/I = 1.0 suggests a high likelihood of recruitment as the volume will be distributed to the recruited lung and to the baby lung in a similar fashion.

Advantages –

  • Can be performed at the bedside.
  • Required only a single breath manoeuvre on any ventilator.
  • Useful in high risk of virus transmission.
  • Minimises transport and complex procedures.

𝑅 /𝐼 π‘Ÿπ‘Žπ‘‘π‘–π‘œ =( 𝑉𝑇𝑒, 𝐻→𝐿 ― 𝑉𝑇𝑒, 𝐻 / V𝑇𝑖 ) Γ— (π‘ƒπ‘π‘™π‘Žπ‘‘, 𝐿 ― 𝑃𝐸𝐸𝑃𝐿) / (𝑃𝐸𝐸𝑃𝐻 ― 𝑃𝐸𝐸𝑃𝐿)Β  ― 1

R/I Ratio may also be measured automatically through various websites and applications.

Result of Study of 12 patients ( 7 males and 5 females, ages 59+/-9 y/o)

On day of admission (Note – patients received various levels of ventilatory support before the 1st day of observation)

  • Mean PaO2/FiO2 = 130 +/- 55 mmHg
  • Mean PaCO2 = 57 +/- 27 mmHg

After 6 days of admission

  • 7 patients received atleast one session of Prone positioning
  • 3 patients received both Prone positioning and ECMO
  • 25% or 3 patients died.

Final Results

  • 83% of patients were poorly recruitable , i.e – R/I ratio = 0.21 +/- 0.14
  • Patients who did not receive prone positioning had poor recruitability.
  • Alternating Body position between Supine and Prone was associated with increased Lung recruit ability.
  • Majority of patients were poorly recruitable with high PEEP but it seemed to change with alternating body positions.


  • Lung recruitability can be assessed at the bedside.
  • Lung recruitability is low in the studied population of COVID-19 induced ARDS.

Reference Link :

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