Ultrasonographic Evaluation of Positive End-Expiratory Pressure–induced Lung Recruitment: Correlation with the Recruitment-to-Inflation Ratio

. Background andIntroduction

Application of an optimal level of positiveend-expiratory pressure (PEEP) is a crucial facet of optimizing mechanicalventilation among hypoxic patients. PEEP titration is usually guided byimprovement in oxygenation and increase in the static compliance (1). TheARDSNet table recommends PEEP levels based on the FiO2 requirement (2).There are drawbacks associated with these methods of PEEP titration. The PaO2levels may rise with an increase in the PEEP level due to reduced right-leftshunt in the lung, unrelated to the extent of recruitment (3).Besides, alveolar recruitment may not always lead to improved lung compliance (4).Ultrasonography enables direct visualization of the extent of lung recruitmenton application of incremental levels of PEEP. However, hyperinflation of therelatively normal lung cannot be identified by ultrasonography (5,6).

 The recruitment to inflation ration (R/I)evaluates lung compliance at a high and a low level of PEEP and compares thelung compliance at both levels. The R/I ratio may be a predictor ofhyperinflation in the relatively normal lung (7).

 2. Objectives of the study : We aim to evaluate lung recruitment by lung ultrasonography and theR/I ratio and correlate recruitability assessed using both techniques. Wepropose to conduct this pilot study to evaluate the feasibility of performing alarger, multicentric study on the use of ultrasonography to evaluate thepotential for lung recruitment, while minimizing the risk of hyperinflation.

 3. Eligibility criteria and participantrecruitment procedure : Consecutivemechanically ventilated patients with focal or diffuse lung pathology includingcollapse, consolidation, acute respiratory distress syndrome (ARDS), andcardiogenic pulmonary edema with the potential for lung recruitment. Diagnosisof ARDS will be based on the Berlin criteria. Patients shall be enrolled within48 hours of admission to the ICU.

4. Methodology –

1. Lung ultrasonography

An observer with more than 2 years ICUexperience and performed lung ultrasonography on more than 20 patients shallassess lung recruitability. A 5 mHz curvilinear or a 8 mHz microconvex probewill be used for ultrasonographic imaging depending on the body habitus. Theobserver will record the lung aeration score based on the assessment describedby Bouhemad et al. (5), ateach incremental level of PEEP from 5 cm H2O to a maximum level of 15 cm H2O.Ventilation will be continued at each incremental level of PEEP for 5 minutes.

 The aeration score, the delta aerationscore, and the re-aeration score in each zone will be recorded at each level ofPEEP.

 2. The recruitment to inflation (R/I) ratio

The procedure involves the following steps:

 1.     Switch to volume controlled –assist controlled mode (VC-AC) using the same set tidal volume and PEEP of 5 cmH2O

Reduce the frequency to 8 breaths/min,ensure that there is an end-inspiratory pause of 0.3 seconds by adjustingthe inspiratory flow (for a maximum of 5 breaths). The inspiratory pause allowscontinuous measurement of plateau pressure (Pplat). Record the PEEP level, andthe Pplat. Switch back to the previous ventilator settings.

 2.     Increase the PEEP to 15 cm ofH2O and continue ventilation for 20 minutes. Switch to (VC-AC) using the sameset tidal volume. Reduce the frequency to 8 breaths/min with an end-inspiratorypause of 0.2 seconds by adjusting the flow (for a maximum of 5 breaths). Thisprocedure enables continuous measurement of Pplat. Drop the PEEP level to 5 cmH2O. As the PEEP is reduced from 15 to 5 cm H2O, a large release volumeis observed for the next breath. Record the release volume and the steady-stateexpired tidal volume at PEEP of 5 cm H2O.

 Switch back to the baseline ventilatorsettings.

 The R/I ratio calculation is based on thefollowing equation.

 Crec = ∆Vrec / (PEEP high – PEEP low) (1)

 (Crec = compliance of the recruited lung;∆Vrec = change in lung volume)

 R/I ratio = Crec / Crs at low PEEP (2)

 (Crs = respiratory system compliance)

 The online tool available at www.rtmaven.comwill be used to calculate the R/I ratio.

 5. Risk and Benefits**:**

Benefits:

i.        assessmentof lung recruitability

ii.       Titration of PEEP levels

iii.     Improvement of oxygenation

iv.      Reduction of driving pressure

v.       Reduction of VILI

 Risks:

vi.      Hemodynamic instability

vii.    Barotrauma

6. ObtainingInformed consent Form**:** Y

7. Statistical Analysis :

Correlation between delta aeration scoreand R/I ratio

Correlation between Re-aeration score andR/I ratio

Correlation between P/F ratio and deltaaeration score

Correlation between P/F ratio andreaeration score

Correlation between P/F ratio and R/I ratio

 In patients who have spontaneousrespiratory efforts only the following scores will be recorded

 Delta aeration score and P/F ratio

Reaeration score and P/F ratio

 All statistical analysis will be performedusing MedCalc Version 20.218.

 8. Confidentialityof the study participants : Y

9. EthicalConsideration : none

 10. Reference****s :

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2.  Brower RG, Lanken PN, MacIntyre N, Matthay MA,Morris A, Ancukiewicz M, et al. Higher versus lower positive end-expiratorypressures in patients with the acute respiratory distress syndrome. N Engl JMed. 2004 Jul 22;351(4):327–36.

3.  Delong P, Murray JA, Cook CK. Mechanicalventilation in the management of acute respiratory distress syndrome. SeminDial. 2006;19(6):517–24.

4.  Hess DR. Recruitment Maneuvers and PEEPTitration. Respir Care. 2015 Nov 1;60(11):1688–704.

5.  Bouhemad B, Brisson H, Le-Guen M, Arbelot C,Lu Q, Rouby JJ. Bedside ultrasound assessment of positive end-expiratorypressure-induced lung recruitment. Am J Respir Crit Care Med. 2011 Feb1;183(3):341–7.

6.  Chiumello D, Mongodi S, Algieri I, Vergani GL,Orlando A, Via G, et al. Assessment of Lung Aeration and Recruitment by CT Scanand Ultrasound in Acute Respiratory Distress Syndrome Patients. Crit Care Med.2018 Nov;46(11):1761–8.

7.  Stevic N, Chatelain E, Dargent A, Argaud L,Cour M, Guérin C. Lung Recruitability Evaluated by Recruitment-to-InflationRatio and Lung Ultrasound in COVID-19 Acute Respiratory Distress Syndrome. Am JRespir Crit Care Med. 2021 Apr 15;203(8):1025–7.

8.  Mercat A, Richard JCM, Vielle B, Jaber S,Osman D, Diehl JL, et al. Positive end-expiratory pressure setting in adultswith acute lung injury and acute respiratory distress syndrome: a randomizedcontrolled trial. JAMA. 2008 Feb 13;299(6):646–55.

9.  Meade MO, Cook DJ, Guyatt GH, Slutsky AS,Arabi YM, Cooper DJ, et al. Ventilation strategy using low tidal volumes,recruitment maneuvers, and high positive end-expiratory pressure for acute lunginjury and acute respiratory distress syndrome: a randomized controlled trial.JAMA. 2008 Feb 13;299(6):637–45.

10.       Chen L, Del Sorbo L, Grieco DL,Junhasavasdikul D, Rittayamai N, Soliman I, et al. Potential for LungRecruitment Estimated by the Recruitment-to-Inflation Ratio in AcuteRespiratory Distress Syndrome. A Clinical Trial. Am J Respir Crit Care Med.2020 Jan 15;201(2):178–87.

11.       Pan C, Chen L, Lu C, Zhang W, Xia JA,Sklar MC, et al. Lung Recruitability in COVID-19-associated Acute RespiratoryDistress Syndrome: A Single-Center Observational Study. Am J Respir Crit CareMed. 2020 May 15;201(10):1294–7.