. Background and
Introduction
Application of an optimal level of positive
end-expiratory pressure (PEEP) is a crucial facet of optimizing mechanical
ventilation among hypoxic patients. PEEP titration is usually guided by
improvement in oxygenation and increase in the static compliance (1). The
ARDSNet table recommends PEEP levels based on the FiO2 requirement (2).
There are drawbacks associated with these methods of PEEP titration. The PaO2
levels may rise with an increase in the PEEP level due to reduced right-left
shunt 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 recruitment
on application of incremental levels of PEEP. However, hyperinflation of the
relatively 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 the
lung compliance at both levels. The R/I ratio may be a predictor of
hyperinflation in the relatively normal lung (7).
2. Objectives of the study : We aim to evaluate lung recruitment by lung ultrasonography and the
R/I ratio and correlate recruitability assessed using both techniques. We
propose to conduct this pilot study to evaluate the feasibility of performing a
larger, multicentric study on the use of ultrasonography to evaluate the
potential for lung recruitment, while minimizing the risk of hyperinflation.
3. Eligibility criteria and participant
recruitment procedure : Consecutive
mechanically ventilated patients with focal or diffuse lung pathology including
collapse, consolidation, acute respiratory distress syndrome (ARDS), and
cardiogenic pulmonary edema with the potential for lung recruitment. Diagnosis
of ARDS will be based on the Berlin criteria. Patients shall be enrolled within
48 hours of admission to the ICU.
4. Methodology –
1. Lung ultrasonography
An observer with more than 2 years ICU
experience and performed lung ultrasonography on more than 20 patients shall
assess lung recruitability. A 5 mHz curvilinear or a 8 mHz microconvex probe
will be used for ultrasonographic imaging depending on the body habitus. The
observer will record the lung aeration score based on the assessment described
by Bouhemad et al. (5), at
each 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 aeration
score, and the re-aeration score in each zone will be recorded at each level of
PEEP.
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 cm
H2O
Reduce the frequency to 8 breaths/min,
ensure that there is an end-inspiratory pause of 0.3 seconds by adjusting
the inspiratory flow (for a maximum of 5 breaths). The inspiratory pause allows
continuous measurement of plateau pressure (Pplat). Record the PEEP level, and
the Pplat. Switch back to the previous ventilator settings.
2.
Increase the PEEP to 15 cm of
H2O and continue ventilation for 20 minutes. Switch to (VC-AC) using the same
set tidal volume. Reduce the frequency to 8 breaths/min with an end-inspiratory
pause of 0.2 seconds by adjusting the flow (for a maximum of 5 breaths). This
procedure enables continuous measurement of Pplat. Drop the PEEP level to 5 cm
H2O. As the PEEP is reduced from 15 to 5 cm H2O, a large release volume
is observed for the next breath. Record the release volume and the steady-state
expired tidal volume at PEEP of 5 cm H2O.
Switch back to the baseline ventilator
settings.
The R/I ratio calculation is based on the
following 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.com
will be used to calculate the R/I ratio.
5. Risk and Benefits
:
Benefits:
i.
assessment
of 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. Obtaining
Informed consent Form: Y
7. Statistical Analysis :
Correlation between delta aeration score
and R/I ratio
Correlation between Re-aeration score and
R/I ratio
Correlation between P/F ratio and delta
aeration score
Correlation between P/F ratio and
reaeration score
Correlation between P/F ratio and R/I ratio
In patients who have spontaneous
respiratory 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 performed
using MedCalc Version 20.218.
8. Confidentiality
of the study participants : Y
9. Ethical
Consideration : none
10. References :
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derecruitment at decremental positive end-expiratory pressure levels in acute
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