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March 2013 RESPIRATORY CARE Journal Webcast
This webcast and any accompanying materials are
copyrighted by the American Association for
Respiratory Care (AARC). Any public display, sale,
copy or distribution of the video or materials may
only be undertaken with the prior written consent
of the AARC. Copyright 2013
Shawna Strickland, PhD, RRT-NPS, AE-C, FAARC
AARC Associate Executive Director-Education
Program Objectives
Identify the research question of the study.
Identify the study design.
Discuss the main results of the study.
Discuss the implication of the study on patient care.
March 2013 RESPIRATORY CARE Journal Webcast
Evaluation of Recruited Lung Volume at Plateau Inspiratory
Pressure with Positive End-Expiratory Pressure Using Bedside
Digital Chest X-ray in Acute Lung Injury/Acute Respiratory
Distress Syndrome Patients
Keith D. Lamb, RRT-ACCS
Surgical Critical Care
Department of Respiratory Care
Christiana Care Health System
Newark, Delaware USA
Chair, AARC Adult Acute Care Section
• Importance of preventing over distension, and loss of
lung volume in ARDS is well known
• This requires finding optimal PEEP
• Optimal PEEP is difficult to find at the bedside
– Ultrasound and Electrical Impedance Tomography
– Expensive Equipment
• Slow flow Pressure/Volume Curves with New
• Formal CT which may not be safe for all patients
Research Question
• Can bedside digital chest radiography be used to
evaluate lung recruitment and therefore appropriate
PEEP levels to maintain recruitment and avoid over
• No COI reported by any of the Authors
• Small Prospective Experiment
• 14 Patients with ALI/ARDS
• Each patient subjected to 5 and 15 of PEEP in a
random order for 10 minutes
• At the end of 10 minutes a portable/digital CXR was
obtained as well as a P/V curve
• PaO2, Cst, Cdyn, and change in EELV were measured
• Radiological attenuation was measured in 7 predetermined ROI 4 from right and 3 from left
• Ratio of lung density (rP15/P5) and the mathematical
mean (µP15/P5) were computed
• Recruited Volume (Vrec) was determined by P/V
Inclusion Criteria
• ALI/ARDS per consensus conference criteria when
using greater than or equal to 5 PEEP.
• Greater than or equal to 18 years of age
• Intubated and Mechanically Ventilated in the ICU
• Continuous IV sedation and analgesia to achieve
Ramsay Score of 6
• Vent capable of low inflation flow P/V curve
Inclusion Criteria
• No pneumothorax per CXR
• Pleural Effusion < 500ml estimated via ultrasound
• Written informed consent by next of kin
Exclusion Criteria
Thoracic surgery in previous 3 months
Recent history of pneumonectomy or lobectomy
Patient under guardianship
Refusal to participate by next of kin
• Median value of (rP15/P5) in all 98 lung levels (14
patients/7 levels each) was 0.91.
• Values were not significantly different between levels
• Median values of Vrec were 288ml
• Median value of (µP15/P5) was 0.90
• Significant negative correlation between Vrec and
• Reduction in µP15/P5 correlated with an increase in
Cdyn, and an increase in PaO2 between PEEP 15 and
Figure 1
Figure 3
Figure 4
• Digital CXR done at the bedside in ALI/ARDS patients
was able to detect a reduction in density between
PEEP of 5 and PEEP 15 which also correlated with
Statistical Analysis
• Continuous variables checked by Shapiro-Wilk test
• Intra-reader reproducibility was evaluated on all
• Primary endpoint was the relationship between
µP15/P5 and Vrec
• Secondary endpoints were the relationships between
µP15/P5 and change in PaO2, Cst, Cdyn, between
PEEP 15 and 5 cmH2O.
Statistical Analysis
• Linear regression analysis was used to evaluate these
• A P value < 0.05 was taken as the statistical
significance threshold.
• What do these findings mean?
There was a significant correlation between a decrease
in µP15/P5 (density) on digital CXR and Vrec from Pplat
corresponding to PEEP of 5 and to Pplat corresponding
to PEEP 15.
Recruited volume can be reliably evaluated with
fairly intense and pre-planned analysis via bedside
digital chest radiography.
• How should these finding impact practice?
The impact on practice that this study will have is not
clear. This method may have a role when attempting
to evaluate lung recruitment and optimal PEEP where
slow inspiratory flow P/V curve analysis, EIT, and
bedside ultrasound are not available.
• How do these findings related to previous
findings from other studies?
I could not find similar studies where density
ratios were used as surrogates for lung
recruitment. P/V curves as well as Lung Ultrasound
have been studied.
• What are the study limitations?
- Digital CXR not as sensitive to density as
other imaging.
- Difficult to evaluate for over-distension
- Regions of interest may be obscured by
lines, tubes, pads etc.
- Inter-reader variability would be difficult
to control outside of study protocols
• What additional work is needed in this area?
Future investigations of this technique to
evaluate lung volume would most likely yield
similar results. Methods to simultaneously
evaluate for over-distension may be helpful
in establishing optimal PEEP and recruitment
for ARDS patients.
Jean-Jacques Rouby MD PhD & Belaïd Bouhemad MD PhD
• The physicians that submitted the
accompanying editorial expand on limitations
of this study, as well as describe commercially
available technology to perform bedside P/V
curves as well as inherent limitations of this
strategy as well, ie the need for NMB. They
also describe bedside ultra-sound techniques
and intra-user variability among
In Summary
• Interesting well designed study looking at a
potential solution to a real life clinical problem
• Small number of patients, but population is
• Is probably safer than travelling to CT scanner
• Is probably cheaper than other methods
• May be more difficult to do than it sounds.
Need U/S to r/o significant effusion(s)

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