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Lung volume calculated from electrical impedance tomography in ICU patients at different PEEP levels.

Bikker IG, Leonhardt S, Bakker J, Gommers D - Intensive Care Med (2009)

Bottom Line: To evaluate repeatability, EELV was measured in quadruplicate in five additional patients.There was a significant but relatively low correlation (r = 0.79; R2 = 0.62) and moderate agreement (bias 194 ml, SD 323 ml) between DeltaEELV and change in lung volume calculated from the DeltaEELI.Good agreement was found between repeated EELV measurements and washin/washout of a simulated nitrogen washout technique.

View Article: PubMed Central - PubMed

Affiliation: Department of Intensive Care Medicine, Room H602, Erasmus MC, Postbox 2040, 3000 CA Rotterdam, The Netherlands.

ABSTRACT

Purpose: To study and compare the relationship between end-expiratory lung volume (EELV) and changes in end-expiratory lung impedance (EELI) measured with electrical impedance tomography (EIT) at the basal part of the lung at different PEEP levels in a mixed ICU population.

Methods: End-expiratory lung volume, EELI and tidal impedance variation were determined at four PEEP levels (15-10-5-0 cm H2O) in 25 ventilated ICU patients. The tidal impedance variation and tidal volume at 5 cm H2O PEEP were used to calculate change in impedance per ml; this ratio was then used to calculate change in lung volume from change in EELI. To evaluate repeatability, EELV was measured in quadruplicate in five additional patients.

Results: There was a significant but relatively low correlation (r = 0.79; R2 = 0.62) and moderate agreement (bias 194 ml, SD 323 ml) between DeltaEELV and change in lung volume calculated from the DeltaEELI. The ratio of tidal impedance variation and tidal volume differed between patients and also varied at different PEEP levels. Good agreement was found between repeated EELV measurements and washin/washout of a simulated nitrogen washout technique.

Conclusion: During a PEEP trial, the assumption of a linear relationship between change in global tidal impedance and tidal volume cannot be used to calculate EELV when impedance is measured at only one thoracic level just above the diaphragm.

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Bland–Altman analysis. Comparison of ∆end-expiratory lung volume (∆EELV) measured with a multibreath nitrogen washout technique and ∆lung volume obtained from changes in end-expiratory lung impedance (EELI) calculated with the slope between tidal impedance variation and tidal volume at 5 cm H2O PEEP. Open triangles represent patients on assisted spontaneous breathing, and black dots represent patients on controlled ventilation. The linear correlation is shown in Fig. A (see Electronic supplementary materials)
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Fig2: Bland–Altman analysis. Comparison of ∆end-expiratory lung volume (∆EELV) measured with a multibreath nitrogen washout technique and ∆lung volume obtained from changes in end-expiratory lung impedance (EELI) calculated with the slope between tidal impedance variation and tidal volume at 5 cm H2O PEEP. Open triangles represent patients on assisted spontaneous breathing, and black dots represent patients on controlled ventilation. The linear correlation is shown in Fig. A (see Electronic supplementary materials)

Mentions: The correlation between ∆lung volume measured with a multibreath simulated nitrogen washout technique and ∆lung volume calculated from EELI is shown in Fig. A (see Electronic supplementary materials); although significant, the correlation was moderate (r = 0.79, R2 = 0.62). To assess the difference between the two methods, a Bland–Altmann analysis was performed (Fig. 2). Calculating ∆lung volume from EELI resulted in an overestimation compared with the multiple breath washout technique (bias 194 ml). Large differences in ∆lung volume were found between the two methods (SD 323 ml). To calculate ∆lung volume from EIT, the ratio or slope between tidal impedance variation and tidal volume at 5 cm H2O was used. This ratio is shown in Fig. 3 for each group of patients at the PEEP levels applied. During the decremental PEEP trial, overall the decrease in the slope was significant (15 vs. 5: P < 0.001; 10 vs. 5: P < 0.001; 0 vs. 5 cm H2O: P = 0.001). In all individual patient categories this ratio was different at 15 versus 5 cm H2O PEEP; between patients the slopes also differed.Fig. 2


Lung volume calculated from electrical impedance tomography in ICU patients at different PEEP levels.

Bikker IG, Leonhardt S, Bakker J, Gommers D - Intensive Care Med (2009)

Bland–Altman analysis. Comparison of ∆end-expiratory lung volume (∆EELV) measured with a multibreath nitrogen washout technique and ∆lung volume obtained from changes in end-expiratory lung impedance (EELI) calculated with the slope between tidal impedance variation and tidal volume at 5 cm H2O PEEP. Open triangles represent patients on assisted spontaneous breathing, and black dots represent patients on controlled ventilation. The linear correlation is shown in Fig. A (see Electronic supplementary materials)
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2712617&req=5

Fig2: Bland–Altman analysis. Comparison of ∆end-expiratory lung volume (∆EELV) measured with a multibreath nitrogen washout technique and ∆lung volume obtained from changes in end-expiratory lung impedance (EELI) calculated with the slope between tidal impedance variation and tidal volume at 5 cm H2O PEEP. Open triangles represent patients on assisted spontaneous breathing, and black dots represent patients on controlled ventilation. The linear correlation is shown in Fig. A (see Electronic supplementary materials)
Mentions: The correlation between ∆lung volume measured with a multibreath simulated nitrogen washout technique and ∆lung volume calculated from EELI is shown in Fig. A (see Electronic supplementary materials); although significant, the correlation was moderate (r = 0.79, R2 = 0.62). To assess the difference between the two methods, a Bland–Altmann analysis was performed (Fig. 2). Calculating ∆lung volume from EELI resulted in an overestimation compared with the multiple breath washout technique (bias 194 ml). Large differences in ∆lung volume were found between the two methods (SD 323 ml). To calculate ∆lung volume from EIT, the ratio or slope between tidal impedance variation and tidal volume at 5 cm H2O was used. This ratio is shown in Fig. 3 for each group of patients at the PEEP levels applied. During the decremental PEEP trial, overall the decrease in the slope was significant (15 vs. 5: P < 0.001; 10 vs. 5: P < 0.001; 0 vs. 5 cm H2O: P = 0.001). In all individual patient categories this ratio was different at 15 versus 5 cm H2O PEEP; between patients the slopes also differed.Fig. 2

Bottom Line: To evaluate repeatability, EELV was measured in quadruplicate in five additional patients.There was a significant but relatively low correlation (r = 0.79; R2 = 0.62) and moderate agreement (bias 194 ml, SD 323 ml) between DeltaEELV and change in lung volume calculated from the DeltaEELI.Good agreement was found between repeated EELV measurements and washin/washout of a simulated nitrogen washout technique.

View Article: PubMed Central - PubMed

Affiliation: Department of Intensive Care Medicine, Room H602, Erasmus MC, Postbox 2040, 3000 CA Rotterdam, The Netherlands.

ABSTRACT

Purpose: To study and compare the relationship between end-expiratory lung volume (EELV) and changes in end-expiratory lung impedance (EELI) measured with electrical impedance tomography (EIT) at the basal part of the lung at different PEEP levels in a mixed ICU population.

Methods: End-expiratory lung volume, EELI and tidal impedance variation were determined at four PEEP levels (15-10-5-0 cm H2O) in 25 ventilated ICU patients. The tidal impedance variation and tidal volume at 5 cm H2O PEEP were used to calculate change in impedance per ml; this ratio was then used to calculate change in lung volume from change in EELI. To evaluate repeatability, EELV was measured in quadruplicate in five additional patients.

Results: There was a significant but relatively low correlation (r = 0.79; R2 = 0.62) and moderate agreement (bias 194 ml, SD 323 ml) between DeltaEELV and change in lung volume calculated from the DeltaEELI. The ratio of tidal impedance variation and tidal volume differed between patients and also varied at different PEEP levels. Good agreement was found between repeated EELV measurements and washin/washout of a simulated nitrogen washout technique.

Conclusion: During a PEEP trial, the assumption of a linear relationship between change in global tidal impedance and tidal volume cannot be used to calculate EELV when impedance is measured at only one thoracic level just above the diaphragm.

Show MeSH
Related in: MedlinePlus