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Regional distribution of blood volume within the preterm infant thorax during synchronised mechanical ventilation

Abstract

Purpose

Perfusion in healthy adults is gravity-dependent. Little is known about lung perfusion in the preterm infant. The aim of this study was to describe the regional distribution of blood volume within the thorax in preterm infants receiving synchronised volume-targeted mechanical ventilation (SIPPV + TTV) and to compare this to regional distribution of tidal ventilation using electrical impedance tomography (EIT).

Methods

Stable supine ventilated preterm infants (<32-week gestation) were studied. Three sets of artefact-free 30-s EIT recordings of the right hemithorax were filtered in the cardiac and respiratory frequency domains to differentiate impedance change due to blood (ΔZ c) and gas volume (ΔZ v). The distribution of ΔZ c and ΔZ v in the anterior-to-posterior regions of the right chest were compared. Infants were subdivided by age (≤7, >7 days) and oxygen requirement.

Results

A total of 5,471 beats were analysed from 26 infants (78 recordings); mean (standard deviation (SD)) gestational age was 26 (2) weeks and mean (SD) postnatal age was 9 (10) days. The median (interquartile range) ΔZ c in the anterior half of the hemithorax was 1.41-fold (0.88–2.11) greater than that in the posterior half. The geometric centre of ΔZ c was located at 46.7% of the anterior-posterior thoracic distance, compared to a more centrally located ΔZ v (49.6%; p < 0.0001). The ΔZ vZ c ratio was 1.7 in the anterior third of the chest and 2.2 in the posterior (p < 0.0001). The area under the curve (AUC) analysis showed that ΔZ c was more evenly distributed in infants >7 days of age and not influenced by oxygen requirement.

Conclusions

There are gravity dependent differences in the distribution of blood volume and ventilation in the ventilated preterm chest.

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Abbreviations

BPM:

Beats/breaths per minute

c.u.:

Countless impedance units

EIT:

Electrical impedance tomography

fEIT:

Functional electrical impedance tomography

F IO2 :

Fraction of inspired oxygen concentration

HR:

Heart rate

PDA:

Patent ductus arteriosus

SIPPV:

Synchronised intermittent positive pressure ventilation

SIPPV + TTV:

Synchronised volume-targeted intermittent positive pressure ventilation

TTV:

Targeted tidal volume (volume guarantee)

ΔZ :

Change in thoracic impedance

ΔZ c :

Amplitude of impedance change in the cardiac frequency domain

ΔZ v :

Amplitude of impedance change in the respiratory frequency domain

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Acknowledgements

The authors wish to thank Brenda Argus and Stephanie Tan-Kristanto for their assistance with this study. D.G.T. is supported by a National Health and Medical Research Council Clinical Research Fellowship (Grant ID 491286), P.G.D. is supported by a NHMRC Practitioner Fellowship.

Conflict of interest

The authors declare that there are no competing interests.

Author information

Correspondence to Hazel R. Carlisle.

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Carlisle, H.R., Armstrong, R.K., Davis, P.G. et al. Regional distribution of blood volume within the preterm infant thorax during synchronised mechanical ventilation. Intensive Care Med 36, 2101–2108 (2010). https://doi.org/10.1007/s00134-010-2049-4

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Keywords

  • Infant
  • Preterm
  • Perfusion
  • Ventilation
  • Lung mechanics
  • Electrical impedance tomography