Publications by authors named "Hazel R Carlisle"

3 Publications

  • Page 1 of 1

Extubation generates lung volume inhomogeneity in preterm infants.

Arch Dis Child Fetal Neonatal Ed 2021 Jun 23. Epub 2021 Jun 23.

Newborn Research, The Royal Women's Hospital, Parkville, Victoria, Australia.

Objective: To evaluate the feasibility of electrical impedance tomography (EIT) to describe the regional tidal ventilation (V) and change in end-expiratory lung volume (EELV) patterns in preterm infants during the process of extubation from invasive to non-invasive respiratory support.

Design: Prospective observational study.

Setting: Single-centre tertiary neonatal intensive care unit.

Patients: Preterm infants born <32 weeks' gestation who were being extubated to nasal continuous positive airway pressure as per clinician discretion.

Interventions: EIT measurements were taken in supine infants during elective extubation from synchronised positive pressure ventilation (SIPPV) before extubation, during and then at 2 and 20 min after commencing nasal continuous positive applied pressure (nCPAP). Extubation and pressure settings were determined by clinicians.

Main Outcome Measures: Global and regional ΔEELV and ΔV, heart rate, respiratory rate and oxygen saturation were measured throughout.

Results: Thirty infants of median (range) 2 (1, 21) days were extubated to a median (range) CPAP 7 (6, 8) cm HO. SpO/FiO ratio was a mean (95% CI) 50 (35, 65) lower 20 min after nCPAP compared with SIPPV. EELV was lower at all points after extubation compared with SIPPV, and EELV loss was primarily in the ventral lung (p=0.04). V was increased immediately after extubation, especially in the central and ventral regions of the lung, but the application of nCPAP returned V to pre-extubation patterns.

Conclusions: EIT was able to describe the complex lung conditions occurring during extubation to nCPAP, specifically lung volume loss and greater use of the dorsal lung. EIT may have a role in guiding peri-extubation respiratory support.
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June 2021

Distribution of tidal ventilation during volume-targeted ventilation is variable and influenced by age in the preterm lung.

Intensive Care Med 2011 May 25;37(5):839-46. Epub 2011 Feb 25.

Neonatal Research, Royal Women's Hospital, Melbourne, Australia.

Purpose: Synchronised volume-targeted ventilation (SIPPV + VTV) attempts to reduce lung injury by standardising volume delivery to the preterm lung. The aim of this study is to describe the regional distribution and variability of ventilation within the preterm lung during SIPPV + VTV.

Methods: Twenty-seven stable, supine, preterm infants with <32 weeks gestation receiving SIPPV + VTV were studied. From each infant, the anterior-to-posterior impedance change due to tidal ventilation (∆Z (VT); countless units) was determined during every breath from three, 30-s, electrical impedance tomography recordings. ∆Z (VT) within the anterior, middle and posterior thirds of the chest were compared using area under the curve analysis. The coefficient of variation (CV) of ∆Z (VT) in the anterior and posterior hemithoraces, inflation pressure and, where available, V (T) at airway opening were compared. Infants were sub-grouped by age (≤7 and >7 days), supplemental oxygen requirement and set tidal volume.

Results: In all sub-groups, the middle third of the chest accounted for the greatest ∆Z (VT) [p < 0.0001, repeated-measures analysis of variance (ANOVA)]. The middle third of the chest constituted a greater relative ∆Z (VT) in infants aged >7 days compared with ≤7 days (p < 0.0001, repeated-measures ANOVA). Set tidal volume and oxygen requirement did not significantly influence the regional distribution of ∆Z (VT). The mean (standard deviation, SD) CV of ∆Z (VTANT) and ∆Z (VTPOST) were 30.6% (14.0%) and 31.9% (12.7%). ∆Z (VTANT) and ∆Z (VTPOST) expressed greater breath-to-breath variability than the variation in inflation pressure and V (T) at airway opening (p = 0.012 and p < 0.0001, respectively, paired t-tests).

Conclusion: During SIPPV + VTV the preterm infant exhibits marked breath-to-breath variability in regional ventilation which is influenced by age.
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May 2011

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

Intensive Care Med 2010 Dec 21;36(12):2101-8. Epub 2010 Sep 21.

Neonatal Research, Royal Women's Hospital, Melbourne, Australia.

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 (v)/ΔZ (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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December 2010