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Parkville, Australia

Kaczka D.W.,University of Iowa | Herrmann J.,University of Iowa | Zonneveld C.E.,Neonatal Research | Tingay D.G.,University of Melbourne | And 5 more authors.
Anesthesiology | Year: 2015

Background: Despite the theoretical benefits of high-frequency oscillatory ventilation (HFOV) in preterm infants, systematic reviews of randomized clinical trials do not confirm improved outcomes. The authors hypothesized that oscillating a premature lung with multiple frequencies simultaneously would improve gas exchange compared with traditional single-frequency oscillatory ventilation (SFOV). The goal of this study was to develop a novel method for HFOV, termed "multifrequency oscillatory ventilation" (MFOV), which relies on a broadband flow waveform more suitable for the heterogeneous mechanics of the immature lung. Methods: Thirteen intubated preterm lambs were randomly assigned to either SFOV or MFOV for 1 h, followed by crossover to the alternative regimen for 1 h. The SFOV waveform consisted of a pure sinusoidal flow at 5 Hz, whereas the customized MFOV waveform consisted of a 5-Hz fundamental with additional energy at 10 and 15 Hz. Per standardized protocol, mean pressure at airway opening () and inspired oxygen fraction were adjusted as needed, and root mean square of the delivered oscillatory volume waveform (Vrms) was adjusted at 15-min intervals. A ventilatory cost function for SFOV and MFOV was defined as, where Wt denotes body weight. Results: Averaged over all time points, MFOV resulted in significantly lower VC (246.9 ± 6.0 vs. 363.5 ± 15.9 ml2 mmHg kg-1) and (12.8 ± 0.3 vs. 14.1 ± 0.5 cm H2O) compared with SFOV, suggesting more efficient gas exchange and enhanced lung recruitment at lower mean airway pressures. Conclusion: Oscillation with simultaneous multiple frequencies may be a more efficient ventilator modality in premature lungs compared with traditional single-frequency HFOV. © 2015, the American Society of Anesthesiologists, Inc. Wolters Kluwer Health, Inc. Source

Tingay D.G.,Murdoch Childrens Research Institute | Tingay D.G.,Neonatal Research | Tingay D.G.,University of Melbourne | John J.,Neonatology | And 8 more authors.
Neonatology | Year: 2015

Background: The mode of waveform generation and circuit characteristics differ between high-frequency oscillators. It is unknown if this influences performance. Objectives: To describe the relationships between set and delivered pressure amplitude (ΔP), and the interaction with frequency and endotracheal tube (ETT) diameter, in eight high-frequency oscillators. Methods: Oscillators were evaluated using a 70-ml test lung at 1.0 and 2.0 ml/cm H2O compliance, with mean airway pressures (PAW) of 10 and 20 cm H2O, frequencies of 5, 10 and 15 Hz, and an ETT diameter of 2.5 and 3.5 mm. At each permutation of PAW, frequency and ETT, the set ΔP was sequentially increased from 15 to 50 cm H2O, or from 20 to 100% maximum amplitude (10% increments) depending on the oscillator design. The ΔP at the ventilator (ΔPVENT), airway opening (ΔPAO) and within the test lung (ΔPTRACH), and tidal volume (VT) at the airway opening were determined at each set ΔP. Results: In two oscillators the relationships between set and delivered ΔP were non-linear, with a plateau in ΔP thresholds noted at all frequencies (Dräger Babylog 8000) or ≥10 Hz (Dräger VN500). In all other devices there was a linear relationship between ΔPVENT, ΔPAO and ΔPTRACH (all r2 >0.93), with differing attenuation of the pressure wave. Delivered VT at the different settings tested varied between devices, with some unable to deliver VT >3 ml at 15 Hz, and others generating VT >20 ml at 5 Hz and a 1:1 inspiratory-to-expiratory time ratio. Conclusions: Clinicians should be aware that modern high-frequency oscillators exhibit important differences in the delivered ΔP and VT. © 2015 S. Karger AG, Basel. Source

Tingay D.G.,Murdoch Childrens Research Institute | Tingay D.G.,Neonatal Research | Tingay D.G.,University of Melbourne | Rajapaksa A.,Murdoch Childrens Research Institute | And 12 more authors.
American Journal of Respiratory Cell and Molecular Biology | Year: 2016

Ineffective aeration during the first inflations at birth creates regional aeration and ventilation defects, initiating injurious pathways. This study aimed to compare a sustained first inflation at birth or dynamic end-expiratory supported recruitment during tidal inflations against ventilation without intentional recruitment on gas exchange, lung mechanics, spatiotemporal regional aeration and tidal ventilation, and regional lung injury in preterm lambs. Lambs (127 ± 2 d gestation), instrumented at birth, were ventilated for 60 minutes from birth with either lung-protective positive pressure ventilation (control) or as per control after either an initial 30 seconds of 40 cm H2O sustained inflation (SI) or an initial stepwise end-expiratory pressure recruitment maneuver during tidal inflations (duration 180 s; open lung ventilation [OLV]). At study completion, molecular markers of lung injury were analyzed. The initial use of an OLV maneuver, but not SI, at birth resulted in improved lung compliance, oxygenation, end-expiratory lung volume, and reduced ventilatory needs compared with control, persisting throughout the study. These changes were due to more uniform inter- and intrasubject gravitydependent spatiotemporal patterns of aeration (measured using electrical impedance tomography). Spatial distribution of tidal ventilation was more stable after either recruitment maneuver. All strategies caused regional lung injury patterns that mirrored associated regional volume states. Irrespective of strategy, spatiotemporal volume loss was consistently associated with upregulation of early growth response-1 expression. Our results show that mechanical and molecular consequences of lung aeration at birth are not simply related to rapidity of fluid clearance; they are also related to spatiotemporal pressure-volume interactions within the lung during inflation and deflation. Copyright © 2016 by the American Thoracic Society. Source

Harcourt E.R.,Neonatology | John J.,Neonatal Research | Dargaville P.A.,Murdoch Childrens Research Institute | Zannin E.,Polytechnic of Milan | And 7 more authors.
Pediatric Critical Care Medicine | Year: 2014

OBJECTIVES:: The differences in performance of early generation high-frequency oscillators have been attributed to their distinct pressure and flow waveforms. Recently, five new oscillators have been commercially released. The objective of this study was to characterize the pressure and flow waveforms of eight commercially available oscillators. DESIGN:: In vitro benchtop study. SETTING:: Tertiary pediatric teaching hospital. INTERVENTIONS:: Eight oscillators were evaluated using a test lung; mean airway pressure 10 and 20 cm H2O; frequencies 5, 10, and 15 Hz; pressure amplitude 30 cm H2O (or equivalent); compliance 1.0 mL/cm H2O; and endotracheal tube 3.5 mm. Ventilators tested were Sensormedics 3100A and B (Carefusion), SLE5000 (SLE), Fabian (Acutronic), Leonie+ (Heinen+Löwenstein), Sophie (Stephan), and VN500 and Babylog 8000 (Dräger). MEASUREMENTS AND MAIN RESULTS:: Pressure (airway opening, at oscillator and within the test lung) and airway opening flow waveforms were recorded. Airway opening waveforms were characterized by type (square or sine) and by determining power spectral density analysis. The Sensormedics A and B and the SLE5000 delivered square waves; all other oscillators generated sine waves. Sensormedics, the SLE5000, and the Sophie had a characteristic inspiratory slope (incisura). The pressure waveform within the test lung was a sine wave for all oscillators. Oscillators with square waves or an inspiratory incisura exhibited the highest number of nonfundamental frequency components on power spectral density analysis, suggesting more complex harmonic waveforms with potentially greater transmissive power to the lungs. At frequencies of 5 and 10 Hz, all ventilators, except Babylog 8000, generated airway pressure amplitudes greater than 28.6 cm H2O and tidal volumes greater than 6 mL at the airway opening. CONCLUSIONS:: Current high-frequency oscillators deliver different waveforms. As these may result in variable clinical performance, operators should be aware that these differences exist. Copyright © 2014 by the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies. Source

Tingay D.G.,Murdoch Childrens Research Institute | Tingay D.G.,Neonatal Research | Tingay D.G.,University of Melbourne | Bhatia R.,Murdoch Childrens Research Institute | And 10 more authors.
Pediatric Research | Year: 2014

Background:Sustained inflation (SI) at birth facilitates establishment of functional residual capacity (FRC) in the preterm lung, but the ideal lung recruitment strategy is unclear. We have compared the effect of SI and a stepwise positive end-expiratory pressure (PEEP; SEP) strategy in a preterm model.Methods:127 d gestation lambs received either 20-s SI (n = 9) or 2 cmH 2 O stepwise PEEP increases to 20 cmH 2 O every 10 inflations, and then decreases to 6 cmH 2 O (n = 10). Ventilation continued for 70 min, with surfactant administered at 10 min. Alveolar-arterial oxygen gradient (AaDO 2), compliance (C dyn), end-expiratory thoracic volume (EEV RIP; respiratory inductive plethysmography), and EEV and C dyn in the gravity-dependent and nondependent hemithoraces (electrical impedance tomography) were measured throughout. Early mRNA markers of lung injury were analyzed using quantitative real-time PCR.Results:From 15 min of life, AaDO2 was lower in SEP group (P < 0.005; two-way ANOVA). SEP resulted in higher and more homogeneous C dyn (P < 0.0001). Mean (SD) EEV RIP at 5 min was 18 (9) ml/kg and 6 (5) ml/kg following SEP and SI, respectively (P = 0.021; Bonferroni posttest); this difference was due to a greater nondependent hemithorax EEV. There was no difference in markers of lung injury.Conclusion:An SEP at birth improved gas exchange, lung mechanics, and EEV, without increasing lung injury, compared to the SI strategy used. © 2014 International Pediatric Research Foundation, Inc. Source

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