B. Foitzik

Accuracy of Volume Measurements in Mechanically Ventilated Newborns: A Comparative Study of Commercial Devices

Objective. Ventilatory measurements in ventilated newborns are increasingly used to monitor and to optimize mechanical ventilation. The aim of this study was to compare the accuracy of volume measurements by different instruments using standardized laboratory conditions. Methods. The accuracy of displayed volume values of different commercial devices (Bicore CP-100, Ventrak 1500, Ventrak 1550, Babylog 8000, PEDS IV and SensorMedics 2600) was investigated using adjustable calibration syringes (volume range 2–60 ml, breathing rates 30/min–60/min) and humidified (>95%), heated (35 °C) breathing gas with adjustable FIO2 (0.21–1.0). The pneumotach and also the tubes were placed within an incubator (37 °C). Results. The relative volume error of all devices was in conformity with clinically allowed tolerances (Bicore CP-100 6.4 ± 0.5% (mean ± SD), Ventrak 1500 3.6 ± 4.2%, Ventrak 1550 6.5 ± 2.7%, Babylog 8000 −5.5 ± 1.5%, PEDS IV −4.0 ± 1.4%, SensorMedics 2600 3.5 ± 1.75%) for the measuring range studied (10 ml < V < 60 ml, rate 30–60/min, FIO2 = 0.21). Unacceptable errors were obtained for volumes lower than 10 ml with Bicore CP-100 (−28.5 ± 26%) and PEDS IV (−10.3 ± 3.4%). Changes in FIO2 had an important influence on volume measurements and only the SensorMedics 2600 and the PEDS IV corrected properly for FIO2 changes. Conclusion. Most of the currently available neonatal spirometry devices allow sufficiently accurate volume measurements in the range of 10–60 ml and at frequencies between 30–60/min provided that an increased FIO2 is taken into account.

Influence of preterm onset of inspiration on tidal breathing parameters in infants with and without CLD.

The preterm onset of inspiration (POI) is a well-known breathing strategy in newborns to increase their end-expiratory lung volume. The aim of this study was to investigate to which extent POI is related to tidal breathing (TB) parameters in healthy neonates (n=54) and infants with chronic lung diseases (CLD, n=45) with same postconceptional age. Using the deadspace free flow-through technique, 10-60 consecutive breaths were evaluated during quiet sleep and POI was derived from the averaged flow-volume loop considering the end-expiratory flow level. Respiratory rate (RR), ventilation (VE) and peak flows were significantly higher in CLD infants compared with controls. The incidence of POI did not differ significantly between both patient groups. POI is strongly associated with TB parameters describing the shape of flow profiles or flow-volume loops. In contrast, TB parameters, which depend only on breathing depth and rate (e.g., RR, VT, VE), were not significantly associated. The study shows that in infants TB parameters describing the flow profile may reflect differences in breathing strategy rather than impaired respiratory functions.

Deadspace free ventilatory measurements in newborns during mechanical ventilation

ObjectiveTo improve the accuracy of ventilatory measurements in ventilated newborns by means of a numerical correction when a deadspace free differential measuring method using two pneumotachographs (PNTs) is applied and to investigate the clinical usefulness of this correction procedure. DesignIn vitro study and prospective animal study. SettingResearch laboratory of the Clinic of Neonatology and the Animal Research Laboratory, Charité Hospital Berlin. SubjectsTen newborn piglets, weighing 610–1340 g (median, 930 g), age <12 hrs. InterventionsThe accuracy of both the deadspace free method and the endotracheal flow measurements (conventional method) was investigated using mechanical lung models. A correction procedure for the deadspace free method was developed considering signal delay time and tube compliance between both PNTs. This method was applied to the piglets measured during partial liquid ventilation (PLV). Measurements were done before and after lung lavage and during 30 and 120 mins of PLV (30 mL/kg body weight perfluorocarbon). Measurements and Main Results In vitro measurements showed volume differences between both methods of 8%, 12%, 16%, and 17%, respectively, depending on the distance between the PNTs of 10, 60, 120, and 180 cm. After applying the correction algorithm, the differences decreased to 3%, 0%, −2%, and −8%, respectively. The piglets were measured with 120-cm tube length between the PNTs. The correction algorithm reduced the measured tidal volume before lavage by 7%, after lavage by 14%, 30-min PLV by 12%, and 120-min PLV by 10%, corresponding to the changes in respiratory compliance of 1.2, 0.6, 1.0, and 1.1 mL/cm H2O. ConclusionsThe deadspace free method can be advantageously used for continuous measurements in newborns despite much higher technical expense. The correcting procedure improved the accuracy of the volume measurement remarkably, especially for lower respiratory compliance.

Einfluß der physikalischen Eigenschaften des Atemgases auf die pneumotachographische Ventilationsmessung bei Neugeborenen - Effect of the Physical Properties of Respiratory Gas on Pneumotachographic Measurement of Ventilation in Neonates

UNLABELLED The measurement of ventilation in neonates has a number of specific characteristics; in contrast to lung function testing in adults, the inspiratory gas for neonates is often conditioned. In pneumotachographs (PNT) based on Hagen-Poiseuilles law, changes in physical characteristics of respiratory gas (temperature, humidity, pressure and oxygen fraction [FiO2]) produce a volume change as calculated with the ideal gas equation p*V/T = const; in addition, the viscosity of the gas is also changed, thus leading to measuring errors. In clinical practice, the effect of viscosity on volume measurement is often ignored. The accuracy of these empirical laws was investigated in a size 0 Fleisch-PNT using a flow-through technique and variously processed respiratory gas. Spontaneous breathing was simulated with the aid of a calibration syringe (20 ml) and a rate of 30 min-1. RESULTS The largest change in viscosity (11.6% at 22 degrees C and dry gas) is found with an increase in FiO2 (21...100%). A rise in temperature from 24 to 35 degrees C (dry air) produced an increase in viscosity of 5.2%. An increase of humidity (0...90%, 35 degrees C) decreased the viscosity by 3%. A partial compensation of these viscosity errors is thus possible. Pressure change (0...50 mbar, under ambient conditions) caused no measurable viscosity error. With the exception of temperature, the measurements have shown good agreement between the measured volume measuring errors and those calculated from viscosity changes. CONCLUSIONS If the respiratory gas differs from ambient air (e.g. elevated FiO2) or if the PNT is calibrated under BTPS conditions, changes in viscosity must not be neglected when performing accurate ventilation measurements. On the basis of the well-known physical laws of Dalton, Thiesen and Sutherland, a numerical correction of adequate accuracy is possible.

Measurement of changes in respiratory mechanics during partial liquid ventilation using jet pulses

ObjectiveTo compare the changes in respiratory mechanics within the breathing cycle in healthy lungs between gas ventilation and partial liquid ventilation using a special forced-oscillation technique. DesignProspective animal trial. SettingsAnimal laboratory in a university setting. SubjectsA total of 12 newborn piglets (age, <12 hrs; mean weight, 725 g) InterventionsAfter intubation and instrumentation, lung mechanics of the anesthetized piglets were measured by forced-oscillation technique at the end of inspiration and the end of expiration. The measurements were performed during gas ventilation and 80 mins after instillation of 30 mL/kg perfluorocarbon PF 5080. Measurements and Main ResultsBrief flow pulses (width, 10 msec; peak flow, 16 L/min) were generated by a jet generator to measure the end-inspiratory and the end-expiratory respiratory input impedance in the frequency range of 4–32 Hz. The mechanical variables resistance, inertance, and compliance were determined by model fitting, using the method of least squares. At least in the lower frequency range, respiratory mechanics could be described adequately by an RIC single-compartment model in all piglets. During gas ventilation, the respiratory variables resistance and inertance did not differ significantly between end-inspiratory and end-expiratory measurements (mean [sd]: 4.2 [0.7] vs. 4.1 [0.6] kPa·L−1·sec, 30.0 [3.2] vs. 30.7 [3.1] Pa·L−1·sec2, respectively), whereas compliance decreased during inspiration from 14.8 (2.0) to 10.2 (2.4) mL·kPa−1·kg−1 due to a slight lung overdistension. During partial liquid ventilation, the end-inspiratory respiratory mechanics was not different from the end-inspiratory respiratory mechanics measured during gas ventilation. However, in contrast to gas ventilation during partial liquid ventilation, compliance rose from 8.2 (1.0) to 13.0 (3.0) mL·kPa−1·kg−1 during inspiration. During expiration, when perfluorocarbon came into the upper airways, both resistance and inertance increased considerably (mean with 95% confidence interval) by 34.3% (23.1%–45.8%) and 104.1% (96.0%–112.1%), respectively. ConclusionsThe changes in the respiratory mechanics within the breathing cycle are considerably higher during partial liquid ventilation compared with gas ventilation. This dependence of lung mechanics from the pulmonary gas volume hampers the comparability of dynamic measurements during partial liquid ventilation, and the magnitude of these changes cannot be detected by conventional respiratory-mechanical analysis using time-averaged variables.

Novel technique to average breathing loops for infant respiratory function testing.

Breathing loops can be obtained by plotting two respiratory signals on an x-y diagram: the resulting loops represent a non-parametric, description of the respiratory system. In infancy, loops are commonly measured during tidal breathing and their interpretation is hampered by high within-subject variability. Therefore a two-dimensional averaging technique for loops has been developed. The algorithm is based on segmentation of the loops and required two steps. First, the total length of the loop of every breathing cycle was divided into a specified number of equidistant intervals and the co-ordinates calculated by stepwise linear approximation of the curve. Second, averaged loops were calculated using the arithmetical mean (or the median if there were artifacts) of the x and y co-ordinates of the loops for all calculated points. To compare the new technique with averaging in the time domain a simulation study was performed using respiratory signals with a coefficient of variation (CV) of 5%, 10%, 15% and 20%. In contrast to the new technique, with increasing CV, averaging in the time domain led to increasing contortions in the averaged flow-volume loops. Mean errors of peak tidal expiratory flow were −3.3%, −13.9%, −21.3% and −34.2%, whereas errors with the new technique were considerably lower (0.5%, 0.4%, 0.5% and −0.1%) and independent of the level of CV.

Time of measurement influences the variability of tidal breathing parameters in healthy and sick infants

The aim of this study was to investigate the influence of the time, when measuring tidal breathing parameters 1 min (epoch 1) and 5 min (epoch 2) after application of the facemask in healthy infants and infants with bronchopulmonary dysplasia (BPD), using the dead space free flow-through technique. In both patient groups, there were no statistically significant differences between epoch 1 and 2, in most of the tidal breathing parameters, except an increased VE and increased correlation dimension of the respiratory signal in the BPD infants in epoch 1. However, in nearly all parameters the coefficient of variation (CV) was significantly higher in epoch 1 compared with epoch 2, and in some infants, we found very high CVs (>50%) in epoch 1, which disappeared in epoch 2. The study shows that after having applied the facemask, a sufficient amount of adaptation time is necessary in order to reduce the within-subject variability and improve the reproducibility and interpretation of tidal breathing measurements in infants.

Einfluß eines Hintergrundflows auf die Genauigkeit der Atemflow- und Atemvolumenmessung bei Neugeborenen - Effect of a Background Flow on the Accuracy of Ventilatory Measurements in Neonates

Bei Neugeborenen hat wegen der geringen Atemzugvolumina der apparative Totraum einen erheblichen Einfluß auf Ventilation und Gasaustausch. Deshalb sind in diesem Alter für Langzeitmessungen totraumfreie Meßverfahren erforderlich. Bei der Flow-Through-Technik wird die Rückatmung des ausgeatmeten CO2 durch einen Hintergrundflow vermieden, welcher Pneumotachograph (PNT) sowie Gesichtsmaske ständig durchströmt. Sein Einfluß auf die Genauigkeit der pneumotachographischen Volumenmessung soll untersucht werden. Die hierfür benutzte Meßanordnung besteht aus zwei identischen Baby-PNT (Jäger/BRD) und einem dazwischen befindlichen Meßaufnehmer (einfaches T-Stück ID 8 mm; Gesichtsmaske, 50 ml; Gesichtskammer FC100 Siemens Elema/Schweden, 850 ml), wobei der Hintergrundflow von 0 bis 7 l/min variierte. Die Spontanatmung wurde mit einer 100-ml-Kalibrierspritze (Rudolph/USA) in den Volumenbereichen 20, 40, 60,100 ml bei einer Frequenz von 30 min~ simuliert. Zur Untersuchung der Meßdynamik der gesamten Anordnung sind mit einem schnellen Magnetventil (Anstiegszeit <2 ms) Flowsprünge erzeugt und die Sprungantworten mittels Fourieranalyse ausgewertet worden. Bei den durchgeführten Untersuchungen konnten keine signifikanten Abhängigkeiten des Volumenmeßfehlers von der Größe des Atemzugvolumens und der Art der Gesichtsmaske festgestellt werden. Eine Erhöhung des Hintergrundflows führte zu einer Unterbestimmung des Volumens von maximal 3 %. Die Volumina der Meßaufnehmer sowie der Hintergrundflow beeinflußten den Frequenzgang der Meßanordnung kaum, während die Längen der PNT-Schläuche einen erheblichen Einfluß auf die Resonanzfrequenz hatten (68 Hz bei 0,5 m; 48 Hz bei l m; 31 Hz bei 1,7 m). Die Untersuchungen haben gezeigt, daß der Einfluß des Hintergrundflows auf die Genauigkeit der pneumotachographischen Volumenmessung vernachlässigbar ist, vorausgesetzt, es werden zwei identische PNT mit einem großen Linearitätsbereich und ausreichend hoher Grenzfrequenz eingesetzt. Dominierend für die dynamischen Systemeigenschaften ist die Schlauchlänge der PNT, die so kurz wie möglich sein sollte.

Interaktives Computerprogramm zur Zerlegung des Beatmungsdruckes bei Neugeborenen in seine elastischen, viskösen und inertiven Bestandteile

EINLEITUNG: Bei der Atemfunktionsdiagnostik an Neugeborenen unterliegen die Meßsignale während der Beatmung zahlreichen Störeinflüssen (z.B. Überlagerung der Beatmungssignale durch Spontanatmung, Auftreten von Lecks am Beatmungstubus, Störungen durch Kondensvvasser), so daß nur durch den Untersucher geeignete Meßintervalle gefunden werden können, was sich vor allem bei gestörten Meßsignalen bewährt hat. Ebenfalls bewährt hat sich die interaktive Auswertung von Atemschleifen, wie Abb. l am Beispiel der Bestimmung von Parametern der Fluß-Volumen-Kurve [1] zeigt:

Modelluntersuchungen zur Bestimmung der Inertance des respiratorischen Systems bei beatmeten Neugeborenen mit Jet-Impulsen

Die Forced Oscillation Technique (FOT) ist ein mitarbeitsunabhangiges, nichtinvasives Verfahren zur Untersuchung der Atemmechanik und auch fur Neugeborene interessant. Eine Miniaturisierung der Mestechnik ist durch Einsatz von Jet-Impulsen moglich. Die FOT ermoglicht die Bestimmung der Inertance des respiratorischen Systems, die bei maschineller Beatmung wegen der hohen Volumenbeschleunigung wie auch bei krankheitsbedingten Flussigkeitseinlagerungen in der Lunge klinisch relevant ist. Die Messung der Inertance eroffnet bei Neugeborenen neue diagnostische Moglichkeiten fur die Atemfunktionsdiagnostik unter Beatmung sowie bei der Surfactant-Therapie oder Partial-Liquid Ventilation.