Roland R. Wauer

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.

Outcome of 60 neonates who had ARED flow prenatally compared with a matched control group of appropriate‐for‐gestational age preterm neonates

To describe the course and outcome of fetuses with absent or reversed end‐diastolic (ARED) flow in the umbilical artery (UA) and to examine the influence of prematurity according to gestational age at delivery.

Effect of apparatus dead space on breathing parameters in newborns: “flow-through” versus conventional techniques

Commercial devices for tidal breathing measurements in newborns allow only short-term measurements, due to the high apparatus dead space of the face mask and pneumotachometer. The flow-through technique (FTT) minimizes the dead space by a background flow, thereby allowing long-term measurements. The aim of this study was to investigate the comparability of tidal breathing parameters using both techniques. Paired measurements of tidal breathing were performed in 86 sleeping infants (median (range) body weight 2.8 kg (1.9-5.3 kg), age 65 days (3-150 days)), using the FTT and SensorMedics 2600 (SM 2600). There was a significant bias (p <0.001) in all tidal breathing parameters. Compared with the FTT, increases (95% confidence interval (CI)) in tidal volume (VT), respiratory frequency (fR), and minute ventilation (VE) were 0.74 (0.5-1.0) mL.kg(-1), 9.0 (6.9-11.2).min(-1) and 92 (74-109) mL.min(-1).kg(-1) when measured with the SM 2600, representing average increases of 13, 17 and 30%, respectively, in response to the added dead space. By contrast, time to peak tidal expiratory flow as a proportion of expiratory time (tPTEF/tE) was changed by -0.09 (-0.11-0.08). The mean (95% CI) change in tPTEF/tE of -54 (-62-45)%, when measured in infants by the SM 2600, was remarkably similar to that observed during in vitro validation studies (-59 (-73-44)%), suggesting that the discrepancies in timing parameters may be largely attributable to differences in signal processing. In conclusion, differences in measurement technique and precision of the devices used can result in significant differences in tidal breathing parameters. This may impede the comparison of results within and between infants and the clinical interpretation of tidal breathing measurements in newborns.

Randomized double blind trial of Ambroxol for the treatment of respiratory distress syndrome

In order to test the ability of Ambroxol to improve the clinical course of respiratory distress syndrome and to reduce the incidence of complications a multicentre, randomized, placebo-controlled double-blind trial was conducted. Entry was limited to infants with a birth weight below 1500g. A total of 179 neonates were enrolled, but 31 were later excluded because they had other diseases. Of the remaining 148 babies, 74 received Ambroxol (birth weight 1190±216g; gestational age 29.1±1.9 weeks) and 74 placebo (birth weight 1168±216g; gestational age 28.9±1.9 weeks). In the Ambroxol group 23 (31%) and in the placebo group 27 (37%) infants died during the first 5 months of life. In 28 day-survivors Ambroxol was able to significantly improve the PaO2/FiO2 ratio, mean airway pressure, phospholipid profile of tracheal effluent and pulmonary mechanics of spontaneously breathing infants. In addition, the incidences of bronchopulmonary dysplasia (29% vs 54%), intraventricular haemorrhage (25% vs 44%) and postnatally acquired pneumonia (15% vs 36%) were significantly reduced in the Ambroxol group as compared to the control group. No adverse events attributed to the Ambroxol treatment were reported.

In vitro assessment of equipment and software to assess tidal breathing parameters in infants

The aim of this in vitro study was to compare the measurement accuracy of two currently available devices for measuring tidal breathing in infants. A mechanical model pump was used to generate flow profiles which simulated those observed in infants. A range of flows was applied simultaneously to two different devices, namely the commercially available SensorMedics 2600 (SM 2600) and more recently developed, custom-made equipment based on the flow-through technique (FTT). Automatically derived values from both devices were compared with one another and with manual calculations of printouts of the same breaths. There were no differences in the raw flow signal obtained from the two devices, nor between values calculated automatically or manually from the FTT. Similarly, the deviations between the FTT and SM 2600 were <3% for tidal volume, respiratory frequency and minute ventilation. However, when comparing either with manually calculated values or those derived automatically from the FTT, there was a systematic and highly significant underestimation of shape-dependent parameters, such as the time to peak tidal expiratory flow as a proportion of tidal expiratory time (tPTEF/tE), derived by the SM 2600. The lower the applied flow, the higher the observed deviations, the underestimation being up to 60% when flows simulating those observed in preterm neonates were applied. These errors appear to result from differences in signal processing such as the algorithms used for breath detection and can only be detected if appropriate nonsinusoidal flow profiles representing those seen in infants are used to evaluate equipment.

Right-sided pulmonary aplasia: longitudinal lung function studies in two cases and comparison to results from term healthy neonates.

Agenesis of the right lung was diagnosed prenatally in two neonates born at 36 and 37 weeks, respectively. Computed tomographic scans and magnetic resonance imaging indicated that both cases had a Type 2 pulmonary agenesis, which was confirmed later by bronchoscopy. Both patients were clinically stable during the neonatal period. Serial pulmonary function tests revealed a decrease in specific respiratory system compliance (sCrs) in both neonates and a marked discrepancy between functional residual capacity measured by the nitrogen washout technique (FRCN2) and by plethysmography (FRCpleth) on follow‐up. Early decrease of respiratory system compliance (Crs) and increase of respiratory system resistance (Rrs) in one infant preceded the onset of tracheal stenosis, which remained asymptomatic until the age of 8 weeks, when the infant developed acute respiratory failure requiring intubation and mechanical ventilation with high airway pressures. Aortopexy, implantation of a tissue expander into the right hemithorax, and laser ablation of fibrotic tissue at the site of tracheal stenosis were performed to achieve successful extubation. The second infant remained asymptomatic. Values for lung mechanics and volumes for both infants with pulmonary aplasia were as follows: Crs, 3.43 and 10.60 mL · kPa−1 · kg−1; sCrs, 0.23 and 1.28 kpa−1; Rrs, 11.1 and 7.4 kpa · s · L−1; FRCN2, 14.9 and 10.2 mL · kg−1; FRCpleth, 28.2 and 25.8 mL · kg−; FRCN2: FRCpleth ratio, 0.56 and 0.54 for patients 1 and 2, respectively. These values differed considerably from results of a control group of nine term healthy neonates (Crs, 10.0 ± 1.8 mL · kPa−1 · kg−1; sCrs, 0.43 ± 0.08 kpa−1; Rrs, 5.10 ± 0.55 kpa · s · L−1; FRCN2, 24.0 ± 2.5 mL · kg−1; FRCpleth, 31.1 ± 6.0 mL · kg−1; FRCN2:FRCpleth ratio, 0.78 ± 0.10). In conclusion, serial assessment of lung mechanics and pulmonary gas volumes detects airway obstruction early in neonates with unilateral lung agenesis. Bronchoscopy is recommended. Along with conventional surgical procedures, an expandable implant may improve management or prevent respiratory failure in selected cases. Pediatr Pulmonol. 1998; 26:138–144.

Changes in pulmonary function in preterm infants recovering from RDS following early treatment with ambroxol: Results of a randomized trial

Several studies have demonstrated that ambroxol stimulates surfactant synthesis and has antioxidative and antiinflammatory effects. We investigated the effect of ambroxol on lung function in newborns with respiratory distress syndrome (RDS) weighing <1,500g. In all, 102 newborns were enrolled (52 received ambroxol and 50 placebo). After extubation, lung function tests were performed weekly using a face mask for ventilatory measurements and a catheter tip pressure transducer (diameter 1.7 mm) for esophageal pressure measurements (Pes). The flow‐through technique was used to eliminate apparatus dead space and to allow long‐term measurements during quiet sleep. Percentile curves of pulmonary function parameters from healthy newborns were used for comparison.

Assessment of volume and leak measurements during CPAP using a neonatal lung model.

Although several commercial devices are available which allow tidal volume and air leak monitoring during continuous positive airway pressure (CPAP) in neonates, little is known about their measurement accuracy and about the influence of air leaks on volume measurement. The aim of this in vitro study was the validation of volume and leak measurement under CPAP using a commercial ventilatory device, taking into consideration the clinical conditions in neonatology. The measurement accuracy of the Leoni ventilator (Heinen & Löwenstein, Germany) was investigated both in a leak-free system and with leaks simulated using calibration syringes (2-10 ml, 20-100 ml) and a mechanical lung model. Open tubes of variable lengths were connected for leak simulation. Leak flow was measured with the flow-through technique. In a leak-free system the mean relative volume error +/-SD was 3.5 +/- 2.6% (2-10 ml) and 5.9 +/- 0.7% (20-60 ml), respectively. The influence of CPAP level, driving flow, respiratory rate and humidification of the breathing gas on the volume error was negligible. However, an increasing F(i)O(2) caused the measured tidal volume to increase by up to 25% (F(i)O(2) = 1.0). The relative error +/- SD of the leak measurements was -0.2 +/- 11.9%. For leaks > 19%, measured tidal volume was underestimated by more than 10%. In conclusion, the present in vitro study showed that the Leoni allowed accurate volume monitoring under CPAP conditions similar to neonates. Air leaks of up to 90% of patient flow were reliably detected. For an F(i)O(2) > 0.4 and for leaks > 19%, a numerical correction of the displayed volume should be performed.

In vitro validation of an ultrasonic flowmeter in order to measure the functional residual capacity in newborns

Ultrasonic transit-time airflow meters (UFM) allow simultaneous measurements of volume flow V(t) and molar mass MM(t) of the breathing gas in the mainstream. Consequently, by using a suitable tracer gas the functional residual capacity (FRC) of the lungs can be measured by a gas wash-in/wash-out technique. The aim of this study was to investigate the in vitro accuracy of a multiple-breath wash-in/wash-out technique for FRC measurements using 4% sulphur hexafluoride (SF6) in air. V(t) and MM(t) were measured with a Spiroson SCIENTIFIC flowmeter (ECO Medics, CH) with 1.3 ml dead space. Linearity of airflow and MM were tested using different tidal volumes (V(T)) and breathing gases with different O2 and SF6 concentrations. To determine the accuracy of FRC measurements SF6 wash-in and wash-out curves from four mechanical lung models (FRC of 22, 53, 102 and 153 ml) were evaluated by the Spiroson. For each model five measurements were performed with a physiological V(T)/FRC ratio of 0.3 and constant respiratory rate of 30 min(-1). The error of measured V(T) (range 4-60 ml) was <2.5%. There was a strong correlation between the measured and calculated MM of different breathing gases (r = 0.989), and the measuring accuracy was better than 1%. The measured FRC of the four models were 20.3, 49.7, 104.3 and 153.4 ml with a coefficient of variation of 16.5%, 4.5%, 4.9% and 3%. Accordingly, for FRC <100 ml the in vitro accuracy was better than 8% and for FRC >100 ml better than 2.5%. The determination of FRC by MM measurements using the UFM is a simple and cost-effective alternative to conventionally used gas analysers with an acceptable accuracy for many clinical purposes.

Does fetal tracheal fluid flow during fetal breathing movements change before the onset of labour

Objective To examine changes in intra‐tracheal fluid flow parameters during fetal breathing movements throughout the second half of pregnancy in the normally developing human fetus.