Accuracy of tidal volume, compliance, and resistance measurements on neonatal ventilator displays: An in vitro assessment
ABSTRACT To determine the accuracy of measures of respiratory mechanics derived from neonatal ventilators using an in vitro passive physical lung model to simulate newborn pulmonary conditions.
Test lung models.
Three test lungs were constructed to simulate three severities of neonatal lung disease, with ranges of compliance from 0.5 to 2.0 mL/cm H2O and resistance from 25 to 150 cm H2O/(L/sec). Each ventilator was tested using 27 combinations of peak inspiratory pressure (15-25 cm H2O), positive end-expiratory pressure (5-7 cm H2O), and rate settings (20-60 B/min). Data were compared for five different ventilators across simulated lung severity as the ratio of ventilator readout to test lung reference value. A ratio of 1.0 indicated a completely unbiased result.
Overall, four of the five ventilators under-read expired tidal volume by about 1%-12% across all lung conditions, whereas the VIP Bird readout ranged from -4% to +4% bias. Changes in ventilator settings had only a modest effect on mechanics readout. As peak inspiratory pressure progressed from 15 to 25 cm H2O, bias in tidal volume readout changed from +5.0% to -2.5% (p < .001) in the VIP Bird, and from -11% to -9% (p < .001) in the Draeger Babylog VN500. Between positive end-expiratory pressure levels of 5 and 7 cm H2O, tidal volume bias in the Babylog varied between -13% and -7% (p < .001). In progressing from simulated normal to severely ill lung condition, bias in compliance measurements by the Avea and SLE5000 increased from -18% to -40% whereas in the VIP Bird it remained between -17% to -13%, and in the Draeger Evita XL-neo it changed from +17% to -13% and from -8% to -16% in the Babylog. Ratio of ventilator resistance readout to reference value with progressing simulated lung condition changed from 2.0 to 1.0 for the Draeger Evita, 1.6 to 1.1 for the Babylog, 4.2 to 2.0 for the SLE, and from 11.7 to 5.6 for the VIP Bird. The Avea, by design, did not display resistances >100 cm H2O/(L/sec), but overestimated the simulated normal lung resistance of 25 cm H2O/(L/sec) by a factor of 2.5.
Neonatal ventilator respiratory mechanics measurements and computation methods need further standardization to be useful in clinical settings.
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ABSTRACT: Increased use of non-invasive forms of respiratory support such as CPAP and HFNC in premature infants has generated a need for further investigation of the pulmonary effects of such therapies. In a series of in vitro tests, we measured delivered proximal airway pressures from a HFNC system while varying both the cannula flow and the ratio of nasal prong to simulated nares diameters. Neonatal and infant sized nasal prongs (3.0 and 3.7 mm O.D.) were inserted into seven sizes of simulated nares (range: 3-7 mm I.D. from anatomical measurements in 1-3 kg infants) for nasal prong-to-nares ratios ranging from 0.43 to 1.06. The nares were connected to an active test lung set at: TV 10 ml, 60 breaths/min, Ti 0.35 sec, compliance 1.6 ml/cm H(2) O and airway resistance 70 cm H(2) O/(L/sec), simulating a 1-3 kg infant with moderately affected lungs. A Fisher & Paykel Healthcare HFNC system with integrated pressure relief valve was set to flow rates of 1-6 L/min while cannula and airway pressures and cannula and mouth leak flows were measured during simulated mouth open, partially closed and fully closed conditions. Airway pressure progressively increased with both increasing HFNC flow rate and nasal prong-to-nares ratio. At 6 L/min HFNC flow with mouth open, airway pressures remained <1.7 cm H(2) O for all ratios; and <10 cm H(2) O with mouth closed for ratios <0.9. For ratios >0.9 and 50% mouth leak, airway pressures rapidly increased to 18 cm H(2) O at 2 L/min HFNC flow followed by a pressure relief valve limited increase to 24 cm H(2) O at 6 L/min. Safe and effective use of HFNC requires careful selection of an appropriate nasal prong-to-nares ratio even with an integrated pressure relief valve. Pediatr Pulmonol. © 2012 Wiley Periodicals, Inc.Pediatric Pulmonology 05/2013; 48(5). DOI:10.1002/ppul.22636 · 2.38 Impact Factor
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ABSTRACT: Several new generation neonatal ventilators that incorporate conventional as well as high frequency ventilation (HFOV) have appeared on the market. Most of them offer the possibility to use HFOV in a volume-targeted mode, despite absence of any preclinical data. With a bench test, we evaluated the performances of 4 new neonatal HFOV devices and compared them to the SensorMedics HFOV device. Expiratory tidal volumes (VT) were measured for various ventilator settings and lung characteristics (ie, modifications of compliance and resistance of the system), to mimic several clinical conditions of pre-term and term infants. Increasing the frequency proportionally decreased the VT for all the ventilators, although the magnitude of the decrease was highly variable between ventilators. At 15 Hz and a pressure amplitude of 60 cm H2O, the delivered VT ranged from 3.5 to 5.9 mL between devices while simulating pre-term infant conditions and from 2.6 to 6.3 mL while simulating term infant conditions. Activating the "volume-targeted" mode in the 3 machines that offer this mode allowed the VT to remain constant over the range of frequencies and with changes of lung mechanical properties, for "pre-term infant" settings only while targeting a VT of 1 mL. These new generation neonatal ventilators were able to deliver adequate VT under pre-term infant, but not term infant respiratory system conditions. The clinical relevance of these findings will need to be determined by further studies. Copyright © 2015 by Daedalus Enterprises Inc.Respiratory care 11/2014; DOI:10.4187/respcare.03048 · 1.84 Impact Factor