International Journal of Chronic Obstructive Pulmonary Disease Dovepress open access to scientific and medical research Open Access Full Text Article ORIGINAL RESEARCH Does the Efficacy of High Intensity Ventilation in Stable COPD Depend on the Ventilator Model? A Bench-to-Bedside Study Cristina Lalmolda 1,2 Purpose: The European Task Force for chronic non-invasive ventilation in stable COPD Pablo Flórez 1 recommends the use of high pressure-support (PS) level to maximize the decrease in PaCO2. Marta Corral 3 It is possible that the ventilator model can influence the need for higher or lower pressure Ana Hernández Voth 3 levels. Research Question: To determine the differences between ventilators in a bench model Carles Grimau 1 with an increased inspiratory demand; and to compare the degree of muscular unloading Javier Sayas 2 measured by parasternal electromyogram (EMGpara) provided by the different ventilators in Manel Luján 1,2,4 real patients with stable COPD. 1 Pneumology Department, Corporació Patients and Methods: Bench: four levels of increasing progressive effort were pro­ Sanitària I Universitària Parc Taulí, Sabadell, Barcelona, Spain; 2CIBERES, grammed. The response of nine ventilators to four levels of PS and EPAP of 5 cm H2O Centro de Investigación Biomédica en was studied. The pressure-time product was determined at 300 and 500 msec (PTP 300/500). red, Mallorca, Spain; 3Pneumology Clinical Study: The ventilators were divided into two groups, based on the result of the Department, Hospital 12 de Octubre, Madrid, Spain; 4Universitat Autònoma de bench test. Severe COPD patients with non-invasive ventilation (NIV) were studied, ran­ Barcelona, Bellaterra, Barcelona, Spain domly comparing the performance of one ventilator from each group. Muscle unloading was measured by the decrease in EMGpara from its baseline value. Results: There were significant differences in PTP 300 and PTP 500 in the bench study. Based on these results, home ventilators were classified into two groups; group 1 included four models with higher PTP 300. Ten COPD patients were recruited for the clinical study. Group 1 ventilators showed greater muscle unloading at the same PS than group 2. Conclusion: The scale of pressure support in NIV for high intensity ventilation may be influenced by the ventilator model. Clinical Trials.gov: NCT03373175. Keywords: chronic obstructive pulmonary disease, parasternal electromyogram, pressure support, pressure-time product, respiratory muscle unloading, rise time Introduction Chronic obstructive pulmonary disease (COPD) is a disease with high mortality and morbidity in clinical practice. A high percentage of patients with advanced disease develop chronic respiratory failure and require nocturnal non-invasive ventilation Correspondence: Manel Luján Pneumology Department, Corporació (NIV) treatment. In some European countries, COPD is already the leading cause of Parc Taulí, Universitat Autònoma de prescription of home ventilation.1 Barcelona, Parc Taulí 1, 08208 Sabadell, Campus de la UAB, Plaça Cívica, The results reported to date in COPD patients undergoing home NIV have been Bellaterra, 08193, Barcelona, Spain variable. Despite the exponential growth in ventilation prescriptions in stable Tel +34937231010 Email mlujan@tauli.cat COPD during the last 15 years, the controlled studies of its use carried out so far International Journal of Chronic Obstructive Pulmonary Disease 2022:17 155–164 155 Received: 23 July 2021 © 2022 Lalmolda et al. This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms. Accepted: 6 December 2021 php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License (http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For Published: 14 January 2022 permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms (https://www.dovepress.com/terms.php). Lalmolda et al Dovepress have yielded variable results in terms of improved survi­ standard 2 m tube with a controlled leak as the expiratory val, dyspnoea, quality of life or impact on arterial blood port (Intersurgical SL, Madrid) placed at its distal end. The gases.2–4 In recent studies, the time to first exacerbation leak port was maintained throughout the experiment, simulat­ after starting chronic NIV has been used as a surrogate of ing the intentional leak used in clinical practice in NIV with efficacy.5 a single limb configuration (Figure 1). For each simulated One of the special features of recent studies is the systema­ sequence, tested ventilators ran for 5 minutes before collecting tic use of high pressure support values and high backup data to ensure stability in the measurements. frequency (respiratory rate) on the ventilator. The goal is to Parameters in the Simulator try and normalize PaCO2 or to obtain a decrease of at least - Lung mechanics: Compliance and resistance were set at 20% from baseline values. This is known as high intensity 60 mL/cm H2O and 18 cm H2O/L/s respectively.10 ventilation. Initially, high-intensity NIV in COPD was used in - Inspiratory effort: Four levels of effort were deter­ short-term studies with the evaluation of physiological mined, progressively increasing to −4, −9, −14 and parameters6,7 but more recently its use has expanded. In fact, −20 cm H2O. the recent European Task Force recommends its use in COPD - Respiratory rate of 15 cycles per minute. patients with stable hypercapnia and in those with persistent Parameters in the ventilators: hypercapnia at 2–4 weeks after a severe exacerbation and - Four levels of pressure support: 10, 15, 20 and advocates the use of high pressure support levels to try to 25 cm H2O. normalize or significantly decrease PaCO2.8 - EPAP at 5 cm H2O. These pressure levels, however, are higher than the ones - Three levels of pressurization time (short, medium, used in clinical practice to treat patients with COPD exacer­ long). bations and respiratory acidosis,9 in which inspiratory pres­ - Backup respiratory rate at 12 cycles per minute. sure does not usually reach 18 cm H2O. One of the primary goals of NIV in stable COPD is to unload the respiratory Ventilator Models muscles.8 One of the factors that might explain these differ­ A total of nine ventilators were studied, two considered for ences is the use of different ventilators in exacerbated hospital use (V60, Philips Respironics, Murrysville, patients in hospital and in chronic patients at home. This Pennsylvania and Carina, Dräger, Lübeck, Germany) and may mean that the pressure level required for optimal seven ventilators for home use: Vivo 40 and Vivo 50 inspiratory muscle unloading in stable COPD patients differs (General Electric, Mölnlycke, Sweden), Stellar 150 and according to the ventilator used. The ventilator performance, Astral 150 (ResMed, North Ryde, Australia), (3) Trilogy 202 including pressurization, is variable between different (Philips Respironics, Murrysville, Pennsylvania), (4) Puritan respirators, even if they have received similar certification. Bennett (PB) 560 (Covidien, Mansfield, Massachusetts) and The main objective of this study was to determine Prisma Vent 30 (Weinmann, Hamburg, Germany). differences in pressurization between different ventilators in a bench model with an increased inspiratory demand. External Signal Acquisition System In the second stage, the aim was to compare the degree An external polygraph (16Sp Powerlab, ADInstruments, of muscular unloading measured by parasternal electro­ Sydney, Australia), equipped with a pressure transducer myography (EMGpara) provided exclusively by the differ­ (model 1050) and pneumotachograph (S300, instrumental ent home ventilators, in a group of patients with dead space = 70 mL, resistance = 0.0018 cm H2O/L/s), hypercapnic chronic respiratory failure and home NIV. both placed at the entrance of the simulator, distal to the intentional leak. The sampling frequency was set at 1 KHz, and the polygraph was connected to a personal com­ Materials and Methods puter equipped with LabChart 8.0 software for Windows. Bench Study The study was carried out under simulation conditions at the Collection and Calculation of Parameters non-invasive mechanical ventilation laboratory of the Hospital A total of six ventilatory cycles at the end of each five- de Sabadell, using an active ventilation simulator (series 1101, minutes step were collected for each sequence, using Peak Hans Rudolph, Inc., Shawnee, Kansas). The ventilators eval­ analysis software (ADInstruments, Sydney, Australia) for uated were connected to the simulator through a single automated data analysis. 156 https://doi.org/10.2147/COPD.S327994 International Journal of Chronic Obstructive Pulmonary Disease 2022:17 DovePress Powered by TCPDF (www.tcpdf.org) Dovepress Lalmolda et al Controlled Leak Ventilator Pneumotachograph Lung Simulator Pressure sensor Controlled Increasing Controlled Increasing Effort Change RT Effort Figure 1 Setup of the bench test. The following parameters were recorded for each ven­ Taulí (Sabadell, Barcelona) and the Hospital 12 de tilatory cycle: tidal volume, obtained from the integration Octubre (Madrid) who met the following criteria: of the flow wave, peak flow and time to peak flow, Inclusion criteria: COPD diagnosis according to the inspiratory time, pressure-time product (PTP) at 300 and Global Initiative for Obstructive Lung Diseases criteria,11 500 milliseconds and percentage of PTP 300 and PTP 500 in a situation of chronic respiratory failure and under with respect to the ideal value, defined by a perfect square treatment with home NIV, with prescribed pressure sup­ whose base is the inspiratory time and the height is the port values equal to or higher than 15 cm H2O and programmed pressure support value (see e-Figure 1 for a period of use longer than six months. The absence of more details). The differences between ideal PTP 300/ hospital admissions in the last three months (disease sta­ 500 and the values in the assisted cycles were used as bility phase) was also required for inclusion. Patients with a surrogate of the measure of ventilator pressurization another concomitant alteration (restrictive, significant obe­ capabilities. The greater the difference between both sity - BMI > 35) and poor adherence to treatment (com­ values, the poorer performance of the tested ventilator. pliance based on ventilator counter less than 4 h/day) were excluded. The study, including bench and bedside, started Clinical Study in December 2017 and ended in May 2021. It was The study was carried out in patients from the approved by the ethical committees of the participating Pneumology Service of the Corporació Sanitària Parc hospitals (Ref. 2,017,632 Corporació Parc Taulí and Ref International Journal of Chronic Obstructive Pulmonary Disease 2022:17 https://doi.org/10.2147/COPD.S327994 157 DovePress Powered by TCPDF (www.tcpdf.org) Lalmolda et al Dovepress 18/046 Hospital 12 de Octubre Madrid). Written informed to the normality study of the variables using the Shapiro– consent was required. This study was conducted in accor­ Wilk test (p < 0.05). The comparison of quantitative variables dance with the Declaration of Helsinki. between ventilators was carried out using the ANOVA test. For the comparison of results between the different pressure Clinical Study Protocol levels and ventilators, the general linear model for repeated Each patient randomly used two ventilators during the test to measures was used. When the sphericity of the model could avoid the effect of long-term muscle unloading in unnecessa­ not be assumed (Mauchly’s test with p < 0.05), the signifi­ rily long tests. Based on the results of the bench study, the four cance of the model was evaluated with the Greenhouse- best home ventilators (with the highest PTP300) were Geisser correction. For the clinical study, quantitative data assigned to group 1 and the three worst home ventilators were expressed as median and interquartile range (IQR). The were assigned to group 2. One ventilator from each group comparison of data were carried out by means of Mann– was selected by means of a table of random numbers. Whitney U-test. The level of significance was established at Procedure: In the supine position, each patient was p < 0.05. connected to the oronasal interface used at home. In the first step, they were not connected to the ventilator (the distal end connected to air). Baseline patient effort was Results recorded by EMGpara, with electrodes placed at the level Bench Study of the second/third intercostal space.12 After this, five- A total of 3150 ventilatory cycles were generated. minute periods in NIV under pressure support mode were E-Figures 2–5 show the differences in tidal volume, recorded at three PS levels (10/15/20) for each ventilator inspiratory time, peak flow and time to peak flow for all and patient, with five-minute breaks between each phase. the ventilators studied. One of the ventilators (Prisma Vent The order of the two ventilators alternated randomly in 30) reached a maximum pressure of only 25 cmH2O, and each of the phases to avoid crossed effects. Establishing so the number of simulations was lower (540 vs 720 in the these short periods of time for NIV and breaks between others). them was decided to avoid respiratory muscles unloading Figure 2 shows the mean value of PTP 300 in absolute because of prolonged NIV that could prevent the detection values as a function of the programmed pressure support of differences in later stages. An EPAP of 5 cmH2O was level. As can be seen, the ventilators present two distinct used in all patients and the shortest pressurization time patterns of performance: a first group, which includes the was selected, given their status as severe COPD patients. two acute ventilators and four of the home ventilators, Triggering, cycling and backup rate were not modified showed a significantly higher PTP 300, while a second with respect to the prescribed values. Similarly, oxygen group comprising three home ventilators presented coupled to the ventilator was used during the test if the a clearly lower PTP 300. Figure 3 shows the percentage patient had it prescribed at home at the same flow rate. from the ideal PTP 300 for each model, and e-Figures 6 The last six cycles of each phase were analysed, record­ and 7 show the same analysis for the PTP 500. As shown ing the peak flow values, time to peak flow and inspiratory in E-Figures 2–5, the ventilators with worse performance time. From the EMGpara signal, the transformation known in the PTP 300 also presented significantly higher inspira­ as Root mean square (RMS) was performed, recording the tory time and time to peak flow. maximum peak and the area under the curve of the Figure 4 shows the mean PTP 300 in absolute values transformation.13 Full musculature unloading was consid­ including only the cycles with high demand (−14 and −20 ered to have been achieved when the RMS peak value fell cmH2O), and the shortest ramp in the ventilator, empha­ below 10% of unsupported baseline values14 The protocol sizing the differences between the groups of ventilators (p was stopped in case of complete muscle unloading, and also < 0.01 inter and intra ventilators, general linear model for in the case of poor patient tolerance. repeated measures). Statistical Analysis Clinical Study In all cases, the analysis was performed with SPSS 22 (SPSS, Based on the results of the bench study, the ventilators Chicago, Illinois). For the bench study, quantitative data were were classified into group 1 (better performance in the expressed as means and standard deviation (µ, sd) according bench study) and group 2 (worse performance). As this 158 https://doi.org/10.2147/COPD.S327994 International Journal of Chronic Obstructive Pulmonary Disease 2022:17 DovePress Powered by TCPDF (www.tcpdf.org) Dovepress Lalmolda et al Figure 2 Absolute mean value of PTP 300 as a function of the programmed PS level (p <0.01 between ventilator models, general linear model for repeated measures). Figure 3 Percentage for each ventilator with respect to the ideal PTP 300 (p <0.01 between ventilator models, general linear model for repeated measures). was a study of home ventilators, acute ventilators that o Group 2: Vivo 40, PB 560 and Prisma Vent 30. were taken as a reference in the bench test (V60 and Ten patients were included in the clinical study. Table 1 Carina) were excluded. Thus, the classification by groups shows the anthropometric and lung function data, as well was as follows: as the ventilator model habitually used, and the two venti­ o Group 1: Stellar 150, Astral 150, Vivo 50, lators assessed in the comparison. In eight patients all the Trilogy 202 phases of the protocol were completed, while in the International Journal of Chronic Obstructive Pulmonary Disease 2022:17 https://doi.org/10.2147/COPD.S327994 159 DovePress Powered by TCPDF (www.tcpdf.org) Lalmolda et al Dovepress Figure 4 Absolute mean value of PTP 300 as a function of the programmed PS level, including only cycles with high demand and fastest ramp (p <0.01 between models, general linear model for repeated measures). remaining two the pressure support phase of 20 cm H2O unloading measured by EMGpara was significantly was not analysed due to complete muscle unloading in the higher in group 1 ventilators, in terms of both percen­ EMGpara. tage decrease in the RMS peak (Figure 5, p < 0.001, Regarding respiratory variables, group 1 ventilators Mann–Whitney U-test) and the area under the RMS showed significantly lower time to peak flow and curve (Figure 6, p < 0.001, Mann–Whitney U-test). inspiratory time than those in group 2 (e-Figures 8 and Finally, SpO2 values did not show any differences 9), whereas peak flow and respiratory rate were not between groups, being always higher than 94% during different between both groups. Finally, the muscular the experiment. Table 1 Anthropometric Data, Respiratory Function, Ventilator Used Regularly, and Ventilators Compared Age Gender FEV1% FVC % FEV1/FVC BMI Ventilator Used Ventilator Group 1 Ventilator Group 2 73 M 15 38 30 26 Lumis 150 Astral 150 Vivo 40 77 M 31 60 37 25 Trilogy Stellar 150 Prisma 77 M 30 38 56 28 Lumis 150 Stellar 150 Prisma 58 M 16 53 24 26 Trilogy Trilogy Vivo 40 59 M 21 58 21 29 Trilogy Astral 150 Prisma 55 M 22 60 29 27 VPAP S/T Resmed Vivo 50 PB560 71 M 28 56 38 29 Lumis 150 Vivo 50 PB560 57 M 20 64 24 26 Lumis 150 Astral 150 PB560 60 M 19 66 23 17 Lumis 150 Trilogy Vivo 40 65 F 44 74 48 19 Lumis 150 Vivo 50 Vivo 40 Abbreviations: COPD, chronic obstructive pulmonary disease; EMGpara, Parasternal electromyography; EPAP, expiratory positive airway pressure; IPAP, inspiratory positive airway pressure; NIV, Non invasive ventilation; PS, pressure support; PTP (300/500), pressure-time product; RMS, root mean square. 160 https://doi.org/10.2147/COPD.S327994 International Journal of Chronic Obstructive Pulmonary Disease 2022:17 DovePress Powered by TCPDF (www.tcpdf.org) Dovepress Lalmolda et al Figure 5 Respiratory muscle unloading measured by median maximum value of parasternal EMG (root mean square) for both groups of ventilators (p <0.001 between groups, Mann Whitney U-test). Baseline activity was taken as the reference. Figure 6 Respiratory muscle unloading measured by median area under the curve of parasternal EMG (root mean square) for both groups of ventilators (p <0.001 between groups, Mann Whitney U-test). Baseline activity was taken as the reference. Discussion relevant intrinsic features that they are not modifiable. The The main findings of this study are the differences in the clinical study also demonstrates that these features may be performance of ventilators in the same clinical situation linked to different degrees of muscle unloading. and with appropriate settings in the devices. Our results In the test bench study, the pressure-time product at suggest that ventilation devices for COPD patients present 300 and 500 milliseconds was used to reflect the ventilator International Journal of Chronic Obstructive Pulmonary Disease 2022:17 https://doi.org/10.2147/COPD.S327994 161 DovePress Powered by TCPDF (www.tcpdf.org) Lalmolda et al Dovepress response. This parameter has already been used to evaluate with surface electrodes.13 However, if the surface dia­ the response of ventilators in a laboratory environment. phragmatic EMG signal is technically acceptable, it corre­ Battisti et al15 studied 10 home ventilators in a bench test lates well with oesophageal diaphragmatic EMG.18 setting with two levels of pressure on the ventilator and The parasternal location is the most reliable and best- four levels of inspiratory effort on the active simulator. known approach for surface respiratory muscle EMG Significant differences were also found in the response of assessment. EMG recordings in the second anterior para­ the ventilator blowers to increasing efforts and leaks, not sternal intercostal space have been used as a reference for only at the PTP 300 level but also in trigger delay (as the categorization of asynchronies in NIV,19 to identify the measured by the pressure-time product during the trigger true start of inspiratory effort in patients with COPD,20 and period. Similar results were found in a group of intermedi­ as a predictive tool for readmissions in COPD patients.21 ate respiratory care ventilators.16 In a model similar to the one in the present study, These differences in pneumatic performance require an Duiverman et al22 demonstrated a decrease in the EMG in-depth analysis in order to establish how the ventilators signal with increasing levels of pressure support, reflecting deliver pressure and flow. A core concept for analysis is inspiratory muscle unloading. Furthermore, it has a good the ramp feature, mistakenly called “rise time” on some correlation with EMG measured by oesophageal multi­ ventilators. In pressure-controlled modes, if the pressure/ electrode probe.23 time curve is split into two phases, the section correspond­ The results of the clinical study demonstrate a greater ing to the plateau would be limited by pressure, while the reduction in neural drive for group 1 ventilators at equal section corresponding to pressurization, if limited by time, pressure support in all the patients included (see example should be constant despite increasing patient effort, with­ in e-Figure 11). The patient-blind design of the ventilator out noting the changes in the PTP 300/500 detected in the used in each phase and the alternation of sequences present study.11 between the ventilators compared, including a rest period Also noteworthy are the different values of time to between phases, make the influence of one ventilation peak flow exhibited by the ventilators, with later peak sequence over the next sequence quite unlikely. flow rates in the ones with poorest performance. This Furthermore, by comparing each phase of pressure support finding was also corroborated in the clinical study. with the baseline signal as a percentage, the influence on Moreover, the only variable with minimal changes due to the interindividual variability of the signal is to some increased effort in the simulator was the first derivative of extent avoided. the flow (e-Figure 10), which, in physical terms, reflects The findings of both studies lead to interesting conclu­ flow acceleration. This lack of change would suggest at the sions regarding the long-term chronic non-invasive venti­ conceptual level that part of the pressurization is limited lation procedure in COPD patients. In recent years, “high by changes in the flow. It is also interesting that each intensity ventilation” has become the technique of choice, device exhibited different profiles of flow acceleration in as it achieves better results than conventional ventilation. terms of duration and intensity of the flow change (data High intensity ventilation combines the use of high pres­ not shown). sures and high back-up respiratory rate, both aimed at These differences observed in the bench test were then reducing the baseline PaCO2 value by at least 20%.6,7 corroborated in a clinical setting. In this connection, the A meta-analysis published some years ago showed that biggest challenge was the reliable measurement of the the use of IPAP values greater than 18 was associated with respiratory impulse. Gold standards such as the determina­ better results.24 Likewise, most recent studies5,25 and the tion of intrathoracic pressure through a gastric and oeso­ European ventilation guidelines in stable COPD8 support phageal pressure probe are invasive measures. Although the use of this “high pressure” approach. the placement of this probe has been used in research Muscle unloading, as determined by parasternal EMG settings,17 it causes a certain degree of discomfort to the has been linked with clinical stability in “ready-to dis­ patients. Therefore, in this study, non-invasive muscle charge” patients.26 In this way, Reilly et al demonstrated assessment was used, through EMG quantification of the in cystic fibrosis patients how neural drive, measured by surface of respiratory muscles. Although the diaphragm is EMGpara, decrease to a great extent (−39%) after an the main inspiratory muscle, its anatomical variability infectious exacerbation resolves.12 In a similar way, neural hampers the systematic use of this non-invasive approach drive measured by EMGpara has been proposed as a tool 162 https://doi.org/10.2147/COPD.S327994 International Journal of Chronic Obstructive Pulmonary Disease 2022:17 DovePress Powered by TCPDF (www.tcpdf.org) Dovepress Lalmolda et al to evaluate the effectiveness of bronchodilators27 or even Data Sharing Statement as marker of hyperinflation. In this latter topic, neural Data of the clinical and bench study, including database respiratory drive may reflect mechanics impairment in and tracings will be available upon request for six months COPD patients, mainly related to expiratory flow limita­ from the publication date. The authors with access to the tion and hyperinflation.28 It can be hypothesized that lower data were: Cristina Lalmolda, clalmolda@tauli.cat; Javier capability of a given ventilator in decreasing neural drive Sayas, jsayascat@gmail.com. (“unloading of inspiratory muscles”) may reflect inability to correct respiratory mechanics impairment of a given Disclosure COPD patient. Whether this issue may be related with Dr Javier Sayas reports personal fees, non-financial sup­ long-term outcomes is yet to be proven. On the other port from Resmed, Philips Respironics, grants from hand, most recent studies on NIV in COPD patients have Menarini, non-financial support from Breas, during the been focused in PaCO2 reduction. There is also a strong conduct of the study. The authors report no other conflicts link between PaCO2 levels and neural drive29 with of interest in this work. increased neural drive as PaCO2 increases. 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