VEMERS 2.0: Upgrading of an Emergency Use Ventilator from a Single Mandatory Volume Control Mode of Ventilation (VEMERS 1.0) to 8 Modes of Ventilation
VEMERS 2.0: Upgrading of an Emergency Use Ventilator from a Single Mandatory Volume Control Mode...
Chiang, Luciano E.;Castro, Felipe A.;Sánchez, Tomás F.
2022-06-06 00:00:00
Hindawi Journal of Healthcare Engineering Volume 2022, Article ID 6965083, 16 pages https://doi.org/10.1155/2022/6965083 Research Article VEMERS 2.0: Upgrading of an Emergency Use Ventilator from a Single Mandatory Volume Control Mode of Ventilation (VEMERS 1.0) to 8 Modes of Ventilation Luciano E. Chiang , Felipe A. Castro, and Toma´s F. Sa´nchez Department of Mechanical Engineering, Ponti cal Catholic University of Chile, Vicuna Mackenna Avenue 4860, Comuna Macul, Region Metropolitana, Chile, CP 7820436 Correspondence should be addressed to Luciano E. Chiang; lchiang@ing.puc.cl Received 29 August 2021; Revised 27 January 2022; Accepted 25 April 2022; Published 6 June 2022 Academic Editor: Fabrizio Taoni Copyright © 2022 Luciano E. Chiang et al. �is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. �e upgrading of an emergency use ventilator from a single mandatory volume control mode of ventilation (VEMERS 1.0) to 8 modes of ventilation (VEMERS 2.0) is described. �e original VEMERS 1.0 was developed in the midst of the COVID-19 crisis in Chile (April to August 2020) following special but nonetheless strict guidelines speci‘ed by local medical associations and national health and scienti‘c ministries. �e upgrade to 8 modes of ventilation in VEMERS 2.0 was made possible with minor but transcendental changes to the original architecture. �e main contribution of this research is that starting from a functional block diagram of an ICU mechanical ventilator and carrying a systematic analysis, the main function blocks are implemented in such a way that combinations of standard o-the-shelf pneumatic and electronic components can be used. �is approach has both economical and technical advantages. No special parts need to be fabricated at all, and because of a wider variety of options, the use of extensively ‘eld-proven o-the-shelf commercial components assures better availability and lower costs when compared to that of conventional ICU mechanical ventilators, without sacri‘cing reliability. Given the promising results obtained with VEMERS 2.0 in the subsequent national certi‘cation process, the production of 40 VEMERS 2.0 units was sponsored by the Ministry of Science and the Ministry of Economy. Twenty units have been distributed among hospitals along the country. �e purpose of VEMERS 2.0, as a low-cost but very reliable option, is to increase the number of mechanical ventilators available (3,000 for a population of 18,000,000) in the country to eventually reach a ratio similar to that of more developed countries. VEMERS is an open-source project for others to use the knowledge gained. evolution of UIC beds and occupancy are shown in Figure 1 1. Introduction [2]. At the maximum peak, there were 3,000 mechanical COVID-19 was designated as a pandemic in 2020 by the ventilators in use (“Pctes. UCI COVID 19 en VMI”), and the WHO. �e high number of active cases, more than capacity of the health system was close to 100% for a long 209.000.000 and more than 4.400.000 deaths in the world at period of time (April-June, 2021), meaning that in practice the time this article was written [1], has overstressed health there must have been regional shortages and many patients systems all over the world. From these, in Chile, more than had to be transported to accommodate for site availability. 1.630.000 cases with 36,605 deaths have been reported [2]. A In fact, there was a localization problem since the vital resource for treating patients with respiratory problems geographic distribution of mechanical ventilators and caused by COVID-19 is mechanical ventilators. trained personnel, generated shortages in regional hospitals In Chile, at the beginning of the pandemic, there were as the active cases in geographic distribution evolved. 1.229 mechanical ventilators [2]. Moreover, Chile reached a In March 2020, at the beginning of the COVID-19 peak of almost 90.000 active cases [2] in June 2020. �e pandemic in Chile, many ideas had been made available 2 Journal of Healthcare Engineering 5.000 4.500 4.000 3.500 3.000 425 2.500 1.697 2.000 1.500 1.000 1.648 *A partir del 23 de febrero se reportan los datos informados de forma agregada, UGCC Pctes. UCI COVID19 en VMI Pctes. UCI COVID19 sin VMI UCI ocupades no coronavirus UCI Disponibles Figure 1: Evolution of the use of mechanical ventilators in Chile. Chilean Ministry of Health Official Report (in Spanish). publicly already in the world to face the shortage of me- decision because the government announced a few weeks chanical ventilators [3, 4]. Many open-source solutions were later that it would only consider funding proposals that proposed, some based on the mechanization of bag-mask complied with the validation protocols issued by the manual ventilators [5–7], and others followed an electro- CMFCC. In addition, MHRA (UK) [12], AAMI (USA) [13], pneumatic principle [8–10]. Existing solutions such as and also ISO 80601-2-12 [14] design guidelines have also E-vent [5], OxVent [6], and OxyGEN [7] were rapidly been taken into account. For the most part, it can be said that adopted by local developers in Chile, and many propositions protocols [11–13] are quite similar to each other since they were submitted to local authorities. Very few are known to have been specifically tailored for emergency mechanical ventilators to be used during the COVID-19 pandemic. In have achieved any clinical validation both in Chile and in the world. fact, VEMERS 1.0 [15] after completing the CMFCC vali- dation process has received 2 grants, one private and another )e entity in Chile that certifies health products, ISP (Public Health Institute), was not prepared to certify so- from the government to produce 40 units in total. phisticated medical equipment such as emergency me- In the following sections, the technical aspects of chanical ventilators. Contacts between government VEMERS 2.0 upgrading will be described in detail. Figure 2 ministries, scientific societies, and professional and industry shows the two versions developed so far. Table 1 shows the associations gave rise to the Multidisciplinary Council for general ranges of operation of VEMERS 2.0. )is article is Facilitation and Management of the COVID-19 Crisis useful because it shows how an EUV can be upgraded and (CMFCC) to fill the void. Its members were all appointed left available for general postpandemic use, especially in low- voluntarily and acted pro-bono. )e CMFCC asked three resource communities. )e COVID-19 pandemic has made patent the short- medical societies: Chilean Society of Intensive Medicine (Sociedad Chilena de Medicina Intensiva (SOCHIMI)), comings of ICU services in the world health system, par- ticularly in low resource settings. It has become clear that Chilean Society of Urgency Medicine (Sociedad Chilena de Medicina de Urgencia (SOCHIMU)), and the Chilean So- there is only a shortage of mechanical ventilators but there is ciety of Anesthesiology (Sociedad de Anestesiolog´ıa de Chile also a shortage of respiratory therapists that can operate (SACH)), to issue a protocol to validate emergency me- correctly and safely these systems which can be very com- chanical ventilators, which could later be produced in large plex. )ere are situations that generate confusion and hence scale. )e final version of the protocol was published on June risk situations even to the most experienced RTs. According 3, 2020 [11], but preliminary versions had begun circulating to recent studies [16–18], the main directions in the future much earlier. At the same time, the CMFCC issued a call for development of mechanical ventilators are as follows: proposals and preselected 5 initiatives to guide in the process (a) Mechanical ventilators should maintain their func- of validation. Initiatives that were not selected or of later appearance were allowed to follow the process but subject to tionality and capabilities or even increase them, but the availability of the authorized validation entities. VEM- personnel with less experience and training should ERS UC came in late but decided to follow the process be able to operate them safely as well. )is requires because validation in an open process would give the adding intelligent and real-time processing of the ventilator output signals to help guide the operator ventilator much more credibility. In the end, it was the right 01-06-20 08-06-20 15-06-20 22-06-20 29-06-20 06-07-20 13-07-20 20-07-20 27-07-20 03-08-20 10-08-20 17-08-20 24-08-20 31-08-20 07-09-20 14-09-20 21-09-20 28-09-20 05-10-20 12-10-20 19-10-20 26-10-20 02-11-20 09-11-20 16-11-20 23-11-20 30-11-20 07-12-20 14-12-20 21-12-20 28-12-20 04-01-21 11-01-21 18-01-21 25-01-21 01-02-21 08-02-21 15-02-21 22-02-21 01-03-21 08-03-21 15-03-21 22-03-21 29-03-21 05-04-21 12-04-21 19-04-21 26-04-21 03-05-21 10-05-21 17-05-21 24-05-21 31-05-21 07-06-21 14-06-21 21-06-21 28-06-21 05-07-21 12-07-21 19-07-21 26-07-21 02-08-21 09-08-21 16-08-21 Journal of Healthcare Engineering 3 (a) (b) (c) (d) Figure 2: (a) VEMERS 1.0. (b) VEMERS 2.0. (c) Electronic circuits VEMERS 2.0. (d) Electropneumatic circuitry, valves, sensors, and parts. VEMERS 2.0. through situations that arise than can be confusing (c) )e ventilators should be teleoperated at a distance for the nonexpert. )is would require, for example, so that the RT does not have to come into close automation of the ventilator settings, something that contact with the patient unless it is necessary. )is in the present state of the art is done manually, would also allow the RT to handle more patients at hence, including intelligent decision-making sys- one time, because it would take less time to check tems and big data processing capabilities. periodically a patient, saving time in such pedestrian chores as getting dressed, for example. (b) )e user interface should be easy to understand and configure. )e interpretations of warnings and alarms when occurring simultaneously should be 2. Methods processed quickly so that it is easier to stabilize the patient, reducing risks. )e ventilator must take 2.1. Choked Inhalation AirFlow. Both VEMERS 1.0 and automatic corrective actions in specific situations VEMERS 2.0 rely on generating a choked flow [19] from the of high risk, especially if there is a mechanical air mixture source to the ventilator inspiratory branch. A ventilator part failure causing this situation. choked flow allows regulating the inhalation flow by con- Hence, reliability is an issue that must continu- trolling the opening of a flow control valve only, thus ously improve. simplifying the construction of the ventilator. 4 Journal of Healthcare Engineering Table 1: Working limits on VEMERS 2.0. Limit Units Value Maximum cycle volume ml 800 Minimum cycle volume ml 125 P , T , ρ 1 C 0 0 0 Failsafe relief pressure cm H20 60 Maximum pressure in pressure control mode cm H20 40 Minimum pressure in pressure control mode cm H20 10 Patient Lung Maximum peep cm H20 25 Highest trigger pressure in assisted mode cm H20 −3 Lowest trigger pressure in assisted mode cm H20 −10 Figure 3: Choked flow principle applied to mechanical ventilator Maximum respiratory frequency bpm 40 inhalation phase. Minimum respiratory frequency bpm 10 Maximum IE ratio 3 Minimum IE ratio 1 Maximum flow lpm 60 Maximum time apnea in pressure support sec 60 mode P , T , ρ 2 2 2 Minimum time apnea in pressure support sec 5 mode Patient Lung P P 3 a Maximum flow O2 therapy lpm 60 Minimum flow O2 therapy lpm 10 To better understand this, let us consider the system in Figure 4: Expiratory flow and pressure control. Figure 3. Reservoir 0 is in stagnant conditions p , T , ρ . 0 0 0 )e flow through A will depend on the value of p (see 1 2 Nomenclature table). Index 2 refers to the patient’s lungs. 2.2. Control of Exhalation Flow. )e expiratory flow is Hence, as long as governed by the same compressible gas flow equations. )e patient’s lung is in varying conditions p , T , ρ as shown in 2 2 2 k/k−1 Figure 4. It is connected to the ambient air at atmospheric (1) p ≤ p � p , 2 0 pressure p through the expiratory branch which has an k + 1 aperture section area A . )e magnitude of patient lung pressure p is such that the corresponding critical pressure then the pressure p will be always p is always lower than p . Hence, the pressure at section A a 3 (the expiratory valve aperture) will be p rather than p . k/k− 1 (2) p � p � p . )e flow through A is thus governed by the following 1 0 3 k + 1 equation: ���������� If this is the case, then the flow through A that enters 1 _ (4) Q � A p − p ρ . 3 3 2 a 2 reservoir 2 is fixed regardless of the value of p and is given by the following expression: A PID control loop of the section area A aperture allows ����������������� � quickly driving p to the desired peep value and keeping its k− 1/k k − 1 variation within acceptable limits. _ (3) Q � A 2 p ρ . 1 1 0 0 R k + 1 2.3. Electropneumatic Upgrade. )e main upgrade done to From the above equation, it is clear that if the the electropneumatic circuit in VEMERS 1.0 (shown in stagnant conditions in reservoir 0 remain constant, then Figure 5) has been the replacement of both the inspiratory the flow entering reservoir 2 (patient lungs) depends and expiratory valves [15]. )ese two valves in the emer- exclusively on the magnitude of the section area A . If the gency mechanical ventilator version VEMERS 1.0 were section area A is set using a proportional flow control directional 2 × 2 on-off valves. In the upgraded version valve as in VEMERS 2.0 or a manual flow control valve as VEMERS 2.0, they have been replaced by proportional 2 × 2 in VEMERS 1.0, then the actual flow going into reservoir valves. VEMERS 1.0, as a basic EUV, has only one mode of 2 can be also accurately fixed. )is is the principle used in ventilation, namely, volume control mode. )e imple- both VEMERS versions in the inspiratory phase of the mentation of the volume control mode of ventilation (VC) respiratory cycle. )e inspiratory phase is achieved with a alone is satisfied using only on-off directional valves. )e choked airflow since the pressure in reservoir 0 is kept at inspiratory phase in the case of VEMERS 1.0 is implemented 2 bar and at ambient temperature, while the pressure in in combination with a manual choke valve since this allows reservoir 2 (i.e., the patient) never rises above 60 cm H20 setting a fixed magnitude inspiratory flow, which is char- (thus p is always much less than p ). acteristic of this mode of ventilation. 2 Journal of Healthcare Engineering 5 P1 Patient Lung Endo Tracheal Tube (ETT) HME-HEPA Filter F2 F3 Exhalation HEPA Inhalation HEPA Filter Filter S4 S3 Exhalation Flow Sensor Inhalation Flow Sensor RV1 Failsafe Relief SDV2 valve Solenoid S2 Directional Valve O2 Sensor Bank 2x2 Normally Closed Exhalation Flow S1 PressureSensor 0-100 cm H20 FCV1 Inhalation Flow Control Valve SDV1 Solenoid Directional Valve S5 2x2 Normally PRV1 O2 Line Pressure Closed FCV2 CV1 O2 Pressure Sensor O2 Flow Inhalation Flow O2 Line Regulating Control Check Valve Valve Valve T1 I1 Mixing O2 Double Tank Action Knob CV2 for FiO2 Air Line blending Check Valve I2 Air S6 Air Line FCV3 PRV2 Pressure Air Flow Air Pressure Sensor Control Emergency Mechanical Regulating Valve Ventilator (EMV) Valve Figure 5: Electropneumatic schematics of original VEMERS 1.0. Directional valves and manual flow control valves are used. However, to implement pressure control mode, it is On the other hand, the expiratory phase of the volume necessary to use a proportional valve in order to con- control mode cycle in VEMERS 1.0 [15] was implemented by tinuously adjust the airflow to reach and maintain the using four 2 × 2 directional valves, which were activated in desired pressure level, which is characteristic of the sequence in order to quickly reach and maintain the desired pressure control mode and its variants. )is has been done peep pressure values. In this case, the four valves are open at in VEMERS 2.0. the beginning of the expiratory phase, and each one is closed 6 Journal of Healthcare Engineering P1 Patient Lung Endo Tracheal Tube (ETT) HME-HEPA Filter F2 F3 Exhalation HEPA Inhalation HEPA Filter Filter S3 S4 Exhalation Flow Inhalation Flow Sensor Sensor SPV2 Solenoid RV1 S2 Proportional Valve O2 Sensor Failsafe Relief 2x2 Normally valve Closed Exhalation Flow S1 PressureSensor 0-100 cm H20 SPV1 Solenoid Proportional Valve 2x2 Normally Closed PRV2 FCV3 S6 Inhalation Flow Air Pressure Air Flow Air Line CV2 Regulating Control Pressure Air Line Valve Valve Sensor Check Valve I2 Air Double Action Knob for FiO2 blending I1 O2 CV1 S5 FCV2 O2 Line O2 Line Pressure O2 Flow Check Valve Upgraded Emergency PRV1 Sensor Control O2 Pressure Mechanical Ventilator Valve (UEMV) Regulating Valve Figure 6: VEMERS 2.0. Upgraded mechanical ventilator schematics. Proportional valves have replaced directional valves and manual flow control valves in both the inhalation and expiratory phases of the cycle. )e respirator has two intakes, one for air and one for sequentially according to the pressure level. In this manner, the pressure level quickly falls at the beginning of the ex- oxygen supply. In a standard hospital ICU, both gases are piration, and when the pressure is close to the desired peep available at 50 psi in wall faucets. In the schematics in value, they are closed in sequence to reduce the expiratory Figure 6, pressure sensors S5 and S6 detect the correct supply flow to the minimum necessary value. of gases. Each gas line then enters a pressure regulator In VEMERS 2.0, these four valves are replaced by a single (PRV1 and PRV2) that set pressure outputs to a value of two proportional valve (SPV2), which allows controlling the bar so the oxygen-air mix (FiO2) can be set properly. expiratory flow so that the pressure quickly falls at the beginning of the expiration and later closes just enough to 2.3.1. Blending Stage. Each gas line enters next to a manual maintain the peep pressure at the end of the cycle. flow control valve arrangement (FCV2 and FCV3). Both Journal of Healthcare Engineering 7 evolves in patients, different modes of ventilation may be valves are connected head to head, allowing the setting of the FiO2 by a common knob. Turning this knob will open one more convenient, as well as for respiratory diseases other than COVID-19 [20]. )e 8 modes of ventilation are listed in valve and at the same time close the other. )is allows controlling in a very simple and reliable way the resulting Table 2. FiO2 because the RT can check its value on the computer screen and adjust the knob by hand. )e air and O2 are then 2.4.1. Ventilation Modes. In this section, a brief description mixed between 21% (standard air) and 100% of oxygen as set of the ventilation modes available in VEMERS is given. We by the RT before passing through electropneumatic pro- do not intend to give a complete and extended discussion portional valve SPV1. )e scheme implemented in VEMERS because of limitations of space and the complexity of the provides a low-cost, reliable, and immediately available subject, but the reader can be referred to [20] for a detailed solution for gas mixing. in-depth discussion of these modes which are well known in the critical care medical community. 2.3.2. Inspiratory Stage. )e gas mixture passes through a Mode 1. Volume Control Mode. )is is a mandatory invasive 2 × 2 proportional solenoid valve (SPV1) which is opened in mode of ventilation. )e respirator essentially delivers a the inspiratory phase and closed in the expiratory phase constant volume of air (the tidal volume) to the patient at a commanded by a PWM controller signal. A PID control fixed frequency in each cycle according to the preset values. loop allows reaching either a set volume or a set pressure For this mode of ventilation to work properly, the inspi- depending on the mode of ventilation. )ere is a choking ratory flow must be controlled to a high degree of accuracy effect which is a key feature because it allows the inspiratory so that at the end of the cycle the desired air volume is gas mixture flow rate to be independent of the discharge precisely delivered. )e patient is not allowed to initiate a pressure downstream of SPV1 and only dependent on the respiratory cycle on its own. In the expiratory phase, the aperture level commanded by the PWM control circuit. In output flow is controlled to maintain the airway pressure at volume control mode, the inhalation gas flow rate remains the desired PEEP level, which is a safe level to avoid patient constant and is adjusted so that the desired tidal volume is alveoli collapse. reached. In pressure control mode, the aperture of SPV1 is In this mode of ventilation, the following parameters continuously set such that the pressure in the inhalation must be set by the RT. branch is maintained at the desired level. Differential pressure sensor S1 allows monitoring the (i) Tidal Volume (ml) instantaneous pressure in the breathing circuit from −100 to (ii) PEEP (cmH20) (positive end-expiratory pressure, 100 MPa. )is sensor is also used to detect patient triggering. the minimum pressure allowed in the respiratory Sensor S2 is a galvanic oxygen sensor that allows measuring system) FiO2. )is type of galvanic sensor is the same commonly (iii) Respiratory Frequency (bpm) used in full-fledged high-end ventilators. )ey have a low- time response. Hence, in VEMERS UC, the RT must wait a (iv) I : E ratio (the ratio between inspiratory time and few seconds until the oxygen sensor signal stabilizes to verify expiratory time in the cycle) on the computer screen that the desired value has been (v) FiO2 (%) percentage of additional oxygen in the air reached. mixture delivered to the patient Unidirectional flow sensor S3 measures the inspiratory (vi) Plateau time/inspiratory pause. )e interval of time flow in a range from 0 to 200 lpm, as it leaves through the in which the flow is paused during the inspiration inspiratory port where the inspiratory tubing leading to the phase (s) endotracheal tubing is connected. (vii) PIP maximum pressure allowed in the respiratory cycle 2.3.3. Exhalation Stage. In VEMERS 2.0, the exhalation Figure 7 shows the characteristic shapes of patient curves stage is controlled by a solenoid 2 × 2 proportional valve in volume control mode. (SPV2). )e controller reads pressure sensor S1 and activates the SPV2 valve according to a PID control scheme that sends Mode 2. Assisted Volume Control. )is mode of ventilation is a PWM signal to SPV2. )e pressure must quickly drop to similar to the above except that if the patient attempts to the desired peep value and later maintained stability. initiate a respiratory cycle on its own (asynchronously) A HEPA filter and water trap are commonly installed in during the exhalation phase, the respirator will immediately this line in between the ventilator and the endotracheal tube. deliver a new cycle provided that the negative pressure level generated by the patient has met a minimum threshold. )e triggering pressure is set by the RT. 2.4. Software Upgrade. VEMERS 1.0 as an emergency me- chanical ventilator was developed with only one mode of Mode 3. Pressure Control Mode of Ventilation. In Pressure ventilation (mandatory volume control). VEMERS 2.0 has been upgraded to 8 modes of ventilation with the archi- Mode of ventilation, the pressure in the respiratory system is tecture shown in Figure 6 and additional ad hoc user in- maintained at a desired fixed level during the inspiratory terface and control software. As the COVID-19 treatment phase. As a result, the pressure curves should look like a 8 Journal of Healthcare Engineering Table 2: Ventilation modes in VEMERS 2.0. See [17] for a detailed description. Mode number Ventilation mode 1 Mandatory volume control 2 Assisted volume control triggered by pressure 3 Mandatory pressure control 4 Assisted pressure control triggered by pressure 5 Pressure support 6 CPAP 7 BiPAP 8 High oxygen flow therapy -10 -20 10 -30 -40 -50 -60 -0.046 19.954 -0.046 19.954 Presion [cm H20] Flujo [lpm] -50 -0.046 19.954 Volumen [ml] Figure 7: Patient curves in volume control mode (legends are in Spanish). square train pulse. In the exhalation phase, the ventilator Mode 5. Pressure Support Mode of Ventilation. )is mode of must reach and maintain the pressure at the desired PEEP ventilation is used to facilitate the patient’s transition to value. In this mode, the ventilator controls the inspiratory autonomous breathing prior to disconnection from the flow starting with a high flow value and then reducing it as ventilator. In this mode, the respirator will wait until the pressure rises and reaches the set value. )e variables to set patient attempts a breathing cycle. If the waiting time (T in this mode of ventilation are the following: apnea) is surpassed, then the ventilator switches back au- tomatically to mandatory volume control. However, if there (i) P insp [cmH2O] is a patient effort strong enough, inspiratory flow is allowed, (ii) PEEP [cmH20] maintaining a fixed support pressure until the flow reduces (iii) Frequency (bpm) to a fraction of the initial maximum, and at this moment, the ventilator switches to the expiratory phase. Hence, in this (iv) IE ratio mode, the ventilator lets the patient set the respiratory pace, (v) Fraction of inspiratory oxygen FiO2 [%] allowing a gradual process of autonomous breathing before Figure 8 shows characteristic curves obtained in pressure disconnection. )e amount of air that is delivered is pro- portional to the patient’s effort. control mode. (i) IE ratio Mode 4. Assisted Pressure Control. )is mode of venti- (ii) PEEP [cmH20] lation is similar to the above (see 2.4.1.3) except that if the patient attempts to initiate a respiratory cycle on its own (iii) FiO2 [%] (asynchronously) during the exhalation phase, the res- (iv) ∆ support pressure [cmH20] above PEEP level pirator will immediately deliver a new cycle provided that (v) Trigger pressure [cmH20] below PEEP level) the pressure level generated by the patient has met a (vi) Frequency in safety volume control mode [bpm] minimum threshold. )e triggering pressure is set by the RT. (vii) Tidal volume in safety volume control mode [ml] Journal of Healthcare Engineering 9 -10 -20 -30 -40 -0.047 19.953 -0.047 19.953 Flujo [lpm] Presion [cm H20] -50 -0.047 19.953 Volumen [ml] Figure 8: Patient curves in pressure control mode (legends in Spanish). (viii) T apnea [s] (waiting time before switching to safety Mode 8. High-Flow Nasal Cannula Oxygenation. In this volume control mode). mode of ventilation, a constant high flow of pure oxygen or air oxygen mixture is delivered to the patient by way of a Figure 9 shows typical patient curves in pressure support cannula entering the nose of the patient. )e parameters that mode. must be set in this mode of ventilation are as follows: (i) Flow [L/min] Mode 6. CPAP (Continuous Positive Airway Pressure). Modes 6 to 8 are nonintubated modes of ventilation that (ii) FiO2 [%] have proven to be useful for standby patients before intu- Figure 12 shows patient curves in this mode of bation. In Mode 6, the patient receives a constant positive ventilation. airway pressure through a breathing mask. )e value of the pressure is set by the RTand it is always constant regardless if the patient is in the inspiratory or expiratory phase. )e 2.5. User Interface. VEMERS 2.0 has an internal micro- parameters that need to be set in this mode are as follows: controller to synchronize the respiration cycle. In addition, it includes a touch screen computer that communicates with (i) CPAP [cmH20] the internal microcontroller so the RT can set the cycle (ii) FiO2 [%] parameters. Hence, in the case of VEMERS 2.0, both the Figure 10 shows typical curves for this mode. internal microcontroller and touchscreen interface com- puter software are much more complex than in VEMERS Mode 7. BiPAP (BiLevel Positive Airway Pressure). )is 1.0. )e internal microcontroller software is written in C++. ventilation mode consists in providing the patient with two )e user interface software in the touchscreen computer is levels of pressure during a respiratory cycle. In the inspi- written in C#. ratory phase, the pressure level is higher while in the ex- User interface screens are shown in Figures 13–15. )e piratory phase the pressure is set to a minimum value to interface has common features for all modes of ventilation as facilitate expiration but avoid the risk of the collapse of the well as specific individual ones. )e text in all user interfaces patient’s alveoli. is in the Spanish language because the RT in Chile prefers to )e operating parameters that must be set in this mode set the ventilator in the native language. At the left of the user are the following: screen, all modes of ventilation show 3 real-time graphs from top to bottom: pressure, flow, and volume. )e mode of (i) High level Bipap pressure [cmH2O] ventilation is selected using the proper radio buttons in the (ii) Low level Bipap pressure [cmH20] boxes with pink and brown backgrounds. Each mode of (iii) Respiratory Frequency (cpm) ventilation has individual input parameters to be set, and output parameters that can be read. )e input parameters set (iv) IE ratio Razon ´ I : E (1:N) by the RT are in the green background boxes. In these, the (v) FiO2 (%) interior textboxes with the white background are the input Figure 11 shows typical patient curves for this mode. parameters entered by the RT, and the inner textboxes in 10 Journal of Healthcare Engineering -10 -20 -30 0 -40 7.201 7.201 Presion [cm H20] Flujo [lpm] -50 7.201 Volumen [ml] Figure 9: Patient curves in pressure support mode (legends are in Spanish). -10 -20 -30 -40 20.001 20.001 Presion [cm H20] Flujo [lpm] Figure 10: Patient curves in CPAP mode of ventilation (legends in Spanish). 20 40 10 0 -10 -20 -30 -40 0.002 20.002 0.002 20.002 Presion [cm H20] Flujo [lpm] Figure 11: Typical patient curves in BiPAP mode of ventilation (legends in Spanish). -10 20.001 20.001 Presion [cm H20] Flujo [lpm] Figure 12: Typical patient curves in high-flow nasal cannula oxygenation mode of ventilation (legends in Spanish). Journal of Healthcare Engineering 11 VEMERS UC 01 Presion [cm H20] 12.002 Flujo [lpm] -10 -20 -30 12.002 Volumen [ml] -50 12.002 Figure 13: Pressure triggered assisted volume control mode of ventilation in VEMERS 2.0. )e text is in Spanish to accommodate the RT native language. of valve SMC 2121-3 allows much better and more reliable grey give the actual instantaneous values. )e cycle output parameters are in the boxes with the cyan background. )ere is control of the operation of the ventilator. A narrower range a message box (“Mensajes”) in the middle of the screen with a gives rise to a jumpy response; hence, the respiratory pa- white background that generates error messages when anom- rameters oscillate more. alies are detected. )ere is also a dropdown menu of options to set general operational alarm limits (“Menu Opciones”). 3.2. Technical Certification. Both VEMERS 1.0 and VEMERS 2.0 have been thoroughly tested, so they can be used safely 3. Results and Discussion and with confidence. Table 3 gives validations that have been performed on both VEMERS 1.0 and VEMERS 2.0. 3.1. Design Issues. )e electropneumatic proportional valves A brief description of tests. are arguably the most important parts of VEMERS 2.0. At the height of the pandemic, these valves were extremely 3.2.1. Technical Validation Tests 1 and 4. Starting tests were difficult to find. )e cost is also 10–100 times that of the combination of a directional valve plus a manual flow the technical validation tests. )e main objectives of these tests were as follows: control valve used in VEMERS 1.0. )e cost of the pro- portional valves used in VEMERS 2.0 is in the order of USD (a) Accuracy verification in individual incremental 250 each. Nevertheless, even though the cost of parts and parameter setting in volume control mode of ven- materials to assemble VEMERS 2.0 increases from USD tilation, that is to say, verification of parameter ac- 1,750 [15] in VEMERS 1.0 to USD 2,000, this is a fraction of curacy in individual incremental setting of tidal the price of a conventional high-end mechanical ventilator volume, PEEP, and frequency. commercially available. (b) Accuracy verification in the combinatorial setting of )e selection of the electropneumatic valve is key to the working parameters in volume control mode of correct functionality and reliability of the mechanical ven- ventilation tilator as a whole. Shown in Figure 16 is the valve flow versus PWM behavior of two proportional valves. )e wider range (c) Documentation Revision 12 Journal of Healthcare Engineering VEMERS UC 01 Presion [cm H20] 0.001 12.001 Flujo [lpm] -10 -20 -30 -40 0.001 12.001 Volumen [ml] -50 12.001 0.001 Figure 14: Pressure triggered assisted pressure control mode of ventilation in VEMERS 2.0. )e text is in Spanish to accommodate the RT native language. (d) Equipment Labeling Revision 3.2.2. Test 2: Usability. A usability evaluation was required. )e VEMERS UC development team was asked to make an (e) Alarm Verification online presentation to a panel of experts consisting of (f) Electric safety verification written documentation and videos explaining the principle of operation of VEMERS UC and the user interface. User- )e methodology for technical validation at the certi- fication bureau (Certemed) consisted of connecting the friendliness, readability of the screen, respiratory parameter ventilator prototype to an Acculung II Fluke test lung with a settings, quality of knobs and switches, among others were of Fluke VT650 gas analyzer in between. Single parameters paramount importance to obtain approval in this test. )e were incremented individually according to a predefined assembly process of VEMERS UC was also discussed to assess production time and cost. sequence, and the accuracy of VEMERS UC readings was assessed as explained above in (a). Next, different combi- nations of working parameters were tested according to a 3.2.3. Preclinic Tests. Preclinic tests were carried out at the predefined sequence, and the accuracy of VEMERS UC Center for Medical Research of the Pontifical Catholic Uni- readings was compared. In all, more than 450 tests and versity of Chile. )e objectives of these tests were as follows: verifications are required in this technical evaluation. (a) Verify the functionality and capability of modifying )e technical evaluation protocol includes a list of ventilation parameters alarms that had to be implemented and activated in a correct (b) Verify compliance of programmed and resulting and timely manner. Using a Umik-1 microphone, the sound ventilation parameters (tidal volume, PEEP, I/E level of the alarms is measured, which must be at least 6 dB ratio, inspiratory pressure) above ambient noise. (c) Evaluate correct functioning of alarms To check electrical safety, a Fluke ESA 620 was used. )is instrument is certified to measure ground protection imped- (d) Verify that the ventilator prototype maintains an ance, ground current leakage, and envelope leakage current. effective gas exchange in a healthy model as well as in Journal of Healthcare Engineering 13 VEMERS UC 01 Presion [cm H20] 0.001 12.001 Flujo [lpm] -10 -20 -30 -40 0.001 12.001 Volumen [ml] -25 -100 0.001 12.001 Figure 15: Pressure support mode of ventilation in VEMERS 2.0. )e text is in Spanish to accommodate the RT native language. Proportional Valves with different PWM control range a model with pulmonary injury (e) Verify that the ventilator prototype is capable of maintaining a protective ventilation (volume 6 ml/ 100 kg, plateau pressure <30 cmH2O, DP< 15) in a model with pulmonary injury )e methodology in these tests consisted of the use of a porcine animal model, subject to 2 consecutive experimental sequences: (i) tests on the healthy model and (ii) tests on the model with induced pulmonary injury. 0 45 65 85 105 125 VEMERS UC preclinic tests proved compliance with all PWM the important aspects in providing ventilation and main- SMC 2121-3 taining a gaseous exchange similar to a conventional me- SMC 2121-1 chanical ventilator under normal as well as in the case of Figure 16: Different control range in two proportional valves. )e moderately altered pulmonary function. range in SMC 2121-3 is much more desirable and allows more reliable and stable control of the mechanical ventilator. 3.2.4. Clinical Tests with COVID-19 Patients. Clinical tests were performed on 5 COVID-19 patients at the Clinical Hospital of the Catholic University of Chile. )e objectives critically ill patients with pulmonary pathology for of these tests were as follows: stretches of 8 hours (a) Evaluate the safety and effectiveness of VEMERS UC )e methodology in these tests was to find patients with for use in patients with acute pulmonary pathology a relation PaO2/FiO2 (PaFi) between 100 and 250, having (b) Evaluate the capacity of VEMERS UC to maintain vasopressor support with Norepinephrine <0.2 μ/kg∗ min, the gaseous exchange and cardiovascular safety in and with medical indications of deep sedation and muscle Flow [lpm] 14 Journal of Healthcare Engineering Table 3: List of certifications for VEMERS project. No. Date Type Institution Version Comments Technical Certemed, University of 1 May 26, 2020 VEMERS 1.0 See [21] validation Valparaiso 2 May 28, 2020 Usability test CMFCC VEMERS 1.0 See [22] 3 June 9, 2020 Preclinic tests Hospital Clinico UC Christus VEMERS 1.0 See [23] Technical Certemed, University of 4 June 23, 2020 VEMERS 1.0 See [21] validation Valparaiso August 3, VEMERS Carried on 5 COVID-19 patients for 8 hours each. 5 Clinical tests Hospital Clinico UC Christus 2020 1.0, See [24–26] March 21, Technical Certemed, University of 6 VEMERS 2.0 Volume control modes. See [26] 2021 validation Valparaiso April 14, Technical Certemed, University of 7 VEMERS 2.0 Pressure control modes. See [26] 2021 validation Valparaiso Table 4: Patient General Data in VEMERS UC Clinical tests. Date Testing hours Volume (ml) Frequency (bp) IE ratio PEEP (cm H O) Fio2 Patient age Gender Position 13/07/2020 13 : 20 to 21 : 20 280 32.0 2.0 8.0 45 a 60 62 male Prono 17/07/2020 11 :15 to 19 : 15 260 33.0 1.8 4.0 45 a70 70 Female Prono 21/07/2020 10 : 00 to 18 : 00 360 20.0 2.1 10.0 35 a 40 72 Female Supina 22/07/2020 9 : 00 to 17 : 00 340 28.0 1.9 6.0 45 a 60 59 Female Supina 29/07/2020 13 : 20 to 20 : 00 275 29.7 1.9 7.9 50 a 55 72 Female Supina Table 5: VEMERS 2.0 distribution in the Chilean health system. Regional health service Quantity Hospital Date Servicio de Salud Metropolitano Sur oriente 4 Sotero ´ del R´ıo (4) April 1, 2021 Servicio de Salud del Maule 4 Curico´ (2) and Linares (2) April 12, 2021 Servicio de Salud de Coquimbo 4 La Serena (1), Coquimbo (1), Illapel (1), Ovalle (1) April 19, 2021 Servicio de Salud de Ñuble 3 San Carlos (3) May 7, 2021 Servicio de Salud B´ıo B´ıo, Concepcion ´ 2 Guillermo Grant Benavente (2) June 1, 2021 Servicio de Salud Iquique 3 Iquique (3) June 15, 2021 blockage. )e test consisted of measurements of oxygenation 3.3. Reliability. VEMERS 1.0 was tested clinically with five COVID-19 intubated patients for 8 hours each [24]. To and cardiovascular parameters during operation. For each patient, the first 2-hour measurements were every 15 further verify the reliability, one VEMERS 2.0 unit was set apart for long-term testing. )at unit has been running minutes and after that every 1 hour. )e working parameter settings in VEMERS UC were the same as the patient had nonstop in different ventilation modes starting on April 23, with the conventional ventilator previously connected 2021, using a test lung. At the moment of writing this article, (Table 4). Patient General Data in VEMERS UC Clinical tests it had been running for 121 straight days without any failure. contain general patient data in the tests. Patients usually stay connected to a mechanical ventilator )e clinical tests on VEMERS UC showed that it is for not longer than one month. Hence, this demonstrates the capable of safely maintaining oxygenation and PaCO2 ex- robustness of the VEMERS design. change. It can provide protective ventilation and gas ex- It is surprising from an engineering point of view that change similar to a traditional mechanical ventilator under extensive reliability tests are not required to certify a me- chanical ventilator. )is aspect seems to be left to the re- conditions of impaired lung function. Since this was the last test specified in the CMFCC protocol [18], after completion, sponsibility of the manufacturer. )is is probably why brand this council issued a final report of overall approval. recognition in the mechanical ventilator market is so im- portant. )e special set of standards for emergency use ventilators recommended by [12] is the only standard that 3.2.5. Advanced Technical Evaluation. )ere are specific tests specifically requires demonstrating the continuous opera- for advanced volume control mode of ventilation, as well as tion of 14 days. )e most cited document relative to cer- pressure control mode of ventilation. In the pressure control tification of conventional high-end ventilators published by mode of ventilation, the most complex set of tests is to verify the WHO [14] does not contain any requirements in terms trigger levels for Pressure Support Systems. Otherwise, the of reliability. In Chile, throughout the pandemic, a number tests are quite similar as described in Section 3.2.1. of units of lesser-known brands failed prematurely, which is Journal of Healthcare Engineering 15 However, it is important to keep in mind that being why the authors think that reliability should be considered in more depth and detail for certification purposes in the VEMERS, a life-supporting device, there are high risks in using consumer/industrial grade electronics and compo- future. nents, although they may be appropriate as an absolute last resort in the absence of alternative medical grade options 3.4. Unit Distribution. At the time of writing this article, 20 during the current pandemic. For this reason, additionally, VEMERS 2.0 units have been distributed in the Chilean VEMERS parts and as a whole are being thoroughly and national health system among 9 hospitals as shown in continuously tested to anticipate situations of failure. Until Table 5. now, VEMERS architecture and components have been Usage of VEMERS 2.0 has been mainly as backup units reliable. In spite of having a smaller set of modes of ven- and mostly in patients in noninvasive ventilation modes tilation than some conventional high-end mechanical ven- (CPAP, BiPAP, and High Oxygen Flow )erapy) in tilators, its demonstrated reliability and functionality are a emergency rooms of hospitals. Given the nature of this good solution for the majority of situations that a patient medical equipment and the evolution of the COVID-19 with respiratory problems such as COVID-19 will face. pandemic, clinical testing of VEMERS 2.0 has required )us, the main contribution of this research that can be much more time than expected. More technical and user stated is that starting from a functional block diagram of an updated information can be found on http://www.vemers.cl, ICU mechanical ventilator and carrying a systematic anal- or on the VEMERS YouTube channel. ysis, the main function blocks were implemented in such a way that combinations of standard off-the-shelf pneumatic and electronic components could be used. No special parts 4. Conclusions need to be fabricated at all. )ese components are inter- An emergency use ventilator VEMERS 1.0 was previously connected and then synchronized by ad hoc software to obtain a reliable working ICU ventilator that has an in- developed to comply with the Chilean requirements spec- ified by CMFCC, an ad hoc task force formed by several creased functionality of 8 modes of ventilation. Because of a wider variety of options, the use of extensively field-proven medical associations, government offices, and industry leaders in Chile. VEMERS 1.0 also complies with MHRA off-the-shelf commercial components assures better avail- ability and lower costs when compared to proprietary parts [12] and AAMI [13] guidelines, according to internal tests performed. As an emergency use ventilator, VEMERS 1.0 is common in conventional ICU mechanical ventilators, only required to work in a mandatory volume control mode without sacrificing reliability. of ventilation. In this article, VEMERS 2.0 is described, Future work will be focused on consolidating and which was expanded to eight different ventilation modes by documenting the reliability of VEMERS, through controlled replacing previous directional electropneumatic valves with clinical tests. In addition, adaptations of VEMERS for use in proportional valves. )is allows not only direct flow control anesthesiology, neonate, and transportation ventilators will be explored. but also pressure control, thus making additional modes of ventilation possible. Proportional valves are more expensive Finally, there is much to be done in generating proce- dures and devices to test mechanical ventilators and also in and more difficult to find than directional valves, but they allow not only to expand the capabilities of the original RT training. For this reason, this research team is working on VEMERS 1.0 but also to automate the setting of the re- devices to systematically test EUV and conventional ven- spiratory cycle possible, since manual flow control valves are tilators in triggered mode and in pressure support for a then not needed. )e expansion of capabilities in VEMERS variety of patient conditions. 2.0 has been certified by a Chilean authorized certification bureau (Certemed). Nomenclature Twenty VEMERS 2.0 units have been distributed within the Chilean national health system. )ese units have Acronyms remained as backup and are used occasionally now that the BiPAP: Bilevel inhalation positive airway pressure COVID-19 pandemic has receded, and that the Chilean CPAP: Continuous positive airway pressure health system has enough conventional mechanical venti- CMFCC: Ad hoc committee to certify emergency lators to satisfy demand. mechanical ventilators in Chile VEMERS 2.0 can be produced buying all its components EUV: Emergency use ventilator in the general industrial pneumatic market, and there is FiO2: Fraction of inhalation oxygen really no component that needs to be specially fabricated. HEPA: High-efficiency particulate air filter )e production is mainly an assembly process that takes I : E Inspiratory-expiratory time interval ratio around 1 day. )e approximate cost of the components in ratio: Chile is USD 2,000, which is much less than that of high-end ICU: Intensive care unit mechanical ventilators today in the market. Considering the PEEP: Positive end-expiratory pressure fact that the general resources in Chile as well as in many PIP: Peak inhalation pressure other countries cause less than ideal availability of medical RR: Respiration rate equipment, the knowledge and experience gained in the RT: Respiratory therapist VEMERS project can be helpful to counter this situation. SDV: Solenoid directional valve (ON-OFF) 16 Journal of Healthcare Engineering [9] C. Galbiati, A. Abba, P. Agnes et al., “Mechanical ventilator SPV1: Solenoid proportional valve 1, controls the milano (mvm): a novel mechanical ventilator designed for inspiratory flow mass scale production in response to the COVID-19 pan- SPV2: Solenoid proportional valve 2, controls the demic,” 2020, https://arxiv.org/abs/2003.10405. expiratory flow [10] adminEia, “Prototipo de ventilador mecanico ´ desarrollado en WHO: World Health Organization la EIA comprobara´ su inocuidad para salvar vidas,” EIA University, 2020, https://www.eia.edu.co/avance- Variables informativo-prototipo-de-ventilador-mecanico-desarrollado- A : Area of the aperture of valve SPV1 (mm ) en-la-eia-comprobara-su-inocuidad-para-salvar-vidas/. A : Area of the aperture of valve SPV2 (mm ) [11] SOCHIMU, SOCHIMI, CMFCC, and SACH, “CONSENSO C : Speed of gas mixture through valve SPV1 1 TECNICO CMFCC-SOCHIMI Chile: Validacion ´ de eficacia y C : Speed of gas mixture through valve SPV2 seguridad de ventiladores mecanicos ´ de emergencia (VME),” c : Specific heat of air [Joule/(Kelvin · kg)] 2020, http://www.minciencia.gob.cl/sites/default/files/consenso_ sochimi-cmfcc_validacion_ventiladores_mecanicos_de_ k: Ratio of specific heats of air [ � 1.4] emergencia_crisis_covid-19.pdf. p : Pressure upstream of valve SPV1 [cm H20] [12] Rapidly Manufactured Ventilator System, “Medicines & p : Pressure at the aperture of valve SPV1 [cm H20] Healthcare Products,” Regulatory Agency, 2020, https:// p : Patient lung pressure [cm H20] assets.publishing.service.gov.uk/government/uploads/system/ p : Absolute ambient pressure [cm H20] uploads/attachment_data/file/874279/RMVS001_Rapidly_ p : Critical pressure in choked flow [cm H20] Manufactured_Ventilator_Specification__PDF.pdf. Q : Flow through SPV1 (lpm) [13] Association for the Advancement of Medical Instrumentation Q : Flow through SPV2 (lpm) (AAMI), “Emergency Use Ventilator Design Guidance,” 2020, R: Air gas constant� 287 [Joule/(Kelvin · kg)] https://www.aami.org/docs/default-source/standardslibrary/ T : Absolute temperature upstream of valve SPV1 (kelvin) 200410_cr501-2020_rev1-2.pdf?sfvrsn�699e62b7_2. ρ : Gas mixture density upstream of valve SPV1 [kg/m ]. [14] Iso 80601-2-12, “Particular Requirements for basic safety and essential performance of critical care ventilators,” 2020, https://www.iso.org/standard/72069.html. Data Availability [15] L. E. Chiang, F. A. Castro, and U. C. Vemers, “Vemers UC: a clinically validated emergency mechanical ventilator for All data are available upon request. COVID-19 and postpandemic use in low resource commu- nities,” Journal of Medical Devices, vol. 15, no. 3, 2021. [16] F. Gordo, A. Abella, and B. Lobo-Valbuena, “Innovations in Conflicts of Interest ICU ventilation: the future delivered,” ICU Management & Practice, vol. 19, no. 1, 2019. )e authors declare that they have no conflicts of interest. [17] C. Dave, P. Cameron, J. Basmaji, G. Campbell, E. Buga, and M. Slessarev, “Frugal innovation: enabling mechanical ven- References tilation during coronavirus disease 2019 pandemic in re- source-limited settings,” Critical Care Explorations, PMCID, [1] Who, “COVID-19 Dashboard,” 2021, https://covid19.who.int. vol. 3, no. 4, p. e0410, 2021. [2] Plan de accion ´ Coronavirus, “Cifras Oficiales,” 2021, https:// [18] M. Alcantara Holanda and B. Valle Pinheiro, “COVID-19 www.gob.cl/coronavirus/cifrasoficiales/#datos. pandemic and mechanical ventilation: facing the present, [3] J. 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[25] Cmfcc, “Cierre de evaluaciones en Prototipos de Ventilacion ´ [7] P. xyz, “Emergency ventilator for COVID-19 crisis approved Mecanica ´ para utilizacion ´ en emergencia COVID: VEMERS by the Spanish medicine agency,” OxyGEN,” 2020, https:// UC,” Unpublished, 2020. www.oxygen.protofy.xyz/. [26] Certemed, “Protocolo de Inspeccion ´ para Analisis ´ de Ven- [8] H. Li, E. Li, D. Krishnamurthy et al., “Utah-Stanford Ven- tilador Desarrollado para la Emergencia Generada por tilator (Vent4US): developing a rapidly scalable ventilator for COVID-19:VEMERS UC,” Unpublished, 2021. COVID-19 patients with ARDS,” medRxiv,” 2020, https:// www.medrxiv.org/content/10.1101/2020.04.18.20070367v1.
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