1. Introduction

The breathing process, essential for human life, has four main periods. 1) Pulmonary ventilation: where air enters and leaves the lungs, 2) diffusion: characterized by the passage of oxygen and carbon dioxide (C_o2) from the lung to the pulmonary capillaries, 3) oxygen transport to different cells, and 4) regulation of the whole process, controlled primarily by the brain. When there are failures in the breathing process, cells, especially in the brain, begin to die after 4-6 minutes, much earlier if we compare it with the failure of blood circulation [1].

Breathing is usually rhythmic, slow, and often stable. Physiologically, it varies with age and physical condition. The normal breathing rate of an adult at rest ranges from 12 to 20 breaths per minute. Figures above normal (Adult > 20 x min.) are called polypnea and values below (Adult < 10 x min.) bradypnea.

SARS Cov2 (COVID19) is a virus that has spread around the world at high speed since the end of 2019 due to its high contagion rate. It mainly affects the respiratory system, as shown by its first cases in the municipality of Wuhan in Hubei province in China, which had symptoms of pneumonia [2].

This new Coronavirus has put public health systems in many countries on alert because, despite its low mortality rate of approximately 3.7%, its rapid spread has led to the activation of protocols to stop its spread [3]. In many cases, these protocols have been insufficient, leading to the collapse of the health system due to the lack of resources, both in supplies and medical equipment to detect, contain, and medically treat the virus.

In this context, since the beginning of the pandemic, the main public and private laboratories have entered a race to find an effective vaccine against the virus, leading to the global development of more than 200 vaccines in different research states [4]; six of which were already tested on healthy volunteers [5], to March 2021 the vaccines of Pfizer/BioNTech, Janssen, Moderna, Sinopharm and the two versions of AstraZeneca/Oxford - (SKBio-Serum Institute of India) have been approved by the World Health Organization (WHO) and are being distributed around the world [6]. These WHO-approved vaccines represent approximately 64% of the doses purchased by Latin American countries, the remaining 36% are from 8 other laboratories [7]. Of the 1,398 million doses purchased for the region, 70% belong to Brazil and Mexico, which are also the two most populous countries in Latin America with more than 50% of the region's population [8].

Figure 1 shows that only six countries in the region have prepared for this pandemic by acquiring the necessary doses to protect 100 percent of their population.

Figure 1
Percentage of both insured and optional doses from some countries in the region.
Source: [8].

The percentage of vaccines expected to be procured by each country in the region is significant because, according to WHO, the proportion of the population that must be vaccinated to achieve a collective immunization is still unknown [9] and some researchers present more in-depth analysis on this topic, such as the article published by science journalist Christie Aschwanden in the journal Nature on March 31, where there are five reasons why herd immunity cannot be trusted against COVID-19 [10].

Another problem with vaccine-only pandemic control plans is the effectiveness of vaccines since WHO recommends that vaccines must be 70 percent effective, although they set a minimum critical value of 50 percent, this means that none of the vaccines will control the pandemic in the entire vaccinated population [11]. Some of the effectiveness values for the most commercially available vaccines are presented in Figure 2, considering that three of these vaccines are below the WHO recommended value and represent approximately 23 percent of the doses purchased in the region, is an element that will affect the development of the pandemic when other alternatives are not analyzed to control the over-quota of the Intensive Care Units (ICU).

Figure 2
Effectiveness of the most commercialized vaccines.
Source: [7].

The last element that is influencing the progressive development of the pandemic (third and fourth peaks) is the timing of vaccination plans, since, as of May 5, 2021, only Chile has reached 80% of the vaccination population with at least one dose. While the other countries of South America are far from these values, Uruguay and Brazil reach 55% and 21% respectively of their population while Argentina and Colombia are between 10% and 20% of their population vaccinated with at least one dose, the other countries of South America are below 10%. Vaccination time can be extended much longer since these vaccination processes have been in progress for 3 to 5 months [12].

When assessing the state of the pandemic in Colombia as of May 5, 2021, it can be seen that the main cities of the country such as Bogotá, Medellín, Cali, and Barranquilla exceed 90% of the occupation of intensive-care rooms[13], while some others such as Tunja reach 100% occupation [14]. It is necessary to implement strategies that allow new procedures to be applied to address this current problem that the country and the Latin American region are experiencing.

One of the fundamental pieces of equipment for this fight against the COVID19 is the assisted mechanical respirators used in the intensive-care rooms of the medical centers, which are currently very busy in our country (Colombia). In this context, an innovative idea has emerged, which allows multiplying the use of artificial mechanical ventilators, by attaching to them a device to distribute the mixture of air and oxygen coming from the ventilator to several patients simultaneously (multiple mechanical ventilation) [15].

This peculiar technique was applied during the Las Vegas (U.S. shootings). However, this solution has created debate among the medical community, as many fears for the safety of their patients, because when coupling the device (flow divider) the ventilator loses control over the variables of the mechanical ventilation of each of the patients and could only be kept a general watch on the ventilator.

Intending to contribute diminishing the controversy surrounding the safety of the mechanical respiration methodology for multiple patients, this article presents a thorough review of the studies carried out on the subject, which provides an objective view of the risks and benefits of the method, in addition to carrying out a comparative cost analysis between the acquisition of a mechanical ventilator and the flow division system.

2. Methods

2.1. Information Flow divider connector

Mechanical ventilation is an essential component in intensive-care units as it is responsible for generating the cycles of inspiration and expiration in people with respiratory system failures. There are different modes in which a mechanical ventilator can operate between which two of them can be highlighted, 1) volume control (VCV) where a certain pre-adjusted inspiratory flow is kept constant uncontrollably varying lung pressure conditions; and 2) pressure control (VCP), where airway pressure is adjusted and remains constant, regardless of changes in lung tissue resistance and diaphragm [16].

The flow splitting device (see Figure 3) is an accessory, usually plastic; it can be coupled to the mechanical ventilator (see Figure 4), to generate multiple pulmonary ventilation for patients, which is an alternative to address the possible shortage of hospital pulmonary ventilation devices.

Figure 3
Flow divider devices for multiple patient lung ventilation. (a) VESper ™ device licensed for emergency use (UAE) by the FDA during times of acute equipment shortages [18]. (b) Different shapes of Flow Splitter Devices for 3D printing manufacturing [19].

Figure 4
Circuit assembled to provide simultaneous ventilation to four adults in the study "A Single Ventilator for Multiple Simulated Patients to Meet Disaster Surge" [20].

The methodology applied for the selection of articles follows the recommendations given for an article, where it is recommended to evaluate the validity of the study, the results obtained, and the relevance or applicability of the same [17]. Thus, the methodology of the review focuses on those studies that help to reduce the controversy over the use of these systems, in the first place the criteria that contribute to the discussion are established, understanding and identification of the effects they may have on patients; the methodology used is then sought, prioritizing the most up-to-date and experimental studies with systems incorporating instruments to measure and control variables; finally, studies that show results that pro or against the use of these multiple patient systems are identified. Concerning comparative cost analyses, quotes from specialized marketers, online sources, and medical staff are sought, to have a comprehensive overview of equipment costs, the average values of the equipment and accessories required to determine the suitability of these mechanical respiration systems for multiple patients will then be taken.

3. Results and discussion

The idea of using a flow-splitting device has been approached experimentally by several research groups, where using simulators of lungs, animals, or in short intervals of time in humans, aim to determine the reliability of the method and the parameters to be configured in the ventilator for multiple pulmonary ventilation. In Table 1 are shown the studies carried out regarding the subject, including, configuration and main results:

Table 1

Consolidated research on multiple mechanical ventilation (1 of 4)

Source: authors.

Some other authors, through letters to journal editors, expressed their concerns about the results of these experimental studies [35], [36], giving their opinions on the significant risks to patient safety (inability to individualize the ventilation of each patient, insufficient monitoring, cross-contamination, rebalancing of the airflow when a patient improves or deteriorates), which is shared by some medical associations that discourage the use of this methodology [37] and add that there would be logistical challenges to implement them and ethical problems.

The first published article analyzed the feasibility of using a ventilator for mechanical ventilation for up to four patients (with the same respiratory requirements) without delving into the medical implications of each one. From the crisis generated by the lack of medical equipment (mechanical ventilators) due to the COVID-19 pandemic, research on this topic was increased, analyzing the connection of patients with different respiratory requirements.

From previous studies, it can be noted that the initial idea, although innovative, carries dangers for patients. These risks were subsequently addressed by other researchers, who tried to solve them through the inclusion of accessories to the respiratory circuits that connect the ventilator to patients, to individualize the ventilation and monitoring system, for everyone connected to the ventilator.

For example, in the work of "A rapidly deployable individualized system for augmenting ventilator capacity" [28] the accessories are shown and where they were located to install the pulmonary ventilation of multiple patients more safely (See Figure 5).

Figure 5
Individualized system design to provide patient simultaneous ventilation more safely "A rapidly deployable individualized system for augmenting ventilator capacity" [28].

The design of the assembly proposed by Srinivasan contains several extra accessories that are not included in the conventional respiratory circuits, which will allow dividing the ventilation with certain safety parameters. A cost analysis of the inclusion of these accessories is shown in Table 2.

Table 2

Cost analysis of multiple mechanical ventilation system for two patients

Source: authors.

The conventional mechanical ventilation, as shown in Figure 6, includes a mechanical ventilator that has a front panel that allows to monitor and control the parameters of the patient to be ventilated, and includes a respiratory circuit and filters. A cost analysis of a conventional system is shown in Table 3.

Figure 6
Conventional mechanical ventilation "Mechanical ventilation".
Source: [38].

Table 3

Cost analysis of conventional mechanical ventilation system for each patient

Source: authors.

4. Conclusions

Analyzing the values of Table 2 and 3, corresponding to the cost analysis of each of the systems, it can be asserted that it is more economical to use a circuit with a connector for flow division in two patients, which would entail a total cost of approximately $74,180,000, to connect each of them separately, which would lead to a total approximate cost of $130,060,000 ($65,030,000 purr patient). In addition, it can be concluded that the inclusion of additional accessories such as filters, unidirectional valves, limiting and pressure-releasing valves, together with monitors and flow-splitting devices, have allowed the division of ventilation with certain safety parameters, as was shown by some experimental studies, which were summarized in Table 1.

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Notes

Author notes

^a Emails: yina.quintero@usantoto.edu.co^bedwin.rua@usantoto.edu.co. ^ccarlos.aguirre@usantoto.edu.co^daradeisita@hotmail.com.