key: cord-320661-p7tyfqyu
authors: Branson, Rich; Dichter, Jeffrey R.; Feldman, Henry; Devereaux, Asha; Dries, David; Perry, John F.; Benditt, Joshua; Hossain, Tanzib; Ghazipura, Marya; King, Mary; Baldisseri, Marie; Christian, Michael D.; Domingiuez-Cherit, Guillermo; Henry, Kiersten; Martland, Anne Marie O.; Huffines, Meredith; Ornoff, Doug; Persoff, Jason; Rodriquez, Dario; Maves, Ryan C.; Kissoon, Niranjan Tex; Rubinson, Lewis
title: The US Strategic National Stockpile (SNS) Ventilators in COVID-19: A Comparison of Functionality and Analysis regarding the Emergency Purchase of 200,000 devices.
date: 2020-09-21
journal: Chest
DOI: 10.1016/j.chest.2020.09.085
sha: 
doc_id: 320661
cord_uid: p7tyfqyu

Background Early in the COVID-19 pandemic, there was serious concern that the United States (US) would encounter a short fall of mechanical ventilators. In response, the US government, utilizing the Defense Production Act ordered the development of 200,000 ventilators from 11 different manufacturers. These ventilators have different capabilities and it is not evident whether all are able to support COVID-19 patients. Research Question Evaluate ventilator requirements for affected COVID-19 patients, assess the clinical performance of current SNS ventilators employed during the pandemic, and finally compare ordered ventilators functionality based on COVID-19 patient needs. Study Design and Methods Current published literature, publicly available documents, and lay press articles were reviewed by a diverse team of disaster experts. Data was assembled into tabular format which formed the basis for analysis and future recommendations. Results COVID-19 patients often develop severe hypoxemic acute respiratory failure and ARDS requiring high levels of ventilator support. Current SNS ventilators were unable to fully support all COVID-19 patients, and only about half of newly ordered ventilators have the capacity to support the most severely affected patients; ventilators with less capacity for providing high level support are still of significant value in caring for many patients. Interpretation Current SNS ventilators and those on order are capable of supporting most but not all COVID-19 patients. Technologic, logistic, and educational challenges encountered from current SNS ventilators are summarized, with potential next generation SNS ventilator updates offered. Clinical Trial Registration N/A

This statement has three objectives. First, it is intended to evaluate the ventilator requirements for COVID-19 and the performance of current SNS ventilators employed during this pandemic. Secondly, this statement will provide a comparison of devices that have been ordered under the EUA and appropriate usage for patient situations. Surplus devices are in consideration for deployment to other countries and this review will assist those nations to appreciate the features and limitations of the equipment received. 4 Lastly, the technologic, logistic, and educational challenges of current SNS ventilators will be summarized and potential future design updates proposed. 

A ventilator is a device used to provide oxygenation and respiratory support in settings in which the patient's own pulmonary system is compromised. 5 Fundamentally, ventilator mechanics involve a mode of operation that incorporates four basic parameters: pressure or volume, fraction of inspired oxygen, respiratory rate, and endexpiratory pressure. Ventilator modes vary based on patients' individual physiologic needs and are set often based on lung compliance, gas exchange, and minute ventilation. 6 In addition, standard ventilators are expected to sense when a patient attempts to breathe and deliver the appropriate breath accordingly. Full-feature mechanical ventilators used to support critically ill patients have advanced instrumentation that gather and display data on the patient's pulmonary mechanics.

These data inform how the ventilator's mode and basic parameters can be adjusted to achieve clinical improvement and liberation from the ventilator. 7, 8 In contrast, positivepressure ventilation devices (e.g., anesthesia machines, non-invasive continuous positive airway pressure and bi-level positive pressure devices, etc.) have a limited number of operational modes and are of limited utility for the prolonged management of patients with COVID-19-associated respiratory failure.

Investigators have described multiple phases of respiratory insufficiency associated with COVID-19. 9 Soon after development of respiratory distress, patients often retain high pulmonary compliance despite poor oxygenation. Minute ventilation in these patients is typically high, and they may not demonstrate overt respiratory distress despite significant hypoxemia. These individuals may be managed with tidal volumes (V T ) above the typical 4-6 milliliters/kilogram ideal body weight (IBW) utilized for acute respiratory distress syndrome (ARDS). Some patients may progress to more classic patterns of hypoxemic respiratory failure with reduced compliance, increased requirements for positive end expiratory pressure (PEEP) and optimal use of smaller tidal volumes. 10 These ventilators are not commonly used in ICU settings, are designed and packed to   withstand delivery by helicopter, and are delivered with an instruction card, video or CD, and a manual (See Figure 3) . The website has extensive links to training; however, due to the rapidity of the surge of COVID-19 patients and the novelty of the organism and its pathogenesis, there was little time for just-in-time education in use of SNS ventilators.

Although these ventilators are intended to be used in austere settings by nonintensivists, the physiology of COVID-19 created challenges for the user. These During Spring 2020 deployment to meet ICU surges additional lessons included reports of battery pack challenges, missing hoses and tubing, and need for equipment repair.

However, when implemented in ICUs, the challenges have not been merely technical, as highlighted by the description from New York (Box 1).

Since volunteers. 21 These devices previously had been suggested for temporary use in limited-resource environments, but a device incapable of meeting patient requirements for pressure, volume, oxygen delivery, and minute ventilation is not a solution during the COVID-19 pandemic.

There were 198,890 ventilators initially ordered by the federal government at a cost of just over 2.9 billion dollars. [22] [23] [24] [25] There are 11 ventilator manufacturers initially contracted to build 15 types of ventilators.

Based on their level of technologic sophistication, at least 58,000 of these nearly 200,000 newly procured ventilators would be considered "full feature" ventilators capable of supporting severe COVID-19 patients, and another 75,000 that could be used on other patients or circumstances (Table 3) . Of note, Philips Corporation was contracted to build 43,000 ventilators which were split between two models, only one of which was a is feature ventilator; and Vyaire Corporation was contracted to build 22,000 ventilators again split between two models only one of which is a full feature ventilator.

Public records do not specify the number each ventilator ordered, thus precluding knowledge of the total number of full function ventilators ordered.

Since the time of the initial orders, some of these orders have been significantly reduced (August 31, 2020). Vyaire will deliver only 4,000 of an initial order of 22,000;

Hamilton up to only 4518 out of 25,574; and Phillips only 12,300 out of 43,000, for a total reduction of 69,576 ventilators. 26, 27 Nonetheless, understanding the functionality of all types of ventilators ordered will inform their best use. Ventilators require iterative preventive maintenance and many require ongoing battery charging to maintain their readiness. Since nearly 200,000 ventilators (now down to 130,000) will not come from a single vendor, most will not have interchangeable parts and most will require massive stockpiling of spare parts for maintenance, which in and of themselves have a storage lifespan. It is therefore important to buy the correct number and type of ventilators, and to ensure future maintenance and parts fulfillment. 33 Ventilators that have full feature support capable of supporting the spectrum of potential The PREP Act provides liability immunity for manufacturers of ventilators and other devices under the EUA (box 2). 28, 29 Evidence for effectiveness includes those devices which "may be effective." An example is the EUA approval of 'splitters' to allow multiple patients to be ventilated using a single ventilator, but these "plumbing solutions" fail to take in to account the physiologic issues that create a potentially dangerous technique which should only be attempted by experts under regulatory approval. 30, 31 In the absence of an EUA, it is likely that none of these 'splitters' could prove safe and otherwise would not obtain FDA approval. If the manufacturer fails to submit additional safety and procedural documents (510K) in a timely manner following expiration of the EUA, the devices will become non-supported and a liability for the recipient. In determining how many additional ventilators are needed to meet the surge capacity demands of COVID-19 across the US with variable waves of disease, it is important to note that the assumption the entire country will be simultaneously impacted may be flawed. During the initial 2020 COVID-19 pandemic wave, the US has not in fact run out of ventilators, although several regions of hot spots have come remarkably close to implementing triage protocols for ventilator allocation, as alluded to in the New York experience. 32 For analysis, we may consider an extreme worst-case second-wave scenario with the 1918 Influenza pandemic as a model, where the second wave is five times 6 worse than the first wave. 33 

Children comprise approximately 25% of the US population and infants and younger Of ventilators currently considered for (or already receiving) federal funding, there are multiple ventilators that are not FDA-approved for pediatric use (see Table 3 ) because their tidal volumes cannot be lowered sufficiently to ventilate the much smaller lungs of a child. These ventilators would be entirely unusable for the majority of pediatric patients.

Pediatric critical care practitioners historically use significantly more non-invasive mechanical ventilation in comparison to adult critical care medicine, in part to avoid the higher risks associated with pediatric intubation and mechanical ventilation. In initial 

Low-and middle-income countries (LMICs), including the countries to the south of the Table 2 As an example, if set VT is 450 mL and the peak pressure is 30 cm H2O and with normal circuit compliance is 2-3 ml/cm H2O, then 90 ml could potentially be lost in the circuit reducing the volume delivered to the patient to 360 ml. The ICU ventilator would increase the VT by 90 mL (540 ml) to assure the patient receives the full 450 ml. VT

The transport ventilator does not compensate for compressible volume loss in the circuit due to tubing compliance.

In the example, the effective VT on the portable ventilator is then 90 ml less than on the ICU ventilator. At a respiratory frequency of 20 bpm this is a decrease in the minute ventilation of almost 2.0 L.

ICU ventilators deliver pressures relative to (above) PEEP.

Aa an example, if PEEP is 10 cm H2O and the set pressure during pressure support or pressure control is 20 cm H2O, then peak pressure would be 30 cm H2O.

In Bi-level devices and some portable ventilators, the pressure is absolute, and not set above PEEP.

In the example, with settings of peak pressure of 20, this includes added PEEP and would therefore be only 10 cms above PEEP or expiratory pressure -a pressure difference of 10 cm H2O vs 20 cm H2O compared to the ICU ventilator.

Set VT = delivered VT. The combination of the three factors above, which may each individually be only slight, can make a large difference in the delivered minute ventilation, reducing carbon dioxide elimination. 

pNeuton is a pneumatic ventilator. Electrical power is not required for patient ventilation. pNeuton has been specifically designed for patient support during transport and noncritical care unit mechanical ventilation. It may be used during intra and inter-hospital transport, in aircraft, on ambulances, in emergency rooms, MRI and other radiology suites.

Use for transport from facility to facility or emergency department to ICU.

Hamilton C1

The HAMILTON-C1 ventilator is intended to provide positivepressure ventilatory support to adults and pediatrics, and optionally infants and neonates. Intended areas of use: 

Mechanical ventilators in US acute care hospitals

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How New York City's Emergency Ventilator Stockpile Ended Up on the Auction Block

New York is putting two coronavirus patients on one ventilator and making them out of anesthesia machines as Cuomo warns patients could be on them for 21 days

Hospitals Cope With Ventilator Shortages

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This Is A Big Deal': New York Hails Ventilator Deliveries From China And Oregon

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