COVID-19 Lessons Learned: Response to the Anticipated Ventilator Shortage.

Early in the COVID-19 pandemic predictions of a worldwide ventilator shortage prompted a worldwide search for solutions. The impetus for the scramble for ventilators was spurred on by inaccurate and often unrealistic predictions of ventilator requirements. Initial efforts looked simply at acquiring as many ventilators as possible from national and international sources. Ventilators from the Strategic National Stockpile were distributed to early hotspots in the Northeast and Northwest United States. In a triumph of emotion over logic, well-intended experts from other industries turned their time, talent, and treasure toward making a ventilator for the first time. Interest in shared ventilation (more than one patient per ventilator) was ignited by an ill-advised video on social media that ignored the principles of gas delivery in deference to social media notoriety. With shared ventilation, a number of groups mistook a physiologic problem for a plumbing problem. The United States government invoked the Defense Production Act to push automotive manufacturers to partner with existing ventilator manufacturers to speed production. The FDA granted emergency use authorization for "splitters" to allow shared ventilation as well as for ventilators and ancillary equipment. Rationing of ventilators was discussed in the lay press and medical literature but was never necessary in the US. Finally, planners realized that staff with expertise in providing mechanical ventilation were the most important shortage. Over 200,000 ventilators were purchased by the United States government, states, cities, health systems, and individuals. Most had little value in caring for patients with COVID-19 ARDS. This paper attempts to look at where miscalculations were made, with an eye toward what we can do better in the future.

Oxygenation and Respiratory System Compliance Associated With Pulmonary Contusion.

BACKGROUND: Blunt pulmonary contusions are associated with severe chest injuries and are independently associated with worse outcomes. Previous preclinical studies suggest that contusion progression precipitates poor pulmonary function; however, there are few current clinical data to corroborate this hypothesis. We examined pulmonary dynamics and oxygenation in subjects with pulmonary contusions to evaluate for impaired respiratory function. METHODS: A chest injury database was reviewed for pulmonary contusions over 5 years at an urban trauma center. This database was expanded to capture mechanical ventilation parameters for the first 7 days on all patients with pulmonary contusion and who were intubated. Daily [Formula: see text]:[Formula: see text], oxygenation indexes (OI), and dynamic compliances were calculated. Pulmonary contusions were stratified by severity. The Fisher exact and chi square tests were performed on categorical variables, and Mann-Whitney U-tests were performed on continuous variables. Significance was assessed at a level of 0.05. RESULTS A TOTAL OF: 1,176 patients presented with pulmonary contusions, of whom, 301 subjects (25.6%) required intubation and had available invasive mechanical ventilation data. Of these, 144 (47.8%) had mild-moderate pulmonary contusion and 157 (52.2%) had severe pulmonary contusion. Overall injury severity score was high, with a median injury severity score of 29 (interquartile range, 22-38). The median duration of mechanical ventilation for mild-moderate pulmonary contusion was 7 d versus 10 d for severe pulmonary contusion (P = .048). All the subjects displayed moderate hypoxemia, which worsened until day 4-5 after intubation. Severe pulmonary contusion was associated with significantly worse early hypoxia on day 1 and day 2 versus mild-moderate pulmonary contusion. Severe pulmonary contusion also had a higher oxygenation index than mild-moderate pulmonary contusion. This trend persisted after adjustment for other factors, including transfusion and fluid administration. CONCLUSIONS: Pulmonary contusions played an important role in the course of subjects who were acutely injured and required mechanical ventilation. Contusions were associated with hypoxemia not fully characterized by [Formula: see text]: [Formula: see text], and severe contusions had durable elevations in the oxygenation index despite confounders.

Maximizing Oxygen Delivery in Portable Ventilators.

BACKGROUND: Military transport of critically ill/injured patients requires judicious use of resources. Maintaining oxygen (O2) supplies for mechanically ventilated is crucial. O2 cylinders are difficult to transport due to the size and weight and add the risk of fire in an aircraft. The proposed solution is the use of a portable oxygen concentrator (POC) to supply O2 for mechanical ventilation. As long as power is available, a POC can provide an endless supply of O2. Anecdotal evidence suggests that as little as 3 L/min of O2 could manage as many as 2/3 of the mechanically ventilated military aeromedical transport patients. MATERIALS AND METHODS: We evaluated two each of the AutoMedx SAVe II, Hamilton T1, Zoll 731, and Ventec VOCSN portable ventilators over a range of settings paired with 1 and 2 Caire SAROS POCs at ground level and simulated altitudes of 8,000 feet, 16,000 feet, and 22,000 feet. The Ventec VOCSN has the capability of utilizing an internal O2 concentrator that uses pulsed dose technology, which was also evaluated. Each ventilator was attached to a Michigan Instruments Training Test Lung. Output from the POC was bled into each ventilator via the mechanism provided with each device. A Fleisch pneumotach was used to measure delivered tidal volume (VT), and a fast-response O2 analyzer was used to measure FiO2 within the simulated lung. Ventilator parameters and FiO2 were continuously measured and recorded at each altitude. One-way analysis of variance was used to determine statistically significant differences (P < .05) in FiO2 between ventilators and among the same ventilator model at each testing condition. RESULTS: Delivered FiO2 varied widely between ventilator models and between devices of the same model with some testing conditions. Differences in FiO2 between ventilators at a majority (98.5%) of testing conditions were statistically significant (P < .05) but not all were clinically important. The Zoll 731 delivered the highest and most consistent FiO2 over all ventilator/POC settings at all altitudes. Differences in FiO2 at a given ventilator/POC setting from ground level to 22,000 feet were not clinically important (<5%) with this device. The VOCSN utilizing the integrated internal O2 concentrator delivered the lowest FiO2 across all ventilator/POC settings and altitudes. Due to the inability of the SAVe II to operate at the minute ventilation and positive end expiratory pressure (PEEP) settings required by the testing protocol, the device was only tested at one ventilator setting. The Hamilton T1 failed to operate appropriately at the highest VT/PEEP setting at 16,000 feet and all but one ventilator setting at 22,000 feet. The delivered FiO2 was not included in the analysis for those ventilator settings. The highest delivered FiO2 was 0.85 ± 0.05 at the 250 mL VT setting using 2 POCs (P < .0001) at ground level with the Zoll 731. CONCLUSIONS: Oxygen delivery utilizing POCs is dependent upon multiple factors including ventilator operating characteristics, ventilator settings, altitude, and the use of pulsed dose or continuous flow O2. Careful patient selection would be paramount to provide safe mechanical ventilation using this method of O2 delivery.

Ketamine Stability over Six Months of Exposure to Moderate and High Temperature Environments.

Background: All medications should be stored within temperature ranges defined by manufacturers, but logistical and operational challenges of prehospital and military settings complicate adherence to these recommendations. Lorazepam and succinylcholine experience clinically relevant heat-related degradation, whereas midazolam does not. Because ketamine's stability when stored outside manufacturer recommendations is unknown, we evaluated the heat-related degradation of ketamine exposed to several temperature ranges. Methods: One hundred twenty vials of ketamine (50 mg/mL labeled concentration) from the same manufacturer lot were equally distributed and stored for six months in five environments: an active EMS unit in southwest Ohio (May-October 2019); heat chamber at constant 120 °F (C1); heat chamber fluctuating over 24 hours from 86 °F-120 °F (C2); heat chamber fluctuating over 24 hours from 40 °F-120 °F (C3); heat chamber kept at constant 70 °F (manufacturer recommended room temperature, C4). Four ketamine vials were removed every 30 days from each environment and sent to an FDA-accredited commercial lab for high performance liquid chromatography testing. Data loggers and thermistors allowed temperature recording every minute for all environments. Cumulative heat exposure was quantified by mean kinetic temperature (MKT), which accounts for additional heat-stress over time caused by temperature fluctuations and is a superior measure than simple ambient temperature. MKT was calculated for each environment at the time of ketamine removal. Descriptive statistics were used to describe the concentration changes at each time point. Results: The MKT ranged from 73.6 °F-80.7 °F in the active EMS unit and stayed constant for each chamber (C1 MKT: 120 °F, C2 MKT: 107.3 °F, C3 MKT: 96.5 °F, C4 MKT: 70 °F). No significant absolute ketamine degradation, or trends in degradation, occurred in any environment at any time point. The lowest median concentration occurred in the EMS-stored samples removed after 6 months [48.2 mg/mL (47.75, 48.35)], or 96.4% relative strength to labeled concentration. Conclusion: Ketamine samples exhibited limited degradation after 6 months of exposure to real world and simulated extreme high temperature environments exceeding manufacturer recommendations. Future studies are necessary to evaluate ketamine stability beyond 6 months.

Antimicrobial Coating Prevents Ventilator-Associated Pneumonia in a 72 hour Large Animal Model.

BACKGROUND: The primary goal of this study was to demonstrate that endotracheal tubes coated with antimicrobial lipids plus mucolytic or antimicrobial lipids with antibiotics plus mucolytic would significantly reduce pneumonia in the lungs of pigs after 72 hours of continuous mechanical ventilation compared to uncoated controls. MATERIALS AND METHODS: Eighteen female pigs were mechanically ventilated for up to 72 hours through uncoated endotracheal tubes, endotracheal tubes coated with the antimicrobial lipid, octadecylamine, and the mucolytic, N-acetylcysteine, or tubes coated with octadecylamine, N-acetylcysteine, doxycycline, and levofloxacin (6 pigs per group). No exogenous bacteria were inoculated into the pigs, pneumonia resulted from the pigs' endogenous oral flora. Vital signs were recorded every 15 minutes and arterial blood gas measurements were obtained for the duration of the experiment. Pigs were sacrificed either after completion of 72 hours of mechanical ventilation or just prior to hypoxic arrest. Lungs, trachea, and endotracheal tubes were harvested for analysis to include bacterial counts of lung, trachea, and endotracheal tubes, lung wet and dry weights, and lung tissue for histology. RESULTS: Pigs ventilated with coated endotracheal tubes were less hypoxic, had less bacterial colonization of the lungs, and survived significantly longer than pigs ventilated with uncoated tubes. Octadecylamine-N-acetylcysteine-doxycycline-levofloxacin coated endotracheal tubes had less bacterial colonization than uncoated or octadecylamine-N-acetylcysteine coated tubes. CONCLUSION: Endotracheal tubes coated with antimicrobial lipids plus mucolytic and antimicrobial lipids with antibiotics plus mucolytic reduced bacterial colonization of pig lungs after prolonged mechanical ventilation and may be an effective strategy to reduce ventilator-associated pneumonia.

2020 Year in Review: Shared Ventilation for COVID-19.

COVID-19 resulting from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in a pandemic of respiratory failure previously unencountered. Early in the pandemic, concentrated infections in high-density population cities threatened to overwhelm health systems, and ventilator shortages were predicted. An early proposed solution was the use of shared ventilation, or the use of a single ventilator to support ≥ 2 patients. Spurred by ill-conceived social media posts, the idea spread in the lay press. Prior to 2020, there were 7 publications on this topic. A year later, more than 40 publications have addressed the technical details for shared ventilation, clinical experience with shared ventilation, as well as the numerous limitations and ethics of the technique. This is a review of the literature regarding shared ventilation from peer-reviewed articles published in 2020.

Performance Characteristics of Fluid Warming Technology in Austere Environments.

Resuscitation of the critically ill or injured is a significant and complex task in any setting, often complicated by environmental influences. Hypothermia is one of the components of the "Triad of Death" in trauma patients. Devices for warming IV fluids in the austere environment must be small and portable, able to operate on battery power, warm fluids to normal body temperature (37°C), and perform under various conditions, including at altitude. The authors evaluated four portable fluid warmers that are currently fielded or have potential for use in military environments.

Enhancing Military Burn- and Trauma-Related Acute Kidney Injury Prediction Through an Automated Machine Learning Platform and Point-of-Care Testing.

CONTEXT.­: Delayed recognition of acute kidney injury (AKI) results in poor outcomes in military and civilian burn-trauma care. Poor predictive ability of urine output (UOP) and creatinine contribute to the delayed recognition of AKI. OBJECTIVE.­: To determine the impact of point-of-care (POC) AKI biomarker enhanced by machine learning (ML) algorithms in burn-injured and trauma patients. DESIGN.­: We conducted a 2-phased study to develop and validate a novel POC device for measuring neutrophil gelatinase-associated lipocalin (NGAL) and creatinine from blood samples. In phase I, 40 remnant plasma samples were used to evaluate the analytic performance of the POC device. Next, phase II enrolled 125 adults with either burns that were 20% or greater of total body surface area or nonburn trauma with suspicion of AKI for clinical validation. We applied an automated ML approach to develop models predicting AKI, using a combination of NGAL, creatinine, and/or UOP as features. RESULTS.­: Point-of-care NGAL (mean [SD] bias: 9.8 [38.5] ng/mL, P = .10) and creatinine results (mean [SD] bias: 0.28 [0.30] mg/dL, P = .18) were comparable to the reference method. NGAL was an independent predictor of AKI (odds ratio, 1.6; 95% CI, 0.08-5.20; P = .01). The optimal ML model achieved an accuracy, sensitivity, and specificity of 96%, 92.3%, and 97.7%, respectively, with NGAL, creatinine, and UOP as features. Area under the receiver operator curve was 0.96. CONCLUSIONS.­: Point-of-care NGAL testing is feasible and produces results comparable to reference methods. Machine learning enhanced the predictive performance of AKI biomarkers including NGAL and was superior to the current techniques.

Top 10 Research Priorities for U.S. Military En Route Combat Casualty Care.

INTRODUCTION: Within the Military Health System, the process of transporting patients from an initial point of injury and throughout the entire continuum of care is called "en route care." A Committee on En Route Combat Casualty Care was established in 2016 as part of the DoD Joint Trauma System to create practice guidelines, recommend training standards, and identify research priorities within the military en route care system. MATERIALS AND METHODS: Following an analysis of currently funded research, future capabilities, and findings from a comprehensive scoping study, members of a sub-working group for research identified the top research priorities that were needed to better guide evidence-based decisions for practice and policy, as well as the future state of en route care. RESULTS: Based on the input from the entire committee, 10 en route care research topics were rank-ordered in the following manner: (1) medical documentation, (2) clinical decision support, (3) patient monitoring, (4) transport physiology, (5) transfer of care, (6) maintaining normothermia, (7) transport timing following damage control resuscitation or surgery, (8) intelligent tasking, (9) commander's risk assessment, and (10) unmanned transport. Specific research questions and technological development needs were further developed by committee members in an effort to guide future research and development initiatives that can directly support operational en route care needs. The research priorities reflect three common themes, which include efforts to enhance or increase care provider capability and capacity; understand the impact of transportation on patient physiology; and increase the ability to coordinate, communicate, and facilitate patient movement. Technology needs for en route care must support interoperability of medical information, equipment, and supplies across the global military health system in addition to adjusting to a dynamic transport environment with the smallest possible weight, space, and power requirements. CONCLUSIONS: To ensure an evidence-based approach to future military conflicts and other medical challenges, focused research and technological development to address these 10 en route care research gaps are urgently needed.

The US Strategic National Stockpile Ventilators in Coronavirus Disease 2019: A Comparison of Functionality and Analysis Regarding the Emergency Purchase of 200,000 Devices.

BACKGROUND: Early in the coronavirus disease 2019 (COVID-19) pandemic, there was serious concern that the United States would encounter a shortfall of mechanical ventilators. In response, the US government, using the Defense Production Act, ordered the development of 200,000 ventilators from 11 different manufacturers. These ventilators have different capabilities, and whether all are able to support COVID-19 patients is not evident. RESEARCH QUESTION: Evaluate ventilator requirements for affected COVID-19 patients, assess the clinical performance of current US Strategic National Stockpile (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 were 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 adult respiratory defense syndrome (ARDS), requiring high levels of ventilator support. Current SNS ventilators were unable to fully support all COVID-19 patients, and only approximately 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.

Intrathoracic Pressure Regulator Performance in the Setting of Hemorrhage and Acute Lung Injury.

INTRODUCTION: Intrathoracic pressure regulation (ITPR) can be utilized to enhance venous return and cardiac preload by inducing negative end expiratory pressure in mechanically ventilated patients. Previous preclinical studies have shown increased mean arterial pressure (MAP) and decreased intracranial pressure (ICP) with use of an ITPR device. The aim of this study was to evaluate the hemodynamic and respiratory effects of ITPR in a porcine polytrauma model of hemorrhagic shock and acute lung injury (ALI). METHODS: Swine were anesthetized and underwent a combination of sham, hemorrhage, and/or lung injury. The experimental groups included: no injury with and without ITPR (ITPR, Sham), hemorrhage with and without ITPR (ITPR/Hem, Hem), and hemorrhage and ALI with and without ITPR (ITPR/Hem/ALI, Hem/ALI). The ITPR device was initiated at a setting of -3 cmH2O and incrementally decreased by 3 cmH2O after 30 minutes on each setting, with 15 minutes allowed for recovery between settings, to a nadir of -12 cmH2O. Histopathological analysis of the lungs was scored by blinded, independent reviewers. Of note, all animals were chemically paralyzed for the experiments to suppress gasping at ITPR pressures below -6 cmH2O. RESULTS: Adequate shock was induced in the hemorrhage model, with the MAP being decreased in the Hem and ITPR/Hem group compared with Sham and ITPR/Sham, respectively, at all time points (Hem 54.2 ± 6.5 mmHg vs. 88.0 ± 13.9 mmHg, p < 0.01, -12 cmH2O; ITPR/Hem 59.5 ± 14.4 mmHg vs. 86.7 ± 12.1 mmHg, p < 0.01, -12 cmH2O). In addition, the PaO2/FIO2 ratio was appropriately decreased in Hem/ALI compared with Sham and Hem groups (231.6 ± 152.5 vs. 502.0 ± 24.6 (Sham) p < 0.05 vs. 463.6 ± 10.2, (Hem) p < 0.01, -12 cmH2O). Heart rate was consistently higher in the ITPR/Hem/ALI group compared with the Hem/ALI group (255 ± 26 bpm vs. 150.6 ± 62.3 bpm, -12 cmH2O) and higher in the ITPR/Hem group compared with Hem. Respiratory rate (adjusted to maintain pH) was also higher in the ITPR/Hem/ALI group compared with Hem/ALI at -9 and - 12 cmH2O (32.8 ± 3.0 breaths per minute (bpm) vs. 26.8 ± 3.6 bpm, -12 cmH2O) and higher in the ITPR/Hem group compared with Hem at -6, -9, and - 12 cmH2O. Lung compliance and end expiratory lung volume (EELV) were both consistently decreased in all three ITPR groups compared with their controls. Histopathologic severity of lung injury was worse in the ITPR and ALI groups compared with their respective injured controls or Sham. CONCLUSION: In this swine polytrauma model, we demonstrated successful establishment of hemorrhage and combined hemorrhage/ALI models. While ITPR did not demonstrate a benefit for MAP or ICP, our data demonstrate that the ITPR device induced tachycardia with associated increase in cardiac output, as well as tachypnea with decreased lung compliance, EELV, PaO2/FIO2 ratio, and worse histopathologic lung injury. Therefore, implementation of the ITPR device in the setting of polytrauma may compromise pulmonary function without significant hemodynamic improvement.

Monitoring During Transport.

Transport of critically ill patients within and between hospitals is a common undertaking in an effort to improve patient outcomes. Intrahospital transports are frequently conducted to aid in diagnosis through advanced imaging techniques or to allow image-guided procedures. Interhospital transport is most frequently conducted to bring patients to specialized care, including centers of excellence for cardiac, trauma, transplant, and respiratory failure. Transport outside the hospital can be accomplished by ground or air, the latter including fixed-wing and rotor-wing aircraft. Often overlooked, transport of patients from the scene of an accident or illness to the hospital by emergency medical services is less sophisticated but more common than the other methods combined. Patients are also routinely transported to and from the operating room, a form of transport not commonly studied. Risks are inherent to transport, and an analysis of risks and benefits must be part of any risk-mitigation strategy. Monitoring the patient during transport by attendants and equipment is a key component of risk mitigation. Quicker transport times and specialized transport teams are associated with improved outcomes, whereas severity of illness is a harbinger of untoward complications. The type of monitoring during transport varies widely with the environment, the skill of the attendants, and the severity of patient illness. Standards for patient monitoring during transport are available, but they are predominantly based on expert opinion. This paper reviews guidelines and the risks of transport as a template for required monitoring, and it discusses common mishaps associated with transport and how these can be avoided with appropriate monitoring.

Pulsed Dose Oxygen Delivery During Mechanical Ventilation: Impact on Oxygenation.

INTRODUCTION: Adequate oxygenation is one of the primary goals of mechanical ventilation. Maintenance of adequate oxygenation and prevention of hypoxemia are the primary goals for the battlefield casualty, but military operations have unique concerns. In military operations, oxygen is a limited resource. A portable oxygen concentrator has the advantage of operating solely from electrical power and theoretically is a never-exhausting supply of oxygen. Our previous bench work demonstrated that the pulsed dose setting of the concentrator can be used in concert with the ventilator to maximize oxygen delivery. We evaluated this ventilator/concentrator system with closed loop control of oxygen output in a porcine model. MATERIALS AND METHODS: The Zoll 731 portable ventilator and Sequal Saros portable oxygen concentrator were used for this study. The ventilator and concentrator were connected via a USB cable to allow communication. The ventilator was modified to allow closed loop control of oxygen based on the oxygen saturation (SpO2) via the integral pulse oximetry sensor. The ventilator communicates with the concentrator to increase or decrease oxygen bolus size to maintain a target SpO2 of 94%. Three separate experiments were conducted in this study. Experiments 1 and 2 used oxygen bolus sizes 16-96 mL in 16-mL increments and experiment 3 used 1 mL increments. The oxygen bolus was delivered from the concentrator and injected into the ventilator circuit at the patient connector. Six pigs were used for each experiment. Experiment 1, done without lung injury, was completed to determine the optimum timing during the respiratory cycle for injecting the oxygen bolus. Lung injury for experiments 2 and 3 was induced in the animals by warmed saline lavage via the endotracheal tube until PaO2/FIO2 decreased to <100. The pigs were then placed on the ventilator/concentrator system and allowed to adjust the oxygen autonomously to determine if the target SpO2 could be maintained. PEEP was manually adjusted. Arterial blood gases were drawn to verify the PaO2 and the SpO2/SaO2 correlation. RESULTS: Experiment 1 showed that the O2 bolus injected into the ventilator circuit 300 ms before breath delivery produced the highest PaO2. Mean PaO2/FIO2 was 500 ± 33 for experiments 2 and 3 before lung lavage and 72 ± 11 after lung lavage (p < 0.001), representing severe acute respiratory distress syndrome. Thirty minutes after placing the animals on the ventilator/concentrator system, the bolus size range was 64-96 mL and 16-96 mL after 2 hours (p < 0.05). The SpO2 range was 81-95% after 30 minutes and 94-98% after 2 hours (p < 0.05). PEEP range was 5-14 cm H2O. The SpO2 to SaO2 difference was ≤4% throughout the evaluation. CONCLUSIONS: The ventilator/concentrator system was able to manage oxygenation of severely injured lungs in a porcine model by injecting oxygen boluses at the front end of the ventilator breath, and appropriate use of PEEP to maximize oxygen delivery at the alveolar level. This proof of concept ventilator system may prove to be of use in situations where high-pressure oxygen is unavailable but electricity is accessible.

A bench study of inhaled nitric oxide delivery during high frequency percussive ventilation.

BACKGROUND: Safe and effective delivery of inhaled nitric oxide (INO) requires the appropriate interface of ventilator and INO delivery device. METHODS: We compared INO delivery using four configurations with the Transport Sinusoidal Bronchotron® and INOmax DSIR Plus® in a lung model. Ventilator settings and lung model values were held constant. Delivered NO, NO2 , and inspired oxygen (FIO2 ) were measured. The mean difference between set and measured NO was calculated and compared using ANOVA. RESULTS: Placement of the injector module in line with the sliding venturi resulted in a ventilator failure. With both continuous flow techniques there was no appreciable NO2 generated and the mean difference between set NO and measured NO at 20 and 40 ppm was -16.5 ppm and -33.2 ppm at flows of 5 and 10 L/min. Placement of the injector module between the sliding venturi and lung model resulted in an increase of NO2 to a peak of 2.4 ppm (mean 2.3 + 0.1) and a mean difference between set and measured NO of + 11.3 ppm and +30 ppm at 20 and 40 ppm, 300 cycles per minute (cpm), and 22.1 ppm and 37.6 ppm, at 20 and 40 ppm, 600 cpm. None of the test configurations delivered INO within 30% of set concentrations. No alarms or interruption of INO delivery occurred. CONCLUSION: The dual gas delivery system of the Bronchotron prevents accurate delivery of INO. The combination of these two devices should be accomplished with caution and vigilance.

Evaluation of Intensive Care Unit Ventilators at Altitude.

INTRODUCTION: Devices may forgo US military air worthiness and safety testing in an attempt to expedite the availability of critical assets such as mechanical ventilators with a waiver for one-time use in extenuating circumstances. METHODS: We evaluated two Intensive Care Unit (ICU) level ventilators: Drager Evita XL and Puritan Bennett (PB) 840 in an altitude chamber at sea level and altitudes of 8,000 and 16,000 feet. RESULTS: Altitude affected delivered tidal volumes (VTs) in volume control mode (VCV) and Pressure Regulated Volume Controlled (PRVC) mode at altitude with the Evita XL but the differences were not considered clinically important with the PB 840. Sixty-seven percent of the VTs were outside the ASTM standard of ± 10% of set VT with the Evita XL at altitude. CONCLUSION: The PB 840 did not deliver VTs that were larger than the ASTM standard up to an altitude of 16,000 feet while the majority of the delivered VTs with the Därger XL were greater than the ASTM standard. This could present a patient safety issue. Caregivers must be aware of the capabilities and limitations of ICU ventilators when utilized in a hypobaric environment in order to provide safe care.