Data automated bag breathing unit for COVID-19 ventilator shortages.

BACKGROUND: The COVID-19 pandemic has caused a global mechanical ventilator shortage for treatment of severe acute respiratory failure. Development of novel breathing devices has been proposed as a low cost, rapid solution when full-featured ventilators are unavailable. Here we report the design, bench testing and preclinical results for an 'Automated Bag Breathing Unit' (ABBU). Output parameters were validated with mechanical test lungs followed by animal model testing. RESULTS: The ABBU design uses a programmable motor-driven wheel assembled for adult resuscitation bag-valve compression. ABBU can control tidal volume (200-800 ml), respiratory rate (10-40 bpm), inspiratory time (0.5-1.5 s), assist pressure sensing (- 1 to - 20 cm H2O), manual PEEP valve (0-20 cm H2O). All set values are displayed on an LCD screen. Bench testing with lung simulators (Michigan 1600, SmartLung 2000) yielded consistent tidal volume delivery at compliances of 20, 40 and 70 (mL/cm H2O). The delivered fraction of inspired oxygen (FiO2) decreased with increasing minute ventilation (VE), from 98 to 47% when VE was increased from 4 to 16 L/min using a fixed oxygen flow source of 5 L/min. ABBU was tested in Berkshire pigs (n = 6, weight of 50.8 ± 2.6 kg) utilizing normal lung model and saline lavage induced lung injury. Arterial blood gases were measured following changes in tidal volume (200-800 ml), respiratory rate (10-40 bpm), and PEEP (5-20 cm H2O) at baseline and after lung lavage. Physiological levels of PaCO2 (≤ 40 mm Hg [5.3 kPa]) were achieved in all animals at baseline and following lavage injury. PaO2 increased in lavage injured lungs in response to incremental PEEP (5-20 cm H2O) (p < 0.01). At fixed low oxygen flow rates (5 L/min), delivered FiO2 decreased with increased VE. CONCLUSIONS: ABBU provides oxygenation and ventilation across a range of parameter settings that may potentially provide a low-cost solution to ventilator shortages. A clinical trial is necessary to establish safety and efficacy in adult patients with diverse etiologies of respiratory failure.

Inspiratory limb carbon dioxide entrainment during high-frequency oscillatory ventilation: characterization in a mechanical test lung and swine model.

BACKGROUND: High-frequency oscillatory ventilation (HFOV) has been utilized as a rescue oxygenation therapy in adults with ARDS over the last decade. The HFOV oscillating piston can generate negative pressure during the exhalation cycle, which has been termed active exhalation. We hypothesized that this characteristic of HFOV entrains CO(2) into the inspiratory limb of the circuit and increases the total dead space. The purpose of this study was to determine if retrograde CO(2) entrainment occurs and how it is altered by HFOV parameter settings. METHODS: An HFOV was interfaced to a cuffed endotracheal tube and connected to a mechanical test lung. Negative pressure changes within the circuit's inspiratory limb were measured while HFOV settings were manipulated. Retrograde CO(2) entrainment was evaluated by insufflating CO(2) into the test lung to achieve 40 mm Hg at the carina. Inspiratory limb CO(2) entrainment was measured at incremental distances from the Y-piece. HFOV settings and cuff leak were varied to assess their effect on CO(2) entrainment. Control experiments were conducted using a conventional ventilator. Test lung results were validated on a large hypercapnic swine. RESULTS: Negative pressure was detectable within the inspiratory limb of the HFOV circuit and varied inversely with mean airway pressure (P(-)(aw)) and directly with oscillatory pressure amplitude (ΔP). CO(2) was readily detectable within the inspiratory limb and was proportional to the negative pressure that was generated. Factors that decreased CO(2) entrainment in both the test lung and swine included low ΔP, high mean airway pressure, high oscillatory frequency (Hz), high bias flow, and endotracheal tube cuff leak placement. CO(2) entrainment was also reduced by utilizing a higher bias flow strategy at any targeted mean airway pressure. CONCLUSIONS: Retrograde CO(2) entrainment occurs during HFOV use and can be manipulated with the ventilator settings. This phenomenon may have clinical implications on the development or persistence of hypercapnia.

A protocol for high-frequency oscillatory ventilation in adults: results from a roundtable discussion.

OBJECTIVE: Ventilator settings typically used for high-frequency oscillatory ventilation (HFO) in adults provide acceptable gas exchange but may not take best advantage of its lung-protective aspects. We provide guidelines for HFO in adults with acute respiratory distress syndrome that should optimize the lung-protective characteristics of this ventilation mode. DESIGN: Roundtable discussions, iterative revisions, and consensus. SETTING: Five academic medical centers. PATIENTS: Not applicable. INTERVENTIONS: Participants addressed how to best maintain ventilation through combinations of oscillation pressure amplitude, frequency, and the use of an endotracheal tube cuff leak, and to maintain oxygenation through combinations of recruitment maneuvers, mean airway pressure, and oxygen concentration. The guiding principles were to provide lung protective ventilation by minimizing the size of tidal volumes, and balance the risks and benefits of lung recruitment and distension. MAIN RESULTS: HFO may provide smaller tidal volumes and more complete lung recruitment than conventional modes. To optimize these features, we recommend use of the maximum pressure-oscillation amplitude coupled with the highest tolerated frequency, targeting a pH of only 7.25-7.35. This will yield a smaller tidal volume than typical HFO settings where frequency is limited to 6 Hz or less and pressure amplitude is submaximal. Lung recruitment can be achieved with the use of recruitment maneuvers, especially during the first several days of HFO. Recruitment may be augmented or sustained with generous mean airway pressures. These may either be chosen from a table of recommended mean airway pressure and oxygen concentration combinations, or individually titrated based on the oxygenation response of each patient. CONCLUSIONS: Modification of the goals and tactics of HFO use may better protect against ventilator-associated lung injury. Further clinical trials are needed to compare the effects on patient outcome of the best use of HFO compared to the most protective use of conventional modes in adult acute respiratory distress syndrome.

Acute respiratory distress syndrome in pregnancy.

OBJECTIVE: To summarize the pathophysiology and treatment of acute lung injury and acute respiratory distress syndrome (ARDS) during pregnancy. DATA SOURCE: Review of select articles from MEDLINE, including published abstracts, case reports, observational studies, controlled trials, review articles, and institutional experience. DATA SUMMARY: ARDS occurs in pregnancy and may have unique causes. Despite extensive clinical research to improve the management of ARDS, mortality remains high, and few strategies have shown a mortality benefit. Furthermore, in most published studies, pregnancy is an exclusionary criterion, and thus, few treatments have been adequately evaluated in obstetric populations. The treatment of ARDS in pregnancy is extrapolated from studies performed in the general ARDS patient population, with consideration given to the normal physiologic changes of pregnancy. In general, the best support of the fetus is support of the mother. From the age of viability (24-26 wks at most institutions) until full term, decisions regarding delivery should be made based primarily on the standard obstetric indications. CONCLUSIONS: Little evidence exists regarding the management of ARDS specifically in pregnancy, and thus, treatment approaches must be drawn from studies performed in a general patient population. A multidisciplinary approach involving maternal-fetal medicine, neonatology, anesthesiology, and intensivist clinicians is essential to optimizing maternal and fetal outcomes.

High-frequency oscillatory ventilation: lessons learned from mechanical test lung models.

OBJECTIVE: Review data obtained from high-frequency oscillatory ventilation (HFOV) and mechanical test lung models with respect to delivered tidal volume, distal pressure transmission, endotracheal tube cuff leaks, and simulated clinical conditions. DESIGN: Review of selected studies from PubMed, published abstracts, and institutional mechanical test lung data. RESULTS: Tidal volume delivery during HFOV is altered by oscillatory pressure amplitude (DeltaP), frequency (Hz), percent inspiratory time (IT%), and patient variables. Distal (carinal) oscillatory pressure amplitude transmission is directly correlated with endotracheal tube diameter and peripheral airway resistance. Endotracheal tube cuff leaks promote egress of tracheal gas while attenuating distal oscillatory pressure amplitude and tidal volume transmission. Simulated clinical conditions (e.g., increased distal airway resistance, mainstem intubation) may increase observed DeltaP, whereas mean airway pressure is decreased with air leaks. CONCLUSION: Mechanical test lung and artificial trachea simulations may provide useful information on the interaction of HFOV with altered lung mechanics and may contribute to the formulation of HFOV clinical strategies. Important limitations of these models include absence of gas exchange, histologic and biologic markers, or hemodynamic data.

High-frequency oscillatory ventilation in adults: respiratory therapy issues.

OBJECTIVE: To summarize clinical information and assessment techniques relevant to respiratory therapists caring for adult patients on high-frequency oscillatory ventilation (HFOV). DATA SOURCE: Review of observational studies, controlled trials, case reports, institutional experience, and hospital HFOV guidelines for adult patients. DATA SUMMARY: Respiratory therapists require unique physical assessment skills and knowledge in managing patients on HFOV. Respiratory therapy procedures relevant to HFOV include setting endotracheal tube cuff leaks, performing lung recruiting maneuvers, endotracheal suctioning, and monitoring ventilator parameters. Respiratory therapists serve as essential team members in the creation and implementation of written HFOV guidelines (e.g., algorithms) to optimize patient care. CONCLUSION: Respiratory therapy assessment and procedural skills are essential in providing optimal care to adult patients on HFOV.

High-frequency oscillatory ventilation for acute respiratory distress syndrome in adult patients.

INTRODUCTION: High-frequency oscillatory ventilation (HFOV) using an open-lung strategy has been demonstrated to improve oxygenation in neonatal and pediatric respiratory failure, without increasing barotrauma. Animal studies using small (<4 mm) endotracheal tubes have shown reduced histopathologic evidence of lung injury and inflammatory mediator release, suggesting reduced ventilator-induced lung injury. CLINICAL STUDIES: During the last decade, case reports and observational studies of HFOV in patients failing conventional ventilation strategies have suggested improved oxygenation in adult patients with severe acute respiratory distress syndrome. These reports have also suggested that early (2 days) initiation of HFOV is more likely to result in survival than delayed initiation (>7 days). A recently published randomized, controlled trial in acute respiratory distress syndrome patients (n = 148) comparing HFOV with a pressure-control ventilation strategy (Pao(2)/Fio(2) ratio of 10 cm H(2)O) demonstrated early (<16 hrs) improvement in Pao(2)/Fio(2) (p =.008) in the HFOV group but no significant difference in oxygenation index between the two groups during the initial 72 hrs of treatment. Thirty-day mortality was 37% in the HFOV group and 52% in the conventional ventilation group (p =.102). There was no significant difference between treatment groups in the prevalence of barotrauma, hemodynamic instability, or mucus plugging. This study suggests that HFOV is as effective and safe as the conventional strategy to which it was compared. CLINICAL APPLICATION: For clinical use in adults, a trial of HFOV may be considered when Fio(2) requirements exceed 60% and mean airway pressure is approaching 20 cm H(2)O or higher (or, alternatively, positive end-expiratory pressure of >15 cm H(2)O). It is currently unknown whether initiating HFOV at a lower severity threshold would result in reduced ventilator-associated lung injury or mortality. FUTURE DIRECTIONS: Future studies should compare different algorithms of applying HFOV to determine the optimal techniques for achieving oxygenation and ventilation, while minimizing ventilator-associated lung injury. The potential role of adjunctive therapies used with HFOV (e.g., prone ventilation, inhaled nitric oxide, aerosolized vasodilators, liquid ventilation) will require further research.

Minimally invasive hemodynamic monitoring for the intensivist: current and emerging technology.

OBJECTIVE: To review minimally invasive cardiac output monitoring devices currently available for use in the intensive care unit. DATA SOURCES: Medline search from 1966 to present plus cited reference studies and abstracts from available product literature. STUDY SELECTION: Selection criteria included published reports and abstracts comparing the accuracy of minimally invasive cardiac output monitors to a "gold standard." DATA SYNTHESIS: Many reports have been published on the accuracy of individual minimally invasive cardiac output monitors, but cumulative data reviewing each type of monitor have not been synthesized and made available to the clinician. CONCLUSIONS: Emerging noninvasive or minimally invasive means of cardiac output monitoring are based on varied physiologic principles and can be used for following hemodynamic trends. Each of these methods has advantages and disadvantages; it is important for the clinician to understand the strengths and limitations of each device to effectively use the information derived.

High-frequency oscillatory ventilation for acute respiratory distress syndrome in adults: a randomized, controlled trial.

Observational studies of high-frequency oscillatory ventilation in adults with the acute respiratory distress syndrome have demonstrated improvements in oxygenation. We designed a multicenter, randomized, controlled trial comparing the safety and effectiveness of high-frequency oscillatory ventilation with conventional ventilation in adults with acute respiratory distress syndrome; 148 adults with acute respiratory distress syndrome (Pa(O2)/fraction of inspired oxygen