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Background: The overwhelming demand for mechanical ventilators due to COVID-19 has stimulated interest in using one ventilator for multiple patients (ie, multiplex ventilation). Despite a plethora of information on the internet, there is little supporting evidence and no human studies. The risk of multiplex ventilation is that ventilation and PEEP effects are largely uncontrollable and depend on the difference between patients' resistance and compliance. It is not clear whether volume control ventilation or pressure control ventilation is safer or more effective. We designed a simulation-based study to allow complete control over the relevant variables to determine the effects of various degrees of resistance-compliance imbalance on tidal volume (V T ), end-expiratory lung volume (EELV), and imputed pH., Methods: Two separate breathing simulators were ventilated with a ventilator using pressure control and volume control ventilation modes. Evidence-based lung models simulated a range of differences in resistance and compliance (6 pairs of simulated patients). Differences in V T , EELV, and imputed pH were recorded., Results: Depending on differences in resistance and compliance, differences in V T ranged from 1% (with equal resistance and compliance) to 79%. Differences in EELV ranged from 2% to 109%, whereas differences in pH ranged from 0% to 5%. Failure due to excessive V T (ie, > 8 mL/kg) did not occur, but failure due to excessive EELV difference (ie, > 10%) was evident in 50% of patient pairs. There was no difference in failure rate between volume control and pressure control ventilation modes., Conclusions: These experiments confirmed the potential for markedly different ventilation and oxygenation for patients with uneven respiratory system impedances during multiplex ventilation. Three critical problems must be solved to minimize risk: (1) partitioning of inspiratory flow from the ventilator individually between the 2 patients, (2) measurement of V T delivered to each patient, and (3) provision for individual PEEP. We provide suggestions for solving these problems., Competing Interests: Mr Chatburn has disclosed relationships with IngMar Medical, and Vyaire Medical. Mr Branson has disclosed relationships with Mallinckrodt, Ventec Life Systems, and Zoll Medical Corporation. Dr Hatipoğlu has disclosed no conflicts of interest., (Copyright © 2020 by Daedalus Enterprises.)

Background: The use of shared ventilation, or the simultaneous support of multiple patients connected in parallel to a single mechanical ventilator, is receiving considerable interest for addressing the severe shortage of mechanical ventilators available during the novel coronavirus pandemic (COVID-19). In this paper we highlight the potentially disastrous consequences of naïve shared ventilation, in which patients are simply connected in parallel to a ventilator without any regard to their individual ventilatory requirements. We then examine possible approaches for individualization of mechanical ventilation, using modifications to the breathing circuit that may enable tuning of individual tidal volumes and driving pressures during either volume-controlled ventilation (VCV) or pressure-controlled ventilation (PCV)., Methods: Breathing circuit modifications included a PEEP valve on each expiratory limb for both VCV and PCV, an adjustable constriction and one-way valve on the inspiratory limb for VCV, and a pressure-relief valve for peak inspiratory pressure reduction on the inspiratory limb for PCV. The ability to regulate individual tidal volumes using these breathing circuit modifications was tested both theoretically in computer simulations as well as experimentally in mechanical test lungs., Results: In both the simulations and experimental measurements, naïve shared ventilation resulted in large imbalances across individual tidal volume delivery, dependent on imbalances across patient mechanical properties. The proposed breathing circuit modifications for shared VCV and shared PCV enabled optimization of tidal volume distributions. Individual tidal volume for one patient during shared VCV was sensitive to changes in the mechanical properties of other patients. By contrast, shared PCV enabled independent control of individual patient-received ventilation., Conclusions: Of the shared ventilation strategies considered, shared PCV, with the inclusion of in-line pressure-relief valves in the individual inspiratory and expiratory limbs, offers the greatest degree of safety and lowest risk of catastrophic mechanical interactions between multiple patients connected to a single ventilator., Competing Interests: Dr Kaczka has disclosed relationships with Zoll Medical Corporation and Monitor Mask. Mr Branson has disclosed relationships with Mallinckrodt, Ventec Life Systems, and Zoll Medical Corporation. Drs Herrmann and Kaczka are co-founders and shareholders of OscillaVent, and Dr Hawley is an employee of OscillaVent. The other authors have disclosed no conflicts of interest., (Copyright © 2020 by Daedalus Enterprises.)

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., (© Association of Military Surgeons of the United States 2018. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Closed loop control of mechanical ventilation is routine and operates behind the ventilator interface. Reducing caregiver interactions is neither an advantage for the patient or the staff. Automated systems causing lack of situational awareness of the intensive care unit are a concern. Along with autonomous systems must come monitoring and displays that display patients' current condition and response to therapy. Alert notifications for sudden escalation of therapy are required to ensure patient safety. Automated ventilation is useful in remote settings in the absence of experts. Whether automated ventilation will be accepted in large academic medical centers remains to be seen., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: This document provides evidence-based clinical practice guidelines on the use of mechanical ventilation in adult patients with acute respiratory distress syndrome (ARDS)., Methods: A multidisciplinary panel conducted systematic reviews and metaanalyses of the relevant research and applied Grading of Recommendations, Assessment, Development, and Evaluation methodology for clinical recommendations., Results: For all patients with ARDS, the recommendation is strong for mechanical ventilation using lower tidal volumes (4-8 ml/kg predicted body weight) and lower inspiratory pressures (plateau pressure < 30 cm H 2 O) (moderate confidence in effect estimates). For patients with severe ARDS, the recommendation is strong for prone positioning for more than 12 h/d (moderate confidence in effect estimates). For patients with moderate or severe ARDS, the recommendation is strong against routine use of high-frequency oscillatory ventilation (high confidence in effect estimates) and conditional for higher positive end-expiratory pressure (moderate confidence in effect estimates) and recruitment maneuvers (low confidence in effect estimates). Additional evidence is necessary to make a definitive recommendation for or against the use of extracorporeal membrane oxygenation in patients with severe ARDS., Conclusions: The panel formulated and provided the rationale for recommendations on selected ventilatory interventions for adult patients with ARDS. Clinicians managing patients with ARDS should personalize decisions for their patients, particularly regarding the conditional recommendations in this guideline.

Background: Successful mechanical ventilation requires that the airway be controlled by an endotracheal tube (ETT) with an inflatable cuff to seal the airway. Aeromedical evacuation represents a unique challenge in which to manage ETT cuffs. We evaluated three methods of automatic ETT cuff pressure adjustment during changes in altitude in an altitude chamber., Methods: Size 7.5 and 8.0 mm ETTs that are currently included in the Critical Care Air Transport Team allowance standard were used for the evaluation. Three automatic cuff pressure controllers-Intellicuff, Hamilton Medical; Pyton, ARM Medical; and Cuff Sentry, Outcome Solutions-were used to manage cuff pressures. The fourth group had cuff pressure set at sea level without further adjustment. Each ETT was inserted into a tracheal model and taken to 8,000 feet and then to 16,000 feet at 2,500 ft/min. Baseline cuff pressure at sea level was approximately 25 cm H2O., Results: Mean cuff pressure at both altitudes with both size ETTs was as follows: Control arm, 141 ± 64 cm H2O; Pyton, 25 ± 0.8 cm H2O; Cuff Sentry, 22 ± 0.3 cm H2O; and Intellicuff, 29 ± 6.6 cm H2O. The mean time that cuff pressure was >30 cm H2O using Intellicuff at both altitudes was 2.8 ± 0.8 minutes. Pressure differences from baseline in the control arm and with Intellicuff were statistically significant. Cuff pressure with the Cuff Sentry tended to be lower than indicated on the device., Conclusions: Mean cuff pressures were within the recommended range with all three devices. Intellicuff had difficulty regulating the cuff pressure initially with increases in altitude but was able to reduce the pressure to a safe level during the stabilization period at each altitude. The Pyton and Cuff Sentry allowed the least variation in pressure throughout the evaluation, although the Cuff Sentry set pressure was less than the actual pressure., Level of Evidence: Therapeutic study, level V.

Intermittent mandatory ventilation (IMV) was introduced nearly 50 years ago. Despite the initial fanfare and early adoption by many, the role of IMV continues to be questioned. The use of small tidal volumes complicates the application of IMV, and issues with work of breathing, weaning and lack of clear advantages have many calling for a moratorium on its use. Spontaneous breathing, however, has a number of salutatory effects on gas exchange, the distribution of ventilation, and hemodynamics. These issues will be explored in light of a growing body of evidence., (Copyright © 2016 by Daedalus Enterprises.)

Oxygen is both lifesaving and toxic. Appropriate use of oxygen aims to provide a balance between the two effects. Although local oxygen toxicity to the lung is well accepted, recent evidence has called into question the negative consequences of hyperoxemia in other organ beds. Hyperoxia following cardiac arrest, traumatic brain injury, and stroke has been shown to worsen outcomes. The role of hyperoxemia in mechanically ventilated patients, in the face of non-toxic inspired oxygen concentrations, is less clear. This paper will review the data for and against the use of conservative oxygen targets and the avoidance of hyperoxemia in mechanically ventilated patients., (Copyright © 2016 by Daedalus Enterprises.)

Background: Addition of an oxygen concentrator into a control loop furthers previous work in autonomous control of oxygenation. Software integrates concentrator and ventilator function from a single control point, ensuring maximum efficiency by placing a pulse of oxygen at the beginning of the breath. We sought to verify this system., Methods: In a test lung, fraction of inspired oxygen (FIO2) levels and additional data were monitored. Tests were run across a range of clinically relevant ventilator settings in volume control mode, for both continuous flow and pulse dose flow oxygenation., Results: Results showed the oxygen concentrator could maintain maximum pulse output (192 mL) up to 16 breaths per minute. Functionality was verified across ranges of tidal volumes and respiratory rates, with and without positive end-expiratory pressure, in continuous flow and pulse dose modes. For a representative test at respiratory rate 16 breaths per minute, tidal volume 550 mL, without positive end-expiratory pressure, pulse dose oxygenation delivered peak FIO2 of 76.83 ± 1.41%, and continuous flow 47.81 ± 0.08%; pulse dose flow provided a higher FIO2 at all tested setting combinations compared to continuous flow (p < 0.001)., Conclusions: These tests verify a system that provides closed loop control of oxygenation while integrating time-coordinated pulse-doses from an oxygen concentrator. This allows the most efficient use of resources in austere environments., (Reprint & Copyright © 2016 Association of Military Surgeons of the U.S.)

Background: Closed-loop controllers (CLCs) embedded within portable mechanical ventilators may allow for autonomous weaning. The ability of CLCs to maintain adequate oxygenation in the setting of hemorrhage and lung injury is unknown. We hypothesized that a portable ventilator with a CLC for inspired fraction of oxygen (FIO2) could provide oxygenation in a porcine model of hemorrhage and lung injury., Methods: Female pigs randomized to the study group (n = 6) underwent a pressure-controlled bleed (mean arterial pressure = 40 mm Hg for 30 minutes). Acute lung injury was induced by saline lung lavage followed by intentional infliction of barotrauma. Sham pigs (n = 6) underwent placement of monitoring devices without hemorrhage or lung injury. All pigs were then placed on a portable ventilator modified with a CLC algorithm, which uses feedback from pulse oximetry (SpO2) and FIO2 trends to adjust FIO2 and maintain a target SpO2 of 94% (2%). The initial FIO2 was set at 0.60. Tidal volume, positive end-expiratory pressure, rate, and inspiratory-to-expiratory ratio were constant unless changes were required clinically., Results: Study pigs had lower mean arterial pressures than shams at all time points except baseline. PaO2/FIO2 ratios were less than 300 and significantly lower than both baseline values and corresponding sham values at all time points. The CLC weaned the FIO2 at a reduced rate in study pigs relative to shams with a final mean FIO2 of 0.54 and 0.29 in study and sham pigs, respectively (p < 0.05). There was a significant divergence in the study and sham FIO2 curves but no significant difference in oxygen saturation or hypoxemia., Conclusion: Adequate oxygenation can be maintained in the setting of hemorrhage and lung injury using a portable ventilator embedded with a CLC of FIO2 based on pulse oximetry. These devices may be valuable for providing advanced medical care in resource-limited environments.

In this article we propose a practical approach to the use of prone therapy for acute respiratory distress syndrome (ARDS). We have attempted to provide information to improve the understanding and implementation of prone therapy based on the literature available and our own experience. We review the basic physiology behind ARDS and the theoretical mechanism by which prone therapy can be of benefit. The findings of the most significant studies regarding prone therapy in ARDS as they pertain to its implementation are summarized. Also provided is a discussion of the nuances of utilizing prone therapy, including potential pitfalls, complications, and contraindications. The specific considerations of prone therapy in open abdomens and traumatic brain injuries are discussed as well. Finally, we supply suggested protocols for the implementation of prone therapy discussing criteria for initiation and cessation of therapy as well as addressing issues such as the use of neuromuscular blockade and nutritional supplementation.

Background: Acute lung injury (ALI) is a condition that leads to impaired oxygen delivery. We demonstrated previously that using a portable oxygen concentrator (POC) with pulsed dose delivery of oxygen is an alternative option to conserve oxygen while still maintaining adequate oxygen delivery in a mechanical model. We hypothesized that using a modified POC, pulsed dose oxygen delivery can provide adequate oxygenation in an animal model., Methods: In a crossover study, we induced ALI in 15 pigs using an oleic acid model. We ventilated the pigs using equipment that is used by Critical Care Air Transport Teams of the US Air Force. We compared oxygen delivery using a POC in both continuous flow and pulsed dose modes, while in both volume-control and pressure-control mechanical ventilation., Results: The PaO(2)/FIO(2) ratios were increased in both the continuous flow and pulsed dose delivery for volume control and pressure control. In volume control, the pulsed dose demonstrated a significant increase in the PaO(2)/FIO(2) ratio (168.8 [96.1] vs. 91.7 [65.4], p = 0.002) compared with continuous flow. However, this was not seen in pressure-control ventilation (89.0 [74.5] vs. 79.1 [65.4], p = 0.67)., Conclusion: We were able to demonstrate that oxygen delivery using a POC in mechanically ventilated pigs with ALI is feasible. We were also able to demonstrate that pulsed dose delivery from a POC is superior to continuous flow oxygen delivery for oxygenation in ALI, when using volume control. We propose that this is a safe alternative to conserve oxygen in the transport of critically ill patients.

Intra- and inter-hospital transport is common due to the need for advanced diagnostics and procedures, and to provide access to specialized care. Risks are inherent during transport, so the anticipated benefits of transport must be weighed against the possible negative outcome during the transport. Adverse events are common in both in and out of hospital transports, the most common being equipment malfunctions. During inter-hospital transport, increased transfer time is associated with worse patient outcomes. The use of specialized teams with the transport of children has been shown to decrease adverse events. Intra-hospital transports often involve critically ill patients, which increases the likelihood of adverse events. Radiographic diagnostics are the most common in-hospital transport destination and the results often change the course of care. It is recommended that portable ventilators be used for transport, because studies show that use of a manual resuscitator alters blood gas values due to inconsistent ventilation. The performance of new generation transport ventilators has improved greatly and now allows for seamless transition from ICU ventilators. Diligent planning for and monitoring during transport may decrease adverse events and reduce risk.

Patient-ventilator synchrony and patient comfort are assumed to go hand in hand, yet few studies provide support for this common sense idea. In reality, synchrony between the patient and ventilator is complex and can be affected by the ventilator settings, type of ventilator, patient-ventilator interface, and sedation. Inspections of airway pressure and flow waveforms are reliable methods for detecting asynchrony, and automated detection seems accurate. A number of types of asynchronies have been defined, and asynchrony during invasive and noninvasive ventilation have different calling cards. There is a clear association between asynchrony, ventilator-induced diaphragmatic dysfunction, and duration of mechanical ventilation. Whether these are cause and effect or simply associated remains to be determined.

Background: Portable ventilators are increasingly utilized in the intra- and inter-hospital transport of patients. We evaluated 4 portable ventilators, Impact EMV, CareFusion LTV 1200, Newport HT70, and Hamilton T1, in terms of triggering, delivered tidal volume (V(T)) accuracy, battery duration, delivered F(IO(2)) accuracy, and gas consumption., Methods: Triggering was tested using a microprocessor controlled breathing simulator that simulated a weak, normal, and aggressive inspiratory effort using muscle pressures of -2, -4, and -8 cm H2O respectively. Delivered V(T) and F(IO(2)) accuracy were evaluated across a range of operation. To determine gas consumption, the ventilators were attached to an E type oxygen cylinder and operated at an F(IO(2)) of 1.0 until the tank was depleted. Battery duration was tested by operating each ventilator at an F(IO(2)) of 0.21 until the device ceased to operate., Results: Differences remain among devices in several aspects of the testing protocol. Gas consumption ranged from 9.2 to 16 L/min. Battery duration ranged from 101 to 640 min. Triggering performance varied among devices but was consistent breath to breath within the same device, using the fastest and slowest rise time settings. F(IO(2)) accuracy varied at the low range on the 50 mL V(T) setting with one device, and at the high range on both the 50 mL and 500 mL V(T) settings with another., Conclusions: Manufacturers continue to improve the performance of portable ventilators. All the ventilators we tested performed well on V(T) delivery across a range of settings, using both the internal drive mechanism (F(IO(2)) 0.21) and compressed oxygen (F(IO(2)) 1.0). Two of the ventilators were unable to deliver accurate F(IO(2)) across the range of V(T). None of the devices was clearly superior to the others in all aspects of our evaluation., (© 2013 Daedalus Enterprises.)

Introduction: A mass-casualty respiratory failure event where patients exceed available ventilators has spurred several proposed solutions. One proposal is use of a single ventilator to support 4 patients., Methods: A ventilator was modified to allow attachment of 4 circuits. Each circuit was connected to one chamber of 2 dual-chambered, test lungs. The ventilator was set at a tidal volume (V(T)) of 2.0 L, respiratory frequency of 10 breaths/min, and PEEP of 5 cm H(2)O. Tests were repeated with pressure targeted breaths at 15 cm H(2)O. Airway pressure, volume, and flow were measured at each chamber. The test lungs were set to simulate 4 patients using combinations of resistance (R) and compliance (C). These included equivalent C and R, constant R and variable C, constant C and variable R, and variable C and variable R., Results: When R and C were equivalent the V(T) distributed to each chamber of the test lung was similar during both volume (range 428-442 mL) and pressure (range 528-544 mL) breaths. Changing C while R was constant resulted in large variations in delivered V(T) (volume range 257-621 mL, pressure range 320-762 mL). Changing R while C was constant resulted in a smaller variation in V(T) (volume range 418-460 mL, pressure range 502-554 mL) compared to only C changes. When R and C were both varied, the range of delivered V(T) in both volume (336-517 mL) and pressure (417-676 mL) breaths was greater, compared to only R changes., Conclusions: Using a single ventilator to support 4 patients is an attractive concept; however, the V(T) cannot be controlled for each subject and V(T) disparity is proportional to the variability in compliance. Along with other practical limitations, these findings cannot support the use of this concept for mass-casualty respiratory failure.

Patient-ventilator synchrony is a complex issue affected by ventilator performance, patient characteristics, and the patient-ventilator interface. The history of patient-ventilator interaction includes avoidance of pharmacalogic paralysis, the development of spontaneous breathing systems, microprocessor technology to maximize interaction, and closed-loop control. While most clinicians agree that patient-ventilator synchrony is desirable, there remain no cause-and-effect data that asynchrony is associated with poor outcome.

Objective: The supply and distribution of mechanical ventilation capacity is of profound importance for planning for severe public health emergencies. However, the capability of US health systems to provide mechanical ventilation for children and adults remains poorly quantified. The objective of this study was to determine the quantity of adult and pediatric mechanical ventilators at US acute care hospitals., Methods: A total of 5,752 US acute care hospitals included in the 2007 American Hospital Association database were surveyed. We measured the quantities of mechanical ventilators and their features., Results: Responding to the survey were 4305 (74.8%) hospitals, which accounted for 83.8% of US intensive care unit beds. Of the 52,118 full-feature mechanical ventilators owned by respondent hospitals, 24,204 (46.4%) are pediatric/neonatal capable. Accounting for nonrespondents, we estimate that there are 62,188 full-feature mechanical ventilators owned by US acute care hospitals. The median number of full-feature mechanical ventilators per 100,000 population for individual states is 19.7 (interquartile ratio 17.2-23.1), ranging from 11.9 to 77.6. The median number of pediatric-capable device full-feature mechanical ventilators per 100,000 population younger than 14 years old is 52.3 (interquartile ratio 43.1-63.9) and the range across states is 22.1 to 206.2. In addition, respondent hospitals reported owning 82,755 ventilators other than full-feature mechanical ventilators; we estimate that there are 98,738 devices other than full-feature ventilators at all of the US acute care hospitals., Conclusions: The number of mechanical ventilators per US population exceeds those reported by other developed countries, but there is wide variation across states in the population-adjusted supply. There are considerably more pediatric-capable ventilators than there are for adults only on a population-adjusted basis.

Background: Transportation of the critically ill or injured war fighter requires the coordinated care and judicious use of resources. Availability of oxygen (O2) supplies for the mechanically ventilated patient is crucial. Size and weight of cylinders makes transport difficult and presents an increased risk of fire. A proposed solution is to use a portable oxygen concentrator (POC) for mechanical ventilation. We tested the SeQual Eclipse II POC paired with the Impact 754 and Pulmonetics LTV-1200 ventilators in the laboratory and evaluated the fraction of inspired oxygen (FIO2) across a range of minute volumes., Methods: Each ventilator was attached to a test lung and pressure, volume, flow, and inspired oxygen (FIO2) was measured by a gas or flow analyzer. Ventilators were tested at a tidal volume (VT) of 500 mL; an inspiratory time of 1.0 second; respiratory rates of 10, 20, and 30 breaths per minute; and positive end-expiratory pressure of 0 and 10 cm H2O. The LTV 1200 was tested with and without the expiratory bias flow. The Eclipse II was modified to provide pulse dosing on inspiration at 3 volumes (64, 128, and 192 mL) and continuous flow at 1 L/min to 3 L/min. Six combinations of ventilator settings were used with each POC setting for evaluation. O2 was injected at the ventilator gas outlet and patient y-piece for pulse dose and continuous flow. Additionally, continuous flow O2 was injected into the oxygen inlet port of the LTV 1200, and a reservoir bag, on the inlet port of the Impact 754. All tests were done with both ventilators using continuous flow, wall source O2 as a control. We also measured the FIO2 with the concentrator on the highest pulse dose setting while decreasing ventilator VT to compensate for the added volume., Results: The delivered FIO2 was highest when oxygen was injected into the ventilator circuit at the patient y-piece using pulse dosing, with the VT corrected. The next highest FIO2 was with continuous flow at the inlet (LTV), and reservoir (Impact). Electrical power consumption was less during pulse dose operation., Summary: Oxygen is a finite resource, which is cumbersome to transport and may present a fire hazard. The relatively high FIO2 delivered by the POC makes this method of O2 delivery a viable alternative to O2 cylinders. However, patients requiring an FIO2 of 1.0 would require additional compressed oxygen. This system allows O2 delivery up to 76% solely using electricity. An integrated ventilator or POC capable of automatically compensating VT for POC output is desirable. Further patient testing needs to be done to validate these laboratory findings.

Background: Hospital electrical power failure represents an important challenge in the intensive care unit. Despite the presence of backup generators, total electrical power failure may still occur. Life-support equipment should have a reliable internal battery to ensure patient safety. We tested the duration of operation of the internal battery of 4 intensive care ventilators., Methods: In our laboratory we evaluated one each of 4 ventilator models available in our facility (Evita XL, Puritan Bennett 840, Avea, and Servo 300), with volume-control and pressure-control ventilation, and with positive end-expiratory pressure (PEEP) of zero and 20 cm H(2)O. We then randomly selected and tested 6 Evita XL and 4 Servo 300 ventilators from our inventory to determine the variability of internal battery duration among ventilators of the same model. The ventilator settings were identical to the previous tests, other than fraction of inspired oxygen, which was set at 0.6, and PEEP was 5 cm H(2)O., Results: The battery-duration range of the tested ventilators was 20.5-170.5 min, and the mean +/- SD battery duration was 80.4 +/- 49.3 min. Changes in breath type and PEEP did not significantly impact battery duration. Among the ventilators of the same model, the battery-duration range was 5-69 min and the mean +/- SD battery duration was 28.9 +/- 21.4 min. Use of a compressor significantly shortened battery duration. There was no correlation between battery duration and battery age (r = -0.263)., Conclusions: The duration of ventilator operation on internal battery ranged widely among the tested devices. Clinicians need to be aware of these differences in the event of power failure.

New features of mechanical ventilators are frequently introduced, including new modes, monitoring techniques, and triggering techniques. But new rarely translates into any measureable improvement in outcome. We describe 4 new techniques and attempt to define what is a new invention versus what is innovative-a technique that significantly improves a measurable variable. We describe and review the literature on automated weaning, automated measurement of functional residual capacity, neural triggering, and novel displays of respiratory mechanics.

Background: Transport of mechanically ventilated patients in a combat zone presents challenges, including conservation of resources. In the battlefield setting, provision of oxygen supplies remains an important issue. Autonomous control of oxygen concentration can allow a reduction in oxygen usage and reduced mission weight., Methods: Trauma patients requiring ventilation and inspired oxygen concentration (FIO(2)) > 0.40 were evaluated for study. Patients were randomized to consecutive 4-hour periods of closed loop control or standard care. The system for autonomous control consisted of a ventilator, oximeter, and a portable computer. The computer housed the control algorithm and collected data every 5 seconds. The controller goal was to maintain pulse oximetry (SpO(2)) at 94 +/- 2% through discrete changes of 1% to 5% every 30 seconds. Ventilator settings and SpO(2) were recorded every 5 seconds for analysis., Results: Forty-five patients were enrolled in this study. Oxygen saturation was maintained in the 92% to 96% saturation range 33 +/- 36% of the time during clinician control versus 83 +/- 21% during closed loop control. Time spent at the target SpO(2) 92% to 96% was 193.3 +/- 59.18 minutes during closed loop control and 87.08 +/- 87.95 minutes during clinician control (p < 0.001). Hyperoxemia was more frequent during clinician control (144.29 +/- 90.09 minutes) than during closed loop control (38.91 +/- 55.86 minutes; p < 0.001). There were no differences in the number of episodes of SpO(2) < 88%. Oxygen usage was reduced by 32% during closed loop control., Conclusion: Closed loop control of FIO(2) offers the opportunity for maximizing oxygen resources, reducing mission weight, and providing targeted normoxemia without increasing risk of hypoxemia in ventilated trauma patients.

Background: Transport of mechanically ventilated patients in a combat zone presents challenges including conservation of resources. In the battlefield setting, the provision of adequate oxygen supplies remains a significant issue. Autonomous control of oxygen concentration may allow a reduction in mission load., Methods: Trauma patients requiring ventilation and inspired oxygen concentration (FIO2) greater than 0.35 were evaluated for study. Patients were randomized to consecutive 4-hour periods of autonomous control or standard care. The system for autonomous control consisted of a ventilator, oximeter, and a portable computer. The portable computer housed the control algorithm and collected ventilator and oxygen saturation (SpO2) data every 5 seconds. The controller goal was to maintain SpO2 at 94% +/- 2% via discrete changes of 1% to 5%. Ventilator settings and SpO2 were recorded every 5 seconds for analysis., Results: Fifteen patients were enrolled in this study. Oxygen saturation was maintained in the 92% to 96% saturation range 33% +/- 36% of the time during clinician control versus 83% +/- 21% during autonomous control. Oxygen usage was reduced by 44% during autonomous control. There was a slight difference in the total duration of SpO2 episodes less than 88% between groups (6.02 +/- 0.83 vs. 6.87 +/- 0.46 minutes, p < 0.05). There were no differences in the number of episodes of SpO2 <88%., Conclusion: Autonomous control of FIO2 offers the opportunity for a reduction in oxygen usage, allowing a weight and resource reduction, without increasing risk of hypoxemia in ventilated trauma patients.

Objective: The objective of this study was to determine the effects of inspired oxygen concentration (FIO2), positive end-expiratory pressure (PEEP), and breath type on the battery life of the LTV-1000 external lithium ion battery (LiB)., Methods: An LTV-1000 ventilator and external LiB were tested in the laboratory. The ventilator was operated using pressure and volume breaths set to deliver a tidal volume of 750 mL. FIO2 was varied from room air (0.21) to 1.0. PEEP was set a 0, 10, and 20 cm of H2O. Duration of operation was determined from measurements of delivered tidal volume., Results: At a baseline of volume control at an FIO2 of 0.21 and a PEEP of 0 cm of H2O, the ventilator operated for 300 +/- 11.6 minutes. Increasing FIO2 to 1.0 reduced battery life to 247 +/- 2.1 minute (p < 0.001). The addition of PEEP to 20 cm of H2O reduced battery life to 211 +/- 3.5 minutes (p < 0.001). The combination of FIO2 of 1.0 and PEEP of 20 cm of H2O further reduced battery life to 188 +/- 6.3 minutes (p < 0.001). At the baseline FIO2 and PEEP (0.21 and 0 cm of H2O), the use of pressure control reduced battery life to 142 +/- 3.5 minutes., Conclusions: Battery life of the external LiB is significantly reduced by the use of pressure control, increasing PEEP, and increasing FIO2. This information is critical to resource planning for medical missions.

The standard of care for mechanical ventilation of the patient who has acute lung injury remains volume control ventilation at 6 mL/kg. Despite this fact, clinicians often employ pressure control ventilation and adaptive pressure control ventilation in an attempt to improve synchrony and limit the possibility for overdistension. Adaptive pressure control uses pressure control breaths to guarantee a minimum delivered tidal volume. Other techniques (such as adaptive support ventilation) use pressure-limited breaths, switching between time and flow cycling based on patient effort. Neither of these techniques has been compared with volume control in a randomized setting. Understanding operation of these techniques is essential for determining any impact on outcome or ventilator induced lung injury.

Objective: En-route care necessitates the evacuation of seriously wounded service members requiring mechanical ventilation in aircraft where low light, noise, vibration, and barometric pressure changes create a unique clinical environment. Our goal was to evaluate ventilatory requirements, oxygenation, and oxygen use in flight and assess the feasibility of a computer interface in this austere environment., Methods: A personal computer was integrated with the pulse oximeter and ventilator data port used in aeromedical evacuation from Iraq to Germany. Ventilator settings, inspired oxygen (FiO2), tidal volume (VT), respiratory rate (RR), minute ventilation (VE), monitored values, heart rate (HR), and oxygen saturation (SpO2), were recorded continuously. Oxygen use was determined using the equation ([FiO2 - 21]/79) x (MVE). Additional data were obtained through the United States Air Force (USAF) Transcom Regulation and Command/Control Evacuation System (TRAC2ES) and the United States Army Institute of Surgical Research Joint Theater Trauma Registry databases., Results: During a 4 month time frame 117 hours of continuous recording was accomplished in 22 patients. Mean age was 27 +/- 9.83 and injury severity score military was 31.75 +/- 20.63 (range, 9-75). All patients survived transport. Mean values for ventilator settings were FiO2 (24-100%) of 49% +/- 13%, positive end-expiratory pressure of 6 +/- 2.5 (range, 0-17 cm H2O), RR of 15 +/- 2.4 (range, 10-22 breaths/min), and VT of 611 +/- 75 (range, 390-700 mL). Delivered VT in mililiter per kilogram was 6.9 +/- 1.30 and VE was 9.1 L/min +/- 1.4 L/min. Oxygen requirements for desired FiO2 and VE resulted in a mean oxygen usage of 3.24 L/min +/- 1.87 L/min (range, 1.6-10.2 L/min). There were 32 changes to FiO2, 18 changes to PEEP, 26 changes to RR, and 20 changes to VT during flight. Five patients under-went no recorded changes in flight. Three desaturation events (<90%) were recorded lasting 35, 115, and 280 seconds. Recorded ventilatory changes averaged less than 1 (0.82) per hour of recorded flight with FiO2 being the most common., Conclusions: A computer interface is feasible in the austere aeromedical environment. Implications to military operations and civilian homeland defense include understanding casualty oxygen requirements for resource planning in support of aeromedical evacuation. Portable oxygen generation systems may be able to provide adequate oxygen flow for transport, reducing the need for compressed gas. Future studies of oxygen conservation systems including closed loop control of FiO2 are warranted.

Mechanical ventilation in a situation of mass casualty respiratory failure will require a substantial increase in the capacity for mechanical ventilation, to prevent unnecessary mortality. Concern over the difficulties of treating large numbers of patients with respiratory failure is exceeded only by our lack of experience on which to base decisions. This review evaluates the likely scenarios that could lead to mass casualty respiratory failure and the types of respiratory failure anticipated. A literature review was conducted, using the National Library of Medicine Medical Subject Headings terms "mass casualty respiratory failure," "pandemic flu," "disaster preparedness," and "mass casualty care." Papers were reviewed for relevance to the topic. There is little historical or empirical evidence upon which to base decisions regarding mass casualty respiratory failure and augmenting positive-pressure ventilation capacity. Matching the degree of respiratory impairment anticipated from the most likely mass casualty scenarios allows conclusions to be drawn regarding the performance characteristics of ventilators required for these situations. Little is known about the success of mechanical-ventilator stockpiling for mass casualty respiratory failure. Careful planning with an emphasis on matching ventilator performance to patient need and caregiver skill is critical to appropriate stockpile choices.

Secretion management in the mechanically ventilated patient includes routine methods for maintaining mucociliary function, as well as techniques for secretion removal. Humidification, mobilization of the patient, and airway suctioning are all routine procedures for managing secretions in the ventilated patient. Early ambulation of the post-surgical patient and routine turning of the ventilated patient are common secretion-management techniques that have little supporting evidence of efficacy. Humidification is a standard of care and a requisite for secretion management. Both active and passive humidification can be used. The humidifier selected and the level of humidification required depend on the patient's condition and the expected duration of intubation. In patients with thick, copious secretions, heated humidification is superior to a heat and moisture exchanger. Airway suctioning is the most important secretion removal technique. Open-circuit and closed-circuit suctioning have similar efficacy. Instilling saline prior to suctioning, to thin the secretions or stimulate a cough, is not supported by the literature. Adequate humidification and as-needed suctioning are the foundation of secretion management in the mechanically ventilated patient. Intermittent therapy for secretion removal includes techniques either to simulate a cough, to mechanically loosen secretions, or both. Patient positioning for secretion drainage is also widely used. Percussion and postural drainage have been widely employed for mechanically ventilated patients but have not been shown to reduce ventilator-associated pneumonia or atelectasis. Manual hyperinflation and insufflation-exsufflation, which attempt to improve secretion removal by simulating a cough, have been described in mechanically ventilated patients, but neither has been studied sufficiently to support routine use. Continuous lateral rotation with a specialized bed reduces atelectasis in some patients, but has not been shown to improve secretion removal. Intrapulmonary percussive ventilation combines percussion with hyperinflation and a simulated cough, but the evidence for intrapulmonary percussive ventilation in mechanically ventilated patients is insufficient to support routine use. Secretion management in the mechanically ventilated patient consists of appropriate humidification and as-needed airway suctioning. Intermittent techniques may play a role when secretion retention persists despite adequate humidification and suctioning. The technique selected should remedy the suspected etiology of the secretion retention (eg, insufflation-exsufflation for impaired cough). Further research into secretion management in the mechanically ventilated patient is needed.

Closed loop control of oxygenation and ventilation during mechanical ventilatory support is essential for remote medical care in an austere environment. Closed loop control allows for expert systems to provide the current standard of care in the absence of on-site expertise. Ventilation may be controlled by simple systems incorporating patient height or by advanced systems incorporating measurements of end-tidal carbon dioxide (ETCO2) and pulmonary impedance. Oxygenation may be controlled by adjustments of inspired oxygen concentrations (FIO2) and positive end-expiratory pressure (PEEP) using pulse oximetry (SpO2) as the input. Control of oxygenation can prevent hypoxemia and has the potential to reduce oxygen requirements. A double closed loop system of oxygenation control including control of FIO2 via SpO2 and control of oxygen generation by a portable oxygen generator (POG) based on FIO2 and minute ventilation (VE) promises safety and efficiency. Remote control of ventilation and oxygenation is possible using existing technology.

Traditional mechanical ventilation is provided with either a constant volume or constant pressure breath. In recent years, dual-control (adaptive pressure control) has been introduced in an attempt to combine the attributes of volume ventilation (constant tidal volume and minute ventilation) with the attributes of pressure ventilation (rapid, variable flow and reduced work of breathing). Adaptive pressure control is a pressure-controlled breath that utilizes closed-loop control of the pressure setting to maintain a minimum delivered tidal volume. Prior to the introduction of adaptive pressure control, no clinical studies were accomplished. Studies have shown that adaptive pressure control reduces peak inspiratory pressure, compared to volume control. When compared to traditional pressure-control ventilation, no differences have been identified. While adaptive pressure control can guarantee a minimum tidal volume, it cannot guarantee a constant tidal volume. One concern is that the ventilator cannot distinguish between improved pulmonary compliance and increased patient effort. Clinicians should be aware of the limitations of adaptive pressure control and understand when other breath delivery techniques are more suitable.

Purpose of Review: The severe acute respiratory syndrome epidemic of 2002-2003, recent natural catastrophes, burgeoning concerns regarding intentional catastrophes, and the looming threat of an influenza pandemic have focused attention on large-scale, survivable respiratory failure. In this article, we review appropriate medical equipment, treatment space, and strategies to augment health professional staff in response to a massive increase in need for sustained critical care., Recent Findings: There is insufficient modern healthcare experience with mass casualty respiratory failure to develop evidence-based preparedness efforts. For this reason, initial efforts to augment critical care capability in response to disasters have relied on extrapolation from the routine critical care knowledge base, military medicine, critical care transport, and expert opinion. We review recently published documents on augmenting supplies of positive pressure ventilation equipment, ongoing projects for increasing health professional staff, and infection control issues during epidemics., Summary: Mass casualty respiratory failure remains a largely unstudied field, but we believe informed decisions about equipment stockpiling and use, the development of creative operational concepts to increase staffing, and the careful implementation of rational infection control practices can lay a foundation for an appropriate response until additional data become available.

Humidification of inspired gases during mechanical ventilation remains a standard of care. Optimal humidity is an elusive target and is not clearly defined in the literature. The choice of a humidification device cannot be made solely on the basis of moisture output, however. The clinician must consider the effects of the device on gas exchange and spontaneous breath-ing. The author's group has used the data reviewed here to modify their previous algorithm for choosing a humidification device (see Fig. 2). Humidification requirements for noninvasive ventilation need further study.

Dual-control ventilation modes were introduced with the goal of combining the advantages of volume-control ventilation (constant minute ventilation) and pressure-control ventilation (rapid, variable flow). Dual-control ventilation modes have gained popularity despite little evidence to support routine use. The individual operation and response of the dual-control modes must be understood by the clinician to allow safe and effective use. Graphic displays of pressure, volume, and flow can aid the clinician in detecting inappropriate use of dual-control modes and adjusting settings accordingly. Inspecting the waveforms will lead clinicians to the realization that dual-control does not guarantee a set tidal volume and that variability in delivered tidal volume is greater with dual-control than with pressure control. These realizations have important implications for low-tidal volume strategies.

New ventilation modes are introduced as answers to current clinical conundrums but also as marketing tools. Rarely is a mode introduced with sound evidence from bench, animal, and patient testing. The industry cannot support the extensive testing required to demonstrate the superiority of a new mode or technique. Instead, clinicians often rely on their own experience and the results of small observational trials that show positive effects on surrogate variables such as oxygenation and work of breathing or less tangible variables such as patient comfort. This report reviews the newer ventilation modes and attempts to find the evidence among the claims and confusion.

Purpose of Review: To review the changes in mechanical ventilation technology over the past year and identify areas that provide a benefit., Recent Findings: The literature demonstrates a continued effort to improve patient ventilator synchrony though the development of new triggering and cycling methods. These techniques include using new signals and using closed loop techniques to respond to changes in patient breathing pattern. New modes of ventilation continue to be introduced, often without proof of efficacy. Fortunately, clinicians have developed alterations to new modes that improve utility and they continue to study these techniques clinically to determine appropriate use. Monitoring the patient remains an important area of investigation, with a flurry of activity surrounding pressure volume curves of the respiratory system. Finally, new ventilators have been introduced that combine high-end performance with small size and weight, while providing an on-board source of air., Summary: Mechanical ventilation is ubiquitous to intensive care. Advances in ventilator technology are rapid, and clinicians must keep abreast of changes in ventilator performance and application.

Introduction: Ventilators possess an anti-asphyxia valve that allows spontaneous breathing of ambient air during ventilator failure. This study examined the imposed work of breathing and pressure-time product of 8 critical care and 9 portable ventilators, using a laboratory simulation of spontaneous breathing during ventilator failure., Methods: A test lung was modified to simulate spontaneous breathing with a tidal volume of 0.5 L and peak inspiratory flow of 60 L/min. A pneumotachograph and pressure tap were placed at the proximal airway between the breathing circuit and endotracheal tube. Flow was derived from the pressure drop across the pneumotachograph. Signals were amplified, integrated, and saved to a spreadsheet program, and imposed work of breathing and pressure-time product were calculated. Also measured were the inspiratory pressure required to open the anti-asphyxia valve (cracking pressure), time to cracking pressure, maximum negative inspiratory pressure, and time to maximum negative inspiratory pressure., Results: For the critical care ventilators the mean +/- SD imposed work of breathing ranged from 213.07 +/- 3.53 to 890.63 +/- 0.88 mJ/L and the pressure-time product ranged from 2.67 +/- 0.01 to 13.37 +/- 0.01 cm H(2)O x s/L. For the portable ventilators the mean +/- SD imposed work of breathing ranged from 361.37 +/- 1.22 to 969.60 +/- 22.70 mJ/L and the pressure-time product ranged from 4.52 +/- 0.01 to 16.70 +/- 0.37 cm H(2)O x s/L., Conclusions: Spontaneous breathing during ventilator failure may impose work approximating the physiologic work of breathing. This imposed work may prevent effective breathing through the anti-asphyxia valve during mechanical ventilator failure due to electrical failure. These results reinforce the need to properly monitor mechanically ventilated patients and to have in place sufficient back-up power supplies and a method of manual ventilation.

Closed-loop mechanical ventilation encompasses a plethora of techniques, ranging from the very simple to the relatively complex. In the simplest form, closed-loop ventilation is the control of one output variable of the mechanical ventilator based on the measurement of an input variable. An example would be pressure support ventilation, in which flow (output) is constantly changing to maintain pressure (input) constant throughout inspiration. More complex forms of closed-loop ventilation involve measurement of multiple inputs (eg, compliance, oxygen saturation, respiratory rate) to control multiple outputs (eg, ventilator frequency, airway pressure, tidal volume). The latter type of control more closely mimics the ventilatory control and response of human physiology. This review discusses both currently available closed-loop ventilation techniques and those only available outside the United States, along with some cutting-edge techniques that have only limited use. The operation, theoretical advantages, and limitations of each technique are reviewed. When available, the literature supporting or refuting each technique will be reviewed, but, unfortunately, little has been published on certain techniques.

Today there are a number of automatic resuscitators and simple and complex transport ventilators on the market. The user must consider the purpose of the device, the patient population to be ventilated and the capabilities of the individual devices before purchasing a transport ventilator.