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Background: The interpretation of ventilator waveforms is essential for effective and safe mechanical ventilation but requires specialized training and expertise. This study aimed to investigate the ability of ICU professionals to interpret ventilator waveforms, identify areas requiring further education and training, and explore the factors influencing their interpretation skills., Methods: We conducted an international online anonymous survey of ICU professionals (physicians, nurses, and respiratory therapists [RTs]), with ≥ 1 y of experience working in the ICU. The survey consisted of demographic information and 15 multiple-choice questions related to ventilator waveforms. Results were compared between professions using descriptive statistics, and logistic regression (expressed as odds ratios [ORs; 95% CI]) was performed to identify factors associated with high performance, which was defined by a threshold of 60% correct answers., Results: A total of 1,832 professionals from 31 countries or regions completed the survey; 53% of respondents answered ≥ 60% of the questions correctly. The 3 questions with the most correct responses were related to waveforms that demonstrated condensation (90%), pressure overshoot (79%), and bronchospasm (75%). Conversely, the 3 questions with the fewest correct responses were waveforms that demonstrated early cycle leading to double trigger (43%), severe under assistance (flow starvation) (37%), and early/reverse trigger (31%). Factors significantly associated with ≥ 60% correct answers included years of ICU working experience (≥ 10 y, OR 1.6 [1.2-2.0], P < .001), profession (RT, OR 2.8 [2.1-3.7], P < .001), highest degree earned (graduate, OR 1.7 [1.3-2.2], P < .001), workplace (teaching hospital, OR 1.4 [1.1-1.7], P = .008), and prior ventilator waveforms training (OR 1.7 [1.3-2.2], P < .001)., Conclusions: Slightly over half respondents correctly identified ≥ 60% of waveforms demonstrating patient-ventilator discordance. High performance was associated with ≥ 10 years of ICU working experience, RT profession, graduate degree, working in a teaching hospital, and prior ventilator waveforms training. Some discordances were poorly recognized across all groups of surveyed professionals., Competing Interests: Dr Li discloses relationships with Fisher & Paykel Healthcare, Aerogen, Vincent Medical, the Rice Foundation, the American Association for Respiratory Care, Vincent, and Heyer. Dr Li is a section editor for Respiratory Care. Mr Miller discloses relationships with Saxe Communications, S2N Health, and Fisher & Paykel. Mr Miller is a section editor for Respiratory Care. Dr Mireles-Cabodevila is a co-owner of a patent for mid-frequency ventilation. Dr Mireles-Cabodevila discloses relationships with IngMar Medical and Elsevier. The remaining authors have disclosed no conflicts of interest., (Copyright © 2024 by Daedalus Enterprises.)

Despite its significant limitations, the P aO 2 /F IO 2 remains the standard tool to classify disease severity in ARDS. Treatment decisions and research enrollment have depended on this parameter for over 50 years. In addition, several variables have been studied over the past few decades, incorporating other physiologic considerations such as ventilation efficiency, lung mechanics, and right-ventricular performance. This review describes the strengths and limitations of all relevant parameters, with the goal of helping us better understand disease severity and possible future treatment targets., Competing Interests: Mr Chatburn discloses relationships with Jones & Bartlett Learning, Elsevier, U.S. patent number 8,550,077, IngMar Medical, Inovytec Medical Solutions, Vyaire Medical, Aires Medical, Ventis Medical, ProMedic, and AutoMedx. Dr Mireles-Cabodevila discloses relationships with IngMar Medical and Jones & Bartlett. The remaining authors have disclosed no conflicts of interest., (Copyright © 2023 by Daedalus Enterprises.)

Over the last decade, the literature exploring clinical applications for esophageal manometry in critically ill patients has increased. New mechanical ventilators and bedside monitors allow measurement of esophageal pressures easily at the bedside. The bedside clinician can now evaluate the magnitude and timing of esophageal pressure swings to evaluate respiratory muscle activity and transpulmonary pressures. The respiratory therapist has all the tools to perform these measurements to optimize mechanical ventilation delivery. However, as with any measurement, technique, fidelity, and accuracy are paramount. This primer highlights key knowledge necessary to perform measurements and highlights areas of both uncertainty and ongoing development., Competing Interests: Dr Mireles-Cabodevila discloses a relationship with IngMar Medical. Mr Chatburn discloses relationships with IngMar Medical, Inovytec, Ventis, AutoMedx, Vyaire, Aires, and Stimdia. The remaining authors have disclosed no conflicts of interest., (Copyright © 2023 by Daedalus Enterprises.)

Background: Patients who are obese are at risk for developing high pleural pressure, which leads to alveolar collapse. Esophageal pressure (P es ) can be used as a surrogate for pleural pressure and can be used to guide PEEP titration. Although recent clinical data on P es -guided PEEP has shown no benefit, its utility in the subgroup of patients who are obese has not been studied., Methods: The Medical Information Mart for Intensive Care-III critical care database was queried to gather data on P es in subjects on mechanical ventilation. P es in obese and non-obese groups were compared, and a subgroup analysis was performed in subjects with class III obesity. Thereafter, empirical and P es -guided PEEP protocols of a recently published trial were theoretically applied to the obese group and ventilator outcomes were compared., Results: A total of 105 subjects were included in the study. The average end-expiratory P es in the obese group was 18.8 ± 5 cm H 2 O compared with 16.8 ± 4.8 cm H 2 O in the non-obese group ( P < .05). If P es -guided PEEP protocol was to be applied to those in the obese group, then the PEEP setting would be significantly higher than empirical PEEP setting. These findings were accentuated in the subgroup of subjects with class III obesity., Conclusions: Individualization of PEEP with P es guidance may have a role in patients who are obese., (Copyright © 2022 by Daedalus Enterprises.)

Mechanical ventilators display detailed waveforms which contain a wealth of clinically relevant information. Although much has been written about interpretation of waveforms and patient-ventilator interactions, variability remains on the nomenclature (multiple and ambiguous terms) and waveform interpretation. There are multiple reasons for this variability (legacy terms, language, multiple definitions). In addition, there is no widely accepted systematic method to read ventilator waveforms. We propose a standardized nomenclature and taxonomy along with a method to interpret mechanical ventilator displayed waveforms., (Copyright © 2022 by Daedalus Enterprises.)

Background: The use of high-frequency oscillatory ventilation (HFOV) is backed by sound physiologic rationale, but clinical data on the elective use of HFOV have been largely disappointing. Nonetheless, HFOV is still occasionally used as a rescue mode in patients with severe hypoxemia. The evidence that supports this practice is sparse., Methods: This was a retrospective single-center analysis that involved subjects admitted to the medical ICU at Cleveland Clinic, Cleveland, Ohio. We included all adult patients (ages > 18 y) who received rescue HFOV between January 1, 2010, and December 31, 2018, and analyzed their clinical outcomes., Results: A total of 48 subjects were included in the analysis. The most common primary diagnosis was pneumonia ( n = 33 [68.8%]), followed by aspiration ( n = 6 [12.5%]) and diffuse alveolar hemorrhage ( n = 2 [4.2%]). Switching to HFOV improved oxygenation but also increased vasopressor requirements at 3 h. The mortality rate of the study population was 92% (44/48)., Conclusions: Our study did not support utilization of HFOV as a "last-ditch" rescue measure in subjects with respiratory failure. The delayed timing of HFOV initiation and its detrimental hemodynamic effects are among the potential reasons for the high mortality rate., (Copyright © 2021 by Daedalus Enterprises.)

Postoperative pulmonary complications have a significant impact on perioperative morbidity and mortality and contribute substantially to health care costs. Surgical stress and anesthesia lead to changes in respiratory physiology, altering lung volumes, respiratory drive, and muscle function that can cumulatively increase the risk of postoperative pulmonary complications. Preoperative medical evaluation requires a structured approach to identify patient-, procedure-, and anesthesia-related risk factors for postoperative pulmonary complications. Validated risk prediction models can be used for risk stratification and to help tailor the preoperative investigation. Optimization of pulmonary comorbidities, smoking cessation, and correction of anemia are risk-mitigation strategies. Lung-protective ventilation, moderate PEEP application, and conservative use of neuromuscular blocking drugs are intra-operative preventive strategies. Postoperative early mobilization, chest physiotherapy, oral care, and appropriate analgesia speed up recovery. High-risk patients should receive inspiratory muscle training prior to surgery, and there should be a focus to minimize surgery time., Competing Interests: Dr Mireles-Cabodevila is a co-owner of a patent for Mid–Frequency Ventilation. He has disclosed relationships with the American College of Physicians and Jones & Bartlett publishers. The remaining authors have disclosed no conflicts., (Copyright © 2021 by Daedalus Enterprises.)

Background: Treatments for ARDS that improve patient outcomes include use of lung-protective ventilation, prone ventilation, and conservative fluid management. Implementation of ARDS protocols via educational programs might improve adherence and outcomes. The objective of this study was to investigate the effects of an ARDS protocol implementation on outcomes and adherence with ARDS guidelines., Methods: This was a single-center, interventional, comparative study before and after protocol implementation. Staff education for the ARDS protocol was implemented between June 2014 and May 2015. A retrospective cohort analysis was conducted during between January 2012 and May 2014 (pre-protocol) and between June 2015 and June 2017 (post-protocol). A total of 450 subjects with ARDS were included. After propensity score matching, 432 subjects were analyzed. Of those, 330 subjects were treated after protocol implementation., Results: The median (interquartile range [IQR]) plateau pressure and tidal volume over the first 3 d decreased significantly after protocol implementation (30.5 [IQR 24.2-33] vs 25.5 [IQR 21.7-30], P = .01 and 7.65 vs 7.4 mL/kg predicted body weight, P = .032, respectively). The percentage of subjects with unsafe tidal volume (> 10 mL/kg predicted body weight) decreased (14.4% vs 5.8%, P = .02). The percentage of subjects with safe plateau pressure (≤ 30 cm H 2 O) increased (47.4% vs 76.5%, P < .001). PEEP deviation from the ARDSNet PEEP/[Formula: see text] table was significantly lower after the implementation. Mortality at 28 and 90 days improved after implementation (53.9% vs 41.8% and 61.8% vs 48.2%, respectively). Adjusted odds ratios for 28-d and 90-d mortality were 0.47 (95% CI 0.28-0.78) and 0.45 (95% CI 0.27-0.76), respectively., Conclusions: ARDS protocol implementation was associated with improved survival and rate of adherence., Competing Interests: The authors have disclosed no conflicts of interest. Supplementary material related to this paper is available at http://www.rcjournal.com., (Copyright © 2021 by Daedalus Enterprises.)

Background: Obese subjects are at higher risk of development and progression of ARDS. There are limited data regarding mechanical ventilation practices and use of adjunctive therapies in subjects with ARDS across different obesity classes. We hypothesized that the adherence to lung-protective ventilation would be worse with rising body mass index class in patients with ARDS., Methods: We conducted a retrospective observational study of subjects with ARDS. We evaluated the differences in ventilator settings, airway pressures, gas exchange, use of rescue therapies, length of hospital stay, and mortality among subjects based on the obesity classes of the WHO., Results: The study included 613 subjects with ARDS: 21.4% were normal weight, 25% were overweight, and 53.7% were obese; 33.3% of the obese subjects met criteria for class I-II obesity, while 20.4% were class III obese (morbid obesity). On day 1, 53% of subjects with class III obesity had tidal volumes > 8 mL/kg, compared to 26% of the subjects with normal weight. In addition, 48% of the morbidly obese subjects received at least one rescue therapy as compared to 37% of normal weight subjects and 36% of overweight subjects. There were significant differences in the use of rescue therapies among the groups. In a multivariable model, subjects with class III obesity were significantly more likely to receive tidal volume > 8 mL/kg predicted body weight on day 1 when compared with subjects with normal weight (odds ratio 3.14, 95% CI 1.78-5.57). There was no difference in length of stay in ICU or hospital, duration of mechanical ventilation, or adjusted ICU or hospital mortality among the 4 groups., Conclusions: In this study, the risk of exposure to higher tidal volumes and the need for specific rescue therapies rose with higher classes of obesity in subjects with ARDS. More research is needed to identify how to better implement lung-protective ventilation in patients with obesity., Competing Interests: Mr Chatburn has disclosed relationships with IngMar Medical, Drive/DeVilbiss, and imtmedical. The remaining authors have disclosed no conflicts of interest., (Copyright © 2020 by Daedalus Enterprises.)

Patient-ventilator synchrony is a popular topic of research on mechanical ventilation. This review puts this research into both contemporary and historical perspective. Five areas of research are described: literature reviews, manual detection of synchrony problems, automated detection of synchrony problems, modes for improving synchrony, and effects of sedation. We note that this type of research lacks a standardized vocabulary and associated taxonomy, which generates difficulty in communication among students and researchers, as well as in comparison of results. Hence, we conclude this paper with some suggestions for improvement in that regard., (Copyright © 2020 by Daedalus Enterprises.)

Background: Neuralgic amyotrophy is an inflammatory peripheral nerve disorder in which phrenic nerve involvement can lead to diaphragm paralysis. The prevalence, magnitude, and time course of diaphragm recovery are uncertain., Methods: This study modeled the course of recovery of lung function in 16 subjects with diaphragm impairment from neuralgic amyotrophy. The first and last available vital capacity, sitting-to-supine decline in vital capacity, and maximal inspiratory pressures were compared., Results: An asymptotic regression model analysis in 11 subjects with at least partial recovery provided estimates of the vital capacity at onset (47%, 95% CI 25-68%), the final vital capacity (81%, 95% CI 62-101%), and the half-time to recovery (22 months, 95% CI 15-43 months). In those subjects, there was a significant improvement between the first and last measured FVC (median 44-66%, P = .004) and maximal inspiratory pressure (mean 34-51%, P = .004). Five subjects (31%) with complete recovery had a final sitting-to-supine drop of vital capacity of 16% and a maximal predicted inspiratory pressure of 63%., Conclusions: Sixty-nine percent of subjects with diaphragm impairment from neuralgic amyotrophy experience recovery of lung function and diaphragm strength, but recovery is slow and may be incomplete., Competing Interests: Dr Aboussouan has disclosed a relationship with UpToDate/Wolters Kluwers. The other authors have disclosed no conflicts of interest., (Copyright © 2017 by Daedalus Enterprises.)

Background: Mid-frequency ventilation, a strategy of using conventional ventilators at high frequencies, may reduce lung injury but has had limited evaluation in neonates. Hence, a randomized crossover study was designed to assess the feasibility of using mid-frequency ventilation in preterm infants with respiratory distress syndrome., Methods: Twelve preterm infants (≥500 g and ≥24 weeks gestational age) who were receiving pressure-limited conventional ventilation with frequencies ≤60 breaths/min for respiratory distress syndrome were randomized to periods of mid-frequency ventilation (conventional ventilation with the fastest frequency up to 150 breaths/min that gave complete inspiration and expiration) or conventional ventilation (frequency ≤60 breaths/min), each lasting 2 h using a crossover design. Ventilator parameters were adjusted to maintain the O 2 saturation and transcutaneous CO 2 at baseline., Results: Mean peak inspiratory pressure (15 ± 4 cm H 2 O vs 18 ± 4 cm H 2 O, P < .001), Δ pressure (9.8 ± 3.3 cm H 2 O vs 13.5 ± 3.9 cm H 2 O, P < .001), and tidal volume (2.6 ± 0.4 mL/kg vs 4.6 ± 0.8 mL/kg, P < .001) were lower, but mean airway pressure (8.9 ± 1.9 cm H 2 O vs 8.4 ± 1.6 cm H 2 O, P = .02) and measured PEEP (5.1 ± 0.5 cm H 2 O vs 4.4 ± 0.5 cm H 2 O, P < .001) were higher with mid-frequency compared with conventional ventilation. F IO2 , gas exchange, and hemodynamic parameters were not affected., Conclusions: Based on this small study, mid-frequency ventilation among preterm infants with respiratory distress syndrome is feasible. Further larger and longer duration trials are necessary to validate our findings. (ClinicalTrials.gov registration NCT01242462)., (Copyright © 2017 by Daedalus Enterprises.)

Airway pressure release ventilation (APRV) was originally described as a mode to treat lung-injured patients with the goal to maintain a level of airway pressure that would not depress the cardiac function, deliver mechanical breaths without excessive airway pressure, and to allow unrestricted spontaneous ventilation. Indeed, based on its design, APRV has technological features that serve the goals of safety and comfort. Animal studies suggest that APRV leads to alveolar stability and recruitment which result in less lung injury. These features are sought in patients at risk for lung injury or with ARDS. APRV allows unrestricted spontaneous ventilation, which is welcome in the era of less sedation and increased patient mobility (the effects in terms of lung injury remain to be explored). However, we must highlight that the performance of APRV is dependent on the operator-selected settings and the ventilator's performance. The clinician must select the appropriate settings in order to make effective the imputed benefits. This is a challenge when the ventilator's performance is not uniform, and the outcomes depend on high precision settings (very short expiratory time), where small variations can lead to undesired outcomes (de-recruitment or large tidal volumes leading to lung injury). Finally, we do not have evidence that APRV (as originally described) improves relevant clinical outcomes of patients with ARDS. For APRV to become the primary mode of ventilation for ARDS, it will require development of sound protocols and technological enhancements to ensure its performance and safety. For now, APRV does have a greater potential for adversely affecting patient outcome than improving it; unless definitive data are forthcoming demonstrating outcome benefits from the use of APRV in ARDS, there is no reason to consider this approach to ventilatory support., (Copyright © 2016 by Daedalus Enterprises.)

It has been shown that mechanical ventilation by itself can cause lung injury and affect outcomes. Ventilator-induced lung injury is associated with high tidal volumes in lungs afflicted with ARDS. However, the question is: Do high tidal volumes have this same effect in normal lungs or lungs that have respiratory compromise stemming from something other than ARDS? Many clinicians believe that a tidal volume strategy of 6 mL/kg predicted body weight should be standard practice in all patients receiving mechanical ventilation. There is a growing body of evidence related to this issue, and this is the debate that will be tackled in this paper from both pro and con perspectives., (Copyright © 2016 by Daedalus Enterprises.)

The American Association for Respiratory Care has declared a benchmark for competency in mechanical ventilation that includes the ability to "apply to practice all ventilation modes currently available on all invasive and noninvasive mechanical ventilators." This level of competency presupposes the ability to identify, classify, compare, and contrast all modes of ventilation. Unfortunately, current educational paradigms do not supply the tools to achieve such goals. To fill this gap, we expand and refine a previously described taxonomy for classifying modes of ventilation and explain how it can be understood in terms of 10 fundamental constructs of ventilator technology: (1) defining a breath, (2) defining an assisted breath, (3) specifying the means of assisting breaths based on control variables specified by the equation of motion, (4) classifying breaths in terms of how inspiration is started and stopped, (5) identifying ventilator-initiated versus patient-initiated start and stop events, (6) defining spontaneous and mandatory breaths, (7) defining breath sequences (8), combining control variables and breath sequences into ventilatory patterns, (9) describing targeting schemes, and (10) constructing a formal taxonomy for modes of ventilation composed of control variable, breath sequence, and targeting schemes. Having established the theoretical basis of the taxonomy, we demonstrate a step-by-step procedure to classify any mode on any mechanical ventilator., (Copyright © 2014 by Daedalus Enterprises.)

Background: Mid-frequency ventilation (MFV) is a mode of pressure control ventilation based on an optimal targeting scheme that maximizes alveolar ventilation and minimizes tidal volume (VT). This study was designed to compare the effects of conventional mechanical ventilation using a lung-protective strategy with MFV in a porcine model of lung injury. Our hypothesis was that MFV can maximize ventilation at higher frequencies without adverse consequences. We compared ventilation and hemodynamic outcomes between conventional ventilation and MFV., Methods: This was a prospective study of 6 live Yorkshire pigs (10 ± 0.5 kg). The animals were subjected to lung injury induced by saline lavage and injurious conventional mechanical ventilation. Baseline conventional pressure control continuous mandatory ventilation was applied with V(T) = 6 mL/kg and PEEP determined using a decremental PEEP trial. A manual decision support algorithm was used to implement MFV using the same conventional ventilator. We measured P(aCO2), P(aO2), end-tidal carbon dioxide, cardiac output, arterial and venous blood oxygen saturation, pulmonary and systemic vascular pressures, and lactic acid., Results: The MFV algorithm produced the same minute ventilation as conventional ventilation but with lower V(T) (-1 ± 0.7 mL/kg) and higher frequency (32.1 ± 6.8 vs 55.7 ± 15.8 breaths/min, P < .002). There were no differences between conventional ventilation and MFV for mean airway pressures (16.1 ± 1.3 vs 16.4 ± 2 cm H2O, P = .75) even when auto-PEEP was higher (0.6 ± 0.9 vs 2.4 ± 1.1 cm H2O, P = .02). There were no significant differences in any hemodynamic measurements, although heart rate was higher during MFV., Conclusions: In this pilot study, we demonstrate that MFV allows the use of higher breathing frequencies and lower V(T) than conventional ventilation to maximize alveolar ventilation. We describe the ventilatory or hemodynamic effects of MFV. We also demonstrate that the application of a decision support algorithm to manage MFV is feasible., (Copyright © 2014 by Daedalus Enterprises.)

Mechanical ventilation is a life-saving intervention for respiratory failure and thus has become the cornerstone of the practice of critical care medicine. A mechanical ventilation mode describes the predetermined pattern of patient-ventilator interaction. In recent years there has been a dizzying proliferation of mechanical ventilation modes, driven by technological advances and market pressures, rather than clinical data. The comparison of these modes is hampered by the sheer number of combinations that need to be tested against one another, as well as the lack of a coherent, logical nomenclature that accurately describes a mode. In this paper we propose a logical nomenclature for mechanical ventilation modes, akin to biological taxonomy. Accordingly, the control variable, breath sequence, and targeting schemes for the primary and secondary breaths represent the order, family, genus, and species, respectively, for the described mode. To distinguish unique operational algorithms, a fifth level of distinction, termed variety, is utilized. We posit that such coherent ordering would facilitate comparison and understanding of modes. Next we suggest that the clinical goals of mechanical ventilation may be simplified into 3 broad categories: provision of safe gas exchange; provision of comfort; and promotion of liberation from mechanical ventilation. Safety is achieved via optimization of ventilation-perfusion matching and pressure-volume relationship of the lungs. Comfort is provided by fostering patient-ventilator synchrony. Liberation is promoted by optimization of the weaning experience. Then we follow a paradigm that matches the technological capacity of a particular mode to achieving a specific clinical goal. Finally, we provide the reader with a comparison of existing modes based on these principles. The status quo in mechanical ventilation mode nomenclature impedes communication and comparison of existing mechanical ventilation modes. The proposed model, utilizing a systematic nomenclature, provides a useful framework to address this unmet need., (© 2013 Daedalus Enterprises.)

There has been a dramatic increase in the number and complexity of new ventilation modes over the last 30 years. The impetus for this has been the desire to improve the safety, efficiency, and synchrony of ventilator-patient interaction. Unfortunately, the proliferation of names for ventilation modes has made understanding mode capabilities problematic. New modes are generally based on increasingly sophisticated closed-loop control systems or targeting schemes. We describe the 6 basic targeting schemes used in commercially available ventilators today: set-point, dual, servo, adaptive, optimal, and intelligent. These control systems are designed to serve the 3 primary goals of mechanical ventilation: safety, comfort, and liberation. The basic operations of these schemes may be understood by clinicians without any engineering background, and they provide the basis for understanding the wide variety of ventilation modes and their relative advantages for improving patient-ventilator synchrony. Conversely, their descriptions may provide engineers with a means to better communicate to end users.

Background: Adaptive pressure control is a mode of mechanical ventilation where inflation pressure is adjusted by the ventilator to achieve a target tidal volume (VT). This means that as patient effort increases, inflation pressure is reduced, which may or may not be clinically appropriate. The purpose of this study was to evaluate the relationship between ventilator work output and patient effort in adaptive pressure control., Methods: A lung simulator (ASL 5000) was set at compliance=0.025 L/cm H2O and resistance=10 cm H2O/L/s. Muscle pressure (Pmus) was a sine wave (20% inspiration, 5% hold, 20% release) that increased from 0-25 cm H2O in steps of 5 cm H2O. The adaptive-pressure-control modes tested were: AutoFlow (Dräger Evita XL), VC+ (Puritan Bennett 840), APV (Hamilton Galileo), and PRVC (Siemens Servo-i and Siemens Servo 300). The target VT was set at 320 mL (Pmus=15 cm H2O, inspiratory pressure=0 cm H2O) to allow delivery of a realistic VT as the simulated patient demanded more volume. All measurements were obtained from the simulator., Results: Patient work of breathing (patient WOB) increased from 0 J/L to 1.88 J/L through the step increase in Pmus. Target VT was maintained as long as Pmus was below 10 cm H2O. VT then increased linearly with increased Pmus. The ventilators showed 3 patterns of behavior in response to an increase in Pmus: (1) ventilator WOB gradually decreased to 0 J/L as Pmus increased; (2) ventilator WOB decreased at the same rate as Pmus increased but plateaued at Pmus=10 cm H2O by delivering a minimum inspiratory pressure level of 6 cm H2O; (3) ventilator WOB decreased as in patterns 1 and 2 to Pmus=10 cm H2O, but then decreased at a much slower rate., Conclusions: Adaptive-pressure-control algorithms differ between ventilators in their response to increasing patient effort. Notably, some ventilators allow the patient to assume all of the WOB, and some provide a minimum level of WOB regardless of patient effort.

Background: Studies have found that increasing the respiratory frequency during mechanical ventilation does not always improve alveolar minute ventilation and may cause air-trapping., Objective: To investigate the theoretical and practical basis of higher-than-normal ventilation frequencies., Methods: We used an interactive mathematical model of ventilator output during pressure-control ventilation to predict the frequency at which alveolar ventilation is maximized with the lowest tidal volume (V(T)) for a given pressure. We then tested our predicted optimum frequencies and V(T) values with various lung compliances and higher-than-normal frequencies, with a lung simulator and 5 mechanical ventilators (Dräger Evita XL, Hamilton Galileo, Puritan Bennett 840, Siemens Servo 300 and Servo-i)., Results: Compliances between 10 mL/cm H(2)O and 42 mL/cm H(2)O yielded V(T) between 4.1 mL/kg (optimum frequency 75 cycles/min) and 6.0 mL/kg (optimum frequency 27 cycles/min). The intrinsic positive end-expiratory pressure at the optimum frequency was always less than 2 cm H(2)O. All the ventilators except the Hamilton Galileo had an optimum frequency near 50 cycles/min, whereas the predicted optimum frequency was 60 cycles/min., Conclusions: With these ventilators and pressure-control ventilation, alveolar minute ventilation can be optimized with higher-than-normal frequency and lower V(T) than is commonly used in patients with acute respiratory distress syndrome. We call this strategy mid-frequency ventilation.