Flow-controlled Ventilation Research Articles

Flow-controlled ventilation - a new and promising method of ventilation presented with a review of the literature.

Substantial efforts have been undertaken to identify and minimise factors responsible for the development of ventilator-induced lung injury. Anovel approach to this problem addresses energy dissipated in lung tissue during the breathing cycle as one of the key problems. Flow-controlled ventilation is anew modality of mechanical ventilation based on aconstant flow during both inspiration and expiration. This review aims to evaluate the current evidence available regarding flow-controlled ventilation. Lastly, three cases of flow-controlled ventilation application are presented: ventilation with asmall lumen tube during tracheal resection, one-lung ventilation during thoracoscopic lobectomy, and ventilation of acritically ill patient with acute respiratory distress syndrome in an intensive care unit setting.

A new perspective during laryngo-tracheal surgery: the use of an ultra-thin endotracheal tube (Tritube®) and flow-controlled ventilation—a retrospective case series and a review of the literature

BackgroundUpper airway surgery often poses a challenge to both anesthesiologists and surgeons, as airway access, mechanical ventilation, and surgical difficulties may occur in a tricky combination. To fulfill the need for a tubeless surgery, techniques such as apneic oxygenation or jet ventilation may be used, which carry the risk of several complications. The ultrathin cuffed endotracheal tube Tritube can be used with flow-controlled ventilation (FCV) to provide adequate surgical field and ventilation. To assess the feasibility, safety, and effectiveness of this technique, we describe a series of 21 patients, with various lung conditions, undergoing laryngo-tracheal surgery with FCV delivered via Tritube. Moreover, we perform a narrative systematic review to summarize clinical data on the use of Tritube during upper airway surgery.ResultsAll patients were successfully intubated in one attempt with Tritube. The median (interquartile range [IQR]) tidal volume was 6.7 (6.2–7.1) mL/kg of ideal body weight, the median end-expiratory pressure was 5.3 (5.0–6.4) cmH2O, and the median peak tracheal pressure was 16 (15–18) cmH2O. The median minute volume was 5.3 (5.0–6.4) L/min. Median global alveolar driving pressure was 8 (7–9) cmH2O. The median maximum level of end-tidal CO2 was 39 (35–41) mmHg. During procedures involving laser, the maximum fraction of inspired oxygen was 0.3, with the median lowest peripheral oxygen saturation of 96% (94–96%). No complications associated with intubation or extubation occurred. In one patient, the ventilator needed to be rebooted for a software issue. In two (10%) patients, Tritube needed to be flushed with saline to remove secretions. In all patients, optimal visualization and accessibility of the surgical site were obtained, according to the surgeon in charge. Thirteen studies (seven case reports, two case series, three prospective observational studies, and one randomized controlled trial) were included in the narrative systematic review and described.ConclusionsTritube in combination with FCV provided adequate surgical exposure and ventilation in patients undergoing laryngo-tracheal surgery. While training and experience with this new method is needed, FCV delivered with Tritube may represent an ideal approach that benefits surgeons, anesthesiologists, and patients with difficult airways and compromised lung mechanics.

Experience with Tritube and Flow-Controlled Ventilation During Airway Surgery.

Experience with Tritube and Flow-Controlled Ventilation During Airway Surgery.

A case report of individualized ventilation in a COVID-19 patient \u2013 new possibilities and caveats to consider with flow-controlled ventilation

BackgroundFlow-controlled ventilation (FCV) is a novel ventilation method increasingly being used clinically, particularly during the current COVID-19 pandemic. However, the continuous flow pattern in FCV during inspiration and expiration has a significant impact on respiratory parameters and ventilatory settings compared to conventional ventilation modes. In addition, the constant flow combined with direct intratracheal pressure measurement allows determination of dynamic compliance and ventilation settings can be adjusted accordingly, reflecting a personalized ventilation approach.Case presentationA 50-year old women with confirmed SARS-CoV-2 infection suffering from acute respiratory distress syndrome (ARDS) was admitted to a tertiary medical center. Initial ventilation occurred with best standard of care pressure-controlled ventilation (PCV) and was then switched to FCV, by adopting PCV ventilator settings. This led to an increase in oxygenation by 30 %. Subsequently, to reduce invasiveness of mechanical ventilation, FCV was individualized by dynamic compliance guided adjustment of both, positive end-expiratory pressure and peak pressure; this intervention reduced driving pressure from 18 to 12 cm H2O. However, after several hours, compliance further deteriorated which resulted in a tidal volume of only 4.7 ml/kg.ConclusionsAn individualized FCV approach increased oxygenation parameters in a patient suffering from severe COVID-19 related ARDS. Direct intratracheal pressure measurements allow for determination of dynamic compliance and thus optimization of ventilator settings, thereby reducing applied and dissipated energy. However, although desirable, this personalized ventilation strategy may reach its limits when lung function is so severely impaired that patient’s oxygenation has to be ensured at the expense of lung protective ventilation concepts.

Flow-controlled ventilation during EVLP improves oxygenation and preserves alveolar recruitment

BackgroundEx vivo lung perfusion (EVLP) is a widespread accepted platform for preservation and evaluation of donor lungs prior to lung transplantation (LTx). Standard lungs are ventilated using volume-controlled ventilation (VCV). We investigated the effects of flow-controlled ventilation (FCV) in a large animal EVLP model.Fourteen porcine lungs were mounted on EVLP after a warm ischemic interval of 2 h and randomized in two groups (n = 7/group). In VCV, 7 grafts were conventionally ventilated and in FCV, 7 grafts were ventilated by flow-controlled ventilation. EVLP physiologic parameters (compliance, pulmonary vascular resistance and oxygenation) were recorded hourly. After 6 h of EVLP, broncho-alveolar lavage (BAL) was performed and biopsies for wet-to-dry weight (W/D) ratio and histology were taken. The left lung was inflated, frozen in liquid nitrogen vapors and scanned with computed tomography (CT) to assess regional distribution of Hounsfield units (HU).ResultsAll lungs endured 6 h of EVLP. Oxygenation was better in FCV compared to VCV (p = 0.01) and the decrease in lung compliance was less in FCV (p = 0.03). W/D ratio, pathology and BAL samples did not differ between both groups (p = 0.16, p = 0.55 and p = 0.62). Overall, CT densities tended to be less pronounced in FCV (p = 0.05). Distribution of CT densities revealed a higher proportion of well-aerated lung parts in FCV compared to VCV (p = 0.01).ConclusionsFCV in pulmonary grafts mounted on EVLP is feasible and leads to improved oxygenation and alveolar recruitment. This ventilation strategy might prolong EVLP over time, with less risk for volutrauma and atelectrauma.

Individualized flow-controlled ventilation compared to best clinical practice pressure-controlled ventilation: a prospective randomized porcine study

BackgroundFlow-controlled ventilation is a novel ventilation method which allows to individualize ventilation according to dynamic lung mechanic limits based on direct tracheal pressure measurement at a stable constant gas flow during inspiration and expiration. The aim of this porcine study was to compare individualized flow-controlled ventilation (FCV) and current guideline-conform pressure-controlled ventilation (PCV) in long-term ventilation.MethodsAnesthetized pigs were ventilated with either FCV or PCV over a period of 10 h with a fixed FiO2 of 0.3. FCV settings were individualized by compliance-guided positive end-expiratory pressure (PEEP) and peak pressure (Ppeak) titration. Flow was adjusted to maintain normocapnia and the inspiration to expiration ratio (I:E ratio) was set at 1:1. PCV was performed with a PEEP of 5 cm H2O and Ppeak was set to achieve a tidal volume (VT) of 7 ml/kg. The respiratory rate was adjusted to maintain normocapnia and the I:E ratio was set at 1:1.5. Repeated measurements during observation period were assessed by linear mixed-effects model.ResultsIn FCV (n = 6), respiratory minute volume was significantly reduced (6.0 vs 12.7, MD − 6.8 (− 8.2 to − 5.4) l/min; p < 0.001) as compared to PCV (n = 6). Oxygenation was improved in the FCV group (paO2 119.8 vs 96.6, MD 23.2 (9.0 to 37.5) Torr; 15.97 vs 12.87, MD 3.10 (1.19 to 5.00) kPa; p = 0.010) and CO2 removal was more efficient (paCO2 40.1 vs 44.9, MD − 4.7 (− 7.4 to − 2.0) Torr; 5.35 vs 5.98, MD − 0.63 (− 0.99 to − 0.27) kPa; p = 0.006). Ppeak and driving pressure were comparable in both groups, whereas PEEP was significantly lower in FCV (p = 0.002). Computed tomography revealed a significant reduction in non-aerated lung tissue in individualized FCV (p = 0.026) and no significant difference in overdistended lung tissue, although a significantly higher VT was applied (8.2 vs 7.6, MD 0.7 (0.2 to 1.2) ml/kg; p = 0.025).ConclusionOur long-term ventilation study demonstrates the applicability of a compliance-guided individualization of FCV settings, which resulted in significantly improved gas exchange and lung tissue aeration without signs of overinflation as compared to best clinical practice PCV.

Anesthetic considerations for tracheobronchial surgery

Tracheobronchial pathology can be related to trauma, infection, tumor, or a combination of these. Per definition, planning for tracheobronchial surgery can be complicated by the overlap of anesthesiological interests in airway management and the primary surgical field. Therefore, following a detailed description of the stenosis, management of tracheobronchial surgery requires an interdisciplinary discussion and individualized planning of the procedure. There are several options for intraoperative ventilation depending on the exact localization of the defect. Hence, different tubes and ventilation techniques from cross-field ventilation, to jet ventilation, or even spontaneous breathing under regional anesthesia, have to be discussed. Moreover, an innovative ventilation mode called flow-controlled ventilation (FVC) has been developed, which allows to apply standard tidal volumes through a narrow-bore endotracheal tube. In addition, the Ventrain has been developed as an emergency device following the same technique of an active expiration based on the Venturi principle and a controlled gas flow. In critical situations, it allows even ventilation through the working channel of a bronchoscope. Overall, tracheobronchial surgery is performed under total intravenous anesthesia and the aim of an early extubation at the end of surgery. Airway management has to be discussed and planned between surgeon and anesthesiologist. All of the steps of the procedure need constant and clear communication.

A linearized expiration flow homogenizes the compartmental pressure distribution in a physical model of the inhomogeneous respiratory system

Objective: Flow-controlled expiration (FLEX) and flow-controlled ventilation (FCV) imply a linearized expiration, and were suggested as new approaches for lung-protective ventilation, especially in the case of an inhomogeneous lung. We hypothesized that a linearized expiration homogenizes the pressure distribution between compartments during expiration, compared to volume-controlled (VCV) and pressure-controlled (PCV) ventilation. Approach: We investigated the expiratory pressure decays in a physical model of an inhomogeneous respiratory system. The model contained four compartments of which two had a high (25 ml cmH2O-1) and two a low compliance (10 ml cmH2O−1). These were combined with either a high (6.5 cmH2O s l−1) or low resistance (2.8 cmH2O s l−1), respectively. The model was ventilated in all modes at various tidal volumes and peak pressures, and we determined in each compartment the expiratory time at which the pressure declined to 50% (t50) of the end-inspiratory pressure, and the maximal differences of t50 (Δt50) and pressure (Δpmax) between all compartments. Main results: During FLEX and FCV, t50 was 6- to 7-fold higher compared to VCV and PCV (all P < 0.001). During VCV and PCV, Δt50 was higher (128 ± 18 ms) compared to FLEX and FCV (49 ± 19 ms; all P < 0.001). Δpmax reached up to 3.8 ± 0.2 cmH2O during VCV and PCV, but only 0.6 ± 0.1 cmH2O during FLEX and FCV (P < 0.001). Significance: FLEX and FCV provide a more homogeneous expiratory pressure distribution between compartments with different mechanical properties compared with VCV and PCV. This may reduce shear stress within inhomogeneous lung tissue.

Flow Controlled Ventilation during EVLP Improves Oxygenation and Preserves Alveolar Recruitment

Ex vivo lung perfusion (EVLP) is considered a useful platform to evaluate, preserve and recondition grafts prior to lung transplantation (LTx). Reducing physical stress due to standard volume-controlled ventilation (VCV), might further prolong EVLP in time and reduce ventilator induced lung injury (VILI). An innovative approach might be the use of flow-controlled ventilation (FCV), a ventilation mode which controls inspiratory and expiratory flow. These properties can reduce atelectrauma and volutrauma related to standard VCV. This is the first study to evaluate the use of FCV during EVLP in a porince model. Porcine lungs were mounted on EVLP after 2 hours of warm ischemia and divided into 2 groups (n=7/group). EVLP was maintained for 6 hours and physiological parameters were continuously recorded. In the first group, lungs on EVLP were ventilated standardly (VCV, 7 ml/kg). In the second group, lungs were ventilated using FCV (7ml/kg). After EVLP, W/D ratios were taken of the right lung and the left lung was frozen while inflated in liquid nitrogen vapors and CT scanned. Results are demonstrated in figure 1. Pulmonary vascular resistance (PVR) was comparable between VCV and FCV (p=0.52). FCV significantly increased oxygenation (P/F ratios) (p=0.01), and better maintained dynamic compliance (p=0.03). There was no difference in W/D ratios between the groups (p=0.16). CT density measurements were decreased by FCV (p=0.05). FCV is feasible to ventilate pulmonary grafts during EVLP and improves oxygenation. The lower decline in compliance and lower CT density measurements in FCV might indicate a better preservation of alveolar recruitment since extravascular water content (W/D ratio) was similar between both groups. In conclusion, FCV ventilation might reduce injury related to standard volume-controlled ventilation. Using FCV mode during EVLP might stabilize and prolong EVLP time in the future and open the perspective to further actively recondition grafts.

Evone® Flow-Controlled Ventilation During Upper Airway Surgery: A Clinical Feasibility Study and Safety Assessment.

Introduction: During upper airway surgery in a narrowed airway due to tumor or stenosis, safe ventilation, good laryngotracheal exposure, and preservation of an adequate surgical working space are of paramount importance. This can be achieved by small-lumen ventilation such as High Frequency Jet Ventilation (HFJV). However, this technique has major drawbacks, such as air-trapping and desaturation in patients with poor pulmonary reserve. Recently, an innovative ventilating system with flow-controlled ventilation (FCV) and a small-lumen endotracheal tube, the Evone® (Ventinova, Eindhoven, The Netherlands), was introduced, claiming to counter the drawbacks of HFJV.Objectives: To evaluate feasibility and safety of the Evone® FCV system in difficult upper airway surgery and to critically appraise this novel ventilation method.Patients and methods: Evone® is a FCV-device using a small-bore cuffed tube (Tritube®). This ventilator actively sucks air out of the lungs, rather than relying on the passive backflow of air like in HFJV. Data related to the medical history, surgery, and anesthesia of all consecutive patients undergoing upper airway surgery with Evone® FCV ventilation were included in a tertiary center retrospective observational study.Results: Fifteen Patients, with a median age of 54 years, were included. Surgical procedures and indications included laser-assisted endoscopic treatment of idiopathic subglottic stenosis (n = 3), tracheal stenosis (n = 1), and posterior glottic stenosis (n = 2), biopsy and/or Transoral Laser Microsurgery for laryngeal (pre)malignancy (n = 7) and resection of benign lesions with posterior (supra)glottic location (n = 2). Mean ventilation duration was 52.0 min (range 30–115 min, SD 19.6 min), mean surgery duration was 31.7 min (range 15–65 min, SD 13.2 min), mean minimal SaO2 was 96.3% (range 89–100%, SD 4.0%) and mean peak pCO2 was 41.4 mmHg (range 31–50 mmHg, SD = 5.5 mmHg). No anesthesia- or surgery-related complications, adverse events or intra-operative difficulties were reported during or after any of the 15 procedures. In all cases, compared to HFJV, Evone® FCV ventilation allowed a superior visualization and working space during the surgical procedure.Conclusion: The Evone® FCV ventilation system provides excellent conditions in patients undergoing upper airway surgery, as it combines excellent accessibility and visibility of the operation site with safe and stable ventilation.

A novel mechanical ventilator providing flow-controlled expiration for small animals.

For investigating the effects of mechanical ventilation on the respiratory system, experiments in small mammal models are used. However, conventional ventilators for small animals are usually limited to a specific ventilation mode, and in particular to passive expiration. Here, we present a computer-controlled research ventilator for small animals which provides conventional mechanical ventilation as well as new type ventilation profiles. Typical profiles of conventional mechanical ventilation, as well as flow-controlled expiration and sinusoidal ventilation profiles can be generated with our new ventilator. Flow control during expiration reduced the expiratory peak flow rate by 73% and increased the mean airway pressure by up to 1 mbar compared with conventional ventilation without increasing peak pressure and end-expiratory pressure. Our new ventilator for small animals allows for the application of various ventilation profiles. We could analyse the effects of applying conventional ventilation profiles, pressure-controlled ventilation and volume-controlled ventilation, as well as the novel flow-controlled ventilation profile. This new approach enables studying the mechanical properties of the respiratory system with an increased freedom for choosing independent ventilation parameters.

Flow-Controlled Ventilation Attenuates Lung Injury in a Porcine Model of Acute Respiratory Distress Syndrome: A Preclinical Randomized Controlled Study.

Lung-protective ventilation for acute respiratory distress syndrome aims for providing sufficient oxygenation and carbon dioxide clearance, while limiting the harmful effects of mechanical ventilation. "Flow-controlled ventilation", providing a constant expiratory flow, has been suggested as a new lung-protective ventilation strategy. The aim of this study was to test whether flow-controlled ventilation attenuates lung injury in an animal model of acute respiratory distress syndrome. Preclinical, randomized controlled animal study. Animal research facility. Nineteen German landrace hybrid pigs. Flow-controlled ventilation (intervention group) or volume-controlled ventilation (control group) with identical tidal volume (7 mL/kg) and positive end-expiratory pressure (9 cm H2O) after inducing acute respiratory distress syndrome with oleic acid. PaO2 and PaCO2, minute volume, tracheal pressure, lung aeration measured via CT, alveolar wall thickness, cell infiltration, and surfactant protein A concentration in bronchoalveolar lavage fluid. Five pigs were excluded leaving n equals to 7 for each group. Compared with control, flow-controlled ventilation elevated PaO2 (154 ± 21 vs 105 ± 9 torr; 20.5 ± 2.8 vs 14.0 ± 1.2 kPa; p = 0.035) and achieved comparable PaCO2 (57 ± 3 vs 54 ± 1 torr; 7.6 ± 0.4 vs 7.1 ± 0.1 kPa; p = 0.37) with a lower minute volume (6.4 ± 0.5 vs 8.7 ± 0.4 L/min; p < 0.001). Inspiratory plateau pressure was comparable in both groups (31 ± 2 vs 34 ± 2 cm H2O; p = 0.16). Flow-controlled ventilation increased normally aerated (24% ± 4% vs 10% ± 2%; p = 0.004) and decreased nonaerated lung volume (23% ± 6% vs 38% ± 5%; p = 0.033) in the dependent lung region. Alveolar walls were thinner (5.5 ± 0.1 vs 7.8 ± 0.2 µm; p < 0.0001), cell infiltration was lower (20 ± 2 vs 32 ± 2 n/field; p < 0.0001), and normalized surfactant protein A concentration was higher with flow-controlled ventilation (1.1 ± 0.04 vs 1.0 ± 0.03; p = 0.039). Flow-controlled ventilation enhances lung aeration in the dependent lung region and consequently improves gas exchange and attenuates lung injury. Control of the expiratory flow may provide a novel option for lung-protective ventilation.

Flow-controlled ventilation – a novel approach to treating acute respiratory distress syndrome

Flow-controlled ventilation – a novel approach to treating acute respiratory distress syndrome

Flow-controlled ventilation (FCV) improves regional ventilation in obese patients \u2013 a randomized controlled crossover trial

BackgroundIn obese patients, high closing capacity and low functional residual capacity increase the risk for expiratory alveolar collapse. Constant expiratory flow, as provided by the new flow-controlled ventilation (FCV) mode, was shown to improve lung recruitment. We hypothesized that lung aeration and respiratory mechanics improve in obese patients during FCV.MethodsWe compared FCV and volume-controlled (VCV) ventilation in 23 obese patients in a randomized crossover setting. Starting with baseline measurements, ventilation settings were kept identical except for the ventilation mode related differences (VCV: inspiration to expiration ratio 1:2 with passive expiration, FCV: inspiration to expiration ratio 1:1 with active, linearized expiration). Primary endpoint of the study was the change of end-expiratory lung volume compared to baseline ventilation. Secondary endpoints were the change of mean lung volume, respiratory mechanics and hemodynamic variables.ResultsThe loss of end-expiratory lung volume and mean lung volume compared to baseline was lower during FCV compared to VCV (end-expiratory lung volume: FCV, − 126 ± 207 ml; VCV, − 316 ± 254 ml; p < 0.001, mean lung volume: FCV, − 108.2 ± 198.6 ml; VCV, − 315.8 ± 252.1 ml; p < 0.001) and at comparable plateau pressure (baseline, 19.6 ± 3.7; VCV, 20.2 ± 3.4; FCV, 20.2 ± 3.8 cmH2O; p = 0.441), mean tracheal pressure was higher (baseline, 13.1 ± 1.1; VCV, 12.9 ± 1.2; FCV, 14.8 ± 2.2 cmH2O; p < 0.001). All other respiratory and hemodynamic variables were comparable between the ventilation modes.ConclusionsThis study demonstrates that, compared to VCV, FCV improves regional ventilation distribution of the lung at comparable PEEP, tidal volume, PPlat and ventilation frequency. The increase in end-expiratory lung volume during FCV was probably caused by the increased mean tracheal pressure which can be attributed to the linearized expiratory pressure decline.Trial registrationGerman Clinical Trials Register: DRKS00014925. Registered 12 July 2018.

Flow-controlled ventilation improves gas exchange in lung-healthy patients- a randomized interventional cross-over study.

Flow-controlled ventilation (FCV) is a new ventilation mode that provides constant inspiratory and expiratory flow. FCV was shown to improve gas exchange and lung recruitment in porcine models of healthy and injured ventilated lungs. The primary aim of our study was to verify the influences of FCV on gas exchange, respiratory mechanics and haemodynamic variables in mechanically ventilated lung-healthy patients. After obtaining ethical approval and informed consent, we measured arterial blood gases, respiratory and haemodynamic variables during volume-controlled ventilation (VCV) and FCV in 20 consecutive patients before they underwent abdominal surgery. After baseline (BL) ventilation, patients were randomly assigned to either BL-VCV-FCV or BL-FCV-VCV. Thereby, BL ventilation settings were kept, except for the ventilation mode-related differences (FCV is supposed to be used with an I:E ratio of 1:1). Compared to BL and VCV, PaO2 was higher [PaO2 : FCV: 38.2 (7.1), BL ventilation: 35.0 (5.8), VCV: 35.2 (7.0) kPa, P<.001] and PaCO2 lower [PaCO2 : FCV: 4.8 (0.5), BL ventilation: 5.1 (0.5), VCV: 5.1 (0.5) kPa, P<.001] during FCV. With comparable plateau pressure [BL: 14.9 (1.9), VCV: 15.3 (1.6), FCV: 15.2 (1.5) cm H2 O), P=.185], tracheal mean pressure was higher during FCV [BL: 10.2 (1.1), VCV: 10.4 (0.7), FCV: 11.5 (1.0) cm H2 O, P<.001]. Haemodynamic variables did not differ between ventilation phases. Flow-controlled ventilation improves oxygenation and carbon dioxide elimination within a short time, compared to VCV with identical tidal volume, inspiratory plateau pressure and end-expiratory pressure.

Flow-controlled ventilation during ear, nose and throat surgery: A prospective observational study.

Flow-controlled ventilation (FCV) is a new mechanical ventilation mode that maintains constant flow during inspiration and expiration with standard tidal volumes via cuffed narrow-bore endotracheal tubes. Originating in manually operated 'expiratory ventilation assistance', FCV extends this technique by automatic control of airway flow, monitoring of intratracheal pressure and control of peak inspiratory pressure and end-expiratory pressure. FCV has not yet been described in a clinical study. The aim of this study was to provide an initial assessment of FCV in mechanically ventilated patients undergoing ear, nose and throat surgery and evaluate its potential for future use. An observational study. Two German academic medical centres from 24 November 2017 to 09 January 2018. Consecutive patients (≥ 18 years) scheduled for elective ear, nose and throat surgery. Exclusion criteria were planned laser surgery, intended fibreoptic awake intubation, emergency procedures, increased risk of aspiration, American Society of Anesthesiologists (ASA) physical status more than III and chronic obstructive pulmonary disease classified as GOLD stage more than II. Peri-operative use of FCV provided by a new type of ventilator (Evone) via a narrow-bore endotracheal tube (Tritube). Minute volume, respiratory rate, intratidal tracheal pressure amplitude (Δp) and end-tidal CO2 (PetCO2) were recorded every 5 min. All adverse events were noted. Data are presented as median [IQR]. Sixteen patients provided 15 evaluable data sets. A minute volume of 5.0 [4.4 to 6.4] l min and a respiratory rate of 9 [8 to 11] min generated a PetCO2 of 4.9 [4.8 to 5.0] kPa. Δp was 10 [9 to 12] cmH2O. Five adverse events were recorded: a tube obstruction due to airway secretions and four tube dislocations (two attributed to coughing, two not study-related). FCV achieves adequate PetCO2 levels with minute volume and Δp in the normal range. Tritube's high flow resistance may increase the likelihood of tube dislocations if the patient coughs. Although further evaluation is necessary, FCV provides a new option for short-term mechanical ventilation. The successful operation of FCV with narrow-bore tubes contributes to the armamentarium for airway management. DRKS00013312.

Flow Controlled Ventilation (FCV) With the Evone Ventilator and Tritube Versus Volume Controlled Ventilation (VCV)

Flow Controlled Ventilation (FCV) With the Evone Ventilator and Tritube Versus Volume Controlled Ventilation (VCV)

Minimisation of dissipated energy in the airways during mechanical ventilation by using constant inspiratory and expiratory flows – Flow-controlled ventilation (FCV)

It has been suggested that energy dissipation in the airways during mechanical ventilation is associated with an increased probability of ventilator induced lung injury (VILI). We hypothesise that energy dissipation in the airways may be minimised by ventilating with constant flow during both the inspiration and expiration phases of the respiratory cycle. We present a simple analysis and numerical calculations that support our hypothesis and show that for ventilation with minimum dissipated energy not only should the flows during inspiration and expiration be controlled to be constant and continuous, but the ventilation should also be undertaken with an I:E ratio that is close to 1:1.

Ventilation for low dissipated energy achieved using flow control during both inspiration and expiration

Mechanical or thermal stresses, which cause injury, do so essentially by dissipating energy in the tissue at a rate above some threshold at which damage occurs. This principle may also be applied to a ventilated lung. Minimizing dissipated energy is therefore a promising strategy to prevent ventilator induced lung injury (VILI) [1].In this special interest paper, we present a qualitative argument to show that dissipated energy as determined from the area enclosed by the pressure-volume (PV) loop may be minimised during ventilation by controlling the flow to be constant during both inspiration and expiration. We then demonstrate the characteristics of the PV loop and concomitant low energy dissipation that occur with this mode of ventilation in a clinical case report. In this case, we ventilated a healthy, male, 51 year old patient undergoing elective, minor laryngeal surgery with a new, specialized ventilator, which achieves accurate control of flow during both inspiration and expiration (Evone; Ventinova Medical, Eindhoven, The Netherlands) through a small-bore (4.4 mm outer diameter), cuffed tracheal tube (Tritube; Ventinova Medical, Eindhoven, The Netherlands). This mode of ventilation is called flow-controlled ventilation (FCV). During ventilation, both inspiratory and expiratory flows were kept nearly constant at 12 ± 0.98 l/min and the I:E ratio was 1:1 with a minute volume of 6.23 ± 0.15 l/min. We recorded pressure-volume loops using pressure measured directly within the patient's trachea and calculated the energy dissipated in the patient from the hysteresis area of the PV loops.Energy dissipation was 0.17 ± 0.02 J/l, which is close to the minimum energy dissipation achievable for this minute volume. It is lower than values quoted in the literature for spontaneous breathing (0.2–0.7 J/l) and indicative values obtained with other methods of flow control (0.32 J/l). This ventilation strategy may have implications for lung-protective ventilation.