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

Sex related differences in applied tidal volume with flow-controlled ventilation: a subgroup analysis

BACKGROUND

Flow-controlled ventilation (FCV) ensures a constant gas flow whereby precise determination of dynamic compliance is feasible. Accordingly, ventilator pressure settings can be adjusted to achieve the highest compliance. This setting will automatically adapt tidal volume to the functionally available lung volume as a personalized approach. This is in contrast to current ventilation settings, where fixed tidal volumes according to predicted body weight (PBW) are recommended. Aim of this subgroup-analysis was to determine whether applied tidal volume differs in male and female patients after compliance guided individualization of ventilation parameters.

METHODS

A sub-group analysis of 24 patients randomized to receive flow-controlled ventilation in cardiac surgery was performed. Linear mixed-effects model was used in order to investigate sex related differences in respiratory parameters.

RESULTS

Compliance guided pressure titration led to comparable pressure settings in male (N.=18) and female (N.=6) patients. In contrast, the applied tidal volume was significantly lower in female patients (8.6 vs. 9.9, 95% CI: -2.3 to -0.2 mL/kg PBW; P=0.029) compared to male individuals, due to a significantly lower compliance (49.3 vs. 70.3, 95% CI: -33.1 to -8.8 mL/cmH2O; P=0.003). Gas exchange parameters were comparable in either sex.

CONCLUSIONS

Female patients were found to receive lower tidal volumes after compliance guided individualization compared to men during cardiac surgery. This finding may indicate that the functionally available lung volume in women is lower and thus using PBW may not adequately comply with sex related differences, which supports the use of a personalized ventilation strategy.

A self-regulated expiratory flow device for mechanical ventilation: a bench study

INTRODUCTION

Unregulated expiratory flow may contribute to ventilator-induced lung injury. The amount of energy dissipated into the lungs with tidal mechanical ventilation may be used to quantify potentially injurious ventilation. Previously reported devices for variable expiratory flow regulation (FLEX) require, either computer-controlled feedback, or an initial expiratory flow trigger. In this bench study we present a novel passive expiratory flow regulation device.

METHODS

The device was tested using a commercially available mechanical ventilator with a range of settings (tidal volume 420 ml and 630 ml, max. inspiratory flow rate 30 L/min and 50 L/min, respiratory rate 10 min-1, positive end-expiratory pressure 5 cmH2O), and a test lung with six different combinations of compliance and resistance settings. The effectiveness of the device was evaluated for reduction in peak expiratory flow, expiratory time, mean airway pressure, and the reduction of tidal dissipated energy (measured as the area within the airway pressure-volume loop).

RESULTS

Maximal and minimal reduction in peak expiratory flow was from 97.18 ± 0.41 L/min to 25.82 ± 0.07 L/min (p < 0.001), and from 44.11 ± 0.42 L/min to 26.30 ± 0.06 L/min, respectively. Maximal prolongation in expiratory time was recorded from 1.53 ± 0.06 s to 3.64 ± 0.21 s (p < 0.001). As a result of the extended expiration, the maximal decrease in I:E ratio was from 1:1.15 ± 0.03 to 1:2.45 ± 0.01 (p < 0.001). The greatest increase in mean airway pressure was from 10.04 ± 0.03 cmH2O to 17.33 ± 0.03 cmH2O. Dissipated energy was significantly reduced with the device under all test conditions (p < 0.001). The greatest reduction in dissipated energy was from 1.74 ± 0.00 J to 0.84 ± 0.00 J per breath. The least reduction in dissipated energy was from 0.30 ± 0.00 J to 0.16 ± 0.00 J per breath. The greatest and least percentage reduction in dissipated energy was 68% and 33%, respectively.

CONCLUSIONS

The device bench tested in this study demonstrated a significant reduction in peak expiratory flow rate and dissipated energy, compared to ventilation with unregulated expiratory flow. Application of the device warrants further experimental and clinical evaluation.

Individualised flow-controlled ventilation reduces applied mechanical power and improves ventilation efficiency in a porcine intra-abdominal hypertension model

BACKGROUND

Aim of this study was to evaluate feasibility and effects of individualised flow-controlled ventilation (FCV), based on compliance guided pressure settings, compared to standard of pressure-controlled ventilation (PCV) in a porcine intra-abdominal hypertension (IAH) model. The primary aim of this study was to investigate oxygenation. Secondary aims were to assess respiratory and metabolic variables and lung tissue aeration.

METHODS

Pigs were randomly assigned to FCV (n = 9) and PCV (n = 9). IAH was induced by insufflation of air into the abdomen to induce IAH grades ranging from 0 to 3. At each IAH grade FCV was undertaken using compliance guided pressure settings, or PCV (n = 9) was undertaken with the positive end-expiratory pressure titrated for maximum compliance and the peak pressure set to achieve a tidal volume of 7 ml/kg. Gas exchange, ventilator settings and derived formulas were recorded at two timepoints for each grade of IAH. Lung aeration was assessed by a computed tomography scan at IAH grade 3.

RESULTS

All 18 pigs (median weight 54 kg [IQR 51-67]) completed the observation period of 4 h. Oxygenation was comparable at each IAH grade, but a significantly lower minute volume was required to secure normocapnia in FCV at all IAH grades (7.6 vs. 14.4, MD - 6.8 (95% CI - 8.5 to - 5.2) l/min; p < 0.001). There was also a significant reduction of applied mechanical power being most evident at IAH grade 3 (25.9 vs. 57.6, MD - 31.7 (95% CI - 39.7 to - 23.7) J/min; p < 0.001). Analysis of Hounsfield unit distribution of the computed tomography scans revealed a significant reduction in non- (5 vs. 8, MD - 3 (95% CI - 6 to 0) %; p = 0.032) and poorly-aerated lung tissue (7 vs. 15, MD - 6 (95% CI - 13 to - 3) %, p = 0.002) for FCV. Concomitantly, normally-aerated lung tissue was significantly increased (84 vs. 76, MD 8 (95% CI 2 to 15) %; p = 0.011).

CONCLUSIONS

Individualised FCV showed similar oxygenation but required a significantly lower minute volume for CO2-removal, which led to a remarkable reduction of applied mechanical power. Additionally, there was a shift from non- and poorly-aerated lung tissue to normally-aerated lung tissue in FCV compared to PCV.

Flow-controlled versus pressure-controlled ventilation in cardiac surgery with cardiopulmonary bypass - A single-center, prospective, randomized, controlled trial

STUDY OBJECTIVE

Multifactorial comparison of flow-controlled ventilation (FCV) to standard of pressure-controlled ventilation (PCV) in terms of oxygenation in cardiac surgery patients after chest closure.

DESIGN

Prospective, non-blinded, randomized, controlled trial.

SETTING

Operating theatre at an university hospital, Austria.

PATIENTS

Patients scheduled for elective, open, on-pump, cardiac surgery.

INTERVENTIONS

Participants were randomized to either individualized FCV (compliance guided end-expiratory and peak pressure setting) or control of PCV (compliance guided end-expiratory pressure setting and tidal volume of 6-8 ml/kg) for the duration of surgery.

MEASUREMENTS

The primary outcome measure was oxygenation (PaO2/FiO2) 15 min after intraoperative chest closure. Secondary endpoints included CO2-removal assessed as required minute volume to achieve normocapnia and lung tissue aeration assessed by Hounsfield unit distribution in postoperative computed tomography scans.

MAIN RESULTS

Between April 2020 and April 2021 56 patients were enrolled and 50 included in the primary analysis (mean age 70 years, 38 (76%) men). Oxygenation, assessed by PaO2/FiO2, was significantly higher in the FCV group (n = 24) compared to the control group (PCV, n = 26) (356 vs. 309, median difference (MD) 46 (95% CI 3 to 90) mmHg; p = 0.038). Additionally, the minute volume required to obtain normocapnia was significantly lower in the FCV group (4.0 vs. 6.1, MD -2.0 (95% CI -2.5 to -1.5) l/min; p < 0.001) and correlated with a significantly lower exposure to mechanical power (5.1 vs. 9.8, MD -5.1 (95% CI -6.2 to -4.0) J/min; p < 0.001). Evaluation of lung tissue aeration revealed a significantly reduced amount of non-aerated lung tissue in FCV compared to PCV (5 vs. 7, MD -3 (95% CI -4 to -1) %; p < 0.001).

CONCLUSIONS

In patients undergoing on-pump, cardiac surgery individualized FCV significantly improved oxygenation and lung tissue aeration compared to PCV. In addition, carbon dioxide removal was accomplished at a lower minute volume leading to reduced applied mechanical power.

Full-lung simulations of mechanically ventilated lungs incorporating recruitment/derecruitment dynamics

This study developed and investigated a comprehensive multiscale computational model of a mechanically ventilated ARDS lung to elucidate the underlying mechanisms contributing to the development or prevention of VILI. This model is built upon a healthy lung model that incorporates realistic airway and alveolar geometry, tissue distensibility, and surfactant dynamics. Key features of the ARDS model include recruitment and derecruitment (RD) dynamics, alveolar tissue viscoelasticity, and surfactant deficiency. This model successfully reproduces realistic pressure-volume (PV) behavior, dynamic surface tension, and time-dependent descriptions of RD events as a function of the ventilation scenario. Simulations of Time-Controlled Adaptive Ventilation (TCAV) modes, with short and long durations of exhalation (T Low - and T Low +, respectively), reveal a higher incidence of RD for T Low + despite reduced surface tensions due to interfacial compression. This finding aligns with experimental evidence emphasizing the critical role of timing in protective ventilation strategies. Quantitative analysis of energy dissipation indicates that while alveolar recruitment contributes only a small fraction of total energy dissipation, its spatial concentration and brief duration may significantly contribute to VILI progression due to its focal nature and higher intensity. Leveraging the computational framework, the model may be extended to facilitate the development of personalized protective ventilation strategies to enhance patient outcomes. As such, this computational modeling approach offers valuable insights into the complex dynamics of VILI that may guide the optimization of ventilation strategies in ARDS management.

Individualised flow-controlled versus pressure-controlled ventilation in a porcine oleic acid-induced acute respiratory distress syndrome model

BACKGROUND

A continuous gas flow provided by flow-controlled ventilation (FCV) facilitates accurate dynamic compliance measurement and allows the clinician to individually optimise positive end-expiratory and peak pressure settings accordingly.

OBJECTIVE

The aim of this study was to compare the efficiency of gas exchange and impact on haemodynamics between individualised FCV and pressure-controlled ventilation (PCV) in a porcine model of oleic acid-induced acute respiratory distress syndrome (ARDS).

DESIGN

Randomised controlled interventional trial conducted on 16 pigs.

SETTING

Animal operating facility at the Medical University Innsbruck.

INTERVENTIONS

ARDS was induced in lung healthy pigs by intravenous infusion of oleic acid until moderate-to-severe ARDS at a stable Horowitz quotient (PaO 2 FiO 2-1 ) of 80 to 120 over a period of 30 min was obtained. Ventilation was then either performed with individualised FCV ( n  = 8) established by compliance-guided pressure titration or PCV ( n  = 8) with compliance-guided titration of the positive end-expiratory pressure and peak pressure set to achieve a tidal volume of 6 ml kg -1 over a period of 2 h.

MAIN OUTCOME MEASURES

Gas exchange parameters were assessed by the PaO 2 FiO 2-1 quotient and CO 2 removal by the PaCO 2 value in relation to required respiratory minute volume. Required catecholamine support for haemodynamic stabilisation was measured.

RESULTS

The FCV group showed significantly improved oxygenation [149.2 vs. 110.4, median difference (MD) 38.7 (8.0 to 69.5) PaO 2 FiO 2-1 ; P  = 0.027] and CO 2 removal [PaCO 2 7.25 vs. 9.05, MD -1.8 (-2.87 to -0.72) kPa; P  = 0.006] at a significantly lower respiratory minute volume [8.4 vs. 11.9, MD -3.6 (-5.6 to -1.5) l min -1 ; P  = 0.005] compared with PCV. In addition, in FCV-pigs, haemodynamic stabilisation occurred with a significant reduction of required catecholamine support [norepinephrine 0.26 vs. 0.86, MD -0.61 (-1.12 to -0.09) μg kg -1  min -1 ; P  = 0.037] during 2 ventilation hours.

CONCLUSION

In this oleic acid-induced porcine ARDS model, individualised FCV significantly improved gas exchange and haemodynamic stability compared with PCV.

TRIAL REGISTRATION

Protocol no.: BMBWF-66.011/0105-V/3b/2019).

Individualised flow-controlled ventilation versus pressure-controlled ventilation in a porcine model of thoracic surgery requiring one-lung ventilation: A laboratory study

BACKGROUND

Flow-controlled ventilation (FCV) enables precise determination of dynamic compliance due to a continuous flow coupled with direct tracheal pressure measurement. Thus, pressure settings can be adjusted accordingly in an individualised approach.

OBJECTIVE

The aim of this study was to compare gas exchange of individualised FCV to pressure-controlled ventilation (PCV) in a porcine model of simulated thoracic surgery requiring one-lung ventilation (OLV).

DESIGN

Controlled interventional trial conducted on 16 domestic pigs.

SETTING

Animal operating facility at the Medical University of Innsbruck.

INTERVENTIONS

Thoracic surgery was simulated with left-sided thoracotomy and subsequent collapse of the lung over a period of three hours. When using FCV, ventilation was performed with compliance-guided pressure settings. When using PCV, end-expiratory pressure was adapted to achieve best compliance with peak pressure adjusted to achieve a tidal volume of 6 ml kg -1 during OLV.

MAIN OUTCOME MEASURES

Gas exchange was assessed by the Horowitz index (= P aO 2 /FIO 2 ) and CO 2 removal by the P aCO 2 value in relation to required respiratory minute volume.

RESULTS

In the FCV group ( n  = 8) normocapnia could be maintained throughout the OLV trial despite a significantly lower respiratory minute volume compared to the PCV group ( n  = 8) (8.0 vs. 11.6, 95% confidence interval, CI -4.5 to -2.7 l min -1 ; P  < 0.001), whereas permissive hypercapnia had to be accepted in PCV ( P aCO 2 5.68 vs. 6.89, 95% CI -1.7 to -0.7 kPa; P  < 0.001). The Horowitz index was comparable in both groups but calculated mechanical power was significantly lower in FCV (7.5 vs. 22.0, 95% CI -17.2 to -11.8 J min -1 ; P  < 0.001).

CONCLUSIONS

In this porcine study FCV maintained normocapnia during OLV, whereas permissive hypercapnia had to be accepted in PCV despite a substantially higher minute volume. Reducing exposure of the lungs to mechanical power applied by the ventilator in FCV offers a possible advantage for this mode of ventilation in terms of lung protection.

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

Background

Upper 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.

Results

All 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.

Conclusions

Tritube 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.

Reconstructing asynchrony for mechanical ventilation using a hysteresis loop virtual patient model

BACKGROUND

Patient-specific lung mechanics during mechanical ventilation (MV) can be identified from measured waveforms of fully ventilated, sedated patients. However, asynchrony due to spontaneous breathing (SB) effort can be common, altering these waveforms and reducing the accuracy of identified, model-based, and patient-specific lung mechanics.

METHODS

Changes in patient-specific lung elastance over a pressure-volume (PV) loop, identified using hysteresis loop analysis (HLA), are used to detect the occurrence of asynchrony and identify its type and pattern. The identified HLA parameters are then combined with a nonlinear mechanics hysteresis loop model (HLM) to extract and reconstruct ventilated waveforms unaffected by asynchronous breaths. Asynchrony magnitude can then be quantified using an energy-dissipation metric, Easyn, comparing PV loop area between model-reconstructed and original, altered asynchronous breathing cycles. Performance is evaluated using both test-lung experimental data with a known ground truth and clinical data from four patients with varying levels of asynchrony.

RESULTS

Root mean square errors for reconstructed PV loops are within 5% for test-lung experimental data, and 10% for over 90% of clinical data. Easyn clearly matches known asynchrony magnitude for experimental data with RMS errors < 4.1%. Clinical data performance shows 57% breaths having Easyn > 50% for Patient 1 and 13% for Patient 2. Patient 3 only presents 20% breaths with Easyn > 10%. Patient 4 has Easyn = 0 for 96% breaths showing accuracy in a case without asynchrony.

CONCLUSIONS

Experimental test-lung validation demonstrates the method's reconstruction accuracy and generality in controlled scenarios. Clinical validation matches direct observations of asynchrony in incidence and quantifies magnitude, including cases without asynchrony, validating its robustness and potential efficacy as a clinical real-time asynchrony monitoring tool.

Flow-controlled ventilation maintains gas exchange and lung aeration in a pediatric model of healthy and injured lungs: A randomized cross-over experimental study

Flow-controlled ventilation (FCV) is characterized by a constant flow to generate active inspiration and expiration. While the benefit of FCV on gas exchange has been demonstrated in preclinical and clinical studies with adults, the value of this modality for a pediatric population remains unknown. Thus, we aimed at observing the effects of FCV as compared to pressure-regulated volume control (PRVC) ventilation on lung mechanics, gas exchange and lung aeration before and after surfactant depletion in a pediatric model. Ten anesthetized piglets (10.4 ± 0.2 kg) were randomly assigned to start 1-h ventilation with FCV or PRVC before switching the ventilation modes for another hour. This sequence was repeated after inducing lung injury by bronchoalveolar lavage and injurious ventilation. The primary outcome was respiratory tissue elastance. Secondary outcomes included oxygenation index (PaO₂/FiO₂), PaCO₂, intrapulmonary shunt (Qs/Qt), airway resistance, respiratory tissue damping, end-expiratory lung volume, lung clearance index and lung aeration by chest electrical impedance tomography. Measurements were performed at the end of each protocol stage. Ventilation modality had no effect on any respiratory mechanical parameter. Adequate gas exchange was provided by FCV, similar to PRVC, with sufficient CO₂ elimination both in healthy and surfactant-depleted lungs (39.46 ± 7.2 mmHg and 46.2 ± 11.4 mmHg for FCV; 36.0 ± 4.1 and 39.5 ± 4.9 mmHg, for PRVC, respectively). Somewhat lower PaO₂/FiO₂ and higher Qs/Qt were observed in healthy and surfactant depleted lungs during FCV compared to PRVC (p < 0.05, for all). Compared to PRVC, lung aeration was significantly elevated, particularly in the ventral dependent zones during FCV (p < 0.05), but this difference was not evidenced in injured lungs. Somewhat lower oxygenation and higher shunt ratio was observed during FCV, nevertheless lung aeration improved and adequate gas exchange was ensured. Therefore, in the absence of major differences in respiratory mechanics and lung volumes, FCV may be considered as an alternative in ventilation therapy of pediatric patients with healthy and injured lungs.

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

BACKGROUND

Flow-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 PRESENTATION

A 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.

CONCLUSIONS

An 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.

Comparative effects of flow vs. volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in pigs

Background

Flow-controlled ventilation (FCV) allows expiratory flow control, reducing the collapse of the airways during expiration. The performance of FCV during one-lung ventilation (OLV) under intravascular normo- and hypovolaemia is currently unknown. In this explorative study, we hypothesised that OLV with FCV improves PaO₂ and reduces mechanical power compared to volume-controlled ventilation (VCV). Sixteen juvenile pigs were randomly assigned to one of two groups: (1) intravascular normovolaemia (n = 8) and (2) intravascular hypovolaemia (n = 8). To mimic inflammation due to major thoracic surgery, a thoracotomy was performed, and 0.5 μg/kg/h lipopolysaccharides from Escherichia coli continuously administered intravenously. Animals were randomly assigned to OLV with one of two sequences (60 min per mode): (1) VCV–FCV or (2) FCV–VCV. Variables of gas exchange, haemodynamics and respiratory signals were collected 20, 40 and 60 min after initiation of OLV with each mechanical ventilation mode. The distribution of ventilation was determined using electrical impedance tomography (EIT).

Results

Oxygenation did not differ significantly between modes (P = 0.881). In the normovolaemia group, the corrected expired minute volume (P = 0.022) and positive end-expiratory pressure (PEEP) were lower during FCV than VCV. The minute volume (P ≤ 0.001), respiratory rate (P ≤ 0.001), total PEEP (P ≤ 0.001), resistance of the respiratory system (P ≤ 0.001), mechanical power (P ≤ 0.001) and resistive mechanical power (P ≤ 0.001) were lower during FCV than VCV irrespective of the volaemia status. The distribution of ventilation did not differ between both ventilation modes (P = 0.103).

Conclusions

In a model of OLV in normo- and hypovolemic pigs, mechanical power was lower during FCV compared to VCV, without significant differences in oxygenation. Furthermore, the efficacy of ventilation was higher during FCV compared to VCV during normovolaemia.

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

BACKGROUND

Flow-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.

METHODS

Anesthetized 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 (P_peak) 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 P_peak was set to achieve a tidal volume (V_T) 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.

RESULTS

In 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). P_peak 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 V_T was applied (8.2 vs 7.6, MD 0.7 (0.2 to 1.2) ml/kg; p = 0.025).

CONCLUSION

Our 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.

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

BACKGROUND

Ex 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).

RESULTS

All 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).

CONCLUSIONS

FCV 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.

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

BACKGROUND

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.

METHODS

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).

RESULTS

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.

CONCLUSION

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.

Anesthetic Management of the Narrowed Airway

Airway narrowing can be idiopathic or can occur as a result of airway tumors, hematomas, infections, and other pathologic conditions. Endoscopic management variously involves balloon dilatation, stent placement, laser vaporization of pathologic tissue, microdebridement, and other interventions, using either a rigid or a flexible bronchoscope. Jet ventilation is frequently used in such settings, especially when the presence of an endotracheal tube would interfere with the procedure. In desperate cases, extracorporeal membrane oxygenation may be used in managing the critical airway.