Volume-controlled Ventilation Research Articles

Continuous estimation of respiratory system compliance and airway resistance during pressure-controlled ventilation without end-inspiration occlusion

BackgroundAssessing mechanical properties of the respiratory system (Cst) during mechanical ventilation necessitates an end-inspiration flow of zero, which requires an end-inspiratory occlusion maneuver. This lung model study aimed to observe the effect of airflow obstruction on the accuracy of respiratory mechanical properties during pressure-controlled ventilation (PCV) by analyzing dynamic signals.MethodsA Hamilton C3 ventilator was attached to a lung simulator that mimics lung mechanics in healthy, acute respiratory distress syndrome (ARDS) and chronic obstructive pulmonary disease (COPD) models. PCV and volume-controlled ventilation (VCV) were applied with tidal volume (VT) values of 5.0, 7.0, and 10.0 ml/kg. Performance characteristics and respiratory mechanics were assessed and were calibrated by virtual extrapolation using expiratory time constant (RCexp).ResultsDuring PCV ventilation, drive pressure (DP) was significantly increased in the ARDS model. Peak inspiratory flow (PIF) and peak expiratory flow (PEF) gradually declined with increasing severity of airflow obstruction, while DP, end-inspiration flow (EIF), and inspiratory cycling ratio (EIF/PIF%) increased. Similar estimated values of Crs and airway resistance (Raw) during PCV and VCV ventilation were obtained in healthy adult and mild obstructive models, and the calculated errors did not exceed 5%. An underestimation of Crs and an overestimation of Raw were observed in the severe obstruction model.ConclusionUsing the modified dynamic signal analysis approach, respiratory system properties (Crs and Raw) could be accurately estimated in patients with non-severe airflow obstruction in the PCV mode.

Dynamic inflation prevents and standardized lung recruitment reverts volume loss associated with percutaneous tracheostomy during volume control ventilation: results from a Neuro-ICU population.

To determine how percutaneous tracheostomy (PT) impacts on respiratory system compliance (Crs) and end-expiratory lung volume (EELV)during volume control ventilation and to test whether a recruitment maneuver (RM) at the end of PT may reverse lung derecruitment. This is a single center, prospective, applied physiology study. 25 patients with acute brain injury who underwent PT were studied. Patients were ventilated in volume control ventilation. Electrical impedance tomography (EIT) monitoring and respiratory mechanics measurements were performed in three steps: (a) baseline, (b) after PT, and (c) after a standardized RM (10 sighs of 30 cmH2O lasting 3s each within 1min). End-expiratory lung impedance (EELI) was used as a surrogate of EELV. PT determined a significant EELI loss (mean reduction of 432 arbitrary units p = 0.049) leading to a reduction in Crs (55 ± 13 vs. 62 ± 13 mL/cmH2O; p < 0.001) as compared to baseline. RM was able to revert EELI loss and restore Crs (68 ± 15 vs. 55 ± 13 mL/cmH2O; p < 0.001). In a subgroup of patients (N = 8, 31%), we observed a gradual but progressive increase in EELI. In this subgroup, patients did not experience a decrease of Crs after PT as compared to patients without dynamic inflation. Dynamic inflation did not cause hemodynamic impairment nor raising of intracranial pressure. We propose a novel and explorative hyperinflation risk index (HRI) formula. Volume control ventilation did not prevent the PT-induced lung derecruitment. RM could restore the baseline lung volume and mechanics. Dynamic inflation is common during PT, it can be monitored real-time by EIT and anticipated by HRI. The presence of dynamic inflation during PT may prevent lung derecruitment.

Tidal volume selection in volume-controlled ventilation guided by driving pressure versus actual body weight in healthy anesthetized and mechanically ventilated dogs: A randomized crossover trial

ObjectiveTo compare static compliance of the respiratory system (CstRS) and the ratio of partial pressure of end-tidal to arterial carbon dioxide (Pe′CO2/PaCO2), in healthy dogs using two approaches for tidal volume (VT) selection during volume-controlled ventilation: body mass based and driving pressure (ΔPaw) guided. Study designRandomized, nonblinded, crossover, clinical trial. AnimalsA total of 19 client-owned dogs anesthetized for castration and ovariohysterectomy. MethodsAfter a stable 10 minute baseline, each dog was mechanically ventilated with a VT selection strategy, randomized to a constant VT of 15 mL kg–1 of actual body mass (VTBW) or ΔPaw-guided VT (VTΔP) of 7–8 cmH2O. Both strategies used an inspiratory time of 1 second, 20% end-inspiratory pause, 4 cmH2O positive end-expiratory pressure and fraction of inspired oxygen of 0.4. Respiratory frequency was adjusted to maintain Pe′CO2 between 35 and 40 mmHg. Respiratory mechanics, arterial blood gases and Pe′CO2/PaCO2 were assessed. Continuous variables are presented as mean ± SD or median (interquartile range; quartiles 1–3), depending on distribution, and compared with Wilcoxon signed-rank tests. ResultsThe VT was significantly higher in dogs ventilated with VTΔP than with VTBW strategy (17.20 ± 4.04 versus 15.03 ± 0.60 mL kg–1, p = 0.036). CstRS was significantly higher with VTΔP than with VTBW strategy [2.47 (1.86–2.86) versus 2.25 (1.79–2.58) mL cmH2O−1 kg–1, p = 0.011]. There were no differences in Pe′CO2/PaCO2 between VTΔP and VTBW strategies (0.94 ± 0.06 versus 0.92 ± 0.06, p = 0.094). No discernible difference in ΔPaw was noted between the strategies. Conclusions and clinical relevanceWhile no apparent difference was observed in the Pe′CO2/PaCO2 between the VT selection strategies employed, CstRS significantly increased during the VTΔP approach. A future trial should explore if VTΔP improves perioperative gas exchange and prevents lung damage.

Adjustment of positive end-expiratory pressure to body mass index during mechanical ventilation in general anesthesia: BodyVent, a randomized controlled trial

BackgroundIn patients requiring general anesthesia, lung-protective ventilation can prevent postoperative pulmonary complications, which are associated with higher morbidity, mortality, and prolonged hospital stay. Application of positive end-expiratory pressure (PEEP) is one component of lung-protective ventilation. The correct strategy for setting adequate PEEP, however, remains controversial. PEEP settings that lead to a lower pressure difference between end-inspiratory plateau pressure and end-expiratory pressure (“driving pressure,” ΔP) may reduce the risk of postoperative pulmonary complications. Preliminary data suggests that the PEEP required to prevent both end-inspiratory overdistension and end-expiratory alveolar collapse, thereby reducing ΔP, correlates positively with the body mass index (BMI) of patients, with PEEP values corresponding to approximately 1/3 of patient’s respective BMI. Thus, we hypothesize that adjusting PEEP according to patient BMI reduces ΔP and may result in less postoperative pulmonary complications.MethodsPatients undergoing general anesthesia and endotracheal intubation with volume-controlled ventilation with a tidal volume of 7 ml per kg predicted body weight will be randomized and assigned to either an intervention group with PEEP adjusted according to BMI or a control group with a standardized PEEP of 5 mbar. Pre- and postoperatively, lung ultrasound will be performed to determine the lung aeration score, and hemodynamic and respiratory vital signs will be recorded for subsequent evaluation. The primary outcome is the difference in ΔP as a surrogate parameter for lung-protective ventilation. Secondary outcomes include change in lung aeration score, intraoperative occurrence of hemodynamic and respiratory events, oxygen requirements and postoperative pulmonary complications.DiscussionThe study results will show whether an intraoperative ventilation strategy with PEEP adjustment based on BMI has the potential of reducing the risk for postoperative pulmonary complications as an easy-to-implement intervention that does not require lengthy ventilator maneuvers nor additional equipment.Trial registrationGerman Clinical Trials Register (DRKS), DRKS00031336. Registered 21st February 2023.Trial statusThe study protocol was approved by the ethics committee of the Christian-Albrechts-Universität Kiel, Germany, on 1st February 2023. Recruitment began in March 2023 and is expected to end in September 2023.

Comparative effects of variable versus conventional volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in thoracic surgery patients: A randomized controlled clinical trial

BackgroundMechanical ventilation with variable tidal volumes (V-VCV) has the potential to improve lung function during general anesthesia. We tested the hypothesis that V-VCV compared to conventional volume-controlled ventilation (C-VCV) would improve intraoperative arterial oxygenation and respiratory system mechanics in patients undergoing thoracic surgery under one-lung ventilation (OLV). MethodsPatients were randomized to V-VCV (n = 39) or C-VCV (n = 39). During OLV tidal volume of 5 mL/kg predicted body weight (PBW) was used. Both groups were ventilated with a positive end-expiratory pressure (PEEP) of 5 cm H2O, inspiration to expiration ratio (I:E) of 1:1 (during OLV) and 1:2 during two-lung ventilation, the respiratory rate (RR) titrated to arterial pH, inspiratory peak-pressure ≤ 40 cm H2O and an inspiratory oxygen fraction of 1.0. ResultsSeventy-five out of 78 Patients completed the trial and were analyzed (dropouts were excluded). The partial pressure of arterial oxygen (PaO2) 20 min after the start of OLV did not differ among groups (V-VCV: 25.8 ± 14.6 kPa vs C-VCV: 27.2 ± 15.3 kPa; mean difference [95% CI]: 1.3 [−8.2, 5.5], P = 0.700). Furthermore, intraoperative gas exchange, intraoperative adverse events, need for rescue maneuvers due to desaturation and hypercapnia, incidence of postoperative pulmonary and extra-pulmonary complications, and hospital free days at day 30 after surgery did not differ between groups. ConclusionsIn thoracic surgery patients under OLV, V-VCV did not improve oxygenation or respiratory system mechanics compared to C-VCV.Ethical Committee: EK 420092019.Trial registration: at the German Clinical Trials Register: DRKS00022202 (16.06.2020).

The effect of oral pregabalin on the minimum alveolar concentration of isoflurane in cats

ObjectiveTo investigate the effect of three different doses of oral pregabalin on minimum alveolar concentration of isoflurane (MACISO) in cats. Study designProspective, randomized, placebo-controlled, blinded, crossover trial. AnimalsA group of eight healthy adult cats aged 24–48 months. MethodsCats were randomly assigned to three oral doses of pregabalin (low dose: 2.5 mg kg–1, medium dose: 5 mg kg–1, high dose: 10 mg kg–1) or placebo 2 hours before MACISO determination, with the multiple treatments administered with a minimum 7 day washout period. Anesthesia was induced and maintained with isoflurane in oxygen until endotracheal intubation was achieved, and maintained with isoflurane with volume-controlled ventilation. MACISO was determined in triplicate using the bracketing technique and tail clamp method 120 minutes after pregabalin or placebo administration. Physiologic variables (including heart rate and blood pressure) recorded during MACISO determination were averaged and compared between the pregabalin and placebo treatments. One-way analysis of variance and the Friedman test were used to assess the difference for normally and non-normally distributed data, respectively. The Tukey test was used as a post hoc analysis. Values of p < 0.05 were considered significant. ResultsThe MACISO with the medium- and high-dose pregabalin treatments were 1.33 ± 0.21% and 1.23 ± 0.17%, respectively. These were significantly lower than MACISO after placebo treatment (1.62 ± 0.13%; p = 0.014, p < 0.001, respectively), representing a decrease of 18 ± 9% and 24 ± 6%. The mean plasma pregabalin concentration was negatively correlated with MACISO values. Physiologic variables did not differ significantly between treatments. Conclusions and clinical relevanceDoses of 5 or 10 mg kg–1 pregabalin, administered orally 2 hours before determining MACISO, had a significant isoflurane-sparing effect in cats.

Effect of Ventilator Settings on Mechanical Power During Simulated Mechanical Ventilation of Patients With ARDS.

In recent years, mechanical power (MP) has emerged as an important concept that can significantly impact outcomes from mechanical ventilation. Several individual components of ventilatory support such as tidal volume (VT), breathing frequency, and PEEP have been shown to contribute to the extent of MP delivered from a mechanical ventilator to patients in respiratory distress/failure. The aim of this study was to identify which common individual setting of mechanical ventilation is more efficient in maintaining safe and protective levels of MP using different modes of ventilation in simulated subjects with ARDS. We used an interactive mathematical model of ventilator output during volume control ventilation (VCV) with either constant inspiratory flow (VCV-CF) or descending ramp inspiratory flow, as well as pressure control ventilation (PCV). MP values were determined for simulated subjects with mild, moderate, and severe ARDS; and whenever MP > 17 J/min, VT, breathing frequency, or PEEP was manipulated independently to bring back MP to ≤ 17 J/min. Finally, the optimum VT-breathing frequency combinations for MP = 17 J/min were determined with all 3 modes of ventilation. VCV-CF always resulted in the lowest MPs while PCV resulted in highest MPs. Reductions in VT were the most efficient for maintaining safer and protective MP. At targeted MPs of 17 J/min and maximized minute ventilation, the optimum VT-breathing frequency combinations were 250-350 mL for VT and 32-35 breaths/min for breathing frequency in mild ARDS, 200-350 mL for VT and 34-40 breaths/min for breathing frequency in moderate ARDS, and 200-300 mL for VT and 37-45 breaths/min for breathing frequency for severe ARDS. VCV-CF resulted in the lowest MP. VT was the most efficient for maintaining safe and protective MP in a mathematical simulation of subjects with ARDS. In the context of maintaining low and safe MPs, ventilatory strategies with lower-than-normal VT and higher-than-normal breathing frequency will need to be implemented in patients with ARDS.

Comparison of volume-controlled ventilation, pressure-controlled ventilation and pressure-controlled ventilation-volume guaranteed in infants and young children in the prone position: A prospective randomized study

Study objectiveTo explore if the pressure-controlled ventilation (PCV) and pressure-controlled ventilation-volume guaranteed (PCV-VG) modes are superior to volume-controlled ventilation (VCV) in optimizing intraoperative respiratory mechanics in infants and young children in the prone position. DesignA single-center prospective randomized study. SettingChildren's Hospital, Zhejiang University School of Medicine. PatientsPediatric patients aged 1 month to 3 years undergoing elective spinal cord detethering surgery. InterventionsPatients were randomly allocated to the VCV group, PCV group and PCV-VG group. The target tidal volume (VT) was 8 mL/kg and the respiratory rate (RR) was adjusted to maintain a constant end tidal CO2. MeasurementsThe primary outcome was intraoperative peak airway pressure (Ppeak). Secondary outcomes included other respiratory and ventilation variables, gas exchange values, serum lung injury biomarkers concentration, hemodynamic parameters and postoperative respiratory complications. Main resultsA total of 120 patients were included in the final analysis (40 in each group). The VCV group showed higher Ppeak at T2 (10 min after prone positioning) and T3 (30 min after prone positioning) than the PCV and PCV-VG groups (T2: P = 0.015 and P = 0.002, respectively; T3: P = 0.007 and P = 0.009, respectively). The prone-related decrease in dynamic compliance was prevented by PCV and PCV-VG ventilation modalities at T2 and T3 than by VCV (T2: P = 0.008 and P = 0.015, respectively; T3: P = 0.015 and P = 0.014, respectively). Additionally, there were no significant differences in other secondary outcomes among the three groups. ConclusionIn infants and young children undergoing spinal cord detethering surgery in the prone position, PCV-VG may be a better ventilation mode due to its ability to mitigate the increase in Ppeak and decrease in Cdyn while maintaining consistent VT.

Comparison of volume-controlled ventilation and pressure-limited ventilation in laparoscopic appendicectomy - a randomized controlled clinical trial

Background: Laparoscopic appendicectomy is a widely performed surgery globally, offering notable benefits such as reduced postoperative pain, quicker mobility, and shorter hospital stays. Aims and Objectives: The study aimed to assess the changes in respiratory mechanics and compare the outcomes of volume-controlled and pressure-limited ventilation (PLV) in patients undergoing laparoscopic appendectomy. Materials and Methods: This randomized, prospective, single-blinded control study was conducted at K.A.P.V. Government Medical College, Tiruchirapalli, on 60 ASA I and II patients scheduled to undergo laparoscopic appendicectomy under general anesthesia. The patients were randomly divided into two groups (volume-controlled ventilation [VCV] group and the PLV group) of 30 patients. A patient’s history includes age, sex, history of diabetes, hypertension, or any cardiovascular disease, respiratory tract infection, wheezing or chronic chest infections, seizures, neuromuscular disease or weakness, etc. Results: There was no significant difference in gender, age, or body mass index between groups. There is no significant difference in the mean arterial pressure or ETCO2 between groups at various intervals. There was a significant difference in the mean heart rate between the VCV and the PLV groups at 5 and 20 min after induction. There was a significant difference in the peak airway pressure, dynamic compliance, and airway resistance between the VCV group and the PLV group at 10 min after induction (T1), 5 min after pneumoperitoneum (T2), 10 min after pneumoperitoneum (T3), and immediately after Trendelenburg position (T4). Conclusion: The airway resistance and peak airway pressure do not increase, and the dynamic compliance was improved in the PLV during laparoscopic appendicectomy.

Effect of increased resistance on dynamic compliance assessed by two clinical monitors during volume-controlled ventilation: A test-lung study

ObjectiveTo evaluate the effect of increased respiratory system resistance (RRS) on dynamic compliance (Cdyn) assessed by the NM3 monitor (Cdyn(NM3)) and the E-CAiOV module (Cdyn(ECAiOV)). Study designProspective laboratory study. MethodsA training test lung (TTL) simulated the mechanical ventilation of a mammal with 50 and 300 mL tidal volumes in three conditions of RRS [normal (RBL), moderately increased (R1) and severely increased (R2)] and a wide range of clinically relevant Cdyn. Simulations at increased RRS were paired with simulations at RBL with the same static compliance for comparisons. Pearson’s correlation coefficient and concordance correlation coefficient between the measurements at RBL with the ones with increased RRS were calculated. Bland–Altman plots were also used to evaluate the agreement of Cdyn(ECAiOV) and Cdyn(NM3) at RBL (control values) with their paired values at R1 and R2. Relative bias and limits of agreement (LOAs) were calculated and LOAs larger than 30% were considered unacceptable. Trending ability of Cdyn(NM3) and Cdyn(ECAiOV) were evaluated by polar plots. Values of p < 0.05 were considered significant. ResultsThe effect of increased RRS was more pronounced for Cdyn(ECAiOV) than for Cdyn(NM3). Unacceptable agreement was only observed in Cdyn(NM3) at R2 in the 300 mL simulation (bias = –18.3% and lower LOA = –45%). For Cdyn(ECAiOV), agreement was unacceptable for all tested RRS in both simulations, being the worst at R2 in the 300 mL simulation (bias = –54.7% and lower LOA = –100.2%). Both levels of increased RRS caused poor trending ability for Cdyn(ECAiOV), whereas the same effect was only observed for Cdyn(NM3) at R2. Conclusions and clinical relevanceIn the presence of increased RRS, Cdyn estimated by the NM3 monitor presented better capability to distinguish between changes in RRS from changes in respiratory system compliance.

Comprehensive study of mechanical power in controlled mechanical ventilation: Prevalence of elevated mechanical power and component analysis

ObjectiveTo determine the prevalence of elevated mechanical power (MP) values (>17J/min) used in routine clinical practice. DesignObservational, descriptive, cross-sectional, analytical, multicenter, international study conducted on November 21, 2019, from 8:00 AM to 3:00 PM. NCT03936231. SettingOne hundred thirty-three Critical Care Units. PatientsPatients receiving invasive mechanical ventilation for any cause. InterventionsNone. Main variables of interestMechanical power. ResultsA population of 372 patients was analyzed. PM was significantly higher in patients under pressure-controlled ventilation (PC) compared to volume-controlled ventilation (VC) (19.20±8.44J/min vs. 16.01±6.88J/min; p<0.001), but the percentage of patients with PM>17J/min was not different (41% vs. 35%, respectively; p=0.382). The best models according to AICcw expressing PM for patients in VC are described as follows: Surrogate Strain (Driving Pressure) + PEEP+Surrogate Strain Rate (PEEP/Flow Ratio) + Respiratory Rate. For patients in PC, it is defined as: Surrogate Strain (Expiratory Tidal Volume/PEEP) + PEEP+Surrogate Strain Rate (Surrogate Strain/Ti) + Respiratory Rate+Expiratory Tidal Volume+Ti. ConclusionsA substantial proportion of mechanically ventilated patients may be at risk of experiencing elevated levels of mechanical power. Despite observed differences in mechanical power values between VC and PC ventilation, they did not result in a significant disparity in the prevalence of high mechanical power values.

Effects of pressure-controlled ventilation targeting end-inspiratory flow rate on pulmonary complications and inflammation levels in patients undergoing spinal surgery in the prone position: a randomized clinical trial

BackgroundThis study assessed the impact of pressure-controlled ventilation (PCV) focusing on end-inspiratory flow rate on the incidence of postoperative pulmonary complications (PPCs) and inflammation levels in patients undergoing spinal surgery in the prone position.MethodsA total of 187 patients who underwent posterior spinal surgery were enrolled and randomly divided into 3 groups: 61 in the volume-controlled ventilation (VCV) group (group V), 62 in the PCV-volume-guaranteed (VG) group (group P1), and 64 in the PCV-VG end-expiratory zero flow rate group (group P2). Indicators including tidal volume (VT), peak airway pressure (Ppeak), and dynamic lung compliance (Cdyn) were recorded. The Ppeak, Cdyn, PETCO2, and oxygenation index (PaO2/FiO2) after intubation (T0), after prone position (T1), 60 min after prone position (T2), and after supine position at the end of surgery (T3) of the three groups were collected.ResultsIn the within-group comparison, compared with T0, Ppeak increased at T1 − 2 in groups V and P1 (P < 0.01), whereas it decreased at T1 − 3 in group P2 (P < 0.01). Cdyn decreased at T1 − 2 and PaO2/FiO2 increased at T1 − 3 in all three groups (P < 0.01), and PaO2/FiO2 increased at T1 − 3 (P < 0.01). Compared with group V, Ppeak decreased at T0 − 3 in group P1 (P < 0.01) and at T1 − 3 in group P2 (P < 0.01), while Cdyn increased at T0 − 3 in groups P1 and P2 (P < 0.01). Compared with group P1, Ppeak was elevated at T0 (P < 0.01) and decreased at T1 − 3 (P < 0.05), and Cdyn was elevated at T0 − 3 in group P2 (P < 0.01). The total incidence of PPCs in group P2 was lower than that in group V (P < 0.01). Compared with the preoperative period, serum interleukin 6 (IL-6) and C-reactive protein (CRP) levels were increased at 24 and 72 h after surgery in group V (P < 0.01), whereas that was increased at 24 h after surgery in group P1 and group P2 (P < 0.01). Compared with group V, serum IL-6 and CRP levels were reduced at 24 h after surgery in groups P1 and P2 (P < 0.01 or < 0.05).ConclusionIn patients undergoing spinal surgery in the prone position, PCV-VG targeting an end-inspiratory zero flow rate lowers the incidence of PPCs and inflammation levels.

Association between mechanical power and intensive care unit mortality in Korean patients under pressure-controlled ventilation.

Mechanical power (MP) has been reported to be associated with clinical outcomes. Because the original MP equation is derived from paralyzed patients under volume-controlled ventilation, its application in practice could be limited in patients receiving pressure-controlled ventilation (PCV). Recently, a simplified equation for patients under PCV was developed. We investigated the association between MP and intensive care unit (ICU) mortality. We conducted a retrospective analysis of Korean data from the Fourth International Study of Mechanical Ventilation. We extracted data of patients under PCV on day 1 and calculated MP using the following simplified equation: MPPCV = 0.098 ∙ respiratory rate ∙ tidal volume ∙ (ΔPinsp + positive end-expiratory pressure), where ΔPinsp is the change in airway pressure during inspiration. Patients were divided into survivors and non-survivors and then compared. Multivariable logistic regression was performed to determine association between MPPCV and ICU mortality. The interaction of MPPCV and use of neuromuscular blocking agent (NMBA) was also analyzed. A total of 125 patients was eligible for final analysis, of whom 38 died in the ICU. MPPCV was higher in non-survivors (17.6 vs. 26.3 J/min, P<0.001). In logistic regression analysis, only MPPCV was significantly associated with ICU mortality (odds ratio, 1.090; 95% confidence interval, 1.029-1.155; P=0.003). There was no significant effect of the interaction between MPPCV and use of NMBA on ICU mortality (P=0.579). MPPCV is associated with ICU mortality in patients mechanically ventilated with PCV mode, regardless of NMBA use.

Comparative study of ventilation techniques with supraglottic airway devices in cats: volume-controlled vs pressure-controlled techniques.

This study compared the effectiveness of a new supraglottic airway device (SGAD) in cats undergoing anaesthesia using two types of mechanical ventilation: volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV). A total of 13 healthy cats (five male, eight female; median age 2 years [range 1-3]) were randomly allocated to either VCV or PCV. Five tidal volumes (6, 8, 10, 12 and 14 ml/kg) and five peak inspiratory pressures (4, 5, 6, 7 and 8 cmH2O) were randomly applied with a minute ventilation of 100 ml/kg/min. Various parameters, such as blood pressure, gas leakage, end-tidal CO2 (ETCO2) and work of breathing (WOB), were measured while using VCV or PCV. The occurrence of hypotension (mean arterial blood pressure <60 mmHg) was slightly less frequent with VCV (38 events, 65 ventilating sessions) than with PCV (40 events, 65 ventilating sessions), but this difference did not reach statistical significance (P = 0.429). The number of leakages did not differ between the VCV group (3 events, 65 ventilating sessions) and the PCV group (3 events, 65 ventilating sessions) (P = 1.000). Hypercapnia was identified when using VCV (10 events, 65 ventilating sessions) less frequently than when using PCV (17 events, 65 ventilating sessions), but this difference did not reach statistical significance (P = 0.194). The study found a significantly higher WOB in the PCV group compared with the VCV group (P <0.034). The present results suggested that both VCV and PCV can be used with an SGAD during anaesthesia, with VCV preferred for prolonged mechanical ventilation due to its lower workload. Adjusting tidal volume or inspiratory pressure corrects hypercapnia.

Pressure-controlled versus Volumecontrolled Ventilation during One Lung Ventilation for Empyema Thoracis: A Randomised Control Trial

Pressure-controlled versus Volumecontrolled Ventilation during One Lung Ventilation for Empyema Thoracis: A Randomised Control Trial

The effect of inspiratory rise time on mechanical power calculations in pressure control ventilation: dynamic approach

BackgroundMechanical power may serve as a valuable parameter for predicting ventilation-induced injury in mechanically ventilated patients. Over time, several equations have been developed to calculate power in both volume control ventilation (VCV) and pressure control ventilation (PCV). Among these equations, the linear model mechanical power equation (MPLM) closely approximates the reference method when applied in PCV. The dynamic mechanical power equation (MPdyn) computes power by utilizing the ventilatory work of breathing parameter (WOBv), which is automatically measured by the mechanical ventilator. In our study, conducted in patients with Covid-19 Acute Respiratory Distress Syndrome (C-ARDS), we calculated mechanical power using both the MPLM and MPdyn equations, employing different inspiratory rise times (Tslope) at intervals of 5%, ranging from 5 to 20% and compared the obtained results.ResultsIn our analysis, we used univariate linear regression at both I:E ratios of 1:2 and 1:1, considering all Tslope values. These analyses revealed that the MPdyn and MPLM equations exhibited strong correlations, with R2 values exceeding 0.96. Furthermore, our Bland–Altman analysis, which compared the power values derived from the MPdyn and MPLM equations for patient averages and all measurements, revealed a mean difference of −0.42 ± 0.41 J/min (equivalent to 2.6% ± 2.3%, p < 0.0001) and −0.39 ± 0.57 J/min (equivalent to 3.6% ± 3.5%, p < 0.0001), respectively. While there was a statistically significant difference between the equations in both absolute value and relative proportion, this difference was not considered clinically relevant. Additionally, we observed that each 5% increase in Tslope time corresponded to a decrease in mechanical power values by approximately 1 J/min.ConclusionsThe differences between mechanical power values calculated using the MPdyn and MPLM equations at various Tslope durations were determined to lack clinical significance. Consequently, for practical and continuous mechanical power estimation in Pressure-Controlled Ventilation (PCV) mode, the MPdyn equation presents itself as a viable option. It is important to note that as Tslope times increased, the calculated mechanical power exhibited a clinically relevant decrease.

Pulmonary response prediction through personalized basis functions in a virtual patient model

Background and ObjectiveRecruitment maneuvers with subsequent positive-end-expiratory-pressure (PEEP) have proven effective in recruiting lung volume and preventing alveoli collapse. However, determining a safe, effective, and patient-specific PEEP is not standardized, and this more optimal PEEP level evolves with patient condition, requiring personalised monitoring and care approaches to maintain optimal ventilation settings. MethodsThis research examines 3 physiologically relevant basis function sets (exponential, parabolic, cumulative) to enable better prediction of elastance evolution for a virtual patient or digital twin model of MV lung mechanics, including novel elements to model and predict distension elastance. Prediction accuracy and robustness are validated against recruitment maneuver data from 18 volume-controlled ventilation (VCV) patients at 7 different baseline PEEP levels (0 to 12 cmH2O) and 14 pressure-controlled ventilation (PCV) patients at 4 different baseline PEEP levels (6 to 12 cmH2O), yielding 623 and 294 prediction cases, respectively. Predictions were made up to 12 cmH2O of added PEEP ahead, covering 6 × 2 cmH2O PEEP steps. ResultsThe 3 basis function sets yield median absolute peak inspiratory pressure (PIP) prediction error of 1.63 cmH2O for VCV patients, and median peak inspiratory volume (PIV) prediction error of 0.028 L for PCV patients. The exponential basis function set yields a better trade-off of overall performance across VCV and PCV prediction than parabolic and cumulative basis function sets from other studies. Comparing predicted and clinically measured distension prediction in VCV demonstrated consistent, robust high accuracy with R2 = 0.90–0.95. ConclusionsThe results demonstrate recruitment mechanics are best captured by an exponential basis function across different mechanical ventilation modes, matching physiological expectations, and accurately capture, for the first time, distension mechanics to within 5–10 % accuracy. Enabling the risk of lung injury to be predicted before changing ventilator settings. The overall outcomes significantly extend and more fully validate this digital twin or virtual mechanical ventilation patient model.

Optimization of lung ventilation and perfusion in anesthetized horses using a ventilation mode with flow-limited expiration.

To investigate the mechanisms underlying the improved arterial oxygenation described with flow-limited expiration (FLEX) ventilation in anesthetized horses. 5 healthy adult research horses. Horses underwent volume-controlled ventilation for 60 minutes (VCV1), followed by 60 minutes of FLEX, and 30 minutes of VCV (VCV2). Main outcomes included the arterial partial pressure of oxygen-to-Fio2 (PF) ratio and electrical impedance tomography (EIT)-derived functional indices at the end of each phase. The EIT data were used to create regional maps of relative lung ventilation and perfusion as well as regional maps of ventilation/perfusion (V/Q) ratios. Ventilation indices derived from EIT included the fraction of expired volume in 1 second (FEV1; %) and the time it took for the EIT signal to drop to 50% of the peak signal at end-inspiration (TClose50; seconds). Data were analyzed with 2-way ANOVA for repeated measures. P < .05 was considered significant. The PF ratio increased significantly with FLEX compared to both VCV1 and VCV2 (P < .01). There were no differences in the relative distribution of ventilation nor perfusion between ventilation strategies. However, when ventilation and perfusion were superimposed and V/Q ratio maps were constructed, FLEX had a homogenizing effect toward values of 1.0. The FEV1 was shorter (P < .01) and the TClose50 was longer (P < .001) in all regions during FLEX compared to both VCV1 and VCV2. Our findings suggest that FLEX ventilation in anesthetized horses enhances regional V/Q matching, likely by prolonging expiratory aeration and reducing airway closure.

Postoperative pulmonary complications with high versus standard FiO2 in adult patients undergoing major abdominal surgery: A noninferiority trial

BackgroundDespite the possible clinical benefit of high intraoperative oxygen therapy on surgical site infection, the effect on postoperative respiratory function is debatable. However, it remains yet to be elucidated whether hyperoxia due to a high fraction of inspired oxygen used in conjunction with lung protective ventilation can lead to increased incidence of postoperative pulmonary complications. MethodsIn this noninferiority randomized trial, an intraoperative high fraction of inspired oxygen of 0.8 (group H) was compared to a standard fraction of inspired oxygen of 0.3 to 0.4 (group S) in adult patients undergoing major elective or emergency surgery. A lung protective ventilation strategy was employed in all patients, including volume control ventilation with a tidal volume of 6 to 8 mL/kg of predicted body weight, respiratory rate of 12 beats per minute, and positive end-expiratory pressure of 5 to 8 cm H2O. Postoperative pulmonary complications were assessed on postoperative days 3 and 5 by the Melbourne group scale. ResultsIn this trial, n = 226 patients were randomized; among them, 130 patients underwent routine surgery, and 96 patients underwent emergency surgery. The median (interquartile range) of the patients was 48 (35–58) years, and 47.3% were female. Melbourne group scale scores at postoperative day 3 (median [interquartile range] 2 [1–4] in group S vs 2 [1–3] in group H; the difference in median [95% confidence interval] 0 [0, –1]; P = .13) and day 5 (median [interquartile range] 1 (0–3) in group S vs 1 [0–3] in group H; the difference in median [95% confidence interval] 0 [0, 0.5]; P = .34) were statistically similar in both the groups and the upper margin was within the predefined margin of 1. Incidence of surgical site infection (P = .46), postoperative hospital stay (P = .29), and days alive without antibiotic therapy at postoperative day 28 (P = .95) were similar in both groups. ConclusionHigh intraoperative fiO2 was noninferior to standard fiO2 in postoperative pulmonary complications in adult patients undergoing major surgery.

Pressure-controlled ventilation-volume guaranteed mode improves bronchial mucus transport velocity in patients during laparoscopic surgery for gynecological oncology: a randomized controlled study

BackgroundMechanical ventilation during general anesthesia may impair airway mucosal function. This study aimed to investigate the effect of pressure-controlled ventilation-volume guaranteed (PCV-VG) on bronchial mucus transport velocity (BTV) in patients during laparoscopic surgery for gynecological oncology compared with volume controlled ventilation (VCV).Methods66 patients undergoing elective a laparoscopic surgery for gynecological oncology. The patients were randomized into two group receiving either PCV-VG or VCV. a drop of methylene blue was placed on the surface of the airway mucosa under the bronchoscopeand, then the distance the dye movement was measured after 2, 4, and 6 min. Outcomes were assessed at T0 (5 min after endotracheal intubation and before initiation of pneumoperitoneum), T1 and T2 (1 and 2 h after stabilization of pneumoperitoneum respectively). BTV at T0, T1 and T2 was the primary outcome. Secondary outcomes included heart rate (HR), mean arterial pressure (MAP), body temperature, end-tidal CO2 pressure (PETCO2), tidal volume(VT), peak inspiratory pressure (PIP), mean inspiratory pressure (Pmean), respiratory rate (RR), and dynamic compliance (CDyn) at T0, T1, and T2.Results64 patients were included in the analysis. The median [interquartile range] BTV was significantly lower in VCV group at T1 and T2 that at T0 (P < 0.05). Furthermore, BTV was slightly reduced in PCV-VG compared with VCV. BTV in PCV-VG was significantly decreased at T2 compared with BTV at T0 (P < 0.05) and slightly decreased at T1 compared with T0(P > 0.05). Compared with the PCV-VG group, BTV in VCV group significantly decreased at T2 (P < 0.05). No participants experienced respiratory complications.ConclusionsPCV-VG is more suitable for patients undergoing laparoscopic surgery for gynecological oncology than VCV since it can protect mucociliary clearance function.Trial registrationThis trial is registered on https://www.chictr.org.cn/ in Chinese Clinical Trial Registry (ChiCTR.2200064564: Date of registration 11/10/2022).