Flow-controlled expiration ventilation using a piston ventilator: effects of expiration time and speed on respiratory and pulmonary mechanics with focus on hysteresis and compliance in healthy horses.

OBJECTIVE: To investigate the effects of FLow-controlled EXpiration (FLEX) ventilation expiration time and speed on respiratory and pulmonary mechanics in anesthetized horses in dorsal recumbency. ANIMALS: 6 healthy adult research horses. METHODS: In this randomized crossover experimental study, horses were anesthetized 3 times and were ventilated each time for 60 minutes using conventional volume-controlled ventilation (VCV), linear emptying of the lung over 50% of the expiratory time (FLEX50), or linear emptying of the lung over 100% of the expiratory time (FLEX100) in a randomized order. The primary outcome variables were dynamic compliance (Cdyn), hysteresis, and alveolar dead space. The data was analyzed using two-factor ANOVA. Significance was set to P < .05. RESULTS: Horses ventilated using FLEX50 and FLEX100 showed significantly higher Cdyn and significantly lower hysteresis values compared to horses ventilated using VCV. Horses ventilated using FLEX50 had significantly lower alveolar dead space compared to horses ventilated using FLEX100 or VCV. Horses ventilated using FLEX100 had significantly lower alveolar dead space compared to VCV horses. CLINICAL RELEVANCE: Our results demonstrate improved Cdyn, hysteresis, and alveolar dead space in horses ventilated with either FLEX50 or FLEX100 relative to traditional VCV. The use of FLEX with a faster exhalation speed (FLEX50) offers additional respiratory advantages.

Assessment of Global and Regional Lung Compliance in Pulmonary Fibrosis With Hyperpolarized Gas MRI.

BACKGROUND: Lung compliance, a biomarker of pulmonary fibrosis, is generally measured globally. Hyperpolarized 129Xe gas MRI offers the potential to evaluate lung compliance regionally, allowing for visualization of changes in lung compliance associated with fibrosis. PURPOSE: To assess global and regional lung compliance in a rat model of pulmonary fibrosis using hyperpolarized 129Xe gas MRI. STUDY TYPE: Prospective. ANIMAL MODEL: Twenty Sprague-Dawley male rats with bleomycin-induced fibrosis model (N = 10) and saline-treated controls (N = 10). FIELD STRENGTH/SEQUENCE: 7-T, fast low-angle shot (FLASH) sequence. ASSESSMENT: Lung compliance was determined by fitting lung volumes derived from segmented 129Xe MRI with an iterative selection method, to corresponding airway pressures. Similarly, lung compliance was obtained with computed tomography for cross-validation. Direction-dependencies of lung compliance were characterized by regional lung compliance ratios (R) in different directions. Pulmonary function tests (PFTs) and histological analysis were used to validate the pulmonary fibrosis model and assess its correlation with 129Xe lung compliance. STATISTICAL TESTS: Shapiro-Wilk tests, unpaired and paired t-tests, Mann-Whitney U and Wilcoxon signed-rank tests, and Pearson correlation coefficients. P < 0.05 was considered statistically significant. RESULTS: For the entire lung, the global and regional lung compliance measured with 129Xe gas MRI showed significant differences between the groups, and correlated with the global lung compliance measured using PFTs (global: r = 0.891; regional: r = 0.873). Additionally, for the control group, significant difference was found in mean regional compliance between areas, eg, 0.37 (0.32, 0.39) × 10-4 mL/cm H2O and 0.47 (0.41, 0.56) × 10-4 mL/cm H2O for apical and basal lung, respectively. The apical-basal direction R was 1.12 ± 0.09 and 1.35 ± 0.13 for fibrosis and control groups, respectively, indicating a significant difference. DATA CONCLUSION: Our findings demonstrate the feasibility of using hyperpolarized gas MRI to assess regional lung compliance. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 1.

Quantitative Computed Tomography and Response to Pronation in COVID-19 ARDS.

BACKGROUND: The use of prone position (PP) has been widespread during the COVID-19 pandemic. Whereas it has demonstrated benefits, including improved oxygenation and lung aeration, the factors influencing the response in terms of gas exchange to PP remain unclear. In particular, the association between baseline quantitative computed tomography (CT) scan results and gas exchange response to PP in invasively ventilated subjects with COVID-19 ARDS is unknown. The present study aimed to compare baseline quantitative CT results between subjects responding to PP in terms of oxygenation or CO2 clearance and those who did not. METHODS: This was a single-center, retrospective observational study including critically ill, invasively ventilated subjects with COVID-19-related ARDS admitted to the ICUs of Niguarda Hospital between March 2020-November 2021. Blood gas samples were collected before and after PP. Subjects in whom the PaO2 /FIO2 increase was ≥ 20 mm Hg after PP were defined as oxygen responders. CO2 responders were defined when the ventilatory ratio (VR) decreased during PP. Automated quantitative CT analyses were performed to obtain tissue mass and density of the lungs. RESULTS: One hundred twenty-five subjects were enrolled, of which 116 (93%) were O2 responders and 51 (41%) CO2 responders. No difference in quantitative CT characteristics and oxygen were observed between responders and non-responders (tissue mass 1,532 ± 396 g vs 1,654 ± 304 g, P = .28; density -544 ± 109 HU vs -562 ± 58 HU P = .42). Similar findings were observed when dividing the population according to CO2 response (tissue mass 1,551 ± 412 g vs 1,534 ± 377 g, P = .89; density -545 ± 123 HU vs -546 ± 94 HU, P = .99). CONCLUSIONS: Most subjects with COVID-19-related ARDS improved their oxygenation at the first pronation cycle. The study suggests that baseline quantitative CT scan data were not associated with the response to PP in oxygenation or CO2 in mechanically ventilated subjects with COVID-19-related ARDS.

The Effect of Recruitment Maneuver on Static Lung Compliance in Patients Undergoing General Anesthesia for Laparoscopic Cholecystectomy: A Single-Centre Prospective Clinical Intervention Study.

Background and Objectives: The aim of this study was to examine whether the use of an alveolar recruitment maneuver (RM) leads to a significant increase in static lung compliance (Cstat) and an improvement in gas exchange in patients undergoing laparoscopic cholecystectomy. Material and Methods: A clinical prospective intervention study was conducted. Patients were divided into two groups according to their body mass index (BMI): normal-weight (group I) and pre-obese and obese grade I (group II). Lung mechanics were monitored (Cstat, dynamic compliance-Cdin, peak pressure-Ppeak, plateau pressure-Pplat, driving pressure-DP) alongside gas exchange, and hemodynamic changes (heart rate-HR, mean arterial pressure-MAP) at six time points: T1 (induction of anesthesia), T2 (formation of pneumoperitoneum), T3 (RM with a PEEP of 5 cm H2O), T4 (RM with a PEEP of 7 cm H2O), T5 (desufflation), and T6 (RM at the end). The RM was performed by increasing the peak pressure by +5 cm of H2O at an equal inspiration-to-expiration ratio (I/E = 1:1) and applying a PEEP of 5 and 7 cm of H2O. Results: Out of 96 patients, 33 belonged to group I and 63 to group II. An increase in Cstat values occurred after all three RMs. At each time point, the Cstat value was measured higher in group I than in group II. A higher increase in Cstat was observed in group II after the second and third RM. Cstat values were higher at the end of the surgical procedure compared to values after the induction of anesthesia. The RM led to a significant increase in PaO2 in both groups without changes in HR or MAP. Conclusions: During laparoscopic cholecystectomy, the application of RM leads to a significant increase in Cstat and an improvement in gas exchange. The prevention of atelectasis during anesthesia should be initiated immediately after the induction of anesthesia, using protective mechanical ventilation and RM.

Comparison of lung aeration loss in open abdominal oncologic surgeries after ventilation with electrical impedance tomography-guided PEEP versus conventional PEEP: a pilot feasibility study.

BACKGROUND: Existing literature lacks high-quality evidence regarding the ideal intraoperative positive end-expiratory pressure (PEEP) to minimize postoperative pulmonary complications (PPCs). We hypothesized that applying individualized PEEP derived from electrical impedance tomography would reduce the severity of postoperative lung aeration loss, deterioration in oxygenation, and PPC incidence. METHODS: A pilot feasibility study was conducted on 36 patients who underwent open abdominal oncologic surgery. The patients were randomized to receive individualized PEEP or conventional PEEP at 4 cmH2O. The primary outcome was the impact of individualized PEEP on changes in the modified lung ultrasound score (MLUS) derived from preoperative and postoperative lung ultrasonography. A higher MLUS indicated greater lung aeration loss. The secondary outcomes were the PaO2/FiO2 ratio and PPC incidence. RESULTS: A significant increase in the postoperative MLUS (12.0 ± 3.6 vs 7.9 ± 2.1, P < 0.001) and a significant difference between the postoperative and preoperative MLUS values (7.0 ± 3.3 vs 3.0 ± 1.6, P < 0.001) were found in the conventional PEEP group, indicating increased lung aeration loss. In the conventional PEEP group, the intraoperative PaO2/FiO2 ratios were significantly lower but not the postoperative ratios. The PPC incidence was not significantly different between the groups. Post-hoc analysis showed the increase in lung aeration loss and deterioration of intraoperative oxygenation correlated with the deviation from the individualized PEEP. CONCLUSIONS: Individualized PEEP appears to protect against lung aeration loss and intraoperative oxygenation deterioration. The advantage was greater in patients whose individualized PEEP deviated more from the conventional PEEP.

The effects of robot-assisted laparoscopic surgery with Trendelenburg position on short-term postoperative respiratory diaphragmatic function.

OBJECTIVE: To study how Pneumoperitoneum under Trendelenburg position for robot-assisted laparoscopic surgery impact the perioperative respiratory parameters, diagrammatic function, etc. METHODS: Patients undergoing robot-assisted laparoscopic surgery in the Trendelenburg position and patients undergoing general surgery in the supine position were selected. The subjects were divided into two groups according to the type of surgery: robot-assisted surgery group and general surgery group. ① Respiratory parameters such as lung compliance, oxygenation index, and airway pressure were recorded at 5 min after intubation, 1 and 2 h after pneumoperitoneum. ② Diaphragm excursion (DE) and diaphragm thickening fraction (DTF) were recorded before entering the operating room (T1), immediately after extubation (T2), 10 min after extubation (T3), and upon leaving the postanesthesia care unit (T4). ③ Peripheral venous blood (5 ml) was collected before surgery and 30 min after extubation and was analyzed by enzyme-linked immunosorbent assay to determine the serum concentration of Clara cell secretory protein 16 (CC16) and surfactant protein D (SP-D). RESULT: ① Compared with the general surgery group (N = 42), the robot-assisted surgery group (N = 46) presented a significantly higher airway pressure and lower lung compliance during the surgery(P < 0.001). ② In the robot-assisted surgery group, the DE significantly decreased after surgery (P < 0.001), which persisted until patients were discharged from the PACU (P < 0.001), whereas the DTF only showed a transient decrease postoperatively (P < 0.001) and returned to its preoperative levels at discharge (P = 0.115). In the general surgery group, the DE showed a transient decrease after surgery(P = 0.011) which recovered to the preoperative levels at discharge (P = 1). No significant difference in the DTF was observed among T1, T2, T3, and T4. ③ Both the general and robot-assisted surgery reduced the postoperative serum levels of SP-D (P < 0.05), while the robot-assisted surgery increased the postoperative levels of CC16 (P < 0.001). CONCLUSION: Robot-assisted laparoscopic surgery significantly impairs postoperative diaphragm function, which does not recover to preoperative levels at PACU discharge. Elevated levels of serum CC16 after surgery suggest potential lung injury. The adverse effects may be attributed to the prolonged Trendelenburg position and pneumoperitoneum during laparoscopic surgery.

A novel adaptive filter with a heart-rate-based reference signal for esophageal pressure signal denoising.

Esophageal pressure (Peso) is one of the most common and minimally invasive methods used to assess the respiratory and lung mechanics in patients receiving mechanical ventilation. However, the Peso measurement is contaminated by cardiogenic oscillations (CGOs), which cannot be easily eliminated in real-time. The field of study dealing with the elimination of CGO from Peso signals is still in the early stages of its development. In this study, we present an adaptive filtering-based method by constructing a reference signal based on the heart rate and sine function to remove CGOs in real-time. The proposed technique is tested using clinical data acquired from 20 patients admitted to the intensive care unit. Lung compliance ( QUOTE ) and esophageal pressure swings (△Pes) are used to evaluate the performance and efficiency of the proposed technique. The CGO can be efficiently suppressed when the constructional reference signal contains the fundamental, and second and third harmonic frequencies of the heart rate signal. The analysis of the data of 8 patients with controlled mechanical ventilation reveals that the standard deviation/mean of the QUOTE is reduced by 28.4-79.2% without changing the QUOTE and the △Pes measurement is more accurate, with the use of our proposed technique. The proposed technique can effectively eliminate the CGOs from the measured Peso signals in real-time without requiring additional equipment to collect the reference signal.

Cell death of alveolar lymphocytes and monocytes is negatively correlated with driving pressure and mechanical power in patients with acute respiratory distress syndrome.

BACKGROUND: Pathogenesis of acute respiratory distress syndrome (ARDS) involves immune cell death and removal from the injured lungs. ARDS severity is related to lung compliance. However, the correlation between the respiratory mechanics and alveolar immune cell death in patients with ARDS remains unclear. METHODS: Twenty-four patients with respiratory failure and ARDS were enrolled in the intensive care unit between November 2019 and November 2021. Neutrophil extracellular traps (NETs) and cell death of lymphocytes and monocytes in bronchoalveolar lavage fluid were detected on days 1 and 8. RESULTS: Lung compliance was positively correlated with the cell death percentage of alveolar CD4/CD8 lymphocytes and monocytes on day 8 (Pearson's correlation coefficient (r) = 0.554, p = 0.005; r = 0.422, p = 0.040; r = 0.569, p = 0.004, respectively). There was no association between lung compliance and the percentage of alveolar NETs on days 1 and 8. The cell death percentages of alveolar CD4/CD8 lymphocytes and monocytes were negatively correlated with driving pressure (DP) on days 1 (r = - 0.440, p = 0.032; r = - 0.613, p = 0.001; r = -0.557, p = 0.005, respectively) and 8 (r = - 0.459, p = 0.024; r = - 0.407, p = 0.048; r = - 0.607, p = 0.002, respectively). The cell death percentages of alveolar CD4/CD8 lymphocytes and monocytes were also negatively correlated with mechanical power (MP) on days 1 (r = - 0.558, p = 0.005; r = - 0.593, p = 0.002; r = - 0.571, p = 0.004, respectively) and 8 (r = - 0.539, p = 0.007; r = - 0.338, p = 0.107; r = - 0.649, p < 0.001, respectively). The percentage of alveolar NETs on days 1 and 8 was not associated with DP or MP. CONCLUSION: Patients with higher cell death rates of alveolar CD4/CD8 lymphocytes and monocytes exhibited lower DP and MP. Patients with less cell death of alveolar CD4/CD8 lymphocytes and monocytes required more DP or MP to maintain adequate ventilation.

Chest CT findings in severe acute respiratory distress syndrome requiring V-V ECMO: J-CARVE registry.

BACKGROUND: Chest computed tomography findings are helpful for understanding the pathophysiology of severe acute respiratory distress syndrome (ARDS). However, there is no large, multicenter, chest computed tomography registry for patients requiring veno-venous extracorporeal membrane oxygenation (V-V ECMO). The aim of this study was to describe chest computed tomography findings at V-V ECMO initiation and to evaluate the association between the findings and outcomes in severe ARDS. METHODS: This multicenter, retrospective cohort study enrolled patients with severe ARDS on V-V ECMO, who were admitted to the intensive care units of 24 hospitals in Japan between January 1, 2012, and December 31, 2022. RESULTS: The primary outcome was 90-day in-hospital mortality. The secondary outcomes were the successful liberation from V-V ECMO and the values of static lung compliance. Among the 697 registry patients, of the 582 patients who underwent chest computed tomography at V-V ECMO initiation, 394 survived and 188 died. Multivariate Cox regression showed that traction bronchiectasis and subcutaneous emphysema increased the risk of 90-day in-hospital mortality (hazard ratio [95% confidence interval] 1.77 [1.19-2.63], p = 0.005 and 1.97 [1.02-3.79], p = 0.044, respectively). The presence of traction bronchiectasis was also associated with decreased successful liberation from V-V ECMO (odds ratio: 0.27 [0.14-0.52], p < 0.001). Lower static lung compliance was associated with some chest computed tomography findings related to changes outside of pulmonary opacity, but not with the findings related to pulmonary opacity. CONCLUSIONS: Traction bronchiectasis and subcutaneous emphysema increased the risk of 90-day in-hospital mortality in patients with severe ARDS who required V-V ECMO.

Dexmedetomidine improves pulmonary outcomes in thoracic surgery under one-lung ventilation: A meta-analysis.

INTRODUCTION: Dexmedetomidine improves intrapulmonary shunt in thoracic surgery and minimizes inflammatory response during one-lung ventilation (OLV). However, it is unclear whether such benefits translate into less postoperative pulmonary complications (PPCs). Our objective was to determine the impact of dexmedetomidine on the incidence of PPCs after thoracic surgery. METHODS: Major databases were used to identify randomized trials that compared dexmedetomidine versus placebo during thoracic surgery in terms of PPCs. Our primary outcome was atelectasis within 7 days after surgery. Other specific PPCs included hypoxemia, pneumonia, and acute respiratory distress syndrome (ARDS). Secondary outcome included intraoperative respiratory mechanics (respiratory compliance [Cdyn]) and postoperative lung function (forced expiratory volume [FEV1]). Random effects models were used to estimate odds ratios (OR). RESULTS: Twelve randomized trials, including 365 patients in the dexmedetomidine group and 359 in the placebo group, were analyzed in this meta-analysis. Patients in the dexmedetomidine group were less likely to develop postoperative atelectasis (2.3% vs 6.8%, OR 0.42, 95%CI 0.18-0.95, P = 0.04; low certainty) and hypoxemia (3.4% vs 11.7%, OR 0.26, 95%CI 0.10-0.68, P = 0.01; moderate certainty) compared to the placebo group. The incidence of postoperative pneumonia (3.2% vs 5.8%, OR 0.57, 95%CI 0.25-1.26, P = 0.17; moderate certainty) or ARDS (0.9% vs 3.5%, OR 0.39, 95%CI 0.07-2.08, P = 0.27; moderate certainty) was comparable between groups. Both intraoperative Cdyn and postoperative FEV1 were higher among patients that received dexmedetomidine with a mean difference of 4.42 mL/cmH2O (95%CI 3.13-5.72) and 0.27 L (95%CI 0.12-0.41), respectively. CONCLUSION: Dexmedetomidine administration during thoracic surgery may potentially reduce the risk of postoperative atelectasis and hypoxemia. However, current evidence is insufficient to demonstrate an effect on pneumonia or ARDS.

Relação entre a Complacência Pulmonar Estática e a Falha de Extubação em Pacientes Pós-Operatório de Cirurgia Cardíaca / Relationship between Static Lung Compliance and Extubation Failure in Postoperative Cardiac Surgery Patients

Resumo Fundamento: Pouco explorada na decisão de extubação no pós-operatório de cirurgia cardíaca, a complacência pulmonar estática seriamente afetada no procedimento cirúrgico pode levar à insuficiência respiratória e à falha na extubação. Objetivo: Avaliar a complacência pulmonar estática no pós-operatório de cirurgia cardíaca e relacionar sua possível redução aos casos de falha na extubação dos pacientes submetidos ao método fast-track de extubação. Métodos: Foram incluídos pacientes que realizaram cirurgia cardíaca com uso de circulação extracorpórea (CEC) em um hospital universitário estadual admitidos na UTI sob sedação e bloqueio residual. Tiveram sua complacência pulmonar estática avaliada no ventilador mecânico por meio do software que utiliza o least squares fitting (LSF) para a medição. No período de 48 horas após a extubação os pacientes foram observados respeito à necessidade de reintubação por insuficiência respiratória. O nível de significância adotado para os testes estatísticos foi de 5%, ou seja, p<0,05. Resultados: Obtiveram sucesso na extubação 77 pacientes (75,49%) e falharam 25 (24,51%). Os pacientes que falharam na extubação tiveram a complacência pulmonar estática mais baixa quando comparados aos que tiveram sucesso (p<0,001). Identificamos o ponto de corte para complacência por meio da análise da curva Receiver Operating Characteristic Curve (ROC) sendo o ponto de corte o valor da complacência <41ml/cmH2O associado com maior probabilidade de falha na extubação (p<0,001). Na análise de regressão múltipla, verificou-se a influência da complacência pulmonar (dividida pelo ponto de corte da curva ROC) com risco de falha 9,1 vezes maior para pacientes com complacência <41ml/cmH2O (p< 0,003). Conclusões: A complacência pulmonar estática <41ml/cmH2O é um fator que compromete o sucesso da extubação no pós-operatório de cirurgia cardíaca.

Abstract Background: Static lung compliance, which is seriously affected during surgery, can lead to respiratory failure and extubation failure, which is little explored in the decision to extubate after cardiac surgery. Objective: To evaluate static lung compliance in the postoperative period of cardiac surgery and relate its possible reduction to cases of extubation failure in patients submitted to the fast-track method of extubation. Methods: Patients undergoing cardiac surgery using cardiopulmonary bypass (CPB) at a state university hospital admitted to the ICU under sedation and residual block were included. Their static lung compliance was assessed on the mechanical ventilator using software that uses least squares fitting (LSF) for measurement. Within 48 hours of extubation, the patients were observed for the need for reintubation due to respiratory failure. The level of significance adopted for the statistical tests was 5%, i.e., p<0.05. Results: 77 patients (75.49%) achieved successful extubation and 25 (24.51%) failed extubation. Patients who failed extubation had lower static lung compliance compared to those who succeeded (p<0.001). We identified the cut-off point for compliance through analysis of the Receiver Operating Characteristic Curve (ROC), with the cut-off point being compliance <41ml/cmH2O associated with a higher probability of extubation failure (p<0.001). In the multiple regression analysis, the influence of lung compliance (divided by the ROC curve cut-off point) was found to be 9.1 times greater for patients with compliance <41ml/cmH2O (p< 0.003). Conclusions: Static lung compliance <41ml/cmH2O is a factor that compromises the success of extubation in the postoperative period of cardiac surgery.

Effect of spine frame on the changes in respiratory dynamics in prone patients under general anaesthesia- a prospective, observational study.

Background and Aims: The prone position is one of the common surgical positions used in clinical practice. Manoeuvring patients from supine to a prone position can impact respiratory dynamics and result in haemodynamic variations. Methods: This study included 64 patients and was conducted after obtaining approval from the ethics committee and registration of the trial. The primary objective was to evaluate the changes in peak inspiratory pressure (PIP), plateau pressure (Pplat) and mean airway pressure (MAP) in patients undergoing surgery under general anaesthesia in the prone position with (Group S) and without (Group P) spine frame. The secondary objective was to evaluate and compare the variations in heart rate and blood pressure. Results: On turning the patient prone, there was statistically significant increase in median PIP (Group S 4 cmH2O vs. Group P 0.5 cmH2O, P < 0.001), Pplat (Group S 3.5 cmH2O vs. Group P 1 cmH2O, P = 0.004) and dynamic compliance (Group S -5.513 vs. Group P -2.78, P < 0.004). Conclusions: Our study found that prone positioning with a spine frame led to a significantly greater increase in airway pressures and a decrease in dynamic compliance when compared to patients positioned prone without the spine frame.

Effects of dexmedetomidine on dynamic lung compliance in general anesthesia with desflurane: A randomized controlled study.

Objective: The aim of this study was to evaluate the effect of dexmedetomidine on lung compliance in patients under general anesthesia with desflurane. Methods: This prospective, randomized, double-blind, controlled trial included 51 patients who received general anesthesia undergoing lower limb fracture surgery. Participants were assigned to either the experimental (loading dose of 0.25 µg/kg dexmedetomidine over 10 min, followed by a maintenance dose of 0.3 µg/kg/h until the end of the surgery) or control (0.9% saline) group. Anesthesia was maintained with desflurane, analgesics and muscle relaxants. The two groups were compared for hemodynamic parameters, dynamic lung compliance, oxygenation index, and postoperative complications. Results: While dynamic lung compliance showed no significant difference between the two groups at T1 (P = 0.321), it was significantly higher in the experimental group at all other time points (all P < 0.001). In the control group, Cdyn at T4, T5, T6, and T7 were lower than that at T1 (P = 0.032, 0.043, 0.032 and 0.018, respectively). There were no significant between-group differences in the mean arterial pressure and heart rate. Compared to the control group, the experimental group had a higher oxygenation index at T1 (P < 0.001), T2 (P < 0.001), T3 (P < 0.001), T4 (P = 0.02), and T5 (P = 0.016) and significantly lower peak airway pressure at all time points (all P < 0.001). Both groups had comparable postoperative outcomes. Conclusions: Dexmedetomidine infusion at a loading dose of 0.25 µg/kg and maintenance dose of 0.3 µg/kg/h improved dynamic lung compliance in patients receiving desflurane during general anesthesia.

Pressure-volume mechanics of inflating and deflating intact whole organ porcine lungs.

Pressure-volume curves of the lung are classical measurements of lung function and are impacted by changes in lung structure due to disease or shifts in air-delivery volume or cycling rate. Diseased and preterm infant lungs have been found to show heterogeneous behavior which is highly frequency dependent. This breathing rate dependency has motivated the exploration of multi-frequency oscillatory ventilators to deliver volume oscillation with optimal frequencies for various portions of the lung to provide more uniform air distribution. The design of these advanced ventilators requires the examination of lung function and mechanics, and an improved understanding of the pressure-volume response of the lung. Therefore, to comprehensively analyze whole lung organ mechanics, we investigate six combinations of varying applied volumes and frequencies using ex-vivo porcine specimens and our custom-designed electromechanical breathing apparatus. Lung responses were evaluated through measurements of inflation and deflation slopes, static compliance, peak pressure and volume, as well as hysteresis, energy loss, and pressure relaxation. Generally, we observed that the lungs were stiffer when subjected to faster breathing rates and lower inflation volumes. The lungs exhibited greater inflation volume dependencies compared to frequency dependencies. This study's reported response of the lung to variations of inflation volume and breathing rate can help the optimization of conventional mechanical ventilators and inform the design of advanced ventilators. Although frequency dependency is found to be minimal in normal porcine lungs, this preliminary study lays a foundation for comparison with pathological lungs, which are known to demonstrate marked rate dependency.

Accuracy of the estimations of respiratory mechanics using an expiratory time constant in passive and active breathing conditions: a bench study.

BACKGROUND: Respiratory mechanics monitoring provides useful information for guiding mechanical ventilation, but many measuring methods are inappropriate for awake patients. This study aimed to evaluate the accuracy of dynamic mechanics estimation using expiratory time constant (RCexp) calculation during noninvasive pressure support ventilation (PSV) with air leak in different lung models. METHODS: A Respironics V60 ventilator was connected to an active breathing simulator for modeling five profiles: normal adult, restrictive, mildly and severely obstructive, and mixed obstructive/restrictive. Inspiratory pressure support was adjusted to maintain tidal volumes (VT), achieving 5.0, 7.0, and 10.0 ml/kg body weight. PEEP was set at 5 cmH2O, and the back-up rate was 10 bpm. Measurements were conducted at system leaks of 25-28 L/min. RCexp was estimated from the ratio at 75% exhaled VT and flow rate, which was then used to determine respiratory system compliance (Crs) and airway resistance (Raw). RESULTS: In non-obstructive conditions (Raw ≤ 10 cmH2O/L/s), the Crs was overestimated in the PSV mode. Peak inspiratory and expiratory flow and VT increased with PS levels, as calculated Crs decreased. In passive breathing, the difference of Crs between different VT was no significant. Underestimations of inspiratory resistance and expiratory resistance were observed at VT of 5.0 ml/kg. The difference was minimal at VT of 7.0 ml/kg. During non-invasive PSV, the estimation of airway resistance with the RCexp method was accurately at VT of 7.0 ml/kg. CONCLUSIONS: The difference between the calculated Crs and the preset value was influenced by the volume, status and inspiratory effort in spontaneously breathing.

Relationship of Extravascular Lung Water and Pulmonary Vascular Permeability to Respiratory Mechanics in Patients with COVID-19-Induced ARDS.

During acute respiratory distress syndrome (ARDS), the increase in pulmonary vascular permeability and lung water induced by pulmonary inflammation may be related to altered lung compliance. A better understanding of the interactions between respiratory mechanics variables and lung water or capillary permeability would allow a more personalized monitoring and adaptation of therapies for patients with ARDS. Therefore, our main objective was to investigate the relationship between extravascular lung water (EVLW) and/or pulmonary vascular permeability index (PVPI) and respiratory mechanic variables in patients with COVID-19-induced ARDS. This is a retrospective observational study from prospectively collected data in a cohort of 107 critically ill patients with COVID-19-induced ARDS from March 2020 to May 2021. We analyzed relationships between variables using repeated measurements correlations. We found no clinically relevant correlations between EVLW and the respiratory mechanics variables (driving pressure (correlation coefficient [CI 95%]: 0.017 [-0.064; 0.098]), plateau pressure (0.123 [0.043; 0.202]), respiratory system compliance (-0.003 [-0.084; 0.079]) or positive end-expiratory pressure (0.203 [0.126; 0.278])). Similarly, there were no relevant correlations between PVPI and these same respiratory mechanics variables (0.051 [-0.131; 0.035], 0.059 [-0.022; 0.140], 0.072 [-0.090; 0.153] and 0.22 [0.141; 0.293], respectively). In a cohort of patients with COVID-19-induced ARDS, EVLW and PVPI values are independent from respiratory system compliance and driving pressure. Optimal monitoring of these patients should combine both respiratory and TPTD variables.

Delivering Low Tidal Volume With Anesthesia and ICU Ventilators in a Neonatal Lung Model.

BACKGROUND: Mechanical ventilation of the neonate requires ventilators than can deliver precise and accurate tidal volume (VT) and PEEP to avoid lung injury. Due to small neonatal VT and the disproportionate effect of endotracheal tube leak in these patients, accomplishing precise and accurate VT delivery is difficult. Whereas neonatal ICU ventilators are validated in this population, thorough studies testing the performance of anesthesia ventilators in delivering small VT in neonates are lacking. METHODS: Three anesthesia ventilators, Dräger Apollo, GE Avance, and Getinge Flow-i; and 2 ICU ventilators, Medtronic PB980 and Nihon Kohden NKV-550, were tested under volume control mode at VT of 5, 20, 40, and 60 mL. Three combinations of lung compliance and airway resistance were tested using a Servo ASL 5000 lung simulator. RESULTS: In a scenario without leak, the measured VT was greater than the set VT by > 10% in the Apollo (21.0% [18.8-26.0]); measured VT was less than the set VT by > 10% in the Flow-i (-19% [-20.8 to -18.7]). The Avance, PB980, and NKV-550 presented a volume error < 10% (-9.50% [-10.8 to -4.4], -5.8% [-11.8 to -3.5], and 5.4% [-4.5 to 18.9], respectively). Considering all combinations of set VT, leaks, and respiratory mechanics, none of the anesthesia ventilators were able to deliver a median measured VT within a 10% error. The bias between measured VT and set VT varied widely among ventilators (from 4.27 mL to -10.59 mL). Additionally, in the Apollo ventilator, PEEP was underdelivered with the largest leak value. CONCLUSIONS: Our results suggest that in comparison with the 2 neonatal ICU ventilators tested, the anesthesia ventilators did not greatly differ in terms of VT delivery in the presence of a gas leak.

Unexpected pulmonary mechanics during positive pressure mechanical ventilation in fibrotic lung disease with concomitant flail chest.

Understanding of pulmonary mechanics is essential to understanding mechanical ventilation. Typically, clinicians are mindful of peak and plateau pressures displayed on the ventilator and lung compliance, which is decreased in lung disease such as idiopathic pulmonary fibrosis (IPF). Decreased lung compliance leads to elevated peak and plateau pressures. We present a patient with IPF undergoing mechanical ventilation after cardiac arrest. Despite low lung compliance, he had normal peak and plateau pressures due to the presence of flail chest and increased chest wall compliance. This case highlights the role chest wall compliance plays in total respiratory system compliance and pulmonary mechanics.