Volume-controlled Ventilation Research Articles

Atelectasis, Shunt, and Worsening Oxygenation Following Reduction of Respiratory Rate in Healthy Pigs Undergoing ECMO: An Experimental Lung Imaging Study

Rationale: Reducing the respiratory rate during extracorporeal membrane oxygenation (ECMO) decreases the mechanical power, but it might induce alveolar de-recruitment. Dissecting de-recruitment due to lung edema vs. the fraction due to hypoventilation may be challenging in injured lungs.Objectives: We characterized changes in lung physiology (primary endpoint: development of atelectasis) associated with progressive reduction of the respiratory rate in healthy animals on ECMO.Methods: Six female pigs underwent general anesthesia and volume control ventilation (Baseline: PEEP 5 cmH2O, Vt 10 ml/kg, I:E = 1:2, FiO2 0.5, rate 24 bpm). Veno-venous ECMO was started and respiratory rate was progressively reduced to 18, 12, and 6 breaths per minute (6-h steps), while all other settings remained unchanged. ECMO blood flow was kept constant while gas flow was increased to maintain stable PaCO2.Measurements and Main Results: At Baseline (without ECMO) and toward the end of each step, data from quantitative CT scan, electrical impedance tomography, and gas exchange were collected. Increasing ECMO gas flow while lowering the respiratory rate was associated with an increase in the fraction of non-aerated tissue (i.e., atelectasis) and with a decrease of tidal ventilation reaching the gravitationally dependent lung regions (p = 0.009 and p = 0.018). Intrapulmonary shunt increased (p < 0.001) and arterial PaO2 decreased (p < 0.001) at lower rates. The fraction of non-aerated lung was correlated with longer expiratory time spent at zero flow (r = 0.555, p = 0.011).Conclusions: Progressive decrease of respiratory rate coupled with increasing CO2 removal in mechanically ventilated healthy pigs is associated with development of lung atelectasis, higher shunt, and poorer oxygenation.

Different Intraoperative Ventilatory Strategies for Prevention of Pulmonary Atelectasis in Obese Patients Undergoing Non-Bariatric Surgeries; Randomized Controlled Trial

Background: Upper abdominal surgeries have been reported to be associated with an increased incidence of postoperative atelectasis. Preventing atelectasis is important for all patients but is more important when caring for obese patients. Objectives: To determine which of the following ventilatory strategies is better in prevention of pulmonary atelectasis in obese patients undergoing non-bariatric surgery: Volume control ventilation VC, Pressure control Ventilation PC, Volume control ventilation + Positive End Expiratory Pressure PEEP, Volume control ventilation + Positive End Expiratory Pressure PEEP + lung recruitment maneuver. Patients and methods: A randomized-controlled trial study was carried out in the operating room (OR) in Zagazig University Hospital including 92 patients. Patients were randomly allocated into four groups. G1: Volume control ventilation VC, G2: Pressure control Ventilation PC, G3: Volume control ventilation + Positive End Expiratory Pressure PEEP, G4: as in G3 + lung recruitment maneuver. Results: There was significant difference between the studied groups as regards PaO2/FiO2 ratio as the 4th group was highly significant. There was also significant difference between the studied groups as regards atelectasis score with the least atelectasis score in group 4. There was a significant difference in group 4 than the other groups as regards length of stay in PACU, and need for 100% Fio2 in PACU.Finally,there was a significant difference between the studied groups as regards postoperative pulmonary complications with the 4th group has the least postoperative complication. Conclusion: Our results suggest that volume control ventilation + Positive End Expiratory Pressure PEEP + lung recruitment maneuver had beneficial effects on oxygenation continued into the early recovery period and decrease pulmonary complications in the early post-operative period in obese patients undergoing non-bariatric upper abdominal surgeries.

Comparison of Volume-Guaranteed or -Targeted, Pressure-Controlled Ventilation with Volume-Controlled Ventilation during Elective Surgery: A Systematic Review and Meta-Analysis.

For perioperative mechanical ventilation under general anesthesia, modern respirators aim at combining the benefits of pressure-controlled ventilation (PCV) and volume-controlled ventilation (VCV) in modes typically named “volume-guaranteed” or “volume-targeted” pressure-controlled ventilation (PCV-VG). This systematic review and meta-analysis tested the hypothesis that PCV-VG modes of ventilation could be beneficial in terms of improved airway pressures (Ppeak, Pplateau, Pmean), dynamic compliance (Cdyn), or arterial blood gases (PaO2, PaCO2) in adults undergoing elective surgery under general anesthesia. Three major medical electronic databases were searched with predefined search strategies and publications were systematically evaluated according to the Cochrane Review Methods. Continuous variables were tested for mean differences using the inverse variance method and 95% confidence intervals (CI) were calculated. Based on the assumption that intervention effects across studies were not identical, a random effects model was chosen. Assessment for heterogeneity was performed with the χ2 test and the I2 statistic. As primary endpoints, Ppeak, Pplateau, Pmean, Cdyn, PaO2, and PaCO2 were evaluated. Of the 725 publications identified, 17 finally met eligibility criteria, with a total of 929 patients recruited. Under supine two-lung ventilation, PCV-VG resulted in significantly reduced Ppeak (15 studies) and Pplateau (9 studies) as well as higher Cdyn (9 studies), compared with VCV [random effects models; Ppeak: CI −3.26 to −1.47; p < 0.001; I2 = 82%; Pplateau: −3.12 to −0.12; p = 0.03; I2 = 90%; Cdyn: CI 3.42 to 8.65; p < 0.001; I2 = 90%]. For one-lung ventilation (8 studies), PCV-VG allowed for significantly lower Ppeak and higher PaO2 compared with VCV. In Trendelenburg position (5 studies), this effect was significant for Ppeak only. This systematic review and meta-analysis demonstrates that volume-targeting, pressure-controlled ventilation modes may provide benefits with respect to the improved airway dynamics in two- and one-lung ventilation, and improved oxygenation in one-lung ventilation in adults undergoing elective surgery.

Use of volume controlled vs. pressure controlled volume guaranteed ventilation in elderly patients undergoing laparoscopic surgery with laryngeal mask airway

BackgroundThe peak inspiratory pressure (PIP) is crucial in mechanical ventilation with supraglottic airway device (SAD). Pressure-controlled ventilation volume-guaranteed (PCV-VG), delivering a preset tidal volume with the lowest required airway pressure, is being increasingly used during general anesthesia. In this study, we compared respiratory mechanics and circulatory parameters between volume-controlled ventilation (VCV) and PCV-VG in elderly patients undergoing laparoscopic surgery using the laryngeal mask airway supreme (LMA).MethodsEighty participants scheduled for laparoscopic surgery were enrolled in this prospective, randomized clinical trial. The participants were randomly assigned to receive VCV or PCV-VG. PIP, dynamic compliance (Cdyn) and mean inspiratory pressure (Pmean) were recorded at 5 min after induction of anesthesia (T1), 5 min after pneumoperitoneum(T2), 30 and 60 min after pneumoperitoneum (T3 and T4). Data including other respiratory variables, hemodynamic variables, and arterial blood gases were also collected. The difference in PIP between VCV and PCV-VG was assessed as the primary outcome.ResultsPIP was significantly lower at T2, T3, and T4 in both groups compared with T1 (all P < 0.0001), and it was significantly lower in the PCV-VG group than the VCV group at T2, T3, and T4 (all P < 0.001). Cydn was decreased at T2, T3, and T4 in two groups compared with T1 (all P < 0.0001), but it was higher in PCV-VG group than in VCV group at T2, T3, and T4 (all P < 0.0001). There were on statistically significant differences were found between the groups for other respiratory and hemodynamic variables.ConclusionIn elderly patients who underwent laparoscopic surgery using an LMA, PCV-VG was superior to VCV in its ability to provide ventilation with lower peak inspiratory pressure and greater dynamic compliance.

Spontaneous breathing for managing analgesia during balanced anesthesia with remifentanil and desflurane: a prospective, single center randomized controlled trial.

The main goal of anesthesiology is to achieve the best level of analgesia and a fast recovery of consciousness following anesthesia. The preservation of spontaneous breathing during general anesthesia with anesthetic gases is practiced by many anesthetists. However, very few studies have dealt with these positive properties of volatile anesthetics such as sevoflurane or desflurane. Remifentanil is a very short half-life opiate that combines sufficient intra-operative analgesia with a fast post-operative recovery time. We tested the hypothesis that spontaneous breathing can reduce overdosing with remifentanil during desflurane anesthesia. In this prospective, single center, multiple anesthetist study, 30 patients were randomized into two groups (volume-controlled ventilation mode and spontaneous breathing). The spontaneous breathing group showed a significantly lower post-operative pain level than the volume-controlled ventilation mode group. Furthermore, less remifentanil as well as less piritramide was needed in the spontaneous breathing group compared with volume-controlled ventilation mode. It was possible to achieve spontaneous breathing in all patients with 0.6 minimum alveolar concentration desflurane, in order to control the remifentanil rate and prevent an overdose. All spontaneous breathing patients had low intra- and post-operative pain levels and the need for analgesics was equal to or lower than that in the volume-controlled ventilation mode group. By reducing the intra-operative amount of opiates, both the post-operative pain and the amount of post-operative analgesia required can be reduced. A balanced anesthesia with spontaneous intra-operative breathing is needed to determine the required amount of opiates. This study was approved by the Ethic Committee of the Ruhr-University of Bochum (approval No. 2435) in September, 2004.

Development and Evaluation of an Automated Manual Resuscitator-Based Emergency Ventilator-Alternative.

Mass casualty incidents such as those that are being experienced during the novel coronavirus disease (COVID-19) pandemic can overwhelm local healthcare systems, where the number of casualties exceeds local resources and capabilities in a short period of time. The influx of patients with lung function deterioration as a result of COVID-19 has strained traditional ventilator supplies. To bridge the gap during ventilator shortages and to help clinicians triage patients, manual resuscitator devices can be used to deliver respirations to a patient requiring breathing support. Bag-valve mask (BVM) devices are ubiquitous in ambulances and healthcare environments, however require a medical professional to be present and constantly applying compression to provide the patient with respirations.We developed an automated manual resuscitator-based emergency ventilator-alternative (AMREV) that provides automated compressions of a BVM in a repetitive manner and is broadly compatible with commercially-available BVM devices approximately 5 inches (128 mm) in diameter. The AMREV device relieves the medical professional from providing manual breathing support and allows for hands-free operation of the BVM. The AMREV supports the following treatment parameters: 1) adjustable tidal volume (VT), 2) positive end-expiratory pressure (PEEP) (intrinsic and/or external), 3) 1:1 inspiratory: expiratory ratio, and 4) a controllable respiratory rate between 10-30 breaths per minute.The relationship between the inherent resistance and compliance of the lung and the delivered breaths was assessed for the AMREV device. Adjustable VT of 110-700 ml was achieved within the range of simulated lung states. A linear increase in mean airway pressure (Paw), from 10-40 cmH2O was observed, as the resistance and compliance on the lung model moved from normal to severe simulated disease states. The AMREV functioned continuously for seven days with less than 3.2% variation in delivered VT and Paw. Additionally, the AMREV device was compatible with seven commercially-available BVM setups and delivered consistent VT and Paw within 10% between models.This automated BVM-based emergency-use resuscitator can provide consistent positive pressure, volume-controlled ventilation over an extended duration when a traditional ventilator is not available. True ventilator shortages may lead to manual resuscitators devices such as the AMREV being the only option for some healthcare systems during the COVID-19 pandemic.

Effects of ventilation mode type on intra-abdominal pressure and intra-operative blood loss in patients undergoing lumbar spine surgery: A randomised clinical study.

Background and Aims:The aim of the study was to evaluate the effect of mode of mechanical ventilation; pressure-controlled ventilation (PCV) vs. volume-controlled ventilation (VCV) on airway pressures, intra-abdominal pressure (IAP) and intra-operative surgical bleeding in patients undergoing lumbar spine surgery.Methods:This was a prospective, randomised study that included 50 American Society of Anesthesiologists class I and II patients undergoing lumbar spine surgery who were mechanically ventilated using PCV or VCV mode. The respiratory parameters (peak and plateau pressures) and IAP were measured after anaesthesia induction in supine position, 10 min after the patients were changed from supine to prone position, at the end of the surgery in prone position, and after the patients were changed from prone to supine position. The amount of intraoperative surgical bleeding was measured by objective and subjective methods.Results:The primary outcome was the amount of intraoperative surgical bleeding. It was significantly less in the PCV group than in the VCV group (137 ± 24.37 mL vs. 311 ± 66.98 mL) (P = 0.000). Similarly, on comparing other parameters like peak inspiratory pressures, plateaupressures and IAP, the patients in PCV group had significantly lower parameters than those in VCV group (P < 0.05). No harmful events were recorded.Conclusion:In patie,nts undergoing lumbar spine surgery, use of PCV mode decreased intraoperative surgical bleeding, which may be related to lower intraoperative respiratory pressures and IAP.

Effects of two stepwise lung recruitment strategies on respiratory function and haemodynamics in anaesthetised pigs: A randomised crossover study.

Lung recruitment manoeuvres and positive end-expiratory pressure (PEEP) can improve lung function during general anaesthesia. Different recruitment manoeuvre strategies have been described in large international trials: in the protective ventilation using high vs. low PEEP (PROVHILO) strategy, tidal volume (VT) was increased during volume-controlled ventilation; in the individualised peri-operative open-lung approach vs. standard protective ventilation in abdominal surgery (iPROVE) strategy, PEEP was increased during pressure-controlled ventilation. To compare the effects of the PROVHILO strategy and the iPROVE strategy on respiratory and haemodynamic variables. Randomised crossover study. University hospital research facility. A total of 20 juvenile anaesthetised pigs. Animals were assigned randomly to one of two sequences: PROVHILO strategy followed by iPROVE strategy or vice-versa (n = 10/sequence). In the PROVHILO strategy, VT was increased stepwise by 4 ml kg-1 at a fixed PEEP of 12 cmH2O until a plateau pressure of 30 to 35 cmH2O was reached. In the iPROVE strategy, at fixed driving pressure of 20 cmH2O, PEEP was increased up to 20 cmH2O followed by PEEP titration according to the lowest elastance of the respiratory system (ERS). We assessed regional transpulmonary pressure (Ptrans), respiratory system mechanics, gas exchange and haemodynamics, as well as the centre of ventilation (CoV) by electrical impedance tomography. During recruitment manoeuvres with the PROVHILO strategy compared with the iPROV strategy, dorsal Ptrans was lower at end-inspiration (16.3 ± 2.7 vs. 18.6 ± 3.1 cmH2O, P = 0.001) and end-expiration (4.8 ± 2.6 vs. 8.8 ± 3.4 cmH2O, P < 0.001), and mean arterial pressure (MAP) was higher (77 ± 11 vs. 60 ± 14 mmHg, P < 0.001). At 1 and 15 min after recruitment manoeuvres, ERS was higher in the PROVHILO strategy than the iPROVE strategy (24.6 ± 3.9 vs. 21.5 ± 3.4 and 26.7 ± 4.3 vs. 24.0 ± 3.8 cmH2O l-1; P < 0.001, respectively). At 1 min, PaO2 was lower in PROVHILO compared with iPROVE strategy (57.1 ± 6.1 vs. 59.3 ± 5.1 kPa, P = 0.013), but at 15 min, values did not differ. CoV did not differ between strategies. In anaesthetised pigs, the iPROVE strategy compared with the PROVHILO strategy increased dorsal Ptrans at the cost of lower MAP during recruitment manoeuvres, and decreased ERS thereafter, without consistent improvement of oxygenation or shift of the CoV. This study was registered and approved by the Landesdirektion Dresden, Germany (DD24-5131/338/28).

Development and validation of a reinforcement learning algorithm to dynamically optimize mechanical ventilation in critical care

The aim of this work was to develop and evaluate the reinforcement learning algorithm VentAI, which is able to suggest a dynamically optimized mechanical ventilation regime for critically-ill patients. We built, validated and tested its performance on 11,943 events of volume-controlled mechanical ventilation derived from 61,532 distinct ICU admissions and tested it on an independent, secondary dataset (200,859 ICU stays; 25,086 mechanical ventilation events). A patient “data fingerprint” of 44 features was extracted as multidimensional time series in 4-hour time steps. We used a Markov decision process, including a reward system and a Q-learning approach, to find the optimized settings for positive end-expiratory pressure (PEEP), fraction of inspired oxygen (FiO2) and ideal body weight-adjusted tidal volume (Vt). The observed outcome was in-hospital or 90-day mortality. VentAI reached a significantly increased estimated performance return of 83.3 (primary dataset) and 84.1 (secondary dataset) compared to physicians’ standard clinical care (51.1). The number of recommended action changes per mechanically ventilated patient constantly exceeded those of the clinicians. VentAI chose 202.9% more frequently ventilation regimes with lower Vt (5–7.5 mL/kg), but 50.8% less for regimes with higher Vt (7.5–10 mL/kg). VentAI recommended 29.3% more frequently PEEP levels of 5–7 cm H2O and 53.6% more frequently PEEP levels of 7–9 cmH2O. VentAI avoided high (>55%) FiO2 values (59.8% decrease), while preferring the range of 50–55% (140.3% increase). In conclusion, VentAI provides reproducible high performance by dynamically choosing an optimized, individualized ventilation strategy and thus might be of benefit for critically ill patients.

Combined Ventilation of Two Subjects with a Single Mechanical Ventilator Using a New Medical Device: An In Vitro Study.

Introduction The SARS-CoV-2 pandemic has created a sudden lack of ventilators. DuplicARⓇ is a novel device that allows simultaneous and independent ventilation of two subjects with a single ventilator. The aims of this study are (a) to determine the efficacy of DuplicARⓇ to independently regulate the peak and positive-end expiratory pressures in each subject, both under pressure-controlled ventilation and volume-controlled ventilation and (b) to determine the ventilation mode in which DuplicARⓇ presents the best performance and safety. Materials and Methods Two test lungs are connected to a single ventilator using DuplicARⓇ. Three experimental stages are established: (1) two identical subjects, (2) two subjects with the same weight but different lung compliance, and (3) two subjects with different weights and lung compliances. In each stage, the test lungs are ventilated in two ventilation modes. The positive-end expiratory pressure requirements are increased successively in one of the subjects. The goal is to achieve a tidal volume of 7 ml/kg for each subject in all different stages through manipulation of the ventilator and the DuplicARⓇ controllers. Results DuplicARⓇ allows adequate ventilation of two subjects with different weights and/or lung compliances and/or PEEP requirements. This is achieved by adjusting the total tidal volume for both subjects (in volume-controlled ventilation) or the highest peak pressure needed (in pressure-controlled ventilation) along with the basal positive-end expiratory pressure on the ventilator and simultaneously manipulating the DuplicARⓇ controllers to decrease the tidal volume or the peak pressure in the subject that needs less and/or to increase the positive-end expiratory pressure in the subject that needs more. While ventilatory goals can be achieved in any of the ventilation modes, DuplicARⓇ performs better in pressure-controlled ventilation, as changes experienced in the variables of one subject do not modify the other one. Conclusions DuplicARⓇ is an effective tool to manage the peak inspiratory pressure and the positive-end expiratory pressure independently in two subjects connected to a single ventilator. The driving pressure can be adjusted to meet the requirements of subjects with different weights and lung compliances. Pressure-controlled ventilation has advantages over volume-controlled ventilation and is therefore the recommended ventilation mode.

Intraoperative Assessment of Fluid Responsiveness in Normotensive Dogs under Isoflurane Anaesthesia.

The aim of this study was to evaluate the incidence of fluid responsiveness (FR) to a fluid challenge (FC) in normotensive dogs under anaesthesia. The accuracy of pulse pressure variation (PPV), systolic pressure variation (SPV), stroke volume variation (SVV), and plethysmographic variability index (PVI) for predicting FR was also evaluated. Dogs were anaesthetised with methadone, propofol, and inhaled isoflurane in oxygen, under volume-controlled mechanical ventilation. FC was performed by the administration of 5 mL/kg of Ringer’s lactate within 5 min. Cardiac index (CI; L/min/m2), PPV, (%), SVV (%), SPV (%), and PVI (%) were registered before and after FC. Data were analysed with ANOVA and ROC tests (p < 0.05). Fluid responsiveness was defined as 15% increase in CI. Eighty dogs completed the study. Fifty (62.5%) were responders and 30 (37.5%) were nonresponders. The PPV, PVI, SPV, and SVV cut-off values (AUC, p) for discriminating responders from nonresponders were PPV >13.8% (0.979, <0.001), PVI >14% (0.956, <0.001), SPV >4.1% (0.793, <0.001), and SVV >14.7% (0.729, <0.001), respectively. Up to 62.5% of normotensive dogs under inhalant anaesthesia may be fluid responders. PPV and PVI have better diagnostic accuracy to predict FR, compared to SPV and SVV.

Effects of positive end-expiratory pressure/recruitment manoeuvres compared with zero end-expiratory pressure on atelectasis in children: A randomised clinical trial.

BACKGROUNDAtelectasis is a common postoperative complication. Peri-operative lung protection can reduce atelectasis; however, it is not clear whether this persists into the postoperative period.OBJECTIVETo evaluate to what extent lung-protective ventilation reduces peri-operative atelectasis in children undergoing nonabdominal surgery.DESIGNRandomised, controlled, double-blind study.SETTINGSingle tertiary hospital, 25 July 2019 to 18 January 2020.PATIENTSA total of 60 patients aged 1 to 6 years, American Society of Anesthesiologists physical status 1 or 2, planned for nonabdominal surgery under general anaesthesia (≤2 h) with mechanical ventilation.INTERVENTIONSThe patients were assigned randomly into either the lung-protective or zero end-expiratory pressure with no recruitment manoeuvres (control) group. Lung protection entailed 5 cmH2O positive end-expiratory pressure and recruitment manoeuvres every 30 min. Both groups received volume-controlled ventilation with a tidal volume of 6 ml kg−1 body weight. Lung ultrasound was conducted before anaesthesia induction, immediately after induction, surgery and tracheal extubation, and 15 min, 3 h, 12 h and 24 h after extubation.MAIN OUTCOME MEASURESThe difference in lung ultrasound score between groups at each interval. A higher score indicates worse lung aeration.RESULTSPatients in the lung-protective group exhibited lower median [IQR] ultrasound scores compared with the control group immediately after surgery, 4 [4 to 5] vs. 8 [4 to 6], (95% confidence interval for the difference between group values −4 to −4, Z = -6.324) and after extubation 3 [3 to 4] vs. 4 [4 to 4], 95% CI −1 to 0, Z = −3.161. This did not persist from 15 min after extubation onwards. Lung aeration returned to normal in both groups 3 h after extubation.CONCLUSIONSThe reduced atelectasis provided by lung-protective ventilation does not persist from 15 min after extubation onwards. Further studies are needed to determine if it yields better results in other types of surgery.TRIAL REGISTRATIONChictr.org.cn (ChiCTR2000033469).

Ultrasound-guided versus conventional lung recruitment manoeuvres in laparoscopic gynaecological surgery

Pneumoperitoneum and steep Trendelenburg position promote the formation of pulmonary atelectasis during laparoscopic gynaecological surgery. To determine whether lung ultrasound-guided alveolar recruitment manoeuvres could reduce peri-operative atelectasis compared with conventional recruitment manoeuvres during laparoscopic gynaecological surgery. Randomised controlled trial. Tertiary hospital, Republic of Korea, from August 2018 to January 2019. Adult patients scheduled for laparoscopic gynaecological surgery under general anaesthesia. Forty patients were randomised to receive either ultrasound-guided recruitment manoeuvres (manual inflation until no visibly collapsed area was seen with lung ultrasonography; intervention group) or conventional recruitment manoeuvres (single manual inflation with 30 cmH2O pressure; control group). Recruitment manoeuvres were performed 5 min after induction and at the end of surgery in both groups. All patients received volume-controlled ventilation with a tidal volume of 8 ml kg-1 and a positive end-expiratory pressure of 5 cmH2O. The primary outcome was the lung ultrasound score at the end of surgery; a higher score indicates worse lung aeration. Lung ultrasound scores at the end of surgery were significantly lower in the intervention group compared with control group (median [IQR], 7.5 [6.5 to 8.5] versus 9.5 [8.5 to 13.5]; difference, -2 [95% CI, -4.5 to 1]; P = 0.008). The intergroup difference persisted in the postanaesthesia care unit (7 [5 to 8.8] versus 10 [7.3 to 12.8]; difference, -3 [95% CI, -5.5 to 1.5]; P = 0.005). The incidence of atelectasis was lower in the intervention group compared with control group at the end of surgery (35 versus 80%; P = 0.010) but was comparable in the postanaesthesia care unit (40 versus 55%; P = 0.527). The use of ultrasound-guided recruitment manoeuvres improves peri-operative lung aeration; these effects may persist in the postanaesthesia care unit. However, the long-term effects of ultrasound-guided recruitment manoeuvres on clinical outcomes should be the subject of future trials. ClinicalTrials.gov (NCT03607240).

Influences of assisted breathing and mechanical ventilator settings on tidal volume and alveolar pressures in acute respiratory distress syndrome: a bench study.

Objective:To evaluate the influences of respiratory muscle efforts and respiratory rate setting in the ventilator on tidal volume and alveolar distending pressures at end inspiration and expiration in volume-controlled ventilation and pressure-controlled ventilation modes in acute respiratory distress syndrome.Methods:An active test lung (ASL 5000™) connected to five intensive care unit ventilators was used in a model of acute respiratory distress syndrome. Respiratory muscle efforts (muscle pressure) were configured in three different ways: no effort (muscle pressure: 0cmH2O); inspiratory efforts only (muscle pressure:-5cmH2O, neural inspiratory time of 0.6s); and both inspiratory and expiratory muscle efforts (muscle pressure:-5/+5cmH2O). Volume-controlled and pressure-controlled ventilation modes were set to deliver a target tidal volume of 420mL and positive end-expiratory pressure of 10cmH2O. The tidal volume delivered to the lungs, alveolar pressures at the end of inspiration, and alveolar pressures at end expiration were evaluated.Results:When triggered by the simulated patient, the median tidal volume was 27mL lower than the set tidal volume (range-63 to +79mL), and there was variation in alveolar pressures with a median of 25.4cmH2O (range 20.5 to 30cmH2O). In the simulated scenarios with both spontaneous inspiratory and expiratory muscle efforts and with a mandatory respiratory rate lower than the simulated patient's efforts, the median tidal volume was higher than controlled breathing.Conclusion:Adjusting respiratory muscle effort and pulmonary ventilator respiratory rate to a value above the patient’s respiratory rate in assisted/controlled modes generated large variations in tidal volume and pulmonary pressures, while the controlled mode showed no variations in these outcomes.

Effects of PEEP on Hemodynamic Variables of Pigs Submitted to Volume-controlled Ventilation under Pneumoperitoneum associated to Cephalodeclive

Background: Videolaparoscopic procedures have gained prominence due to their low invasiveness, causing less surgical trauma and better post-surgical recovery. However, the increase in intra-abdominal pressure due to the institution of pneumoperitoneum can alter the patient's homeostasis. Therefore, volume-controlled ventilation, associated with positive end-expiratory pressure (PEEP), improves arterial oxygenation and prevents pulmonary collapse, but it can lead to important hemodynamic changes. The aim of this study was to evaluate, comparatively, the effects of positive end expiratory-pressure (PEEP) on hemodynamic variables of pigs submitted to volume-controlled ventilation, during pneumoperitoneum and maintained in head-down tilt and determine which PEEP value promotes greater stability on hemodynamic variables. Materials, Methods &amp; Results: Twenty-four pigs were used, between 55 and 65-day-old, weighing between 15 and 25 kg, randomly divided into 3 distinct groups differentiated by positive end-expiratory pressure: PEEP 0 (volume-controlled ventilation and PEEP of 0 cmH2O), PEEP 5 (volume-controlled ventilation and PEEP of 5 cmH2O) and PEEP 10 (volume-controlled ventilation and PEEP of 10 cmH2O). Volume-controlled ventilation was adjusted to 8 mL/kg of tidal volume and a respiratory rate of 25 movements per min. Anesthesia was maintained with continuous infusion of propofol (0.2 mg/kg/min) and midazolam (1 mg/kg/h). Pneumoperitoneum was performed with carbon dioxide (CO2), keeping the intra-abdominal pressure at 15 mmHg and the animals were positioned on a 30° head-down tilt. The evaluations of hemodynamic variables started 30 min after induction of anesthesia (M0), followed by measurements at 15-min intervals (from M15 to M90), completing a total of 7 evaluations. The variables of interest were collected over 90 min and submitted to analysis of variance followed by Tukey´s post-hoc test, with P &lt; 0.05. The PEEP 10 group had higher values of CVP and mCPP, while the PEEP 5 group, mPAP and PVR were higher. The PEEP 0 group, on the other hand, had higher means of CI. Regarding the moments, there were differences in HR, SAP, DAP, MAP, CO, IC and TPR.Discussion: According to the literature, important hemodynamic effects due to pneumoperitoneum are reported, which can be caused by the pressure used in abdominal insufflation, CO2 accumulation, duration of the surgical procedure, hydration status and patient positioning. Mechanical ventilation associated with PEEP can also cause an increase in intrathoracic pressure and, therefore, reduce cardiac output. Cardiovascular changes are proportional to the PEEP used. Central venous pressure (PVC) measure the patient's preload, and intrathoracic pressure can interfere with this parameter. The peak pressure values in the PEEP 10 group were higher than the other groups, demonstrating that the increase in intrathoracic pressure results in higher PVC values. Regarding PAPm and PCPm, these variables can be influenced according to the PEEP values and the patient's position. In relation to CI, the increase in PEEP may reflect on intrathoracic pressure, resulting in greater compression of the heart, with a consequent reduction in cardiac output and cardiac index. Therefore, it is concluded that the PEEP effects of 0 cmH2O and 5 cmH2O on hemodynamics are discrete, under the proposed conditions. Keywords: mechanical ventilation, PEEP, head-down tilt, VCV, swine. Descritores: ventilação mecânica, PEEP, posição de Trendelenburg, suínos.

COMPARATIVE STUDY BETWEEN THE EFFECT OF VOLUME-CONTROLLED VENTILATION AND PRESSURE CONTROLLED VENTILATION VOLUME GUARANTEED ON GAS EXCHANGE AND RESPIRATORY DYNAMICS DURING ONE-LUNG VENTILATION

ABSTRACT Background: Impairment of gas exchange is a common problem during one lung ventilation (OLV) with a hazardous effect on morbidity and mortality. The current study compares the effect of volume-controlled ventilation (VCV) versus pressure-controlled ventilation volume guaranteed (PCV-VG) on gas exchange during OLV. Settings and Design: This study was a prospective randomized study. Methods: The study was carried out on 30 adult patients who were randomly assigned to two groups. Group VCV: VCV was performed throughout the operation. Group PCV-VG: PCV-VG was performed throughout the operation. Haemodynamic parameters ((HR), MAP), and (CVP)), blood gas analysis, and PaO2/FiO2 were recorded: before induction of anaesthesia (T0); during TLV (T1); ½ an hour after OLV (T2); 1 h after OLV (T3); 20 minutes after resuming TLV (T4); 6, 12, and 24 hours after surgery (T5, 6, and T7). (Ppeak), (Pmean) and (Cdyn) were recorded during (T1, 2, 3, and T4) time intervals. TNFα level was measured in venous Samples in the following times: (1) before induction of anaesthesia (T0); (2) Directly after surgery (T1); (3) 5th postoperative day (T2). The patients were followed for 5 days for recording of PPCs. Results: PCV-VG ventilation leads to a significant decrease in Ppeak and Pmean and significant increase in Cdyn (P ≤ 0.05). However, it had no effect on intra- and postoperative oxygenation values. Conclusion: PCV-VG is superior to VCV as regard respiratory dynamics during one lung ventilation (OLV), while it does not differ as regard items of gas exchange, inflammatory response and PPCs. Abbreviations: OLV: one lung ventilation; TLV: two lung ventilation; VCV: volume-controlled ventilation; PCV-VG: pressure-controlled ventilation volume guaranteed; PaO2: arterial oxygen tension; FiO2: fraction of inspired oxygen; Ppeak: Peak inspiratory pressure; Pmean: mean inspiratory pressure; Cdyn: dynamic compliance TNFα: Tumour necrosis factor α; PPCs: postoperative pulmonary complications.

Assessment of Perioperative Atelectasis Using Lung Ultrasonography in Patients Undergoing Pneumoperitoneum Surgery in the Trendelenburg Position: Aspects of Differences according to Ventilatory Mode.

BackgroundDuring robotic gynecologic pneumoperitoneum surgery in the Trendelenburg position, aeration loss leads to perioperative atelectasis. Recently developed ventilator mode pressure-controlled ventilation volume-guaranteed (PCV-VG) mode could provide adequate ventilation with lower inspiratory pressure compared to volume-controlled ventilation (VCV); we hypothesized that PCV-VG mode may be beneficial in reducing perioperative atelectasis via low tidal volume (VT) of 6 mL/kg ventilation during robotic gynecologic pneumoperitoneum surgery in the Trendelenburg position. We applied lung ultrasound score (LUS) for detecting perioperative atelectasis. We aimed to compare perioperative atelectasis between VCV and PCV-VG with a low VT of 6 mL/kg during pneumoperitoneum surgery in the Trendelenburg position using LUS.MethodsPatients scheduled for robotic gynecologic surgery were randomly allocated to the VCV (n = 41) or PCV-VG group (n = 41). LUS, ventilatory, and hemodynamic parameters were evaluated at T1 (before induction), T2 (10 minutes after induction in the supine position), T3 (10 minutes after desufflation of CO2 in the supine position), and T4 (30 minutes after emergence from anesthesia in the recovery room).ResultsEighty patients (40 with PCV-VG and 40 with VCV) were included. Demographic data showed no significant differences between the groups. The total LUS has changed from baseline to T4, 0.63 (95% confidence interval [CI], 0.32, 0.94) to 1.77 (95% CI, 1.42, 2.21) in the VCV group and 0.86 (95% CI, 0.56, 1.16) to 1.43 (95% CI, 1.08, 1.78) in the PCV-VG group (P = 0.170). In both groups, total LUS increased significantly compared to the baseline values.ConclusionUsing a low VT of 6 mL/kg during pneumoperitoneum surgery in the Trendelenburg position, our study showed no evidence that PCV-VG ventilation was superior to VCV in terms of perioperative atelectasis.Trial RegistrationClinical Research Information Service Identifier: KCT0006404

Minimal Lung Mechanics Basis-functions for a Mechanical Ventilation Virtual Patient

Abstract Mechanical ventilation (MV) is used in the intensive care unit (ICU) to treat patients with respiratory failure. However, MV settings are not standardized due to significant inter- and intra- patient variability in response to care, leading to variability in care, outcome, and cost. There is thus a need to personalize MV. This research extends a single compartment lung mechanics model with physiologically relevant basis functions, to identify patient-specific lung mechanics and predict response to changes in MV care. The nonlinear evolution of pulmonary elastance as positive-end-expiratory pressure (PEEP) changes is captured by a physiologically relevant, simplified compensatory equation as a function of PEEP and pressure identification error at the baseline PEEP level. It allows both patient-specific and general prediction of lung elastance of higher PEEP. The prediction outcome is validated with data from two volume-controlled ventilation (VCV) trials and one pressure-controlled ventilation (PCV) trial, where the biggest PEEP prediction interval is a clinically unrealistic 20cmH2O, comprising 210 prediction cases over 36 patients (22 VCV; 14 PCV). Predicted absolute peak inspiratory pressure (PIP) errors are within 1.0cmH2O and 3.3cmH2O for 90% cases in the two VCV trials, while predicted peak inspiratory tidal volume (PIV) errors are within 0.073L for 85% cases in studied PCV trial. The model presented provides a highly accurate, predictive virtual patient model across multiple MV modes and delivery methods, and over clinically unrealistically large changes. Low computational cost, and fast, easy parameterization enable model-based, predictive decision support in real-time to safely personalize and optimize MV care.

Mechanical ventilation in Spain, 1998-2016: Epidemiology and outcomes.

To evaluate changes in the epidemiology of mechanical ventilation in Spain from 1998 to 2016. A post hoc analysis of four cohort studies was carried out. A total of 138 Spanish ICUs. A sample of 4293 patients requiring invasive mechanical ventilation for more than 12h or noninvasive ventilation for more than 1h. None. Demographic variables, reason for mechanical ventilation, variables related to ventilatory support (ventilation mode, tidal volume, PEEP, airway pressures), complications during mechanical ventilation, duration of mechanical ventilation, ICU stay and ICU mortality. There was an increase in severity (SAPSII: 43 points in 1998 vs. 47 points in 2016), changes in the reason for mechanical ventilation (decrease in chronic obstructive pulmonary disease and acute respiratory failure secondary to trauma, and increase in neurological disease and post-cardiac arrest). There was an increase in noninvasive mechanical ventilation as the first mode of ventilatory support (p<0.001). Volume control ventilation was the most commonly used mode, with increased support pressure and pressure-regulated volume-controlled ventilation. A decrease in tidal volume was observed (9ml/kg actual b.w. in 1998 and 6.6ml/kg in 2016; p<0.001) as well as an increase in PEEP (3cmH2O in 1998 and 6cmH2O in 2016; p<0.001). In-ICU mortality decreased (34% in 1998 and 27% in 2016; p<0.001), without geographical variability (median OR 1.43; p=0.258). A significant decrease in mortality was observed in patients ventilated in Spanish ICUs. These changes in mortality could be related to modifications in ventilation strategy to minimize ventilator-induced lung injury.

Predicting Pulmonary Distension in a Virtual Patient Model for Mechanical Ventilation

Abstract Recruitment maneuvers (RMs) following with positive-end-expiratory-pressure (PEEP) have proved effective in recruiting lung volume and preventing alveoli collapse. To date, standards for optimal patient-specific PEEP are unknown, resulting in variability in care and reduced outcomes, both indicating the need for personalized care. This research extends a well-validated virtual patient model by adding novel elements to model, which is able to utilize bedside available respiratory data, without increasing modelling complexity, to predict patient-specific lung distension and thus to minimise barotrauma risk. Prediction accuracy and robustness are validated against clinical data from 18 volume controlled ventilation (VCV) patients at 7 different baseline PEEP levels (0 to 12cmH2O), where predictions were made up to 12cmH2O of PEEP ahead. Using an exponential basis function set for prediction yields an absolute median peak inspiratory pressure prediction error of 1.50cmH2O for 623 prediction cases. Comparing predicted and clinically measured distension prediction in VCV demonstrated consistent, robust high accuracy with R2=0.90 (623 predictions), which is a measurable improvement in prediction error compared to predictions without using the proposed distension function (R2=0.82). Moreover, the R2 value increases to 0.93-0.95 if only clinically relevant ΔPEEP steps (2-6cmH2O) are considered with an overall median absolute error in peak pressure prediction of 1.04cmH2O. Overall, the results demonstrate the potential and significance for accurately capturing distension mechanics, allowing better risk assessment, as well as extending and more fully validating this virtual mechanical ventilation patient model.