Volume-controlled Mode Research Articles

Intraoperative Protective Mechanical Ventilation in Dogs: A Randomized Clinical Trial.

ObjectiveTo evaluate gas exchange, respiratory mechanics, and hemodynamic impact of mechanical ventilation with low tidal volume (VT) in dogs with the use of positive end-expiratory pressure (PEEP) or preceded by alveolar recruitment maneuver (ARM).Study DesignProspective randomized clinical trial.AnimalsTwenty-one healthy client-owned mesocephalic healthy dogs, 1–7 years old, weighing 10–20 kg, and body condition scores 4–6/9 admitted for periodontal treatment.MethodsIsoflurane-anesthetized dogs in dorsal recumbency were ventilated until 1 h with a volume-controlled ventilation mode using 8 mL kg−1 of VT. The dogs were distributed in 2 groups: in the ARM group, PEEP starts in 0 cmH2O, increasing gradually 5 cmH2O every 3 min, until reach 15 cmH2O and decreasing in the same steps until 5 cmH2O, maintaining this value until the end; and PEEP group, in which the pressure 5 cmH2O was instituted from the beginning of anesthesia and maintained the same level up to the end of the anesthesia. Cardiopulmonary, metabolic, oxygenation parameters, and respiratory mechanics were recorded after the anesthesia induction (baseline—BL), 15, 45, and 75 min after BL and during the recovery.ResultsThe ARM increased the static compliance (Cst) (15 min after baseline) when compared with baseline moment (24.9 ± 5.8 mL cmH20−1 vs. 20.7 ± 5.4 mL cmH20−1–p = 0.0364), oxygenation index (PaO2/FIO2) (505.6 ± 59.2 mmHg vs. 461.2 ± 41.0 mmHg—p = 0.0453) and reduced the shunt fraction (3.4 ± 2.4% vs. 5.5 ± 1.6%—p = 0.062). In the PEEP group, no statistical differences were observed concerning the variables evaluated. At the beginning of the evaluation, the driving pressure (DP) before ARM was significantly greater than all other evaluation time points (6.9 ± 1.8 cmH20).Conclusions and Clinical RelevanceThe use of 8 mL kg−1 of VT and 5 cmH20 PEEP without ARM maintain adequate oxygenation and mechanical ventilation in dental surgeries for up to 1 h. The use of ARM slightly improved compliance and oxygenation during the maneuver.

Pressure-Regulated Volume Control and Pressure-Control Ventilation Modes in Pediatric Acute Respiratory Failure

ObjectiveThe objective of this study is to present our experience using the pressure-regulated volume control and the pressure-control ventilation modes in children.MethodsPatients with acute respiratory failure ventilated with pressure-regulated volume control or pressure-control modes were retrospectively evaluated. The patient’s ventilation parameters (of the first 7 days of ventilation or of the whole ventilation period, if the patient had been ventilated less than 7 days), SpO2, blood gases, and demographic data were collected from the pediatric intensive care unit database. ResultsSixty-one patients (median age 12 [4.8-36.4] months) were enrolled in the study. The pressure-control ventilation mode was used on 40 patients (65.6%) and the pressure-regulated volume-control mode was used on 21 (34.4%) patients. Twenty-eight patients (45.9%) had hypoxemic respiratory failure and 44 (72.1%) had hypercapnic respiratory failure. The median positive end-expiratory pressure was higher in pressure-control ventilation mode (5.4 [4.2-6.3] cmH2O) than the pressure-regulated volume-control mode (4.05 [3.68-4.41] H2O, P < .001). Pressure-control mode was used more frequently in hypoxemic cases but both modes were used equally in hypercapnic cases. Hypoxic respiratory failure (yes/no), odds ratio: 3.9 (95% CI 1.2-12.3, P = .02), Ph (nadir), odds ratio: 0.004 (95% CI 0.000-0.275, P = .01), and base excess, odds ratio: 0.88 (95% CI 0.79-0.98, P = .02) were associated with intensive care mortality.ConclusionsAlthough the pressure-control ventilation mode was preferred more frequently in hypoxemic respiratory failure, there was no significant difference between the 2 respiratory modes in terms of length of pediatric intensive care unit stay, MV duration, and mortality. The pressure-regulated volume-control mode seems to be a safer option for physicians who do not have enough experience in using pressure-control ventilation mode.

Abstract No.: ABS0586: Is pressure control ventilation better than volume control in patients undergoing spine surgery in prone position?

Background & Aims:Optimisation of intraoperative ventilation is feasible nowadays due to availability of several new modes in anaesthesia workstations. Spine surgery in prone position leads to pulmonary and haemodynamic alterations. The present study aimed to compare PCV and VCV modes of ventilation in patients undergoing spine surgeries.Methods:After obtaining approval from institutional ethics committee the present, prospective, randomised study was conducted in 50 adult patient of either sex, ASA I or II undergoing thoracic or lumbar spine surgery in prone position. Standard anaesthesia protocols using Thiopentone, Fentanyl and Vecuroniun was followed. Patients in VCV group (n=25) were ventilated with volume control mode with TV = 7 ml/kg, PEEP=5cm H2O, I: E=1:2 and respiratory rate adjusted to keep Et CO2 between 35-40 mmHg and FiO2 =0.4. While in PCV mode (n=25) patients were ventilated with similar settings except PIP was adjusted to determine TV=7ml/kg. Draeger Primus workstation was used.Results:Demographic profile, duration of surgery, intraoperative dry and fluid consumption were comparable in two groups. Peak inspiratory pressure was higher in VCV (20 vs 18) and dynamics compliance was low in VCV (31.3 vs 35.93). Minute ventilation, EtCO2, dead space, O2 saturation was comparable in two groups though alveolar oxygenation was better in PCV. Diastolicblood pressure was low in VCV. Postoperative PFT decreased in both groups but were comparable.Conclusion:PCV is better than VCV in maintaining intraoperative respiratory mechanisms but whether they offer long term benefit require more studies comprising of larger sample sizes.

COMPARATIVE STUDY OF PRESSURE CONTROL VENTILATION VERSUS VOLUME CONTROL VENTILATION IN PEDIATRIC ICU PATIENTS NEEDING MECHANICAL VENTILATION FOR OXYGENATION AND AIRWAY PRESSURES

Background: To evaluate whether in pediatric patients requiring mechanical ventilation does volume control ventilation as compared to pressure control ventilation improve the oxygenation and other airway parameters . We conducted a randomized , prospective study on 133 patient who were randomly allocated in volume control and pressure control modes and the partial pressure of oxygen and carbon-di-oxide in the blood gas analysis of patients in both the groups were compared . Results: The results of outcome variables were suggestive of improved oxygenation but raised airway pressure in VC group compared to PC. Conclusions: Improved oxygenation was observed in Volume control mode as compared to pressure control mode . However airway pressure was significantly higher in the volume control group . The difference in outcome due to these differences needs further research.

Assessment of Regional Ventilation During Recruitment Maneuver by Electrical Impedance Tomography in Dogs.

BackgroundDuring protective mechanical ventilation, electrical impedance tomography (EIT) is used to monitor alveolar recruitment maneuvers as well as the distribution of regional ventilation. This technique can infer atelectasis and lung overdistention during mechanical ventilation in anesthetized patients or in the ICU. Changes in lung tissue stretching are evaluated by monitoring the electrical impedance of lung tissue with each respiratory cycle.ObjectiveThis study aimed to evaluate the distribution of regional ventilation during recruitment maneuvers based on the variables obtained in pulmonary electrical impedance tomography during protective mechanical ventilation, focusing on better lung recruitment associated with less or no overdistention.MethodsProspective clinical study using seven adult client–owned healthy dogs, weighing 25 ± 6 kg, undergoing elective ovariohysterectomy or orchiectomy. The animals were anesthetized and ventilated in volume-controlled mode (7 ml.kg−1) with stepwise PEEP increases from 0 to 20 cmH2O in steps of 5 cmH2O every 5 min and then a stepwise decrease. EIT, respiratory mechanics, oxygenation, and hemodynamic variables were recorded for each PEEP step.ResultsThe results show that the regional compliance of the dependent lung significantly increased in the PEEP 10 cmH2O decrease step when compared with baseline (p < 0.027), and for the nondependent lung, there was a decrease in compliance at PEEP 20 cmH2O (p = 0.039) compared with baseline. A higher level of PEEP was associated with a significant increase in silent space of the nondependent regions from the PEEP 10 cmH2O increase step (p = 0.048) until the PEEP 15 cmH2O (0.019) decrease step with the highest values at PEEP 20 cmH20 (p = 0.016), returning to baseline values thereafter. Silent space of the dependent regions did not show any significant changes. Drive pressure decreased significantly in the PEEP 10 and 5 cmH2O decrease steps (p = 0.032) accompanied by increased respiratory static compliance in the same PEEP step (p = 0.035 and 0.018, respectively).ConclusionsThe regional ventilation distribution assessed by EIT showed that the best PEEP value for recruitment maintenance, capable of decreasing areas of pulmonary atelectasis in dependent regions promoting less overinflation in nondependent areas, was from 10 to 5 cmH2O decreased steps.

Oxygen Delivery With an Open Oxygen Mask and Other Conventional Masks: A Simulation-Based Study.

A recently introduced open oxygen mask design was marketed in 2021 (open mask A). The manufacturer claims that the mask "…provides one solution for all your oxygen delivery needs across your patients' continuum of care." The new oxygen mask specifies flow (1-15 L/min and flush) with an expected FIO2 from 0.25-0.85. This suggests that this mask eliminates the need for multiple oxygen delivery devices as FIO2 requirements change. This study aimed to describe the FIO2 performance of the new open oxygen mask and other commonly used oxygen masks. The following oxygen masks were studied: open mask A, open mask B, simple mask, partial rebreather, and non-rebreather. An adult mannequin head was attached to a breathing simulator, which recorded FIO2 at the simulated alveolar level. The simulator was set to a closed-loop volume control mode: VT = 320 mL, compliance = 50 mL/cm H2O, resistance = 4 cm H2O/L/s, breathing frequency = 15 breaths/min, increase = 25%, hold = 0%, and release = 30%. Oxygen was run through each mask at the recommended flows. Each flow was verified with a flow analyzer before attaching the mask for oxygen measurement. Each experiment was performed twice. The FIO2 measurements were averaged and compared using a 2-way ANOVA with P < .05 indicating significance. The FIO2 delivery was significantly different for each device. The measured FIO2 range was open mask A, 0.30-0.60; open mask B, 0.28-0.64; simple mask, 0.55-0.73; partial non-rebreather, 0.73-1.0; non-rebreather, 0.93-1.00. The performance of each oxygen mask from highest to lowest FIO2 : non-rebreather, partial rebreather, simple mask, open mask A, and open mask B. These findings suggest that no oxygen mask tested serves as a substitute for the others across a flow range of 1-15 L/min and flush.

High-flow nasal cannula therapy, factors affecting effective inspired oxygen fraction: an experimental adult bench model

Oxygenation through High Flow Delivery Systems (HFO) is described as capable of delivering accurate FiO2. Meanwhile, peak inspiratory flow dot{V}_{{text{I}}} ) of patients with acute hypoxemic respiratory failure can reach up to 120 L/min, largely exceeding HFO flow. Currently, very few data on the reliability of HFO devices at these high dot{V}_{{text{I}}} are available. We sought to evaluate factors affecting oxygenation while using HFO systems at high dot{V}_{{text{I}}} in a bench study. Spontaneous breathing was generated with a mechanical test lung connected to a mechanical ventilator Servo-i®, set to volume control mode. Gas flow from a HFO device was delivered to the test lung. The influence on effective inspired oxygen fraction of three parameters (FiO2 0.6, 0.8, and 1, dot{V}_{{text{I}}} from 28 to 98.1 L/min, and HFO Gas Flows from 40 to 60 L/min) were analyzed and are reported. The present bench study demonstrates that during HFO treatment, measured FiO2 in the lung does not equal set FiO2 on the device. The substance of this variation (ΔFiO2) is tightly correlated to dot{V}_{{text{I}}} (Pearson’s coefficient of 0.94, p-value < 0.001). Additionally, set FiO2 and Flow at HFO device appear to significatively affect ΔFiO2 as well (p-values < 0.001, adjusted to dot{V}_{{text{I}}} ). The result of multivariate linear regression indicates predictors (dot{V}_{{text{I}}} , Flow and set FiO2) to explain 92% of the variance of delta FiO2 through K-Fold Cross Validation. Moreover, adjunction of a dead space in the breathing circuit significantly decreased ΔFiO2 (p < 0.01). The present bench study did expose a weakness of HFO devices in reliability of delivering accurate FIO2 at high dot{V}_{{text{I}}} as well as, to a lesser extent, at dot{V}_{{text{I}}} below equivalent set HFO Flows. Moreover, set HFO flow and set FIO2 did influence the variability of effective inspired oxygen fraction. The adjunction of a dead space in the experimental set-up significantly amended this variability and should thus be further studied in order to improve success rate of HFO therapy.

Accuracy of pulse pressure variations for fluid responsiveness prediction in mechanically ventilated patients with biphasic positive airway pressure mode.

The accuracy of pulse pressure variation (PPV) to predict fluid responsiveness using pressure-controlled (PC) instead of volume-controlled modes is under debate. To specifically address this issue, we designed a study to evaluate the accuracy of PPV to predict fluid responsiveness in severe septic patients who were mechanically ventilated with biphasic positive airway pressure (BIPAP) PC-ventilation mode. 45 patients with sepsis or septic shock and who were mechanically ventilated with BIPAP mode and a target tidal volume of 7-8ml/kg were included. PPV was automatically assessed at baseline and after a standard fluid challenge (Ringer's lactate 500ml). A 15% increase in stroke volume (SV) defined fluid responsiveness. The predictive value of PPV was evaluated through a receiver operating characteristic (ROC) curve analysis and "gray zone" statistical approach. 20 (44%) patients were considered fluid responders. We identified a significant relationship between PPV decrease after volume expansion and SV increase (spearman ρ = -0.5, p < 0.001). The area under ROC curve for PPV was 0.71 (95%CI 0.56-0.87, p = 0.007). The best cut-off (based on Youden's index) was 8%, with a sensitivity of 80% and specificity of 60%. Using a gray zone approach, we identified that PPV values comprised between 5 and 15% do not allow a reliable fluid responsiveness prediction. In critically ill septic patients ventilated under BIPAP mode, PPV appears to be an accurate method for fluid responsiveness prediction. However, PPV values comprised between 5 and 15% constitute a gray zone that does not allow a reliable fluid responsiveness prediction.

Performance of Different Low-Flow Oxygen Delivery Systems.

The delivery of a high and consistent [Formula: see text] is imperative to treat acute hypoxemia. The objective of this study was to analyze the effective inspired oxygen concentration delivered by different low-flow oxygen therapy systems challenged with different oxygen flows and respiratory patterns in an experimental lung model. An adult lung model ventilated in volume control mode simulated different respiratory patterns to obtain mean inspiratory flow of 22.5, 30.0, 37.5, or 45.0 L/min. The oxygen concentration sampled inside the lung model by nasal cannula, simple face mask, non-rebreather mask, and double-trunk mask above nasal cannula tested at oxygen flows of 10, 12.5, and 15 L/min was quantified. The 3 masks were sealed tight onto the model's airway opening. They were also tested with standardized leaks to determine their clinical performance. All oxygen delivery systems delivered higher oxygen concentration with increasing oxygen flows, regardless of the respiratory pattern. Within each device, the increase in inspiratory flow decreased oxygen concentration when using nasal cannula (P = .03), the simple face mask (P = .03), but not the non-rebreather mask (P = .051) nor the double-trunk mask (P = .13). In sealed condition, the double-trunk mask outperformed the non-rebreather mask and simple face mask (P < .001); mean oxygen concentration was 84.2%, 68.5%, and 60.8%, respectively. Leaks amplified oxygen concentration differences between the double-trunk mask and the other masks as the oxygen delivery decreased by 4.6% with simple face mask (95% CI 3.1-6.1%, P < .001), 7.8% with non-rebreather mask (95% CI 6.3-9.3%, P < .001), and 2.5% with double-trunk mask (95% CI 1-4%, P = .002). With leaks, the oxygen concentration provided by the simple face mask and the non-rebreather mask was similar (P = .15). Lung oxygen concentration values delivered by the double-trunk mask were higher than those obtained with other oxygen delivery systems, especially when leaks were present.

Comparison between pressure-controlled ventilation with volume-guaranteed mode and volume-controlled mode in one-lung ventilation in infants undergoing video-assisted thoracoscopic surgery.

BackgroundThe appropriate ventilation mode for one-lung ventilation (OLV) in infants undergoing video-assisted thoracoscopic surgery (VATS) remains controversial. Here we investigated the effect of ventilatory mode “pressure-controlled ventilation-volume guaranteed” (PCV-VG) on the airway pressures and oxygenation parameters by comparing it with volume-controlled ventilation (VCV).MethodsWe retrospectively analyzed the clinical data of infants aged 2 to 12 months who underwent extratracheal bronchial blockage for OLV in our center between January 2017 and August 2020. The infants were divided into two groups according to the OLV pattern: group G (n=30, receiving PCV-VG) and group V (n=28, receiving VCV). Mean arterial pressure (MAP), heart rate (HR), maximum inspiratory pressure (Ppeak), mean airway pressure (Pmean), dynamic compliance (Cdyn), partial arterial pressure of oxygen (PaO2) was measured and compared between these two groups 10 min before OLV (T1), 30 min after the onset of OLV (T2) and 15 min after OLV (T3). The possible occurrence of hypoxemia and hypotension during OLV was monitored.ResultsCompared to group V, group G had significantly higher PaO2and Cdyn (both P<0.05) and significantly lower Ppeak and Pmean (both P<0.05) in T2. However, all indicators did not show significant differences between these two groups at T1 and T3 (all P>0.05). The incidence of hypoxemia was significantly higher in group V than in group G (P<0.05), while the difference in the incidence of hypotension was not statistically significant (P>0.05).ConclusionsMechanical ventilation using the PCV-VG mode is possible in infants when performing OLV during VATS. Compared to VCV, PCV-VG can offer lower Ppeak and Pmean, improve lung compliance, and achieve better oxygenation.

INFLUENCE OF RESPIRATORY SUPPORT STRATEGY DURING CARDIOPULMONARY BYPASS ON LUNGS OXYGENATING FUNCTION

Introduction There are high incidence of pulmonary complications and acute respiratory failure (3,2—28,6%)¹ after cardiac surgery with cardiopulmonary bypass. The study aimed to evaluate the effectiveness of various tactics of respiratory support during cardiopulmonary bypass (CPB) for the prevention of postoperative pulmonary complications. Methods This is a prospective, randomized, controlled clinical study in parallel groups. The study was approved by a local ethics committee. Informed consent was obligatory for all participants. Sixty patients were divided into two groups. In group 1 we provided a continuous positive airway pressure (CPAP) of +5 cm H2O during CPB. In group 2 patients underwent mechanical ventilation with reduced volume (volume control (VC) mode, tidal volume 3 ml / kg of ideal body weight) and respiratory rate of 6 breathes per minute with positive end-expiratory pressure + 5 cm H2O. The primary end-point of the study was the value of the partial pressure of oxygen in arterial blood to oxygen fraction in inhaled gas mixture ratio (paO2/FiO2) at different stages of perioperative management: T1 (after the beginning of mechanical ventilation, T2 (before the CPB), T3 (after CPB), T4 (at the end of the surgery), T5 (upon admission to the ICU), T6 and T7 (6 and 12 hours after surgery, respectively). Secondary end-points were the common lung complications rate (pneumonia, pleural effusion, atelectasis, pneumothorax), the frequency of recruitment maneuvers during the mechanical ventilation, the need for non-invasive ventilation after extubation, the frequency of re-intubation of the trachea. Statistical analysis was carried out in SPSS for Mac v19 (IBM, Inc, USA). Data were presented as mean (±standard deviation) or number (percent). A comparison of the quantitative characteristics was performed using the Mann Whitney U-test. Fisher's exact test was used for the incidence of complications between groups. A p value of less than 0.05 was considered statistically significant. Results The results are presented in Tables 1 and 2. The paO2/FiO2 in the VC group was higher than in the CPAP group at stages T3 and T5. The frequency of recruiting maneuvers in the VC group was lower than in the CPAP group. There was a lower incidence of atelectasis in the VC group than in the CPAP group (Table 2). The low-volume lung ventilation during the CPB is beneficial for oxygenating function of the lungs in comparison with CPAP respiratory support. Discussion The low-volume lung ventilation during the CPB is beneficial for oxygenating function of the lungs in comparison with CPAP respiratory support.

SARS-COV-2-RELATED PNEUMOMEDIASTINUM: A RARE PRESENTATION OF AN EQUALLY RARE COMPLICATION

TOPIC: Critical Care TYPE: Fellow Case Reports INTRODUCTION: Pneumomediastinum is a rare entity in viral pneumonias. Only about 1% of patients in the ARDSNet trials developed pneumomediastinum as an early complication in the first four days of mechanical ventilation. With SARS-CoV-1, there were reports of late development of barotrauma complications, but there are very few case reports of pneumomediastinum in the current pandemic. We present a case of a tension pneumomediastinum and pneumoperitoneum as a complication of SARS-CoV-2. CASE PRESENTATION: An 86-year-old female was hospitalized for respiratory failure secondary to COVID-19. She was treated and discharged to a nursing facility requiring supplemental oxygen. Two days later, she developed worsening respiratory failure requiring intubation and mechanical ventilation with pressure-regulated volume control mode. CT imaging on admission revealed only viral pneumonia changes. Despite open lung ventilation strategy, she required plateau pressures of 32cmH20 to maintain adequate gas exchange. Hospital day 10, her respiratory failure worsened with increased plateau pressures of 40cmH20 despite no changes in her ventilator settings. She required paralysis and proning at that time with no changes on chest x-ray and no abnormalities were appreciated on exam other than developing ventilator dyssynchrony. She deteriorated further on hospital day 15 with development of shock and chest x-ray demonstrating possible free air in the mediastinum and abdomen. CT confirmed massive amounts of intraperitoneal, retroperitoneal, and mediastinal air without pneumothorax. Given her poor prognosis, she was transitioned to comfort measures and expired. DISCUSSION: COVID-19-related pneumomediastinum is thought to develop from diffuse alveolar injury and fibrosis leading to increased alveolar pressures, which ultimately rupture. Barotrauma from mechanical ventilation exacerbates this. Patients may be asymptomatic or they may have signs of tachycardia, tachypnea, and/or subcutaneous emphysema with upper chest and neck swelling. Tension pneumomediastinum is an exceedingly rare but life threatening development in critically ill patients. The development of pneumomediastinum related to SARS-CoV-2 seems to occur later in the disease course when compared to ARDSNet trials, however this may be similar to reports in SARS-CoV-1. CONCLUSIONS: Despite the rare occurrence of pneumomediastinum in viral pneumonia, providers should be aware of this potential late complication in SARS-CoV-2 and take measures for prevention and early recognition. Without adjusting treatment, tension pneumomediastinum may develop and lead to a significant increase in mortality. REFERENCE #1: Chu CM, et al. Spontaneous pneumomediastinum in patients with severe acute respiratory syndrome. European Respiratory Journal 2004 23: 802-804;DOI: 10.1183/09031936.04.00096404 REFERENCE #2: Mart M, et al. Pneumomediastinum in Acute Respiratory Distress Syndrome from COVID-19. Am J Respir Crit Care Med Vol 203, Iss 2, pp 237–238. DOI: 10.1164/rccm.202008-3376IM REFERENCE #3: Clancy DJ, et al. Tension pneumomediastinum: a literal form of chest tightness. J Intensive Care Soc 2017;18(1): 52–56. DISCLOSURES: No relevant relationships by Rayan Ihle, source=Web Response No relevant relationships by Mark Radow, source=Web Response

Aerosol delivery of inhalation devices with different add-on connections to invasively ventilated COPD subjects: An in-vivo study

Aerosol delivery to mechanically ventilated patients requires add-on connections to place the inhalation device within the ventilation circuit. The study aimed to evaluate the performance of Combihaler in dual limb invasive mechanical ventilation (IMV).A ventilator with a humidified dual limb circuit was adjusted to volume-controlled mode to imitate the adult breathing parameters. 24 (12 females) intubated chronic obstructive pulmonary disease (COPD) subjects had undergone the study. All patients were prescribed inhaled salbutamol dose delivered by either a metered-dose inhaler (pMDI) or vibrating mesh nebulizer (VMN). Each subject received salbutamol in four different inhalation device/connection conditions; pMDI+VMN+Combihaler, VMN+Combihaler, VMN+T-piece, and pMDI+T-piece. They were individually placed in the inspiratory limb at Y-piece. 5mg salbutamol was delivered by VMN with and without 2 pMDI puffs of salbutamol (100 µg), and 500µg was delivered by pMDI+T-piece. After aerosol delivery, two urine samples were collected from the patient; 30 min post-inhalation (USAL0.5) and cumulatively 24 h post-inhalation (USAL24) as indexes of lung deposition and systemic absorption, respectively. For the ex-vivo study, a collecting filter was placed before an endotracheal tube (ETT) to collect the delivered inhalable dose. In-vitro aerodynamic characteristics were also investigated.pMDI+VMN+Combihaler delivered more salbutamol to the lung and the ex-vivo filter than VMN+T-piece (p˂0.05, p≤0.01, respectively). VMN delivered a higher salbutamol amount to the lung, systemically, and the ex-vivo filter than pMDI+T-piece (p˂0.001). pMDI+VMN+Combihaler and VMN+Combihaler delivered aerosols with a less mass median aerodynamic diameter (MMAD) and higher fine particle fraction (FPF) compared to VMN+T-piece (p≤0.01 for MMAD, p˂0.01 for FPF) and pMDI+T-piece (p˂0.01 for both MMAD and FPF).Results of the study showed that pMDI+VMN+ Combihaler delivered more salbutamol than VMN+T-piece in IMV and demonstrate that 5 puffs (500-µg) of salbutamol with pMDI+T-piece has a lower aerosol delivering power at the level of USAL0.5, USAL24, and the ex-vivo inhalable dose than 5 mg nebulized salbutamol by VMNs in IMV.

A Simple Ventilator Designed To Be Used in Shortage Crises: Construction and Verification Testing

BackgroundThe COVID-19 pandemic has demonstrated the possibility of severe ventilator shortages in the near future.ObjectiveWe aimed to develop an acute shortage ventilator.MethodsThe ventilator was designed to mechanically compress a self-inflating bag resuscitator, using a modified ventilator patient circuit, which is controlled by a microcontroller and an optional laptop. It was designed to operate in both volume-controlled mode and pressure-controlled assist modes. We tested the ventilator in 4 modes using an artificial lung while measuring the volume, flow, and pressure delivered over time by the ventilator.ResultsThe ventilator was successful in reaching the desired tidal volume and respiratory rates specified in national emergency use resuscitator system guidelines. The ventilator responded to simulated spontaneous breathing.ConclusionsThe key design goals were achieved. We developed a simple device with high performance for short-term use, made primarily from common hospital parts and generally available nonmedical components to avoid any compatibility or safety issues with the patient, and at low cost, with a unit cost per ventilator is less than $400 US excluding the patient circuit parts, that can be easily manufactured.

Flow-controlled expiration (FLEX) homogenizes pressure distribution in a four compartment physical model of the respiratory system with chest wall compliance

Objective. Flow-controlled expiration (FLEX) has been shown to attenuate ventilator-induced lung injury in animal models. It has also shown to homogenize compartmental pressure distribution in a physical model of the inhomogeneous respiratory system having independent compartments. We hypothesized that the homogenizing effects of FLEX are also effective in this regard when the independence of compartments is suspended by simulated chest wall compliance. Approach. A four compartment physical model of the respiratory system having chest wall compliance (137 ml/cmH2O) was developed. Two of the four compartments had high compliance (18 ml/cmH2O) and two had low compliance (10 ml/cmH2O). These compartments were each combined with either high (6.8 cmH2O·s/l) or low resistance (3.5 cmH2O·s/l). The model was ventilated in the volume-controlled ventilation mode with either passive expiration or with FLEX. The maximal pressure differences (ΔP max) and the maximal differences of mean pressure (ΔP mean) between the compartments during expiration were determined. Main results. With passive expiration ΔP max reached up to 3.4 ± 0.03 cmH2O but only 0.9 ± 0.01 cmH2O with FLEX (p < 0.001). Maximal differences of ΔP mean were significantly lower with FLEX as compared to passive expiration (extending up to 0.4 ± 0.04 cmH2O versus 2.0 ± 0.15 cmH2O, p < 0.001). Significance. The homogenizing effects of FLEX on compartmental pressure distribution could be reproduced in a more complex physical model of the inhomogeneous respiratory system having chest wall compliance and might be a mechanism underlying the lung protective effects of ventilation with FLEX.

Design and simulation of mechanical ventilators.

During this period of COVID-19 pandemic, the lack of medical equipment (like ventilators) leads to complications arising in the medical field. A low-cost ventilator seems to be an alternative substitute to fill the lacking. This paper presents a numerical analysis for predicting the delivered parameters of a low-cost mechanical ventilator. Based on several manufactured mechanical ventilators, two proposed designs are investigated in this study. Fluid-structure interaction (FSI) analysis is used for solving any problems with the first design, and computational fluid dynamic (CFD) analysis with moving boundary is used for solving any issues with the second design. For this purpose, ANSYS Workbench platform is used to solve the set of equations. The results showed that the Ambu-bag-based mechanical ventilator exhibited difficulties in controlling ventilation variables, which certainly will cause serious health problems such as barotrauma. The mechanical ventilator based on piston-cylinder is more satisfactory with regards to delivered parameters to the patient. The ways to obtain pressure control mode (PCM) and volume control mode (VCM) are identified. Finally, the ventilator output is highly affected by inlet flow, length of the cylinder, and piston diameter.

VEMERS UC: A Clinically Validated Emergency Mechanical Ventilator for COVID-19 and Postpandemic Use in Low Resource Communities

Abstract In this article, we present a clinically validated invasive emergency mechanical ventilator developed in Chile called VEMERS UC. It has been clinically tested and validated in intubated Covid-19 patients. Once the pandemic hit Chilean soil in March 2020, it was quite clear that the number of mechanical ventilators available would not be enough. As in other parts of the world many initiatives sprung, most of them naively simple. Chilean medical societies joined engineering specialists and agreed early on in an organized and regulated open process for validating emergency mechanical ventilators, thus allowing for rapid development but with the required functionality, reliability, and safety features. VEMERS UC was one of a few that completed successfully all stages of the validating process, the final test being on five critically ill intubated Covid-19 patients for eight hours each. VEMERS UC is based on an electropneumatic circuit architecture, and its components are all low cost, off-the-shelf pneumatic, and electronic products easily obtained in industrial markets. It works in continuous mandatory volume control mode. The novel technical features of VEMERS UC are discussed here as well as the results obtained in each stage of the validating process. The validating process carried out in Chile is noteworthy by itself, and it could be used as an example in other developing countries. Furthermore, VEMERS UC can be used as a guiding design reference in other countries as well, since this design has already been thoroughly tested in human patients and has proven to work successfully.

Electrical Impedance Tomography for Positive End-Expiratory Pressure Setting after Bilateral Lung Transplantation

Purpose After lung transplantation (LT) the magnitude of graft recruitability is variable, therefore postoperative personalized positive end-expiratory pressure (PEEP) setting is desirable in order to minimize ventilator-induced lung injury and to reduce pulmonary complications [1]. Electrical impedance tomography (EIT) offers this opportunity by bedside estimating both alveolar collapse and overdistension throughout a decremental PEEP trial [2]. This study aims to assess the reliability of EIT-based PEEP selection compared to PEEP titration to the best respiratory system static compliance (Crs) after LT [3]. Methods All patients were deeply sedated without spontaneous breathing efforts and ventilated in volume control mode with lung-protective settings [1]. At Intensive Care Unit admission after LT, PEEP was adjusted to best Crs (PEEPCrs). Subsequently, an EIT-based decremental PEEP trial was performed through a dedicated device (Pulmovista500, Drӓger-Medical, Germany). EIT optimal PEEP (PEEPEIT) was defined as the best compromise between lung collapse and overdistension [2]. PEEPEIT was compared with PEEPCrs using Mann-Whitney test. Data are expressed as median and interquartile ranges. Results Six bilateral LT patients were enrolled (4 pulmonary fibrosis, 1 bronchiectasis and 1 bronchiolitis obliterans syndrome). Age was 57 (52-63) years and body mass index was 23.3 (20.0-25.6) kg/m2. PEEPEIT was 9 (8-13) cmH2O, not significantly different from PEEPCrs [9 (7-9) cmH2O, p = 0.413]. The loss of lung compliance due to lung collapse observed with PEEPEIT [4.8% (4.1-7.3%)] was comparable to that obtained with PEEPCrs [8.0% (6.5-12.3%) (p = 0.195)]. The loss of lung compliance consequent to lung overdistension was similar between PEEPEIT and PEEPCrs [4.0% (2.5-5.0%) vs. 1.8% (1.1-2.4%) (p = 0.134)]. Conclusion After LT, EIT is a reliable tool for individualized PEEP setting, with analogous performances to PEEP titration to the best Crs. Whether EIT is to be preferred for this purpose and the overall clinical influence of personalizing PEEP based on EIT after LT remain to be determined.

Respiratory and Hemodynamic Effects of Prophylactic Alveolar Recruitment During Liver Transplant: A Randomized Controlled Trial.

Prolonged surgical retraction may cause atelectasis. We aimed to recruit collapsed alveoli, stepwise, monitored by lung dynamic compliance and observe effects on arterial oxygenation and systemic and graft hemodynamics. Secondarily, we observed alveolar recruitment effects on postoperative mechanical ventilation, international normalized ratio, and pulmonary complications. For 58 recipients (1 excluded), randomized with optimal positive end-expiratory pressure (n = 28) versus control (fixed positive end-expiratory pressure, 5 cm H₂O; n = 29), alveolar recruitment was initiated (pressure-controlled ventilation guided by lung dynamic compliance) to identify optimal conditions. Ventilation shifted to volume-control mode with 0.4 fraction of inspired oxygen, 6 mL/kg tidal volume, and 1:2 inspiratory-to-expiratory ratio. Alveolar recruitment was repeated postretraction and at intensive care unit admission. Primary endpoints were changes in lung dynamic compliance, arterial oxygenation, and hemodynamics (cardiac output, invasive arterial and central venous pressures, graft portal and hepatic vein flows). Secondary endpoints were mechanical ventilation period and postoperative international normalized ratio, aspartate/alanine aminotransferases, lactate, and pulmonary complications. Alveolar recruitment increased positive end-expiratory pressure, lung dynamic compliance, and arterial oxygenation (P < .01) and central venous pressure (P = .004), without effects on corrected flow time (P = .7). Cardiac output and invasive arterial pressure were stable with (P = .11) and without alveolar recruitment (P = .1), as were portal (P = .27) and hepatic vein flow (P = .30). Alveolar recruitment reduced postoperative pulmonary complications (n = 0/28 vs 8/29; P = .001), without reduction in postoperative mechanical ventilation period (P = .08). International normalization ratio, aspartate/alanine aminotransferases, and lactate were not different from control (P > .05). Stepwise alveolar recruitment identified the optimal positive end-expiratory pressure to improve lung mechanics and oxygenation with minimal hemodynamic changes, without liver graft congestion/dysfunction, and was associated with significant reduction in postoperative pulmonary complications.

Ventilated Patients With COVID-19 Show Airflow Obstruction

Objective:Many patients with coronavirus disease 2019 (COVID-19) need mechanical ventilation secondary to acute respiratory distress syndrome. Information on the respiratory system mechanical characteristics of this disease is limited. The aim of this study is to describe the respiratory system mechanical properties of ventilated COVID-19 patients.Design, Setting, and Patients:Patients consecutively admitted to the medical intensive care unit at the University of Iowa Hospitals and Clinics in Iowa City, USA, from April 19 to May 1, 2020, were prospectively studied; final date of follow-up was May 1, 2020.Measurements:At the time of first patient contact, ventilator information was collected including mode, settings, peak airway pressure, plateau pressure, and total positive end expiratory pressure. Indices of airflow resistance and respiratory system compliance were calculated and analyzed.Main Results:The mean age of the patients was 58 years. 6 out of 12 (50%) patients were female. Of the 21 laboratory-confirmed COVID-19 patients on invasive mechanical ventilation, 9 patients who were actively breathing on the ventilator were excluded. All the patients included were on volume-control mode. Mean [±standard deviation] ventilator indices were: resistive pressure 19 [±4] cmH2O, airway resistance 20 [±4] cmH2O/L/s, and respiratory system static compliance 39 [±16] ml/cmH2O. These values are consistent with abnormally elevated resistance to airflow and reduced respiratory system compliance. Analysis of flow waveform graphics revealed a pattern consistent with airflow obstruction in all patients.Conclusions:Severe respiratory failure due to COVID-19 is regularly associated with airflow obstruction.