Pressure-controlled Ventilation Research Articles

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

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

Lived experiences of caregivers with infants treated at home with continuous invasive or noninvasive ventilation.

Caring for children dependent upon continuous invasive ventilation in the home setting requires extensive expertise, coordination, and can result in impaired caregiver quality of life. Less is known regarding the experiences of caregivers with children requiring continuous noninvasive ventilation. To evaluate caregiver experiences with invasive and noninvasive home mechanical ventilation, and to compare parental quality of life based on the child's mode of ventilation. Caregivers of infants who were discharged home with continuous ventilatory support were recruited to complete semi-structured qualitative interviews. Interviews explored their decision-making process, the transition to home, and health related quality of life. Caregivers of 16 children were interviewed, of whom eight were treated with continuous invasive ventilation, and eight with continuous noninvasive ventilation. The decision to pursue home ventilation in both groups was greatly influenced by the desire to be discharged and reunite the family at home. Following the transition to home, caregivers from both groups described high rates of insomnia, emotional distress, work disruption and familial hardship. Despite this, parents were overwhelmingly pleased with the decision to proceed with home ventilation and perceived their children to be living enriched lives outside of the hospital. Factors associated with easing the transition to home were in-hospital training and the presence of a robust support system. Lives of families with children dependent on continuous mechanical ventilation are characterized by isolation, lifestyle disruption, adverse mental and physical health consequences, and impaired interpersonal relationships, irrespective of the mode of ventilation.

Incidence and risk factors of postoperative delirium following hepatic resection: a retrospective national inpatient sample database study

BackgroundPostoperative delirium (POD) is a common complication after major surgery and can cause a variety of adverse effects. However, no large-scale national database was used to assess the occurrence and factors associated with postoperative delirium (POD) following hepatic resection.MethodsPatients who underwent hepatic resection from 2015 to 2019 were screened using the International Classification of Diseases (ICD) 10th edition clinical modification code from the National Inpatient Sample (NIS) Database. Peri-operative factors associated with delirium were screened and underwent statistical analysis to identify independent predictors for delirium following hepatic resection.ResultsA total of 80,070 patients underwent hepatic resection over a five-year period from 2015 to 2019. The overall occurrence of POD after hepatic resection was 1.46% (1039 cases), with a slight upward trend every year. The incidence of elective admission was 6.66% lower (88.60% vs. 81.94%) than that of patients without POD after hepatic resection and 2.34% (45.53% vs. 43.19%) higher than that of patients without POD in teaching hospitals (P < 0.001). In addition, POD patients were 6 years older (67 vs. 61 years) and comprised 9.27% (56.69% vs. 47.42%) more male patients (P < 0.001) compared to the unaffected population. In addition, the occurrence of POD was associated with longer hospitalization duration (13 vs. 5 days; P < 0.001), higher total cost ($1,481,89 vs. $683,90; P < 0.001), and higher in-hospital mortality (12.61% vs. 4.11%; P < 0.001). Multivariate logistic regression identified hepatic resection-independent risk factors for POD, including non-elective hospital admission, teaching hospital, older age, male sex, depression, fluid and electrolyte disorders, coagulopathy, other neurological disorders, psychoses, and weight loss. In addition, the POD after hepatic resection has been associated with sepsis, dementia, urinary retention, gastrointestinal complications, acute renal failure, pneumonia, continuous invasive mechanical ventilation, blood transfusion, respiratory failure, and wound dehiscence / non-healing.ConclusionAlthough the occurrence of POD after hepatic resection is relatively low, it is beneficial to investigate factors predisposing to POD to allow optimal care management and improve the outcomes of this patient population.

An open-source research platform for mechanical ventilation based on Simulink® and STM32 nucleo

Abstract Gain in knowledge in experimental fields of research is mostly achieved using commercial hardware platforms. The linked costs however can limit a broad access by scientists and in the specific case of mechanical ventilation the pandemic demonstrated that further and collective research is essential and necessary. This contribution presents the modular design and implementation of a research platform which is based on STM32 Nucleo boards and Simulink®. The hardware required such as the pneumatic circuit are covered as well as the software architecture in which clinician related settings are processed for control references. The core functionality of mandatory volume controlled (VCV) and pressure controlled ventilation (PCV) while ensuring a positive end-expiratory pressure for the patient ( PEEP ) $(\text{PEEP})$ is evaluated and the foundational software models are published in a repository.

A novel collision avoidance strategy for highway overtaking considering the driver’s steering intent

Intelligent driving has been prevailing worldwide and is also challenging, which can be complicated by the factors of human drivers. In this paper, a novel collision avoidance strategy is proposed to enhance driving safety in highway overtaking by comprehensively considering the driver’s steering intent. First, in order to capture the driver’s operational characteristics from the driving data, we formulate the prediction of the driver’s steering intent and the ego vehicle’s states as a multivariate time series (MTS) forecasting problem, which is then handled by deep learning with a time pattern attention mechanism (DL-Attn). Second, a predictive risk field (PRF) model is proposed to quantify the real-time overtaking risk based on the above prediction results. Then, the overtaking is evaluated via a personalized risk threshold which can be set for a specific driver via experiments. Next, a linear time-varying model predictive control (LTV-MPC) -based assistance controller is designed so as to interfere in the risky overtaking and take over the ego vehicle from the driver to avoid possible collisions. And the feasibility and stability of the closed system are ensured theoretically. Finally, experiments are carried out in three typical cases. The results demonstrate that the proposed strategy can not only effectively improve driving safety for highway overtaking, but also identify safe overtaking to avoid unnecessary interference.

An Audio - Visual Virtual Personal Assistant

Current traits in smart assistants and smart home automation are currently attracting the interests of customers and researchers. Speech enabled smart virtual assistants (named smart speakers) offer a wide sort of network orientated services and, in some instances, can connect to smart environments, accordingly improving them with new and effective user interfaces. But, such gadgets also reveal new desires and a few weaknesses. Specially, they constitute faceless and blind assistants, not able to reveal a face, and therefore an emotion, and not able to ‘see’ the person. For this reason, the interaction is impaired and, in a few cases, ineffective. One of the goals of artificial intelligence is the realization of natural talk among humans and machines. In latest years, the dialogue systems, known as interactive conversational systems are the fastest developing vicinity in AI. Many companies have used the dialogue systems technology to set up various sorts of VPAs based on their application areas, including Apple’s Siri, Amazon Alexa, etc. To triumph over such troubles, in this project we combine a number of advance techniques. The proposed Assistant is powerful and resource-efficient, interactive and customizable. We use the multi-modal dialogue structures and screen projection which process two or more combined user input modes, which includes speech, image, video, touch, manual gestures, body movements with the intention to design the NextGeneration of VPAs. The new version of VPAs can be used to increase the interaction between humans and machines by the usage of distinctive technologies, consisting of gesture recognition, image/video recognition, speech recognition, dialogue system, conversational information base, and the overall knowledge base. Furthermore, this VPA device can be utilized in different areas such as education, medical assistance, disabilities systems, home automation and security access control.

Bedside critical care training: A quasi-experimental study in the paediatric emergency department of a referral hospital in Nigeria

Background. There is a need for critical care services outside intensive care units (ICUs), especially in emergency departments (EDs). However, there is a paucity of skilled manpower for ED critical care or emergency critical care (ECC) in resource-limited settings. Objective. To evaluate the impact of bedside training on emergency critical care practices of clinical staff. Methods. This was a quasi-experimental study using a pretest - post-test design in a paediatric ED. The intervention was a six-week structured bedside training on bubble continuous positive airway pressure (CPAP) high-flow nasal cannula (HFNC) and mechanical ventilation. Participants’ actual ECC practices pre and post training were evaluated, including their perceived proficiency on an uncalibrated 100 mm visual analogue scale (VAS). Descriptive and inferential analyses were done; p&lt;0.05 was considered significant. Results. A total of 35 clinical staff participated in the training, comprising 9 (24.3%) paediatric registrars, 12 (32.5%) senior registrars, 10 (27.0%) nurses, 4 (10.8%) house officers and 2 (5.4%) paediatric consultants. The male:female ratio of the participants was 1:1.6, and their mean (SD) age was 33.24 (6.30 years. Participants’ understanding of testing the CPAP circuit, connecting the patient and weaning significantly improved following training (p=0.004). Their capacity to select appropriate HFNC parameters improved (p=0.013). They performed more endotracheal intubations in the post-training period (p=0.001). Their pretest-post-test proficiency in mechanical ventilation increased on VAS (mean scores 45.26+31.99 v. 63.26+22.26; p=0.038). Also, there was a significant increase in their perceived proficiency in paediatric analgesia/sedation (30.83+29.86 v. 49.83+23.90; p=0.029). Conclusion. Short-term bedside critical care training enhanced the self-reported competency of paediatric ED staff. There is a need for on-the-job ECC training and retraining of clinical staff in our setting.

Novel Extension Control Instrument for Power Wheelchair Based on Kalman Filter Head Motion Detection

People with upper limb disabilities or high quadriplegia have extremely high requirements for the maneuverability and functionality of power wheelchairs. Normal wheelchairs cannot meet travel tasks, while smart customized wheelchairs are expensive and cannot be popularized. Therefore, a novel extension control instrument for power wheelchairs with low cost, strong scalability, and convenient usage is proposed, which can realize the control of the wheelchair by sensing a change of head posture. The device is divided into a head motion sensing unit (HMSU) and a wheelchair assistance control unit (WACU). The mapping relationship between the head attitude and the subject’s motion intention is established. The inertial measurement module in the HMSU collects the head attitude data and uses the Kalman filtering method to obtain the accurate Euler angle. The WACU is fixed on the original controller of the wheelchair. The joystick is inserted into the extended control mechanism and controlled, instead of the hand, through a 2-degree-of-freedom servo system combined with the pinion and rack push rod structure, thus controlling the movement of the wheelchair. In proceeding, the system can also detect the distance of objects in the environment in real time through the three-direction (front, left, right) ultrasonic ranging sensors installed on the WACU, with a certain obstacle avoidance function. The prototype experiments prove that the extension control instrument developed in this paper based on the Kalman filter can quickly and accurately identify head motion and accurately control the movement of the wheelchair. It is easy to operate and has strong universality, which presents a new low-cost solution for the travel of patients with disabilities.

Aspects of state control of social assistance as a function of social protection management in the Republic of Moldova

World experience proves that no state can successfully carry out radical reforms in economic and political, social and cultural life without also having a developed network of social assistance services and specialists, able to protect people in difficulty. In this context, in addition to regulations, reforms, training, financing, programs, projects, the need to control their application and capitalization is imposed. As a result, the field of social assistance, which includes a wide spectrum of specific benefits and services, each with particularities in regulation, application, financing, but indispensable for the categories of beneficiaries to whom they are addressed, it is necessary to establish and apply the control function through to institutions with attributions and functions in that direction.

Nocturnal Pressure Controlled Ventilation Improves Sleep Efficiency in Patients Receiving Mechanical Ventilation.

Patients receiving mechanical ventilation commonly experience sleep fragmentation. The present meta-analysis compared the effects of pressure controlled ventilation (PCV) and pressure support ventilation (PSV) on sleep quality. We conducted a search of the PubMed, Embase, and Cochrane Library databases for studies published before November 2023. In this meta-analysis, individual effect sizes were standardized, and the pooled effect size was determined by using random-effects models. The primary outcome was sleep efficiency. The secondary outcomes were wakefulness, percentages of REM (rapid eye movement) sleep and stages 3 and 4 non-REM sleep, the fragmentation index, and the incidence of apneic events. This meta-analysis examined 4 trials that involved 67 subjects. Sleep efficiency was significantly higher in the PCV group than in the PSV group (mean difference 15.57%, 95% CI 8.54%-22.59%). Wakefulness was significantly lower in the PCV group than in the PSV group (mean difference -18.67%, 95% CI -30.29% to -7.04%). The percentage of REM sleep was significantly higher in the PCV group than in the PSV group (mean difference 2.32%, 95% CI 0.20%-4.45%). Among the subjects with a tendency to develop sleep apnea, the fragmentation index was significantly lower in those receiving PCV than PSV (mean difference -40.00%, 95% CI -51.12% to -28.88%). The incidence of apneic events was significantly lower in the PCV group than in the PSV group (risk ratio 0.06, 95% CI 0.01-0.45). Compared with PSV, PCV may improve sleep quality in patients receiving nocturnal mechanical ventilation.

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

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

Albuterol delivery via in-line intrapulmonary percussive ventilation superimposed on conventional mechanical ventilation in an adult lung model.

Background: Intrapulmonary percussive ventilation (IPV) is frequently used for airway clearance, together with delivery of aerosols containing medications. Drug delivery via IPV alone increases with decreasing percussion frequency and correlates with tidal volume (VT) while drug delivery via IPV during conventional mechanical ventilation (IPV/CMV) is not well characterized. We hypothesized that drug delivery via IPV/CMV would take place differently from that via IPV alone due to control of ventilation by CMV. Methods: An adult ventilator circuit was used for IPV/CMV. A normal or diseased lung model was configured to airway resistance (Raw) 5 cm H2O/L/s and lung compliance (CL) 100 mL/cm H2O or Raw 20 cm H2O/L/s and CL 50 mL/cm H2O, respectively. The ventilator settings were: pressure control continuous mandatory ventilation mode, 10 breaths/min, PEEP 5 cm H2O, FIO2 0.21, inspiratory time 1 s, no bias flow, and inspiratory pressure 10 or 15 cm H2O for the normal or diseased lung model, respectively, to reach VT 500 mL with IPV off. Albuterol nebulized from Phasitron 5 was captured in a filter placed before the lung model and quantitated by spectrophotometry. Results: The maximal efficiency of albuterol delivery via IPV/CMV was not different from that via IPV alone (3.7 ± 0.2% vs 4.2 ± 0.3%, mean ± SD of loading dose, P= .12). Albuterol delivery efficiency with IPV/CMV was lower for the diseased lung model than for the normal model (1.6 ± 0.3% vs 3.2 ± 0.5%, mean ± SD, P < .001), which increased with decreasing percussion frequency. In contrast, VT was lower for the normal lung model than for the diseased model (401 ± 14 mL vs 470 ± 11 mL, mean ± SD, P < .001). Conclusions: Albuterol delivery via IPV/CMV was modulated by percussion frequency but not increased with increasing VT The delivery efficiency was not sufficiently high for clinical use, in part due to nebulizer retention and extrapulmonary deposition.

Respiratory entrainment related reverse triggering in mechanically ventilated children

BackgroundThe underlying pathophysiological pathways how reverse triggering is being caused are not fully understood. Respiratory entrainment may be one of these mechanisms, but both terms are used interchangeably. We sought to characterize reverse triggering and the relationship with respiratory entrainment among mechanically ventilated children with and without acute lung injury.MethodsWe performed a secondary phyiology analysis of two previously published data sets of invasively mechanically ventilated children < 18 years with and without lung injury mechanically ventilated in a continuous or intermittent mandatory ventilation mode. Ventilator waveforms, electrical activity of the diaphragm measured with surface electromyography and oesophageal tracings were analyzed for entrained and non-entrained reverse triggered breaths.ResultsIn total 102 measurements (3110 min) from 67 patients (median age 4.9 [1.8 ; 19,1] months) were analyzed. Entrained RT was identified in 12 (12%) and non-entrained RT in 39 (38%) recordings. Breathing variability for entrained RT breaths was lower compared to non-entrained RT breaths. We did not observe breath stacking during entrained RT. Double triggering often occurred during non-entrained RT and led to an increased tidal volume. Patients with respiratory entrainment related RT had a shorter duration of MV and length of PICU stay.ConclusionsReverse triggering is not one entity but a clinical spectrum with different mechanisms and consequences.Trial registrationNot applicable.

Effects of unilateral superimposed high-frequency jet ventilation on porcine hemodynamics and gas exchange during one-lung flooding.

Superimposed high-frequency jet ventilation (SHFJV) is suitable for respiratory motion reduction and essential for effective lung tumor ablation. Fluid filling of the target lung wing one-lung flooding (OLF) is necessary for therapeutic ultrasound applications. However, whether unilateral SHFJV allows adequate hemodynamics and gas exchange is unclear. To compared SHFJV with pressure-controlled ventilation (PCV) during OLF by assessing hemodynamics and gas exchange in different animal positions. SHFJV or PCV was used alternatingly to ventilate the non-flooded lungs of the 12 anesthetized pigs during OLF. The animal positions were changed from left lateral position to supine position (SP) to right lateral position (RLP) every 30 min. In each position, ventilation was maintained for 15 min in both modalities. Hemodynamic variables and arterial blood gas levels were repeatedly measured. Unilateral SHFJV led to lower carbon dioxide removal than PCV without abnormally elevated carbon dioxide levels. SHFJV slightly decreased oxygenation in SP and RLP compared with PCV; the lowest values of PaO2 and PaO2/FiO2 ratio were found in SP [13.0; interquartile range (IQR): 12.6-5.6 and 32.5 (IQR: 31.5-38.9) kPa]. Conversely, during SHFJV, the shunt fraction was higher in all animal positions (highest in the RLP: 0.30). In porcine model, unilateral SHFJV may provide adequate ventilation in different animal positions during OLF. Lower oxygenation and CO2 removal rates compared to PCV did not lead to hypoxia or hypercapnia. SHFJV can be safely used for lung tumor ablation to minimize ventilation-induced lung motion.

Flow-controlled ventilation decreases mechanical power in postoperative ICU patients

BackgroundMechanical power (MP) is the energy delivered by the ventilator to the respiratory system and combines factors related to the development of ventilator-induced lung injury (VILI). Flow-controlled ventilation (FCV) is a new ventilation mode using a constant low flow during both inspiration and expiration, which is hypothesized to lower the MP and to improve ventilation homogeneity. Data demonstrating these effects are scarce, since previous studies comparing FCV with conventional controlled ventilation modes in ICU patients suffer from important methodological concerns.ObjectivesThis study aims to assess the difference in MP between FCV and pressure-controlled ventilation (PCV). Secondary aims were to explore the effect of FCV in terms of minute volume, ventilation distribution and homogeneity, and gas exchange.MethodsThis is a physiological study in post-cardiothoracic surgery patients requiring mechanical ventilation in the ICU. During PCV at baseline and 90 min of FCV, intratracheal pressure, airway flow and electrical impedance tomography (EIT) were measured continuously, and hemodynamics and venous and arterial blood gases were obtained repeatedly. Pressure–volume loops were constructed for the calculation of the MP.ResultsIn 10 patients, optimized FCV versus PCV resulted in a lower MP (7.7 vs. 11.0 J/min; p = 0.004). Although FCV did not increase overall ventilation homogeneity, it did lead to an improved ventilation of the dependent lung regions. A stable gas exchange at lower minute volumes was obtained.ConclusionsFCV resulted in a lower MP and improved ventilation of the dependent lung regions in post-cardiothoracic surgery patients on the ICU.Trial registration Clinicaltrials.gov identifier: NCT05644418. Registered 1 December 2022, retrospectively registered.

An improved adaptive cruise control law

To increase the efficiency of road transport and reduce exhaust emissions, research has been intensified in assisted control systems, where adaptive cruise control (ACC) and cooperative adaptive cruise control (CACC) stand out. While ACC uses data from onboard sensors and radars, CACC also uses data from inter-vehicle wireless communication. In this context, this paper proposes a new control law for ACC systems that provides a competitive performance compared to CACC, despite not requiring wireless communication between vehicles. The new control law formulation employs both the vehicle acceleration and the relative speed, which generalizes similar ones. The design methodology formulated as a convex optimization problem ensures string and internal stability as well closed-loop pole placement if a set of linear matrix inequalities (LMIs) is satisfied. At the end of the paper, simulations demonstrate the effectiveness of the proposed methodology.

Perception and Action Augmentation for Teleoperation Assistance in Freeform Telemanipulation

Teleoperation enables controlling complex robot systems remotely, providing the ability to impart human expertise from a distance. However, these interfaces can be complicated to use as it is difficult to contextualize information about robot motion in the workspace from the limited camera feedback. Thus, it is required to study the best manner in which assistance can be provided to the operator that reduces interface complexity and effort required for teleoperation. Some techniques that provide assistance to the operator while freeform teleoperating include: (1) perception augmentation, like augmented reality visual cues and additional camera angles, increasing the information available to the operator; (2) action augmentation, like assistive autonomy and control augmentation, optimized to reduce the effort required by the operator while teleoperating. In this article, we investigate: (1) which aspects of dexterous telemanipulation require assistance; (2) the impact of perception and action augmentation in improving teleoperation performance; and (3) what factors impact the usage of assistance and how to tailor these interfaces based on the operators’ needs and characteristics. The findings from this user study and resulting post-study surveys will help identify task-based and user-preferred perception and augmentation features for teleoperation assistance.

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

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

Six methods to determine expiratory time constants in mechanically ventilated patients: a prospective observational physiology study

BackgroundExpiratory time constant (τ) objectively assesses the speed of exhalation and can guide adjustments of the respiratory rate and the I:E ratio with the goal of achieving complete exhalation. Multiple methods of obtaining τ are available, but they have not been compared. The purpose of this study was to compare six different methods to obtain τ and to test if the exponentially decaying flow corresponds to the measured time constants.MethodsIn this prospective study, pressure, flow, and volume waveforms of 30 postoperative patients undergoing volume (VCV) and pressure-controlled ventilation (PCV) were obtained using a data acquisition device and analyzed. τ was measured as the first 63% of the exhaled tidal volume (VT) and compared to the calculated τ as the product of expiratory resistance (RE) and respiratory system compliance (CRS), or τ derived from passive flow/volume waveforms using previously published equations as proposed by Aerts, Brunner, Guttmann, and Lourens. We tested if the duration of exponentially decaying flow during exhalation corresponded to the duration of the predicted second and third τ, based on multiples of the first measured τ.ResultsMean (95% CI) measured τ was 0.59 (0.57–0.62) s and 0.60 (0.58–0.63) s for PCV and VCV (p = 0.45), respectively. Aerts method showed the shortest values of all methods for both modes: 0.57 (0.54–0.59) s for PCV and 0.58 (0.55–0.61) s for VCV. Calculated (CRS * RE) and Brunner’s τ were identical with mean τ of 0.64 (0.61–0.67) s for PCV and 0.66 (0.63–069) s for VCV. Mean Guttmann’s τ was 0.64 (0.61–0.68) in PCV and 0.65 (0.62–0.69) in VCV. Comparison of each τ method between PCV and VCV was not significant. Predicted time to exhale 95% of the VT (i.e., 3*τ) was 1.77 (1.70–1.84) s for PCV and 1.80 (1.73–1.88) s for VCV, which was significantly longer than measured values: 1.27 (1.22–1.32) for PCV and 1.30 (1.25–1.35) s for VCV (p < 0.0001). The first, the second and the third measured τ were progressively shorter: 0.6, 0.4 and 0.3 s, in both ventilation modes (p < 0.0001).ConclusionAll six methods to determine τ show similar values and are feasible in postoperative mechanically ventilated patients in both PCV and VCV modes.

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

BackgroundAim of this study was to evaluate feasibility and effects of individualised flow-controlled ventilation (FCV), based on compliance guided pressure settings, compared to standard of pressure-controlled ventilation (PCV) in a porcine intra-abdominal hypertension (IAH) model. The primary aim of this study was to investigate oxygenation. Secondary aims were to assess respiratory and metabolic variables and lung tissue aeration.MethodsPigs were randomly assigned to FCV (n = 9) and PCV (n = 9). IAH was induced by insufflation of air into the abdomen to induce IAH grades ranging from 0 to 3. At each IAH grade FCV was undertaken using compliance guided pressure settings, or PCV (n = 9) was undertaken with the positive end-expiratory pressure titrated for maximum compliance and the peak pressure set to achieve a tidal volume of 7 ml/kg. Gas exchange, ventilator settings and derived formulas were recorded at two timepoints for each grade of IAH. Lung aeration was assessed by a computed tomography scan at IAH grade 3.ResultsAll 18 pigs (median weight 54 kg [IQR 51–67]) completed the observation period of 4 h. Oxygenation was comparable at each IAH grade, but a significantly lower minute volume was required to secure normocapnia in FCV at all IAH grades (7.6 vs. 14.4, MD − 6.8 (95% CI − 8.5 to − 5.2) l/min; p < 0.001). There was also a significant reduction of applied mechanical power being most evident at IAH grade 3 (25.9 vs. 57.6, MD − 31.7 (95% CI − 39.7 to − 23.7) J/min; p < 0.001). Analysis of Hounsfield unit distribution of the computed tomography scans revealed a significant reduction in non- (5 vs. 8, MD − 3 (95% CI − 6 to 0) %; p = 0.032) and poorly-aerated lung tissue (7 vs. 15, MD − 6 (95% CI − 13 to − 3) %, p = 0.002) for FCV. Concomitantly, normally-aerated lung tissue was significantly increased (84 vs. 76, MD 8 (95% CI 2 to 15) %; p = 0.011).ConclusionsIndividualised FCV showed similar oxygenation but required a significantly lower minute volume for CO2-removal, which led to a remarkable reduction of applied mechanical power. Additionally, there was a shift from non- and poorly-aerated lung tissue to normally-aerated lung tissue in FCV compared to PCV.