Airway Pressure Measurements Research Articles

A non-invasive method to monitor respiratory muscle effort during mechanical ventilation.

This study introduces a method to non-invasively and automatically quantify respiratory muscle effort (Pmus) during mechanical ventilation (MV). The methodology hinges on numerically solving the respiratory system's equation of motion, utilizing measurements of airway pressure (Paw) and airflow (Faw). To evaluate the technique's effectiveness, Pmus was correlated with expected physiological responses. In volume-control (VC) mode, where tidal volume (VT) is pre-determined, Pmus is expected to be linked to Paw fluctuations. In contrast, during pressure-control (PC) mode, where Paw is held constant, Pmus should correlate with VT variations. The study utilized data from 250 patients on invasive MV. The data included detailed recordings of Paw and Faw, sampled at 31.25Hz and saved in 131.1-second epochs, each covering 34 to 41 breaths. The algorithm identified 51,268 epochs containing breaths on either VC or PC mode exclusively. In these epochs, Pmus and its pressure-time product (PmusPTP) were computed and correlated with Paw's pressure-time product (PawPTP) and VT, respectively. There was a strong correlation of PmusPTP with PawPTP in VC mode (R² = 0.91 [0.76, 0.96]; n = 17,648 epochs) and with VT in PC mode (R² = 0.88 [0.74, 0.94]; n = 33,620 epochs), confirming the hypothesis. As expected, negligible correlations were observed between PmusPTP and VT in VC mode (R² = 0.03) and between PmusPTP and PawPTP in PC mode (R² = 0.06). The study supports the feasibility of assessing respiratory effort during MV non-invasively through airway signal analysis. Further research is warranted to validate this method and investigate its clinical applications.

Bedside test for estimating stiff index in mechanically ventilated ARDS patient: a pilot study

Stiff index is defined as the proportion of lung tissue elasticity in relation to chest wall elasticity to pertain to its cyclic tidal volume. It is meant to reflect the risk of overloading lung pressure. Introducing the Stiff index into bedside management determines the pressure needed to keep the lung open with no risk of barotrauma.Aim of the work The primary endpoint was to highlight the stiff index in ARDS patients as a potential surrogate for detecting the changes in lung mechanics and the assumptions underlying the estimation of relevant respiratory parameters. Secondly, we aimed to assess intrathoracic pressure ITP in view of chest wall elastance Ecw in relation to respiratory system elastance Ers within the same population.Subjects and methods Data were collected from forty ARDS patients, diagnosed according to Berlin definition, who were admitted to ICUS Ain Shams University hospitals during the period between December 2022 and April 2023. These populations were patients’ purposive samples who underwent volume‐controlled ventilation at least 2 days prior to study enrollment. Their mean age was 64.68 ± 15.01 years with males (N = 22) to females (N = 18) ratio 55%. Measurements of peak airway pressure, plateau pressure, and delta airway pressure change ∆Paw measured three times on end-expiratory (ee) and on end-inspiratory (ei) occlusion tests, and the higher of the three readings were reported.Results The calculated mean Stiff index was (0.66 ± 0.159) which was correlated with Peak pressure (r = − 0.377, P = 0.017) and with trans-pulmonary end inspiration TPPei (r = 0.312, P = 0.05). The stiff index was also found to be correlated with intra-thoracic pressure ITP (r = 0.769, P 0.001), but is not statistically significant with inspiratory tidal volume (r = 0.132, P 0.416).Conclusion Lung pressure loading in ARDS could be recognized by estimating an increase in stiff index. The cut point of stiff factor that limited the plateau at or below 30 cmH2o was 0.75 with 71% sensitivity and 0.63% specificity, respectively. The more the Stiff index the more was the ITP, and it had no relation to TV.

Oxygen saturation levels and retinopathy of prematurity in extremely preterm infants - a case control study

PurposeTo investigate the association of risk factors, including oxygen exposure, for developing retinopathy of prematurity (ROP) in preterm infants at increased risk of ROP.MethodsA case-control study was conducted where each infant born at < 28 weeks gestation with ROP was matched with another without ROP over five years (July 2015 – June 2020). Clinical information about the infants was collected from electronic medical records, including method of oxygen delivery, oxygen saturation (SpO2), fraction of inspired oxygen (FiO2) and mean airway pressure (MAP) measurements. MATLAB was used for a time-averaged analysis. Stata/SE 16.0 was used for statistical analysis.Results123 ROP/non-ROP pairs were included in this study. The time-averaged SpO2 analysis showed non-ROP group spent more time in hyperoxia than the ROP group (p < 0.001). The non-ROP group had lower respiratory severity scores and analysis when FiO2 > 21% showed that were was no difference in SpO2 between the two groups when the infants were receiving oxygen support. Conditional logistic regressions showed neonatal surgery significantly increased the risk of ROP (OR = 1.4347, p = 0.010), while the influence of birthweight (odds ratio of 0.9965, p = 0.001) and oxygen exposure (OR = 0.9983, p = 0.012) on ROP outcome was found to be negligible as their odds ratios indicated no influence.ConclusionsAt times when infants were receiving respiratory support (FiO2 > 21%) the SpO2 data indicated no difference in SpO2 between the ROP and non-ROP groups. Analysis of clinical variables found that neonatal surgery increased the odds of developing ROP.

Changes in endotracheal tube cuff pressure with the changes in peak airway pressures during total laparoscopic hysterectomy and pelvic surgeries. A prospective and observational study

Background: The abdominal insufflation and changes in endotracheal tube (ETT) cuff pressure due to creation of pneumoperitoneum and changes in patient positioning during laparoscopic abdominal surgeries have not been explored thoroughly. Aims and Objectives: The aim of our study was to see the changes in ETT cuff pressures during creation, maintenance, release of pneumoperitoneum, and during surgical positioning. Materials and Methods: A total of 60 patients were finally taken for study. Written informed consent was taken for participation in the study as well as consent for surgery. Inclusion criteria were patients of age above 30 years, American society of anesthesiology physical status 1 and 2, patients undergoing total laparoscopic hysterectomy requiring trendelenburg positioning. Exclusion criteria were patients with pre-existing pulmonary or cardiac disease, patients with pre-existing vocal cord palsy, goitre or any other airway or thoracic pathology, pregnant or lactating females, BMI more than 25 or &lt;18.5. Changes of cuff and airway pressures before and after abdominal insufflation in supine position and after head-down or head-up positioning were analyzed and compared. Results: Baseline cuff pressure after manual inflation was 28.85±11.4 cm H2O. Significant correlation was observed between change in cuff pressure and increase in peak airway pressure at the end of the surgery (P&lt;0.05). Serial measurements of ETT cuff pressure, peak airway pressure, and ETCO2 were significantly increased compared to baseline (P&lt;0.05). Conclusion: Pneumoperitoneum in Trendelenburg position increases ETT cuff pressure probably due to increase in airway pressure. Therefore, it seems advisable to include routine monitoring of ETT cuff pressure. Objective adjusted measurement of cuff pressure and airway pressures is recommended for such surgeries.

Monitoring Respiratory Effort and Lung-distending Pressure Noninvasively during Mechanical Ventilation: Ready for Prime Time.

Monitoring Respiratory Effort and Lung-distending Pressure Noninvasively during Mechanical Ventilation: Ready for Prime Time.

Paradoxical Positioning: Does "Head Up" Always Improve Mechanics and Lung Protection?

OBJECTIVES:Head-elevated body positioning, a default clinical practice, predictably increases end-expiratory transpulmonary pressure and aerated lung volume. In acute respiratory distress syndrome (ARDS), however, the net effect of such vertical inclination on tidal mechanics depends upon whether lung recruitment or overdistension predominates. We hypothesized that in moderate to severe ARDS, bed inclination toward vertical unloads the chest wall but adversely affects overall respiratory system compliance (Crs).DESIGN:Prospective physiologic study.SETTING:Two medical ICUs in the United States.PATIENTS:Seventeen patients with ARDS, predominantly moderate to severe.INTERVENTION:Patients were ventilated passively by volume control. We measured airway pressures at baseline (noninclined) and following bed inclination toward vertical by an additional 15°. At baseline and following inclination, we manually loaded the chest wall to determine if Crs increased or paradoxically declined, suggestive of end-tidal overdistension.MEASUREMENTS AND MAIN RESULTS:Inclination resulted in a higher plateau pressure (supineΔ: 2.8 ± 3.3 cm H2O [p = 0.01]; proneΔ: 3.3 ± 2.5 cm H2O [p = 0.004]), higher driving pressure (supineΔ: 2.9 ± 3.3 cm H2O [p = 0.01]; proneΔ: 3.3 ± 2.8 cm H2O [p = 0.007]), and lower Crs (supine Δ: 3.4 ± 3.7 mL/cm H2O [p = 0.01]; proneΔ: 3.1 ± 3.2 mL/cm H2O [p = 0.02]). Following inclination, manual loading of the chest wall restored Crs and driving pressure to baseline (preinclination) values.CONCLUSIONS:In advanced ARDS, bed inclination toward vertical adversely affects Crs and therefore affects the numerical values for plateau and driving tidal pressures commonly targeted in lung protective strategies. These changes are fully reversed with manual loading of the chest wall, suggestive of end-tidal overdistension in the upright position. Body inclination should be considered a modifiable determinant of transpulmonary pressure and lung protection, directionally similar to tidal volume and positive end-expiratory pressure.

Physiological trend analysis of a novel cardio-pulmonary model during a preload reduction manoeuvre

Background and objective: Mechanical ventilation causes adverse effects on the cardiovascular system. However, the exact nature of the effects on haemodynamic parameters is not fully understood. A recently developed cardio-vascular system model which incorporates cardio-pulmonary interactions is compared to the original 3-chamber cardiovascular model to investigate the exact effects of mechanical ventilation on haemodynamic parameters and to assess the trade-off of model complexity and model reliability between the 2 models.Methods: Both the cardio-pulmonary and three chamber models are used to identify cardiovascular system parameters from aortic pressure, left ventricular volume, airway flow and airway pressure measurements from 4 pigs during a preload reduction manoeuvre. Outputs and parameter estimations from both models are contrasted to assess the relative performance of each model and to further investigate the effects of mechanical ventilation on haemodynamic parameters.Results: Both models tracked measurements accurately as expected. There was no identifiable increase in error from the added complexity of the cardio-pulmonary model, with both models having a mean average error below 0.5% for all pigs. Identified left ventricle and vena cava elastances of the 3-chamber model was found to diverge exponentially with PEEP from identified left ventricle and vena cava elastances of the cardio-pulmonary model. The r2 of the fit for each pig ranged from 0.888 to 0.998 for left ventricle elastance divergence and from 0.905 to 0.999 for vena cava elastance divergence. All other identified parameters showed no significant difference between models.Conclusions: Despite the increase in model complexity, there was no loss in the cardio-pulmonary model’s ability to accurately estimate haemodynamic parameters and reproduce system dynamics. Furthermore, the cardio-pulmonary model was able to demonstrate how mechanical ventilation affected parameter estimations as PEEP was increased. The 3-chamber model was shown to produce parameter estimations which diverged exponentially with PEEP, while the cardiopulmonary model estimations remained more stable, suggesting its ability to produce more physiologically accurate parameter estimations under higher PEEP conditions.

Transient Heat Stress During Ex-Vivo Lung Perfusion Induces the Heat Shock Response and Preserves Lung Function in Pig Model

<h3>Purpose</h3> The heat shock response (HSR) is a highly conserved adaptative response to thermic stress, related to the induced expression of heat shock proteins (HSPs) which promote significant cytoprotection. We hypothesized that thermal preconditioning (TP) with a well-calibrated heat stress (HS) applied during EVLP elicits a HSR and improves lung graft function by interfering with immune inflammation and oxidative stress pathways. <h3>Methods</h3> Donor lungs (n=12) underwent extended hypothermic preservation of 16h. Lungs were assigned into two groups: 1) Control (n=6): 4h EVLP at 37°C; and 2) TP, (n=6): normothermic EVLP (37°C, 2h), followed by hyperthermic EVLP (42°, 30min), and normothermic EVLP (37°C, 1.5h). Ex-vivo lung function was assessed by measuring airway pressure, lung compliance and pulmonary vascular resistance. We determined expression of HSPs in tissue, and lung damage and oxidative stress biomarkers in tissue, BAL and perfusate at multiple time points. <h3>Results</h3> Lungs undergoing thermal preconditioning (TP group) showed significantly lower pulmonary arterial pressure and vascular resistance, increased dynamic and static pulmonary compliance and reduced airway pressure with no changes in oxygenation capacity as compared to lungs in the control group. At the end of EVLP, lungs in TP group had significant increase of lung mRNA of Hspa1a, Hsc70 and Hmox-1, reduction of nitrotyrosine (3-NT) in lung tissue, and reduction of LDH, CK18-M30 and proteins in BAL fluid. TP during ELVP decreased the expression of TNFα, IL6/IL10, MPO and IL-8 in BAL consistent with inflammasome inhibition. <h3>Conclusion</h3> Transient heat stress during EVLP induces HSR and reduces nitroxidative stress, cellular injury and edema, and prevents functional deterioration of pig lungs after extended cold ischemia. These data indicate the therapeutic potential of thermal preconditioning as a way to recondition damaged lungs and to improve current preservation strategies.

A prospective observational study on changes in endo-tracheal tube cuff pressure and its correlation with airway pressures during various stages of robotic pelvic surgeries.

Background and Aims:Robotic surgeries often require a relatively long duration of pneumo-peritoneum and trendelenburg position which may accentuate changes in endo-tracheal tube (ETT) cuff pressure leading to pressure related complications. The aim of this study was to analyze changes in ETT cuff pressures during various stages of pneumo-peritoneum and surgical positioning and its correlation with airway pressure changes.Material and Methods:A prospective observational study was planned after approval of institutional review board on 60 patients undergoing elective robotic pelvic surgery requiring head down position. Baseline cuff pressure was adjusted to 25 cm H2O. ETT cuff pressure, peak airway pressure and end tidal CO2 (ETCO2) was measured at various time intervals before and after pneumo-peritoneum and head down. Ventilatory parameters were kept fixed after baseline setting. Those requiring any change were excluded. Pearson’s coefficient was used for correlation and ANOVA for trend of parameters at different time intervals (P value <0.05 was considered significant).Results:Baseline cuff pressure after manual inflation was 46.2 ± 17.4 cm H2O. Significant correlation was observed between change in cuff pressure and increase in peak airway pressure at the end of the surgery (r = 0.4, P < 0.05). Serial measurements of ETT cuff pressure, peak airway pressure and ETCO2 were significantly increased compared to baseline (P < 0.05).Conclusion:Significant increases in ETT cuff pressure may be seen in robotic surgeries, with a positive correlation between change in cuff pressure and increase in airway pressures. Objective adjusted measurement of cuff pressure and airway pressures is recommended for such surgeries.

Highly Sensitive Air Pressure Sensor Based on Fabry-Perot Interference

A highly sensitive optical fiber air pressure sensor based on Fabry–Perot interferometer is proposed and demonstrated. The sensor is fabricated by flat-cut single-mode optical fiber, capillary glass tube, stainless steel sleeve, nylon substrate, and metal aluminum film. The finite element simulation was performed in two steps using the COMSOL Multiphysics software. In the first step, the structural mechanics module is used to simulate the deformation of the membrane under a fixed pressure, so as to obtain the corresponding sensor cavity lengths under different pressure. In the second step, the wave optics module is used to get the reflection spectrum of the sensor under different cavity lengths. Then the linear relationship between the reflection spectral shift of the sensor and the pressure is obtained. Thus, the average spectral sensitivity of the sensor under air pressure is −3.10335 nm/KPa. A metal-aluminum thin film F-P cavity sensor was fabricated for experimental verification. According to the experimental results, when the air pressure ranges from 0 Pa to 1000 Pa, the spectral sensitivity of the sensor is as high as −3.10 nm/KPa. This is almost consistent with the simulation result. The sensor has exhibited potential application in the fields of measurement of airway pressure and environmental monitoring.

COMPARISON OF FLEXIBLE LARYNGEAL MASK INSERTION AND ENDOTRACHEAL INTUBATION IN ADENOTONSILLECTOMY SURGERY.

This study compared the effectiveness of flexible laryngeal mask (F-LMA) insertion and endotracheal intubation in pediatric patients undergoing adenotonsillectomy surgery. A total of 60 patients aged 2-12 years were included in the study. Patients were divided into the F-LMA group (n=30) and endotracheal tube (ETT) group (n=30). The groups were compared according to intubation time, heart rate, SpO2, EtCO2, airway pressure, surgical field of view, and recovery time. Both the insertion time and recovery time were shorter in the F-LMA group than in the ETT group (16.93±4.84 s vs. 23.93±8.74 s; and 10±2 min vs. 14.5±3 min; p<0.001 both). The airway pressure measurements at 5-min intervals were significantly lower in the F-LMA group than in the ETT group (p<0.001). F-LMA may be a useful alternative to ETT for adenotonsillectomy surgery because it is safe, provides shorter induction and recovery times, reduces intraoperative airway pressure, and provides an adequate operative field of view.

Measurement validity of an electronic training device to assess breathing characteristics during inspiratory muscle training in patients with weaning difficulties.

Inspiratory muscle training (IMT) improves respiratory muscle function and might enhance weaning outcomes in patients with weaning difficulties. An electronic inspiratory loading device provides valid, automatically processed information on breathing characteristics during IMT sessions. Adherence to and quality of IMT, as reflected by work of breathing and power generated by inspiratory muscles, are related to improvements in inspiratory muscle function in patients with chronic obstructive pulmonary disease. The aim of this study was to investigate the validity of an electronic training device to assess and provide real-time feedback on breathing characteristics during inspiratory muscle training (IMT) in patient with weaning difficulties. Patients with weaning difficulties performed daily IMT sessions against a tapered flow-resistive load of approximately 30 to 50% of the patient's maximal inspiratory pressure. Airflow and airway pressure measurements were simultaneously collected with the training device (POWERbreatheKH2, POWERbreathe International Ltd, UK) and a portable spirometer (reference device, Pocket-Spiro USB/BT100, M.E.C, Belgium). Breath by breath analysis of 1002 breaths of 27 training sessions (n = 13) against a mean load of 46±16% of the patient's maximal inspiratory pressure were performed. Good to excellent agreement (Intraclass correlation coefficients: 0.73-0.97) was observed for all breathing characteristics. When individual differences were plotted against mean values of breaths recorded by both devices, small average biases were observed for all breathing characteristics. To conclude, the training device provides valid assessments of breathing characteristics to quantify inspiratory muscle effort (e.g. work of breathing and peak power) during IMT in patients with weaning difficulties. Availability of valid real-time data of breathing responses provided to both the physical therapist and the patient, can be clinically usefull to optimize the training stimulus. By adapting the external load based on the visual feedback of the training device, respiratory muscle work and power generation during IMT can be maximized during the training.

Comparison of disc and wire electrodes to restore cough via lower thoracic spinal cord stimulation

Objective To compare the safety and effectiveness of wire (WE) vs. disc (DE) electrodes to restore cough in subjects with spinal cord injury (SCI). Design Clinical trials assessing the effectiveness and clinical outcomes associated with two electrode systems to activate the expiratory muscles. Setting Inpatient hospital setting for DE or WE electrode insertion; outpatient evaluation of cough efficacy and instructions for home use. Participants Twenty-nine subjects with SCI; 17 participants with DE and 12 with WE implants. Intervention Surgical implantation of WE or DE to restore cough. Daily application of spinal cord stimulation (SCS) at home. Main outcome measure(s) Airway pressure (P) and peak airflow (F) generation achieved with SCS; clinical parameters including ease in raising secretions, incidence of acute respiratory tract infections (RTI) and side effects. Results P and F achieved with DE and WE were not significantly different. For example, at total lung capacity (TLC) with participant effort, P was 128 ± 12 cmH2O and 118 ± 14 cmH2O, with DE and WE, respectively. The degree of difficulty in raising secretions improved markedly in both groups. The incidence of RTI per year fell from 1.3 ± 0.3 and 1.3 ± 0.5–0.3 ± 0.1 and 0.1 ± 0.1 for DE and WE groups, respectively (P < 0.01 for both when compared to pre-implant values and NS between DE and WE groups). The only significant side effect i.e. short-term autonomic dysreflexia was also similar between groups. Conclusions The results of this investigation indicate that both DE and WE result in comparable degrees of expiratory muscle activation, clinical benefits and side effects. Importantly, SCS to restore cough can be achieved with use of WE which can be placed using minimally invasive techniques and associated reduction in cost, surgical time and overall risk. Trial registration: ClinicalTrials.gov identifier: NCT00116337., NCT01659541, FDA IDE: G980267

Airway compliance measurements in mouse models of respiratory diseases.

The quantification of airway compliance (Caw) is essential to the study of airway alterations in disease models. However, the required measurements of airway pressure and volume are difficult to acquire in mice. We hypothesized that the inflation limb of full-range pressure-volume (PV) curves could be used to quantify Caw, as it contains a segment where only the airway tree is distended. The study objective was to assess the feasibility of the approach by analysis of full-range PV curves previously collected in three mouse models: an elastase model of emphysema, a genetic model spontaneously developing emphysema (leukotriene C4 synthase knockout; LTC4S-KO), and a bleomycin model of lung fibrosis. Attempts to validate results included Caw change relative to respiratory system compliance (ΔCaw/ΔC), the minute work of breathing (mWOB), and the elastance at 20.5 Hz (Ers_20.5) from prior respiratory mechanics measurements in the same subjects. Caw was estimated at 3% of total compliance in healthy mice or 2.3 ± 1 μL/cmH2O (n = 17). The technique detected changes in models of respiratory obstructive and restrictive diseases relative to control mice as well as differences in the two emphysema models studied. The changes in Caw were consistent with those seen in ΔCaw/ΔC, mWOB, or Ers_20.5, with some variations according to the model, as well as with results reported in the literature in humans and mice. Direct Caw measurements in subjects as small as mice could prove useful to further characterize other respiratory disease models associated with airway remodeling or to assess treatment effects.

Nasopharyngeal tubes in pediatric anesthesia: Is the flow-dependent pressure drop across the tube suitable for calculating oropharyngeal pressure?

BackgroundNasopharyngeal tubes are useful in pediatric anesthesia for insufflating oxygen and anesthetics. During nasopharyngeal tube‐anesthesia, gas insufflation provides some positive oropharyngeal pressure that differs from the proximal airway pressure owing to the flow‐dependent pressure drop across the nasopharyngeal tube (ΔPNPT).AimsThis study aimed to investigate whether ΔPNPT could be used for calculating oropharyngeal pressure during nasopharyngeal tube‐assisted anesthesia.MethodsIn a physical model of nasopharyngeal tube‐anesthesia, using Rohrer's equation, we calculated ΔPNPT for three nasopharyngeal tubes (3.5, 4.0, and 5.0 mm inner diameter) under oxygen and several sevoflurane in oxygen combinations in two ventilatory scenarios (continuous positive airway pressure and intermittent positive pressure ventilation). We then calculated oropharyngeal pressure as proximal airway pressure minus ΔPNPT. Calculated and measured oropharyngeal pressure couples of values were compared with the root mean square deviation to assess accuracy. We also investigated whether oropharyngeal pressure accuracy depends on the nasopharyngeal tube diameter, flow rate, gas composition, and leak size. Using ΔPNPT charts, we tested whether ΔPNPT calculation was feasible in clinical practice.ResultsWhen we tested small‐diameter nasopharyngeal tubes at high‐flow or high‐peak inspiratory pressure, proximal airway pressure measurements markedly overestimated oropharyngeal pressure. Comparing measured and calculated maximum and minimum oropharyngeal pressure couples yielded root mean square deviations less than 0.5 cmH2O regardless of ventilatory modality, nasopharyngeal tube diameter, flow rate, gas composition, and leak size.ConclusionDuring nasopharyngeal tube‐assisted anesthesia, proximal airway pressure readings on the anesthetic monitoring machine overestimate oropharyngeal pressure especially for smaller‐diameter nasopharyngeal tubes and higher flow, and to a lesser extent for large leaks. Given the importance of calculating oropharyngeal pressure in guiding nasopharyngeal tube ventilation in clinical practice, we propose an accurate calculation using Rohrer's equation method, or approximating oropharyngeal pressure from flow and pressure readings on the anesthetic machine using the ΔPNPT charts.

Effect of Therapeutic Hypothermia on Physiologic, Histologic and Metabolomic Markers of Lung Injury in Experimental Acute Respiratory Distress Syndrome

Background Acute respiratory distress syndrome (ARDS) is a severe lung injury characterized by noncardiogenic pulmonary edema and rapid hypoxic respiratory failure. Therapeutic hypothermia improves outcomes of traumatic brain injury and cardiac injuries; however, it has not been widely used or studied in ARDS. Hypothermia may be helpful in reducing injury and inflammation associated with ARDS by reducing pro-inflammatory molecule production. Objective To evaluate the effect of therapeutic hypothermia on the development of injury and inflammation in experimental, short-term ARDS. Hypothesis Hypothermia induced at the onset of lung injury would mitigate histological and serum metabolic changes, as well as changes in respiratory elastance (E) and resistance (R). Methods The Animal Research Committee of the University of British Columbia approved all experimental procedures. Twenty female Yorkshire pigs were divided into 4 groups (n= 5 per group): normothermic control (C), normothermic injured (I), hypothermic control (HC), and hypothermic injured (HI). ARDS was induced via intrapulmonary injection of oleic acid. Hypothermia was induced with a cooling catheter placed into the left jugular vein. The normothermic groups had core temperatures maintained at 36.5-38°C and the hypothermic groups were cooled to 32°C. Animals were euthanized after a 12-hour follow-up period. Respiratory mechanical variables were quantified based the measurements of flow, airway pressure, and esophageal pressure. Tissue samples from the right diaphragmatic lobe were collected after euthanasia and examined for injury score. Plasma samples were collected and 1H-NMR spectroscopy analysis was performed to determine metabolite concentration. Results Therapeutic hypothermia reduced injury in the HI vs. I group (injury score= 0.51±0.18 vs. 0.76±0.06; p<0.05). All cohorts expressed distinct phenotypes with the HI cohort having a reduction in inflammatory metabolites (i.e., succinate) compared to the I cohort. Changes to respiratory mechanics were due to changes in lung E and R (ΔE from pre-injury= 45.55±14.17 cmH2O·l-1; ΔR from pre-injury= 3.07±1.99 cmH2O·l-1·s-1, p<0.05) and not chest-wall E and R (ΔE from pre-injury= 0.73±1.59 cmH2·l-1; ΔR from pre-injury= 0.59±0.14 cmH2O·l-1s-1, p>0.05), with trends for the HI group to have a lower lung R (p=0.99) and E (p=0.93) compared to the I group. Control groups showed no significant change in respiratory mechanics. Conclusion Therapeutic hypothermia canreduce some markers of injury and inflammation associated with ARDS. Further studies are required to determine the effect on longer term outcomes and mortality.

Comparison of wire and disc electrodes to electrically activate the inspiratory muscles in dogs

ObjectiveTo compare the effectiveness of wire versus disc electrodes to activate the inspiratory muscles via high frequency spinal cord stimulation. DesignAnimal study. SettingResearch laboratory. AnimalsDogs (n = 5) InterventionsIn separate trials, spinal cord stimulation (SCS) was applied via disc (DE) and two parallel wire electrodes (WE) on the ventral epidural space at the T2-T3 spinal region. Main Outcome Measure(s)Airway pressure (P) and inspired volume (V) generation following stimulation with DE and WE were compared. Given our previous success with (DE), outcome variables with this electrode were used as our gold standard to which all comparisons were made. ResultsTwo configurations of WE using monopolar stimulation (MS) resulted in P and V that were similar to those generated with MS with DE. For example, MS with parallel WE connected together to function as a common cathode (Y-connection) and a 2-channel system (separate cathodes with a remote ground), resulted in P that were 91 ± 6 and 92 ± 4%, respectively, of those achieved with DE (NS for both). Bipolar stimulation with parallel WE using a Y-connection and with a 2-channel system, resulted in P that were 96 ± 4 and 94 ± 4%, of the P achieved with DE (NS for both). Conclusion(s)These results suggest that specific configurations of WE, which can be placed via minimally invasive techniques, provide comparable activation of the inspiratory muscles compared to DE and may be a useful technique to restore ventilatory support in persons with spinal cord injury.

Coronavirus Disease 2019: Anesthesia Machine Circuit Pressure During Use as an Improvised Intensive Care Unit Ventilator.

Use of anesthesia machines as improvised intensive care unit (ICU) ventilators may occur in locations where waste anesthesia gas suction (WAGS) is unavailable. Anecdotal reports suggest as much as 18 cm H2O positive end-expiratory pressure (PEEP) being inadvertently applied under these circumstances, accompanied by inaccurate pressure readings by the anesthesia machine. We hypothesized that resistance within closed anesthesia gas scavenging systems (AGSS) disconnected from WAGS may inadvertently increase circuit pressures. An anesthesia machine was connected to an anesthesia breathing circuit, a reference manometer, and a standard bag reservoir to simulate a lung. Ventilation was initiated as follows: volume control, tidal volume (TV) 500 mL, respiratory rate 12, ratio of inspiration to expiration times (I:E) 1:1.9, fraction of inspired oxygen (Fio2) 1.0, fresh gas flow (FGF) rate 2.0 liters per minute (LPM), and PEEP 0 cm H2O. After engaging the ventilator, PEEP and peak inspiratory pressure (PIP) were measured by the reference manometer and the anesthesia machine display simultaneously. The process was repeated using prescribed PEEP levels of 5, 10, 15, and 20 cm H2O. Measurements were repeated with the WAGS disconnected and then were performed again at FGF of 4, 6, 8, 10, and 15 LPM. This process was completed on 3 anesthesia machines: Dräger Perseus A500, Dräger Apollo, and the GE Avance CS2. Simple linear regression was used to assess differences. Utilizing nonparametric Bland-Altman analysis, the reference and machine manometer measurements of PIP demonstrated median differences of -0.40 cm H2O (95% limits of agreement [LOA], -1.00 to 0.55) for the Dräger Apollo, -0.40 cm H2O (95% LOA, -1.10 to 0.41) for the Dräger Perseus, and 1.70 cm H2O (95% LOA, 0.80-3.00) for the GE Avance CS2. At FGF 2 LPM and PEEP 0 cm H2O with the WAGS disconnected, the Dräger Apollo had a difference in PEEP of 0.02 cm H2O (95% confidence interval [CI], -0.04 to 0.08; P = .53); the Dräger Perseus A500, <0.0001 cm H2O (95% CI, -0.11 to 0.11; P = 1.00); and the GE Avance CS2, 8.62 cm H2O (95% CI, 8.55-8.69; P < .0001). After removing the hose connected to the AGSS and the visual indicator bag on the GE Avance CS2, the PEEP difference was 0.12 cm H2O (95% CI, 0.059-0.181; P = .0002). Displayed airway pressure measurements are clinically accurate in the setting of disconnected WAGS. The Dräger Perseus A500 and Apollo with open scavenging systems do not deliver inadvertent continuous positive airway pressure (CPAP) with WAGS disconnected, but the GE Avance CS2 with a closed AGSS does. This increase in airway pressure can be mitigated by the manufacturer's recommended alterations. Anesthesiologists should be aware of the potential clinically important increases in pressure that may be inadvertently delivered on some anesthesia machines, should the WAGS not be properly connected.

Correcting esophageal pressure measurements for patients undergoing mechanical ventilation

Abstract During invasive mechanical ventilation, knowledge of the patient’s respiratory effort is valuable in guiding the clinical team to perform a personalized therapy. The same adjustment of the ventilator can produce excessive transpulmonary pressures for different patients, capable of generating or aggravating pre-existing lung injuries. The measurement of transpulmonary pressure (the difference between airway and pleural pressures) is not easily performed in practice. Although airway pressure measurement is available on most current mechanical ventilators, pleural pressure measurement is indirectly performed using an esophageal balloon. In many cases, esophageal pressure reading takes other phenomena into account and is not a reliable measure of pleural pressure. This work will study system identification techniques to obtain reliable pleural pressures based on esophageal pressure readings, aiming to provide the clinical team with information about the patient’s ventilatory therapy’s real status. By estimating transfer function models, autoregressive with external input (ARX) and output error (OE) polynomial models, waveforms were adjusted in two different patients’ occlusion maneuver data. Different metrics were used to assess the quality of the models obtained. The analysis results showed that the estimation methods used provided plausible representations of the underlying dynamic system. Therefore, there are indications that the system identification techniques presented in this work can be used in general, in a clinical environment, to provide reliable estimates of pleural pressure based on esophageal pressure measurements.

MANOVACUÔMETRO DIGITAL PARA MEDIÇÃO DE PRESSÃO RESPIRATÓRIA PULMONAR

Dentre as possíveis áreas de aplicação da Internet das Coisas (IoT), a área da saúde tem grande potencial com inúmeras possibilidades de aplicabilidade, sobretudo no que se refere à prevenção de doenças crônicas e à redução de infecções hospitalares – um dos principais agravantes da qualidade de vida dos pacientes e dos altos custos das instituições. O objetivo do presente trabalho é o de desenvolver um manovacuômetro digital que permite a medição local da pressão nas vias aéreas de pacientes em tempo real e que utiliza a comunicação do tipo sem fio e a interface com dispositivos móveis, possibilitando o armazenamento das medidas em nuvens. Este dispositivo apresenta interface amigável, confiabilidade de aquisição e dimensões reduzidas. Dessa forma, os dados ficam disponíveis para análise de profissionais especializados remotamente. A interface é desenvolvida em software de código aberto para realizar a coleta de dados e utiliza dispositivos móveis que são parte fundamental da sociedade