Measurements Of Respiratory Mechanics Research Articles

Impact of the transpulmonary pressure on right ventricle impairment incidence during acute respiratory distress syndrome: a pilot study in adults and children

BackgroundRight ventricle impairment (RVI) is common during acute respiratory distress syndrome (ARDS) in adults and children, possibly mediated by the level of transpulmonary pressure (PL). We sought to investigate the impact of the level of PL on ARDS-associated right ventricle impairment (RVI).MethodsAdults and children (> 72 h of life) were included in this two centers prospective study if they were ventilated for a new-onset ARDS or pediatric ARDS, without spontaneous breathing and contra-indication to esophageal catheter. Serial measures of static lung, chest wall, and respiratory mechanics were coupled to critical care echocardiography (CCE) for 3 days. Mixed-effect logistic regression models tested the impact of lung stress (ΔPL) along with age, lung injury severity, and carbon dioxide partial pressure, on RVI using two definitions: acute cor pulmonale (ACP), and RV dysfunction (RVD). ACP was defined as a dilated RV with septal dyskinesia; RVD was defined as a composite criterion using tricuspid annular plane systolic excursion, S wave velocity, and fractional area change.Results46 patients were included (16 children, 30 adults) with 106 CCE (median of 2 CCE/patient). At day one, 19% of adults and 4/7 children > 1 year exhibited ACP, while 59% of adults and 44% of children exhibited RVD. In the entire population, ACP was present on 17/75 (23%) CCE. ACP was associated with an increased lung stress (mean ΔPL of 16.2 ± 6.6 cmH2O in ACP vs 11.3 ± 3.6 cmH2O, adjusted OR of 1.33, CI95% [1.11–1.59], p = 0.002) and being a child. RVD was present in 59/102 (58%) CCE and associated with lung stress. In children > 1 year, PEEP was significantly lower in case of ACP (9.3 [8.6; 10.0] cmH2O in ACP vs 15.0 [11.9; 16.3] cmH2O, p = 0.03).ConclusionLung stress was associated with RVI in adults and children with ARDS, children being particularly susceptible to RVI.Trial registration Clinical trials identifier: NCT0418467.

Peak inspiratory pressure lacks accuracy to estimate plateau pressure in infants with severe obstructive lower airway disease.

In children with acute respiratory distress syndrome receiving mechanical ventilation, the peak inspiratory pressure (PIP) is close to plateau pressure (PPLAT) when inspiratory flow approaches zero. We aimed to evaluate the reliability of PIP to estimate PPLAT in infants with severe respiratory viral infection (SRVI), characterized by increased airway resistance, and the accuracy of an equational model to estimates PPLAT (ePPLAT) based on PIP. This was a retrospective observational study including mechanically ventilated children (1 to 24 month old) with SRVI, whose respiratory mechanics measurements were performed to evaluate PIP and PPLAT. The measured PPLAT was compared with the result of the equation: ePPLAT = PIP - [5.067 - (0.858 × static compliance) - (0.018 × inspiratory resistance) - (0.390 × pressure above positive-end expiratory pressure) + (4.989 × inspiratory time)]. Thirty-seven patients were included, with a median age of 3 (2-5) months. They presented a high inspiratory and expiratory resistance (136 ± 43 and 168 ± 66 cmH2O/L/s, respectively) and a moderate reduction in static compliance: 0.75 ± 0.3 mL/kg/cmH2O. PIP overestimated PPLAT (33 ± 3 and 26 ± 5 cmH2O, p = 0.01), with a mean difference of 7.3 ± 4 cmH2O. Moreover, the Bland-Altman analysis demonstrated a mean difference between PPLAT and ePPLAT of 1.0 ± 4.0 cmH2O, with 95% limits of agreement of -6.9 and 8.8. A significant difference between PIP and PPLAT was observed in infants with SRVI. The equation model was inaccurate for estimating PPLAT based on PIP. Any estimation of PPLAT from PIP needs to consider the resistance component of the respiratory system.

Central and peripheral mechanisms underlying respiratory deficits in a mouse model of accelerated senescence.

Aging invariably decreases sensory and motor stimuli and affects several neuronal systems and their connectivity to key brain regions, including those involved in breathing. Nevertheless, further investigation is needed to fully comprehend the link between senescence and respiratory function. Here, we investigate whether a mouse model of accelerated senescence could develop central and peripheral respiratory abnormalities. Adult male Senescence Accelerated Mouse Prone 8 (SAMP8) and the control SAMR1 mice (10months old) were used. Ventilatory parameters were assessed by whole-body plethysmography, and measurements of respiratory input impedance were performed. SAMP8 mice exhibited a reduction in the density of neurokinin-1 receptor immunoreactivity in the entire ventral respiratory column. Physiological experiments showed that SAMP8 mice exhibited a decreased tachypneic response to hypoxia (FiO2 = 0.08; 10min) or hypercapnia (FiCO2 = 0.07; 10min). Additionally, the ventilatory response to hypercapnia increased further due to higher tidal volume. Measurements of respiratory mechanics in SAMP8 mice showed decreased static compliance (Cstat), inspiratory capacity (IC), resistance (Rn), and elastance (H) at different ages (3, 6, and 10months old). SAMP8 mice also have a decrease in contractile response to methacholine compared to SAMR1. In conclusion, our findings indicate that SAMP8 mice display a loss of the NK1-expressing neurons in the respiratory brainstem centers, along with impairments in both central and peripheral respiratory mechanisms. These observations suggest a potential impact on breathing in a senescence animal model.

Dynamic inflation prevents and standardized lung recruitment reverts volume loss associated with percutaneous tracheostomy during volume control ventilation: results from a Neuro-ICU population.

To determine how percutaneous tracheostomy (PT) impacts on respiratory system compliance (Crs) and end-expiratory lung volume (EELV)during volume control ventilation and to test whether a recruitment maneuver (RM) at the end of PT may reverse lung derecruitment. This is a single center, prospective, applied physiology study. 25 patients with acute brain injury who underwent PT were studied. Patients were ventilated in volume control ventilation. Electrical impedance tomography (EIT) monitoring and respiratory mechanics measurements were performed in three steps: (a) baseline, (b) after PT, and (c) after a standardized RM (10 sighs of 30 cmH2O lasting 3s each within 1min). End-expiratory lung impedance (EELI) was used as a surrogate of EELV. PT determined a significant EELI loss (mean reduction of 432 arbitrary units p = 0.049) leading to a reduction in Crs (55 ± 13 vs. 62 ± 13 mL/cmH2O; p < 0.001) as compared to baseline. RM was able to revert EELI loss and restore Crs (68 ± 15 vs. 55 ± 13 mL/cmH2O; p < 0.001). In a subgroup of patients (N = 8, 31%), we observed a gradual but progressive increase in EELI. In this subgroup, patients did not experience a decrease of Crs after PT as compared to patients without dynamic inflation. Dynamic inflation did not cause hemodynamic impairment nor raising of intracranial pressure. We propose a novel and explorative hyperinflation risk index (HRI) formula. Volume control ventilation did not prevent the PT-induced lung derecruitment. RM could restore the baseline lung volume and mechanics. Dynamic inflation is common during PT, it can be monitored real-time by EIT and anticipated by HRI. The presence of dynamic inflation during PT may prevent lung derecruitment.

Driving Pressure: Clinical Applications and Implications in the Intensive Care Units

Acute respiratory distress syndrome (ARDS) is considered a frequent and serious lung disease that is continuously linked with an increase in both morbidity and mortality. Mechanical ventilation (MV) is considered as the gold standard therapy in the management of ARDS; although MV support is lifesaving, it is also associated with potentially harmful threats such as ventilator-induced lung injury (VILI). It is understood from the physiological background itself that VILI has a considerable impact on the prognosis of a patient. Therefore, the current studies show that focusing on key therapeutic elements causing over-distension of the available lung units is more imperative for indicating further damage than how much pressure is used to ventilate. In the past two decades, there has been an increasing trend toward using driving pressure (DP) in the management of ARDS patients in intensive care units (ICUs). Recent studies propose that measuring DP in ARDS patients, in addition to the other respiratory mechanics measurements, may support selecting and customizing appropriate ventilator parameters, which, in turn, improves patient outcomes and decreases mortality rate. Therefore, this review is intended to outline the physiological meaning of DP, the clinical measurement and application of DP and factors limiting DP. Furthermore, measuring DP in non-ARDS patients and recent clinical evidence for the use of DP in the ICUs will be discussed in detail.

Heterogeneity of Ventilation/Perfusion Mismatch at Different Levels of PEEP and in Mechanical Phenotypes of COVID-19 ARDS.

COVID-19-related ARDS is characterized by severe hypoxemia with initially preserved lung compliance and impaired ventilation/perfusion (V̇/Q̇) matching. PEEP can increase end-expiratory lung volume, but its effect on V̇/Q̇ mismatch in COVID-19-related ARDS is not clear. We enrolled intubated and mechanically ventilated subjects with COVID-19 ARDS and used the automatic lung parameter estimator (ALPE) to measure V̇/Q̇. Respiratory mechanics measurements, shunt, and V̇/Q̇ mismatch (low V̇/Q̇ and high V̇/Q̇) were collected at 3 PEEP levels (clinical PEEP = intermediate PEEP, low PEEP [clinical - 50%], and high PEEP [clinical + 50%]). A mixed-effect model was used to evaluate the impact of PEEP on V̇/Q̇. We also investigated if PEEP might have a different effect on V̇/Q̇ mismatch in 2 different respiratory mechanics phenotypes, that is, high elastance/low compliance (phenotype H) and low elastance/high compliance (phenotype L). Seventeen subjects with COVID-related ARDS age 66 [60-71] y with a PaO2 /FIO2 of 141 ± 74 mm Hg were studied at low PEEP = 5.6 ± 2.2 cm H2O, intermediate PEEP = 10.6 ± 3.8 cm H2O, and high PEEP = 15 ± 5 cm H2O. Shunt, low V̇/Q̇, high V̇/Q̇, and alveolar dead space were not significantly influenced, on average, by PEEP. Respiratory system compliance decreased significantly when increasing PEEP without significant variation of PaO2 /FIO2 (P = .26). In the 2 phenotypes, PEEP had opposite effects on shunt, with a decrease in the phenotype L and an increase in phenotype H (P = .048). In subjects with COVID-related ARDS placed on invasive mechanical ventilation for > 48 h, PEEP had a heterogeneous effect on V̇/Q̇ mismatch and, on average, higher levels were not able to reduce shunt. The subject's compliance could influence the effect of PEEP on V̇/Q̇ mismatch since an increased shunt was observed in subjects with lower compliance, whereas the opposite occurred in those with higher compliance.

Relationship between clinician documented blast exposure and pulmonary function: a retrospective chart review from a national specialty clinic

BackgroundService member exposure to explosive blast overpressure waves is common with considerable attention to traumatic brain injury (TBI) and neuropsychological sequalae. Less is known about the impacts on the respiratory system, particularly long-term effects, despite vulnerability to overpressure. Using a national registry, we previously observed an independent relationship between self-reported blast exposure and respiratory symptoms; however, the impact on objective measures of pulmonary function is poorly understood.Methods307 Veterans referred to our national specialty center for post-deployment health concerns underwent a comprehensive multi-day evaluation that included complete pulmonary function testing (PFT), occupational and environmental medicine history, neuropsychological or psychological evaluation. We developed an a priori chart abstraction process and template to classify Veterans into blast exposure groups: (1) none, (2) single-mild, or (3) multiple-mild. This template focused primarily on clinician documented notes of blast related TBI that were used as proxy for blast overpressure injury to thorax. PFT variables characterizing flow (FEV1%; %∆FEV1), volume (TLC%), diffusion (DLCO%) and respiratory mechanics (forced oscillometry) were selected for analysis.ResultsVeterans (40.5 ± 9.7 years; 16.3% female) were referred 8.6 ± 3.6 years after their last deployment and presented with considerable comorbid conditions and health problems (e.g., 62% post-traumatic stress, 55% dyspnea). After chart abstraction, Veterans were assigned to none (n = 208), single mild (n = 52) and multiple mild (n = 47) blast exposure groups. Among the blast exposed, clinicians documented 73.7% were < 50 m from the blast and 40.4% were physically moved by blast. PFT outcome measures were similar across all groups (p value range: 0.10–0.99).ConclusionsIn this referred sample of deployed Veterans, PFT measures of flow, volume, diffusion, and respiratory mechanics were not associated with clinician documented blast exposure per the retrospective chart abstraction methodology applied. Yet, these clinical findings suggest future research should determine and assess distinction between Veteran recollections of perceived blast experiences versus overpressure wave exposure to the respiratory system.

Donor Age and Recipient-Donor Sex and Height Mismatch Are Associated with Abnormal Pulmonary Reactance (X5) in Stable Recipients After Bilateral Lung Transplantation

<h3>Purpose</h3> Respiratory system reactance at 5Hz (X₅) reflects tissue elastance and inertance and is measured using oscillometry, a novel measurement of respiratory mechanics. Abnormal reactance (stiffness) has been observed in baseline and chronic lung allograft dysfunction. This study aims to assess predictors of pulmonary reactance in stable lung transplant (LTx) recipients. <h3>Methods</h3> A cross-sectional study was performed on bilateral lung transplant (LTx) recipients at 2 Australian centres between Jan-20 and Jun-21. Spirometry and oscillometry (TremoFlo C-100) were performed to obtain FEV₁ and FVC and X₅, respectively. Patients with acute and chronic lung allograft dysfunction (LAD) were excluded. Baseline lung allograft dysfunction (BLAD) was defined as failure to achieve FEV₁ or FVC >80%-predicted. Oostveen equations were used to generate predicted X₅ values. Abnormal X₅ was defined as Z-score ≤ -1.64. Logistic regression measured associations between baseline transplant predictors and risk of abnormal X_5. <h3>Results</h3> A total of 326 bilateral lung transplant recipients underwent oscillometry. 173 patients with LAD were excluded and 153 included for final analysis. Patients were at median (IQR) 1.9 (2.7) years after transplant. The median (IQR) concurrent FEV₁ as %-baseline FEV₁ was 96% (7). Abnormal X₅ was detected in 21 (13.7%) and normal X₅ in 132 (86.3%). Increasing donor age (OR 1.03, 95%CI 1.00-1.06, p=0.047), recipient-donor sex mismatch (Male:Female OR 5.15, 95%CI 1.70-15.59, p=0.004), donor-recipient height difference (OR 0.95, 95% CI 0.90-0.99, p=0.027) and spirometric BLAD (OR 7.21, 95%CI 2.59-20.06, p<0.001) were associated with an increased risk of abnormal X_5. <h3>Conclusion</h3> Undersizing of lungs, recipient-donor sex mismatch and increasing donor age are significantly associated with abnormal X₅. Differences in lung volume due to sex and size matching may partly explain this association. Increasing age is associated with decreased lung elastic recoil. Preliminary analysis is limited by the use of recipient anthropometrics to generate predicted values. Longitudinal studies are required to determine if the reactance trajectory may help predict patients at risk of poor outcomes.

Distribution and Magnitude of Regional Volumetric Lung Strain and Its Modification by PEEP in Healthy Anesthetized and Mechanically Ventilated Dogs.

The present study describes the magnitude and spatial distribution of lung strain in healthy anesthetized, mechanically ventilated dogs with and without positive end-expiratory pressure (PEEP). Total lung strain (LSTOTAL) has a dynamic (LSDYNAMIC) and a static (LSSTATIC) component. Due to lung heterogeneity, global lung strain may not accurately represent regional total tissue lung strain (TSTOTAL), which may also be described by a regional dynamic (TSDYNAMIC) and static (TSSTATIC) component. Six healthy anesthetized beagles (12.4 ± 1.4 kg body weight) were placed in dorsal recumbency and ventilated with a tidal volume of 15 ml/kg, respiratory rate of 15 bpm, and zero end-expiratory pressure (ZEEP). Respiratory system mechanics and full thoracic end-expiratory and end-inspiratory CT scan images were obtained at ZEEP. Thereafter, a PEEP of 5 cmH2O was set and respiratory system mechanics measurements and end-expiratory and end-inspiratory images were repeated. Computed lung volumes from CT scans were used to evaluate the global LSTOTAL, LSDYNAMIC, and LSSTATIC during PEEP. During ZEEP, LSSTATIC was assumed zero; therefore, LSTOTAL was the same as LSDYNAMIC. Image segmentation was applied to CT images to obtain maps of regional TSTOTAL, TSDYNAMIC, and TSSTATIC during PEEP, and TSDYNAMIC during ZEEP. Compliance increased (p = 0.013) and driving pressure decreased (p = 0.043) during PEEP. PEEP increased the end-expiratory lung volume (p < 0.001) and significantly reduced global LSDYNAMIC (33.4 ± 6.4% during ZEEP, 24.0 ± 4.6% during PEEP, p = 0.032). LSSTATIC by PEEP was larger than the reduction in LSDYNAMIC; therefore, LSTOTAL at PEEP was larger than LSDYNAMIC at ZEEP (p = 0.005). There was marked topographic heterogeneity of regional strains. PEEP induced a significant reduction in TSDYNAMIC in all lung regions (p < 0.05). Similar to global findings, PEEP-induced TSSTATIC was larger than the reduction in TSDYNAMIC; therefore, PEEP-induced TSTOTAL was larger than TSDYNAMIC at ZEEP. In conclusion, PEEP reduced both global and regional estimates of dynamic strain, but induced a large static strain. Given that lung injury has been mostly associated with tidal deformation, limiting dynamic strain may be an important clinical target in healthy and diseased lungs, but this requires further study.

Reverse Trigger in Ventilated Non-ARDS Patients: A Phenomenon Can Not Be Ignored!

IntroductionThe role of reverse trigger (RT) was unknown in ventilated non-acute respiratory distress syndrome (ARDS) patients. So we conducted a retrospective study to evaluate the incidence, characteristics and physiologic consequence of RT in such population.MethodSix ventilated non-ARDS patients were included, the esophageal balloon catheter were placed for measurements of respiratory mechanics in all patients. And the data were analyzed to identified the occurrence of RT, duration of the entrainment, the entrainment pattern or ratio, the phase difference (dP) and the phase angle (θ), phenotypes, Effects and clinical correlations of RT.ResultRT was detected in four patients of our series (66.7%), and the occurrence of RT varying from 19 to 88.6% of their recording time in these 4 patients. One patient (No.2) showed a stable 1:1 ratio and Mid-cycle RT was the most common phenotype. However, the remained patients showed a mixed ratios, and Late RT was the most common phenotype, followed by RT with breath stacking. The average values of mean phase delay and phase angles were 0.39s (0.32, 0.98) and 60.52° (49.66, 102.24). Mean phase delay and phase angles were shorter in early reverse triggering with early and delayed relaxation, and longer in mid, late RT and RT with breath stacking. Pmus was variable between patients and phenotypes, and larger Pmus was generated in Early RT, Delayed Relaxation and mid cycle RT. When the RT occurred, the Peso increased 17.27 (4.91, 19.71) cmH2O compared to the controlled breathing, and the average value of incremental ΔPeso varied widely inter and intra patients (Table 3B and Figure 1). Larger ΔPeso was always generated in Early RT, Delayed Relaxation and mid cycle RT, accompanied by an significant increase of PL with 19.12 (0.75) cmH2O and 16.10 (6.23) cmH2O.ConclusionRT could also be observed in ventilated non-ARDS patients. The characteristics of pattern and phenotype was similar to RT in ARDS patients to a large extent. And RT appeared to alter lung stress and delivered volumes.

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.

Novel Measurements of Respiratory System Mechanics Demonstrate Important Features of Donor-Recipient Lung Volume Matching That May Link to Subsequent Chronic Lung Allograft Dysfunction

<h3>Purpose</h3> The effect of matching donor and lung transplant (LTx) recipient lung volumes on LTx outcomes is unknown. The Forced Oscillation Technique (FOT) is a simple measure of the mechanical properties of the respiratory system. We have recently developed novel measures of airway closure using FOT. This study aims to assess the effect of matching donor and recipient lung volumes on respiratory system mechanics using FOT. <h3>Methods</h3> A multi-centre (Alfred Hospital, Melbourne and St Vincent's Hospital, Sydney) prospective study of (n=19) subjects (63% male, age 56 ±13yrs) at one time point 3-6 months post bilateral LTx were divided into two groups: G1 - Recipient measured pre-LTx total lung capacity (rTLC) < predicted donor TLC (dTLC) n=9; G2 - rTLC > predicted dTLC, n=10. All subjects underwent pulmonary function testing including, spirometry, plethysmography and FOT (Tremoflo 2000, Thorasys, Canada). <h3>Results</h3> In G1, respiratory system elastance (stiffness=AX5) positively correlated with difference between dTLC and rTLC (p<0.01, r²=0.45) in non-obstructed subjects (<b>Figure 1A)</b>; i.e. implanting oversized lungs increases respiratory system stiffness. In G2, airway closure occurred at a higher lung volume as size mismatching increased (p<0.01, r²=0.37); i.e. implanting undersized lungs can increase airway closure (<b>Figure 1B</b>). <h3>Conclusion</h3> Novel measurements of respiratory mechanics from FOT demonstrate both oversizing and under-sizing donor TLC can alter recipient respiratory mechanics post-LTx. Longitudinal studies are underway to correlate these effects with the incidence and extent of baseline or chronic lung allograft dysfunction (BLAD & CLAD).

Airway Resistance and Respiratory Compliance in Children with Acute Viral Bronchiolitis Requiring Mechanical Ventilation Support.

BackgroundAcute viral bronchiolitis (AVB) is a very frequent disease that affects the lower airways of young children increasing the inspiratory and expiratory resistance in variable degree as well as reducing the pulmonary compliance. It would be desirable to know whether these variables are associated with the outcome.ObjectivesTo evaluate the respiratory mechanics in infants with AVB requiring mechanical ventilation (MV) support and to evaluate if respiratory mechanics predict outcomes in children with AVB supported on MV. To evaluate the respiratory mechanics in infants with AVB submitted to MV.Materials and methodsA prospective observational study was conducted in two pediatric intensive care units (PICUs) between February 2016 and March 2017. Included were infants (1 month to 1 year old) admitted with AVB and requiring MV for >48 hours. Auto-PEEP, dynamic compliance (Cdyn), static compliance (Cstat), expiratory resistance (ExRes), and inspiratory resistance (InRes) were evaluated once daily on the second and third day of MV.ResultsA total of 64 infants (median age of 2.8 months and a mean weight of 4.8 ± 1.7 kg) were evaluated. A mean positive inspiratory pressure (PIP) of 31.5 ± 5.2 cmH2O, positive end-expiratory pressure (PEEP) of 5.5 ± 1.4 cmH2O, resulting in a mean airway pressure (MAP) of 12.5 ± 2.2 cmH2O and delta pressure of 22.5 ± 4.4 cmH2O without difference between the two hospitals. Measurements of respiratory mechanics showed high values of InRes and ExRes (median 142 [IQ25–75 106–180] cmH2O/L/s and 158 [IQ25–75 130–195.3] cmH2O/L/s, respectively), accompanied by decreased Cdyn and Cstat (0.46 ± 0.19 and 0.81 ± 0.25 mL/kg/cmH2O, respectively). None of the variables was associated with mortality, length of MV, or length of PICU stay.ConclusionInfants with AVB requiring MV support present very high InRes and ExRes values. These findings might be the reason for the aggressive ventilatory parameters, especially PIP, required to ventilate this group of children with lower airway obstruction.Clinical significanceMonitoring respiratory mechanics could represent a useful tool to guide the ventilatory strategy to be adopted in patients with AVB.How to cite this articleAndreolio C, Piva JP, Bruno F, da Rocha TS, Garcia PCR. Airway Resistance and Respiratory Compliance in Children with Acute Viral Bronchiolitis Requiring Mechanical Ventilation Support. Indian J Crit Care Med 2021;25(1):88–93.

Nonlinear parametric quantile models.

Quantile regression is widely used to estimate conditional quantiles of an outcome variable of interest given covariates. This method can estimate one quantile at a time without imposing any constraints on the quantile process other than the linear combination of covariates and parameters specified by the regression model. While this is a flexible modeling tool, it generally yields erratic estimates of conditional quantiles and regression coefficients. Recently, parametric models for the regression coefficients have been proposed that can help balance bias and sampling variability. So far, however, only models that are linear in the parameters and covariates have been explored. This paper presents the general case of nonlinear parametric quantile models. These can be nonlinear with respect to the parameters, the covariates, or both. Some important features and asymptotic properties of the proposed estimator are described, and its finite-sample behavior is assessed in a simulation study. Nonlinear parametric quantile models are applied to estimate extreme quantiles of longitudinal measures of respiratory mechanics in asthmatic children from an epidemiological study and to evaluate a dose-response relationship in a toxicological laboratory experiment.

Effect of mechanical power on intensive care mortality in ARDS patients

BackgroundIn ARDS patients, mechanical ventilation should minimize ventilator-induced lung injury. The mechanical power which is the energy per unit time released to the respiratory system according to the applied tidal volume, PEEP, respiratory rate, and flow should reflect the ventilator-induced lung injury. However, similar levels of mechanical power applied in different lung sizes could be associated to different effects. The aim of this study was to assess the role both of the mechanical power and of the transpulmonary mechanical power, normalized to predicted body weight, respiratory system compliance, lung volume, and amount of aerated tissue on intensive care mortality.MethodsRetrospective analysis of ARDS patients previously enrolled in seven published studies. All patients were sedated, paralyzed, and mechanically ventilated.After 20 min from a recruitment maneuver, partitioned respiratory mechanics measurements and blood gas analyses were performed with a PEEP of 5 cmH2O while the remaining setting was maintained unchanged from the baseline. A whole lung CT scan at 5 cmH2O of PEEP was performed to estimate the lung gas volume and the amount of well-inflated tissue.Univariate and multivariable Poisson regression models with robust standard error were used to calculate risk ratios and 95% confidence intervals of ICU mortality.ResultsTwo hundred twenty-two ARDS patients were included; 88 (40%) died in ICU. Mechanical power was not different between survivors and non-survivors 14.97 [11.51–18.44] vs. 15.46 [12.33–21.45] J/min and did not affect intensive care mortality. The multivariable robust regression models showed that the mechanical power normalized to well-inflated tissue (RR 2.69 [95% CI 1.10–6.56], p = 0.029) and the mechanical power normalized to respiratory system compliance (RR 1.79 [95% CI 1.16–2.76], p = 0.008) were independently associated with intensive care mortality after adjusting for age, SAPS II, and ARDS severity. Also, transpulmonary mechanical power normalized to respiratory system compliance and to well-inflated tissue significantly increased intensive care mortality (RR 1.74 [1.11–2.70], p = 0.015; RR 3.01 [1.15–7.91], p = 0.025).ConclusionsIn our ARDS population, there is not a causal relationship between the mechanical power itself and mortality, while mechanical power normalized to the compliance or to the amount of well-aerated tissue is independently associated to the intensive care mortality. Further studies are needed to confirm this data.

Reproducibility of respiratory mechanics measurements in patients on invasive mechanical ventilation.

ObjectiveTo evaluate the intra- and interexaminer reproducibility of measurements of the resistance and static and dynamic compliance of the respiratory system in patients on mechanical ventilation.MethodsThis was an analytical study conducted with individuals aged ≥ 18 years who were on invasive mechanical ventilation and had no clinical diagnosis of respiratory system disease and/or chest abnormality. Three measurements of respiratory mechanics were performed with a 1-minute interval between them. The first and third measurements were performed by examiner A, the second by examiner B. The values for the resistance and static and dynamic compliance of the respiratory system were compared using the intraclass correlation coefficient.ResultsA total of 198 measurements of respiratory mechanics were performed for 66 patients on mechanical ventilation. The patients had a mean age of 52.6 ± 18.6 years and a mean body mass index of 21.6 ± 2.1kg/m2; a surgical profile (61.5%) and female sex (53.8%) were predominant. Mean values were obtained for the three measurements of respiratory system resistance (A1: 15.7 ± 6.8cmH2O/L/s; B1: 15.7 ± 6.4cmH2O/L/s and A2: 15.9 ± 6.2cmH2O/L/s), respiratory system static compliance (A1: 42.1 ± 13.7mL/cmH2O; B1: 42.4 ± 14.6mL/cmH2O and A2: 42.2 ± 14.5mL/cmH2O) and respiratory system dynamic compliance (A1: 21.3 ± 7.3mL/cmH2O; B1: 21.4 ± 7.5mL/cmH2O and A2: 21.3 ± 6.2mL/cmH2O). The intraclass correlation coefficient was also calculated for respiratory system resistance (R = 0.882 and p = 0.001; R = 0.949 and p = 0.001 - interexaminer A1 versus B and B versus A2, respectively; R = 0.932 and p = 0.001 - intraexaminer); respiratory system static compliance (R = 0.951 and p = 0.001; R = 0.958 and p = 0.001 - interexaminer A1 versus B and B versus A2, respectively; R = 0.965 and p = 0.001 - intraexaminer) and respiratory system dynamic compliance (R = 0.957 and p = 0.001; R = 0.946 and p = 0.001 - interexaminer A1 versus B and B versus A2, respectively; R = 0.926 and p = 0.001 - intraexaminer).ConclusionThe measurements of resistance and static and dynamic compliance of the respiratory system show good intra- and interexaminer reproducibility for ventilated patients.

Negative results for ketamine use in severe acute bronchospasm: a randomised controlled trial.

Ketamine has bronchodilation properties. The aim of the single-centre, evaluator-blinded, randomised clinical trial study was to evaluate whether continuous infusion of ketamine is associated with improvement in respiratory mechanics correlated with bronchospasm relief, as compared with continuous infusion of fentanyl. Adult patients submitted to invasive mechanical ventilation were included if they had an acute severe bronchospasm, due to status asthmaticus or COPD exacerbation. They were randomised to ketamine or a standard IV analgesia with fentanyl, both in bolus and continuous infusion. Measurements of respiratory mechanics (airway resistance - R_smax, dynamic compliance - C_dyn and intrinsic PEEP - PEEPi) both at baseline and 3 and 24 h after randomisation were performed. The main outcome of this study was to evaluate the improvement of R_smax in 3 h of continuous infusion of the study drugs. Ketamine use was not associated with greater reduction in R_smax when compared with fentanyl, either after 3 h (0 cm H₂O L-1 s-1 ± 6 vs. -3 cm H₂O L-1 s-1 ± 7.7, respectively; P = 0.16) or after 24 h (-3 cm H₂O L-1 s-1 ± 17 vs. -3.5 cm H₂O L-1 s-1 ± 13.7, respectively; P = 0.73). Patients randomized to the ketamine group did not have better improvements in delta PEEPi as compared with fentanyl in 3 h (P = 0.77) or in 24 h (P = 0.72). In this study, ketamine use was not associated with improvement in ventilatory variables associated with bronchospasm.

How to measure respiratory mechanics during controlled mechanical ventilation

Bedside measurement of respiratory mechanics allows to closely monitor the lung function in critically ill patients. The two fundamental parameters describing the respiratory system mechanics are resistance and compliance. Resistance of the respiratory system describes the opposition to gas flow during inspiration. During volume-controlled ventilation, resistance can be calculated as the ratio between the peak to plateau pressure drop and the resulting flow rate. Compliance describes the elastic property of the respiratory system, comprising the lung and the chest wall. It is the ratio between a change in volume (i.e. tidal volume) and the corresponding change in pressure, calculated as the difference between plateau pressure and total positive end-expiratory pressure, measured by end-inspiratory and end-expiratory manual occlusion, respectively. In this review, we describe how to measure respiratory mechanics at the bedside, starting from the physiological background of the equation of motion of the respiratory system. (Intensive care)

Non-invasive measurements of respiratory system mechanical properties by the forced oscillation technique in spontaneously breathing, mixed-breed, normal term lambs from birth to five months of age

Objective: To provide a non-invasive approach to monitoring lung function in spontaneously breathing lambs, from birth to five months of life, by the forced oscillation technique (FOT). This report describes the experimental set-up, data processing, and identification of normal predicted values of resistance (Rrs) and reactance (Xrs) of the respiratory system, along with normal bronchodilator response for bronchial reversibility testing. Approach: Rrs and Xrs at 5, 11, and 19 Hz were measured monthly for five months in 20 normal term lambs that breathed spontaneously. In seven lambs, repeated measurements also were made within the first month of life (at 3, 7, 14, and 21 d of life). We determined the repeatability and reproducibility of the measurements and characterized the relationship between lung mechanics and age, sex, and body dimensions, using regression analysis, and measured changes in lung mechanics in response to inhaled bronchodilator. Main results: The measurements provided repeatable and reproducible data. Rrs decreased, whereas Xrs increased, with growth from birth through the first two months of life, after which no statistically significant differences were detected. We identified normal value equations for Rrs and Xrs and for each of the measured anthropometric variables. Respiratory system mechanics were not affected by the bronchodilator. Significance: The FOT provides reliable non-invasive measurement of respiratory system mechanics in spontaneously breathing term lambs from birth to five months of age. The methods and normal reference values defined in this study will facilitate testing of the pathophysiological consequences of preterm birth and prolonged respiratory support on respiratory system mechanics.

Accuracy of the Ventilator Automated Displayed Respiratory Mechanics in Passive and Active Breathing Conditions: A Bench Study.

New-generation ventilators display dynamic measures of respiratory mechanics, such as compliance, resistance, and auto-PEEP. Knowledge of the respiratory mechanics is paramount to clinicians at the bedside. These calculations are obtained automatically by using the least squares fitting method of the equation of motion. The accuracy of these calculations in static and dynamic conditions have not been fully validated or examined in different clinical conditions or various ventilator modes. A bench study was performed by using a lung simulator to compare the ventilator automated calculations during passive and active conditions. Three clinical scenarios (normal, COPD, and ARDS) were simulated with known compliances and resistance set per respective condition: normal (compliance 50 mL/cm H2O, resistance 10 cm H2O/L/s), COPD (compliance 60 mL/cm H2O, resistance 22 cm H2O/L/s), and ARDS (compliance 30 mL/cm H2O, and resistance 13 cm H2O/L/s). Each scenario was subjected to 4 different muscle pressures (Pmus): 0, -5, -10, and -15 cm H2O. All the experiments were done using adaptive support ventilation. The resulting automated dynamic calculations of compliance and resistance were then compared based on the clinical scenarios. There was a small bias (average error) and level of agreement in the passive conditions in all the experiments; however, these errors and levels of agreement got progressively higher proportional to the increased Pmus. There was a strong positive correlation between Pmus and compliance measured as well as a strong negative correlation between Pmus and resistance measured. Automated displayed calculations of respiratory mechanics were not dependable or accurate in active breathing conditions. The calculations were clinically more reliable in passive conditions. We propose different methods of calculating Pmus, which, if incorporated into the calculations, would improve the accuracy of respiratory mechanics made via the least squares fitting method in actively breathing conditions.