Positive end-expiratory pressure limits inspiratory effort through modulation of the effort-to-drive ratio: an experimental crossover study.

BACKGROUND: How assisted spontaneous breathing should be used during acute respiratory distress syndrome is questioned. Recent evidence suggests that high positive end-expiratory pressure (PEEP) may limit the risk of patient self-inflicted lung injury (P-SILI). The aim of this study was to assess the effects of PEEP on esophageal pressure swings, inspiratory drive, and the neuromuscular efficiency of ventilation. We hypothesized that high PEEP would reduce esophageal pressure swings, regardless of inspiratory drive changes, by modulating the effort-to-drive ratio (EDR). This was tested retrospectively in an experimental animal crossover study. Anesthetized pigs (n = 15) were subjected to mild to moderate lung injury and different PEEP levels were applied, changing PEEP from 0 to 15 cmH2O and back to 0 cmH2O in steps of 3 cmH2O. Airway pressure, esophageal pressure (Pes), and electric activity of the diaphragm (Edi) were collected. The EDR was calculated as the tidal change in Pes divided by the tidal change in Edi. Statistical differences were tested using the Wilcoxon signed-rank test. RESULTS: Inspiratory esophageal pressure swings decreased from - 4.2 ± 3.1 cmH2O to - 1.9 ± 1.5 cmH2O (p < 0.01), and the mean EDR fell from - 1.12 ± 1.05 cmH2O/µV to - 0.24 ± 0.20 (p < 0.01) as PEEP was increased from 0 to 15 cmH2O. The EDR was significantly correlated to the PEEP level (rs = 0.35, p < 0.01). CONCLUSIONS: Higher PEEP limits inspiratory effort by modulating the EDR of the respiratory system. These findings indicate that PEEP may be used in titration of the spontaneous impact on ventilation and in P-SILI risk reduction, potentially facilitating safe assisted spontaneous breathing. Similarly, ventilation may be shifted from highly spontaneous to predominantly controlled ventilation using PEEP. These findings need to be confirmed in clinical settings.

Quantifying heterogeneity in an animal model of acute respiratory distress syndrome, a comparison of inspired sinewave technique to computed tomography.

The inspired sinewave technique (IST) is a non-invasive method to measure lung heterogeneity indices (including both uneven ventilation and perfusion or heterogeneity), which reveal multiple conditions of the lung and lung injury. To evaluate the reproducibility and predicted clinical outcomes of IST heterogeneity values, a comparison with a quantitative lung computed tomography (CT) scan is performed. Six anaesthetised pigs were studied after surfactant depletion by saline-lavage. Paired measurements of lung heterogeneity were then taken with both the IST and CT. Lung heterogeneity measured by the IST was calculated by (a) the ratio of tracer gas outputs measured at oscillation periods of 180 s and 60 s, and (b) by the standard deviation of the modelled log-normal distribution of ventilations and perfusions in the simulation lung. In the CT images, lungs were manually segmented and divided into different regions according to voxel density. A quantitative CT method to calculate the heterogeneity (the Cressoni method) was applied. The IST and CT show good Pearson correlation coefficients in lung heterogeneity measurements (ventilation: 0.71, and perfusion, 0.60, p < 0.001). Within individual animals, the coefficients of determination average ventilation (R2 = 0.53) and perfusion (R2 = 0.68) heterogeneity. Strong concordance rates of 98% in ventilation and 89% when the heterogeneity changes were reported in pairs measured by CT scanning and IST methods. This quantitative method to identify heterogeneity has the potential to replicate CT lung heterogeneity, and to aid individualised care in ARDS.

Intra-tidal PaO2 oscillations associated with mechanical ventilation: a pilot study to identify discrete morphologies in a porcine model.

BACKGROUND: Within-breath oscillations in arterial oxygen tension (PaO2) can be detected using fast responding intra-arterial oxygen sensors in animal models. These PaO2 signals, which rise in inspiration and fall in expiration, may represent cyclical recruitment/derecruitment and, therefore, a potential clinical monitor to allow titration of ventilator settings in lung injury. However, in hypovolaemia models, these oscillations have the potential to become inverted, such that they decline, rather than rise, in inspiration. This inversion suggests multiple aetiologies may underlie these oscillations. A correct interpretation of the various PaO2 oscillation morphologies is essential to translate this signal into a monitoring tool for clinical practice. We present a pilot study to demonstrate the feasibility of a new analysis method to identify these morphologies. METHODS: Seven domestic pigs (average weight 31.1 kg) were studied under general anaesthesia with muscle relaxation and mechanical ventilation. Three underwent saline-lavage lung injury and four were uninjured. Variations in PEEP, tidal volume and presence/absence of lung injury were used to induce different morphologies of PaO2 oscillation. Functional principal component analysis and k-means clustering were employed to separate PaO2 oscillations into distinct morphologies, and the cardiorespiratory physiology associated with these PaO2 morphologies was compared. RESULTS: PaO2 oscillations from 73 ventilatory conditions were included. Five functional principal components were sufficient to explain ≥ 95% of the variance of the recorded PaO2 signals. From these, five unique morphologies of PaO2 oscillation were identified, ranging from those which increased in inspiration and decreased in expiration, through to those which decreased in inspiration and increased in expiration. This progression was associated with the estimates of the first functional principal component (P < 0.001, R2 = 0.88). Intermediate morphologies demonstrated waveforms with two peaks and troughs per breath. The progression towards inverted oscillations was associated with increased pulse pressure variation (P = 0.03). CONCLUSIONS: Functional principal component analysis and k-means clustering are appropriate to identify unique morphologies of PaO2 waveform associated with distinct cardiorespiratory physiology. We demonstrated novel intermediate morphologies of PaO2 waveform, which may represent a development of zone 2 physiologies within the lung. Future studies of PaO2 oscillations and modelling should aim to understand the aetiologies of these morphologies.

Fluid restrictive resuscitation with high molecular weight hyaluronan infusion in early peritonitis sepsis.

Sepsis is a condition with high morbidity and mortality. Prompt recognition and initiation of treatment is essential. Despite forming an integral part of sepsis management, fluid resuscitation may also lead to volume overload, which in turn is associated with increased mortality. The optimal fluid strategy in sepsis resuscitation is yet to be defined. Hyaluronan, an endogenous glycosaminoglycan with high affinity to water is an important constituent of the endothelial glycocalyx. We hypothesized that exogenously administered hyaluronan would counteract intravascular volume depletion and contribute to endothelial glycocalyx integrity in a fluid restrictive model of peritonitis. In a prospective, blinded model of porcine peritonitis sepsis, we randomized animals to intervention with hyaluronan (n = 8) or 0.9% saline (n = 8). The animals received an infusion of 0.1% hyaluronan 6 ml/kg/h, or the same volume of saline, during the first 2 h of peritonitis. Stroke volume variation and hemoconcentration were comparable in the two groups throughout the experiment. Cardiac output was higher in the intervention group during the infusion of hyaluronan (3.2 ± 0.5 l/min in intervention group vs 2.7 ± 0.2 l/min in the control group) (p = 0.039). The increase in lactate was more pronounced in the intervention group (3.2 ± 1.0 mmol/l in the intervention group and 1.7 ± 0.7 mmol/l in the control group) at the end of the experiment (p < 0.001). Concentrations of surrogate markers of glycocalyx damage; syndecan 1 (0.6 ± 0.2 ng/ml vs 0.5 ± 0.2 ng/ml, p = 0.292), heparan sulphate (1.23 ± 0.2 vs 1.4 ± 0.3 ng/ml, p = 0.211) and vascular adhesion protein 1 (7.0 ± 4.1 vs 8.2 ± 2.3 ng/ml, p = 0.492) were comparable in the two groups at the end of the experiment. In conclusion, hyaluronan did not counteract intravascular volume depletion in early peritonitis sepsis. However, this finding is hampered by the short observation period and a beneficial effect of HMW-HA in peritonitis sepsis cannot be discarded based on the results of the present study.

Quantitative assessment of atelectasis formation under high frequency jet ventilation during liver tumour ablation-A computer tomography study.

BACKGROUND: High frequency jet ventilation (HFJV) can be used to minimise sub-diaphragmal organ displacements. Treated patients are in a supine position, under general anaesthesia and fully muscle relaxed. These are factors that are known to contribute to the formation of atelectasis. The HFJV-catheter is inserted freely inside the endotracheal tube and the system is therefore open to atmospheric pressure. AIM: The aim of this study was to assess the formation of atelectasis over time during HFJV in patients undergoing liver tumour ablation under general anaesthesia. METHOD: In this observational study twenty-five patients were studied. Repeated computed tomography (CT) scans were taken at the start of HFJV and every 15 minutes thereafter up until 45 minutes. From the CT images, four lung compartments were defined: hyperinflated, normoinflated, poorly inflated and atelectatic areas. The extension of each lung compartment was expressed as a percentage of the total lung area. RESULT: Atelectasis at 30 minutes, 7.9% (SD 3.5, p = 0.002) and at 45 minutes 8,1% (SD 5.2, p = 0.024), was significantly higher compared to baseline 5.6% (SD 2.5). The amount of normoinflated lung volumes were unchanged over the period studied. Only a few minor perioperative respiratory adverse events were noted. CONCLUSION: Atelectasis during HFJV in stereotactic liver tumour ablation increased over the first 45 minutes but tended to stabilise with no impact on normoinflated lung volume. Using HFJV during stereotactic liver ablation is safe regarding formation of atelectasis.

PET Imaging of Neutrophil Elastase with 11C-GW457427 in Acute Respiratory Distress Syndrome in Pigs.

Today, there is a lack of clinically available imaging techniques to detect and quantify specific immune cell populations. Neutrophils are one of the first immune cells at the site of inflammation, and they secrete the serine protease neutrophil elastase (NE), which is crucial in the fight against pathogens. However, the prolonged lifespan of neutrophils increases the risk that patients will develop severe complications, such as acute respiratory distress syndrome (ARDS). Here, we evaluated the novel radiolabeled NE inhibitor 11C-GW457427 in a pig model of ARDS, for detection and quantification of neutrophil activity in the lungs. Methods: ARDS was induced by intravenous administration of oleic acid to 5 farm pigs, and 4 were considered healthy controls. The severity of ARDS was monitored by clinical parameters of lung function and plasma biomarkers. Each pig was studied with 11C-GW457427 and PET/CT, before and after pretreatment with the NE inhibitor GW311616 to determine in vivo binding specificity. PET image data were analyzed as SUVs and correlated with immunohistochemical staining for NE in biopsies. Results: The binding of 11C-GW457427 was increased in pig lungs with induced ARDS (median SUVmean, 1.91; interquartile range [IQR], 1.67-2.55) compared with healthy control pigs (P < 0.05 and P = 0.03, respectively; median SUVmean, 1.04; IQR, 0.66-1.47). The binding was especially strong in lung regions with high levels of NE and ongoing inflammation, as verified by immunohistochemistry. The binding was successfully blocked by pretreatment of an NE inhibitor drug, which demonstrated the in vivo specificity of 11C-GW457427 (P < 0.05 and P = 0.04, respectively; median SUVmean, 0.60; IQR, 0.58-0.77). The binding in neutrophil-rich tissues such as bone marrow (P < 0.05 and P = 0.04, respectively; baseline median SUVmean, 5.01; IQR, 4.48-5.49; block median SUVmean, 1.57; IQR, 0.95-1.85) and spleen (median SUVmean, 2.14; IQR, 1.19-2.36) was also high in all pigs. Conclusion: 11C-GW457427 binds to NE in a porcine model of oleic acid-induced lung inflammation in vivo, with a specific increase in regional lung, bone marrow, and spleen SUV. 11C-GW457427 is a promising tool for localizing, tracking, and quantifying neutrophil-facilitated inflammation in clinical diagnostics and drug development.

Homogenizing effect of PEEP on tidal volume distribution during neurally adjusted ventilatory assist: study of an animal model of acute respiratory distress syndrome.

BACKGROUND: The physiological response and the potentially beneficial effects of positive end-expiratory pressure (PEEP) for lung protection and optimization of ventilation during spontaneous breathing in patients with acute respiratory distress syndrome (ARDS) are not fully understood. The aim of the study was to compare the effect of different PEEP levels on tidal volume distribution and on the ventilation of dependent lung region during neurally adjusted ventilatory assist (NAVA). METHODS: ARDS-like lung injury was induced by using saline lavage in 10 anesthetized and spontaneously breathing farm-bred pigs. The animals were ventilated in NAVA modality and tidal volume distribution as well as dependent lung ventilation were assessed using electric impedance tomography during the application of PEEP levels from 0 to 15 cmH20, in steps of 3 cmH20. Tidal volume distribution and dependent fraction of ventilation were analysed using Wilcoxon signed rank test. Furthermore, airway, esophageal and transpulmonary pressure, as well as airway flow and delivered volume, were continuously measured during the assisted spontaneous breathing. RESULTS: Increasing PEEP improved oxygenation and re-distributed tidal volume. Specifically, ventilation distribution changed from a predominant non-dependent to a more even distribution between non-dependent and dependent areas of the lung. Dependent fraction of ventilation reached 47 ± 9% at PEEP 9 cmH20. Further increasing PEEP led to a predominant dependent ventilation. CONCLUSION: During assisted spontaneous breathing in this model of induced ARDS, PEEP modifies the distribution of ventilation and can achieve a homogenizing effect on its spatial arrangement. The study indicates that PEEP is an important factor during assisted spontaneous breathing and that EIT can be of valuable interest when titrating PEEP level during spontaneous breathing, by indicating the most homogeneous distribution of gas volumes throughout the PEEP spectrum.

Chest dual-energy CT to assess the effects of steroids on lung function in severe COVID-19 patients.

BACKGROUND: Steroids have been shown to reduce inflammation, hypoxic pulmonary vasoconstriction (HPV) and lung edema. Based on evidence from clinical trials, steroids are widely used in severe COVID-19. However, the effects of steroids on pulmonary gas volume and blood volume in this group of patients are unexplored. OBJECTIVE: Profiting by dual-energy computed tomography (DECT), we investigated the relationship between the use of steroids in COVID-19 and distribution of blood volume as an index of impaired HPV. We also investigated whether the use of steroids influences lung weight, as index of lung edema, and how it affects gas distribution. METHODS: Severe COVID-19 patients included in a single-center prospective observational study at the intensive care unit at Uppsala University Hospital who had undergone DECT were enrolled in the current study. Patients' cohort was divided into two groups depending on the administration of steroids. From each patient's DECT, 20 gas volume maps and the corresponding 20 blood volume maps, evenly distributed along the cranial-caudal axis, were analyzed. As a proxy for HPV, pulmonary blood volume distribution was analyzed in both the whole lung and the hypoinflated areas. Total lung weight, index of lung edema, was estimated. RESULTS: Sixty patients were analyzed, whereof 43 received steroids. Patients not exposed to steroids showed a more extensive non-perfused area (19% vs 13%, p < 0.01) and less homogeneous pulmonary blood volume of hypoinflated areas (kurtosis: 1.91 vs 2.69, p < 0.01), suggesting a preserved HPV compared to patients treated with steroids. Moreover, patients exposed to steroids showed a significantly lower lung weight (953 gr vs 1140 gr, p = 0.01). A reduction in alveolar-arterial difference of oxygen followed the treatment with steroids (322 ± 106 mmHg at admission vs 267 ± 99 mmHg at DECT, p = 0.04). CONCLUSIONS: The use of steroids might cause impaired HPV and might reduce lung edema in severe COVID-19. This is consistent with previous findings in other diseases. Moreover, a reduced lung weight, as index of decreased lung edema, and a more homogeneous distribution of gas within the lung were shown in patients treated with steroids. TRIAL REGISTRATION: Clinical Trials ID: NCT04316884, Registered March 13, 2020.

What is new in respiratory monitoring?

This paper provides a review of a selection of papers published in the Journal of Clinical Monitoring and Computing in 2020 and 2021 highlighting what is new within the field of respiratory monitoring. Selected papers cover work in pulse oximetry monitoring, acoustic monitoring, respiratory system mechanics, monitoring during surgery, electrical impedance tomography, respiratory rate monitoring, lung ultrasound and detection of patient-ventilator asynchrony.

PET-CT imaging of pulmonary inflammation using [68Ga]Ga-DOTA-TATE.

PURPOSE: In the characterization of severe lung diseases, early detection of specific inflammatory cells could help to monitor patients' response to therapy and increase chances of survival. Macrophages contribute to regulating the resolution and termination of inflammation and have increasingly been of interest for targeted therapies. [68Ga]Ga-DOTA-TATE is an established clinical radiopharmaceutical targeting somatostatin receptor subtype 2 (SSTR 2). Since activated macrophages (M1) overexpress SSTR 2, the aim of this study was to investigate the applicability of [68Ga]Ga-DOTA-TATE for positron emission tomography (PET) imaging of M1 macrophages in pulmonary inflammation. METHODS: Inflammation in the pig lungs was induced by warm saline lavage followed by injurious ventilation in farm pigs (n = 7). Healthy pigs (n = 3) were used as control. A 60-min dynamic PET scan over the lungs was performed after [68Ga]Ga-DOTA-TATE injection and [18F]FDG scan was executed afterward for comparison. The uptake of both tracers was assessed as mean standardized uptake values (SUVmean) 30-60-min post-injection. The PET scans were followed by computed tomography (CT) scans, and the Hounsfield units (HU) were quantified of the coronal segments. Basal and apical segments of the lungs were harvested for histology staining. A rat lung inflammation model was also studied for tracer specificity using lipopolysaccharides (LPS) by oropharyngeal aspiration. Organ biodistribution, ex vivo autoradiography (ARG) and histology samples were conducted on LPS treated, octreotide induced blocking and control healthy rats. RESULTS: The accumulation of [68Ga]Ga-DOTA-TATE on pig lavage model was prominent in the more severely injured dorsal segments of the lungs (SUVmean = 0.91 ± 0.56), compared with control animals (SUVmean = 0.27 ± 0.16, p < 0.05). The tracer uptake corresponded to the damaged areas assessed by CT and histology and were in line with HU quantification. The [68Ga]Ga-DOTA-TATE uptake in LPS treated rat lungs could be blocked and was significantly higher compared with control group. CONCLUSION: The feasibility of the noninvasive assessment of tissue macrophages using [68Ga]Ga-DOTA-TATE/PET was demonstrated in both porcine and rat lung inflammation models. [68Ga]Ga-DOTA-TATE has a great potential to be used to study the role and presence of macrophages in humans in fight against severe lung diseases.

Limitations of the ARDS criteria during high-flow oxygen or non-invasive ventilation: evidence from critically ill COVID-19 patients.

BACKGROUND: The ratio of partial pressure of arterial oxygen to inspired oxygen fraction (PaO2/FIO2) during invasive mechanical ventilation (MV) is used as criteria to grade the severity of respiratory failure in acute respiratory distress syndrome (ARDS). During the SARS-CoV2 pandemic, the use of PaO2/FIO2 ratio has been increasingly used in non-invasive respiratory support such as high-flow nasal cannula (HFNC) and non-invasive ventilation (NIV). The grading of hypoxemia in non-invasively ventilated patients is uncertain. The main hypothesis, investigated in this study, was that the PaO2/FIO2 ratio does not change when switching between MV, NIV and HFNC. METHODS: We investigated respiratory function in critically ill patients with COVID-19 included in a single-center prospective observational study of patients admitted to the intensive care unit (ICU) at Uppsala University Hospital in Sweden. In a steady state condition, the PaO2/FIO2 ratio was recorded before and after any change between two of the studied respiratory support techniques (i.e., HFNC, NIV and MV). RESULTS: A total of 148 patients were included in the present analysis. We find that any change in respiratory support from or to HFNC caused a significant change in PaO2/FIO2 ratio. Changes in respiratory support between NIV and MV did not show consistent change in PaO2/FIO2 ratio. In patients classified as mild to moderate ARDS during MV, the change from HFNC to MV showed a variable increase in PaO2/FIO2 ratio ranging between 52 and 140 mmHg (median of 127 mmHg). This made prediction of ARDS severity during MV from the apparent ARDS grade during HFNC impossible. CONCLUSIONS: HFNC is associated with lower PaO2/FIO2 ratio than either NIV or MV in the same patient, while NIV and MV provided similar PaO2/FIO2 and thus ARDS grade by Berlin definition. The large variation of PaO2/FIO2 ratio indicates that great caution should be used when estimating ARDS grade as a measure of pulmonary damage during HFNC.

Imaging Regional Lung Structure and Function in Small Animals Using Synchrotron Radiation Phase-Contrast and K-Edge Subtraction Computed Tomography.

Synchrotron radiation offers unique properties of coherence, utilized in phase-contrast imaging, and high flux as well as a wide energy spectrum which allow the selection of very narrow energy bands of radiation, used in K-edge subtraction imaging (KES) imaging. These properties extend X-ray computed tomography (CT) capabilities to quantitatively assess lung morphology, and to map regional lung ventilation, perfusion, inflammation, aerosol particle distribution and biomechanical properties, with microscopic spatial resolution. Four-dimensional imaging, allows the investigation of the dynamics of regional lung functional parameters simultaneously with structural deformation of the lung as a function of time. These techniques have proven to be very useful for revealing the regional differences in both lung structure and function which is crucial for better understanding of disease mechanisms as well as for evaluating treatment in small animal models of lung diseases. Here, synchrotron radiation imaging methods are described and examples of their application to the study of disease mechanisms in preclinical animal models are presented.

Lung tissue biomechanics imaged with synchrotron phase contrast microtomography in live rats.

The magnitude and distribution of strain imposed on the peripheral airspaces by mechanical ventilation at the microscopic level and the consequent deformations are unknown despite their importance for understanding the mechanisms occurring at the onset of ventilator-induced lung injury. Here a 4-Dimensional (3D + time) image acquisition and processing technique is developed to assess pulmonary acinar biomechanics at microscopic resolution. Synchrotron radiation phase contrast CT with an isotropic voxel size of 6 µm3 is applied in live anesthetized rats under controlled mechanical ventilation. Video animations of regional acinar and vascular strain are acquired in vivo. Maps of strain distribution due to positive-pressure breaths and cardiovascular activity in lung acini and blood vessels are derived based on CT images. Regional strain within the lung peripheral airspaces takes average values of 0.09 ± 0.02. Fitting the expression S = kVn, to the changes in peripheral airspace area (S) and volume (V) during a positive pressure breath yields an exponent n = 0.82 ± 0.03, suggesting predominant alveolar expansion rather than ductal expansion or alveolar recruitment. We conclude that this methodology can be used to assess acinar conformational changes during positive pressure breaths in intact peripheral lung airspaces.

Development of a method to measure regional perfusion of the lung in anesthetized ponies using computed tomography angiography and the maximum slope model.

OBJECTIVE: To develop a method based on CT angiography and the maximum slope model (MSM) to measure regional lung perfusion in anesthetized ponies. ANIMALS: 6 ponies. PROCEDURES: Anesthetized ponies were positioned in dorsal recumbency in the CT gantry. Contrast was injected, and the lungs were imaged while ponies were breathing spontaneously and while they were mechanically ventilated. Two observers delineated regions of interest in aerated and atelectatic lung, and perfusion in those regions was calculated with the MSM. Measurements obtained with a computerized method were compared with manual measurements, and computerized measurements were compared with previously reported measurements obtained with microspheres. RESULTS: Perfusion measurements obtained with the MSM were similar to previously reported values obtained with the microsphere method. While ponies were spontaneously breathing, mean ± SD perfusion for aerated and atelectatic lung regions were 4.0 ± 1.9 and 5.0 ± 1.2 mL/min/g of lung tissue, respectively. During mechanical ventilation, values were 4.6 ± 1.2 and 2.7 ± 0.7 mL/min/g of lung tissue at end expiration and 4.1 ± 0.5 and 2.7 ± 0.6 mL/min/g of lung tissue at peak inspiration. Intraobserver agreement was acceptable, but interobserver agreement was lower. Computerized measurements compared well with manual measurements. CLINICAL RELEVANCE: Findings showed that CT angiography and the MSM could be used to measure regional lung perfusion in dorsally recumbent anesthetized ponies. Measurements are repeatable, suggesting that the method could be used to determine efficacy of therapeutic interventions to improve ventilation-perfusion matching and for other studies for which measurement of regional lung perfusion is necessary.

A quantitative analysis of extension and distribution of lung injury in COVID-19: a prospective study based on chest computed tomography.

BACKGROUND: Typical features differentiate COVID-19-associated lung injury from acute respiratory distress syndrome. The clinical role of chest computed tomography (CT) in describing the progression of COVID-19-associated lung injury remains to be clarified. We investigated in COVID-19 patients the regional distribution of lung injury and the influence of clinical and laboratory features on its progression. METHODS: This was a prospective study. For each CT, twenty images, evenly spaced along the cranio-caudal axis, were selected. For regional analysis, each CT image was divided into three concentric subpleural regions of interest and four quadrants. Hyper-, normally, hypo- and non-inflated lung compartments were defined. Nonparametric tests were used for hypothesis testing (α = 0.05). Spearman correlation test was used to detect correlations between lung compartments and clinical features. RESULTS: Twenty-three out of 111 recruited patients were eligible for further analysis. Five hundred-sixty CT images were analyzed. Lung injury, composed by hypo- and non-inflated areas, was significantly more represented in subpleural than in core lung regions. A secondary, centripetal spread of lung injury was associated with exposure to mechanical ventilation (p < 0.04), longer spontaneous breathing (more than 14 days, p < 0.05) and non-protective tidal volume (p < 0.04). Positive fluid balance (p < 0.01), high plasma D-dimers (p < 0.01) and ferritin (p < 0.04) were associated with increased lung injury. CONCLUSIONS: In a cohort of COVID-19 patients with severe respiratory failure, a predominant subpleural distribution of lung injury is observed. Prolonged spontaneous breathing and high tidal volumes, both causes of patient self-induced lung injury, are associated to an extensive involvement of more central regions. Positive fluid balance, inflammation and thrombosis are associated with lung injury. Trial registration Study registered a priori the 20th of March, 2020. Clinical Trials ID NCT04316884.

Comparison of two injectable anaesthetic techniques on induction and subsequent anaesthesia in pigs.

Pig experiments often require anaesthesia, and a rapid stress-free induction is desired. Induction drugs may alter the subsequent anaesthesia. Therefore, the aim of the present study was to compare, in pigs, the effects of two different injectable anaesthetic techniques on the induction and on the physiological variables in a subsequent eight hours of total intravenous anaesthesia (TIVA). Twelve domestic castrates (Swedish Landrace/Yorkshire) 27‒31 kg were used. The pigs were randomly assigned to different induction drug combinations of zolazepam-tiletamine and medetomidine intramuscularly (ZTMe) or midazolam, ketamine intramuscularly and fentanyl intravenously (MiKF). Time from injection to unconsciousness was recorded and the ease of endotracheal intubation assessed. The TIVA infusion rate was adjusted according to the response exhibited from the nociceptive stimulus delivered by mechanically clamping the dewclaw. The time from injection to unconsciousness was briefer and intubation was easier in the ZTMe group. Results from the recorded heart rate, cardiac index and arterial blood pressure variables were satisfactorily preserved and cardiovascular function was maintained in both groups. Shivering was not observed in the ZTMe group, but was observed in four of the pigs in the MiKF group. The requirement of TIVA was lower in the ZTMe group. In conclusion, ZTMe had better results than MiKF in areas such as shorter induction time, better intubation scoring results and less adjustment and amount of TIVA required up to six hours of anaesthesia. The results may have been due to a greater depth of anaesthesia achieved with the ZTMe combination at the dose used.

Pathophysiology of musculoskeletal pain: a narrative review.

Musculoskeletal pain (excluding bone cancer pain) affects more than 30% of the global population and imposes an enormous burden on patients, families, and caregivers related to functional limitation, emotional distress, effects on mood, loss of independence, and reduced quality of life. The pathogenic mechanisms of musculoskeletal pain relate to the differential sensory innervation of bones, joints, and muscles as opposed to skin and involve a number of peripheral and central nervous system cells and mediators. The interplay of neurons and non-neural cells (e.g. glial, mesenchymal, and immune cells) amplifies and sensitizes pain signals in a manner that leads to cortical remodeling. Moreover, sex, age, mood, and social factors, together with beliefs, thoughts, and pain behaviors influence the way in which musculoskeletal pain manifests and is understood and assessed. The aim of this narrative review is to summarize the different pathogenic mechanisms underlying musculoskeletal pain and how these mechanisms interact to promote the transition from acute to chronic pain.

Physiological changes and compensatory mechanisms by the action of respiratory muscles in a porcine model of phrenic nerve injury.

Phrenic nerve damage may occur as a complication of specific surgical procedures, prolonged mechanical ventilation, or physical trauma. The consequent diaphragmatic paralysis or dysfunction can lead to major complications. The purpose of this study was to elucidate the role of the nondiaphragmatic respiratory muscles during partial or complete diaphragm paralysis induced by unilateral and bilateral phrenic nerve damage at different levels of ventilatory pressure support in an animal model. Ten pigs were instrumented, the phrenic nerve was exposed from the neck, and spontaneous respiration was preserved at three levels of pressure support, namely, high, low, and null, at baseline condition, after left phrenic nerve damage, and after bilateral phrenic nerve damage. Breathing pattern, thoracoabdominal volumes and asynchrony, and pressures were measured at each condition. Physiological breathing was predominantly diaphragmatic and homogeneously distributed between right and left sides. After unilateral damage, the paralyzed hemidiaphragm was passively dragged by the ipsilateral rib cage muscles and the contralateral hemidiaphragm. After bilateral damage, the drive to and the work of breathing of rib cage and abdominal muscles increased, to compensate for diaphragmatic paralysis, ensuing paradoxical thoracoabdominal breathing. Increasing level of pressure support ventilation replaces this muscle group compensation. When the diaphragm is paralyzed (unilaterally and/or bilaterally), there is a coordinated reorganization of nondiaphragmatic respiratory muscles as compensation that might be obscured by high level of pressure support ventilation. Noninvasive thoracoabdominal volume and asynchrony assessment could be useful in phrenic nerve-injured patients to estimate the extent and type of inspiratory muscle dysfunction.NEW & NOTEWORTHY This was the first (to our knowledge) implanted porcine model of phrenic nerve injury with a detailed multidimensional analysis of different degrees of diaphragmatic paralysis (unilateral and bilateral). Noninvasive thoracoabdominal volume and asynchrony assessment was shown to be useful in estimating the extent of diaphragmatic dysfunction and the consequent coordinated reorganization of nondiaphragmatic respiratory muscles. High level of pressure support ventilation was proved to obscure the interaction and compensation of respiratory muscles to deal with phrenic nerve injury.

The use of positive end expiratory pressure in patients affected by COVID-19: Time to reconsider the relation between morphology and physiology.

Coronavirus disease 2019 (COVID-19) is a new disease with different phases that can be catastrophic for subpopulations of patients with cardiovascular and pulmonary disease states at baseline. Appreciation for these different phases and treatment modalities, including manipulation of ventilatory settings and therapeutics, has made it a less lethal disease than when it emerged earlier this year. Different aspects of the disease are still largely unknown. However, laboratory investigation and clinical course of the COVID-19 show that this new disease is not a typical acute respiratory distress syndrome process, especially during the first phase. For this reason, the best strategy to be applied is to treat differently the single phases and to support the single functions of the failing organs as they appear.