Ventilation-perfusion Matching Research Articles

Computational modelling of cardiovascular pathophysiology to risk stratify commercial spaceflight.

For more than 60 years, humans have travelled into space. Until now, the majority of astronauts have been professional, government agency astronauts selected, in part, for their superlative physical fitness and the absence of disease. Commercial spaceflight is now becoming accessible to members of the public, many of whom would previously have been excluded owing to unsatisfactory fitness or the presence of cardiorespiratory diseases. While data exist on the effects of gravitational and acceleration (G) forces on human physiology, data ontheeffects of the aerospace environment in unselected members of the public, and particularly in those with clinically significant pathology, are limited. Although short in duration, these high acceleration forces can potentiallyeither impair the experience or, more seriously, pose a risk to health in some individuals. Rather than expose individuals with existing pathology to G forces to collect data, computational modelling might be useful to predict the nature and severity of cardiovascular diseases that are of sufficient risk to restrict access, require modification, or suggest further investigation or training before flight. In this Review, we explore state-of-the-art, zero-dimensional, compartmentalized models of human cardiovascular pathophysiology that can be used to simulate the effects of acceleration forces, homeostatic regulation and ventilation-perfusion matching, using data generated by long-arm centrifuge facilities of the US National Aeronautics and Space Administration and the European Space Agency to riskstratify individuals and help to improve safety in commercial suborbital spaceflight.

Assessing the pulmonary vascular responsiveness to oxygen with proton MRI.

Ventilation-perfusion matching occurs passively and is also actively regulated through hypoxic pulmonary vasoconstriction (HPV). The extent of HPV activity in humans, particularly normal subjects, is uncertain. Current evaluation of HPV assesses changes in ventilation-perfusion relationships/pulmonary vascular resistance with hypoxia and is invasive, or unsuitable for patients because of safety concerns. We used a noninvasive imaging-based approach to quantify the pulmonary vascular response to oxygen as a metric of HPV by measuring perfusion changes between breathing 21% and 30%O2 using arterial spin labeling (ASL) MRI. We hypothesized that the differences between 21% and 30%O2 images reflecting HPV release would be 1) significantly greater than the differences without [Formula: see text] changes (e.g., 21-21% and 30-30%O2) and 2) negatively associated with ventilation-perfusion mismatch. Perfusion was quantified in the right lung in normoxia (baseline), after 15 min of 30% O2 breathing (hyperoxia) and 15 min normoxic recovery (recovery) in healthy subjects (7 M, 7 F; age = 41.4 ± 19.6 yr). Normalized, smoothed, and registered pairs of perfusion images were subtracted and the mean square difference (MSD) was calculated. Separately, regional alveolar ventilation and perfusion were quantified from specific ventilation, proton density, and ASL imaging; the spatial variance of ventilation-perfusion (σ2V̇a/Q̇) distributions was calculated. The O2-responsive MSD was reproducible (R2 = 0.94, P < 0.0001) and greater (0.16 ± 0.06, P < 0.0001) than that from subtracted images collected under the same [Formula: see text] (baseline = 0.09 ± 0.04, hyperoxia = 0.08 ± 0.04, recovery = 0.08 ± 0.03), which were not different from one another (P = 0.2). The O2-responsive MSD was correlated with σ2V̇a/Q̇ (R2 = 0.47, P = 0.007). These data suggest that active HPV optimizes ventilation-perfusion matching in normal subjects. This noninvasive approach could be applied to patients with different disease phenotypes to assess HPV and ventilation-perfusion mismatch.NEW & NOTEWORTHY We developed a new proton MRI method to noninvasively quantify the pulmonary vascular response to oxygen. Using a hyperoxic stimulus to release HPV, we quantified the resulting redistribution of perfusion. The differences between normoxic and hyperoxic images were greater than those between images without [Formula: see text] changes and negatively correlated with ventilation-perfusion mismatch. This suggests that active HPV optimizes ventilation-perfusion matching in normal subjects. This approach is suitable for assessing patients with different disease phenotypes.

The biological role and future therapeutic uses of nitric oxide in extracorporeal membrane oxygenation, a narrative review.

Nitric oxide (NO) is a gas naturally produced by the human body that plays an important physiological role. Specifically, it binds guanylyl cyclase to induce smooth muscle relaxation. NO's other protective functions have been well documented, particularly its protective endothelial functions, effects on decreasing pulmonary vascular resistance, antiplatelet, and anticoagulation properties. The use of nitric oxide donors as vasodilators has been known since 1876. Inhaled nitric oxide has been used as a pulmonary vasodilator and to improve ventilation perfusion matching since the 1990s. It is currently approved by the United States Food and Drug Administration for neonates with hypoxic respiratory failure, however, it is used off-label for acute respiratory distress syndrome, acute bronchiolitis, and COVID-19. In this article we review the currently understood biological action and therapeutic uses of NO through nitric oxide donors such as inhaled nitric oxide. We will then explore recent studies describing use of NO in cardiopulmonary bypass and extracorporeal membrane oxygenation and speculate on NO's future uses.

Oxygen-sensing pathways and the pulmonary circulation.

The unique property of the pulmonary circulation to constrict in response to hypoxia, rather than dilate, brings advantages in both health and disease. Hypoxic pulmonary vasoconstriction (HPV) acts to optimise ventilation-perfusion matching - this is important clinically both in focal disease (such as pneumonia) and in one-lung ventilation during anaesthesia for thoracic surgery. However, during global hypoxia such as that encountered at high altitude, generalised pulmonary vasoconstriction can lead to pulmonary hypertension. There is now a growing body of evidence that links the hypoxia-inducible factor (HIF) pathway and pulmonary vascular tone - in both acute and chronic settings. Genetic and pharmacological alterations to all key components of this pathway (VHL - von Hippel-Lindau ubiquitin E3 ligase; PHD2 - prolyl hydroxylase domain protein 2; HIF1 and HIF2) have clear effects on the pulmonary circulation, particularly in hypoxia. Furthermore, knowledge of the molecular biology of the prolyl hydroxylase enzymes has led to an extensive and ongoing body of research into the importance of iron in both HPV and pulmonary hypertension. This review will explore these relationships in more detail and discuss future avenues of research.

Ventilation-perfusion Matching During Exercise In Patients With Heart Failure With Preserved Ejection Fraction: Impact Of Phenotype

Ventilation-perfusion Matching During Exercise In Patients With Heart Failure With Preserved Ejection Fraction: Impact Of Phenotype

Gaining consensus on expert rule statements for acute respiratory failure digital twin patient model in intensive care unit using a Delphi method.

Digital twin technology is a virtual depiction of a physical product and has been utilized in many fields. Digital twin patient model in healthcare is a virtual patient that provides opportunities to test the outcomes of various interventions virtually without subjecting an actual patient to possible harm. This can serve as a decision aid in the complex environment of the intensive care unit (ICU). Our objective is to develop consensus among a multidisciplinary expert panel on statements regarding respiratory pathophysiology contributing to respiratory failure in the medical ICU. We convened a panel of 34 international critical care experts. Our group modeled elements of respiratory failure pathophysiology using directed acyclic graphs (DAGs) and derived expert statements describing associated ICU clinical practices. The experts participated in three rounds of modified Delphi to gauge agreement on 78 final questions (13 statements with 6 substatements for each) using a Likert scale. A modified Delphi process achieved agreement for 62 of the final expert rule statements. Statements with the highest degree of agreement included the physiology, and management of airway obstruction decreasing alveolar ventilation and ventilation-perfusion matching. The lowest agreement statements involved the relationship between shock and hypoxemic respiratory failure due to heightened oxygen consumption and dead space. Our study proves the utility of a modified Delphi method to generate consensus to create expert rule statements for further development of a digital twin-patient model with acute respiratory failure. A substantial majority of expert rule statements used in the digital twin design align with expert knowledge of respiratory failure in critically ill patients.

Phase-resolved Functional Lung (PREFUL) MRI-derived Ventilation and Perfusion Parameters Predict Future Lung Transplant Loss.

Background Chronic lung allograft dysfunction (CLAD), the physiologic correlate of chronic rejection, remains a major barrier to long-term survival following lung transplant. Biomarkers for early prediction of future transplant loss or death due to CLAD might open a window of opportunity for early diagnosis and treatment of CLAD. Purpose To evaluate the prognostic use of phase-resolved functional lung (PREFUL) MRI in predicting CLAD-related transplant loss or death. Materials and Methods In this prospective, longitudinal, single-center study, PREFUL MRI-derived ventilation and parenchymal lung perfusion parameters of bilateral lung transplant recipients without clinically suspected CLAD were assessed 6-12 months (baseline) and 2.5 years (follow-up) after transplant. MRI scans were acquired between August 2013 and December 2018. Regional flow volume loop (RFVL)-based ventilated volume (VV) and perfused volume were calculated using thresholds and spatially combined as ventilation-perfusion (V/Q) matching. Spirometry data were obtained on the same day. Exploratory models were calculated using receiver operating characteristic analysis, and subsequent survival analyses (Kaplan-Meier, hazard ratios [HRs]) of CLAD-related graft loss were performed to compare clinical and MRI parameters as clinical end points. Results At baseline MRI examination, 132 clinically stable patients of 141 patients (median age, 53 years [IQR, 43-59 years]; 78 men) were included (nine were excluded for deaths not associated with CLAD), 24 of which had CLAD-related graft loss (death or retransplant) within the observational period of 5.6 years. PREFUL MRI-derived RFVL VV was a predictor of poorer survival (cutoff, 92.3%; log-rank P = .02; HR for graft loss, 2.5 [95% CI: 1.1, 5.7]; P = .02), while perfused volume (P = .12) and spirometry (P = .33) were not predictive of differences in survival. In the evaluation of percentage change at follow-up MRI (92 stable patients vs 11 with CLAD-related graft loss), mean RFVL (cutoff, 97.1%; log-rank P < .001; HR, 7.7 [95% CI: 2.3, 25.3]), V/Q defect (cutoff, 498%; log-rank P = .003; HR, 6.6 [95% CI: 1.7, 25.0]), and forced expiratory volume in the first second of expiration (cutoff, 60.8%; log-rank P < .001; HR, 7.9 [95% CI: 2.3, 27.4]; P = .001) were predictive of poorer survival within 2.7 years (IQR, 2.2-3.5 years) after follow-up MRI. Conclusion Phase-resolved functional lung MRI ventilation-perfusion matching parameters were predictive of future chronic lung allograft dysfunction-related death or transplant loss in a large prospective cohort who had undergone lung transplant. © RSNA, 2023 Supplemental material is available for this article. See also the editorial by Fain and Schiebler in this issue.

Proof-of-concept study of compartmentalized lung ventilation using system for asymmetric flow regulation (SAFR).

Asymmetrical distribution of acute lung injury in mechanically ventilated patients can result in a heterogeneity of gas distribution between different regions, potentially worsening ventilation-perfusion matching. Furthermore, overdistension of healthier, more compliant lung regions can lead to barotrauma and limit the effect of increased PEEP on lung recruitment. We propose a System for Asymmetric Flow Regulation (SAFR) which, combined with a novel double lumen endobronchial tube (DLT) may offer individualized lung ventilation to the left and right lungs, better matching each lung's mechanics and pathophysiology. In this preclinical experimental model, the performance of SAFR on gas distribution in a two-lung simulation system was tested. Our results indicate that SAFR may be a technically feasible and potentially clinically useful although further research is warranted.

Prone Positioning in COVID-19 ARDS: Comment.

We read with interest the recent article by Zarantonello et al.1 on the physiologic effects of prone positioning on ventilation and perfusion distribution, oxygenation, and lung mechanics in COVID-19 acute respiratory distress syndrome patients. We would like to first congratulate the authors for the nicely conducted study that once again proved the clinical applicability of electrical impedance tomography for the assessment of ventilation–perfusion matching at the bedside. We acknowledge the clinical significance of the findings, but we wish to point out that several parts of the electrical impedance tomography methodology were incorrectly described in the article.In the Methods section, the authors described how the lung areas that were (1) perfused but not ventilated, (2) ventilated but not perfused, and (3) both ventilated and perfused were “divided by the sum of ventilated and perfused pixels” to calculate the corresponding relative fractions of the lung area in percentages, i.e., (1) “% shunt area,” (2) “% dead space area,” and (3) “% matched area,” respectively. However, the denominator must be the number of pixels that were ventilated or perfused, i.e., using the logical operator “or,” otherwise the calculated relative areas would be incorrect. The authors also determined “the percentage of total ventilated lung area that was located in the dorsal half of the thorax,” which they inaccurately termed as “dorsal ventilation.” According to the consensus electrical impedance tomography terminology and definitions,2 regional ventilation is determined as the sum of all pixel values of tidal impedance variation not as the pixel count, which defines just the ventilated area.The authors further introduced a new electrical impedance tomography parameter, the “homogeneity index,” which they “calculated as 1 – global inhomogeneity index,” based on the assumption of the global inhomogeneity index ranging from 1 to 0. However, the global inhomogeneity index values are commonly higher than 1 in patients with pronounced ventilation inhomogeneity, as shown already in some of the examined mechanically ventilated subjects in the original description of the global inhomogeneity index3 or recently in patients with exacerbated chronic lung disease.4 An example patient case is presented in figure 1, in which a global inhomogeneity index value of 2.59 was noted in the presence of pendelluft, which is a frequent cause of out-of-phase impedance variation both in spontaneously breathing and ventilated patients.5 The “homogeneity index” proposed by the authors would be negative in this case and assume the confusing value of –1.59. We therefore strongly advise against using the “homogeneity index” as a surrogate for the well established global inhomogeneity index.The authors pointed out that electrical impedance tomography perfusion assessment with saline bolus injection had been validated only in two animal studies. In fact, this technique of contrast-enhanced electrical impedance tomography has been studied in several other animal studies as well.6–9 Last, we agree with the authors that electrical impedance tomography images do not cover the whole lungs, but as summarized in the consensus paper on chest electrical impedance tomography,2 an electrical impedance tomography image does not originate from “only the area of the lung surrounded by the belt.”Electrical impedance tomography receives increasing attention due to its noninvasive bedside monitoring features. Correct description and implementation of the electrical impedance tomography technique and analysis procedures are crucial for further development and clinical use.Dr. Zhao receives a consulting fee from Dräger Medical (Lübeck, Germany). Dr. Frerichs reports funding from the European Union’s Framework program for Research and Innovation Horizon 2020 (WELMO, grant No. 825572).

Prone Positioning Improved Ventilation-Perfusion Matching in Severe Pediatric Acute Respiratory Distress Syndrome.

Prone Positioning Improved Ventilation-Perfusion Matching in Severe Pediatric Acute Respiratory Distress Syndrome.

Bronchoalveolar lavage improved ventilation/perfusion matching in pediatric severe mycoplasma pneumoniae pneumonia with lung consolidation.

A 15-year-old girl was admitted to our Pediatric Intensive Care Unit (PICU) due to respiratory failure and septic shock. She was intubated and mechanically ventilated and received vasoactive drugs therapy. Chest CT scan showed opacities in both lungs with marked consolidation in the right (figure 1A). Saline contrast-enhanced electrical impedance tomography (EIT) was conducted with 10 ml 5% NaCl bolus injection through the central venous catheter.1 Significant reductions in ventilation and perfusion were observed in the right dorsal regions (figure 2A). Shunt percentage was much higher in the dorsal regions. The patient received bedside bronchoalveolar lavage with fiberoptic bronchoscope therapy in PICU. The airway mucosa was congested, edematous and diffusely hemorrhagic. White mucus plugs were observed in the right airway, especially in the basal segment of the right lower lobe. The terminal bronchioles (generations 5-7) were completely blocked (figure 3A-B). A total of 100 ml sterilized isotonic saline was instilled in five aliquots and the lavage fluid and sputum were sucked out subsequently with 100 mmHg negative pressure after each insufflation (figure 3C-D). The bronchoalveolar lavage fluid next-generation sequencing test suggested that the pathogen was mycoplasma pneumoniae and the patient was treated with levofloxacin. After receiving bronchoscopy and bronchoalveolar lavage for three consecutive days, bedside EIT measurement suggested improvements of ventilation and perfusion in the right dorsal regions (figure 2B). Shunt percentage was significantly reduced. The findings were coincided with subsequent CT scans (figure 1B). The patient was successfully weaned from ventilator 1 day after last bronchoalveolar lavage. To our knowledge, this is the first clinical report to evaluate the efficacy of bronchoalveolar lavage on regional ventilation and perfusion at the bedside in severe mycoplasma pneumoniae pneumonia with lung consolidation. In severe mycoplasma pneumoniae pneumonia, about 24.9% patients were accompanied with lung consolidation. Fiberoptic bronchoscopy and bronchoalveolar lavage therapy can help detecting mycoplasma pneumoniae pneumonia pathogen in time, with detecting infection, locating sputum plug and inflammatory polyps, and improving consolidation. 22 However, a real-time bedside tool for evaluating the effectiveness of bronchoalveolar lavage in PICU was still missing. Saline-bolus based EIT evaluating the ventilation-perfusion matching has been implemented in adult lung diseases. 1,31,3 This case shows that EIT has the potential to identify regional ventilation and perfusion defects in the lesion areas, as well as to evaluate the corresponding improvement after bronchoalveolar lavage. No side effects were observed after the 10 ml 5% NaCl bolus injection. Further studies are warranted to confirm the clinical use of EIT in bronchoalveolar lavage in various pediatric age group and lung diseases This article is protected by copyright. All rights reserved.

This Month in Anesthesiology

This Month in Anesthesiology

Effect of body position on the redistribution of regional lung aeration during invasive and non-invasive ventilation of COVID-19 patients

Severe COVID-19-related acute respiratory distress syndrome (C-ARDS) requires mechanical ventilation. While this intervention is often performed in the prone position to improve oxygenation, the underlying mechanisms responsible for the improvement in respiratory function during invasive ventilation and awake prone positioning in C-ARDS have not yet been elucidated. In this prospective observational trial, we evaluated the respiratory function of C-ARDS patients while in the supine and prone positions during invasive (n = 13) or non-invasive ventilation (n = 15). The primary endpoint was the positional change in lung regional aeration, assessed with electrical impedance tomography. Secondary endpoints included parameters of ventilation and oxygenation, volumetric capnography, respiratory system mechanics and intrapulmonary shunt fraction. In comparison to the supine position, the prone position significantly increased ventilation distribution in dorsal lung zones for patients under invasive ventilation (53.3 ± 18.3% vs. 43.8 ± 12.3%, percentage of dorsal lung aeration ± standard deviation in prone and supine positions, respectively; p = 0.014); whereas, regional aeration in both positions did not change during non-invasive ventilation (36.4 ± 11.4% vs. 33.7 ± 10.1%; p = 0.43). Prone positioning significantly improved the oxygenation both during invasive and non-invasive ventilation. For invasively ventilated patients reduced intrapulmonary shunt fraction, ventilation dead space and respiratory resistance were observed in the prone position. Oxygenation is improved during non-invasive and invasive ventilation with prone positioning in patients with C-ARDS. Different mechanisms may underly this benefit during these two ventilation modalities, driven by improved distribution of lung regional aeration, intrapulmonary shunt fraction and ventilation-perfusion matching. However, the differences in the severity of C-ARDS may have biased the sensitivity of electrical impedance tomography when comparing positional changes between the protocol groups.Trial registration: ClinicalTrials.gov (NCT04359407) and Registered 24 April 2020, https://clinicaltrials.gov/ct2/show/NCT04359407.

Early Physiologic Effects of Prone Positioning in COVID-19 Acute Respiratory Distress Syndrome.

The mechanisms underlying oxygenation improvement after prone positioning in COVID-19 acute respiratory distress syndrome have not been fully elucidated yet. The authors hypothesized that the oxygenation increase with prone positioning is secondary to the improvement of ventilation-perfusion matching. In a series of consecutive intubated COVID-19 acute respiratory distress syndrome patients receiving volume-controlled ventilation, the authors prospectively assessed the percent variation of ventilation-perfusion matching by electrical impedance tomography before and 90 min after the first cycle of prone positioning (primary endpoint). The authors also assessed changes in the distribution and homogeneity of lung ventilation and perfusion, lung overdistention and collapse, respiratory system compliance, driving pressure, optimal positive end-expiratory pressure, as assessed by electrical impedance tomography, and the ratio of partial pressure to fraction of inspired oxygen (Pao2/Fio2; secondary endpoints). Data are reported as medians [25th to 75th] or percentages. The authors enrolled 30 consecutive patients, all analyzed without missing data. Compared to the supine position, prone positioning overall improved ventilation-perfusion matching from 58% [43 to 69%] to 68% [56 to 75%] (P = 0.042), with a median difference of 8.0% (95% CI, 0.1 to 16.0%). Dorsal ventilation increased from 39% [31 to 43%] to 52% [44 to 62%] (P < 0.001), while dorsal perfusion did not significantly vary. Prone positioning also reduced lung overdistension from 9% [4 to 11%] to 4% [2 to 6%] (P = 0.025), while it did not significantly affect ventilation and perfusion homogeneity, lung collapse, static respiratory system compliance, driving pressure, and optimal positive end-expiratory pressure. Pao2/Fio2 overall improved from 141 [104 to 182] mmHg to 235 [164 to 267] mmHg (P = 0.019). However, 9 (30%) patients were nonresponders, experiencing an increase in Pao2/Fio2 less than 20% with respect to baseline. In COVID-19 acute respiratory distress syndrome patients, prone positioning overall produced an early increase in ventilation-perfusion matching and dorsal ventilation. These effects were, however, heterogeneous among patients.

Prone positioning improves ventilation–perfusion matching assessed by electrical impedance tomography in patients with ARDS: a prospective physiological study

BackgroundThe physiological effects of prone ventilation in ARDS patients have been discussed for a long time but have not been fully elucidated. Electrical impedance tomography (EIT) has emerged as a tool for bedside monitoring of pulmonary ventilation and perfusion, allowing the opportunity to obtain data. This study aimed to investigate the effect of prone positioning (PP) on ventilation–perfusion matching by contrast-enhanced EIT in patients with ARDS.DesignMonocenter prospective physiologic study.SettingUniversity medical ICU.PatientsTen mechanically ventilated ARDS patients who underwent PP.InterventionsWe performed EIT evaluation at the initiation of PP, 3 h after PP initiation and the end of PP during the first PP session.Measurements and main resultsThe regional distribution of ventilation and perfusion was analyzed based on EIT images and compared to the clinical variables regarding respiratory and hemodynamic status. Prolonged prone ventilation improved oxygenation in the ARDS patients. Based on EIT measurements, the distribution of ventilation was homogenized and dorsal lung ventilation was significantly improved by PP administration, while the effect of PP on lung perfusion was relatively mild, with increased dorsal lung perfusion observed. The ventilation–perfusion matched region was found to increase and correlate with the increased PaO2/FiO2 by PP, which was attributed mainly to reduced shunt in the lung.ConclusionsProlonged prone ventilation increased dorsal ventilation and perfusion, which resulted in improved ventilation–perfusion matching and oxygenation.Trial registration: ClinicalTrials.gov, NCT04725227. Registered on 25 January 2021.

Effects of Prone Position on Lung Recruitment and Ventilation-Perfusion Matching in Patients With COVID-19 Acute Respiratory Distress Syndrome: A Combined CT Scan/Electrical Impedance Tomography Study.

OBJECTIVES:Prone positioning allows to improve oxygenation and decrease mortality rate in COVID-19–associated acute respiratory distress syndrome (C-ARDS). However, the mechanisms leading to these effects are not fully understood. The aim of this study is to assess the physiologic effects of pronation by the means of CT scan and electrical impedance tomography (EIT).DESIGN:Experimental, physiologic study.SETTING:Patients were enrolled from October 2020 to March 2021 in an Italian dedicated COVID-19 ICU.PATIENTS:Twenty-one intubated patients with moderate or severe C-ARDS.INTERVENTIONS:First, patients were transported to the CT scan facility, and image acquisition was performed in prone, then supine position. Back to the ICU, gas exchange, respiratory mechanics, and ventilation and perfusion EIT-based analysis were provided toward the end of two 30 minutes steps (e.g., in supine, then prone position).MEASUREMENTS AND MAIN RESULTS:Prone position induced recruitment in the dorsal part of the lungs (12.5% ± 8.0%; p < 0.001 from baseline) and derecruitment in the ventral regions (–6.9% ± 5.2%; p < 0.001). These changes led to a global increase in recruitment (6.0% ± 6.7%; p < 0.001). Respiratory system compliance did not change with prone position (45 ± 15 vs 45 ± 18 mL/cm H2O in supine and prone position, respectively; p = 0.957) suggesting a decrease in atelectrauma. This hypothesis was supported by the decrease of a time-impedance curve concavity index designed as a surrogate for atelectrauma (1.41 ± 0.16 vs 1.30 ± 0.16; p = 0.001). Dead space measured by EIT was reduced in the ventral regions of the lungs, and the dead-space/shunt ratio decreased significantly (5.1 [2.3–23.4] vs 4.3 [0.7–6.8]; p = 0.035), showing an improvement in ventilation-perfusion matching.CONCLUSIONS:Several changes are associated with prone position in C-ARDS: increased lung recruitment, decreased atelectrauma, and improved ventilation-perfusion matching. These physiologic effects may be associated with more protective ventilation.

Origins of and lessons from quantitative functional X-ray computed tomography of the lung.

Functional CT of the lung has emerged from quantitative CT (qCT). Structural details extracted at multiple lung volumes offer indices of function. Additionally, single volumetric images, if acquired at standardized lung volumes and body posture, can be used to model function by employing such engineering techniques as computational fluid dynamics. With the emergence of multispectral CT imaging including dual energy from energy integrating CT scanners and multienergy binning using the newly released photon counting CT technology, function is tagged via use of contrast agents. Lung disease phenotypes have previously been lumped together by the limitations of spirometry and plethysmography. QCT and its functional embodiment have been imbedded into studies seeking to characterize chronic obstructive pulmonary disease, severe asthma, interstitial lung disease and more. Reductions in radiation dose by an order of magnitude or more have been achieved. At the same time, we have seen significant increases in spatial and density resolution along with methodologic validations of extracted metrics. Together, these have allowed attention to turn towards more mild forms of disease and younger populations. In early applications, clinical CT offered anatomic details of the lung. Functional CT offers regional measures of lung mechanics, the assessment of functional small airways disease, as well as regional ventilation-perfusion matching (V/Q) and more. This paper will focus on the use of quantitative/functional CT for the non-invasive exploration of dynamic three-dimensional functioning of the breathing lung and beating heart within the unique negative pressure intrathoracic environment of the closed chest.

Non-intubated Thoracoscopic Surgery-Tips and Tricks From Anesthesiological Aspects: A Mini Review.

BackgroundIn the last few decades, surgical techniques have been developed in thoracic surgery, and minimally invasive strategies such as multi-and uniportal video-assisted thoracic surgery (VATS) have become more favorable even for major pulmonary resections. With this surgical evolution, the aesthetic approach has also changed, and a paradigm shift has occurred. The traditional conception of general anesthesia, muscle relaxation, and intubation has been re-evaluated, and spontaneous breathing plays a central role in our practice by performing non-intubated thoracoscopic surgeries (NITS-VATS).MethodsWe performed a computerized search of the medical literature (PubMed, Google Scholar, Scopus) to identify relevant articles in non-intubated thoracoscopic surgery using the following terms [(non-intubated) OR (non-intubated) OR (awake) OR (tubeless) OR (regional anesthesia)] AND [(VATS) OR (NIVATS)], as well as their Medical Subject Headings (MeSH) terms.ResultsBased on the outcomes of the reviewed literature and our practice, it seems that pathophysiological concerns can be overcome by proper surgical and anesthetic management. All risks are compensated by the advantageous physiological changes that result in better patient outcomes. With the maintenance of spontaneous breathing, the incidence of potential adverse effects of mechanical ventilation, such as ventilator-induced lung injury and consequent postoperative pulmonary complications, can be reduced. The avoidance of muscle relaxants also results in the maintenance of contraction of the dependent hemidiaphragm and lower airway pressure levels, which may lead to better ventilation-perfusion matching. These techniques can be challenging for surgeons as well as for anesthetists; hence, a good knowledge of physiological and pathophysiological changes, clear inclusion and exclusion and intraoperative conversion criteria, and good communication between team members are essential.ConclusionNITS-VATS seems to be a feasible and safe method in selected patients with evolving importance as a part of the minimally invasive surgical and anesthetic conception and has a role in reducing perioperative complications, which is crucial in the thoracic surgical patient population.

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

To develop a method based on CT angiography and the maximum slope model (MSM) to measure regional lung perfusion in anesthetized ponies. 6 ponies. 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. 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. 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.

Inter-hospital transfer of a pregnant prone patient with COVID-19 as a bridge to ECMO.

Sir, Pregnant women are at a higher risk of severe coronavirus disease 2019 (COVID-19) compared to non-pregnant women and are associated with worse outcomes.[1] The management of acute respiratory distress syndrome (ARDS) in a pregnant woman is challenging because of physiological changes of pregnancy and the detrimental effects of hypoxaemia and hypercarbia on the foetus. Prone ventilation and extracorporeal membrane oxygenation (ECMO) are effective rescue strategies in severe ARDS requiring invasive mechanical ventilation. We transferred a pregnant patient with critical COVID-19 on invasive mechanical ventilation (IMV) and prone position as a bridge to ECMO. A 28-year-old primigravida at 24 weeks’ gestation, with laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was admitted for breathing difficulty and cough since 8 days. She was started on oxygen by face mask to target oxygen saturation (Spo2) ≥94%, dexamethasone 6 mg intravenous once daily and enoxaparin 40 mg subcutaneous 12 hourly. Laboratory parameters showed C-reactive protein 140 mg/L, haemoglobin 12.8 gm%, white cell count 4200/mm3, procalcitonin 1.1 ng/ml, lactate dehydrogenase 680 U/L, D-dimer 1011 ng/ml and normal renal and liver function tests. Her oxygenation worsened the next day, and a trial of continuous positive airway pressure (CPAP) was given in the intensive care unit (ICU). However, because of worsening oxygenation and respiratory distress, the patient was tracheal-intubated and started on IMV with lung-protective ventilation strategy. The patient remained hypoxaemic (partial pressure of oxygen to a fraction of inspired oxygen (PaO2/FiO2) ratio of 67 mm Hg) and higher plateau pressure (Pplat) of 32 cm H2O. She was proned with shoulder and thigh support and adequate padding of pressure areas. The abdomen and pelvis were kept in a suspended position. Periodical foetal assessment was performed using cardiotocography and portable Doppler ultrasound, while the suspended abdomen was checked manually for any obstruction or tension. The patient continued to be severely hypoxaemic (PaO2/FiO2 <80 mm Hg) despite two sessions of prone ventilation of 16 h each. The case was discussed with the ECMO team at Central Command Centre as a potential candidate for ECMO. Given the absence of retrieval ECMO and level III neonatal ICU, an inter-hospital transfer was planned. Due to rapid desaturation on supine positioning, a decision to transfer the patient in prone position was taken. A team of two anaesthesiologist-intensivists and three ICU trained nurses accompanied the patient. Heart rate, rhythm, arterial blood pressure, end-tidal continuous waveform capnography, SpO2 and ventilator waveforms were monitored continuously throughout the patient care [Table 1]. The tracheal tube was firmly secured with a tube holder and standard tie. An intravenous infusion of propofol and midazolam was used for sedation, and cisatracurium was used for neuromuscular blockade. The patient was transferred as a single unit with shoulder and pelvic support from the ICU bed to the ambulance stretcher. One staff was solely dedicated for foetal assessment and airway. An intensivist was responsible for IMV, and another supervised the transfer. The transfer was uneventful with continuous monitoring of the patient and foetus. The ECMO facility was approximately 9 km away and took a travel time of 28 min.Table 1: Vitals of the patient during inter-hospital transportProne ventilation is an effective rescue strategy for the management of refractory hypoxaemia in severe ARDS by improving ventilation-perfusion matching and reducing mortality.[2] Pregnancy is traditionally excluded from trials on ARDS. However, protocolised proning with due consideration to physiological changes of pregnancy and adequate monitoring is recommended as a low-cost and effective strategy in ARDS management.[3] The transfer in the prone position can be catastrophic with a risk of the misplaced airway and rapid deoxygenation or inability to perform cardiopulmonary resuscitation during an emergency.[4] The systematic planning of transfer with attention to airway, monitoring and pressure areas was found to have been successful in a smaller case series.[56] The twin issues of second-trimester pregnancy and prone position made this case challenging. However, adequate planning, team briefing and continuous patient and foetal monitoring ensured a safe transfer. In conclusion, safe transfer of a pregnant, prone patient was possible with adequate planning, risk management and an experienced team. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.