Prone position ameliorates lung elastance and increases functional residual capacity independently from lung recruitment

Semirecumbent Positioning During Anesthesia Recovery and Postoperative Hypoxemia: A Randomized Clinical Trial

Importance

The efficacy of a semirecumbent position (SRP) in reducing postoperative hypoxemia during anesthesia emergence is unclear despite its widespread use.

Objective

To determine the differences in postoperative hypoxemia between patients in an SRP and a supine position.

Design, Setting, and Participants

This randomized clinical trial was performed at a tertiary hospital in China between March 20, 2021, and May 10, 2022. Patients scheduled to undergo laparoscopic upper abdominal surgery under general anesthesia were enrolled. Study recruitment and follow-up are complete.

Interventions

Patients were randomized to 1 of the following positions at the end of the operation until leaving the postanesthesia care unit: supine (group S), 15° SRP (group F), or 30° SRP (group T).

Main Outcomes and Measures

The primary outcome was the incidence of postoperative hypoxemia in the postanesthesia care unit. Severe hypoxemia was also evaluated.

Results

Out of 700 patients (364 men [52.0%]; mean [SD] age, 47.8 [11.3] years), 233 were randomized to group S (126 men [54.1%]; mean [SD] age, 48.2 [10.9] years), 233 to group F (122 men [52.4%]; mean [SD] age, 48.1 [10.9] years), and 234 to group T (118 women [50.4%]; mean [SD] age, 47.2 [12.1] years). Postoperative hypoxemia differed significantly among the 3 groups (group S, 109 of 233 [46.8%]; group F, 105 of 233 [45.1%]; group T, 76 of 234 [32.5%]; P = .002). This difference was statistically significant for groups T vs S (risk ratio [RR], 0.69 [95% CI, 0.55-0.87]; P = .002) and groups T vs F (RR, 0.72 [95% CI, 0.57-0.91]; P = .007), but not for groups F vs S (RR, 0.96 [95% CI, 0.79-1.17]; P = .78). Severe hypoxemia also differed among the 3 groups (group S, 61 of 233 [26.2%]; group F, 53 of 233 [22.7%]; group T, 36 of 234 [15.4%]; P = .01). This difference was statistically significant for groups T vs S (RR, 0.59 [95% CI, 0.41-0.85]; P = .005).

Conclusions and Relevance

In this randomized clinical trial of SRP during anesthesia recovery in patients undergoing laparoscopic upper abdominal surgery, postoperative hypoxemia was significantly reduced in group T compared with group F or group S.

Trial Registration

Chinese Clinical Trial Registry Identifier: ChiCTR2100045087.

Estimation of normal lung weight index in healthy female domestic pigs

INTRODUCTION

Lung weight is an important study endpoint to assess lung edema in porcine experiments on acute respiratory distress syndrome and ventilatory induced lung injury. Evidence on the relationship between lung-body weight relationship is lacking in the literature. The aim of this work is to provide a reference equation between normal lung and body weight in female domestic piglets.

MATERIALS AND METHODS

177 healthy female domestic piglets from previous studies were included in the analysis. Lung weight was assessed either via a CT-scan before any experimental injury or with a scale after autopsy. The animals were randomly divided in a training (n = 141) and a validation population (n = 36). The relation between body weight and lung weight index (lung weight/body weight, g/kg) was described by an exponential function on the training population. The equation was tested on the validation population. A Bland-Altman analysis was performed to compare the lung weight index in the validation population and its theoretical value calculated with the reference equation.

RESULTS

A good fit was found between the validation population and the exponential equation extracted from the training population (RMSE = 0.060). The equation to determine lung weight index from body weight was: [Formula: see text] At the Bland and Altman analyses, the mean bias between the real and the expected lung weight index was - 0.26 g/kg (95% CI - 0.96-0.43), upper LOA 3.80 g/kg [95% CI 2.59-5.01], lower LOA - 4.33 g/kg [95% CI = - 5.54-(- 3.12)].

CONCLUSIONS

This exponential function might be a valuable tool to assess lung edema in experiments involving 16-50 kg female domestic piglets. The error that can be made due to the 95% confidence intervals of the formula is smaller than the one made considering the lung to body weight as a linear relationship.

An appraisal of lung computer tomography in very early anti-inflammatory treatment of two different ovine ARDS phenotypes

Mortality and morbidity of Acute Respiratory Distress Syndrome (ARDS) are largely unaltered. A possible new approach to treatment of ARDS is offered by the discovery of inflammatory subphenotypes. In an ovine model of ARDS phenotypes, matching key features of the human subphenotypes, we provide an imaging characterization using computer tomography (CT). Nine animals were randomized into (a) OA (oleic acid, hypoinflammatory; n = 5) and (b) OA-LPS (oleic acid and lipopolysaccharides, hyperinflammatory; n = 4). 48 h after ARDS induction and anti-inflammatory treatment, CT scans were performed at high (H) and then low (L) airway pressure. After CT, the animals were euthanized and lung tissue was collected. OA-LPS showed a higher air fraction and OA a higher tissue fraction, resulting in more normally aerated lungs in OA-LPS in contrast to more non-aerated lung in OA. The change in lung and air volume between H and L was more accentuated in OA-LPS, indicating a higher recruitment potential. Strain was higher in OA, indicating a higher level of lung damage, while the amount of lung edema and histological lung injury were largely comparable. Anti-inflammatory treatment might be beneficial in terms of overall ventilated lung portion and recruitment potential, especially in the OA-LPS group.

Prone Positioning and Molecular Biomarkers in COVID and Non-COVID ARDS: A Narrative Review

Prone positioning (PP) represents a therapeutic intervention with the proven capacity of ameliorating gas exchanges and ventilatory mechanics indicated in acute respiratory distress syndrome (ARDS). When PP is selectively applied to moderate-severe cases of ARDS, it sensitively affects clinical outcomes, including mortality. After the COVID-19 outbreak, clinical application of PP peaked worldwide and was applied in 60% of treated cases, according to large reports. Research on this topic has revealed many physiological underpinnings of PP, focusing on regional ventilation redistribution and the reduction of parenchymal stress and strain. However, there is a lack of evidence on biomarkers behavior in different phases and phenotypes of ARDS. Patients response to PP are, to date, decided on PaO2/FiO2 ratio improvement, whereas scarce data exist on biomarker tracking during PP. The purpose of this review is to explore current evidence on the clinical relevance of biomarkers in the setting of moderate-severe ARDS of different etiologies (i.e., COVID and non-COVID-related ARDS). Moreover, this review focuses on how PP may modulate biomarkers and which biomarkers may have a role in outcome prediction in ARDS patients.

Prone position decreases acute lung inflammation measured by [11C](R)-PK11195 positron emission tomography in experimental acute respiratory distress syndrome

Whether prone positioning (PP) modulates acute lung inflammation by the modulation of biomechanical forces of ventilator-induced lung injuries (VILIs) remains unclear. We aimed to demonstrate that PP decreases acute lung inflammation in animals with experimental acute respiratory distress syndrome (ARDS). Animals were under general anesthesia and protective ventilation (tidal volume 6 mL·kg^-1, PEEP 5 cmH₂O). ARDS was induced by intratracheal instillation of chlorohydric acid. Animals were then randomized to PP, or to supine position (SP). After 4 h, a positron emission tomography (PET) acquisition with [¹¹C](R)-PK11195 was performed coupled with computerized tomography (CT) acquisitions, allowing the CT quantification of VILI-associated parameters. [¹¹C](R)-PK11195 lung uptake was quantified using pharmacokinetic multicompartment models. Analyses were performed on eight lung sections distributed along the antero-posterior dimension. Six animals were randomized to PP, five to SP (median [Formula: see text]/[Formula: see text] [interquartile range]: 164 [102-269] mmHg). The normally aerated compartment was significantly redistributed to the posterior lung regions of animals in PP, compared with SP. Dynamic strain was significantly increased in posterior regions of SP animals, compared with PP. After 4 h, animals in PP had a significantly lower uptake of [¹¹C](R)-PK11195, compared with SP. [¹¹C](R)-PK11195 regional uptake was independently associated with the study group, dynamic strain, tidal hyperinflation, and regional respiratory system compliance in multivariate analysis. In an experimental model of ARDS, 4 h of PP significantly decreased acute lung inflammation assessed with PET. The beneficial impact of PP on acute lung inflammation was consecutive to the combination of decreased biomechanical forces and changes in the respiratory system mechanics.NEW & NOTEWORTHY Prone position decreases acute lung macrophage inflammation quantified in vivo with [¹¹C](R)-PK11195 positron emission tomography in an experimental acute respiratory distress syndrome. Regional macrophage inflammation is maximal in the most anterior and posterior lung section of supine animals, in relation with increased regional tidal strain and hyperinflation, and reduced regional lung compliance.

Deriving Regionally Specific Biomarkers of Emphysema and Small Airways Disease Using Variable Threshold Parametric Response Mapping on Volumetric Lung CT Images

PURPOSE

This study aims to develop and validate a parametric response mapping (PRM) methodology to accurately identify diseased regions of the lung by using variable thresholds to account for alterations in regional lung function between the gravitationally-independent (anterior) and gravitationally-dependent (posterior) lung in CT images acquired in the supine position.

METHODS

34 male Sprague-Dawley rats (260-540 g) were imaged, 4 of which received elastase injection (100 units/kg) as a model for emphysema (EMPH). Gated volumetric CT was performed at end-inspiration (EI) and end-expiration (EE) on separate groups of free-breathing (n = 20) and ventilated (n = 10) rats in the supine position. To derive variable thresholds for the new PRM methodology, voxels were first grouped into 100 bins based on the fractional distance along the anterior-to-posterior direction. Lower limits of normal (LLN) for x-ray attenuation in each bin were set by determining the smallest region that enclosed 98% of voxels from healthy, ventilated animals.

RESULTS

When utilizing fixed thresholds in the conventional PRM methodology, a distinct posterior-anterior gradient was seen, in which nearly the entire posterior region of the lung was identified as HEALTHY, while the anterior lung was labeled as significantly less so (t(29) = -3.27, p = 0.003). In both cohorts, %SAD progressively increased from posterior to anterior, while %HEALTHY lung decreased in the same direction. After applying our PRM methodology with variable thresholds to the same rat images, the posterior-anterior trend in %SAD quantification was removed from all rats and the significant increase of diseased lung in the anterior was removed.

CONCLUSIONS

The PRM methodology using variable thresholds provides regionally specific markers of %SAD and %EMPH by correcting for alterations in regional lung function associated with the naturally occurring vertical gradient of dependent vs. non-dependent lung density and compliance.

Altered responses of end-expiratory lung volume and upper airway patency to body posture in diet-induced obese mice

OBJECTIVE

Although both obesity and body posture are important factors affecting end-expiratory lung volume (EELV) and upper airway patency, the influence of those factors on EELV and the association between EELV and upper airway calibers are still unknown in mice. This study examined such interaction effects in obese mice to test the hypothesis that obese mice have decreased EELV accompanied by structural alterations of the upper airway.

METHODS

A high-resolution in vivo micro-computed tomography was utilized to scan anesthetized lean and diet-induced obese mice in the prone and supine positions, followed by quantifying lung volume and analyzing upper airway morphology.

RESULTS

There was a statistically significant interaction between the effects of body weight and posture on both EELV (p = 0.0049, η 2  = 0.1041) and upper airway calibers (p = 0.0215, η 2  = 0.6304). In lean mice, EELV in the prone position was significantly larger than in the supine position (prone EELV = 193.22 ± 9.10 µl vs. supine EELV = 176.01 ± 10.91 µl; p = 0.0072), whereas obese mice did not have such an improvement in EELV in the prone position (prone EELV = 174.37 ± 20.23 µl vs. supine EELV = 183.39 ± 17.49 µl; p = 0.0981) and tended to have a smaller upper airway when EELV was low based on Spearman's correlation analysis.

CONCLUSIONS

These data indicate that obesity is an important factor compromising both EELV and upper airway calibers in a posture-dependent manner even in mice, which should be taken into consideration in future studies regarding upper airway collapse and lung mechanical properties using mice.

Lung ultrasound guided pulmonary recruitment during mechanical ventilation in neonates: A case series

BACKGROUND

Recently, the first report of lung ultrasound (LUS) guided recruitment during open lung ventilation in neonates has been published. LUS guided recruitment can change the approach to open lung ventilation, which is currently performed without any measure of lung function/lung expansion in the neonatal population.

METHODS

We included all the newborn infants that underwent a LUS-guided recruitment maneuver during mechanical ventilation as a rescue attempt for an extremely severe respiratory condition with oxygen saturation/fraction of inspired oxygen (SpO2/FIO2) ratio below 130 or the inability to wean off mechanical ventilation.

RESULTS

We report a case series describing 4 LUS guided recruitment maneuvers, underlying crucial aspects of this technique that can improve the effectiveness of the procedure. In particular, we describe a novel pattern (the S-pattern) that allows us to distinguish the recruitable from the unrecruitable lung and guide the pressure titration phase. Additionally, we describe the optimal LUS-guided patient positioning.

CONCLUSIONS

We believe that the inclusion of specifications regarding patient positioning and the S-pattern in the LUS-guided protocol may be beneficial for the success of the procedure.

Broad individual immersion-scattering of respiratory compliance likely substantiates dissimilar breathing mechanics

Head-out water immersion alters respiratory compliance which underpins defining pressure at a “Lung centroid” and the breathing “Static Lung Load”. In diving medicine as in designing dive-breathing devices a single value of lung centroid pressure is presumed as everyone’s standard. On the contrary, we considered that immersed respiratory compliance is disparate among a homogenous adult group (young, healthy, sporty). We wanted to substantiate this ample scattering for two reasons: (i) it may question the European standard used in designing dive-breathing devices; (ii) it may contribute to understand the diverse individual figures of immersed work of breathing. Resting spirometric measurements of lung volumes and the pressure–volume curve of the respiratory system were assessed for 18 subjects in two body positions (upright Up, and supine Sup). Measurements were taken in air (Air) and with subjects immersed up to the sternal notch (Imm). Compliance of the respiratory system (Crs) was calculated from pressure–volume curves for each condition. A median 60.45% reduction in Crs was recorded between Up-Air and Up-Imm (1.68 vs 0.66 L/kPa), with individual reductions ranging from 16.8 to 82.7%. We hypothesize that the previously disregarded scattering of immersion-reduced respiratory compliance might participate to substantial differences in immersed work of breathing.

Evidence of Air Trapping During Ex Vivo Lung Perfusion: A Swine Experimental Lung Imaging and Mechanics Study

Ex vivo lung perfusion (EVLP) allows the ventilation and perfusion of lungs to evaluate their viability for transplantation. The aim of this study is to compare the mechanical, morphologic and functional properties of lungs during EVLP with values obtained in vivo to guide a safe mechanical ventilation strategy. Lungs from 5 healthy pigs were studied in vivo and during 4 hours of EVLP. Lung compliance, airway resistance, gas exchange, and hemodynamic parameters were collected at positive end-expiratory pressure (PEEP) of 5 cm H₂O. Computed tomography was performed at PEEP 0, PEEP 5, and total lung capacity (TLC). Lung pressure-volume (PV) curves were performed from PEEP 0 to TLC. Lung compliance decreased during EVLP (53 ± 5 mL/cm H₂O vs 29 ± 7 mL/cm H₂O, P < .05), and the PV curve showed a lower inflection point. Gas content (528 ± 118 mL vs 892 ± 402 mL at PEEP 0) and airway resistance (25 ± 5 vs 44 ± 9 cmH₂O/L∗s^-1, P < .05) were higher during EVLP. Alveolar dead space (5% ± 2% vs 17% ± 6%, P < .05) and intrapulmonary shunt (9% ± 2% vs 28% ± 13%, P < .05) increased ex vivo compared to in vivo, while the partial pressure of oxygen to inspired oxygen fraction ratio (PO₂/FiO₂) did not differ (468 ± 52 mm Hg vs 536 ± 14 mm Hg). In conclusion, during EVLP lungs show signs of air trapping and bronchoconstriction, resulting in low compliance and increased alveolar dead space. Intrapulmonary shunt is high despite oxygenation levels acceptable for transplantation.

A quantitative CT parameter for the assessment of pulmonary oedema in patients with acute respiratory distress syndrome

Objectives

The aim of this study was to establish quantitative CT (qCT) parameters for pathophysiological understanding and clinical use in patients with acute respiratory distress syndrome (ARDS). The most promising parameter is introduced.

Materials and methods

28 intubated patients with ARDS obtained a conventional CT scan in end-expiratory breathhold within the first 48 hours after admission to intensive care unit (ICU). Following manual segmentation, 137 volume- and lung weight-associated qCT parameters were correlated with 71 clinical parameters such as blood gases, applied ventilation pressures, pulse contour cardiac output measurements and established status and prognosis scores (SOFA, SAPS II).

Results

Of all examined qCT parameters, excess lung weight (ELW), i.e. the difference between a patient’s current lung weight and the virtual lung weight of a healthy person at the same height, displayed the most significant results.

ELW correlated significantly with the amount of inflated lung tissue [%] (p<0.0001; r = -0.66) and was closely associated with the amount of extravascular lung water (EVLW) (p<0.0001; r = 0.72). More substantially than the oxygenation index (PaO₂/FiO₂) or any other clinical parameter it correlated with the patients’ mean SOFA- (p<0.0001, r = 0.69) and SAPS II-Score (p = 0.0005, r = 0.62). Patients who did not survive intensive care treatment displayed higher values of ELW in the initial CT scans.

Conclusions

ELW could serve as a non-invasive method to quantify the amount of pulmonary oedema. It might serve as an early radiological marker of severity in patients with ARDS.

Positional Therapy and Regional Pulmonary Ventilation

BACKGROUND

Prone ventilation redistributes lung inflation along the gravitational axis; however, localized, nongravitational effects of body position are less well characterized. The authors hypothesize that positional inflation improvements follow both gravitational and nongravitational distributions. This study is a nonoverlapping reanalysis of previously published large animal data.

METHODS

Five intubated, mechanically ventilated pigs were imaged before and after lung injury by tracheal injection of hydrochloric acid (2 ml/kg). Computed tomography scans were performed at 5 and 10 cm H2O positive end-expiratory pressure (PEEP) in both prone and supine positions. All paired prone-supine images were digitally aligned to each other. Each unit of lung tissue was assigned to three clusters (K-means) according to positional changes of its density and dimensions. The regional cluster distribution was analyzed. Units of tissue displaying lung recruitment were mapped.

RESULTS

We characterized three tissue clusters on computed tomography: deflation (increased tissue density and contraction), limited response (stable density and volume), and reinflation (decreased density and expansion). The respective clusters occupied (mean ± SD including all studied conditions) 29.3 ± 12.9%, 47.6 ± 11.4%, and 23.1 ± 8.3% of total lung mass, with similar distributions before and after lung injury. Reinflation was slightly greater at higher PEEP after injury. Larger proportions of the reinflation cluster were contained in the dorsal versus ventral (86.4 ± 8.5% vs. 13.6 ± 8.5%, P < 0.001) and in the caudal versus cranial (63.4 ± 11.2% vs. 36.6 ± 11.2%, P < 0.001) regions of the lung. After injury, prone positioning recruited 64.5 ± 36.7 g of tissue (11.4 ± 6.7% of total lung mass) at lower PEEP, and 49.9 ± 12.9 g (8.9 ± 2.8% of total mass) at higher PEEP; more than 59.0% of this recruitment was caudal.

CONCLUSIONS

During mechanical ventilation, lung reinflation and recruitment by the prone positioning were primarily localized in the dorso-caudal lung. The local effects of positioning in this lung region may determine its clinical efficacy.

EDITOR’S PERSPECTIVE

Management of critically ill patients with COVID-19 in ICU: statement from front-line intensive care experts in Wuhan, China

BACKGROUND

The ongoing coronavirus disease 2019 (COVID-2019) pandemic has swept all over the world, posing a great pressure on critical care resources due to large number of patients needing critical care. Statements from front-line experts in the field of intensive care are urgently needed.

METHODS

Sixteen front-line experts in China fighting against the COVID-19 epidemic in Wuhan were organized to develop an expert statement after 5 rounds of expert seminars and discussions to provide trustworthy recommendation on the management of critically ill COVID-19 patients. Each expert was assigned tasks within their field of expertise to provide draft statements and rationale. Parts of the expert statement are based on epidemiological and clinical evidence, without available scientific evidences.

RESULTS

A comprehensive document with 46 statements are presented, including protection of medical personnel, etiological treatment, diagnosis and treatment of tissue and organ functional impairment, psychological interventions, immunity therapy, nutritional support, and transportation of critically ill COVID-19 patients. Among them, 5 recommendations were strong (Grade 1), 21 were weak (Grade 2), and 20 were experts' opinions. A strong agreement from voting participants was obtained for all recommendations.

CONCLUSION

There are still no targeted therapies for COVID-19 patients. Dynamic monitoring and supportive treatment for the restoration of tissue vascularization and organ function are particularly important.

Surviving sepsis campaign international guidelines for the management of septic shock and sepsis-associated organ dysfunction in children

OBJECTIVES

To develop evidence-based recommendations for clinicians caring for children (including infants, school-aged children, and adolescents) with septic shock and other sepsis-associated organ dysfunction.

DESIGN

A panel of 49 international experts, representing 12 international organizations, as well as three methodologists and three public members was convened. Panel members assembled at key international meetings (for those panel members attending the conference), and a stand-alone meeting was held for all panel members in November 2018. A formal conflict-of-interest policy was developed at the onset of the process and enforced throughout. Teleconferences and electronic-based discussion among the chairs, co-chairs, methodologists, and group heads, as well as within subgroups, served as an integral part of the guideline development process.

METHODS

The panel consisted of six subgroups: recognition and management of infection, hemodynamics and resuscitation, ventilation, endocrine and metabolic therapies, adjunctive therapies, and research priorities. We conducted a systematic review for each Population, Intervention, Control, and Outcomes question to identify the best available evidence, statistically summarized the evidence, and then assessed the quality of evidence using the Grading of Recommendations Assessment, Development, and Evaluation approach. We used the evidence-to-decision framework to formulate recommendations as strong or weak, or as a best practice statement. In addition, "in our practice" statements were included when evidence was inconclusive to issue a recommendation, but the panel felt that some guidance based on practice patterns may be appropriate.

RESULTS

The panel provided 77 statements on the management and resuscitation of children with septic shock and other sepsis-associated organ dysfunction. Overall, six were strong recommendations, 49 were weak recommendations, and nine were best-practice statements. For 13 questions, no recommendations could be made; but, for 10 of these, "in our practice" statements were provided. In addition, 52 research priorities were identified.

CONCLUSIONS

A large cohort of international experts was able to achieve consensus regarding many recommendations for the best care of children with sepsis, acknowledging that most aspects of care had relatively low quality of evidence resulting in the frequent issuance of weak recommendations. Despite this challenge, these recommendations regarding the management of children with septic shock and other sepsis-associated organ dysfunction provide a foundation for consistent care to improve outcomes and inform future research.

Surviving Sepsis Campaign International Guidelines for the Management of Septic Shock and Sepsis-Associated Organ Dysfunction in Children

OBJECTIVES

To develop evidence-based recommendations for clinicians caring for children (including infants, school-aged children, and adolescents) with septic shock and other sepsis-associated organ dysfunction.

DESIGN

A panel of 49 international experts, representing 12 international organizations, as well as three methodologists and three public members was convened. Panel members assembled at key international meetings (for those panel members attending the conference), and a stand-alone meeting was held for all panel members in November 2018. A formal conflict-of-interest policy was developed at the onset of the process and enforced throughout. Teleconferences and electronic-based discussion among the chairs, co-chairs, methodologists, and group heads, as well as within subgroups, served as an integral part of the guideline development process.

METHODS

The panel consisted of six subgroups: recognition and management of infection, hemodynamics and resuscitation, ventilation, endocrine and metabolic therapies, adjunctive therapies, and research priorities. We conducted a systematic review for each Population, Intervention, Control, and Outcomes question to identify the best available evidence, statistically summarized the evidence, and then assessed the quality of evidence using the Grading of Recommendations Assessment, Development, and Evaluation approach. We used the evidence-to-decision framework to formulate recommendations as strong or weak, or as a best practice statement. In addition, "in our practice" statements were included when evidence was inconclusive to issue a recommendation, but the panel felt that some guidance based on practice patterns may be appropriate.

RESULTS

The panel provided 77 statements on the management and resuscitation of children with septic shock and other sepsis-associated organ dysfunction. Overall, six were strong recommendations, 52 were weak recommendations, and nine were best-practice statements. For 13 questions, no recommendations could be made; but, for 10 of these, "in our practice" statements were provided. In addition, 49 research priorities were identified.

CONCLUSIONS

A large cohort of international experts was able to achieve consensus regarding many recommendations for the best care of children with sepsis, acknowledging that most aspects of care had relatively low quality of evidence resulting in the frequent issuance of weak recommendations. Despite this challenge, these recommendations regarding the management of children with septic shock and other sepsis-associated organ dysfunction provide a foundation for consistent care to improve outcomes and inform future research.

Noninvasive quantification of macrophagic lung recruitment during experimental ventilation-induced lung injury

Macrophagic lung infiltration is pivotal in the development of lung biotrauma because of ventilation-induced lung injury (VILI). We assessed the performance of [¹¹C](R)-PK11195, a positron emission tomography (PET) radiotracer binding the translocator protein, to quantify macrophage lung recruitment during experimental VILI. Pigs (n = 6) were mechanically ventilated under general anesthesia, using protective ventilation settings (baseline). Experimental VILI was performed by titrating tidal volume to reach a transpulmonary end-inspiratory pressure (∆P_L) of 35-40 cmH₂O. We acquired PET/computed tomography (CT) lung images at baseline and after 4 h of VILI. Lung macrophages were quantified in vivo by the standardized uptake value (SUV) of [¹¹C](R)-PK11195 measured in PET on the whole lung and in six lung regions and ex vivo on lung pathology at the end of experiment. Lung mechanics were extracted from CT images to assess their association with the PET signal. ∆P_L increased from 9 ± 1 cmH₂O under protective ventilation, to 36 ± 6 cmH₂O during experimental VILI. Compared with baseline, whole-lung [¹¹C](R)-PK11195 SUV significantly increased from 1.8 ± 0.5 to 2.9 ± 0.5 after experimental VILI. Regional [¹¹C](R)-PK11195 SUV was positively associated with the magnitude of macrophage recruitment in pathology (P = 0.03). Compared with baseline, whole-lung CT-derived dynamic strain and tidal hyperinflation increased significantly after experimental VILI, from 0.6 ± 0 to 2.0 ± 0.4, and 1 ± 1 to 43 ± 19%, respectively. On multivariate analysis, both were significantly associated with regional [¹¹C](R)-PK11195 SUV. [¹¹C](R)-PK11195 lung uptake (a proxy of lung inflammation) was increased by experimental VILI and was associated with the magnitude of dynamic strain and tidal hyperinflation.NEW & NOTEWORTHY We assessed the performance of [¹¹C](R)-PK11195, a translocator protein-specific positron emission tomography (PET) radiotracer, to quantify macrophage lung recruitment during experimental ventilation-induced lung injury (VILI). In this proof-of-concept study, we showed that the in vivo quantification of [¹¹C](R)-PK11195 lung uptake in PET reflected the magnitude of macrophage lung recruitment after VILI. Furthermore, increased [¹¹C](R)-PK11195 lung uptake was associated with harmful levels of dynamic strain and tidal hyperinflation applied to the lungs.

[Effect of prone positioning on respiratory function in very preterm infants undergoing mechanical ventilation]

OBJECTIVE

To explore the effect of prone positioning on respiratory function in very preterm infants undergoing mechanical ventilation.

METHODS

A total of 83 very preterm infants treated with mechanical ventilation were enrolled in the study and were randomly assigned to supine group and prone group. Four infants withdrew from the study and 79 infants completed treatment and observation (37 in the supine group and 42 in the prone group). Infants in both groups were mechanically ventilated in a volume assist-control mode. Infants in the prone group were ventilated in the supine position for 4 hours and in the prone position for 2 hours. Ventilator parameters, arterial blood gas analysis, and vital signs were recorded before grouping, every 6 hours in the supine group, and every hour after conversion into the prone position in the prone group, respectively.

RESULTS

Fraction of inspired oxygen (FiO2), peak inspiratory pressure, mean inspiratory pressure, and duration of ventilation were significantly lower in the prone group than in the supine group (P<0.05); there were no significant differences in tidal volume or positive end-expiratory pressure between the two groups (P>0.05). The prone group had a significantly higher PO2/FiO2 ratio but significantly lower oxygenation index and respiratory rate than the supine group (P<0.05). There were no significant differences in arterial oxygen tension, pH, base excess, heart rate, or mean blood pressure between the two groups (P>0.05).

CONCLUSIONS

Alternating ventilation between the prone position and supine position can improve oxygenation function, decrease the fraction of inspired oxygen, and shorten the duration of mechanical ventilation in very preterm infants undergoing mechanical ventilation.

[Effect of prone positioning on respiratory function in very preterm infants undergoing mechanical ventilation]

OBJECTIVE

To explore the effect of prone positioning on respiratory function in very preterm infants undergoing mechanical ventilation.

METHODS

A total of 83 very preterm infants treated with mechanical ventilation were enrolled in the study and were randomly assigned to supine group and prone group. Four infants withdrew from the study and 79 infants completed treatment and observation (37 in the supine group and 42 in the prone group). Infants in both groups were mechanically ventilated in a volume assist-control mode. Infants in the prone group were ventilated in the supine position for 4 hours and in the prone position for 2 hours. Ventilator parameters, arterial blood gas analysis, and vital signs were recorded before grouping, every 6 hours in the supine group, and every hour after conversion into the prone position in the prone group, respectively.

RESULTS

Fraction of inspired oxygen (FiO²), peak inspiratory pressure, mean inspiratory pressure, and duration of ventilation were significantly lower in the prone group than in the supine group (P<0.05); there were no significant differences in tidal volume or positive end-expiratory pressure between the two groups (P>0.05). The prone group had a significantly higher PO²/FiO² ratio but significantly lower oxygenation index and respiratory rate than the supine group (P<0.05). There were no significant differences in arterial oxygen tension, pH, base excess, heart rate, or mean blood pressure between the two groups (P>0.05).

CONCLUSIONS

Alternating ventilation between the prone position and supine position can improve oxygenation function, decrease the fraction of inspired oxygen, and shorten the duration of mechanical ventilation in very preterm infants undergoing mechanical ventilation.

Positional effects on the distributions of ventilation and end-expiratory gas volume in the asymmetric chest-a quantitative lung computed tomographic analysis

Background

Body positioning affects the configuration and dynamic properties of the chest wall and therefore may influence decisions made to increase or decrease ventilating pressures and tidal volume. We hypothesized that unlike global functional residual capacity (FRC), component sector gas volumes and their corresponding regional tidal expansions would vary markedly in the setting of unilateral pleural effusion (PLEF), owing to shifting distributions of aeration and collapse as posture changed.

Methods

Six deeply anesthetized swine underwent tracheostomy, thoracostomy, and experimental PLEF with 10 mL/kg of radiopaque isotonic fluid randomly instilled into either pleural space. Animals were ventilated at V_T = 10 mL/kg, frequency = 15 bpm, I/E = 1:2, PEEP = 1 cmH₂O, and FiO₂ = 0.5. Quantitative lung computed tomographic (CT) analysis of regional aeration and global FRC measurements by nitrogen wash-in/wash-out technique was performed in each of these randomly applied positions: semi-Fowler’s (inclined 30° from horizontal in the sagittal plane); prone, supine, and lateral positions with dependent PLEF and non-dependent PLEF.

Results

No significant differences in total FRC were observed among the horizontal positions, either at baseline (p = 0.9037) or with PLEF (p = 0.58). However, component sector total gas volumes in each phase of the tidal cycle were different within all studied positions with and without PLEF (p = < .01). Compared to other positions, prone and lateral positions with non-dependent PLEF had more homogenous V_T distributions among quadrants (p = .051). Supine position was associated with most dependent collapse and greatest tendency for tidal recruitment (48 vs ~ 22%, p = 0.0073).

Conclusions

Changes in body position in the setting of effusion-caused chest asymmetry markedly affected the internal distributions of gas volume, collapse, ventilation, and tidal recruitment, even though global FRC measurements provided little indication of these potentially important positional changes.

Electronic supplementary material

The online version of this article (10.1186/s40635-018-0175-4) contains supplementary material, which is available to authorized users.

Lung volumes and lung volume recruitment in ARDS: a comparison between supine and prone position

Background

The use of positive end-expiratory pressure (PEEP) and prone position (PP) is common in the management of severe acute respiratory distress syndrome patients (ARDS). We conducted this study to analyze the variation in lung volumes and PEEP-induced lung volume recruitment with the change from supine position (SP) to PP in ARDS patients.

Methods

The investigation was conducted in a multidisciplinary intensive care unit. Patients who met the clinical criteria of the Berlin definition for ARDS were included. The responsible physician set basal PEEP. To avoid hypoxemia, FiO₂ was increased to 0.8 1 h before starting the protocol. End-expiratory lung volume (EELV) and functional residual capacity (FRC) were measured using the nitrogen washout/washin technique. After the procedures in SP, the patients were turned to PP and 1 h later the same procedures were made in PP.

Results

Twenty-three patients were included in the study, and twenty were analyzed. The change from SP to PP significantly increased FRC (from 965 ± 397 to 1140 ± 490 ml, p = 0.008) and EELV (from 1566 ± 476 to 1832 ± 719 ml, p = 0.008), but PEEP-induced lung volume recruitment did not significantly change (269 ± 186 ml in SP to 324 ± 188 ml in PP, p = 0.263). Dynamic strain at PEEP decreased with the change from SP to PP (0.38 ± 0.14 to 0.33 ± 0.13, p = 0.040).

Conclusions

As compared to supine, prone position increases resting lung volumes and decreases dynamic lung strain.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0371-0) contains supplementary material, which is available to authorized users.

Prone position ventilation support for acute exacerbation of interstitial lung disease?

INTRODUCTION

Prone position ventilation (PPV) has been shown to improve oxygenation and decrease pulmonary vascular resistance and mortality in patients with severe acute respiratory distress syndrome (ARDS). Whether these benefits of PPV occur similarly in acute exacerbations of interstitial lung disease (ILD) is not clear. We retrospectively explored the use of PPV in acute exacerbation with ILD versus those with severe acute respiratory distress syndrome (severe ARDS).

METHODS

Retrospective study of the application of PPV in 17 patients with acute exacerbations of ILD and in 19 patients with severe ARDS. Pre- and post-PPV hemodynamic parameters, respiratory mechanics, prognostic indicators, complications and mortality rates at 28, 60 and 90 days were compared.

RESULTS

There was no difference in baseline characteristics between the two groups except for higher driving pressure and more diastolic dysfunction in ILD group than severe ARDS group Compared with pre-PPV, cardiac index and driving pressure remained unchanged post-PPV in both groups. PPV increased PaO₂ /FiO₂ [118.7 (92.0, 147.8) pre-PPV vs 132.0 (93.5, 172.0) post-PPV; P < 0.05] and central venous oxygenation in patients with ILD. In patients with severe ARDS, PPV significantly increased PaO₂ /FiO₂ [109.23 (89,135) pre- PPV vs 126.13 (100.93, 170) post-PPV; P < 0.05] and intrathorax blood volume index. However, mortality rates at 28, 60 and 90 days remained high in both groups (76.4%, 88.2% and 88.2% vs 36.8%, 57.9% and 57.9% in ILD and severe ARDS, respectively; P < 0.05).

CONCLUSION

Our findings suggest that PPV may improve oxygenation and partially improve hemodynamic parameters during acute exacerbations of ILD.

Prone position in patients with acute respiratory distress syndrome

Acute respiratory distress syndrome occupies a great deal of attention in intensive care units. Despite ample knowledge of the physiopathology of this syndrome, the focus in intensive care units consists mostly of life-supporting treatment and avoidance of the side effects of invasive treatments. Although great advances in mechanical ventilation have occurred in the past 20 years, with a significant impact on mortality, the incidence continues to be high. Patients with acute respiratory distress syndrome, especially the most severe cases, often present with refractory hypoxemia due to shunt, which can require additional treatments beyond mechanical ventilation, among which is mechanical ventilation in the prone position. This method, first recommended to improve oxygenation in 1974, can be easily implemented in any intensive care unit with trained personnel.

Prone position has extremely robust bibliographic support. Various randomized clinical studies have demonstrated the effect of prone decubitus on the oxygenation of patients with acute respiratory distress syndrome measured in terms of the PaO₂/FiO₂ ratio, including its effects on increasing patient survival.

The members of the Respiratory Therapists Committee of the Sociedad Argentina de Terapia Intensiva performed a narrative review with the objective of discovering the available evidence related to the implementation of prone position, changes produced in the respiratory system due to the application of this maneuver, and its impact on mortality. Finally, guidelines are suggested for decision-making.