Electrical impedance tomography (EIT) has undergone 30 years of development. Functional chest examinations with this technology are considered clinically relevant, especially for monitoring regional ...lung ventilation in mechanically ventilated patients and for regional pulmonary function testing in patients with chronic lung diseases. As EIT becomes an established medical technology, it requires consensus examination, nomenclature, data analysis and interpretation schemes. Such consensus is needed to compare, understand and reproduce study findings from and among different research groups, to enable large clinical trials and, ultimately, routine clinical use. Recommendations of how EIT findings can be applied to generate diagnoses and impact clinical decision-making and therapy planning are required. This consensus paper was prepared by an international working group, collaborating on the clinical promotion of EIT called TRanslational EIT developmeNt stuDy group. It addresses the stated needs by providing (1) a new classification of core processes involved in chest EIT examinations and data analysis, (2) focus on clinical applications with structured reviews and outlooks (separately for adult and neonatal/paediatric patients), (3) a structured framework to categorise and understand the relationships among analysis approaches and their clinical roles, (4) consensus, unified terminology with clinical user-friendly definitions and explanations, (5) a review of all major work in thoracic EIT and (6) recommendations for future development (193 pages of online supplements systematically linked with the chief sections of the main document). We expect this information to be useful for clinicians and researchers working with EIT, as well as for industry producers of this technology.
OBJECTIVES:Atelectasis develops in critically ill obese patients when undergoing mechanical ventilation due to increased pleural pressure. The current study aimed to determine the relationship ...between transpulmonary pressure, lung mechanics, and lung morphology and to quantify the benefits of a decremental positive end-expiratory pressure trial preceded by a recruitment maneuver.
DESIGN:Prospective, crossover, nonrandomized interventional study.
SETTING:Medical and Surgical Intensive Care Units at Massachusetts General Hospital (Boston, MA) and University Animal Research Laboratory (São Paulo, Brazil).
PATIENTS/SUBJECTS:Critically ill obese patients with acute respiratory failure and anesthetized swine.
INTERVENTIONS:Clinical data from 16 mechanically ventilated critically ill obese patients were analyzed. An animal model of obesity with reversible atelectasis was developed by placing fluid filled bags on the abdomen to describe changes of lung mechanics, lung morphology, and pulmonary hemodynamics in 10 swine.
MEASUREMENTS AND MAIN RESULTS:In obese patients (body mass index, 48 ± 11 kg/m), 21.7 ± 3.7 cm H2O of positive end-expiratory pressure resulted in the lowest elastance of the respiratory system (18.6 ± 6.1 cm H2O/L) after a recruitment maneuver and decremental positive end-expiratory pressure and corresponded to a positive (2.1 ± 2.2 cm H2O) end-expiratory transpulmonary pressure. Ventilation at lowest elastance positive end-expiratory pressure preceded by a recruitment maneuver restored end-expiratory lung volume (30.4 ± 9.1 mL/kg ideal body weight) and oxygenation (273.4 ± 72.1 mm Hg). In the swine model, lung collapse and intratidal recruitment/derecruitment occurred when the positive end-expiratory transpulmonary pressure decreased below 2–4 cm H2O. After the development of atelectasis, a decremental positive end-expiratory pressure trial preceded by lung recruitment identified the positive end-expiratory pressure level (17.4 ± 2.1 cm H2O) needed to restore poorly and nonaerated lung tissue, reestablishing lung elastance and oxygenation while avoiding increased pulmonary vascular resistance.
CONCLUSIONS:In obesity, low-to-negative values of transpulmonary pressure predict lung collapse and intratidal recruitment/derecruitment. A decremental positive end-expiratory pressure trial preceded by a recruitment maneuver reverses atelectasis, improves lung mechanics, distribution of ventilation and oxygenation, and does not increase pulmonary vascular resistance.
Abstract Background Bronchoscopic lung volume reduction (BLVR) with one-way endobronchial valves (EBV) has better outcomes when the target lobe has poor collateral ventilation, resulting in complete ...lobe atelectasis. High-inspired oxygen fraction (F I O 2 ) promotes atelectasis through faster gas absorption after airway occlusion, but its application during BLVR with EBV has been poorly understood. We aimed to investigate the real-time effects of F I O 2 on regional lung volumes and regional ventilation/perfusion by electrical impedance tomography (EIT) during BLVR with EBV. Methods Six piglets were submitted to left lower lobe occlusion by a balloon-catheter and EBV valves with F I O 2 0.5 and 1.0. Regional end-expiratory lung impedances (EELI) and regional ventilation/perfusion were monitored. Local pocket pressure measurements were obtained (balloon occlusion method). One animal underwent simultaneous acquisitions of computed tomography (CT) and EIT. Regions-of-interest (ROIs) were right and left hemithoraces. Results Following balloon occlusion, a steep decrease in left ROI-EELI with F I O 2 1.0 occurred, 3-fold greater than with 0.5 ( p < 0.001). Higher F I O 2 also enhanced the final volume reduction (ROI-EELI) achieved by each valve ( p < 0.01). CT analysis confirmed the denser atelectasis and greater volume reduction achieved by higher F I O 2 (1.0) during balloon occlusion or during valve placement. CT and pocket pressure data agreed well with EIT findings, indicating greater strain redistribution with higher F I O 2 . Conclusions EIT demonstrated in real-time a faster and more complete volume reduction in the occluded lung regions under high F I O 2 (1.0), as compared to 0.5. Immediate changes in the ventilation and perfusion of ipsilateral non-target lung regions were also detected, providing better estimates of the full impact of each valve in place. Trial registration Not applicable.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In normal lungs, local changes in pleural pressure (P(pl)) are generalized over the whole pleural surface. However, in a patient with injured lungs, we observed (using electrical impedance ...tomography) a pendelluft phenomenon (movement of air within the lung from nondependent to dependent regions without change in tidal volume) that was caused by spontaneous breathing during mechanical ventilation.
To test the hypotheses that in injured lungs negative P(pl) generated by diaphragm contraction has localized effects (in dependent regions) that are not uniformly transmitted, and that such localized changes in P(pl) cause pendelluft.
We used electrical impedance tomography and dynamic computed tomography (CT) to analyze regional inflation in anesthetized pigs with lung injury. Changes in local P(pl) were measured in nondependent versus dependent regions using intrabronchial balloon catheters. The airway pressure needed to achieve comparable dependent lung inflation during paralysis versus spontaneous breathing was estimated.
In all animals, spontaneous breathing caused pendelluft during early inflation, which was associated with more negative local P(pl) in dependent regions versus nondependent regions (-13.0 ± 4.0 vs. -6.4 ± 3.8 cm H2O; P < 0.05). Dynamic CT confirmed pendelluft, which occurred despite limitation of tidal volume to less than 6 ml/kg. Comparable inflation of dependent lung during paralysis required almost threefold greater driving pressure (and tidal volume) versus spontaneous breathing (28.0 ± 0.5 vs. 10.3 ± 0.6 cm H2O, P < 0.01; 14.8 ± 4.6 vs. 5.8 ± 1.6 ml/kg, P < 0.05).
Spontaneous breathing effort during mechanical ventilation causes unsuspected overstretch of dependent lung during early inflation (associated with reciprocal deflation of nondependent lung). Even when not increasing tidal volume, strong spontaneous effort may potentially enhance lung damage.
OBJECTIVES:We recently described how spontaneous effort during mechanical ventilation can cause “pendelluft,” that is, displacement of gas from nondependent (more recruited) lung to dependent (less ...recruited) lung during early inspiration. Such transfer depends on the coexistence of more recruited (source) liquid-like lung regions together with less recruited (target) solid-like lung regions. Pendelluft may improve gas exchange, but because of tidal recruitment, it may also contribute to injury. We hypothesize that higher positive end-expiratory pressure levels decrease the propensity to pendelluft and that with lower positive end-expiratory pressure levels, pendelluft is associated with improved gas exchange but increased tidal recruitment.
DESIGN:Crossover design.
SETTING:University animal research laboratory.
SUBJECTS:Anesthetized landrace pigs.
INTERVENTIONS:Surfactant depletion was achieved by saline lavage in anesthetized pigs, and ventilator-induced lung injury was produced by ventilation with high tidal volume and low positive end-expiratory pressure. Ventilation was continued in each of four conditionspositive end-expiratory pressure (low or optimized positive end-expiratory pressure after recruitment) and spontaneous breathing (present or absent). Tidal recruitment was assessed using dynamic CT and regional ventilation/perfusion using electric impedance tomography. Esophageal pressure was measured using an esophageal balloon manometer.
MEASUREMENTS AND RESULTS:Among the four conditions, spontaneous breathing at low positive end-expiratory pressure not only caused the largest degree of pendelluft, which was associated with improved ventilation/perfusion matching and oxygenation, but also generated the greatest tidal recruitment. At low positive end-expiratory pressure, paralysis worsened oxygenation but reduced tidal recruitment. Optimized positive end-expiratory pressure decreased the magnitude of spontaneous efforts (measured by esophageal pressure) despite using less sedation, from –5.6 ± 1.3 to –2.0 ± 0.7 cm H2O, while concomitantly reducing pendelluft and tidal recruitment. No pendelluft was observed in the absence of spontaneous effort.
CONCLUSIONS:Spontaneous effort at low positive end-expiratory pressure improved oxygenation but promoted tidal recruitment associated with pendelluft. Optimized positive end-expiratory pressure (set after lung recruitment) may reverse the harmful effects of spontaneous breathing by reducing inspiratory effort, pendelluft, and tidal recruitment.
Spontaneous breathing during mechanical ventilation increases transpulmonary pressure and Vt, and worsens lung injury. Intuitively, controlling Vt and transpulmonary pressure might limit injury ...caused by added spontaneous effort.
To test the hypothesis that, during spontaneous effort in injured lungs, limitation of Vt and transpulmonary pressure by volume-controlled ventilation results in less injurious patterns of inflation.
Dynamic computed tomography was used to determine patterns of regional inflation in rabbits with injured lungs during volume-controlled or pressure-controlled ventilation. Transpulmonary pressure was estimated by using esophageal balloon manometry Pl(es) with and without spontaneous effort. Local dependent lung stress was estimated as the swing (inspiratory change) in transpulmonary pressure measured by intrapleural manometry in dependent lung and was compared with the swing in Pl(es). Electrical impedance tomography was performed to evaluate the inflation pattern in a larger animal (pig) and in a patient with acute respiratory distress syndrome.
Spontaneous breathing in injured lungs increased Pl(es) during pressure-controlled (but not volume-controlled) ventilation, but the pattern of dependent lung inflation was the same in both modes. In volume-controlled ventilation, spontaneous effort caused greater inflation and tidal recruitment of dorsal regions (greater than twofold) compared with during muscle paralysis, despite the same Vt and Pl(es). This was caused by higher local dependent lung stress (measured by intrapleural manometry). In injured lungs, esophageal manometry underestimated local dependent pleural pressure changes during spontaneous effort.
Limitation of Vt and Pl(es) by volume-controlled ventilation could not eliminate harm caused by spontaneous breathing unless the level of spontaneous effort was lowered and local dependent lung stress was reduced.
Pneumoperitoneum and nonphysiological positioning required for robotic surgery increase cardiopulmonary risk because of the use of larger airway pressures (Paws) to maintain tidal volume (VT). ...However, the quantitative partitioning of respiratory mechanics and transpulmonary pressure (PL) during robotic surgery is not well described. We tested the following hypothesis: (1) the components of driving pressure (transpulmonary and chest wall components) increase in a parallel fashion at robotic surgical stages (Trendelenburg and robot docking); and (2) deep, when compared to routine (moderate), neuromuscular blockade modifies those changes in PLs as well as in regional respiratory mechanics.
We studied 35 American Society of Anesthesiologists (ASA) I-II patients undergoing elective robotic surgery. Airway and esophageal balloon pressures and respiratory flows were measured to calculate respiratory mechanics. Regional lung aeration and ventilation was assessed with electrical impedance tomography and level of neuromuscular blockade with acceleromyography. During robotic surgical stages, 2 crossover randomized groups (conditions) of neuromuscular relaxation were studied: Moderate (1 twitch in the train-of-four stimulation) and Deep (1-2 twitches in the posttetanic count).
Pneumoperitoneum was associated with increases in driving pressure, tidal changes in PL, and esophageal pressure (Pes). Steep Trendelenburg position during robot docking was associated with further worsening of the respiratory mechanics. The fraction of driving pressures that partitioned to the lungs decreased from baseline (63% ± 15%) to Trendelenburg position (49% ± 14%, P < .001), due to a larger increase in chest wall elastance (Ecw; 12.7 ± 7.6 cm H2O·L) than in lung elastance (EL; 4.3 ± 5.0 cm H2O·L, P < .001). Consequently, from baseline to Trendelenburg, the component of Paw affecting the chest wall increased by 6.6 ± 3.1 cm H2O, while PLs increased by only 3.4 ± 3.1 cm H2O (P < .001). PL and driving pressures were larger at surgery end than at baseline and were accompanied by dorsal aeration loss. Deep neuromuscular blockade did not change respiratory mechanics, regional aeration and ventilation, and hemodynamics.
In robotic surgery with pneumoperitoneum, changes in ventilatory driving pressures during Trendelenburg and robot docking are distributed less to the lungs than to the chest wall as compared to routine mechanical ventilation for supine patients. This effect of robotic surgery derives from substantially larger increases in Ecw than ELs and reduces the risk of excessive PLs. Deep neuromuscular blockade does not meaningfully change global or regional lung mechanics.
BACKGROUND:Pneumoperitoneum and nonphysiological positioning required for robotic surgery increase cardiopulmonary risk because of the use of larger airway pressures (Paws) to maintain tidal volume ...(VT). However, the quantitative partitioning of respiratory mechanics and transpulmonary pressure (PL) during robotic surgery is not well described. We tested the following hypothesis(1) the components of driving pressure (transpulmonary and chest wall components) increase in a parallel fashion at robotic surgical stages (Trendelenburg and robot docking); and (2) deep, when compared to routine (moderate), neuromuscular blockade modifies those changes in PLs as well as in regional respiratory mechanics.
METHODS:We studied 35 American Society of Anesthesiologists (ASA) I-II patients undergoing elective robotic surgery. Airway and esophageal balloon pressures and respiratory flows were measured to calculate respiratory mechanics. Regional lung aeration and ventilation was assessed with electrical impedance tomography and level of neuromuscular blockade with acceleromyography. During robotic surgical stages, 2 crossover randomized groups (conditions) of neuromuscular relaxation were studiedModerate (1 twitch in the train-of-four stimulation) and Deep (1–2 twitches in the posttetanic count).
RESULTS:Pneumoperitoneum was associated with increases in driving pressure, tidal changes in PL, and esophageal pressure (Pes). Steep Trendelenburg position during robot docking was associated with further worsening of the respiratory mechanics. The fraction of driving pressures that partitioned to the lungs decreased from baseline (63% ± 15%) to Trendelenburg position (49% ± 14%, P < .001), due to a larger increase in chest wall elastance (Ecw; 12.7 ± 7.6 cm H2O·L) than in lung elastance (EL; 4.3 ± 5.0 cm H2O·L, P < .001). Consequently, from baseline to Trendelenburg, the component of Paw affecting the chest wall increased by 6.6 ± 3.1 cm H2O, while PLs increased by only 3.4 ± 3.1 cm H2O (P < .001). PL and driving pressures were larger at surgery end than at baseline and were accompanied by dorsal aeration loss. Deep neuromuscular blockade did not change respiratory mechanics, regional aeration and ventilation, and hemodynamics.
CONCLUSIONS:In robotic surgery with pneumoperitoneum, changes in ventilatory driving pressures during Trendelenburg and robot docking are distributed less to the lungs than to the chest wall as compared to routine mechanical ventilation for supine patients. This effect of robotic surgery derives from substantially larger increases in Ecw than ELs and reduces the risk of excessive PLs. Deep neuromuscular blockade does not meaningfully change global or regional lung mechanics.
Introdução - Pacientes com enfisema pulmonar avançado submetidos a redução volumétrica pulmonar endoscópica (ELVR) com válvulas unidirecionais (EBV) apresentam melhores resultados quando o lobo ...tratado não possui ventilação colateral e atelectasia lobar é alcançada. No entanto, a resposta positiva de desinsuflação está associada a maior ocorrência de pneumotórax nessa população. Recomendações recentes enfatizam a importância de condutas no intra- e pós-operatório que busquem minimizar os riscos associados, porém muito pouco é abordado em relação ao manejo da ventilação mecânica durante a intervenção. Elevada fração inspirada de oxigênio (FiO2) é reconhecida na indução de atelectasia por absorção e pode desempenhar um papel relevante na modulação de redução volumétrica após oclusão seletiva. Atualmente não se monitora os efeitos regionais da ELVR com EBV em tempo real. A tomografia de impedância elétrica (TIE) é uma ferramenta de imagem não-invasiva e sem radiação que fornece dados regionais em tempo real de variação de volume pulmonar por meio de uma cinta de eletrodos aplicadas no tórax. Neste contexto, o objetivo deste estudo é usar a TIE para avaliar a influência da FiO2 na ELVR com EBV em um modelo experimental de pulmão normal suíno, animal que não possui ventilação colateral. Métodos - 5 suínos foram submetidos a um estudo cruzado de oclusão do lobo inferior esquerdo por dois métodos, válvulas unidirecionais (válvulas) e cateter-balão intrabronquial (balão), com FiO2 de 50% e 100% por 15 minutos em cada etapa. O balão serviu como um controle, com oclusão assegurada por visão direta via broncoscópio e medida da pressão expiratória distal à oclusão em um animal representativo. A pressão expiratória positiva final usada foi titulada pela TIE para cada animal e recrutamento alveolar foi realizado ao final de cada etapa para reverter o colapso induzido. Foram analisados o mínimo Z (MinZ), como estimativa do volume pulmonar ao final da expiração, e o DeltaZ, variação cíclica proporcional ao volume corrente, ambos expressos em unidades arbitrárias de variação relativa, desde antes da oclusão (Pré) e em cada minuto do momento da oclusão (T0) até 15 minutos (T15). Em um animal adicional foi realizada aquisição simultânea de tomografia computadorizada (TC) e TIE para quantificação do conteúdo de gás. Em todas as análises as regiões de interesse foram direita (Dir) e esquerda (Esq). Resultados - Houve redução rápida e progressiva do MinZ Esq após oclusão com balão, sendo a magnitude quase 3 vezes maior na FiO2 de 100% comparada a 50% (p < 0,001). Com válvulas a 50% o MinZ Esq apresentou redução inicial, mas teve incremento progressivo de forma que em T15 não mostrou diferença em relação ao Pré (p=0,20). Em média, o MinZ Dir não sofreu alteração significativa. Os dados da TC e pressão distal tiveram padrão similar aos achados de MinZ da TIE. O DeltaZ Esq apresentou redução imediata após oclusão e se manteve estável ao longo dos 15 minutos, sem diferença entre as FiO2 em cada método de oclusão. Conclusão- FiO2 a 100% promove maior taxa de redução volumétrica secundária a oclusão lobar seletiva quando comparado a 50% e a TIE apresentou resultados coerentes e concordantes com métodos complementares
Introduction - Patients with advanced pulmonary emphysema undergoing endoscopic lung volume reduction (ELVR) with one-way endobronchial valves (EBV) present better results when the treated lobe has negative collateral ventilation and lobar atelectasis is achieved. However, the positive response of deflation is associated with a higher occurrence of pneumothorax in this population. Recent recommendations emphasize the importance of intra- and postoperative procedures that seek to minimize the associated risks, but very little is addressed regarding the management of mechanical ventilation during the intervention. High inspired oxygen fraction (FiO2) is known to induce atelectasis by absorption and may play a relevant role in the modulation of volumetric reduction after selective occlusion. Currently, regional effects of ELVR with EBV is not monitored in real-time. Electrical impedance tomography (EIT) is a non-invasive and radiation-free imaging tool that provides regional real-time lung volume variation data by means of an electrode belt applied to the chest. In this context, the objective of this study is to use EIT to evaluate the influence of FiO2 on ELVR with EBV in an experimental normal lung swine model, an animal that lacks collateral ventilation. Methods - Five pigs were used in a crossover study of left lower lobe occlusion by two methods, one-way valves (valves) and intrabronchial balloon catheter (balloon), with FiO2 of 50% and 100% for 15 minutes at each stage. The balloon served as a control, where occlusion was ensured by direct bronchoscopic inspection and allowed a measurement of expiratory pressure distal to the occlusion in a representative animal. The positive end-expiratory pressure used was titrated by EIT for each animal and alveolar recruitment was performed at the end of each step to reverse the induced collapse. Minimum impedance value (MinZ) was recorded as an estimate of end-expiratory lung volume and tidal impedance variation (DeltaZ) as proportional to tidal volume, both expressed in arbitrary units of relative variation, from pre-occlusion (Pre) and every minute since occlusion (T0) up to 15 minutes (T15). In an additional animal, simultaneous acquisition of computed tomography (CT) and EIT was performed to quantify gas content. In all the analysis, regions of interest were right (R) and left (L). Results - There was a rapid and progressive reduction of MinZ-L after occlusion, with almost 3 times greater magnitude in FiO2 100% compared to 50% (p < 0.001). With valves at 50%, the MinZ-L presented initial reduction, but had a progressive increase so that in T15 there was no difference in relation to Pre (p = 0.20). On average, MinZ-R did not change significantly. CT and distal pressure data were consistent with EIT MinZ findings. DeltaZ-L presented immediate reduction after occlusion and remained stable throughout all 15 minutes, with no difference between FiO2 in each method of occlusion. Conclusion- FiO2 of 100% promotes greater rate of volumetric reduction following selective lobar occlusion when compared to 50%, and EIT presented coherent results in agreement with complementary methods
Background
There is a lack of non-invasive methods for monitoring the upper airway patency during sleep. Electrical impedance tomography (EIT) is a non-invasive, radiation-free tool that has been ...validated to monitor lung ventilation. We hypothesized that electrical impedance tomography (EIT) can be used for monitoring upper airway patency during sleep.
Methods
Sleep was induced in 21 subjects (14 males, age 43 ± 13 years, body mass index 32.0 ± 5.3 kg/m
2
) with suspected obstructive sleep apnea (apnea-hypopnea index: 44 ± 37 events/h, range: 1–122 events/h) using low doses of midazolam. Patients wore a nasal mask attached to a modified CPAP device, allowing variable and controlled degrees of upper airway obstruction. Confirmation of upper airway patency was obtained with direct visualization of the upper airway using nasofibroscopy (
n
= 6). The changes in total neck impedance and in impedance in four cranio-caudal regions of interest (ROIs) were analyzed.
Results
Total neck impedance varied in concert with breathing cycles and peaked during expiration in all patients. Group data showed a high cross-correlation between flow and impedance curves (
r
= −0.817,
p
< 0.001). Inspiratory peak flow correlated with simultaneous neck impedance (
r
= 0.866,
p
< 0.001). There was a high correlation between total neck impedance and velopharynx area (
r
= 0.884,
p
< 0.001), and total neck impedance and oropharynx area (
r
= 0.891,
p
< 0.001).
Conclusions
Neck EIT is sensitive and captures pharyngeal obstruction under various conditions. Neck EIT is a promising method for real-time monitoring of the pharynx during sleep.
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