Das Auftreten pulmonaler Belüftungsstörungen nach Injektion von Xylazin beim Schaf ist in der wissenschaftlichen Literatur an Einzeltieren beschrieben. Der dabei noch ausstehende Nachweis eines postulierten Lungenödems anhand objektiver Parameter in statistisch relevanter Anzahl wurde in der hier vorliegenden Arbeit angestrebt. Weiterhin wurden ein Einfluss der wiederholten Exposition und eine Dosisabhängigkeit überprüft. Zur Bearbeitung dieser Fragen wurden 16 weibliche Merinolandschafe dreimalig in einem Abstand von 8 Wochen untersucht. Nach Prämedikation mit Midazolam (0,25 mg/kg) und Sufentanil (0,6 µg/kg) erfolgte die Allgemeinanästhesie mit Propofol (5-10 mg/kg/h). Zu den ersten beiden Versuchsabschnitten wurde Xylazin in einer Dosis von 0,15 mg/kg, im dritten Versuchsdurchgang in Höhe von 0,3 mg/kg intravenös verabreicht. Jeweils 10 Minuten vor und 5, 15, 30 Minuten nach Applikation von Xylazin wurden computertomographische Untersuchungen durchgeführt. Mit Hilfe der quantitativen computertomographischen Analyse konnte das totale Lungengewicht, der Anteil nicht belüftetes Lungengewicht und das totale Lungenvolumen ermittelt werden. Zusätzlich wurden mittels arterieller Blutgasanalysen der arterielle Sauerstoff- und Kohlenstoffdioxidpartialdruck bestimmt. In der dieser Arbeit zu Grunde liegenden Annahme nimmt im Falle eines Lungenödems das totale Lungengewicht bei konstantem Lungenvolumen zu. Eine Zunahme des totalen Lungengewichts war in allen drei Versuchsdurchgängen statitisch signifikant nachweisbar. Im Vergleich zu den Angaben in der Literatur wurden dabei jedoch keine Zunahmen in Höhe eines klinisch relevanten Lungenödems erreicht. Unerwartet konnte zusätzlich ein signifikanter Rückgang des totalen Lungenvolumens detektiert werden. Weiterhin waren bereits 5 Minuten nach Xylazininjektion bis zu einem Drittel des totalen Lungengewichts nicht belüftet. Diese pulmonalen Belüftungsstörungen nach Applikation von Xylazin beim Schaf wurden aufgrund der vorliegenden Ergebnisse nicht ausschließlich der Entstehung eines Lungenödems zugeordnet. Die detektierte Reduktion des totalen Lungenvolumens bei konstanter Beatmung kann nur durch Atelektasen begründet werden. Entsprechend dem Ausmaß der detektierten pulmonalen Reaktionen nach Xylazingabe wurden eine schwere Hypoxämie sowie eine Hyperkapnie festgestellt. Durch die mehrfache Exposition von Xylazin erfolgte der Nachweis der Wiederholbarkeit dieser Ergebnisse. Eine Dosisabhängigkeit des Ausprägungsgrades der pulmonalen Befunde hingegen konnte nicht statistisch signifikant bestätigt werden. Anhand der hier vorliegenden Ergebnisse muss die Ätiologie der pulmonalen Veränderungen nach Injektion von Xylazin beim Schaf neu durchdacht und in weiteren Studien verfolgt werden. Einflussfaktoren wie die Form der Applikation oder eine genetische Prädisposition gilt es in Zukunft zu analysieren. Neben der klinischen Anwendung von Xylazin sind die erarbeiteten Resultate relevant für humanmedizinische Fragestellungen in der Pulmologie. Dort sollte in der häufigen Verwendung des Schafes als Tiermodell in Hinblick auf mögliche Interaktionen mit den experimentellen Ergebnissen auf die Applikation von Xylazin verzichtet werden.

Computed tomography (CT) has become a standard in pulmonary imaging which allows the analysis of diseases like lung nodules, emphysema and embolism. The improved spatial and temporal resolution involves a dramatic increase in the amount of data that has to be stored and processed. This has motivated the development of computer aided diagnostics (CAD) systems that have released the physician from the tedious task of manually delineating the boundary of the structures of interest from such a large number of images, a pre-processing step known as image segmentation. Apart from being impractical, the manual segmentation is prone to high intra and inter observer subjectiveness. Automatic segmentation of the lungs with atelectasis poses a challenge because in CT images they have similar texture and gray level as the surrounding tissue. Consequently, the available graphical information is not sufficient to distinguish the boundary of the lung. The present work aims to close the existing gap left by the segmentation of atelectatic lungs in volume CT data. A-priori knowledge of anatomical information plays a key role in the achievement of this goal.

Background: Atelectasis can provoke pulmonary and non-pulmonary complications after general anaesthesia. Unfortunately, there is no instrument to estimate atelectasis and prompt changes of mechanical ventilation during general anaesthesia. Although arterial partial pressure of oxygen (PaO2) and intrapulmonary shunt have both been suggested to correlate with atelectasis, studies yielded inconsistent results. Therefore, we investigated these correlations. Methods: Shunt, PaO2 and atelectasis were measured in 11 sheep and 23 pigs with otherwise normal lungs. In pigs, contrasting measurements were available 12 hours after induction of acute respiratory distress syndrome (ARDS). Atelectasis was calculated by computed tomography relative to total lung mass (Mtotal). We logarithmically transformed PaO2 (lnPaO2) to linearize its relationships with shunt and atelectasis. Data are given as median (interquartile range). Results: Mtotal was 768 (715–884) g in sheep and 543 (503–583) g in pigs. Atelectasis was 26 (16–47)% in sheep and 18 (13–23) % in pigs. PaO2 (FiO2 = 1.0) was 242 (106–414) mmHg in sheep and 480 (437–514) mmHg in pigs. Shunt was 39 (29–51)% in sheep and 15 (11–20) % in pigs. Atelectasis correlated closely with lnPaO2 (R2 = 0.78) and shunt (R2 = 0.79) in sheep (P-values<0.0001). The correlation of atelectasis with lnPaO2 (R2 = 0.63) and shunt (R2 = 0.34) was weaker in pigs, but R2 increased to 0.71 for lnPaO2 and 0.72 for shunt 12 hours after induction of ARDS. In both, sheep and pigs, changes in atelectasis correlated strongly with corresponding changes in lnPaO2 and shunt. Discussion and Conclusion: In lung-healthy sheep, atelectasis correlates closely with lnPaO2 and shunt, when blood gases are measured during ventilation with pure oxygen. In lung-healthy pigs, these correlations were significantly weaker, likely because pigs have stronger hypoxic pulmonary vasoconstriction (HPV) than sheep and humans. Nevertheless, correlations improved also in pigs after blunting of HPV during ARDS. In humans, the observed relationships may aid in assessing anaesthesia-related atelectasis.

Computed tomography (CT) has become a standard in pulmonary imaging which allows the analysis of diseases like lung nodules, emphysema and embolism. The improved spatial and temporal resolution involves a dramatic increase in the amount of data that has to be stored and processed. This has motivated the development of computer aided diagnostics (CAD) systems that have released the physician from the tedious task of manually delineating the boundary of the structures of interest from such a large number of images, a pre-processing step known as image segmentation. Apart from being impractical, the manual segmentation is prone to high intra and inter observer subjectiveness. Automatic segmentation of the lungs with atelectasis poses a challenge because in CT images they have similar texture and gray level as the surrounding tissue. Consequently, the available graphical information is not sufficient to distinguish the boundary of the lung. The present work aims to close the existing gap left by the segmentation of atelectatic lungs in volume CT data. A-priori knowledge of anatomical information plays a key role in the achievement of this goal.

Quantitative computertomographische Studie zu den pulmonalen Auswirkungen intramuskulär applizierten Xylazins beim Schaf Einleitung. α2-Agonisten wie z.B. Xylazin werden in der veterinärmedizinischen Praxis häufig zur Se-dierung eingesetzt. Dabei ist für das Schaf eine besonders ausgeprägte Sensibilität gegenüber Xylazin nachgewiesen. Bisher nur unzureichend untersucht wurde der Einfluss der Applikationsform des α2-Agonisten Xylazin (intravenöse versus intramuskuläre Injektion) auf den Ausprägungsgrad der entste-henden Lungenveränderungen. Ziele der Untersuchungen. Ziel der vorliegenden Arbeit war es, die Xylazin-induzierten pulmonalen Reaktionen nach intramuskulärer Applikation zu quantifizieren und mit den Auswirkungen einer intrave-nösen Gabe beim Schaf zu vergleichen. Um wissenschaftlich konsequent zu arbeiten, wurde weiterhin die Wirkung der in Xylazin-Präparaten enthaltenen sonstigen Bestandteile untersucht. Material und Methode. Als Studientiere wurden sieben weibliche Schafe der Rasse Merinoland zwei-malig in einem Abstand von acht Wochen untersucht. Bei diesen Tieren handelte es sich um die Scha-fe, welche in einem vorausgegangenen Projekt zu den pulmonalen Wirkungen von intravenös appliziertem Xylazin in identischer Dosierung am deutlichsten reagiert hatten. Nach Prämedikation der Tiere mit Midazolam (0,25 mg/kg KM) und Sufentanil (0,6 µg/kg KM) wurde die Narkose mit Propofol aufrechterhalten (5-10 mg/kg KM/h). Nach abgeschlossener Instrumentierung wurden die Schafe in Rückenlage im Computertomographen positioniert und mit einer inspiratorischen Sauerstoffkonzentration von 100 Vol.-% beatmet. Zur Reduktion lagerungsbedingter Atelektasen wurde vor Versuchsbeginn ein Recruit¬ment¬ma¬nö¬ver (druckkontrollierte Beatmung, inspiratorischer Spitzendruck 60 cmH2O, PEEP 40 cmH2O, Atemfrequenz 10/min, Dauer zwei Minuten) durchgeführt. Nach abgeschlossenem Recruitmentmanöver wurden die Schafe bis zum Ende des Versuchsabschnittes volumenkontrolliert beatmet (Atemzugvolumen 8 ml/kg KM, PEEP 10 cmH2O, Adjustierung der Atemfrequenz, Ziel endexspiratorische Kohlendioxidkonzentration etwa 4,5 Vol.-%). Im Versuchsabschnitt „i.m.“ wurde Xylazin intramuskulär in einer Dosierung von 0,3 mg/kg KM injiziert. 10 Minuten vor sowie 5, 15, 30 und 60 Minuten nach der Xylazin-Injektion wurden computertomographische Untersuchungen des Thorax durchgeführt. Im Versuchsabschnitt „Vehikel“ wurde den Schafen eine dem verwendeten Xylazin-Präparat analoge, jedoch Xylazin-freie Lösung intravenös appliziert (enthält 1 mg/ml des Konservierungsstoffs Methyl-para-hydroxybenzoat). Als Dosis wurde eine der Xylazin-Gabe entsprechende Dosis von 0,015 ml/kg KM gewählt. Zusätzlich wurde 45 Minuten nach Versuchsbeginn Xylazin® 2 % in einer Dosis von 0,3 mg/kg KM intravenös injiziert. Die computertomographischen Untersuchungen wurden 10 Minuten vor sowie 5, 15, 30 Minuten nach erfolgter Injektion des Vehikel-Präparates und 5 Minuten nach erfolgter Injektion von Xylazin® durchgeführt. Unter Anwendung der Extrapolationsmethode wurden mit der quantitativen computertomographischen Analyse jeweils das totale Lungenvolumen (Vtot), das totale Lungengewicht (Mtot) und der Anteil der nicht belüfteten Lungenmasse (% Mnon) bestimmt. Dabei galt ein Abfall im totalen Lungenvolumen als Nachweis für Atelektasen, ein Anstieg im totalen Lungengewicht war gleichbedeutend mit der Entstehung eines Lungenödems. Als klinisch relevant galt eine Zunahme der totalen Lungenmasse um 100 g. In beiden Versuchsabschnitten wurden mittels arterieller Blutgasanalysen zusätzlich der arterielle Sauerstoff- und Kohlenstoffdioxidpartialdruck (PaO2, PaCO2) erfasst. Ergebnisse. Vor der intramuskulären Xylazin-Gabe wurden folgende Medianwerte ermittelt: Vtot: 4220 ml, Mtot: 1280 g, % Mnon: 3 %, PaO2: 443 mmHg, PaCO2: 48 mmHg. Nach intramuskulärer Xylazin-Injektion zeigten sich die nachfolgenden statistisch signifikanten Maximaländerungen: Vtot-Abfall: 516 ml (Interquartilbereich 408-607), Mtot bzw. % Mnon-Zunahme: 108 g (Interquartilbereich 70-140) bzw. 15 % (Interquartilbereich 8-24) PaO2-Abfall: 280 mmHg (Interquartilbereich 200-346), PaCO2-Anstieg: 17 mmHg (Interquartilbereich 7-27). Die intramuskuläre Gabe von Xylazin verursachte im Vergleich zur intravenösen tendenziell, aber statistisch nicht signifikant, geringere Abnahmen im totalen Lungenvolumen sowie eine tendenziell, aber statistisch nicht signifikant geringere Zunahme im Anteil der nicht belüfteten Lungenmasse. Des Weiteren konnte ein statistisch signifikant geringerer Abfall im arteriellen Sauerstoffpartialdruck bei intramuskulär erfolgter Injektion nachgewiesen werden. Die Xylazin-induzierte Hypoxämie erreichte unter Beatmung mit 100 Vol.-% Sauerstoff auch nach intramuskulärer Gabe des α2-Agonisten im Mittel einen moderaten Ausprägungsgrad, wobei 50 % der Studientiere sogar eine schwere Belüftungsstörung zeigten (PaO2 < 100 mmHg). Entsprechend dem Schweregrad der durch den α2-Agonisten induzierten Belüftungsstörung trat eine Hyperkapnie auch nach intramuskulärer Xylazin-Gabe auf. Auch die korrespondierenden % Mnon-Zunahmen erreichten bei intramuskulärer Xylazin-Injektion neben der statistischen Signifikanz erhebliche klinische Relevanz. So waren im Mittel 18 % (Interquartilbereich 10-28) des Lungengewebes nach intramuskulärer Gabe des α2-Ago¬nis¬ten nicht belüftet. Bei jeweils 50 % der Tiere konnte für beide Applikationsformen ein klinisch relevantes Lungenödem nachgewiesen werden. Eine Reaktion der Versuchstiere auf die sonstigen im Xylazin-Präparat enthaltenen Bestandteile konnte ausgeschlossen werden. So konnte für keinen der untersuchten Parameter eine statistisch signifikante Änderung nach Injektion der Vehikel-Lösung nachgewiesen werden. Statistisch signifikante Zu- bzw. Abnahmen in den untersuchten Parametern konnten eindeutig der Wirkung des α2-Agonisten Xylazin zugewiesen werden. Schlussfolgerungen. Trotz quantitativ geringerer Ausprägung in den detektierten Änderungen von Vtot, PaO2 und % Mnon zeigten die Xylazin-induzierten pulmonalen Reaktionen bei der Mehrzahl der Studientiere auch nach intramuskulär erfolgter Applikation des α2-Agonisten erhebliche klinische Relevanz. Ein zeitlich verzögertes Eintreten im Vergleich zur intravenösen Gabe des α2-Agonisten konnte nur für die Formation des Xylazin-induzierten Lungenödems festgestellt werden. Analog zu den Ergebnissen des vorausgegangenen Projektes zur Wirkung von intravenös verabreichtem Xylazin, kann das morphologische Bild der Xylazin-induzierten Lungenveränderungen durch eine Koexistenz von Atelektasen und Lungenödem beschrieben werden. Derzeit konnte noch kein logisches Muster gefunden werden, dass die interindividuelle Variabilität in der Reaktion auf Xylazin beim Schaf aufzuklären vermag. Ebenso ist der Erkenntnisstand bezüglich einer möglicherweise vorhandenen Rasseabhängigkeit bis dato nicht ausreichend, um im Vorfeld die Sensibilität gegenüber Xylazin bei einem Schaf abschätzen zu können. Demzufolge muss beim Schaf auf der Grundlage der vorliegenden Ergebnisse im Einzelfall auch nach einer intramuskulären Xylazin-Gabe mit einer Dosierung von 0,3 mg/kg KM von schwerwiegenden Lungenveränderungen ausgegangen werden. Sofern Schafe als Tier-Modell in der experimentellen Lungenforschung verwendet werden, sollte aufgrund der Gefahr von fehlerhaften Forschungsergebnissen sowohl auf den intramuskulären Einsatz von Xylazin zur Prämedikation verzichtet werden als auch auf die intravenöse Verabreichung des α2-Agonisten als Narkosebestandteil. Um in der Praxis zukünftig unnötiges Leiden oder gar Versterben von Tieren verhindern zu können, muss die Problematik der Xylazin-induzierten Lungenveränderungen beim Schaf weiter verfolgt und näher erforscht werden.

Introdução: A individualização da pressão positiva ao final da expiração (PEEP) pode reduzir a pressão de distensão e a formação de atelectasias em pacientes sendo submetidos a cirurgia abdominal eletiva. Objetivos: Titular a PEEP e comparar a mecânica respiratória de pacientes ventilados com PEEP titulada a pacientes ventilados com PEEP de 4 cmH2O. Após a extubação, comparar a formação de atelectasias. Métodos: Pacientes submetidos à cirurgia laparoscópica ou cirurgia aberta foram incluídos de forma não consecutiva, estratificada e randomizados em dois braços: PEEP titulada (PEEPT) e PEEP de 4 cmH2O (PEEP4). A PEEP foi titulada com tomógrafo de impedância elétrica (TIE). Dados de mecânica e três gasometrias foram coletadas durante o intraoperatório. Após extubação, os pacientes realizaram a uma tomografia computadorizada de tórax. Resultados: Vinte pacientes submetidos à cirurgia laparoscópica e vinte pacientes submetidos à cirurgia aberta foram incluídos. A mediana de PEEP titulada foi 12 cmH2O (10-14), com uma ampla variação de 6-16 (IC 95% 10-14). O uso da PEEP titulada determinou uma redução da pressão de distensão (p < 0,001), melhora da complacência (p < 0,001), melhora a oxigenação (p < 0,001) apenas dos pacientes de cirurgia laparoscópica e redução da massa de tecido pulmonar não-aerada após a extubação (P < 0,05). Conclusão: A PEEP individualizada apresentou ampla distribuição. A individualização da PEEP reduziu a quantidade de atelectasia após a extubação e, também, melhorou a mecânica respiratória e a oxigenação / Rationale: Individualized PEEP may reduce driving pressure and the formation of atelectasis in patients undergoing elective abdominal surgery. Objectives: To titrate PEEP and compare respiratory mechanics of patients submitted to titrated PEEP to PEEP 4 cmH2O. After extubation, to compare the non-aerated lung mass. Methods: Patients undergoing laparoscopic or open abdominal surgery were stratified and randomized non-consecutively to titrated PEEP (PEEPT) and PEEP 4 cmH2O. PEEP was titrated using electrical impedance tomography. Respiratory mechanics arterial blood gas analysis were performed during surgery. After extubation, the patients were submitted to a chest computadorized tomography (CT) scan. Measurements and Main Results: Twenty patients undergoing laparoscopic surgery and twenty patients undergoing open abdominal surgery were included. The median PEEP was 12 cmH2O with a wide variation from 6 to 16 (IC 95% 10-14). Titrated PEEP reduced driving pressure (p < 0.001), improved respiratory system compliance (p < 0.001), improved oxygenation (p < 0.001) (only in patients being submitted to laparoscopic surgery) and reduced non-aerated lung mass on CT scan (p < 0.05) after extubation. Conclusions: Titrated PEEP had a wide variation. PEEP individualization reduced postoperative atelectasis and also improved respiratory mechanics and oxygenation

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

Introdução: As estratégias ventilatórias protetoras têm contribuído para a redução da letalidade da Síndrome do Desconforto Respiratório Agudo (SDRA), mas ainda está em debate qual, entre as diversas existentes, é a mais eficaz. A estratégia ARDSNet, muito utilizada na prática clínica, prioriza a redução do volume corrente para minimizar a hiperdistensão. As estratégias Open Lung Approach (OLA), além de procurarem reduzir a hiperdistensão, buscam minimizar o colapso pulmonar para evitar a atelectasia cíclica. Os métodos para ajuste da PEEP ideal nas estratégias OLA apresentam imperfeições: difícil implementação, não permitem avaliação regional do pulmão ou não podem ser realizados a beira leito. Uma estratégia OLA guiada por Tomografia de Impedância Elétrica (TIE) que permite a avaliação regional pulmonar de modo contínuo e a beira leito pode trazer benefícios. Objetivo: Comparar os efeitos fisiológicos (imagem, mecânica e trocas gasosas) ao longo de 42 h entre duas estratégias ventilatórias protetoras em um modelo suíno de SDRA (estratégia ARDSNET X estratégia guiada por TIE: (PEEPTIE). Comparar a mecânica pulmonar e troca gasosa nas duas estratégias ao final das 42 h de ventilação, em uma mesma condição de ventilação, para avaliar efeitos duradouros das estratégias sobre o parênquima pulmonar. Métodos: Sete porcos foram submetidos a ventilação mecânica por 42 horas em cada uma das duas estratégias. A lesão pulmonary foi induzida com lavagem de solução fisiológica associada a ventilação lesiva. No grupo PEEPTIE, a PEEP foi ajustada pela TIE após manobra de recrutamento, mantendo o pulmão com o mínimo de colapso menor que 5%), enquanto que na estratégia ARDSNet era ajustada através da tabela PEEPxFiO2. O volume corrente foi mantido entre 4-6ml/Kg em ambas estratégias, com a pressão de platô menor que 30 cmH2O. Resultados: Oxigenação e mecânica pulmonary eram semelhantes em ambos os grupos após a lesão pulmonar. Durante as 42h de protocolo, a troca gasosa foi significativamente maior no grupo PEEPTIE quando comparado ao grupo ARDSNet tanto no início (p< 0.01) quanto ao final do protocolo(p< 0.01). A PEEP inicial não foi diferente nas duas estratégias (p= 0.14), mas foi significantemente maior no grupo PEEPTIE (p< 0.01) em grande parte do período de 42 h e também ao final. Não houve diferença na pressão de platô entre os grupos (p=0.05). O delta de pressão foi significativamente maior no grupo ARDSNet no começo (p= 0.03) e ao final do protocolo (p= 0.00). Atelectasia cíclica (p < 0.01) e a porcentagem de tecido não-aerado (p= 0.029) foram significativamente maiores no grupo ARDSNet. Ao final do protocolo, nos mesmos ajuste de ventilação, a complacência pulmonar global (p=0.021) e regional (p= 0.002) foram significativamente maiores no grupo PEEPTIE, bem como a troca gasosa (p= 0.048). Conclusões: a estratégia PEEPTIE, quando comparada a estratégia ARDSNet determinou melhor oxigenação, menor grau de colapso e de atelectasia cíclica, além de melhor mecânica pulmonar, tanto global, quanto regional. Esta melhora foi mantida ao final das 42 horas, quando os dois grupos eram ventilados com os mesmos ajustes, sugerindo que a estratégia PEEPTIE determinou menor dano pulmonar / Introduction: Protective ventilatory strategies have contributed for the reduction in Acute Respiratory Distress Syndrome (ARDS) mortality, but so far there is still debate which strategy is more effective. The ARDSNet strategy, used widely in the clinical practice, emphasizes in tidal volume reduction to minimize hiperdistension. The Open Lung Approach (OLA), besides the reduction of hiperdistension, emphasizes reduction of lung collapse to avoid tidal recruitment. The methods to adjust ideal PEEP in the OLA strategies have some imperfections: difficult implementation, do not allow regional lung evaluation or cant be performed at the bedside. The OLA strategy guided by Electrical Impedance Tomography (EIT) which allows a continuous and regional lung evaluation can bring benefits. Objective: Compare physiological effects (image, mechanics and gas exchange) during a period of 42 hours between two protective ventilatory strategies in an ARDS suine model (ARDSNet strategy x strategy guided by EIT PEEPTIE). Compare lung mechanics and gas exchange in both strategies at the end of 42 hours of ventilation, in the same ventilation condition, to evaluate the strategies longtime effects on lung parenchyma. Methods: Seven suines were submitted to mechanical ventilation for 42 hours in each ventilator strategy. Lung injury was induced by saline lavage associated to injurious mechanical ventilation. In the PEEPTIE arm, PEEP was selected by the electrical impedance tomography after a recruitment maneuver, trying to keep lung collapse at minimum, while the ARDSnet group followed a PEEPxFiO2 table. Tidal volume of 4-6ml/kg was maintained in both strategies, with a plateau pressure not higher than 30 cmH2O. Results: Oxygenation and lung mechanics were equally impaired in both arms after injury. During the 42 hours of protocol, gas exchange was significantly higher in the PEEPTIE arm as compared to the ARDSNet arm in the beginning (p< 0.01) and at the end of the protocol (p< 0.01). PEEP at the beginning of the protocol was similar between groups (p= 0.14), but at most part of the protocol and at the end, PEEP was significantly higher in the PEEPTIE arm (p< 0.01).There were no difference in plateau pressure (p=0.06). Driving pressure was significantly higher in the ARDSNet arm at the beginning (p= 0.03) and at the end (p= 0.00). Tidal recruitment was significantly higher in the ARDSNet arm (p < 0.01), and a higher percentage of non-aerated lung tissue (p= 0.029). At the end of the protocol, global lung compliance was significantly higher in the PEEPTIE arm (p=0.021), as for regional lung compliance (p= 0.002) and gas exchange (p= 0.048). Conclusion: The PEEPTIE strategy when compared to the ARDSNet strategy determined better gas exchange, lower percentage of collapse and tidal recruitment, besides better lung mechanics (global and regional). This improvement was maintained at the end of the 42 hours, when both groups were ventilated with the same parameters, suggesting that the PEEPTIE strategy determined less lung injury

Introdução: A Abertura e fechamento alveolar a cada ciclo respiratório (TR) é mecanismo de lesão pulmonar associada à ventilação mecânica. É frequente, especialmente em pacientes com lesão pulmonar aguda/ sindrome do desconforto respiratório agudo, mas pode ocorrer em pulmões normais, devido à pressão expiratória final positiva (PEEP) insuficiente. A fração inspirada de oxigênio (FiO2) também pode ter um papel na modulação da lesão pulmonar: frações mais baixas, em situação de relação ventilação perfusão (V/Q) crítica, podem retardar o colapso alveolar. A Tomografia de Impedância Elétrica (TIE) é uma nova ferramenta de imagem não invasiva, à beira do leito, que reconstrói imagens transversas da resistividade dos tecidos torácicos, obtidas a partir de uma corrente elétrica injetada por eletrodos colocados circunferencialmente no tórax. Atualmente, o padrão ouro de detecção de TR é a tomografia computadorizada (TC), que utiliza radiação, transporte de pacientes para sua execução, exigindo manobras que podem ocasionar a instabilização dos pacientes. Hipótese deste estudo: é possível detectar e quantificar a ocorrência de TR com TIE. Métodos: 7 suinos traqueostomizados, sob sedação, bloqueio neuromuscular e ventilação mecânica, foram submetidos a manobra de recrutamento alveolar (MRA) em pressão controlada, com pressão platô=50 cmH2O, PEEP=35 cmH2O, aplicada por 2 minutos. Seguiu-se ventilação com volume controlado, posição supina, volume corrente (VT) = 10 ml/kg, fluxo 10l/min FR=10irpm, FiO2=100% e PEEP decremental (20-10-3cmH2O), em passos de 10 minutos. Ao final de cada passo, os animais foram submetidos a uma pressão positiva contínua sobre as vias aéreas em dois níveis, quando se procedeu à TC: pressão de platô (representando inspiração) e PEEP (expiração). Imagens de TIE foram adquiridas continuamente. Os animais foram submetidos à nova MRA, repetindo-se o protocolo em FiO2=40%. Após lesão pulmonar (lavagem pulmonar com SF 0,9% até atingir SpO2< 95%), os passos acima foram repetidos. Para detecção de TR pela TIE, dois métodos foram testados, um método original proposto por este estudo, baseado nas variações de complacência regional (pixel a pixel) ao longo do volume corrente (Método1) e um método descrito em estudo recente por Putensen et al. (Método2). Ambos foram comparados à TC. Resultados: Ocorreu colapso progressivo durante PEEP decremental, sempre maior na FiO2=100% (versus 40%) e após lesão (versus pré-lesão) para as PEEPs correspondentes. A análise de regressão linear, Métodos 1 e 2 para TR em relação à TC evidenciou; Método 1 - R²=0,578 e Método 2 - R²=0,409. As correlações foram melhores quando se considerou apenas as medidas a 100%: R²=0,756 (Método 1) e R2=0,646 (Método 2). Curva ROC; Método 1- área sob a curva: 0,86 e Método2 - 0,79. Regressão logística; Método1 superior ao Método2. Pela ANOVA avaliamos PEEP, lesão, FiO2 e P.Platô na detecção de TR pela TC e Método1..A principal difrerença foi não haver influência da FiO2 sobre TR, Método1 Conclusão: O Método 1 foi superior ao Método2 na detecção de TR, com sensibilidade e especificidade suficiente para se avaliar a utilização clínica. A detecção de TR pelo Método1, não foi influenciada pela FiO2, ao contrário da TC. Estes achados foram compatíveis com os resultados de mecânica pulmonar ( pressão de platô). Portanto, o Método1 foi mais sensível que a TC, pois foi capaz de detectar TR mesmo em situações de ventilação pouco acima do V/Q crítico nas situações de FiO2 de 40%, ao contrário da TC. A TIE não sofreu alterações como o efeito de volume parcial como a TC / Introduction: Cyclic opening and closure of alveolar units during the respiratory cycle, or tidal recruitment (TR), is a harmful mechanism of ventilation induced lung injury. It is frequent, especially in acute lung injury and acute respiratory distress syndrome patients, but can occur in normal lungs under mechanical ventilation, because of an insufficient PEEP. Oxygen concentration (FiO2) can modulate collapse and low FiO2 can delay it. Electrical Impedance tomography (EIT) is a noninvasive imaging tool that reconstructs a cross-sectional image of lungs regional resistivity using electrodes placed around the thorax. EIT is a useful imaging tool for regional ventilation monitoring, as proved by many studies. We hypothesized that is possible to detect and quantify the occurrence of TR by EIT. Seven pigs tracheostomized, sedated and using neuromuscular blockade were submitted to mechanical ventilation. A recruitment maneuver (RM) using plateau pressure = 50cmH2O and positive end expiratory pressure (PEEP) = 35cmH2O for 2 minutes was applied. After, animals were ventilated in volume controlled ventilation mode (VCV), with a tidal volume (Vt) =10ml/kg, inspiratory flow=10l/min, respiratory frequency=10irpm, FiO2=100%. Decremental PEEP (20-10-3cmH2O) steps were applied with 10 minutes intervals between them. Thoracic computed tomography (CT) images were done with a continuous positive airway pressure (CPAP) = Plateau pressure achieved in VCV and PEEP applied, simulating an inspiration and expiration respectively. EIT was acquired continuously during the protocol. RM was repeated and then protocol was repeated, using FiO2=40%. Lung injury was induced (with lung lavage - SF 0.9% until SpO2< 95%). After protocol was repeated including both FiO2. Two TR detectors were tested; an original imaging tool created by our group (Method 1) and a second imaging tool created in a recent study by Putensen. (Method 2). Both methods were compared to CT. Results: A progressive alveolar collapse during decremental PEEP was observed, always greater with FiO2=100% (versus FiO2=40%) and after lung injury (versus before lung injury). Linear regression analysis for Methods 1 and 2 showed for Method1 R2=0.578 and Method 2 R2=0,409. Correlations were better when FiO2=100% was considered individually; Method1 - R²=0,756 and Method2 - R²=0,646. ROC curve presented an area under the curve better for Method1 (0,86) related to Method2 (0,79). Logistic regression also showed better result for Method1. ANOVA was used to test influence of variables as PEEP, lung lesion, FiO2 and Plateau pressure on tidal recruitment. Method1 and CT were tested. The main difference between them was that Method 1 was not influenced by FiO2. Conclusion: Method 1 was superior than 2 for TR detection with sufficient specificity and sensibility for a trial on clinical application. Tidal recruitment detection by Method1 was not influenced by FiO2, but it was for CT, what was supported by results of lung mechanic (plateau pressure). Under lower FiO2 (40%) occurred an underestimation of TR by CT, once the change in ventilation occurs even in lower FiO2 which is not detected by CT. CT is also influenced by partial volume effect, what didn´t occurred with EIT

by Ivor Wong (Nga Chung). / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 114-120). / Abstract also in Chinese. / Chapter PART I --- INTRODUCTION / Chapter 1. --- CHAPTER 1 BACKGROUND --- p.2 / Chapter 1.1 --- Objectives --- p.3 / Chapter 1.2 --- Effects of chest physiotherapy --- p.3 / Chapter 1.2.1 --- Aims of chest physiotherapy --- p.4 / Chapter 1.2.1.1 --- Mucus Removal --- p.4 / Chapter 1.2.1.2 --- Re-expansion of atelectatic lung --- p.9 / Chapter 1.2.2 --- Chest physiotherapy for neonates --- p.10 / Chapter 1.2.2.1 --- Pulmonary characteristics in neonates --- p.10 / Chapter 1.2.3 --- Chest physiotherapy for infants on mcchanical ventilation --- p.12 / Chapter 1.2.3.1 --- Conventional ventilation --- p.12 / Chapter 1.2.3.2 --- High frequency ventilation --- p.13 / Chapter 2. --- CHAPTER 2 NEONATAL CHEST PHYSIOTHERAPY --- p.15 / Chapter 2.1 --- Traditional physiotherapy means --- p.15 / Chapter 2.1.1 --- Percussion and Chest vibration --- p.15 / Chapter 2.1.2 --- Cup percussion (Cupping) --- p.16 / Chapter 2.1.3 --- Postural drainage (PD) --- p.16 / Chapter 2.1.4 --- Endotracheal Suctioning --- p.17 / Chapter 2.1.4.1 --- Adverse effects of endotracheal suctioning --- p.17 / Chapter 2.2 --- Possible Complications of chest physiotherapy --- p.20 / Chapter 2.2.1 --- Haemodynamic disturbances --- p.20 / Chapter 2.2.2 --- Fluctuation of Cerebral Perfusion --- p.21 / Chapter 2.2.3 --- Cystic brain lesions --- p.22 / Chapter 2.3 --- Modified manual techniques --- p.23 / Chapter 2.3.1 --- Theoretical model of lung squeezing technique --- p.23 / Chapter 2.3.2 --- Lung squeezing technique as a volume recruitment manoeuvre --- p.30 / Chapter 2.3.2.1 --- Squeezing phase of lung squeezing technique --- p.30 / Chapter 2.3.2.2 --- Release phase of lung squeezing technique --- p.31 / Chapter 3. --- CHAPTER 3 PHYSIOTHERAPY PRACTICE IN LOCAL NEONATAL ICU --- p.33 / Chapter 3.1 --- Current physiotherapy practice in Hong Kong Neonatal ICU settings --- p.33 / Chapter 3.1.1 --- Endotracheal suctioning protocol in Prince of Wales Hospital --- p.33 / Chapter 3.1.1.1 --- Suctioning Procedures --- p.34 / PART II MAIN STUDY / Chapter 4. --- CHAPTER 4 RESEARCH DESIGN --- p.37 / Chapter 4.1 --- Ethics --- p.37 / Chapter 4.2 --- Methods --- p.37 / Chapter 4.2.1 --- Pilot study --- p.37 / Chapter 4.2.2 --- Main study --- p.39 / Chapter 4.2.2.1 --- Hypothesis --- p.39 / Chapter 4.2.2.2 --- Study Design --- p.39 / Chapter 4.3 --- Methodology --- p.44 / Chapter 4.3.1 --- Treatment protocol --- p.44 / Chapter 4.3.1.1 --- Experimental Group protocol --- p.44 / Chapter 4.3.1.2 --- Control Group protocol --- p.44 / Chapter 4.3.2 --- Outcome Measure --- p.45 / Chapter 4.3.2.1 --- Chest X-ray --- p.45 / Chapter 4.3.2.2 --- Other Measurements --- p.45 / Chapter 4.3.3 --- Statistics --- p.48 / Chapter 5. --- CHAPTER 5 RESULTS --- p.50 / Chapter 5.2 --- Demographic Data --- p.50 / Chapter 5.3 --- Resolution of lung atelectasis --- p.56 / Chapter 5.3.1 --- Distribution of lung atelectasis --- p.56 / Chapter 5.3.2 --- First re-expansion of lung atelectasis --- p.59 / Chapter 5.3.3 --- Complete resolution of lung atelectasis --- p.62 / Chapter 5.3.3.1 --- Sites of rccurrencc of lung atelectasis --- p.65 / Chapter 5.4 --- Factors correlated with number of treatment sessions required to attain resolution of atelectasis --- p.68 / Chapter 5.5 --- Ventilator parameters changes --- p.73 / Chapter 5.6 --- Haemodynamic changes --- p.75 / Chapter 5.7 --- Arterial blood gas --- p.78 / Chapter 5.8 --- Other clinical outcome --- p.80 / Chapter 5.8.1 --- Bronchopulmonary dysplasia --- p.80 / Chapter 5.8.2 --- Intra-ventricular haemorrhage (IVH) --- p.82 / Chapter 5.8.3 --- Mortality rate --- p.86 / Chapter PART III --- EFFECTS OF LUNG SQUEEZING TECHNIQUE ON LUNG MECHANICS / Chapter 6. --- CHAPTER 6 LUNG MECHANICS STUDY FOR NEONATES --- p.88 / Chapter 6.1 --- Methods --- p.91 / Chapter 6.1.1 --- Statistical Analysis --- p.93 / Chapter 6.2 --- Results --- p.94 / Chapter PART IV --- DISCUSSION AND CONCLUSION / Chapter 7. --- CHAPTER 7 SUMMARY AND CONCLUSION --- p.105 / Chapter PART V --- REFERENCE / Chapter 8. --- BIBLIOGRAPHY --- p.114 / Chapter PART VI --- GLOSSARY / Chapter PART VII --- APPENDICES