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Examine This Report on impedanztomographie

Non-invasive monitoring of maximalflow of expiratory and inspiratory(MIF and MEFrespectively)via electrical impedance tmography(EIT)may allow foran early detection of changes toour respiratory tract’s propertiesin responsetonew circumstances or inresponse totreatments.Our goal was to testEIT-basedmeasurementsforMIFas well asMEF against spirometryof intubatedhypoxemic patients during controlled ventilationand spontaneous breathing.Additionally, the regional distribution ofmaximum airflows may interact withlungdiseases and increasetherisk of further ventilatorinjuries.This is why we wantedtostudy the impactofmechanical ventilation settings onregionalMIFas well asMEF.

Methods

We performed a new studyofdatathat came from two prospectively randomized,crossoverstudies.We included patients who wereadmitted to theintensive care unit suffering fromacute hypoxemic respiratory failure(AHRF)or acute respiratory distress(ARDS)with pressure supportbreathing(PSV, n=10) andVCV, n=20).(VCV, n20).We assessed MIF and MIFthrough spirometry and EIT insix different combinations of ventilation settings withhigherthan. lower supportinPSV and greaterrelative to. lowerpressure of positive end-expiratory(PEEP)throughoutbothVCV and PSV.Regional airflows were assessed byEITin non-dependent and dependentlung regionsas well.

Results

MIF and impedanztomographie determinedbyEIT wereclosely correlated tothe results of spirometry inthe entire range of conditions(rangeofR2 0.629-0.776 and R2 0.606-0.772respectively, p<0.05acrossall) in accordance with the clinically acceptableboundaries of disagreement.A higher PEEP was able to improvehomogeneity in the regionalareaof MIF and MEFwhen ventilated with volume control,through increasing airflows independent lung regions and loweringthem in non-dependent areas.

Conclusions

EITis a precise, noninvasive way to monitor the healthofMIFandMEF.The current study also supportstheideathat EITcould guidePSV and PEEPsettings aimedto increase the homogeneity and consistency ofstretching and deflating regional airflows.

Introduction

The electrical impedance imaging(EIT)can be described asanon-invasive bedside, radiation-freeactive lung imaging technique. EITcan provide maps of intrathoracicthe changes in lung impedance that are measured againstthe baseline(i.e.,the volume of the lungs at the end of expiration frompreviousbreath) every20-50 ms [11.Changes in intrathoracic impedance as measuredviaEIT are linearlyassociated withregional and global tidal volume, and the correlation ismaintained at increasing positive end-expiratorypressure (PEEP) levels [22.Thus,EITgives a noninvasive bedside continuousmeasurement oflung volumefluctuations duringinspiratory and expiration.

Inspiratory and expiratory airflows relateto thespeed oflung volume changeintime.In intubated patients,they arenormally measured withan spirometer that is connectedin the ventilator’s circuit, prior totheendotracheal tube , or insidethe ventilator.Global maximum inspiratory andexpiratoryflows(MIF and MEF as well)recorded bystandard spirometry rely onthe mechanical properties of the respiratory system(namely lung compliance, lung volume andresistance to airways) [3The latter is a function of lung compliance and airway resistance.Therefore, monitoring ofMIF andMEF canaid in guiding thebreathing settings(e.g. by choosingthepressure level positive associatedwithbettermechanics)and/or to measuretheeffectiveness of pharmacologic treatments(e.g. increasingMIFand/or MEF afterbronchodilator medication) [44.However, spirometry only yieldsgeneral measurements of MIF as well asMEF, and heterogeneous distributionofaffected lung mechanics is thehallmark of acute hypoxemic respiratoryfailing(AHRF)or acute respiratory distress(ARDS) [5It is also a sign of ARDS.In the event of an alveolar injury, it can lead to thecollapse of lung unitsthat are bordered by normal-, partial-and over-inflated units and can causedifferenceswithin regionalMIFas well asMEF values.These imbalances can raisethechance of developing a ventilator-induced lung disease(VILI)through various mechanisms[6, 7], whileobtaining more homogenous regional flowscan reduce it. Externalspirometry can leadtoaltered respiratory patterns as well asinaccurate measures,as well[77.Thus, a noninvasivebedsidedynamic method to determineglobal and regional MIF values as well asMEFlevels wouldbe an important addition tostudyingAHRF and ARDSsufferers’ pathophysiology, andto provide personalized treatment.

In this study,with the help of preliminary data obtained from anthe animal model of[8], we set outtotest the validity ofpatients who are intubatedAHRFandARDS patientsreceivingcontrolledventilation andEIT-based measurements of spontaneous breathing ofglobal MIF and MEF compared tostandardspirometry.We also investigatedtheeffects of higher vs. lowerthe levels of pressure support onregionalflows.Our hypothesis wasthat higherlevels of PEEPand lower pressure support couldproduce a more homogenous distribution oflocalMIFandMEF.

Materials and methods

StudyPopulation

We performed a new analysis of data collected during two prospective randomized crossover studies: in the first (pressure support ventilation (PSV) study) [9], ten intubated patients recovering from ARDS [10], lightly sedated (RASS – 2/0), undergoing PSV and admitted to the intensive care unit (ICU) of the university-affiliated San Gerardo Hospital, Monza, Italy, were enrolled; and in the second (volume-controlled ventilation (VCV) study) [11], twenty intubated, deeply sedated and paralyzed patients with AHRF (i.e., PaO2/FiO2 <=300, PEEP >=5 cmH2O, acute onset, no cardiac failure) or ARDS admitted to the same ICU were enrolled. Theethics committee atSan Gerardo Hospital, Monza, Italy, approved thestudyin accordance with the informed consent givenfollowinglocalguidelines.Additional details ontheinclusion and exclusion criteriaforthe twostudies are containedinthe online data supplement(Additionalfile1).

Demographic data collection

Wecollected sex, age, Simplified Acute Physiology Score IIscores, etiology, diagnosis andseverityof ARDS days undermechanical ventilationprior study enrollmentforeverypatient.In-hospital mortality was recorded,as well.

EIT andventilation monitoring

Inall patients, an EIT-specificbelt,containing 16 equallyspaced electrodes, was positionedaround the thorax atthesixth or fifthintercostalspace and connected toan industrialEIT monitor (PulmoVista 500, Drager Medical GmbH, Lubeck, Germany).All study phases includedEITdata were recorded byuse of small alternationelectrical currents rotating aroundpatients thorax. These were recorded continuouslyat 20 Hz. The data were then savedfor offline analysis, just asdescribed in [1212.Synchronized toEITtracer data or airway pressures andthe flow of air fromthe mechanical ventilator werecontinuously recorded.

Interventions

Additional information onthe two protocolscan be foundin thedata supplement online(Additionaldocument1.).

In brief, duringThePSV study,participants underwentthe followingrandomized steps which lasted each for 20 minutes:

  1. 1.

    The support level at PEEP for clinical patients is low(PSV low)vs.greater support atPEEP in the clinical setting(PSV high);

  2. 2.

    Clinical supportatvery low levels of pressure(PSV-PEEP low)in contrast to.clinical support at higher PEEP(PSV-PEEP high).

For theVCV study,,the following phaseswere executedwith randomized crossoverseach lasting20 min:

  1. 1.

    Secure VCV during low PEEP(VCV-PEEP low)as compared to.protective VCV at clinicalPEEP+ 5cmH 2O (VCV-PEEP high).

EIT andventilation data

Based on offline analysis ofEITtraced duringthefinal minutesduring each stage(analysis of10breaths) we determined thelocal and global(same-sizedependent and non-dependent lung regions) noninvasive airflows’ waveforms,similar to what was previously described[8].Briefly, instantaneous global andregionalinspiratory and expiratoryairflowsare measured asvariationsin regional and globalimpedance , measured every 50 milliseconds and multiplied by theintensity ratio forthesame study period anddivided by 50ms. EIT airflow data werechanged from mL/msec toL/min (Fig. 1) and the maximalEIT-derived regional and global MIFand MEF (MIFglob MIFglob, MIFnon-dep,and MIFdepMEFglob, MEFnon-dep , andMEFdep according to) wereidentified , and thevalue averaged over5-10breathingcycles.

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