5 Simple Statements About impedanztomographie Explained

Noninvasive monitoring of maximalexpiratory and inspiratory flows(MIF and MEFrespectively)by electrical impedance tomography(EIT)may allow forearlier detection of changes inbreathing system mechanical characteristicsin responsetothe new condition orresponse totreatment.The aim of this study was to verifyEIT-basedmeasuresforMIFas well asMEF against spirometryof intubatedhypoxemic patients under controlled ventilationand breathing spontaneously.Furthermore, the distribution of regionalmaximal airflows may be influenced bylungdisease and increasethepossibility of further ventilationinjuries.Therefore, we also soughttodescribe the effectsofdifferent settings for mechanical ventilation onthe regional distribution ofMIFas well asMEF.


We conducted a fresh analysisofthe dataof two randomised, prospectivecross-sectionalstudies.We included intubated patientsadmitted to theunit for intensive care withchronic hypoxemic respiratory dysfunction(AHRF)in addition to acute respiratory distress syndrome(ARDS)with pressure supportbreathing(PSV, n10) andthe volume-controlled ventilation(VCV, n=20).We assessed MIF and MIFvia spirometry as well as EIT oversix different combinations of ventilation settings that werehigherthan. lower supportduringPSV, and highersupport vs. lowerpositive end-expiratory pressure(PEEP)forbothVCV and PSV.Regional airflows were determined byEITin non-dependent and dependentlung regions.


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), with clinically acceptablelimits of agreement.A higher PEEP was able to improvehomogeneity and consistency in thelocationof MIF and MEFduring volume-controlled ventilation,through increasing airflows inareas of the lung that are dependent and decreasingtheir levels in the non-dependent lung regions.


EITgives accurate, non-invasive measurementforMIFas well asMEF.This study also suggeststhehypothesisthat EITcould help guidePSV and PEEPparametersto increase homogeneity ofstretching and deflating regional airflows.


EI tomography(EIT)can be described asanon-invasive, bedside, radiation-free,technology for lung imaging that is dynamic. EITgives intrathoracic maps oflung impedance fluctuations that are referenced toa baseline(i.e.the end-expiratory lung volume frompreviousbreath) every20 to 50 milliseconds1.Changes in intrathoracic impedance as measuredwithEIT are linearlyrelated tothe volume of the tidal system in both regions and this correlation issustained at higher positive end-expiratorypressure (PEEP) levels [22.Thus,EIToffers a noninvasive continuous bedsidemeasure of regionallung volumechanges betweenthe process of inspiration and expiration.

The inspiratory and expiratory flow of air correspondsto thevelocity at whichlung volume changeovertime.In patients with intubation,they aretypically measured byan spirometer connectedto the ventilator’s circuit prior totheendotracheal tube , or insidethe ventilator.Global maximum inspiratory as well asexpiratoryflow(MIF and MEF as well)that are measured usingstandard spirometry are influenced byphysical properties in the respiratory system(namely lung compliance, lung pressure andresistance of the airway) [3The latter is a function of lung compliance and airway resistance.Therefore, monitoring ofMIF andthe MEF canhelp to determineventilatory settings(e.g., by selectingthepressure level positive associatedwithbettermechanics)or to assesstheefficacy of pharmacologic treatments(e.g. higherMIFand/or MEF afteran bronchodilator drug) [4(e.g., increased MIF and/or MEF after bronchod.However, spirometry only yieldsgeneral measurements of MIF as well asMEF, and heterogeneous distributionofaffected lung mechanics is thecharacteristic of acute hypoxemicdysfunction(AHRF)as well as acute respiratory distress syndrome(ARDS) [55.Alveolar damage leads tocollapse of lung unitsbordering normal-, partial- and over-inflated units, potentially yieldingvariationsof regionalMIFandMEF values.Such imbalances can increasetherisk of ventilator-induced lung injury(VILI)via a myriad of mechanisms[6], while settingto achieve more homogeneous regional flowscould decrease the risk. Externalspirometry could leadtoaltered patterns in the respiratory system andinaccurate measures,too[77.Therefore, a non-invasivebedsidedynamic technique to measureglobal and regional MIF andMEFvalues couldmake a great contribution tolearning aboutAHRF and ARDSsufferers’ pathophysiology, andto aid in the development of personalized treatment.

In the present studyfollowing preliminary findings from anthe animal model[8], we set outtotest the validity ofventilatedAHRFandARDS patientsundergoingcontrolledventilation andspontaneous breathing EIT-based measures ofglobal MIF and MEF compared tothe standardspirometry.We also investigatedtheeffects of higher. lowerthe levels of pressure support onregionalflows.Our hypothesis wasthat higherlevels of PEEPas well as lower pressure support wouldgive a more homogenous distributionregionalMIFas well asMEF.

Materials and methods


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 thestudywhile informed consent was soughtfollowinglocalguidelines.Additional details onthecriteria for inclusion and exclusionforbothstudies are providedinthe online data supplement(Additionalfile1.).

Demographic data collection

Werecorded sex, age, Simplified Acute Physiology Score IIscores, etiology, diagnosis andthe severityof ARDS days onmechanical ventilationprior to study enrollmentforeachpatient.The mortality rate in hospital was also recordedas well.

EIT andmonitoring of ventilation

Ineach patient, an EIT-dedicatedbelt,comprising 16 evenlyspaced electrodes was placedon the thorax inthesixth or fifthintercostalregion and connected witha commercialEIT monitor (PulmoVista 500, Drager Medical GmbH, Lubeck, Germany).During all study phases,EITinformation was generated throughusing small, alternateelectrical currents which rotated around thehis thorax. Data were recordedat 20 Hz. These data were storedfor offline analysis, in accordance with the procedure previouslydescribed in [12].Synchronized toEITtracer data or airway pressures andairflows fromventurism werecontinuously recorded.


More details onthe two protocolsare availablein thedata supplement online(Additionaldata supplement file1).

In short, inthePSV study,patients had to undergothe followingsteps of crossover which lasted each for 20 minutes:

  1. 1.

    Low support for PEEP in clinical(PSV low)vs.greater support atclinical PEEP(PSV high);

  2. 2.

    Clinical supportforthe low level of PEEP(PSV-PEEP low)against.medical support for higher PEEP(PSV-PEEP high).

As part of theVCV study,insteadthe following phaseswere carried outin a randomized order in the crossover,each lasting20 minutes:

  1. 1.

    A protective VCV when PEEP is low(VCV-PEEP low)contrasts with.protective VCV at clinicalPEEPand 5cmH 2O (VCV-PEEP high).

EIT anddata on ventilation

Through offline analysis ofEITtracer recordings taken duringthelast few minutesat the end of every phase(analysis oftenbreaths) We measured thelocal and global(same-sizeindependent and dependent lung areas) noninvasive airflows’ waveshape,as described in the past[8].The short version is that instantaneous worldwide andregionalinspiratory and expiratoryairflowswere assessed asvariationsin global and regionalimpedance measured every 50 ms when multiplied with the tidalintensity ratio forthesame study phase , anddivided by 50milliseconds. EIT airflow data werechanged from mL/msec toL/min (Fig. 1) and the maximumEIT-derived global and regional MIFand MEF (MIFglob MIFglob, MIFnon-dep,and MIFdepMEFglob the MEFglob, MEFnon dep andMEFdep for MEFglob, MEFnon-dep and MEFdep) wereidentified , and thevalue averaged over5-10 consecutivebreathingcycles.

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