Fabio FerrariZhi-Hai LiuQin LuMarie-Helene BecqueminKamel LouchahiGuy AymardCharles-Hugo MarquetteJean-Jacques Rouby

Comparison of lung tissue concentrationsof nebulized ceftazidime in ventilated piglets:ultrasonic versus vibrating plate nebulizers

Received: 5 July 2007Accepted: 6 April 2008Published online: 30 April 2008� Springer-Verlag 2008

Vibrating plate nebulizers were provided byAerogen Nektar Corporation, Galway,Ireland. Other support was provided frominstitutional and/or departmental source.None of the authors received any financialsupport from the manufacturers ofultrasonic and vibrating plate nebulizers.

F. FerrariDepartment of Anesthesiology,Faculdade de Medicina da UniversidadeEstadual Paulista Julio de Mesquita Filho,Botucatu, Brazil

Z.-H. LiuDepartment of Emergency Medicine,School of Medicine,Second Affiliated Hospital,Zhejiang University,Hangzhou, China

Q. Lu � J.-J. RoubySurgical Intensive Care Unit Pierre Viars,Department of Anesthesiologyand Critical Care Medicine,Assistance Publique–Hopitaux de Paris,La Pitie-Salpetriere Hospital,University of Paris-6, Paris, France

M.-H. BecqueminDepartment of Respiratory Physiology,Assistance Publique–Hopitaux de Paris,La Pitie-Salpetriere Hospital, Denis DiderotUniversity, UPRES 2397, Paris, France

K. LouchahiDepartment of Pharmacology,Assistance Publique-Hopitaux de Paris,Avicenne Hospital, Bobigny, France

G. AymardDepartment of Pharmacology,Assistance Publique–Hopitaux de Paris,La Pitie-Salpetriere Hospital, Paris, France

C.-H. MarquetteDepartement Hospitalo-Universitaire deRecherche Experimentale and INSERM U416 of Institut Pasteur, Universirty of Lille,Lille, France

Q. Lu ())Reanimation Chirurgicale PolyvalentePierre Viars, Department of Anesthesiologyand Critical Care, La Pitie-SalpetriereHospital, 47-83 boulevard de l’Hopital,75013 Paris, Francee-mail: qin.lu@psl.aphp.frTel.: +33-1-42177305Fax: +33-1-42177326

Abstract Objective: To comparethe efficiency of an Aeroneb Provibrating plate and an AtomisorMegaHertz ultrasonic nebulizer forproviding ceftazidime distal lungdeposition. Design: In vitroexperiments. One gram of cetazidimewas nebulized in respiratory circuitsand mass median aerodynamicdiameter of particles generated byultrasonic and vibrating platenebulizers was compared using alaser velocimeter. In vivoexperiments. Lung tissueconcentrations and extrapulmonarydepositions were measured in tenanesthetized ventilated piglets withhealthy lungs that received 1 g ofceftazidime by nebulization with

either an ultrasonic (n = 5), or avibrating plate (n = 5) nebulizer.Setting: A two-bed ExperimentalIntensive Care Unit of a UniversitySchool of Medicine.Intervention: Following sacrifice, 5subpleural specimens were sampledin dependent and nondependent lungregions for measuring ceftazidimelung tissue concentrations by high-performance liquid chromatography.Measurements and results: Massmedian aerodynamic diametersgenerated by both nebulizers weresimilar with more than 95% of theparticles between 0.5 and 5 lm. Lungtissue concentrations were 553 ± 123[95% confidence interval: 514–638]lg g-1 using ultrasonic nebulizer,and 452 ± 172 [95% confidenceinterval: 376–528] lg g-1 usingvibrating plate nebulizers (NS).Extrapulmonary depositions were,respectively, of 38 ± 5% (ultrasonic)and 34 ± 4% (vibrating plate) (NS).Conclusions: Vibrating platenebulizer is comparable to ultrasonicnebulizers for ceftazidimenebulization. It may represent a newattractive technology for inhaledantibiotic therapy.

Keywords Ultrasonic �Vibrating plate � Nebulizer �Nebulization of antibiotics �Lung tissue concentration

Intensive Care Med (2008) 34:1718–1723DOI 10.1007/s00134-008-1126-4 EXPERIMENTAL

Introduction

Optimisation of antibiotic nebulization during mechanicalventilation requires reduced tidal volume, low respiratoryfrequency, prolonged inspiration and an aerodynamicdiameter of aerosolized particles ranging between 1 and5 lm [1–3]. Jet nebulizers are considered as the referencefor delivering bronchodilatators and antibiotics to thetracheobronchial tree of patients with asthma and cysticfibrosis [2]. Two comparative studies, however, suggestthat jet nebulizers are less efficient than ultrasonic orvibrating plate nebulizers as far as distal lung deposition isconcerned. In mechanically ventilated patients receivingaerosolized radiolabelled albumin, a significant higherlung deposition was obtained with a DP100 ultrasonicnebulizer compared to a Medic-Aid jet nebulizer Medic-Aid [4]. In ventilated neonate animals receiving radiola-belled aerosols, a higher lung deposition was obtainedwith an Aeroneb Professional vibrating plate nebulizercompared to a MistyNeb jet nebulizer [5]. High lung tissueconcentrations of amikacin and ceftazidime have beenreported following ultrasonic nebulization in experimentaland human ventilator-associated pneumonia [6–8]. Ultra-sonic nebulizers, however, are voluminous and quartzvibrations increase the temperature into the nebulizerchamber, a factor that may alter chemical properties ofantibiotics. Vibrating plate nebulizers belong to the lastgeneration of nebulizers. The aerosol is generated from avibrating plate with multiple apertures, whose diameterdetermines aerodynamic diameter of aerosolized particles[5]. Because of their small size, vibrating plate nebulizersare quite ergonomic and are easy to use.

The aim of this experimental study was to compare theefficiency of an Aeroneb Pro vibrating plate and anAtomisor MegaHertz ultrasonic nebulizer for aerosolizingceftazidime to the distal lung of healthy mechanicallyventilated piglets.

Materials and methods

In vitro measurement of mass median aerodynamicdiameter of particles (MMAD)

The experimental set-up including the ventilator, theventilator settings used throughout the in vitro and in vivoexperiments, the respiratory circuits and the nebulizers isshown in Fig. 1. One gram of ceftazidime was nebulizedcontinuously into the circuits by the ultrasonic nebulizer(Atomisor MegaHertz�; Diffusion Technique Francaise,Saint-Etienne, France) and by the vibrating plate nebulizer(Aeroneb Pro�; Aerogen Nektar Corporation, Galway,Ireland). Without connecting the animals to the ventilatorand according to a technique previously described [9]MMAD was measured at the outlet of the nebulizer and at

the distal tip of the endotracheal tube using a laser velo-cimeter (Malvern Instrument, Worcestershire, UK).

Animal preparation

Ten healthy bred domestic Largewhite-Landrace piglets,aged 3 months and weighting 20 ± 1 kg, were anesthe-tized and orotracheally intubated with a 7.5 Hi-Lo JetMallinckrodt tube (Mallinckrodt Incorporation, Argyle,NY) and ventilated as described in Fig. 1. The study wasconducted according to French law concerning experi-mental studies.

Aerosol generation

All piglets received 1 g of ceftazidime powder diluted insterile water. In five animals, nebulization was performedby the ultrasonic nebulizer and in five by the vibratingplate nebulizer. As shown in Fig. 1, experiments wereperformed without humidification of inspired gas [10]using ventilator settings recommended for promoting lungdeposition. In addition, a 65%/35% helium–oxygenmixture was used for ventilation during the period ofnebulization to optimize lung deposition as previouslydemonstrated [8].

Assessment of ceftazidime lung tissue concentrations

Piglets were killed by exsanguination 15 min after com-pletion of nebulization as previously described [8]. Thelungs were then removed from the thorax and five sub-pleural lung specimens were excised from the upper lobe,the middle lobe, the apical-dependent segment of thelower lobe, the anterior-nondependent segment of lowerlobe, and the postero-caudal segment of lower lobe. Tis-sue samples were cryomixed in liquid nitrogen, weighedand homogenized, and ceftazidime concentrations weremeasured in a blinded fashion by high-performance liquidchromatography (HPLC) with correction for contaminat-ing blood [8].

Assessment of extrapulmonary deposition

At the end of the experiment, nebulizer chamber, inspi-ratory and expiratory circuits, Y piece, connecting tube,endotracheal tube, and expiratory filter were rinsed,respectively, with 1 l of distilled water. The amount ofceftazidime of the different parts was separately measuredby HPLC. Extrapulmonary deposition was defined as thetotal amount of ceftazidime recovered from respiratorycircuits. Percentage of total extrapulmonary depositionwas calculated as the amount of ceftazidime recovered inthe different respiratory circuits divided by the dose of

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ceftazidime inserted in the nebulizer chamber. Percentageof ceftazidime entering the respiratory system was definedas 100 minus percentage of extrapulmonary deposition.

Statistical analysis

The present study was considered as a pilot study andpower calculation was not performed. The 95% confi-dence interval of the lung tissue concentrations wascalculated as recommended [11]. Data were analysedusing Sigmastat Software (SPSS, Inc., San Raphael, CA).The normal distribution of data was verified by a Kol-mogorov–Smirnov test. Extrapulmonary depositionsobtained after nebulization performed by ultrasonic and

vibrating plate nebulizers were compared by a pairedStudent’s t test. Lung tissue ceftazidime concentrationsmeasured in the two groups of piglets (ultrasonic andvibrating plate nebulizers) in different lung segmentswere compared by a two-way analysis of variance forrepeated measures. A p value less than 0.05 was consid-ered as significant. All data are expressed as mean ± SD.

Results

In vitro experiments

As shown in Table 1, MMAD was not influenced by neb-ulizer, tidal volume and site of measurement. As shown in

VentilatorFilter

40 cm

Ultrasonicnebulizer

Inspiratory limb

Expiratory limb

Ventilator

Inspiratory limb

Expiratory limbFilter

Vibrating plate nebulizer

T-adapter

15 cm

Endotracheal tube

Endotracheal tube

Fig. 1 Experimental design for ceftazidime nebulization. Respira-tory circuits were composed of a Cesar ventilator (Taema, Antony,France), two 150-cm-long inspiratory and expiratory circuits, a Ypiece and one 15- or 40-cm long connecting tube. One gram ofceftazidime was nebulized continuously in the circuits by theultrasonic nebulizer, positioned 40 cm from the Y piece and by thevibrating plate nebulizer positioned 15 cm from the Y piece. Theconnecting tube between nebulizer and Y piece serves as a reservoircontaining the aerosol generated during the expiratory phase, whichis entrained into the tracheobronchial tree during the nextinspiration (bolus effect). A filter with a pore size of 0.2 lm

(Hygrobac; Mallinckrodt Medical, Mirandola, Italy) is placed onthe expiratory limb to collect expired aerosolized particles.According to previous studies that identified ventilator settingspromoting distal lung deposition of aerosolized particles [1–3], thefollowing ventilator settings were used: absence of heat andmoisture exchanger, volume controlled mode, administration of aconstant and low inspiratory flow (9 l/min), a tidal volume of300 ml, respiratory rate of 15 breaths/min, inspiratory/expiratoryratio of 50%, an end-inspiratory pause representing 20% of the dutycycle, positive end-expiratory pressure of 5 cmH2O and FiO2 0.21

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Table 2, extrapulmonary deposition was similar betweenultrasonic and vibrating plate nebulizers. Extrapulmonarydeposition was predominant in the nebulizer chamber

during ultrasonic nebulization and predominant in theinspiratory circuits during vibrating plate nebulization.

Lung tissue concentrations of ceftazidime

The lungs were pink and healthy. Ceftazidime lung tissueconcentrations were homogeneously distributed betweennondependent and dependent pulmonary segments, what-ever the technique used (Fig. 2). Lung tissue concentrationswere not statistically different among lung segments andbetween vibrating plate and ultrasonic nebulizers. Meanlung tissue concentrations were 452 ± 172 [95% confi-dence interval: 376–528] lg g-1 and 553 ± 123 [95%confidence interval: 514–638] lg g-1).

Discussion

The present study demonstrates that ultrasonic andvibrating plate nebulizers have a comparable efficiencyfor nebulizing 1 g of ceftazidime in anesthetized andventilated healthy piglets.

MMAD and extrapulmonary deposition resultingfrom ultrasonic and vibrating plate nebulizers

Aerosol particle size is one of the key factors influencinglung deposition. Particles bigger than 5 lm rapidlyimpact respiratory circuits and large airways. The optimalMMAD ranges between 0.5 and 5 lm [12] and it is wellknown that nebulizer technology influences MMAD [13,14]. In the present study, ultrasonic and vibrating platenebulizers were equivalent for producing a high per-centage of particle size ranging between 0.5 and 5 lm.

Bench studies have shown that extrapulmonarydeposition ranges between 60 and 80% with optimizedventilatory settings [14, 15]. In the present study, in vivoextrapulmonary deposition was 38 and 34% for ultrasonicand vibrating plate nebulizers, respectively. Discrepanciesin aerosol deposition between in vitro and in vivo

Table 1 Mass median aerodynamic diameter generated by ultrasonic and vibrating plate nebulizers

Nebulizer TV (ml) MMAD (lm) rg (lm) %0.5–5 lm

Outlet of NBZ Tip of ET Outlet of NBZ Tip of ET Outlet of NBZ Tip of ET

USN 300 1.43 1.38 1.86 1.76 95.40 95.63VPN 300 2.35 2.42 1.57 1.60 98.10 98.50USN 500 1.24 1.60 1.85 1.51 94.70 97.20VPN 500 2.24 1.63 1.56 1.75 96.30 95.30

USN ultrasonic nebulizer, VPN vibrating plates nebulizer, TV tidal volume, MMAD mass median aerodynamic diameter, rg geometricSD, % 0.5–5 lm optimal breathable range defined as percentage of particles size between 0.5 and 5 lm, NBZ nebulizer, ET endotrachealtube

Table 2 Aerosol deposition in 10 piglets nebulized with an ultra-sonic or a vibrating plate nebulizer expressed in percentage of thetotal dose initially inserted into the chamber (1 g)

USN (%) VPN (%)

Extrapulmonary deposition 38 ± 5 34 ± 4Nebulizer chamber 11 ± 1 4 ± 2*Inspiratory circuit and tubing 7 ± 1 18 ± 5§

Endotracheal tube 6 ± 2 3 ± 1Expiratory filter 14 ± 4 9 ± 4Lung availability 62 ± 5 66 ± 4

Lung availability = Percentage of the total nebulized dose ofceftazidime delivered to the respiratory systemUSN Ultrasonic nebulizer, VPN Vibrating plate nebulizer*p \ 0.05; §p \ 0.01

Lung tissue concentrations of ceftazidime (µg.g-1)

Lung segmentsB2 B3 B6 B8 B10

0

200

400

600

800

1000 USNVPN

NS

Fig. 2 Regional distribution of ceftazidime lung tissue concentra-tions in dependent (B3, B6 and B10) and nondependent (B2 andB8) lung segments after nebulization of 1 g of ceftazidime byultrasonic and vibrating plate nebulizers. Lung tissue concentra-tions are homogeneously distributed among the different lungsegments. USN ultrasonic nebulizer, VPN vibrating plates nebulizer

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conditions have been previously reported [16]. During invitro conditions, the filter serving to estimate ‘‘pulmon-ary’’ deposition captures small particles and increasesrespiratory resistance, both effects influencing extrapul-monary deposition [17]. Use of a helium–oxygen mixturein the present study was aimed at converting turbulentinto laminar flows in order to further decrease extrapul-monary deposition and increase pulmonary deposition[8, 18].

Despite the reduction of the inspiratory circuit volume,deposition into the inspiratory circuit was higher withvibrating plate nebulizer, likely because local turbulencesresulting from vibrating plate technology are greater thanthose generated by ultrasonic vibration and promoteimpaction of aerosolized particles into the inspiratorycircuits [19]. Deposition into the chamber of the ultra-sonic nebulizer was greater because of its larger volume.

Comparative ceftazidime lung tissue deposition

Lung tissue deposition of ceftazidime was similarbetween vibrating plate and ultrasonic nebulizer. A recentbench study has also shown comparable aerosol deliverybetween both techniques [14]. As discussed above, 60%of the dose inserted in the nebulizer chamber entered therespiratory system. Because nebulization was performedin healthy lungs, as previously demonstrated [12], a

homogeneous distribution of ceftazidime was found(Fig. 2). Based on this homogeneous distribution, anapproximate estimate of the total dose of ceftazidimereaching the distal lung can be calculated. The weight oftwo exsanguinated 20-kg piglets with healthy lungs, isaround 200 g [20]. As mean lung tissue concentrationswere measured at 553 and 452 lg/g with ultrasonic andvibrating plate nebulizers, it can be assumed that 553 lg/g 9 200 g = 110.6 mg reached the distal lung with theultrasonic nebulizer and 452 lg/g 9 200 g = 90.4 mgwith the vibrating plate nebulizer. Therefore, around 50%of the nebulized dose reaches proximal airways and 10%the lung parenchyma, a result higher than that previouslyreported [4].

In conclusion, in ventilated piglets with healthy lungs,vibrating plate nebulizers and ultrasonic nebulizers have asimilar efficiency: among 60% of the ceftazidime dosedelivered to the respiratory system, 50% reach the tra-cheobronchial tree and 10% the distal lung. Because ofbetter ergonomics and simplicity of use, vibrating platenebulizers may provide an attractive alternative forinhaled antibiotic therapy as a treatment of ventilator-associated pneumonia.

Acknowledgments The authors thank Benoıt Lecuelle, ArnoldDive and Michel Pottier, Departement Hospitalo-Universitaire deRecherche Experimentale and INSERM U 416 of Institut Pasteur,University of Lille, France for the preparation of the animals.

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