DOI: 10.1542/peds.2009-0126 2009;124;e950-e957; originally published online Oct 12, 2009; Pediatrics

Rondina, Aldo Baritussio, Gianna Maria Toffolo and Virgilio Paolo Carnielli Paola Elisa Cogo, Maddalena Facco, Manuela Simonato, Giovanna Verlato, Clementina

Distress SyndromeDosing of Porcine Surfactant: Effect on Kinetics and Gas Exchange in Respiratory

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Dosing of Porcine Surfactant: Effect on Kinetics andGas Exchange in Respiratory Distress Syndrome

WHAT’S KNOWN ON THIS SUBJECT: Multiple surfactant dosesversus a single dose and porcine surfactant doses of 200versus 100 mg/kg seem to be more effective in infants with

RDS. Little is known regarding surfactant pharmacokinetics inhuman patients with RDS.

WHAT THIS STUDY ADDS: We report exogenous surfactant DSPCpharmacokinetics in 61 infants who received 100 or 200 mg/kgporcine surfactant as treatment for RDS. The dose of 200 mg/kg

was associated with a longer DSPC half-life, fewer retreatments, andbetter oxygenation index values.

abstractOBJECTIVE: The goal was to study exogenous surfactant disaturatedphosphatidylcholine (DSPC) kinetics in preterm infants with respira-tory distress syndrome (RDS) who were treated with 100 or 200 mg/kgporcine surfactant.

METHODS: Sixty-one preterm infants with RDS undergoing mechan-ical ventilation received, within 24 hours after birth, 100 mg/kg(N � 40) or 200 mg/kg (N � 21) porcine surfactant mixed with[U-13C]dipalmitoylphosphatidylcholine. Clinical and respiratory pa-rameters were recorded, and DSPC half-life and pool size and endoge-nous DSPC synthesis rate were calculated.

RESULTS: Clinical characteristics and short-term outcomes did notdiffer between groups. In the 100 mg/kg group, 28 infants (70%) re-ceived a second dose after 25 � 11 hours and 9 (22.5%) a third doseafter 41� 11 hours; in the 200mg/kg group, 6 infants (28.6%) receiveda second dose after 33� 8 hours and 1 a third dose. The DSPC half-lifewas longer in the 200 mg/kg group (first dose: 32 � 19 vs 15 � 15hours [P� .002]; second dose: 43� 32 vs 21� 13 hours [P� .025]).DSPC synthesis rates and pool sizes before the first and second dosesdid not differ between the groups. The 200 mg/kg group exhibited agreater reduction in the oxygenation index than did the 100 mg/kggroup after the first (P� .009) and second (P� .018) doses.

CONCLUSIONS: Porcine surfactant given to preterm infants with RDSat a dose of 200 mg/kg resulted in a longer DSPC half-life, fewer re-treatments, and better oxygenation index values. Pediatrics 2009;124:e950–e957

AUTHORS: Paola Elisa Cogo, MD, PhD,a Maddalena Facco,MD,a Manuela Simonato, PhD,a Giovanna Verlato, MD,PhD,a Clementina Rondina, MD,b Aldo Baritussio, MD,c

Gianna Maria Toffolo, PhD,d and Virgilio Paolo Carnielli,MD, PhDb

Departments of aPediatrics, cMedical and Surgical Sciences, anddInformation Engineering, University of Padua, Padua, Italy; andbNeonatal Division, Institute of Maternal-Infantile Sciences,Polytechnic University of Marche and University Hospital ofAncona, Ancona, Italy

KEY WORDSpulmonary surfactant, isotopes, low birth weight infants,respiratory distress syndrome

ABBREVIATIONSDSPC—disaturated phosphatidylcholineRDS—respiratory distress syndromeDPPC—dipalmitoylphosphatidylcholineFIO2—fraction of inspired oxygenMAP—mean airway pressureTTR—tracer/tracee ratio

www.pediatrics.org/cgi/doi/10.1542/peds.2009-0126

doi:10.1542/peds.2009-0126

Accepted for publication Jun 5, 2009

Address correspondence to Paola Elisa Cogo, MD, PhD,Department of Pediatrics, University of Padua, Via Giustiniani 3,Padua 35128, Italy. E-mail: cogo@pediatria.unipd.it

PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275).

Copyright © 2009 by the American Academy of Pediatrics

FINANCIAL DISCLOSURE: Dr Carnielli received a fee forspeaking at an educational event sponsored by DeyLaboratories (Napa, CA) and received funds for research fromChiesi Pharmaceuticals (Parma, Italy).

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The alveolar pool of surfactant in new-borns with respiratory distress syn-drome (RDS) does not differ muchfrom the alveolar pool in adults with-out respiratory disease.1 Withoutsurfactant supplementation, however,newborns with RDS develop severe re-spiratory failure, possibly through acombination of mechanisms includingaltered surfactant composition, lungstructural immaturity, and increasedsurfactant inactivation.2

Dosages and modes of administrationof exogenous surfactant have beenstudiedmostly in animalmodels.3–5 Forexample, in premature lambs treatedwith natural sheep surfactant at dosesof 19, 53, 64, or 173 mg/kg, pressure-volume curves improved progressivelyup to a dose of 64mg/kg but no furthergain was observed with the adminis-tration of 173 mg/kg.3 Information onthe effect of exogenous surfactant dos-ing in human subjects is limited. In astudy by Halliday et al,6 cumulativedoses of exogenous surfactant up to600 mg/kg were no better than 300mg/kg. Other studies with newborn in-fants compared different doses of sur-factant in the range of 50 to 200 mg/kg.7–12

Four studies compared beractant(Survanta [Abbott Laboratories, Ab-bott Park, IL]) administered at 100mg/kg and poractant � (Curosurf[Chiesi Pharmaceuticals, Parma, It-aly]) administered at either 100 or 200mg/kg to infants with moderate/se-vere RDS.8,11,13,14 Poractant�was foundto have a more-rapid onset of actionand was associated with lower neona-tal mortality rates. However, the re-duction in mortality rates was not sta-tistically significant when poractant �and beractant at the initial dose of 100mg/kg were compared, which sug-gests that the most significant effectsonmortality rates were seen when 200mg/kg poractant � was comparedwith 100mg/kg beractant or poractant

�.15 Data suggest that, for infants withmoderate/severe RDS, a porcine sur-factant dose of 200 mg/kg may bemore effective than 100 mg/kg.8,11,13,14

After the first surfactant dose, irre-spective of the amount administered,some neonates respond to treatmentonly transiently and require furthersurfactant administration. A recentmeta-analysis comparing single ver-sus multiple surfactant doses for pre-term infants with established RDSshowed greater improvements inoxygenation and ventilatory require-ments, a decreased risk of pneumo-thorax, and a trend toward improvedsurvival rates for infants who receivedmultiple surfactant doses.16 When theretreatment should be performed isstill unclear. In clinical practice, someneonatologists prefer to retreat theirpatients after a fixed time, whereasothers choose to retreat them if theirrespiratory function deteriorates.17

It is likely that better knowledge of thepharmacokinetic features of exoge-nous surfactant in RDS could help tooptimize the treatment of preterm in-fants. Few studies, with small numbersof infants, have been published.18–20

In this study, we administered to new-borns with RDS 100 or 200 mg/kg por-cine surfactant mixed with 13C-labeleddipalmitoylphosphatidylcholine (DPPC),and we measured exogenous surfac-tant kinetics by analyzing the isotopicenrichment of disaturated phosphati-dylcholine (DSPC) isolated from tra-

cheal aspirates.16–18 Apart from theirsafety,21 stable isotopes have the ad-vantage that their enrichment is notaffected by sample dilution. From theenrichment curves, we derived thesurfactant pool size at the time of dos-ing, the rate of endogenous surfactantsynthesis, and the half-life of adminis-tered exogenous surfactant.

METHODS

Patients and Study Design

We studied 61 newborn infants withRDS who were admitted to the NICU ofthe Department of Pediatrics, Univer-sity of Padua, or the Division of Neona-tology of the Polytechnic University ofMarche (Ancona, Italy). Infants wererecruited if they required synchro-nized intermittent mandatory ventila-tion and received exogenous surfac-tant within the first 24 hours of life. Thestudy protocol was approved by theethics committees of both institutions,and written informed consent was ob-tained from both parents. The studylasted from 2000 to 2004.

Newborns with congenital malforma-tions, sepsis, or renal or liver failurewere excluded from the study. The di-agnosis of RDS was based on clinicaldata and on chest radiograms,22 afterexclusion of infections. All infants,whose clinical characteristics are re-ported in Table 1, received either 100or 200 mg/kg porcine surfactant (Cu-rosurf [Chiesi]) as rescue treatmentfor RDS. Administered surfactant

TABLE 1 Clinical Characteristics of Study Infants

200 mg/kg(N� 21)

100 mg/kg(N� 40)

P

Birth weight, mean� SD, g 1058� 413 1110� 429 .65Gestational age, mean� SD, wk 28.4� 2.6 28.9� 2.7 .46Prenatal steroid treatment, n (%) 17 (80.9) 27 (67.5) .45Full steroid treatment, n (%) 10 (47.6) 19 (47.5) .93Delivery through cesarean section, % 61.9 72.5 .40Patent ductus arteriosus, % 73.7 75.0 .36Age at study start, mean� SD, h 3.7� 2.9 6.0� 5.8 .09FIO2 before first surfactant dose, mean� SD 0.50� 0.20 0.54� 0.20 .45MAP before first surfactant dose, mean� SD, cmH2O 8.5� 2.5 8.2� 2.1 .58Oxygenation index before first surfactant dose, mean� SD 9.2� 7.0 9.5� 6.6 .86

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doses were labeled with 2.5 mg/kg[U-13C-palmitic acid]DPPC (Martek Bio-sciences, Columbia, MD) per dose astracer. [U-13C-palmitic acid]DPPC wassuspended in normal saline solution23

and was mixed with the exogenoussurfactant during surfactant prepara-tion. The choice of surfactant dosingwas at the discretion of the attendingneonatologists, who were blinded tolaboratory and kinetic results.

The indications for surfactant treat-ment were a fraction of inspired oxy-gen (FIO2) of�0.40 and a mean airwaypressure (MAP) of �7.5 cm H2O. Sur-factant was administered as a bolusthrough a small catheter insertedthrough the endotracheal tube. Afterthe procedure, the neonates were re-connected to the mechanical ventila-tor at pretreatment settings. Themodeof ventilation at the beginning of thestudy period was standardized, withan inspiratory time of 0.3 to 0.5 sec-onds, an initial respiratory rate of 50 to65 breaths per minute, and a positiveend expiratory pressure of 3 to 4cm H2O. Peak inspiratory pressure andFIO2 were adjusted so that PaO2 was be-tween 50 and 70 mm Hg, oxygen satu-ration was�88% but�96%, and PaCO2was between 40 and 50 mm Hg. Venti-latory parameters were recorded be-fore the start of the study and then ev-ery 6 hours. The oxygenation index wascalculated as follows: oxygenation in-dex� [(MAP� FIO2)/PaO2]� 100. Tra-cheal aspirations were performed asdescribed previously,20 and sampleswere collected before administrationof the first dose of surfactant (time 0),every 6 hours until 72 hours, and thenevery 12 hours until extubation. Pa-tients received additional surfactantdoses if FIO2 returned to �0.35 andMAP was�7.5 cm H2O. On the basis ofour previous work20 and the policy ofthe 2 participating neonatal units, re-treatment was not given earlier than18 hours after the previous dose un-

less there was a high index of suspi-cion regarding surfactant maldistribu-tion, on the basis of clinical evidence orradiologic findings.24

Analytical Methods

Lipids from tracheal aspirates and fromexogenous surfactant were extractedaccording to the method described byBligh and Dyer,25 after addition of theinternal standard heptadecanoylphos-phatidylcholine. One third of the extractwas oxidized with osmium tetroxide.26

DSPC was isolated from the lipid ex-tract through thin-layer chromatog-raphy, after oxidation with osmiumtetroxide.26 DSPC fatty acids were deri-vatized27 as pentafluorobenzyl deriva-tives, extracted with hexane, andstored at �20°C. A half-spot of exoge-nous surfactant DSPC was derivatizedas the methyl ester,28 and the amountof DSPC was measured through gaschromatography, as described previ-ously.20 Tracheal aspirates with visibleblood were discarded.

The enrichment of [U-13C-palmitic acid]DPPC from the tracheal aspirates wasmeasured through gas chromatography-mass spectrometry in negative ioniza-tionmode, and results were expressedinmole percent excess.20 Themole per-cent excess represents the increase inthe mole percentage of [U-13C]palmiticacid above the baseline value obtainedat time 0 of the study.

Calculations

Data were analyzed under the follow-ing assumptions: (1) exogenous sur-factant DSPC is distributed in thealveolar pool and subsequently inter-nalized and recycled by the type II cells;(2) endogenous DSPC is synthesized bylung parenchyma, secreted in the alve-oli, and recycled before degradation;(3) exogenous surfactant DSPC is dis-tributed homogeneously in the lungs,and the system is at steady state; and(4) DSPC kinetics are linear. Under

these assumptions, DSPC kinetics canbe modeled conveniently on the basisof the tracer/tracee ratio (TTR), that is,the ratio of exogenous (tracer) to en-dogenous (tracee) DSPC.29,30 This vari-able is different from enrichment,which measures the ratio of the la-beled component of exogenous surfac-tant to unlabeled DSPC, originatingfrom both exogenous and endogenoussources. Therefore, enrichment (E)measured at time t was converted toTTR by using the following formula (de-rived in the Appendix): TTR(t)� E(t)[(EI�1)/[EI� E(t)]], where EI is the percent-age of [U-13C-palmitic acid]DPPC withrespect to unlabeled DSPC in the ad-ministered surfactant dose, equal to7� 3%, on average. TTR datawere fittedto either a monoexponential or biexpo-nential decay model (Fig 1), and DSPCkinetic parameters were calculated asfollows. In themonoexponential model,that is, TTR(t) � Ae�Kt, the DSPC half-life (in hours) is ln(2)/k, the DSPC poolsize (in milligrams per kilogram) isdose/A, and the DSPC synthesis rate (inmilligrams per day per kilogram) is(DSPC pool size � k � 24) � [dose/(A/k) � 24]. In the biexponential model,that is, TTR(t) � A1e�k1t � A2e�k2t,the DSPC half-life (in hours) is ln(2)/k2,the DSPC pool size (in milligrams perkilogram) is dose/(A1 � A2), and theDSPC synthesis rate (in milligrams perday per kilogram) is [dose/[A1/k1 �A2/k2]] � 24. Dose (in milligrams perkilogram) is the administered surfactantDSPC dose, t is time (in hours), and, forthe biexponential model, k2 indicatesthe rate constant of the slower compo-nent, responsible for the late portionof TTR decay.

When data collected after administra-tion of the second dose were analyzed,equations were modified to accountfor the contribution of the first dose.For example, for the monoexponentialmodel, DSPC pool size is dose/(A �

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TTRpre), where TTRpre is the TTR valueimmediately before administration ofthe second dose.

The derived DSPC pool size is an esti-mate of the amount of tracee (ie,endogenous DSPC) present in the air-

ways during each surfactant adminis-tration and is designated as the DSPCpool. DSPC kinetic parameters were

y = -0.0706x + 3.0278R2 = 0.8891

y = -0.0525x + 6.1915R2 = 0.9767

-3

-2

-1

0

1

2

3

0 24 48 72 96 120 144 168

Time, h

ln, T

TR

Second doseFirst dose

A

B

y = -0.0388x + 2.2823R 2 = 0.989

-4

-3

-2

-1

0

1

2

3

0 24 48 72 96 120 144 168

Time, h

ln, T

TR

First doseSecond dose

C

0 24 48 72 96 120 144 168- 5

- 4

- 3

- 2

- 1

0

1

2

y = 2.9e-0.07x + 1.2e-0.02x- - 0.8

Time, h

ln, T

TR

FIGURE 1Three typical surfactant DSPC kinetic patterns (semilogarithmic plots). A, The half-life of the first dose was not computable (�3 samples available beforethe second dose). B, DSPC disappeared from the airways monoexponentially after 2 surfactant doses but with different slopes. C, DSPC disappeared fromthe airways according to a biexponential decay.

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missing when DSPC decay curves had�3 enrichment points, that is, too fewpoints for calculation of DSPC kinetics(Fig 1A).

Data were expressed as mean� SD ormedian and interquartile range, ac-cording to variable distribution, andthey were compared with independentt tests or Mann-Whitney U tests for con-tinuous variables and �2 tests for bi-nary data. Statistical analyses wereperformed with SPSS for Windows XP15.00 (SPSS, Chicago, IL).

RESULTS

Surfactant DSPC pharmacokineticscould be calculated reliably after 74surfactant administrations to 61 in-fants who received �1 dose of exoge-nous surfactant. Forty infants weretreated with 100 mg/kg surfactant(100 mg/kg group) and 21 with 200mg/kg surfactant (200 mg/kg group),at the discretion of the attending neo-natologist. All first doses were admin-istered within 24 hours after birth. The2 groups were similar with regard toall recorded clinical variables (Table1). The study was conducted in 2 neo-natal units, and the proportions of 200mg/kg doses were 35% and 27% (notsignificant). The average ventilator set-tings, including inspiratory time, didnot differ between the 2 units or be-tween infants receiving 100 versus 200mg/kg doses of exogenous surfactant.

In the 100mg/kg group, a second surfac-tant dosewas administered to 28 infants(70.0%) after 25� 11 hours, and a thirddose was administered to 9 infants(22.5%) 41� 11 hours after the seconddose. In the 200 mg/kg group, 6 infants(28.6%) received a second dose after33� 8 hours, and only 1 received a thirddose. The interval between the first andsecond doses tended to be longer in the200 mg/kg group than in the 100 mg/kggroup, but the difference did not reachstatistical significance (Table 1). Afterthe first and second doses, infants as-

signed to the 200mg/kg group showed abetter oxygenation index, comparedwiththe 100 mg/kg group (Table 2). The 2groups were not statistically differentwith respect to duration of mechanicalventilation, survival rates, rates of bron-chopulmonary dysplasia (defined as ox-ygen dependency at 36 weeks), or ratesof the combination of death and bron-chopulmonary dysplasia (P � .860)(Table 2).

DSPC enrichment could be measured inall tracheal aspirates, but decay curveswith �2 enrichment points were ob-tained for 74 of the 99 surfactant doses.In most cases, decay curves weremono-exponential (Fig 1). Biexponential decaywas more frequent in the 200 mg/kggroup, without reaching statistical sig-nificance (43% vs 29% after the firstdose [P� .3] and 43% vs 13% after thesecond dose [P� .15]). In the 200mg/kggroup, DSPC kineticswere calculated for

15 infants (71.4%) after the first doseand 5 (83.3%) after the second dose. Inthe100mg/kggroup,DSPCkineticswerecalculated for 31 infants (77.5%) afterthe first dose and 23 (82.1%) after thesecond dose.

The DSPC pool sizes were similar in the100 and 200 mg/kg groups during thefirst and second surfactant adminis-trations (Table 3). The DSPC half-lifewas significantly longer in the 200mg/kg group after both the first andsecond doses, whereas endogenoussurfactant DSPC synthesis rateswere similar in the 2 groups (Table3). DSPC kinetic variables did notseem to be influenced by the mode ofTTR decay (ie, monoexponential ver-sus biexponential).

DISCUSSION

Exogenous surfactant therapy is a cor-nerstone of modern neonatology, be-

TABLE 2 Surfactant Dose Effects on Oxygenation and Outcome Parameters

200 mg/kg(N� 21)

100 mg/kg(N� 40)

P

Conventional ventilation, mean� SD, d 12� 13 10� 10 .59Survival, % 90.0 82.5 .44Bronchopulmonary dysplasia at 36 wk, % 52.9 44.1 .81�1 surfactant dose, % 28.6 70.0 �.01Total surfactant dose, mean� SD, mg/kg 250� 89 192� 73 .02Oxygenation index after first surfactant dose,mean� SD

4.0� 1.9 6.9� 5.4 �.01

Oxygenation index after second surfactantdose, mean� SD

3.2� 1.5 6.0� 2.6 .02

Interval between first and second doses,mean� SD, h

33� 8 25� 11 .09

TABLE 3 DSPC Half-Life, Endogenous DSPC Pool Size, and Synthesis Rate for Preterm NewbornsTreated With 200 or 100 mg/kg Porcine Surfactant Extract

200 mg/kg (N� 21) 100 mg/kg (N� 40) P

DSPC half-life, mean� SD, hFirst dose 32� 19 (n� 15) 15� 15 (n� 31) �.01Second dose 43� 32 (n� 5) 21� 13 (n� 23) .02Third dose 17� 7 (n� 7)Endogenous DSPC pool size, median(interquartile range), mg/kgFirst dose 5.3 (1–12.7) (n� 15) 2.5 (0.5–6.8) (n� 31) .32Second dose 2.6 (0.7–18.5) (n� 5) 4.4 (1.2–16.1) (n� 23) .67DSPC synthesis, median (interquartile range),mg/kg per dFirst dose 4.8 (0.1–14.4) (n� 15) 7.2 (3.8–10.8) (n� 31) .80Second dose 2.4 (1.7–5.8) (n� 5) 4.8 (2.2–13.4) (n� 23) .35

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cause it reducesmortality andmorbid-ity rates for neonates with RDS.24

Current treatment schemes are de-rived from human and animal stud-ies with very high doses of surfac-tant.3,5,7,8,11–13,17,31 Studies performedwith different animal species showedthat the amount of surfactant presentin the airways at birth is correlatedwith the severity of RDS and that ad-ministered surfactant disappears witha half-life of 4 to 12 hours.32–35 Little isknown about surfactant turnover inpremature newborns, and studiesmeasuring surfactant pools in thispopulation are limited.18–20 Further-more, most clinical trials have beenperformedwith intention-to-treat anal-yses, and the effectiveness of differentdosing schemes remains unclear.

This report describes pharmacokinet-ics and clinical outcomes after the ad-ministration of 100 or 200 mg/kg po-ractant � to preterm infants withmoderate/severe RDS. Stable-isotopeDSPC labeling of the administered sur-factant dose allowed us to trace exog-enous surfactant DSPC and to calcu-late the TTR, that is, the exogenous(tracer)/endogenous (tracee) surfac-tant DSPC ratio. This variable is themostconvenient way to express data from ex-perimentswith stable isotopes. Pharma-cokinetic parameters such as DSPC half-life, pool size (estimation of the alveolarDSPC pool size), and synthesis rate canbe estimated easily by fitting a multiex-ponential model to TTR data and thenapplying simple formulas to the modelparameters.

The main clinical findings of this studywere that the larger dose had a longerhalf-life and that newborns receiving itneeded fewer additional doses andhad better oxygenation index values.There were no differences in durationsof mechanical ventilation, mortalityrates, or development of broncho-pulmonary dysplasia. The cumulativedose of exogenous surfactant was sig-

nificantly greater in the 200 mg/kggroup, but the 100 mg/kg group re-quired more redosing, in agreementwith data by Ramanathan et al.11 Inboth groups, the alveolar surfactantDSPC level was on the order of 2.5 to 5mg/kg, which is markedly lower thanthat found in mature newborns.36 TheDSPC pool in preterm newborns withRDS during the first day of life rangedfrom 1 to 15 mg/kg,20 whereas terminfants without RDS have 3 times thatvalue.36 In this study, for both groups ofnewborns, the pool of DSPC was �6mg/kg (median) before the first doseand�5mg/kg before the second dose.Therefore, patients who needed a sec-ond dose had endogenous surfactantDSPC pool values similar to thosefound before the first dose, which sug-gests incomplete retention of the firstdose, high catabolic rates, or insuffi-cient endogenous synthesis. Infantswho required a second dose had sur-factant deficiency and were at risk ofmechanical and alveolar instability.31,37

Endogenous DSPC synthesis rateswere not different between our studygroups. It must be noted that this ki-netic parameter represents only thesurfactant DSPC synthesized de novo,is not affected by surfactant recycling,and does not reflect other DSPC syn-thetic pathways. Among our infants,the DSPC synthesis rates ranged be-tween 2.4 and 7.2mg/kg per day, whichsuggests that preterm infants withRDS need at least 3 or 4 days to accu-mulate adequate amounts of surfac-tant in their airways. These findingsare in agreement with previous esti-mates of DSPC synthesis obtainedthrough intravenous administration ofstable-isotope glucose and palmitate.In those studies, the DSPC synthesisrates ranged between 2.7 and 4.8mg/kg per day among preterm infantswith respiratory failure who requiredno surfactant or �1 dose of exoge-nous surfactant.38,39 Therefore, in RDS,

surfactant administration is needed tocompensate for slow de novo synthe-sis and to substitute for surfactant de-graded or lost through the conductingairways.

Little is known regarding exogenoussurfactant turnover in human RDS18–20

and, to the best of our knowledge, thisis the first time the half-life of exoge-nous surfactant has been measured inpreterm infantswith RDS receiving 100or 200 mg/kg doses of exogenous sur-factant. We found that, after adminis-tration of 200 mg/kg, the half-life of ad-ministered surfactant was longer. Thisdifference is unlikely to be attributableto heterogeneity of the study groups,because all infants had received a sin-gle mode of ventilation (synchronizedintermittent mandatory ventilation)from birth and patients with signs ofinfection, such as increased whiteblood cell and neutrophil counts, in-creased C-reactive protein levels, andtemperature instability, were excludedprospectively from analyses.40

An interesting finding is that adminis-tered surfactant left the airways mo-noexponentially most of the time andin a biexponential mode only in somecases (Fig 1). This might have hap-pened through several mechanisms.For example, a slow rate of uptake ofadministered material or a low rate ofde novo synthesis might have favoreda biexponential mode of decay. On thewhole, however, it seems that the ki-netic differences between the 100mg/kg group and the 200 mg/kg groupwere not attributable to differences indata fitting, because the distributionsof decay modes did not differ signifi-cantly between the 2 groups.

The major limitation of the presentstudy was that patients were not as-signed randomly to the treatmentgroups, because of different orienta-tions regarding surfactant administra-tion among attending neonatologists.However, the 2 groups were well

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matched with respect to all clinical pa-rameters, respiratory disease sever-ity, and DSPC pool sizes during the firstand second doses. Furthermore, to ob-tain reliable kinetic measurements,we needed to collect tracheal aspi-rates for at least 18 to 24 hours. There-fore, our design might have favoredthe selection of preterm infants withintermediate to severe RDS. Studiesare needed to analyze DSPC kinetics ininfants with less-severe respiratoryfailure and those receiving differenttypes of ventilatory support.

CONCLUSIONS

The present study compared the phar-macokinetics of different doses of por-cine surfactant (100 or 200 mg/kg) inpreterm infants with moderate/severeRDS. We found that, after administra-tion of 200 mg/kg, the half-life of ad-ministered surfactant was longer, oxy-genation was better, and the need forredosing was reduced. Further studies

are in progress to explore the possibil-ity that the higher dose alsomight leadto earlier extubations and/or fewerreintubations.

APPENDIX

The calculation of TTR from enrich-ment (E) measurements is described.At any time t, the following equationsexpress TTR and E as functions of[U-13C-palmitic acid]DPPC levels, com-ing from the surfactant dose (q), unla-beled DSPC levels, also coming fromthe surfactant dose (Qexo), and endog-enous unlabeled DSPC levels (Qendo):

TTR�t �q�t � Qexo�t

Qendo�t(1)

E�t �q�t

Qexo�t � Qendo�t(2)

Dividing the left sides of eqs 1 and 2 byQexo(t) yields

TTR�t �q�t/Qexo�t � 1

Qendo�t/Qexo�t�

E I� 1

Qendo�t/Qexo�t

(3)

E�t �q�t/Qexo�t

1 � Qendo�t/Qexo�t

�E I

1 � Qendo�t/Qexo�t(4)

In eq 4, the result given in ref 29 wasused, namely, that the percentage of[U-13C-palmitic acid]DPPC (q) with re-spect to exogenous DSPC (Qexo) re-mains constant in the system andequal to the percentage (EI) of [U-13C-palmitic acid]DPPC with respect toDSPC in the administered surfactantdose. Solving eq 4 for Qendo(t)/Qexo(t)and substituting into eq 3 yields

TTR�t � E�tE I� 1

E I� E�t(5)

which is the desired expression for TTRin terms of E.

ACKNOWLEDGMENTSThis study was supported by labora-tory core funds and by the Departmentof Pediatrics, University of Padua, for 1doctoral salary.

REFERENCES

1. Rebello CM, Jobe AH, Eisele JW, Ikegami M.Alveolar and tissue surfactant pool sizes in hu-mans.AmJRespir Crit CareMed. 1996;154(3):625–628

2. Jobe AH, Ikegami M. Protein permeability ab-normalities in the preterm. In: Effros RM,Chang HK, eds. Lung Biology in Health andDisease: Fluid and Solute Transport in the Air-spaces of the Lung. New York, NY: MarcelDekker; 1994:335–355

3. IkegamiM, Adams FH, TowersB, Osher AB. Thequantity of natural surfactant necessary toprevent the respiratory distress syndrome inpremature lambs. Pediatr Res. 1980;14(9):1082–1085

4. Pettenazzo A, Jobe AH, Ikegami M, Rider E,Seidner SR, Yamada T. Cumulative effects ofrepeated surfactant treatments in the rabbit.Exp Lung Res. 1990;16(2):131–143

5. Alvarez FJ, Alfonso LF, Gastiasoro E, Lopez-Heredia J, Arnaiz A, Valls-i-Soler A. The effectsof multiple small doses of exogenous surfac-tant on experimental respiratory failure in-duced by lung lavage in rats. Acta Anaesthe-siol Scand. 1995;39(7):970–974

6. Halliday HL, Tarnow-Mordi WO, Corcoran JD,Patterson CC. Multicentre randomised trialcomparing high and low dose surfactant reg-

imens for the treatment of respiratory dis-tress syndrome (the Curosurf 4 Trial). ArchDis Child. 1993;69(3 Spec No):276–280

7. Speer CP, Robertson B, Curstedt T, et al. Ran-domized Europeanmulticenter trial of surfac-tant replacement therapy for severe neonatalrespiratory distress syndrome: single versusmultiple doses of Curosurf. Pediatrics. 1992;89(1):13–20

8. SpeerCP, Gefeller O, GroneckP, et al. Random-ised clinical trial of two treatment regimens ofnatural surfactant preparations in neonatalrespiratory distress syndrome. ArchDis ChildFetal Neonatal Ed. 1995;72(1):F8–F13

9. Walti H, Relier JP, Huon C, et al. Treatment ofsevere hyaline membrane disease with a sin-gle dose of natural exogenous surfactant ofporcine origin: a randomized trial: immediateeffects and outcome at 28 days of life [inFrench]. Arch Fr Pediatr. 1990;47(5):329–334

10. Walti H, Paris-Llado J, Breart G, Couchard M.Porcine surfactant replacement therapy innewborns of 25–31 weeks’ gestation: a ran-domized, multicentre trial of prophylaxis ver-sus rescue with multiple low doses. Acta Pae-diatr. 1995;84(8):913–921

11. Ramanathan R, Rasmussen MR, GerstmannDR, Finer N, Sekar K. A randomized, multi-

center masked comparison trial of poractantalfa (Curosurf) versus beractant (Survanta) inthe treatment of respiratory distress syn-drome in preterm infants. Am J Perinatol.2004;21(3):109–119

12. Dunn MS, Shennan AT, Possmayer F. Single-versus multiple-dose surfactant replacementtherapy in neonates of 30 to 36 weeks’ gesta-tionwith respiratory distress syndrome.Pedi-atrics. 1990;86(4):564–571

13. Baroutis G, Kaleyias J, Liarou T, Papathoma E,Hatzistamatiou Z, Costalos C. Comparison ofthree treatment regimens of natural surfac-tant preparations in neonatal respiratory dis-tress syndrome. Eur J Pediatr. 2003;162(7–8):476–480

14. Malloy CA, Nicoski P, Muraskas JK. A random-ized trial comparing beractant and poractanttreatment in neonatal respiratory distresssyndrome. Acta Paediatr. 2005;94(6):779–784

15. Halliday HL. History of surfactant from 1980.Biol Neonate. 2005;87(4):317–322

16. Soll R, Ozek E. Multiple versus single doses ofexogenous surfactant for the prevention ortreatment of neonatal respiratory distresssyndrome.CochraneDatabaseSyst Rev. 2009;(1):CD000141

17. Kattwinkel J, Bloom BT, Delmore P, et al. High-

e956 COGO et al

. Provided by Chiesi Framaceutici S.P.A. on November 2, 2009 www.pediatrics.orgDownloaded from

versus low-threshold surfactant retreatmentfor neonatal respiratory distress syndrome.Pediatrics. 2000;106(2):282–288

18. Hallman M, Merritt TA, Pohjavuori M, Gluck L.Effect of surfactant substitution on lung efflu-ent phospholipids in respiratory distresssyndrome: evaluation of surfactant phospho-lipid turnover, pool size, and the relationshipto severity of respiratory failure. Pediatr Res.1986;20(12):1228–1235

19. Griese M, Dietrich P, Reinhardt D. Pharmaco-kinetics of bovine surfactant in neonatal re-spiratory distress syndrome. Am J Respir CritCare Med. 1995;152(3):1050–1054

20. Torresin M, Zimmermann LJ, Cogo PE, et al.Exogenous surfactant kinetics in infant respi-ratory distress syndrome: a novel methodwith stable isotopes. Am J Respir Crit CareMed. 2000;161(5):1584–1589

21. Jones PJ, Leatherdale ST. Stable isotopes inclinical research: safety reaffirmed. Clin Sci(Lond). 1991;80(4):277–280

22. Thome U, Topfer A, Schaller P, Pohlandt F.Comparisonof lungvolumemeasurementsbyantero-posterior chest X-ray and the SF6washout technique inmechanically ventilatedinfants.Pediatr Pulmonol. 1998;26(4):265–272

23. Ikegami M, Jobe A, Duane G. Liposomes of di-palmitoylphosphatidylcholine associate withnatural surfactant. Biochim Biophys Acta.1985;835(2):352–359

24. Sweet D, Bevilacqua G, Carnielli V, et al. Euro-pean consensus guidelines on the manage-ment of neonatal respiratory distress syn-drome. J Perinat Med. 2007;35(3):175–186

25. Bligh EG, DyerWJ. A rapidmethod of total lipid

extraction and purification. Can J BiochemPhysiol. 1959;37(8):911–917

26. Mason RJ, Nellenbogen J, Clements JA. Isola-tion of disaturated phosphatidylcholine withosmium tetroxide. J Lipid Res. 1976;17(3):281–284

27. Christie W. Gas Chromatography and Lipids: APracticalGuide. Ayr, Scotland:OilyPress; 1989:64–84

28. Carnielli VP, Pederzini F, Vittorangeli R, et al.Plasma and red blood cell fatty acid of very lowbirth weight infants fed exclusively with ex-pressed preterm human milk. Pediatr Res.1996;39(4):671–679

29. Cobelli C, Toffolo G. Constant specific activityinput allows reconstruction of endogenousglucose concentration in non-steady state.Am J Physiol. 1990;258(6):E1037–E1040

30. Cobelli C, Toffolo G, Foster D. Tracer-to-traceeratio foranalysisof stable isotope tracerdata:link with radioactive kinetic formalism. Am JPhysiol. 1992;262(6):E968–E975

31. Glatz T, Ikegami M, Jobe A. Metabolism of ex-ogenously administered natural surfactant inthe newborn lamb. Pediatr Res. 1982;16(9):711–715

32. IkegamiM, Jobe A, Yamada T, et al. Surfactantmetabolism in surfactant-treated pretermventilated lambs. J Appl Physiol. 1989;67(1):429–437

33. Jobe AH, Ikegami M, Seidner SR, Pettenazzo A,Ruffini L. Surfactant phosphatidylcholine me-tabolism and surfactant function in preterm,ventilated lambs. Am Rev Respir Dis. 1989;139(2):352–359

34. Kramer BW, Ikegami M, Jobe AH. Surfactant

phospholipid catabolic rate ispool sizedepen-dent in mice. Am J Physiol Lung Cell MolPhysiol. 2000;279(5):L842–L848

35. Seidner SR, Jobe AH, Ruffini L, Ikegami M, Pet-tenazzo A. Recovery of treatment doses of sur-factants from the lungs and vascular com-partments of mechanically ventilatedpremature rabbits. Pediatr Res. 1989;25(4):423–428

36. Cogo PE, Zimmermann LJ, Meneghini L, etal. Pulmonary surfactant disaturated-phosphatidylcholine (DSPC) turnover and poolsize in newborn infants with congenital dia-phragmatic hernia (CDH). Pediatr Res. 2003;54(5):653–658

37. Jobe AH, IkegamiM, Jacobs HC, Jones SJ. Sur-factant pool sizes and severity of respiratorydistress syndrome in prematurely deliveredlambs. Am Rev Respir Dis. 1983;127(6):751–755

38. Bunt JE, Carnielli VP, Janssen DJ, et al.Treatment with exogenous surfactantstimulates endogenous surfactant syn-thesis in premature infants with respira-tory distress syndrome. Crit Care Med.2000;28(10):3383–3388

39. Cavicchioli P, Zimmermann LJ, Cogo PE, et al.Endogenous surfactant turnover in preterminfants with respiratory distress syndromestudiedwith stable isotope lipids. AmJRespirCrit Care Med. 2001;163(1):55–60

40. Verlato G, Cogo PE, Pesavento R, et al. Surfac-tant kinetics in newborn infantswith pneumo-nia and respiratory distress syndrome. ItalJ Pediatr. 2003;29(11):414–419

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PEDIATRICS Volume 124, Number 5, November 2009 e957

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DOI: 10.1542/peds.2009-0126 2009;124;e950-e957; originally published online Oct 12, 2009; Pediatrics

Rondina, Aldo Baritussio, Gianna Maria Toffolo and Virgilio Paolo Carnielli Paola Elisa Cogo, Maddalena Facco, Manuela Simonato, Giovanna Verlato, Clementina

Distress SyndromeDosing of Porcine Surfactant: Effect on Kinetics and Gas Exchange in Respiratory

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