Table Of ContentHindawiPublishingCorporation
AnesthesiologyResearchandPractice
Volume2011,ArticleID371594,4pages
doi:10.1155/2011/371594
Research Article
The Effect of Airway Pressure Release Ventilation on
Pulmonary Catheter Readings: Specifically Pulmonary
Capillary Wedge Pressure in a Swine Model
AhmadM.Slim,ShaunMartinho,JenniferSlim,EddieDavenport,
LuadinoM.Castillo-Rojas,andEricA.Shry
CardiologyService,BrookeArmyMedicalCenter,3851RogerBrookeDrive,FortSamHouston,TX78234-6200,USA
CorrespondenceshouldbeaddressedtoAhmadM.Slim,[email protected]
Received15November2010;Revised10January2011;Accepted15January2011
AcademicEditor:ChristophK.Hofer
Copyright©2011AhmadM.Slimetal. This is an open access article distributed under the Creative Commons Attribution
License,whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperly
cited.
Background.Airwaypressurereleaseventilation(APRV)isamodeofmechanicalventilationthattheoreticallybelievedtoimprove
cardiacoutputbyloweringrightatrialpressure.However,hemodynamicparametershaveneverbeenformallyassessed.Methods.
Sevenhealthyswinewereintubatedandsedated.Abaselineassessmentofconventionalventilation(assistcontrol)andpositive
end-expiratorypressure(PEEP)of5cmH Owasinitiated.VentilatormodewaschangedtoAPRVwithincrementalelevations
2
of CPAP-high from 10 to 35cm H O. After a 3-to-5-minute stabilization period, measurements of hemodynamic parameters
2
(PCWP,LAP,andCVP)wererecordedateachlevelofAPRVpressuresettings.Results.IncreasingCPAPcausedincreasedPCWP
andLAPmeasurementsabovetheirbaselinevalues.MeanPCWPandLAPwerelinearlyrelated(LAP=0.66∗PCWP+4.5cmH O,
2
R2=0.674,andP<.001)overawiderangeofhighandlowCPAPvaluesduringAPRV.Withreturntoconventionalventilation,
PCWP and LAP returned to their baseline values. Conclusion. PCWP is an accurate measurement of LAP during APRV over
variablelevelsofCPAP.However,PCWPandLAPmaynotbeaccuratemeasurementsofvolumewhenCPAPisutilized.
1.Background pressure is reflective of left atrial pressure (LAP). Left atrial
pressureisreflectiveofleftventricularend-diastolicpressure
Theeffectsofpositivepressureventilationonhemodynamic (LVEDP), which is a measure of preload, and preload is an
parameters are known to be complex. They are determined estimation of volume. These relationships hold true when
by an integral relationship betweenvascular resistance and cardiac compliance is constant and pulmonary capillary
intrathoracicpressure[1,2]. pressureisgreaterthanalveolarpressure[4].
Positivepressureventilationincreasesintrathoracicpres- Other effects of positive pressure ventilation can be less
sure (ITP), which increases right atrial (RA) pressure, beneficial. For example, juxtacardiac ITP due to hyperex-
leading to a decrease in venous return. Subsequently, this panding lungs can decrease left ventricular diastolic com-
decreasedrightventricle(RV)fillingdecreasesleftventricle pliance and subsequently impair LV contractility [2]. In
(LV) preload and allows for greater LV contraction with somestudies,thishasbeenassociatedwithdecreasedcardiac
decreased energy expenditure. In patients who are volume output[5].Also,positiveendexpiratorypressure(PEEP)can
overloaded, this could be beneficial. However, in hypov- induce regional hyperinflation, which compresses alveolar
olemicpatients,thismayinducecardiovascularinsufficiency vessels and increases pulmonary vascular resistance (PVR),
[2, 3]. Therefore, knowledge of the volume status of which can potentially lead to RV failure, or cor pulmonale
mechanicallyventilatedpatientsisessential.Oncriticallyill [2].
patients, pulmonary artery catheters (PACs) can be used Despite these hemodynamic effects, mechanical ven-
for hemodynamic monitoring. Pulmonary capillary wedge tilation improves pulmonary gas exchange and restores
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4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
The Effect Of Airway Pressure Release Ventilation on Pulmonary
5b. GRANT NUMBER
Catheter Readings: Specifically Pulmonary Capillary Wedge Pressure In
A Swine Model 5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
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13. SUPPLEMENTARY NOTES
Anesthesiology Research and Practice, Volume 2011
14. ABSTRACT
Airway pressure release ventilation (APRV) is a mode of mechanical ventilation that theoretically believed
to improve cardiac output by lowering right atrial pressure. However, hemodynamic parameters have
never been formally assessed. Methods. Seven healthy swine were intubated and sedated. A baseline
assessment of conventional ventilation (assist control) and positive end-expiratory pressure (PEEP) of 5 cm
H2O was initiated. Ventilator mode was changed to APRV with incremental elevations of CPAP-high from
10 to 35 cm H2O. After a 3-to-5-minute stabilization period, measurements of hemodynamic parameters
(PCWP, LAP, and CVP) were recorded at each level of APRV pressure settings. Results. Increasing CPAP
caused increased PCWP and LAP measurements above their baseline values.Mean PCWP and LAP were
linearly related (LAP = 0.66∗PCWP + 4.5 cm H2O,R2 = 0.674, and P < .001) over a wide range of
high and low CPAP values during APRV. With return to conventional ventilation PCWP and LAP
returned to their baseline values. Conclusion. PCWP is an accurate measurement of LAP during APRV
over variable levels of CPAP. However, PCWP and LAP may not be accurate measurements of volume
when CPAP is utilized.
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2 AnesthesiologyResearchandPractice
30 pressure(MAP)andcentralvenouspressure(CVP),respec-
tively. Then, a Medtronic 8 French transseptal sheath was
25 introducedthroughatrialseptumandconnectedtopressure
transducer to continuously record LAP. Finally, pulmonary
g) 20 arterycatheterwasadvanceduntildistaltipwasplacedinto
H
m thepulmonaryartery,radio-graphicallybelowthelevelofthe
m
( 15 leftatria,formeasurementofPCWPattheendofexpiration.
e
ur All connections to the pressure transducer were zeroed
ess 10 andmeasurementsconfirmed.Thepressuretransducerwas
Pr
zeroed at the level of the atria prior to obtaining measure-
5 ments.Theanimalswereplacedonconventionalventilation
(assisted control) with tidal volume 6cc/kg and PEEP of
0 5cmH2O.MeanPCWPandLAPwererecordedasbaseline
5 10 15 20 25 30 35 40 values. APRV protocol initiated with changing CPAP-high
HighPEEP/lowPEEP=5cmH2O from 10 to 35cm H2O and CPAP-low varied from 5 to
30cm H O in 5 unit increments with a ratio of T to
LAP 2 High
T of4:1.Hemodynamicparameterswererecordedfor30
PCWP Low
secondsaftereachAPRVpressurechangefollowingaperiod
of stabilization that ranged from 3 to 5 minutes. Linear
Figure1:IllustrationofvariabilityinLAPandPCWPashighPEEP
isincreaseswithconstantlowPEEPof5cmH O. regression analysis (Sigma Stat version 3.1) was employed
2
to assess changes in mean PCWP and mean LAP with
increases in high PEEP and at constant low PEEP (5cm
H O).TherelationshipbetweenmeanPCWP(mmHg)and
2
arterial blood acid-base balance. There are many modes
LAP (mmHg) was assessed by regression analysis for each
of mechanical respiratory support but airway pressure
animaltoassessindividualvariabilityandallanimalspooled
release ventilation (APRV) has offered clinical advantages withARPV.Pvalues<.05wereconsideredsignificant.
for ventilator management of acute lung injury (ALI) and
acute respiratory distress syndrome (ARDS) in comparison
3.Results
to conventional mechanical ventilation [6, 7]. APRV is a
method of ventilation that uses continuous airway pressure
With increasing levels of CPAP during APRV, mean PCWP
in time-released cyclical fashion that was first described in
andLAPincreasedinresponsetoincreasingairwaypressure.
1987[8].Thismodeofventilationistheoreticallyknownfor
Mean PCWP and LAP of the group were linearly related
improvedventilation-perfusionmatchingthroughimproved (LAP = 0.66∗PCWP + 4.5cm H O, R2 = 0.674, and P <
2
alveolar recruitment, leading to improved airway exchange. .001)overawiderangeofhighandlowCPAPduringARPV
Manyadvantagesofthismodehavebeendescribed,suchas: (Figure1).Theslopeofthisregressionlinedifferedwitheach
lower airway pressures, lower minute ventilation, minimal
individual animal (Figure2). A Bland-Altman analysis also
adverse effects on cardiocirculatory function, ability to
demonstratesagreementbetweenmeanPCWPandLAPover
spontaneously breathe throughout the entire ventilatory
a95%confidenceinterval(CI).
cycle, decrease of sedation use, and near elimination of
neuromuscular blockade [6, 7, 9]. In addition, APRV is
4.Discussion
theoreticallybelievedtoimprovecardiacoutputbylowering
the right atrial pressure and improving preload due to
Toourknowledge,thisisthefirststudytoevaluatechangesin
decrease of pleural pressures and increase in abdominal
cardiovascularparameters during increasing levels ofCPAP
pressure[9].
with APRV mode of ventilation. The linear relationship
TherelationshipbetweenLAPandPCWPhasnotbeen
betweenPCWPandLAP,conferredbytwomethodsofagree-
formally assessed with APRV. In this study, we compare
ment,demonstrateshowPCWPisanaccurateassessmentof
PCWP with LAP in a swine model while APRV mode
LAPwithAPRVmodeofventilationoverCPAPrangesof10
of ventilation is used to establish the reliability of this
to35cmH O.Theindividualizedrelationshipbetweenthese
2
measurementinestimatingvolume.
values for each animal likely represents the unique cardiac
andpulmonarycomplianceofeachanimal.
2.Method This experimental swine model also demonstrates that
increasing levels of CPAP transpire to elevations of PCWP
Seven 30–45kg male swine were sedated with propofol to and LAP from baseline values. Since no interventions
facilitatetrachealintubationandinstrumentation.However, in volume were made during this assessment and these
musclerelaxantswerenotgiventotheanimalssotheywere values returned to baseline when convention ventilation
able to ventilate spontaneously. A pressure transducer was was restored, this suggests that the temporary elevation in
placed down the endotracheal tube and used to monitor thesepressureswasnotcausedbypermanentvolumechange
meanairwaypressure(Paw).Rightandleftfemoralarterial but by temporary pressure change (Figure3). Also, when
andvenousaccesseswereobtainedtomonitormeanarterial evaluating pressure changes during periods of T and
High
AnesthesiologyResearchandPractice 3
30 at placement were aborted in study model. Despite these
limitations, thewaveformtracingsclearlydemonstratehow
25 increased positive pressure increases hemodynamic param-
eters without any changes in volume status. Future studies
20 withanimalmodelsmimickingARDSareplannedtoaddress
g)
H theselimitationsanddefinethechangeincardiacoutputand
m
m 15 leftventricularchambersizewithAPRV.
(
P
A
L 10 5.Conclusion
PCWPaccuratelyreflectsLAPduringAPRVwithincreasing
5
LAP=0.66×PCWP+4.5mmHg CPAP. However, PCWP and LAP may not be accurate esti-
N=143;R2=0.674;P<.001 matesofvolume.ThepoorcorrelationofPCWPtoleftven-
0
0 5 10 15 20 25 30 tricularend-diastolicvolumeinpatientswithelevatedPEEP
PCWP(mmHg) is a well-investigated finding under conventional modes of
ventilationandappearstoholdtruewithAPRV.Whetherthis
Pignumber1 Pignumber5
disparityissecondarytothehypotheticalinfluencesofITPor
Pignumber2 Pignumber6
cardiopulmonarycompliancehasyettobedemonstrated.
Pignumber3 Pignumber7
Pignumber4 Alldata
Abbreviations
Figure2:Regressiondatacomparingleftatrialpressure(LAP)to
pulmonarycapillarywedgepressure(PCWP). ALI: Acutelunginjury
ARDS: Acuterespiratorydistresssyndrome
APRV: Airwaypressurereleaseventilation
30 CVP: Centralvenouspressure
CPAP: Continuouspositiveairwaypressure
25
ITP: Increasesinintrathoracicpressure
20
LAP: Leftatrialpressure
O) 15 LV: Leftventricle
H2
LVEDP: Leftventricularend-diastolicpressure
m 10
(c MAP: Meanarterialpressure
e 5
ur PAC: Pulmonaryarterycatheters
ess 0 PEEP: Positiveend-expiratorypressure
Pr AC APRV AC
−5 PCWP: Pulmonarycapillarywedgepressure
RA: Rightatrial
−10
RV Rightventricle
Time(s) RVR: Rightventricularresistance.
PCWP LAP
CVP Airway
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