CVVH.docx

CVVH.docx

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CVVH

CVVH1/03

Anotherone!

Asusual,pleaserememberthatthepreceptorisnotthefinalauthorityonanythinginanyway–justold,beat-up,andover-experienced.（WhatisthatnoiseImake,anyway?

Probablygoingtoneedanewtransmissionsoon.Mightnotbeworthit.）

Thesequalificationsdonotequal“correct”–checkwithyourownreferences,andletusknowwhenyoufindthingswrong.Thistimetherewillprobablybelots!

Also–thisarticlewaswrittenwithourcurrentmachineinmind.Ifthatchanges,we’llupdateit.

BasicIdeas

1-WhatisCVVH?

2-Whatis“renalreplacementtherapy”?

3-Whydokidneysshutdown?

-Pre-renal

-Intra-renal

-Post-renal

4-Whatisdialysis?

5-Whatisdialysate?

6-Whatisultrafiltration?

Hemofiltration?

7-WhatisSCUF?

8-IsCVVHthesameashemodialysis?

9-WhyuseCVVHinsteadofhemodialysis?

10-Whatiscreatinineclearance?

11-Whatisthe“filtrationspectrum”?

12-WhatwillCVVHclearfromapatient’sblood,andwhatwon’titclear?

13-WhatarethemainreasonsforstartingapatientonCVVH?

Hardware

14-Whatisthebasichardwaresetup?

15-Whatisthebloodpath?

16-Whatistheultrafiltratepath?

17-Whatisthefluidreplacementpath?

18-Whichmachinedoweuse?

19-WhatisaPrisma?

20-WhatisaQuintoncatheter?

21-DoesitmatterwheretheQuintonisplaced?

22-Whatisthecatheterflushedwith?

23-Whatisthehemofilter?

24-Whatarethetwospacesinthefilter?

25-Whatisthemembrane?

26-Whatisthetransmembranepressure?

27-Whatisthe“bloodflowrate”?

28-Whatisthe“turnover”?

29-Whatistheairdetectorfor?

30-Whatisthebloodleakdetector?

31-Whatareallthetransducersfor?

32-Whatdoesthearterialtransducertellme?

33-Thevenoustransducer?

34-Whatabouttheothertwotransducers?

35-Whatisthecircuitheaterfor?

36-HowdoIprimethecircuit?

37-WhywouldIprimewithheparinorwithoutit?

38-HowdoImakesurethatthecircuitisreadytorun?

ChoicesofTreatment

39-Whywouldmypatientgetcitratereplacementfluid?

40-Whatis“citratetoxicity”?

41-Whywouldshegetbicarbreplacement?

42-IfI’mrunningheparinintothecircuit,amIanticoagulatingthemachine,thepatient,orboth?

43-Whatifthepatientisalreadyonheparin?

44-Howdotheyfigureouthowmuchfluidtogiveortakeoffeveryhour?

45-Howdothepatient’sCVP,PCWandhematocritcomeintothatdecision?

UpandRunning

46-HowdoIprepthecatheterbeforestartingupthemachine?

47-HowdoIgetthingsstartedup?

48-HowdoIcalculatethefirsthour’sfluidremoval?

49-HowdoIcalculatetheTBBuptothepointwheretheCVVHstarted?

50-HowdoIfigureoutwhatratetostartthecalciumdripat?

51-HowshouldItakecareoftheQuinton?

52-Howlongcanasystemstayup?

53-Whatisspecifictorunningacitratesystem?

54-Abicarbsystem?

55-WhatcanIinfusethroughthecircuit,andwhatcan’tI?

Labs

56-WhatlabsdoIneedtolookatbeforeIstartmypatientonCVVH?

57-Whataboutlabswhilethesystemisupandrunning?

58-Whatabouthemes?

Problems

59-Whywouldthemachine“godown”?

60-Aretherewaysthatcanbeprevented?

61-Whatifthemachinegoesdown,andIcan’tfigureoutwhat’swrong?

62-Whereareclotslikelytoforminthecircuit?

63-Whatdoesitmeanifthearterialpressurestartsgettingverylow?

64-Whatifthevenouspressurestartsgettingveryhigh?

65-Whatifbloodbacksupintooneofthetransducers?

66-Bothtransducers?

67-CouldsomethingbewrongwiththeQuinton?

68-WhatdoesitmeaniftheTMPstartsgettingveryhigh?

69-Whatiftheairdetectorstopsthemachine?

70-Whatifthebloodleakdetectorgoesoff?

71-Whatiftheheateralarmgoesoff?

72-WhenshouldIstartthinkingabouttakingthesystemdown?

73-WhatshouldIdoifIthinkthesystemisgoingtocrash?

74-Couldsomethingonthemachinepop,andspray?

BasicIdeas

1-  WhatisCVVH?

 “ContinuousVeno-VenousHemofiltration”isasubstituteforhemodialysisthatrunscontinuouslyonamachinethatstandsatthebedside.Therearedifferentkinds,allcomingunderthegeneralheadingof“renalreplacmenttherapy”.

That’sitthere,ontherightsideofthebed.

http:

//www.aic.cuhk.edu.hk/web8/cvvh.JPG

2-  Whatis“continuousrenalreplacementtherapy?

”?

Iguessthathemodialysisandperitonealdialysisweretheonlygamesintownforalongtime,butnowadayswe’reeversomuchmoremodernthanthat,andthereareseveralmethodsaroundfordoingwhatthekidneyswouldordinarilydo.

Weonlyuseoneofthematthebedsideinourunit:

CVVH;it’scalled“V-V”becauseitrunsfromvein-to-vein.Systemsthatwedon’tuse:

an“arterio-venous”method（CAVH）,meaningthatthecircuitofbloodrunsfromanartery,tothemachine,andbackintothepatientthroughavein,andathirdtreatmentcalled“SCUF”:

“SlowContinuousUltrafiltration”,whichdoesn’tuseabloodpumptheywayoursystemdoes–it’sdriveninsteadbythepatients’ownbloodpressure.

It’simportanttopointoutthatwhatwe’redoingwiththissystemisn’tdialysisexactly;it’sactually“hemofiltration”,alsocalled“ultrafiltration”.Dialysisandfiltrationworkondifferentprinciples,andwe’lllookatthosebrieflyinabit.Sufficetosay,we’vefoundthatoursystemworksquitewelltoclearuremicwastesinpatientswhosekidneyshavequitforonereasonoranother.

3- Whydokidneysshutdown?

Rememberallthatstuffaboutpre-renal,intra-renal,andpost-renal?

Theydescribethethreemainwaysthatkidneysgethurt.Thefourthwayistoxicity,butwe’llleavethatforthetoxFAQthatoughttocometogethersomeday.

Onceagain,（andasalways,“withalotofliesthrownin”）,thisstuffisn’tthathardJustthinkofwheretheurinecomesfrom,andwhereitgoes:

Pre-renalstuffhastodowiththebloodsupplyarrivingtothekidney,here…attheartery.

Intra-renal:

badthingsarehappeningwithinthestructureofthekidney–ATN,thatkindofthing.

Postrenalstuffhappenshere,wheretheurineistryingtoflowouttowardstheoutsideworld…

Pre-renal:

Infrontofthekidney.Theurineiscomingfromthebloodstream–beforeitreachesthekidney.Mostoftentheproblemissimplythatthereisn’tenoughbloodvolumeinfrontofthekidney–reachingit.Thepatientisdry.RemembertheBUN/creatinineratiothing?

Nottoohard.PuttheBUNoverthecreatinine,likeso:

10/1.0–soyoucouldcallthattentoone.

Nowtrythisone:

100/1.0–ahundredtoone.Thisoneis“way”dry–thepatient’skidneysareworking,youknowthatbecausethecreatinineisstillnormal（won’tbeforlong!

）.ButtheBUNis,aswesayinMA,wickedhigh–meaningnotanexcessofBUNsomuchasalossofwater.Thispatientmighthaveahematocritof50–it’snotthatshehastoomanyredcells,butthatshe’slostalotofthewaterthattheyshouldbefloatingaroundin.

Intra-renal:

Insidethekidney,wheretheurineisbeingmade.Thekidneyitselfhas“takenahit”–inourpatientsthisusuallytheevilATN:

AcuteTubularNecrosis,usuallyfromhypotension.Ihateitwhenthathappens.Itturnsoutthatkidneysareverysensitivecreatures;theydon’ttoleratebeinginsulted（“Stupidkidney!

”）,andtheyfailifthey’reunderperfusedforanyseriouslengthoftime.Itvaries,butsometimesitseemsthatanelderlypatientwhobecomeshypotensivefor20minuteswilldevelopkidneyfailure.

Probablyrelated:

itseemsasthoughsomepatientswithhypertensionatbaselinedon’tmakemuchurineatwhatwewouldconsidernormalMAPs,butturnintoNiagaraFallswhentheirpressurerises–maybeforthehourwhenyouweredoingtheirbath.Theinterpretationputonthisisusuallythatthesepeoplearetheoneswithrenalarterystenosis:

theirkidneysareusedtoseeingahigherperfusionpressuremostofthetime,andeventhoughthey’renotfailingyet,exactly,they’restillnotdoingtheirstuffatwhattheythinkarehypotensivepressures.Makessense,inthatavasculopathwithbadcoronariesmayhavebadrenesforthesamereason.Ithinkitwasin“TheTennisPartner”thatIreadAbrahamVerghese’sdescriptionoffeelingapatient’sradialarterialpulse,andtryingtointuithowmuchdiffusevasculopathyshemighthavefromthefeeloftheradial’sstiffness.That’srealdoctoring!

PostRenal:

Afterthekidney–enoughbloodgotthere,theurinegotmadeokay,butnowit’shavingtroublegettingout,afterthekidney.Maybeaureterisblocked（oof–Iknowaboutthatone!

）,maybetheurethraisblocked.Flushthefoley!

4- Whatisdialysis?

It’saninterestingthingaboutmolecules–they’readventurous.Theywanttogoplaces.But–andthey’reveryseriousaboutthis-it’sreallyimportantforthemtospreadthemselvesaroundevenly;theywanttotravelwiththeirfriends,ornotatall.Iftheyseeaplacewherethey’reunder-represented,overacrossyondersemi-permeablemembraneforexample,（Montana,maybe）,well,offthey’regonnago,untilthere’sjustasmanyoverthereacrosstheborderinMontanaasthereareoverhereinIdaho.Wyomingmaybe.Nice,compulsivelittleICU-personalitymolecules–socute.

http:

//www.chem.umass.edu/~botch/Chem112S05/Chapters/Ch14/Osmosis2.jpg

That’sthebasicideabehind“diffusionacrossaconcentrationgradient”.Whycan’tthesepeoplejustspeakEnglish?

Ifthere’stoomuchmoleculesoverhereonthisside,andnothardlynoneof‘emoveronthatside,whythen,they’rejustgonnagetupandgooveracrossthere–it’swhattheydo,astheGreatPhysicistdecreed,waybackthereintheBang.

Ofcoursethemembranehastohaveholesinittolet‘emthrough,right?

Justtherights