115 Early Detection of Cerebral Ischemia During Carotid Endarterectomy Using Transcranial Doppler Sonography and Somatosensory Evoked Potentials A. Thiel. W Russ. If. W ,\'estle -, and G. Jlempelmann nepertmem of Anarslhl"!iiol0lO' I nd Imens jve Care Mt"die inl' • Depan mem orCa rdiouscular Surgl'f)' Summa r)' Cerebral function du ring carotid enda rt erectomy ca n reliably be mnnitnred using soma tose nsory evoked potentials (SEI'). 'rrauscranta t Doppler sonograph y (TeD) is a noninvasive method providing on-line dat a about ce rebral hemodyna mics. The combination of both tech niques dur ing ca rotid surgery is hr lpful in evaluating the he modyna mic r' tnp ut") an d the func- tional ,"outp un consequences of ca rotid cla mping withi n a short time . In the presen t report, combined Ten a nd SEP monitoring ea rly detected It'fi he mispheric isc he mia in a 68-)'ea r -old woma n subjected to len ca rot id endarterectomy. The imp a irment of cere bral perfusjon occurred bcrc re ca rotid cla mping due 10 a n intraope ra tive thrombos is of th l' len inte rn al ca rotid a rtl' ry as co uld be revealed ane r declarnping . A te mporary sh unt was not inse rted . Postoper atively. the patient had a new tra nsie m neurological deficit. In this case, TCD co rrect ly indicated ce rebra! ischemia as eonnrmed by SEP reco rd ing. f or carotid arte ry surgery , combined Tel> an d SEP ma y be helpful in detect ing those pa tie nts who will profit from temp or ary shunt ing if th is is not done routinely. I'ril hprlo.rnnu ng l'inl' r ze rebralen 1S('h iim h' mmcls tr an sk r anit'lIl'r no ppterse nc grap hto und som amsensorisch p\'lillt' r lt' n Puu-nrlalen wiihrl' nd Karotls(l pl' ration nre nuraoporattvc Dbcrwa chung dor Ilirnfu nktion bpi Th rombendartcrtcktornfon der Ka rous gab ol ba siert im wes c ntltc bon auf ham od ynamisch bzw. elek tr oph ys iologisrh orientierll' n MI,thudl'll. lJil' Ableitung der sumatosensorisrh evozierten I'ott'nt ialc ISEI' I na r h Stimu lat ion de s N. m('dia nus zeigt die funktillnd ll'll Auswirk unge n l'in er d rohe odl'n ze rebralen Isch limie mit hoh l'r Se nsitivitiit und Spl'zilitlit an . Mit de r tra nskra nielll'n I:lupp lersonog raph il' tTCDI ste ht sri t t'in igt'n Ja hr t'n t'in noninvasin's Verfah re n zur Vl'rfugung, da s d UTC h Mt'ss ung der In t r od u c ti o n I'\e w neurologi cal d e(j cit s afte r ca r oti d e n da rte recto m y h a ve remained a seri o us problem d e spite imp roved s u rgica l a n d a nat's thetic techniques . In o r der to m on ito r c e r e h r a l func t io n in t r a o p e r a ti vely. va r ious m ethods have he en propo s ed includ in g the el ectr oence p h al og ram IEEG) in it'> r aw o r co m p u te r -assis ted fo r m s. Co m p a red to com p ute r iz ed EEG ThuflU:, ca rdiovasc. Surgeun 37 (1989I t I5- l l l1 \£I (;l'or l(Thil'lIle Verlag Slullgar1' Nl'WYurk mut nuBgeschwi ndig keit in bastsnahen Ilirng t'ni13e n ein e kon unule rhr he Beurteilu ng de r znrebr ah-n Ila rnodyna mik gestauet. Die Komb inat ion border Methoden erla ubr. sowoh t die hamod ynamischen I' Tnput"] als au ch diu funktionellen I''output"! Effekte der Abklem rnung dee A, ca rotis int. innerhalb kurzer Ze il zu beuneilen. Dor voruegende Benc ht bes ch retb t d ie Anwrnd un g de r stm uha nen Ablcit ung von 5EI' und TCII br i om er 6Rjiihrillr n Pa ucnun. d ie sich a ufgrund rezidivk-ren de r n ensnonsc h ischa nnsc ber Auacke n eme r Desoblne reuon dcr lm ken Ka rotisga bel unt erztehe n muBte. Nach zuna r hs t una ulT.i lligrn Ausga ngsbefunde n von SEP und Tel) zu Begtn n der Opereuon tra t be rens vcr Ab Ul' mm ung dcr A. carotis int. elnc knnscho vorand erun g de r TCI),Paraml'le r auf. Der so ermlnehe vordacbt au f eine drohe nde tscham te de s llnken Media-Stromgebietes wurde dUTCh d ie Ableitung der 5EP bl'stitigt . Die medtkamentosc Anhe bu ng des artertetle n Blutdruckes lo nnie dte se v e ran deru ngen nieh t vo!ls\iin dlg beSl'itil!:t'n . n it' Abklr- mm ung der A . ca rol is int . im weiteren verlaur der Dperanon hane keinen Einnu B auf die SF-P- und TCJ)' \\'l'rtt', so daB auf die Einlagt' emes te mpcr a ren intralumi nalen Shunts \,t'r-/iC" htt' t wurde. Als Ursac he cteser une rwartet au fgctre tem-n ze re bra k-n lscha rme konme et ne intraope rauv entsta ndr-ne Thrombose der A, ca rotis im . gcskhen werd en . Postoperanv haue d ie Pa tientin t-in ne ues neurologisches Dcflztt. das innvrhalh von 24 Stunden fast vollstiind ig rcve rsfb et wa r . Der vorhegendo f'all zl'igt. da 8 mit dl'r TCll ctn c drohcnd c zercbrale Ischiim ie korrr kt c rkannt worden konn to.Im Ra hme n dc r Karotischiru rgic kon ntc die komblnk-rte Anwen dung von SEI' und TCD helfen. int raoper ati v feslzustdl r n . welcher Patie nl vun der Ein lage einl's ShuOls hiimod ynamisr h prolilie. rt'n wlird e. Dies gilt a ller d ings nur mr dl'n Fa ll. daB nicht routi· Ol' miiBig ~gcsh u n l{'\M wird . K (')' ",or ds Carot id e nda rtl'fl"Ctomy - SomatOSl'nsory I'vukl>d ~IP n t ials ­ Tran sr ran ia l Doppll' r sonog rap hy a n a lys is . somatose n sory e vo ked potent ia ll SEPI reco rd in g is m o re sens itive a n d s pecific in d ell'cting ce r e h r a l isc h £'mia du ri n g ca r ot id enda rtectomy and pro vides prog n o sti c in form ati on conce r ni n g th e postope r ati ve n e u rolog ica l statu s (8 ), \ Vh ere a s e lec t r o physio lo gic al met hods measu re the fun ct ional Moutpu t ~ of cereh ra l ischem ia , s ever a l s tu d ies M h a ve bt~tm u nd ertake n to e va lua te thl' Min p u t i.e. ce n ' h ra l hem ody na mics d u r ing ca r oti d end arte recto my (6 , 91. Downloaded by: National University of Singapore. Copyrighted material. Justus-Lleblg-Universlty, Gil' !>.w n, I' RG norae. cordim}(} sc. SlIrgeoll.17 (1989 ) Recently. transcrantat Doppler sonography \TCD), as a noninvasive metho d providing on-line data about flow velocities in basal cerebral arteries, has bee n app lied to carotid surg ery 13, 7, to). In the following case, combin ed SEP and TCD monitoring detected early dur ing carotid endarterectomy cerebral ischemia caused by intr ao perat ive thrombosis of the internal carotid artery distal to the clamp. Case pr esentation A 68-year-old woman (weight 78 kg, height 166 cm) was admitt ed for left carotid endarterectomy. She had had a reversible neu rological deficit (RIND) 3 weeks before and multiple episodes of left-hemispheric tra nsitory ischemic attack s lTIA). Preoperative angiography revealed a 90 % stenosis of the left internal carotid artery and a 80 %stenosis contralatera tly. The EEG showed a mild focus on the right temporoprecentral region and cra nial comp uted tomog raphy revealed a subcortical infarction without clinical symptoms. Just priur to operation she suffered a TIA related to the right hemis pher e. After oral premedication with lOm g diazepam, a nesthesia was induced with 375mg thiopentone and 2mg veeuronium an d maintai ned with isoflurane (0.5-1 .0%). Intubation was facilitated using 80mg succinylcholine. Further muscle relaxation required an other 6mg of vecuro nium . Hypocapnic ventilation (paCOl '"' 30mml lg) was controlled by endtidal CO 2 rccordtng u.apnolog. Draeger Co.I and arterial blood gas analys is. Arterial blood pressure was reg iste red continuously via a 22(; catheter placed in the right radial artery. Somatosens ory evoked potential s (SEP)were recorde d after right median nerve stimulation at the wrist using a NICOLET CA 1000 ave rager. Stimulation rate was 3.1Is and duration 0.2ms using constant cur rent of 19.9 mA. Filters were set at :10 1lz and 1500 liz. Analysis time was 75ms after stimulus. Accordin g to the Intern ational 1n-zu- system . surface electrodes were placed to obtai n cortical (C3') and cervical (IIWK2) SEP's both referenced to frontal central (F2). The right elbow served as a ground . Latencies and amplitudes of both cortical and cervical SEP were evaluated using an oscilloscope cursor. Central conduction time (CCT), which is the tran sit time of the afferent volley between cervical spine and cortex , was calculated as the difference of N20 (cortical) and N14 Icervicall. Before clamping of the intern al carotid arte ry, 256 responses were averaged to obtain baseline values. After clamping. 100 averages were suffic ient to produce stable SEI'. For further methodological information see (4)and (8). Trunscranta l Doppler sonograpby (TCll ) was performed tran stemporatly by a pulsed 2-Mllz device cre 2-64, EME Co.]. The blood flow velocity of the middle cerebral artery (MCA)was recorded using a handheld Doppler probe placed just above the zyg-omatic arch. Depth was set at 50 mrn to obtain transcranial Doppler signals of the Mlsegme nt of the MeA. We avoided an exact identification of the vessels insonated by carotid compression because of possible cerebral embolization. Time-averaged value s of mean flow velocity Icm/s l and pulsatility (systolic/diastolic flow velocity) were calculated automatically, whereas systolic blood flow velocity was determined by setting a cursor on the TCD oscilloscope. Detailed infor mation rega rding Te D method s can be taken from the literature (1 , 5l. A. Thiel. W Russ. II. ~v. Nestle, G. tt emp etmcnn Baseline values ofS EP and TCD(MCA flow velocities of both sides) were reco rded before surgery and showe d no abno rmalities (Fig. 1). At the beginning of surgery, the pat ient ha d arteri al hypert en sion (RR 200/ 110mmHg) which was treated with vasodilators (nitroglyceri ne 0.1 mg! min) thus loweri ng her arterial blood pressure to the postinduction level (H B 150/80 mmUgl. lO min late r, duri ng preparation of the carotid bifurcation , TCD showed a mar ked reduction of the ipsilateral MCA mean blood flow velocity compared to the preceedtng values . The pulsatility of the obtained ultrasound wave form was reduced from 1.9 to 1.5 (Fig. 2). A critical reduction of left MCA perfusion indicated by TCDwas verified using SEP which now showed a ma rked depression of the primary cortical response with a complete loss of middle latency compon ents (Fig. 3). With the internal carotid artery still under preparation and unclamped we had no explanation for this unexpected cerebral ische mia. Raising the patient' s arterial blood pressure to 195/95 mm Hg slightly imp roved both TCDan d SEP parameters but could not nor malize them. 13 min later, 7500 units of heparine were given 1. v. an d the internal ca rotid artery clamped for 24 min withou t any effects on TCDor SEP values (Fig. 3, Fig. 4). For this reason, we felt that temporary intralum inal shunting would not improve the situation. Carotid endarterectomy and patch enlargemen t as routinely done were performed without surgical problems . The internal carotid artery wa s then declamped to allow retrograde bleeding. Unexpectedly, no bleeding was seen until the vessel had been digitally mass aged for a few seconds thus removing a thrombus which had totally uccluded the lumen. After carotid declam ping, TCD now showed a mar ked acceleration of MCA blood flow velocity which ret urned to nea r baseline value s within the following 7 min (Fig. 5). These cha nges were associated with improved cortical SEP. However , the am plitude of the primary cortical complex was . ccr , :; ~~<;" ,~~ ~~".., " Fig. 1 BaselineTeO (a) and SEP(b}recordings after inductionof ana esthesia andbetoresurgery Bloodflowvelocity of the left middlecerebralartery(V·MCA) iswithin normal ranges (peakvelocity 82cm/s. mean velocity 56cm/s).At the sametime (15: 30),normal SEPenerright medianre rvestmuanon ere registered(time base 75 ms). Byconvention.negativity isenupward deflection. The latenciesof the primarycortical (upper trace) andthecervical response (below) are givenin msalt erstimulus. The centralconductiontime (eeT) (N21.0- N13.8)is slightlyincreased (7.2ms)possibly dueto the inhalationof O,8 Xisoflurane Downloaded by: National University of Singapore. Copyrighted material. 116 Early Detection ojCerebral lsch emia Thorac. cardiovasc. Su rgeon]? (1989) 117 V-Me A (, .. /sJ J ••"?R .Ri .,. ...... § g -. -l-" ' . '. 1. ~ RR 21)(1/110 '" ~ ••i>f? "'-fbA ar~ ~~ i od '. ~ RIll90/9'i .2!- -"\:", .00 . . .1. . . . . . . . . . . . . . . Fig. 2 TCD records beforecarotid clamping. With arterial hypertension (RR 200 /1 10mmHg)atthebeginning of surgery. left V·MCAdiffersminimally frombaselinevalues(top).10 minlater (16: OOt V·MCA andt hepulsatllity ofthe obtainedwaveformare markedlyreduced(middle)indicatinga criticalimpairmentof MCA perfusionwiththeinternal carotid arterystill unclarnped, Byraising the arterial blood pressure,V· MCA and pulsatihtyare slightly increased {bottom) ccr 1..1 Fig.4 TCD registration revealsnoeffect of carotid clamping onMCA perfusion (top,middle). Thrombus removal after carotid declampingleadsto a marke d acceleration of V-MCA indicating postscbermc hyperperfusion of the MCA temtory (bottom) ••• "" ' "~::., •• .,. ... " " /- {i-', .., . ., . ",' , .. •• R:Il M JI5 ,. cj_ ', "~ . •• •:oiR .U li ." 2..1 -" -"on ... ""'1-" .. • ;;l • 1· . 1 Fig.3 Median nerveSEP inthecourse oftheoperation,left hemispheric ischemia indicated by TCD isverified (uppertrace). Theprimary cortical response isnowmarkedlyreduced in amplifude andprolongedinlatency (N22.5)associatedwith an increase ofCCT (8.7ms). Re-establishingarlerial hypertension improves theamplitude (16: 10-16: 20)without aneffect on latency. Clamping ofthe left internal carotidartery doesnotfurtherdeteriorate thecorticalSEP. After declampingand thrombus removal, the cortical response amplitude isstill reduced and CCT increased compared to the baselinevalues Fi&- 5 TCD records after carotid declamping.V·MCAretumst o near baseline valueswithin 7 min after declamping. Note the different graduation ofthe vertical scale inthe bottom trace Downloaded by: National University of Singapore. Copyrighted material. -" A. Thie l. W HIISS,1/. t1-: N est le. G. l1r mp eifl/u lIIl Thome. Cllrd illl'llsC. S /lr gf'o/l.1 1 ( 1989) reduced a nd CCT still increased compa red to the preopera tive reco rdings. After surgery was completed . the patient awo ke promptly but had a complete paresis of her righ t a rm . She .....as ad mitted 10 the intensive ca re unit wh e re she regained norm al brachia l function wi thin 24 hours except for a mild se nso ry weakness of th e right for ea rm as confirm ed by neurologtcet exa mination. On th e first postoperative day. TCD Investigat ion showed norm al MCA velocities bilaterally. Disc usslon The intraoper ati ve detection of cerebra l isch em ia is ma inly based upon registra tion of the br ain' s electr ical activity IEEG, SEPI a nd/or evaluat ion of cerebra l he modynamics . For SEI' monitoring du ring carotid enda rterectomy, Rus s an d co-w orke rs lSI showed th at th is method pr ovides highly sensl uve a nd specific data . Furthermo re. defined SEP cha nges a re of pr ognostic value rega rdi ng th e patient' s neurologicaloutcome. As one of the ca uses of cereb ra l ische mia du r ing ca ro tid e nda rte rectom y is the de terior ation of blood su pply to the bra in a fter ca rot id clam ping, the eva lua tion of ce rebral hem od ynamics is "closer to the roots - tha n are elect ro physiologica l method s. Howeve r. the mea surement of regional ce re bra l blood now (rCBFI is invasive and ca nnot provide on -line data . Transcranial Doppler so nogre phy may so lve this problem as it is a non invas ive method of me asuring blood no w velocities in basal cerebra l a neries . Compa ra tive studi es sho wed that cha nges in rCBF a re highly co rrelated to cha nges in MCAnowwlocitiesl 21. ~f oreover, intra cranial hem odynam ics in patients suffering from ca rotid artery disease ca n be determined byTCD investigat ion (51. Paday achee a nd co-wo rker s a pplied TeD monitoring during ca rotid endarterectom y 171 in 19 pat ients. An intraluminal shunt was inserted in all cas es . After carotid clam ping. a significa nt decrease of MCA flow velocity of all pat ients occur red (ra nge 0-30 cm/s l wh ich reversed to near baseline values afte r shunt inse rtion . Rlectro phystologtca l mon ttori ng was not performed in this stud y, So the functional releva nce of the reported events remai ns obsc ure . Wi dingI'll an d associates (3) exa mined 100 cas es of carotid enda rte rectomy using TCD. In 10 pa tien ts . TCD could not be perfo rmed for tec hn ica l rea so ns . After clamping. MCAflow velocity va ried widely (a-Flow in 15 cases. no cha nge in J 3 ca ses t. A tempora ry shunt wa s indwelled if MCA now velocity was red uced less th an 50 % comp a red to baseline va lues . Alolain, no electrophystologtca l mon itoring was und ertaken in this study. Using SEP during ca rotid enda rte rec tomy. at least I minut e is nee ded to detect ce re bral ischemia a fte r ca ro tid clamping. As we could show in a previous report including 40 patients (10 ), mean !\tCAIlowv elocity reduction less than 60 % after damping is highly re lated to critica l SEP cha nges. Therefore, combined TCD and SEI' registra tion allows a mor e ra pid evalua tion of cere bra l perfusion tha n does SEP monitoring alone, In the prese nt case, TCD regist rati on revea led a cr itica l impairment of left !\ICA perfusion even before carotid clamp ing. The functiona l re levance of this event w as verified by SEP recordi ng. Raising the pat ient' s blood press ure in th is situation was an atte mpt to increase MCA perfusion , an d TeD and SEP pa ra mete rs slightly improved, Acute thro mbos is of the inter na l carotid a rtery, as in this case, re ma ins a rath er ra re ca use of cerebra l ischemia during ca rotid en da rte rectom y, It is worth noting that TCD monitoring throughout the ope ra tion was helpful in detect ing a n unexpected impairme nt of left ~I CA perfusion, Fur th ermore. the present case st resses the need for monito ring methods w hich provid e on-line data about ce rebra l hemodynamics in order to initiate therapeutic procedures as ea rly as possib le if ische mia lea ds to functional Impai r ment. In this res pect. furthe r studies are necessary to evaluat e how far TCD monitori ng during ca rotid enda rte rectomy ca n provide re liable , sens itive, and specific da ta indi cati ng ce re bra l ischemia offunc tiona l relev an ce. lI aslid. H, tea.t. Transcranta! Doppler SUllugrllphy. Wi" II-Nt'w Yor k, Sp rin g,'r I I qH6 ) 1 IJislwp. C. C. R.• S Pou'l'lI. O. HUll . a nd N. l., IJrOlI'SI': Tra nsr ran ia l Dopple r meas urem e nt olmld dle con-b ra l a rtery blood now \'('I ~ SUlldl . 7: M .. F 11'. Sli a rbrollgh. and II r;. Piepgras: Cor relati on of rerebra l blood now a nd elcctroence pha lcg rap hic c han ges d uring ra ro tid r-nd a rterec tom y. Mayo Clin . Proe . 5611 '1/(115 33- 54 3 10 Thil'l. II.. W. HlIs$. W.A. SEertma nn u nd G. U,.mp f'/nUlIIn: lntr aoperauves Mon ituri liR be i desohluerterenden Eing rirrr-n an der " IIrn tis· gabl"l mit somarosensonsch evoz te rte n PolI'ntiall'n ISEPI un d transkranielle r Dopplerso nogra phte (Te ll i. Thura c. ca rdiovase . Surgeon 3(•• Suppl. 1119 118 1t3 I Dr... 1. Thiel Ablt·HunR rur Aniisthl's iotoRit' u nd Op-ra uve In ll'ns i\'mlod il in Ju stus ·!.it'big· unrverstm Klinikstra Bl' 29 1l·(,30 n C, jo'ss"lvFHG Downloaded by: National University of Singapore. Copyrighted material. 118