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Anesth Pain Med 2014; 9: 87-92 종설 심박출량감시의최근경향과경심폐열희석법을이용한혈역학지표들 울산대학교의과대학서울아산병원마취통증의학과, 심혈관역동연구실 황규삼 Recent trend in cardiac output monitoring and trans-cardiopulmonary thermodilution-derived hemodynamic parameters Gyu Sam Hwang Department of Anesthesiology and Pain Medicine, Laboratory for Cardiovascular Dynamics, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea Currently, hemodynamic monitoring system is developing rapidly, with many different devices now available, which makes anesthesiologists feel somewhat confused by the various possibilities and issue of noninvasiveness. By the order of degree of invasiveness, these devices can be classified into the highly invasive pulmonary artery catheter and the completely noninvasive bioimpedance/ bioreactance technique and Doppler echocardiography. Recently, trans-cardiopulmonary thermodilution-derived hemodynamic parameters, such as global end-diastolic volume, global ejection fraction, cardiac function index, extravascular lung water, pulmonary vascular permeability index and its cardiac output, are available in anesthetic practice by PiCCO R (Pulsion Medical Systems) and VolumeView R (Edwards Life Sciences). This article provides objective review of the monitoring systems, as well as the advantages and limitations, in order to offer better management of the critically ill patients undergoing surgery. (Anesth Pain Med 2014; 9: 87-92) Key Words: Cardiac output, Extravascular lung water index, Transpulmonary thermodilution. 마취통증의학과의사는수술장에환자가입실하면심전도와혈압을측정하는것으로부터전신마취를시작한다. 이 Received: March 10, 2014. Revised: March 20, 2014. Accepted: March 24, 2014. Corresponding author: Gyu Sam Hwang, M.D., Ph.D., Department of Anesthesiology and Pain Medicine, Laboratory for Cardiovascular Dynamics, Asan Medical Center, University of Ulsan College of Medicine, 388-1, Pungnap-dong, Songpa-gu, Seoul 138-736, Korea. Tel: 82-2-3010-3989, Fax: 82-2-470-1363, E-mail: kshwang@amc.seoul.kr 후수술이끝날때까지혈역학을감시하므로전신마취감시의가장중요한부분은시작부터끝까지혈역학이전부라고해도과언은아닐것이다. 우리신체에서 혈액순환! (the circulation!) 이존재하는가장큰이유는전신에특히주요장기에산소와영양을공급하기위함이며, 이는혈관내의압력 ( 혈압, blood pressure, BP) 과혈류 ( 심박출량, cardiac output, CO) 에의해서결정된다. 따라서 BP와 CO의감시는혈역학감시의가장중요한부분이다. 그런데의문점은 과연우리는수술중 CO 감시가필요한가? 이다 [1]. 왜냐하면 BP는 ohm의법칙 ( 전압 = 전류 저항 ) 에의하여 CO과전신혈관저항 (systemic vascular resistance, SVR) 의곱 (BP = CO SVR) 으로표현되므로우리가마취중 BP를감시하면일정부분 CO의변화도포함하고있다고볼수있다. 그러나 BP가잘유지된다하더라도 CO의감소를 SVR의증가로보상하는경우가생길수있으므로실제로는조직에산소를예상보다많이전달할수없는상황이발생할수있다. 이는많은연구에서일정수준이상의큰수술에서는 BP만감시하는것보다는 CO을같이감시하는것이수술후예후에확연한차이를보인다는많은연구들이이를뒷받침하고있다 [2,3]. 전신마취중집중혈역학감시는심전도, BP, 심장충만압, CO, 그리고혼합혈정맥산소포화 (mixed venous oxygen saturation, SvO 2) 도그리고폐동맥압을포함한다. 이중폐동맥압을감시할수있는폐동맥카테터 (pulmonary artery catheter, PAC) 는 J. Swan과그의제자인 W. Ganz가 1970년 New England Journal of Medicine에 flow-directed balloon-tip을가진 PAC 사용을보고한후 Swan-Ganz 카테터로불리며이후널리사용되었다 [4]. 한때 PAC의사용은모든중환자의 40% 까지육박하였으나현재는환자의수술후성과나예후에도움을준다는증거가없으며, 매우침습적인감시방법이라하여중환자의학자들에서사용을꺼리는경향이생겼으며, 보다비침습적인방법을선호하게되어 PAC 사용은현재급감하는추세이다 [5,6]. 심지어 PAC의사망 (obituary: pulmonary artery catheter 1970 to 2013) 를선언하는종설이있을정도이다 [7]. 하지만여러가지단점에도불구하고마취통증의학과에 87

88 Anesth Pain Med Vol. 9, No. 2, 2014 서는심장수술과간이식수술과같은큰수술에서혈역학변화의작은변화까지도장시간동안연속적감시가가능한 PAC가여전히사용되고있지만 [8] 최근의확실한흐름은비침습적혹은조금이라도덜 (less) 침습적인방법을선호한다는것이다. CO를측정하는여러장비들열희석법 (Thermodilution, PAC 사용 ) 차가운얼음물을 PAC를통해우심방으로주입하고온도변화를이용하여 CO을간헐적으로측정하는방법으로아직까지 gold standard로여겨지며새로개발된 CO 측정기기는모두이방법과의차이를비교하는것을원칙으로하고있다. 하지만이는필요시마다찬물을주입해야하는매우번거로운방법이다. 이러한간헐적측정법의변형으로열섬유 (thermal filament) 를이용하는 Vigilance TM (Edwards life science, Irvine, CA, USA) 와열코일 (thermal coil) 을이용하는 OptiQ TM (ICU Medical, San Clemente, CA, USA) 가있는데상대정맥과폐동맥혈액온도차이를감지하여간헐적이아닌지속적 CO를보여준다. 하지만직전 5 10분정도의평균치를보여주므로부정맥에의한변이도를최소화할수있는장점도있지만혈역학이불안정한환자에서실시간값을보여주지못하는단점이있다. PAC 사용의가장큰장점은 CO과동시에폐동맥압, 좌우측충만압, 그리고무엇보다도 SvO 2 를볼수있다는것이다. 최근혈압이감소하였을때수액투여여부를결정하는전부하 (preload) 의지표를정적지표 (static index) 보다 stroke volume variation (SVV) 같은동적지표 (dynamic index) 를선호하면서좌우측충만압의전부하로서의중요성은크게감소하였다 [9]. 하지만 PAC는폐동맥압을지속감시할수있으므로술전폐동맥고혈압을동반하거나수술중폐색전이발생할가능성이높은환자의전신마취중에는여전히중요한의미를지니며현재사용되고있다 [10]. 특히시간에따른지속적변화 (trending information) 를보여주는것과비록 CO이실시간값을보여주지못한다하더라도 SvO 2 의감시가이를대체할수있을정도로실시간변화를매우잘반영하므로일부수술에서 PAC는마취의에게여전히유용하다고할수있다 [8]. 동맥파형추출법동맥파형을분석하여 CO을추출하는방법이다. 동맥압의상승시작부터 dicrotic notch까지의아래면적을이용하여일회심박출량을추정하므로매심박마다박출량을계산할수도있다. 측정된압력과혈류량사이의관계는환자의키, 몸무게그리고제작회사별로다른알고리즘을이용하 여압력파형을혈류로변환하는데외부보정 (calibration) 을하지않는장비로는 Vigileo TM (Edwards life science, Irvine, CA, USA) 와 PRAM (Pressure Recording Analytical Method) 이라는방법을이용하는 MostCare TM (Vytech, Padova, Italy) 가있다. PiCCO R (Pulsion Medical Systems, Munich, Germany) 와 LiDCO TM (LiDCO Ltd, London, UK) 는외부보정을이용한다. PiCCO R 는혈압파형을이용한분석을하고 LiDCO TM 는펄스파워 (pulse power) 분석을하며 2가지모두동적지표 (dynamic index) 인 stroke volume variation (SVV) 을제공한다. PiCCO R 는열희석법의표식자 (indicator) 로생리식염수를이용하지만 LiDCO TM 는리튬희석법을이용하여보정을하므로치료목적으로리튬을사용하고있는환자에게는 LiDCO TM 를사용할수없다. PiCCO2 R 와 LiDCOplus TM 는지속적으로 CO을보여주지만혈관탄성이변화하면 6 12시간마다재보정이필요하고, LidCOrapid TM 는환자의특징에따른 Pulse CO 알고리즘을사용하므로최고 24시간까지재보정을필요로하지않는다 [11]. Swan-Ganz 카테터와비교한 CO은임상적상황에따라모두다르게나타나지만가장큰장점은덜침습적이라는점이며환자가불안정할때도지속적으로수치를볼수있다. 단점은혈관탄성증감, 대동맥폐쇄부전증, 동맥압파형이정확하지않은경우에큰영향을받는다 [12]. 심장초음파와도플러이용법심장초음파를이용하여 CO을측정하는방법은좌심실출구의직경과도플러를이용하여 velocity-time integral을측정하여공식에넣으면매우간단하고쉽게측정할수있다. 그러나 PAC처럼지속적변화를볼수는없고필요시마다측정해야한다. 심장초음파는 CO을측정하는것이외에 2D 이미지를이용하여심장기능의다른측면, 즉수축기능, 이완기능과좌심실출구폐쇄와같은다른심장기능과판막, 심막들을동시에정확히평가할수있다는것이장점이다. 무엇보다도심근수축기능을다른어떤 CO 측정장비보다가장정확히그리고가장빠르게평가할수있는장비이다. 특히심장수축기능에가장많이이용되고있는심박구출률 (ejection fraction) 은눈대중 (eyeballing) 으로대충짐작해도실제측정치와매우유사하다는보고가많으므로심장초음파장비를갖춘마취과의사도이에대한연습이필요하다고하겠다 [13]. 심장초음파를보고심실크기가작을경우수액을, 수축기능이감소했을경우 dobutamine을일차적으로선택할수있고우심실의크기가커졌을경우폐색전증이나우측심근경색을의심할수있다 [14]. 심장압전 (tamponade) 과판막질환도쉽게찾을수있다. 도플러심장초음파를이용하거나 M 모드를이용하면 CO 이외에상대정맥혹은하대정맥

황규삼 :Cardiac output and novel hemodynamic parameters 89 Fig. 1. Disposable trans-esophageal echocardiography probe that can be detached from handle. Note that the size of probe is comparable to that of Levin tube. 변이도 (superior or inferior vena cava variation) 와같은여러가지동적지표도평가할수있다 [15]. 하지만전신마취중에는경흉 (trans-thoracic) 심장초음파는사용이불가능하거나, 이미지가항상선명하지않을수있으므로경식도 (trans-esophageal) 심장초음파를이용할수있지만, 의식있는환자에서의사용은경흉심장초음파에비해침습적이고환자에게큰불편을줄수있다. 따라서경식도심장초음파는금식후진정을시키는약물투여를필요로하는단점이있다. 가장큰단점은측정자에따라변이가클수있으므로일정기간수련이필요하다는점과고가의장비이며, CO을지속적으로볼수없다는점이다. 최근 Levin 튜브정도의크기인일회용경식도초음파 (htee; ImaCor, Garden City, NY, USA) probe가개발되어중환자실이나수술중혈역학평가에사용되고있다 (Fig. 1). 현재까지는혈류도플러가불가능하여 CO은측정할수없고 72시간까지만사용이가능하며거리면적등은측정가능하지만각도를변화시킬수없으므로 0도에서볼수있는 3가지기본단면도 (superior vena cava view, four-chamber view, LV short axis view) 를복합적으로응용하여평가하여야한다. 하지만, 심장을직접들여다볼수있을뿐아니라폐공기색전, 수술중심근허혈및심근경색, 급성우심실확장, 좌심실유출로의폐쇄, 초음파를이용한동적전부하등을즉시측정할수있는장비이므로수술중에도사용할수있는매우흥미로운장비이다 [16]. 바이오임피던스와바이오리액턴스 (Bioimpedance and Bioreactance) 흉부를가로지르는전류의 frequency가매심박동마다다르다는원리를이용하며 Cheetah Medical의 NICOM R 이임상에사용되고있다. 흉부에 electrodes를붙이기만함으로 써측정이가능하므로비침습적이며매우빠르게측정할수있다 [17-20]. 주로생리학적검사에많이이용되지만수술중에도이용되고있으나, 심한중환자에서는신뢰성이낮을수있다 [19,21]. 경심폐 (Trans-cardiopulmonary) 열희석법현재까지중심정맥압카테터와동맥압카테터를이용해 CO을측정할수있는장비는 4가지가알려져있는데 PiCCO R (Pulsion Medical Systems), LiDCO TM (LiDCO Ltd), VolumeView TM (Edwards Life Sciences) 그리고초음파를이용하는 COstatus R (Transonic Systems Inc., Ithaca, NY, USA) 이다. PAC를삽입하지않고도열희석법과같은전통적인방법을사용하며여러가지새로운혈역학지표들을제공할수있다는것이가장큰장점이다. 대신 PiCCO R 와 VolumeView TM 는고동맥 (femoral artery) 이나완동맥 (brachial artery) 에 4 5F 사이즈 16 20 cm 길이의카테터를삽입해야한다. 측정원리는 PiCCO R 와 VolumeView TM 는차가운식염수를중심정맥카테터에주입하여심장과폐 (trans-cardiopulmonary) 를거쳐서고동맥에도달했을때온도가얼마나변화했는지를측정하며, LiDCO TM 는소량의리튬을주입하여리튬의변화를측정하며, COstatus R 는따뜻한식염수를주사하고초음파속도의변화를측정한다. 경심폐열희석법으로측정한 CO 는 PAC 열희석법으로측정한값과상관관계가높으며, 호흡에의한변화도적은것으로알려져있다 [22]. PiCCO R 와 VolumeView TM 는 CO 이외에도심장좌우방실의모든용적을나타내는 global-end diastolic volume index (GEDVI) 와폐부종의여부를판단할수있는 extravascular lung water index (EVLWI) 와같은유용한혈역학지표를제공한다.

90 Anesth Pain Med Vol. 9, No. 2, 2014 Fig. 2. Quality of thermodilution curve that shows temperature changes. Quality of thermodilution is optimized when changes in blood temperature is >0.3 o C. Fig. 3. Schematic diagrams of different volumes that can be measured (dark shaded areas) with the trans-cardiopulmonary thermodilution technique. ITTV: intrathoracic thermal volume (A), PTV: pulmonary thermal volume (B), GEDV: global end-diastolic volume (C), ITBV: intrathoracic blood volume (D), EVLW: extravascular lung water (E), RA: right atrium, LA: left atrium, RV: right ventricle, LV: left ventricle, EDV: end diastolic volume.

황규삼 :Cardiac output and novel hemodynamic parameters 91 경심폐열희석법을이용한새로운혈역학지표들중심정맥카테터에찬물을주입하여심장과폐를거쳐서고동맥에도달했을때온도가얼마나변화했는지를열희석커브로그릴수있다. 온도의차이는 0.3 o C 이상이적절하다 (Fig. 2). 열희석커브에서얻어지는기울기와시간간격을이용하여여러가지열용적 (thermal volume) intrathoracic thermal volume (ITTV), pulmonary thermal volume (PTV), intrathoracic blood volume (ITBV), GEDVI, EVLWI를계산할수있다 (Fig. 3) [23]. PAC는우측심장에서의열희석법을이용하므로우심실확장기말용적 (right ventricular end-diastolic volume index, RVEDVI) 과우심실구출률 (right ventricular ejection frection, RVEF) 같은우측심장의지표만측정할수있지만, 경심폐열희석법을이용하면좌우측심장의모든용적 (GEDV = 우심방 + 우심실 + 좌심방 + 좌심실, GEDVI 정상치 = 700 800 ml/m 2 ) 와 global ejection fraction (GEF) 같은심장전체의구출률을계산할수있다 (GEF = stroke volume*4/gedv, 정상치 25 35%). GEDVI는폐혈증환자에서도심장의전부하를잘반영한다고알려져있다 [24]. 하지만우측심장이확장되어있는환자에서좌측전부하를과대평가하게되거나, 지속적지표가아닌차가운식염수를주입하여열희석법을사용할때만나타나는간헐적지표인점이단점이다. 그리고좌우측심장의모든용적을반영한다해도이또한동적 (dynamic) 이아닌정적 (static) 전부하지표인점은고려해야한다. EVLWI (=PTV PBV; 정상치, 3 7 ml/kg) 는폐부종의정량화라는점에서흥미있는지표이다 (Fig. 4). EVLWI가높으면중환자실환자의사망률이증가하는것으로알려져있다 [25,26]. 특히성인호흡곤란증후군에서 3일간의평균 EVLW가 16 ml/kg이면사망률은 100% specificity와 86% sensitivity를보이며 Vd/Vt, PaO2/FiO2보다더예민한생존예측인자로알려져있다 [27]. 더욱흥미로운점은 pulmonary vascular permeability index (PVPI) 를계산하면폐부종의감별진단을할수있다는점이다 (PVPI = EVLW/Pulmonary blood volume, 정상치, 1 3). PVPI는폐미세혈관의투과성을나타내는지표이다. 즉, 폐 부종이발생한환자에서 PVPI가 >3이면급성폐손상 (acute lung injury)/ 성인호흡곤란증후군에의해투과성 (permeability) 이증가한폐부종이며 1 3이면투과성은정상인심장기인성 (cardiogenic hydrostatic) 폐부종을시사한다 [28]. 또한 cardiac function index (CFI) 를계산하면심장수축기능도평가할수있다 (CFI = CO / GEDV). CFI는 LVEF와좋은상관관계를보이며 CFI < 3.2이면 LVEF < 35% 를의미하므로심장초음파를이용해수축기능을확인해야한다 [29]. 심장수술환자에서경심폐열희석법을이용한혈역학지표들을치료목표로하여 GEDVI > 640 ml/m 2, cardiac index > 2.5 L/min/m 2, mean BP > 70 mmhg, EVLWI < 10 ml/kg로환자관리를하면카테콜아민과혈관수축제의사용을줄일수있다는알고리듬이알려져있다 [30]. 혈역학평가에서꼭고려해야할점들결론적으로환자의수술후성과를좋게하기위해서는여러가지혈역학측정기기의장단점을고려하여그환자에게가장적합한감시장치를선택해야할것이다. 다음은최근에개발된 CO 및혈역학측정기기의장단점을분석하고이를평가함에서꼭고려해야할점들을세계중환자학회전문가 16인이정리한컨센서스 (consensus) 이다 [12]. 원칙 1. 혈역학감시테크닉그자체만으로는환자의성과를향상시킬수없다. 원칙 2. 혈역학감시의필요성은시간이흐르면변할수있고각병원의장비유무와수련정도에따른다. 원칙 3. 모든환자에게적용할수있는최적의혈역학지표는없다. 원칙 4. 여러가지혈역학지표를합쳐서종합해야한다. 원칙 5. SvO 2 는도움이된다. 원칙 6. 높은 CO과높은 SvO 2 가항상최선은아니다. 원칙 7. CO은추청치 (estimated) 이지측정치 (measured) 가아니다. 원칙 8. 빠르게변하는혈역학변화를측정할수있는것이중요하다. 원칙 9. 혈역학변수는지속적측정 (continuous measurement) 할수있는것이좋다. 원칙 10. 비침습적방법이항상단하나의이슈는아니다. 참고문헌 Fig. 4. Schematic diagram of extravascular lung water (EVLW), PTV: pulmonary thermal volume, PBV: pulmonary blood volume. 1. Vincent JL, Fagnoul D. Do we need to monitor cardiac output during major surgery? Anesthesiology 2012; 117: 1151-2. 2. Gan TJ, Soppitt A, Maroof M, el-moalem H, Robertson KM, Moretti E, et al. Goal-directed intraoperative fluid administration

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