每搏變異度在肝葉切除術(shù)中應(yīng)用的可行性

謝 海 綜述，趙建農(nóng)，陳 勇 審校

(1.海南醫(yī)學(xué)院附屬醫(yī)院麻醉科，海南 ?？?570102；2.海南省人民醫(yī)院神經(jīng)外科，海南 ?？?570311；3.海南省人民醫(yī)院麻醉科，海南 ?？?570311)

肝內(nèi)血管分布廣泛復(fù)雜，肝葉切除術(shù)中大量出血一直是手術(shù)面臨的主要問題。大量出血可導(dǎo)致血流動(dòng)力學(xué)不穩(wěn)定，增加并發(fā)癥的發(fā)生率和手術(shù)麻醉風(fēng)險(xiǎn)。而大量輸血可增加傳染性疾病、凝血功能障礙等的發(fā)生率，抑制人體免疫功能導(dǎo)致術(shù)后腫瘤的早期復(fù)發(fā)[1-2]。因此如何減少失血量的方法一直是肝切除手術(shù)的一個(gè)重要研究方向。

1 肝葉切除術(shù)和低中心靜脈壓

近年來(lái)國(guó)內(nèi)外一些有關(guān)降低中心靜脈壓減少肝切除術(shù)中的出血量的研究逐漸增多[3-9]，其理論基礎(chǔ)可能是：在行肝葉切除時(shí)，阻斷肝門后，肝靜脈、肝竇成為切除肝實(shí)質(zhì)過程中主要的出血因素，肝靜脈和肝竇壓力大小直接決定了出血量的多少，肝靜脈壓力又受到下腔靜脈壓(IVCP)壓力的影響，降低IVCP可降低肝靜脈壓力減少出血，而IVCP與中心靜脈壓(CVP)的壓力幾乎是一致的[10]。因此，可通過降低CVP達(dá)到降低IVCP的目的，最終降低肝靜脈和肝竇的壓力，使肝血管壁內(nèi)外壓力差和血管半徑都降低，最終能明顯減少患者術(shù)中的出血量。低中心靜脈壓(LCVP)技術(shù)除了能減少出血量，使無(wú)意損傷肝靜脈的大量出血更容易控制[11]，還能縮短手術(shù)時(shí)間，減少并發(fā)癥發(fā)生，縮短術(shù)后住院時(shí)間[4-12]。目前LCVP是通過麻醉深度調(diào)節(jié)、降壓藥物控制、限制液體輸注等方法將CVP控制在≤5 cmH2O(1 cmH2O=0.133 kPa)的水平，這是通過LCVP應(yīng)用于肝葉切除手術(shù)中失血量的分析得出的[8,11,13-14]。Rees等[4]報(bào)道CVP控制于0～5 cmH2O的水平，很少會(huì)導(dǎo)致全身低血壓發(fā)生的情況。LCVP技術(shù)能夠應(yīng)用于臨床，在降低CVP的同時(shí)不降低動(dòng)脈血壓，不發(fā)生全身低血壓狀況，達(dá)到減少出血的目的。然而CVP作為心臟對(duì)回心血量的泵出能力的反映和右心房的前負(fù)荷的指標(biāo)有一定的局限性。首先，它是靜態(tài)的、通過壓力代容積方法間接反映心臟前負(fù)荷的指標(biāo)，靜態(tài)血流動(dòng)力學(xué)監(jiān)測(cè)有較大的局限性，會(huì)帶來(lái)錯(cuò)誤的臨床決策[15]；其次，CVP高低取決于心室順應(yīng)性、血容量、靜脈血管張力、胸腔內(nèi)壓、靜脈回流血量和肺循環(huán)阻力等因素，尤以靜脈回流血量與右室排血量之間的平衡關(guān)系最為重要。再次，CVP數(shù)值會(huì)受到手術(shù)體位、手術(shù)操作和機(jī)械通氣等因素的影響[16-17]。術(shù)中肝臟拉鉤對(duì)膈肌的牽拉使呼吸受限，胸腔壓力升高，CVP升高；手術(shù)過程中阻斷肝臟周圍血管靜脈回流減少，中心靜脈受壓扭轉(zhuǎn)，回心血量減少，CVP降低等。總之，應(yīng)用LCVP技術(shù)減少肝葉切除術(shù)出血量時(shí)，如果單純以CVP作為評(píng)判指標(biāo)可能會(huì)給臨床準(zhǔn)確判斷帶來(lái)困難，甚至導(dǎo)致臨床決策錯(cuò)誤。因此有必要尋找一種能輔助、聯(lián)合CVP的準(zhǔn)確容量監(jiān)測(cè)手段。

2 每搏量變異度(SVV)

SVV是近年來(lái)預(yù)測(cè)機(jī)體對(duì)于液體治療反應(yīng)性的動(dòng)態(tài)的容量監(jiān)測(cè)指數(shù)，通過計(jì)算CO所得，它能很好地反映患者的血容量狀況[18-23]。SVV是在一定時(shí)間(至少一個(gè)呼吸周期)內(nèi)，每次心臟搏動(dòng)時(shí)的每搏量(SV)，計(jì)算出它們?cè)谠摱螘r(shí)間內(nèi)的變異程度(以百分?jǐn)?shù)表示)，以此預(yù)測(cè)心血管系統(tǒng)對(duì)液體負(fù)荷的反應(yīng)。機(jī)械通氣過程中呼吸對(duì)循環(huán)的影響是SVV的基礎(chǔ)，通氣過程中隨著胸腔內(nèi)壓力反復(fù)增減的周期性增減變化，回心血量也隨之變化，所以導(dǎo)致左室每搏量也發(fā)生周期性增減改變。機(jī)械通氣吸氣相引起胸腔內(nèi)壓力增高，一方面肺靜脈毛細(xì)血管床內(nèi)大量血液被擠入左心室，左心室的血量此刻立即增加，SV上升，即肺靜脈系統(tǒng)血量輸出上升；另一方面肺靜脈血管床被擠壓，使肺血管阻力增加，腔靜脈回流受阻，即肺靜脈血量供給下降；輸出的上升和供給的下降，肺靜脈系統(tǒng)血量空虛，左心室在2～3個(gè)心動(dòng)周期后表現(xiàn)出SV的下降[24]。所以接受正壓機(jī)械通氣的患者，其左心室的每搏量會(huì)在吸氣相時(shí)增加到最大，呼氣相減少到最小，這種周期性變化反映了左室舒張末容積的大小，反映了血容量的多少。SV的最大值與最小值相差越大，說(shuō)明有效循環(huán)血量越不足，在此情況下，如果增加容量負(fù)荷，CO增加的程度就會(huì)更明顯。SVV能很好地反映患者的血容量狀況，是心臟前負(fù)荷反應(yīng)性的敏感指標(biāo)[25-26]。其計(jì)算公式為SVV=(SVmax-SVmin)/SVmean。SVV的正常參考值<13%，其數(shù)值越大，給予容量負(fù)荷后的CO增加得越多，表明有效血容量不足越明顯。如果SVV<13%，那么給予容量負(fù)荷后就很難出現(xiàn)CO的增加，應(yīng)避免輸入過多液體。許多文獻(xiàn)報(bào)道和其他傳統(tǒng)監(jiān)測(cè)指標(biāo)(HR、MAP、CVP、PAD、PAOP)相比，SVV有更高的敏感性與特異性[27-29]。其優(yōu)于心臟前負(fù)荷的靜態(tài)參數(shù)，特別是對(duì)于優(yōu)化心輸出量、保證重要臟器血供更有優(yōu)勢(shì)[30]?？傊?，SVV作為動(dòng)態(tài)的容量監(jiān)測(cè)指數(shù)，能夠準(zhǔn)確地預(yù)測(cè)手術(shù)中心臟對(duì)容量負(fù)荷的反應(yīng)性及前負(fù)荷狀態(tài)。

3 FloTrac/Vigileo心輸出量監(jiān)測(cè)系統(tǒng)

臨床上目前用于連續(xù)監(jiān)測(cè)SVV的方法主要是動(dòng)脈壓力波形分析技術(shù)，包括Flotrac/Vigileo系統(tǒng)和PiCCOplus系統(tǒng)，具有微創(chuàng)、設(shè)置簡(jiǎn)單快速等特點(diǎn)。PiCCOplus系統(tǒng)計(jì)算CO是通過測(cè)量動(dòng)脈壓力波形收縮期部分的面積，并用主動(dòng)脈阻抗除以收縮期面積，得到相應(yīng)結(jié)果。兩者監(jiān)測(cè)SVV都是獲取單位時(shí)間內(nèi)的SV，通過公式SVV=(SVmax-SVmin)/SVmean計(jì)算所得。其中FloTrac/Vigileo系統(tǒng)(愛德華生命科學(xué)世界貿(mào)易公司)由FloTrac傳感器和Vigileo監(jiān)測(cè)儀組成，可以在無(wú)需校正，操作簡(jiǎn)單，微創(chuàng)的情況下為臨床醫(yī)生提供相關(guān)血流動(dòng)力學(xué)監(jiān)測(cè)指標(biāo)。其2005年開始用于臨床血流動(dòng)力學(xué)監(jiān)測(cè)，運(yùn)用連接于動(dòng)脈壓力導(dǎo)管的Flo-Trac壓力傳感器，通過橈動(dòng)脈或股動(dòng)脈導(dǎo)管采集患者外周動(dòng)脈壓力波形，結(jié)合患者年齡、性別、身高、體重、體表面積運(yùn)算分析出血流動(dòng)力學(xué)指標(biāo)包括CO/Cl、SV/SVI、SVV、SVR/SVRI(結(jié)合 CVP 計(jì)算)[31]。相比“金標(biāo)準(zhǔn)”溫度稀釋法操作復(fù)雜，有創(chuàng)傷性，費(fèi)用昂貴、易引起并發(fā)癥等[32]不足，該法具有微創(chuàng)、自動(dòng)、連續(xù)、重復(fù)性好、操作簡(jiǎn)單、使用方便等優(yōu)點(diǎn)，適用于手術(shù)室、ICU和急診室等地方。國(guó)外學(xué)者[22,33-35]通過Flotrac/Vigileo進(jìn)行的APCO監(jiān)測(cè)與溫度稀釋法PAC測(cè)心排量(CCO)進(jìn)行比較，結(jié)果顯示，兩種方法CO的監(jiān)測(cè)結(jié)果具有很好的相關(guān)性。當(dāng)然Flotrac/Vigileo系統(tǒng)有其局限性，它不適合監(jiān)測(cè)嚴(yán)重心律失?；颊吆陀邪昴ぜ膊〉幕颊遊36]。而SVV可以應(yīng)用于血管活性藥物治療下的監(jiān)測(cè)[37]，但必須是機(jī)械通氣的患者，且潮氣量和PEEP不能過大[38-39]，強(qiáng)烈的疼痛刺激對(duì)其有影響[40]。因此，在LCVP下肝葉切除術(shù)中，可以通過FloTrac/Vigileo心輸出量監(jiān)測(cè)儀監(jiān)測(cè)SVV的變化，同時(shí)監(jiān)測(cè) CO/Cl、SV/SVI和 SVR/SVRI，不但有連續(xù)監(jiān)測(cè)和反應(yīng)敏感的優(yōu)勢(shì)，而且還能全面了解血流動(dòng)力學(xué)變化，是一種可行的、更安全有效的方法。

綜上所述，SVV是動(dòng)態(tài)的功能性指標(biāo)，這種依靠循環(huán)系統(tǒng)對(duì)液體治療反應(yīng)判斷其容量狀態(tài)的功能性監(jiān)測(cè)方式可使LCVP減少肝葉切除術(shù)出血的臨床治療更為準(zhǔn)確、有效，患者更安全。所以，引入新指標(biāo)SVV，作為一種能輔助、聯(lián)合CVP的準(zhǔn)確容量監(jiān)測(cè)手段成為必要，將為臨床上輔助、聯(lián)合LCVP應(yīng)用于肝葉切除術(shù)減少出血提供了新的、更全面的、更安全的臨床思路。

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