二氧化碳激光器的臨床應(yīng)用

氧化碳激光器的臨床應(yīng)用以下程序演示了多功能CO2激光器在馬外科手術(shù)中的廣泛應(yīng)用。這些程序中均應(yīng)用到了二氧化碳波長(zhǎng)的獨(dú)特性質(zhì)，并經(jīng)受了時(shí)間的考驗(yàn)。這項(xiàng)技術(shù)可以廣泛的應(yīng)用于馬屬動(dòng)物外科手術(shù)，作為外科醫(yī)生要熟悉使用激光切割，體積燒蝕和凝血儀。一般來(lái)說(shuō)，二氧化碳激光的益處在于鄰近組織極小創(chuàng)傷的精確解剖，良好的止血效果。利用激光束的熱性能，以殺死細(xì)菌或剝離腫瘤細(xì)胞相鄰面。當(dāng)考慮使用該儀器進(jìn)行外科手術(shù)時(shí)，外科醫(yī)生應(yīng)該考慮到靶組織的熱特性，并了解一個(gè)特定波長(zhǎng)對(duì)該組織的影響。相鄰組織（如骨和韌帶）的差熱吸收特性為解剖面的精細(xì)選擇和附近熱敏感組織能量謹(jǐn)慎應(yīng)用的需求提供了機(jī)會(huì)。外科手術(shù)中，在使用激光之前，外科醫(yī)生應(yīng)該首先確定手術(shù)的目標(biāo)。如果精確的組織破壞或切口是必要的，則說(shuō)明要使用大功率超脈沖模式和聚焦光斑尺寸。如果要使組織凝血且溫和加熱，則需求低功耗連續(xù)模式的散焦斑尺寸。直到醫(yī)生習(xí)慣于預(yù)測(cè)激光能量在組織中的影響，選擇功率設(shè)置基于能源的可觀察性，通常建議在正式開(kāi)始手術(shù)切口之前選取不相關(guān)組織的一處“測(cè)試點(diǎn)”進(jìn)行試驗(yàn)。在一般情況下，外科醫(yī)生應(yīng)該選擇使用自己可控的安全和精度的范圍內(nèi)可獲得的最高功率。初學(xué)者則應(yīng)該從較低的功率開(kāi)始逐漸增加功率設(shè)置，以獲得使用激光器的經(jīng)驗(yàn)在沒(méi)有深入了解二氧化碳波長(zhǎng)對(duì)組織的影響，也沒(méi)有使用激光器的外科醫(yī)生實(shí)習(xí)經(jīng)驗(yàn)的情況下嘗試這些操作將不會(huì)得到滿意的結(jié)果。皮膚腫瘤對(duì)于馬來(lái)說(shuō)，黑色素瘤，乳頭狀瘤，肉狀瘤，纖維瘤，鱗狀細(xì)胞癌是常見(jiàn)的皮膚腫瘤。這些腫塊可用二氧化碳激光燒灼或汽化。在病變處用鹽酸甲哌卡因進(jìn)行局部浸潤(rùn)麻醉，脫敏手術(shù)部位，避免鄰近正常組織受到激光熱效應(yīng)的影響（圖6）。

當(dāng)需要進(jìn)行組織學(xué)診斷時(shí)，通常在大規(guī)模切除或汽化腫瘤之前進(jìn)行腫瘤的切除活檢，一般使用50W的超脈沖模式與0.2毫米聚焦光斑（比功率約150000W/cm2）。這種模式和電源功率設(shè)置保證了將細(xì)胞結(jié)構(gòu)損傷降低到最小且提供了高效的組織切除技術(shù)。大疣狀腫塊最好以高功率連續(xù)的模式將其從它們生長(zhǎng)的組織處分離并最大限度的止血。腫瘤的基部可采用50W的功率、1毫米散焦斑（比功率約為7000W/平cm2）進(jìn)行汽化，以脈沖向心模式從正常皮膚邊緣開(kāi)始向病變中心作用。使用這種技術(shù)可以完全除去耳廓結(jié)節(jié)而不損壞下面的軟骨。站立的馬的眼瞼腫瘤在適當(dāng)保定的情況下可以被很好的剔除，但對(duì)于眼角膜、球結(jié)膜鱗狀細(xì)胞癌來(lái)說(shuō)，最好的治療方案是馬進(jìn)行全身麻醉以提供足夠的穩(wěn)定性來(lái)保證此類(lèi)病變組織的精確剔除（圖7）。空心塑料波導(dǎo)可通過(guò)二氧化碳激光鉸接臂的存在來(lái)蒸發(fā)馬病變的皮膚。因?yàn)樵?米的纖維路徑中能量衰減的變化從10%到50%，激光試驗(yàn)脈沖在最初得到應(yīng)用，并調(diào)節(jié)功率達(dá)到理想的臨床效果。一般外科手術(shù)中推薦將50W功率應(yīng)用于靈活可控的波導(dǎo)中的應(yīng)用。二氧化碳激光對(duì)汽化的精確控制是治療皮膚腫瘤的一個(gè)優(yōu)點(diǎn)。只要有足夠的皮膚，我們可以通過(guò)常規(guī)縫合皮下組織和皮膚來(lái)彌補(bǔ)腫瘤的切除或造成燒灼的缺陷。如果沒(méi)有，可以采用第二種辦法來(lái)促進(jìn)手術(shù)部位切口的愈合。可以外用抗菌藥膏直至傷口收縮并形成完整的上皮組織。除去大的播散性皮膚損傷后，可以進(jìn)行一次皮膚移植用健康的肉芽組織填充缺陷皮膚部位。這些病變成功治療的預(yù)后主要是靠特定腫瘤生物學(xué)行為的功能。經(jīng)過(guò)上述皮膚腫瘤激光治療后可能會(huì)通過(guò)控制其復(fù)發(fā)做到長(zhǎng)期緩解效果。這組腫瘤中，鱗狀細(xì)胞癌的復(fù)發(fā)率最高。為此，病變的可視區(qū)域要盡可能的與大面積的正常皮膚一起被清除。此外，在手術(shù)結(jié)束時(shí)，要用功率30W的連續(xù)模式、1mm散焦光斑（比功率約3800W/cm2）照射組織，對(duì)瘤床進(jìn)行清潔消毒。這樣做的目的是要小心加熱燒灼腫瘤邊緣來(lái)殺死殘余腫瘤或轉(zhuǎn)移性病變的邊界細(xì)胞。對(duì)皮膚腫瘤激光治療的主要優(yōu)點(diǎn)是在很多案例或其他治愈的病例中，激光的動(dòng)態(tài)效應(yīng)和熱殺傷效應(yīng)對(duì)腫瘤邊緣細(xì)胞的影響能夠提供長(zhǎng)久有效的緩解治療效果。激光清創(chuàng)、消毒清創(chuàng)、受污染的傷口均能對(duì)馬造成傷害。常規(guī)的外科手術(shù)治療包括清創(chuàng)，抗生素沖洗，并使用排水管清理傷口中累積的血清和血液。二氧化碳激光器提供了清創(chuàng)和消毒傷口的有效手段。局部浸潤(rùn)麻醉之后，使用高功率連續(xù)模式（50到80W），1mm散焦斑（功率密度約7000至10000W/cm2）來(lái)汽化失活和壞死組織。將功率降低至30W的連續(xù)模式并使用5mm光斑（功率密度約150W/cm2），此時(shí)激光束可以順利通過(guò)一個(gè)網(wǎng)狀圖案的手術(shù)視野落在消毒傷口的表面。使用快速激光輔助治療可以讓外科醫(yī)生在低功率設(shè)置的情況下順利、有效的消毒大面積組織。創(chuàng)面應(yīng)保持濕潤(rùn)，防止組織局部脫水。視覺(jué)端點(diǎn)用于確定給定區(qū)域的適當(dāng)治療，用一縷蒸汽引起組織非常輕微的收縮。組織出現(xiàn)明顯的收縮和熱燙表明應(yīng)用過(guò)熱致使組織蛋白變性凝固。在傷口處來(lái)回反復(fù)加熱比一次性操作使組織過(guò)熱的治療方法更好。二氧化碳激光器的精確效果使得它非常適合于這種類(lèi)型的程序。用激光清創(chuàng)消毒后，組織平面近似于完成一次多層次的常規(guī)原發(fā)性閉合。除非組織缺損非常嚴(yán)重，否則術(shù)后不需要使用排水管。在適當(dāng)?shù)臅r(shí)候給予全身抗生素和預(yù)防破傷風(fēng)。對(duì)污染傷口進(jìn)行激光治療的優(yōu)勢(shì)在于有效清除失活組織，減少活菌在其中存活的能力。這些相同的優(yōu)點(diǎn)可以通過(guò)使用二氧化碳激光剝離軟組織或馬的骨髓炎病灶來(lái)體現(xiàn)。激光血管吻合術(shù)激光將一定量的熱能應(yīng)用于組織的獨(dú)特能力已被用于開(kāi)拓一個(gè)被稱(chēng)為“組織融合”或“組織焊接”的軟組織外科學(xué)新領(lǐng)域。雖然許多波長(zhǎng)可以用來(lái)完成這項(xiàng)任務(wù)，但二氧化碳激光是一種用于燒灼血管壁來(lái)切斷血管的有效工具。激光修復(fù)血管的生物力學(xué)與縫合修補(bǔ)術(shù)相似。筆者采用了以下協(xié)議成功修復(fù)了兩匹指掌側(cè)固有動(dòng)脈切斷，有嚴(yán)重腕掌側(cè)傷口的兩匹馬。在全麻的狀態(tài)下對(duì)馬采用激光聚變技術(shù)斷開(kāi)指狀血管并且每單位繃帶放置在與球關(guān)節(jié)水平位置。切斷的邊緣動(dòng)脈應(yīng)用小牛頭犬血管夾固定住并用鋒利的解剖刀清創(chuàng)。四在5-0鉻制腸線縫合線被放置在90度的間隔血管壁周?chē)杂糜谠谑褂眉す饽芰繒r(shí)穩(wěn)定動(dòng)脈的切割表面。這個(gè)激光儀必須能夠精確、穩(wěn)定的輸出非常低的功率，從而使膠原血管壁內(nèi)無(wú)壞死或汽化。根據(jù)激光的光斑尺寸調(diào)整輸出功率，使組織表面能量密度達(dá)到100?175W/cm2。例如，2.5mm的光斑大小，7W的連續(xù)功率時(shí)的比能量密度為150W/cm2。加熱組織時(shí)，在確認(rèn)光點(diǎn)的精確尺寸要通過(guò)由激光燒灼濕潤(rùn)的木制壓舌板來(lái)精確測(cè)量激光束的直徑。醫(yī)生應(yīng)該意識(shí)到雖然氦-氖瞄準(zhǔn)照射和二氧化碳的能量束在一個(gè)適當(dāng)?shù)恼{(diào)諧激光器中是同心的，但兩光束的直徑的精確可能不完全相同。機(jī)頭離靶組織的精確距離要求在使用激光能量的整個(gè)過(guò)程中用聚焦傳導(dǎo)，使得光斑直徑為2.5mm,確保組織表面使用正確的功率密度。在使用激光能量時(shí)組織要保持干燥，液化組織和變色區(qū)域的視覺(jué)終端用于確定組織充分加熱。組織表面上不存在含炭物質(zhì)。焦炭的形成表明，能量密度過(guò)高，發(fā)生碳化。組織焊接過(guò)程中重復(fù)旋轉(zhuǎn)血管，沿著表面的四個(gè)吻合邊緣溫施加激光能量直到整個(gè)確保邊緣密封。松開(kāi)夾子和eschmark繃帶來(lái)評(píng)價(jià)血管修復(fù)的安全性。如果當(dāng)時(shí)滲血，就要收緊止血帶，然后用生理鹽水沖洗滲血區(qū)域。重復(fù)這個(gè)過(guò)程，直到得到血被止住。四處縫線留在原處，為修復(fù)提供旋轉(zhuǎn)穩(wěn)定性。組織焊縫張力較強(qiáng)，但在扭轉(zhuǎn)應(yīng)變能力很弱。使用激光輔助血管修復(fù)的優(yōu)點(diǎn)是減少血管壁中出現(xiàn)外來(lái)物質(zhì)。這有助于傷口愈合，減少局部肉芽腫或瘢痕組織的形成，降低后續(xù)的管腔閉塞的傾向。激光去勢(shì)馬采取背側(cè)臥保定，在陰囊基底沿著睪丸大彎處用50W超脈沖和0.2mm的聚焦光斑做一個(gè)橢圓形的皮膚切口（平均功率密度約75000W/平cm2）。切口是先通過(guò)皮膚，皮下組織，陰囊筋膜，用激光棒將這些組織放置在張力下，可支持激光束（見(jiàn)圖2）睪丸本身可以支撐激光束，但睪丸表面的血管會(huì)在不必要的復(fù)雜解剖時(shí)意外出血。通過(guò)用50W連續(xù)功率、1mm散焦光斑模式來(lái)分開(kāi)正中中線，去除整塊陰囊正中中線來(lái)增強(qiáng)止血（功率密度約7000W/cm2）。結(jié)扎腹中線上直徑大于1mm的血管，采用鈍性分離將疏松的網(wǎng)狀筋膜從睪丸上剝離，激光采用后者的功率和模式設(shè)置。結(jié)扎精索，用#1聚對(duì)二氧環(huán)己酮（PDS）采用單一連續(xù)垂直褥式縫合方式縫合切口，縫合順序?yàn)殛幠医钅?，皮下組織和剩余的正中中縫。使用激光器的優(yōu)點(diǎn)是切開(kāi)血管豐富或淋巴淤滯的組織時(shí)出血較少。

清除肉芽組織肉芽傷口在馬的四肢極為普遍的，對(duì)于簡(jiǎn)單愈合來(lái)說(shuō)是一個(gè)困難的挑戰(zhàn)。旺盛的肉芽組織（“傷口愈合后的疤”）必須被清除，來(lái)延遲或使傷口二次愈合。因?yàn)槿庋拷M織由豐富的毛細(xì)血管組成，使用二氧化碳激光器有助于清創(chuàng)。類(lèi)似于清除皮膚腫瘤的治療方案，這種類(lèi)型的操作程序說(shuō)明了二氧化碳激光器可以作為一種“體積燒灼”儀器使用。清除大部分肉芽組織首先使用50-80W的連續(xù)功率，1mm散焦光斑的激光照射周?chē)陌薪M織（功率密度約7000至10000W/cm2）來(lái)達(dá)到良好的止血作用。清除時(shí)先用無(wú)創(chuàng)傷鉗輕輕夾起病變一角，然后通過(guò)激光束來(lái)回照射擴(kuò)大病灶直徑（圖8）。遇到直徑大于1或2mm的血管時(shí)要進(jìn)行結(jié)扎。一旦清除了肉芽組織，該區(qū)域?qū)⒂?0W連續(xù)功率，2mm光斑的激光束畫(huà)出交叉陰影線（功率密度約2500W/cm2）。大的光斑尺寸和“噴槍消融技術(shù)”確保了比較均勻的清創(chuàng)技術(shù)及良好的止血效果。快速激光輔助技術(shù)可以在規(guī)定的區(qū)域傳遞能量一個(gè)光滑的表面。一旦皮表之下的肉芽組織順利清除，傷口可以用整形外科技術(shù)縫合使其恢復(fù)健康或后期皮膚移植。使用激光進(jìn)行清除的主要優(yōu)點(diǎn)是能使清創(chuàng)組織表面出血顯著減少。手掌/腳掌的指關(guān)節(jié)神經(jīng)切斷術(shù)手掌/足底指關(guān)節(jié)神經(jīng)切除術(shù)通常作為手指和足趾后三分之一慢性跛行和對(duì)翼尾第三關(guān)節(jié)骨折的最后治療手段。切斷神經(jīng)后正常的愈合反應(yīng)的結(jié)果是在神經(jīng)切斷面形成一個(gè)小的組織良好的神經(jīng)瘤。從以往病例分析，這個(gè)過(guò)程的主要并發(fā)癥之一是神經(jīng)瘤的形成。這個(gè)過(guò)程的特征在于神經(jīng)末梢切割端雜亂的再吻合并伴隨著兩神經(jīng)組織和鞘（雪旺氏細(xì)胞）的增生。盡管在一些情況下努力減少創(chuàng)傷和出血，避免神經(jīng)瘤的形成，密封神經(jīng)外膜，以防止切割端神經(jīng)軸漿的泄露，但馬神經(jīng)瘤的形成發(fā)展的主要因素仍保持猜測(cè)的態(tài)度。在對(duì)十匹超過(guò)23個(gè)月的馬的研究調(diào)查中，用18426W/cm2CO2激光理療儀來(lái)使被手術(shù)刀片切斷的神經(jīng)斷端有足夠的熱密封性，防止神經(jīng)再支配或形成神經(jīng)瘤。經(jīng)過(guò)多年使用CO2激光理療儀對(duì)馬進(jìn)行手掌/足底指關(guān)節(jié)神經(jīng)切斷來(lái)看，筆者認(rèn)為當(dāng)激光器使用的參數(shù)與描述的治療Morton神經(jīng)瘤相似，那么神經(jīng)瘤是極其罕見(jiàn)的。將馬圈養(yǎng)在畜欄中十四天，每天更換繃帶，之后再牽溜兩周直至馬恢復(fù)正常的日?；顒?dòng)。應(yīng)在術(shù)后前十天用非類(lèi)固醇抗炎藥物治療來(lái)減少手術(shù)部位的炎癥反應(yīng)。使用CO2激光理療儀進(jìn)行手掌指關(guān)節(jié)神經(jīng)切斷術(shù)的優(yōu)點(diǎn)在于神經(jīng)瘤的形成率低。應(yīng)避免使用高于推薦值的功率密度，否則術(shù)后馬將出現(xiàn)跛行且數(shù)周內(nèi)觸診切口部位敏感性增強(qiáng)。雖然此類(lèi)神經(jīng)炎癥是暫時(shí)的，也可以用藥物治療，但是這種可以輕松避免的并發(fā)癥也不是我們希望看到的。SELECTEDCLINICALAPPLICATIONSFORTHECARBONDIOXIDELASERThefollowingproceduresdemonstratetheversatilitythecarbondioxidelaserinequinegeneralsurgery.Eachoftheseproceduresmakesuseofuniquepropertiesofthecarbondioxidewavelengthandhaswithstoodthetestoftime.Thetechniquesdescribedcanbeappliedtoawiderangeofproceduresinequinesurgeryasthesurgeonbecomesfamiliarwithuseofthelaserasacutting,volume-ablating,andcoagulatinginstrument.Ingeneral,thebenefitsofthecarbondioxidelaserrelatetoprecisedissectionwithminimaltraumatoadjacenttissues,goodhemostasis,anduseofthethermalpropertiesofthelaserbeamtokillbacteriaortumorcollsadjacenttotheplaneofdissection.Whencontemplatinguseofthisinstrumentforsurgery,thesurgeonshouldconsiderthethermalpropertiesofthetargettissuesandunderstandtheeffectofaparticularwavelengthonthattissue.Differentialthermalabsorptionpropertiesofadjacenttissues(suchasboneandligament)provideopportunitiesforselectiveandpreciseplanesofdissectionaswellasaneedforcarefulapplicationoftheenergynearthermallysensitivetissues.Beforeusingalaserinsurgery,thesurgeonshouldfirstidentifythesurgicalgoal.Ifprecisetissuedestructionorincisionisrequired,useofhigh-powersuperpulsemodeandnfocusedspotsizeareindicated.Ifalargeareaoftissueablationorvaporizationisdesired,highpowerandacontinuousmodewithdefocusedspotsizearebest.Ifcoagulationandgentleheatingoftissueisthegoal,lowpower,acontinuousmode,andadefocusedspotsizeaivrequired.Untilthesurgeonbecomesaccustomedtothepredictableeffectsoflaserenergyontissue,selectingpowersettingsbasedonanobservableeffectoftheenergyasitiscarefullyappliednoncritidatostspot''oftissueisrecommendedbeforeactuallybeginningthesurgicalincision.Ingeneral,thesurgeonshouldusethehighestpoweravailablethatthesurgeoncancontrolsafelyandwithprecision.Havingsaidthat,novicesshouldstartwithlowerpowersandincreasepowersettingsasexperiencewiththelaserisachieved.Attemptingtheseprocedureswithoutathoroughunder-standingofthetissueeffectsofthecarbondioxidewavelengthandpracticaltrainingfromsurgeonsexperiencedwithuseoflasersmayresultinlessthansatisfactoryresults.CutaneousNeoplasiaMelanomas,papillomas,sarcoids,fibromas,andsquamouscellcarcinomasarecommoncutaneoustumorsinthehorse.Thesemassescanbeexcisedorvaporizedusingthecarbondioxidelaser.Anesthesiaisachievedwithlocalinfiltrationofmepivacainehydrochloridebeneaththelesion,desensitizingtheoperativesiteandprotectingadjacentnor-maltissuefromthethermaleffectsofthelaser(Fig.6).Whenahistologicdiagnosisisdesired,anexcisionalbiopsyofthetumorismadeusing50Wofpowerinthesuperpulsemodewithafocusedspotsizeof0.2mm(powerdensity,approximately150,000W/cm2)beforeablationorvaporizationofthemass.Thismodeandpowersettingprovideefficientexcisionoftissuewithminimaldisruptionofcellulararchitecture.Largeverrucousmassesarebestseparatedfromtheirbaseusinghighpowerandcontinuousmodetomaximizehemostasis.Thebaseofthetumormaythenbevaporizedusing50Wofpower,adefocusedspotsizeof1mm(powerdensityapproximately7000W/cm2),andapulsedmodeinacentripetalpattern,beginningwithamarginofnormalskinandworkingtowardthecenterofthelesion.Auricularsarcoidcanbecompletelyremovedusingthistechniquewithoutdamagingtheunder-lyingcartilage.Althougheyelidtumorsmayberemovedinthestandinghorseprovidedadequatecontrolofthepatientcanbeassured,squamouscellcarcinomaofthecorneaandbulbarconjunctivaarebesttreatedwiththehorseundergeneralanesthesiatoprovidethestabilityrequiredtoremovesuchlesionsprecisely(Fig.7).Thewoundshouldbekeptmoistduringthistreatmenttopreventlocaldehydrationoftissues.Thevisualendpointusedtodetermineadequatetreatmentofagivenareaistheproductionofawispofsteamandveryslightshrinkageoftissue.Markedcontractionandblanchingoftissuesindicatetheapplicationofexcessiveheat,whichcausescoagulationanddenaturationoftissueprotein.Makingmultiplepassesoverthewoundisbetterthanoverheatingthetissueswithasingletreatment.Thepreciseeffectofthecarbondioxidelasermakesitideallysuitedforthistypeofprocedure.Subsequenttolaserdebridementandsanitization,thetissueplanesareapproximatedwithmultiplelayerstoaccomplisharoutineprimaryclosure.Exceptinthemostextremecasesoftissueloss,theuseofdrainspostoperativelyisnotnecessary.Systemicantibioticsandtetanusprophylaxisareadministeredwhenappropriate.Theadvantageoflasertreatmentofcontaminatedwoundsistheefficientdebridementofdevitalizedtissueandtheabilitytodiminishthepopulationofviablebacteriapresenttherein.Thesesameadvantagescanbeappreciatedbyusingthecarbondioxidelaserforthesofttissuedissectionofdrainagetractsassociatedwithosteomyelitislesionsinhorses.Laser—AssistedVascularAnastomosisTheuniqueabilityoflaserstoapplyacontrolledamountofthermalenergytotissuehasbeenusedtopioneeranewareaofsofttissuesurgerydescribedas"tissuefusion"or"tissuewelding."Althoughmanywavelengthscanbeusedtoaccomplishthistask,thecarbondioxidelaserisaneffectivetoolforfusingthewallsofseveredbloodvessels.Thebiomechanicsofthelaserrepairofvesselsaresimilartothoseofsuturerepair.14Theauthorhasusedthefollowingprotocoltosuccessfullyrepairseveredpalmardigitalarteriesintwohorseswhosustainedseverelacerationsofthepalmaraspectofthepastern.LaserfusionofsevereddigitalvesselsisperformedwiththehorseundergeneralanesthesiaandanEschmarkbandageplacedatthelevelofthefetlockjoint.Theseveredmarginsofthearteryshouldbestabilizedwithsmallbulldogvascularclampsanddebridedusingsharpdissectionwithascalpel.Fourstaysuturesof5-0chromicgutareplacedat90-degreeintervalsaroundthevesselwalltostabilizethecutsurfacesofthearteryduringapplicationofthelaserenergy.Thelasermustbecapableofpreciseandstablepoweroutputatverylowpowerinordertocoagulatethecollagenwithinthevesselwallwithoutnecrosisorvaporization.Thepoweroutputisadjustedforthespotsizeofthelaserinordertoachieveanenergydensityofbetween100to175W/cm2atthetissuesurface.Ataspotsizeof2.5mm,forexample,7Wofcontinuouspowerproducesanenergydensityof150W/cm2.Thelaserenergyisappliedbetweenthestaysutures,whichareplacedundertensionbyanassistanttorigidlyapposethecutmarginsofthevessel.Anaccuratespotsizeisconfirmedbeforeheatingthetissuebyfiringthelaserontoamoistenedwoodentonguebladeandmeasuringtheprecisediameterofthepointofimpactofthelaserbeam.Thesurgeonshouldbeawarethatalthoughtheheliumneonaimingbeamandthecarbondioxideenergybeamareconcentricinaproperlytunedlaser,theprecisediameterofthetwobeamsmaynotbeexactlythesame.Theprecisedistanceofthehandpiecetothetargettissuerequiredtoachievethe2.5mmspotsizemustbemaintainedbyuseofafocusingguidethroughouttheapplicationoflaserenergytoensurecorrectpowerdensityatthetissuesurface.Thetissueiskeptdryduringtheapplicationoflaserenergyandthevisualendpointoftissueliqueficationanddiscolorationisusedtodetermineadequateheatingofthetissue.Nocharformationshouldexistatthetissuesurface.Thedevelopmentofcharindicatesthattheenergydensityistoohighandthecarbonizationisoccurring.Thetissueweldingprocessisrepeatedbyrotatingthevesselandapplyinglaserenergyalongallfoursurfacesoftheanastomosisuntiltheentiremarginissealed.TheclampsareremovedandtheEschmarkbandageisloosenedtoevaluatethesecurityofthevascularrepair.Ifleakageispresent,thetourniquetistightenedandtheareaofleakageiscleanedofbloodbyrinsingwithsaline.Theprocessisrepeateduntilanadequatesealisobtained.Thefourstaysuturesareleftinplacetoproviderotationalstabilitytotherepair.Tissueweldshavereasonablygoodstrengthintension,butareweakwhensubjectedtotorsionalstrain.Theadvantageofusingthelasertoassistinvascularrepairistoreducetheamountofforeignmaterialpresentinthevascularwall.Thisaidshealingandminimizesthetendencyforlocalizedgranulomaorscartissueformationandsubsequentluminalocclusion.ScrotalAblationCastrationThecarbondioxidelaserisveryusefulforgeneraldissectionofvasculartissuesaroundthehead,neck,andperinealregion.Descriptionoftheuseofthecarbondioxidelaserforcastrationofhorsesservesasanexampleofgeneralsofttissuedissectionthatusespthelaserasacuttinginstrumentandillustratestechniquesthatcanbeusedinmanyotherprocedures.Thehorseispositionedindorsalrecumbencyandanellipticalskinincisionismadeoverthebaseofthescrotumalongthegreatercurvatureofthetesticlesusing50Wofsuperpulsepowerinfocuswithaspotsizeof0.2mm(averagepowerdensity,approximately75,000W/cm2).Theincisionisadvancedthroughtheskin,subcutaneoustissue,anddartosfasciabyplacingthosetissuesundertensionwithalaserrod,whichalsoservestobackstopthelaserbeam(seeFig.2).Thetesticleitselfcanservetobackstopthelaserbeam,buthemorrhageofvesselsonthesurfaceofthetesticleinadvertentlyoccursandneedlesslycomplicatesthedissection.Themedianraphaeandthescrotumarethenremoveden-blocbydividingthebaseofthemedianraphaewith50Wofcontinuouspowerinthedefocusedmode,usinga1-mmspotsizetoenhancehemostasis(powerdensity,approximately7000W/cm2).Vesselsinthemedianraphaewithadiameterlargerthan1-mmareligated.Thelooseareolarfasciaisthenstrippedfromthetesticlesusingbluntdissectionandthelaserusingthelatterpowerandmodesettings.Thespermaticcordsareligatedandtheincisionisclosedwith#1polydioxanonesuture(PDS)inasinglecontinuousverticalmattresssuturepatternthatincorporatesthednrtosfascia,thesubcuticulartissues,andtheremnantofthemedianraphae.Jheadvantagesofusingthelaserforthistypeofprocedurearerelativelybloodlessdissectionofvascular-richtissuesandlymphostasis.RemovalofGranulationTissueGranulatingwoundsareextremelycommonintheextremitiesofhorsesandareadifficultchallengeforuncomplicatedhealing.Exuberantgranulationtissue("proudflesh")mustbeeliminatedtopermitdelayedorsecondarywoundclosure.Becausethistissueisextremelyvascular,useofthecarbondioxidelaserishelpfulfordebridement.Similartotheprotocolusedforremovalofcutaneoustumors,thistypeofprocedureillustratestheuseofthecarbondioxidelaserasa"volumeablation"instrument.Thebulkofthegranulatingmassisremovedbyfirstpassingthelaserbeamaroundtheperipheryofthetargettissueusing50to80Wofcontinuouspowerwithadefocused1-mmspotsize(powerdensity,approximately7000to10,000W/cm2)toachievegoodhemostasis.Thedissectionisadvancedbygentlyelevatingonecomerofthelesionwithatraumaticforcepsandpassingthelaserbeambackandforthacrosstheexpandingdiameterofthelesion(Fig.8).Vesselsgreaterthan1or2mmindiameterareligatedastheyareencountered.Oncethemassofgranulationtissuehasbeenremoved,thebasemaythenbesculptedbypassingthelaserbeamacrossthetissuebedinacrosshatchpatternusing80Wofcontinuouspoweranda2-mmspotsize(powerdensity,approximately2500W/cnr).Thelargespotsizeandan''airbrushablationtechniqueCensurearelativelyevendebridementandgoodhemostasis.TheSwiftlaseattachmentcanalsoaidinaccomplishingasmoothsurfacebyspreadingtheenergyoverauniformarea.Oncethegranulationtissuehasbeendebridedsmoothlybelowtheskinsurface,thewoundcanbeclosedusingplasticsurgicaltechniques,lefttohealbysecondintention,orgraftedatalatertime.Theprincipaladvantageofusingthelaserforthisdissectionisadramaticreductioninhemorrhagefromthesurfaceofthedebridedtissue.Palmar/PlantarDigitalNeurectomyPalmar/plantardigitalneurectomyisusuallyperformedasalastresorttreatmentforchroniclamenessofthecaudalonethirdofthedigitandwingfracturesofthethirdphalanx.Thenormalhealingresponsetoseveringanerveendingistheformationofasmallwell-organizedneuromaattheendofthecutsurfaceofthenerve.Historically,oneoftheprincipalcomplicationsofthisprocedurehasbeenpainfulneuromaformation.Thisprocessischaracterizedbyadisorganizedreanastomosisofthecutendsoftheseverednerveendingsthatisaccompaniedbyhyperplasiaofbothneuraltissueandsheath(Schwann)cells.Factorsresponsibleforthedevelopmentofpainfulneuromasinhorsesremainamatterofspeculation,althougheffortstoavoidpainfulneuromaformationhavegenerallyincludedeffortstominimizetraumaandhemorrhageandinsomecasestosealtheepineuriumtopreventleakageofaxoplasmfromthecutendsofthenerve.Inonestudy,applicationof18,426W/cm2ofC02laserenergytothedistalstumpofnervesthatwereseveredwithascalpelbladeresultedinadequatethermalsealingofthenervestumptopreventreinnervationorpainfulneuromaformationin10horsesovera23-monthperiod6Aftermanyyearsofusingthecarbondioxidelasertoperformpalmar/plantardigitalneurectomyonhorses,theauthor'simpressionisthatpainfulneuromasareextremelyrarewhenthefollowingprotocol,whichuseslaserparameterssimilartothosedescribedfortreatmentofMorton'sneuromasinhumans,isused.3Thesurgeryisperformedwiththehorseundergeneralanesthesia.Eschmarkbandagesareplacedatthelevelofthefetlockjointtoelimi-natehemorrhage.A2-cmskinincisionismadewithascalpelimmedi-atelydorsaltotheligamentoftheergot.Theincisionisadvancedwithacombinationofbluntandsharpdissectiontoexposetheneurovascularbundlethatcontainsthepalmardigitalarteryandnerve.Careistakennottodisruptthelargelymphaticvesselsthatcommonlycrosstheincisionatthissite.ThesevesselsareeasilyidentifiedonlywithcorrectapplicationoftheEschmarkbandage.Theconnectivetissuethatsur-roundstheneurovascularbundleisopenedandthepalmardigitalnerveisisolatedwithcaretakentopreservethenervesheathorepineurium.A3-or4-cmsectionofthenerveisremovedbyfirstdividingthenervedistallyusing10Wofcontinuouspowerwithaspotsizeof0.2mm(powerdensity,approximately30,000W/cm2)(Fig.9).Theepineuriumisretractedandtheproximaldivisionismadeusingthesamelaserparameters.Theepineuriumisthenpulledbackovertheproximalcutsurfaceofthenerveandisligatedwith3-0silk.Theincisionisclosedwithasinglesubcutaneoushorizontalmattresssutureof3-0PDSandskinsuturesof2-0nyloninacruciatepattern.Figure9.Anopticalbackstopisusedtoisolatetheposteriordigitalnervefromtheadjacenttissuesbeforeactivationofthelaser.Thehorseisconfinedtoastallfor14dayswithdailybandagechangesandiswalkedinhandforanother2weeksbeforereturningtonormaldailyactivity.Nonsteroidalanti-inflammatorymedicationshouldbeadministeredforthefirst10postoperativedaystominimizeinflammationatthesurgerysite.Theadvantageofusingthecarbondioxidelaserforpalmardigitalneurectomyislowincidenceofneuromaformation.Useofpowerdensitiesabovethoserecommendedshouldboavoidedbecauseuseofhighpowerscancauseapostoperativeneuritis,withhorsesshowingl