分享-Review:Hemodialysis access thrombosis

剛剛看到一篇血管通路血栓的綜述，個人感覺內瘺檢查和監測這部分內容概括的比較得當，摘錄部分分享給各位知友。

Hemodialysis access thrombosis

Keith Bertram Quencer1, Rahmi Oklu2

1Division of Interventional Radiology, Department of Radiology, University of Utah, Salt Lake City, UT, USA; 2Division of Interventional Radiology,Department of Radiology, Mayo Clinic, Phoenix, AZ, USA

Monitoring and surveillance

Monitoring and surveillance are employed in order to identify a dialysis access at risk of thrombosis with the goal of intervening before thrombosis occurs (6,7). The effcacy of monitoring and surveillance in preventing access thrombosis and polonging the life of the access is uncertain (8,9).

監測和監測是否能預防通路血栓、延長通路壽命，作者持不確定態度，但是其所搜集的文獻有點少。

Monitoring consists of focused physical examination of the access and review of data gathered during the normal course of dialysis such as Kt/V, serum potassium, pump pressures and problems with access cannulation (e.g.,prolonged bleeding after needle removal) (6).

查體、血透過程的一些情況包括Kt/V、血鉀、管路壓力和穿刺止血問題都是屬於檢查（Monitoring）的範疇，Monitoring是不依賴於特殊器械的。

Physical examination, performed at least monthly by a qualified practitioner, includes looking at, feeling and listening to the access to identify possible stenoses that place the access at risk of thrombosis. Signs of outflow stenosis include development of aneurysmal dilation of the access, abnormally increased pulsatility, a discontinuous thrill and a high-pitched bruit in the outflow vein.

流出道狹窄的徵象包括：靜脈流出道出現動脈瘤樣擴張、搏動異常增強、非連續的震顫和雜音(單純動脈收縮期）、高調雜音。所以內瘺搏動不是越強越好，搏動強而震顫弱是流出道狹窄的常見表現。

Signs of in?ow stenosis include a ?at fstula, poor turgor or a weak bruit (10).

流入道狹窄（吻合口或動脈狹窄）徵象有所不同，主要表現是內瘺塌癟，充盈不佳，雜音減弱，當然搏動也不強。

Kt/V quantifes dialysis adequacy. K represents the clearance of urea, t represents the dialysis time and V represents the volume of distribution of urea. Low Kt/V denotes inadequate dialysis, which adversely affects the patients quality of life and is associated with lower survival (11). A low Kt/V may indicate poor access flow which places the access at risk for subsequent thrombosis (12). A Kt/V of <1.2 or an interval decrease by more than 0.20 should prompt intervention both to increase dialysis adequacy as well as forestall potential access thrombosis (13).

Kt/V是血透充分性指標，而充分性又常常和透析血流量相關。Kt/V低於1.2或者下降0.2以上要注意內瘺流量下降和血栓的問題。

Prolonged bleeding after needle withdrawal is a common sign of outflow stenosis. Excessively negative pre-pump arterial pressure is a sign of in?ow stenosis.

止血時間延長提示流出道狹窄（靜脈穿刺點的下游狹窄），泵前動脈壓負值增大（負壓，動脈端抽吸狀態）提示流入道狹窄。

Surveillance is the periodic employment of specialized instrument based testing. Examples include access flow measurements (Qa), static venous pressure measurements, quantifcation of recirculation and Duplex ultrasound (6).

監測（Surveillance）是指周期性的利用一些特殊的設備對血管通路進行檢測。比如：通路血流量、靜態靜脈壓、重複循環率、多普勒超聲。

Access flow measurement is the most reliable and validated surveillance tool (14). AVGs are at risk of thrombosis when Qa falls below 500 mL/min. AVFs are at risk of thrombosis when Qa is less than 300 mL/min. The main reason AVGs thrombose at higher flow rates than AVFs is that they lack an endothelium (15). Falling Qa is highly predictive of subsequent access thrombosis; one study showed a near 14-fold increase in access thrombosis when Qa dropped to 65% of baseline (16).

血流量測定是可靠的監測工具。人工血管內瘺血流量低於500ml/min、自體血管內瘺低於300ml/min時，血栓風險增高。

Static venous pressure measurements are useful in AVGs where the site of stenosis predictably occurs just downstream from the graft-to-vein anastomosis. Static venous pressure measurements in AVFs are of lower utility in predicting access thrombosis for multiple reasons. For one, AVFs often have stenosis involving the inflow. Additionally collateral vessels may develop and enlarge, dissipating the increased intra-access pressures in the setting of out?ow stenosis. An access to systemic pressure ratio less than 0.4 is normal; a ratio greater than 0.5 should trigger evaluation (17).

靜態靜脈壓測定對於發現AVG的靜脈吻合口及流出道狹窄有意義，對AVF意義可能有限。當靜態靜脈壓與平均動脈壓比值大於0.5時，要注意流出道狹窄的可能。

Recirculation occurs when blood that has just been through the dialysis machine returns back into the dialysis machine rather than ?owing towards the right atrium. This can occur with both with inflow and outflow stenoses. By defnition recirculation can only occur when Qa is less than pump ?ow rate (Qb). When recirculation is due to out?ow stenosis, it occurs because the path of least resistance is retrograde, through the AV access (i.e., towards the feeding artery) and into the arterial needle, rather than antegrade (i.e., through the outflow stenosis). When recirculation occurs secondary to inflow stenosis it is because the in?ow is unable to support the amount of ?ow required to maintain the set Qb; the arterial needle has to 「borrow」blood returning into the access via the venous needle to maintain the flow rate demanded by the pump (13).

Recirculation is an ineffective surveillance technique. First, it is only an indirect measure of Qa, which can be measured more precisely by other methods. Second, it is insensitive in identifying an AVG at risk of thrombosis. This because Qb is typically set at 300 mL/min and recirculation will only occur when Qa is less than this set Qb. An AVG is at risk of thrombosis when flow rates are less than 500 mL/min. Additionally, stenosis between the two needles cannot be detected by measuring recirculation. Finally, recirculation can occur when there is accidental needle reversal, making it a non-specifc finding.

Ultrasound can be used as a surveillance tool. A >50% stenosis is likely when there is a focally elevated peak systolic velocity of >400 cm/s or a local peak systolic velocity ratio of >2.5. Gray scale and color Doppler ultrasound can also directly show a focal lumen diameter reduction. Caution should be taken when applying these thresholds at the arterial anastomosis where the normal turbulent flow leads to elevated peak systolic velocities. Ultrasound can also be used to measure ?ow volumes within the access (18).

超聲是良好的監測工具，狹窄局部的收縮期峰值流速通常大於400cm/s，收縮期峰值流速比大於2.5（我推測應該是和上游正常血管相比，美國超聲協會一般是指上游2cm）。但是這個標準的運用在動脈吻合口附近要小心，吻合口湍流大，收縮期峰值流速可能本身就比較高。

Controversy surrounds the efficacy of surveillance. Studies have shown that surveillance of AVGs increases the discovery of stenoses and the number of interventions performed but does not seem to prolong their lifespan (9). In contrast, studies have shown surveillance for AVFs decreases the frequency of thrombosis and prolongs access survival (8).

這篇文章認為，監測對於通路意義對於AVG和AVF是不一樣的。對於AVG，定期監測可以狹窄的檢出和干預的次數，但似乎不能增加通路壽命（但是AVG即使是血栓形成也可以被反覆開通，所以再次開通時間確實可能不太受影響，但是監測可以避免急性血栓事件的概率，急性事件干預總是需要更多的精力和更多的不確定性，還有時間窗的限定）。對於AVF，監測是可以降低血栓發生率、延長通路壽命。

原文里還有血栓的處理等內容。原文鏈接：