上一篇講電腦斷層(CT)、心導管檢查、或者血管攝影等檢查所需要借助的顯影劑,卻沒講核磁共振的顯影劑,這是因為這兩類的檢查,所用的顯影劑,特性、原理不同,所以分兩篇講,比較清楚。(其實也是因為太長了,怕大家看不下去)
先複習結論:
電腦斷層、心導管、血管攝影的顯影劑,按照原本規則的時程透析即可!
核磁共振的顯影劑,最好將透析安排在檢查後,不要隔太久。
和顯影劑有關的不良反應中,不能不提的就是腎因性全身纖維化(Nephrogenic Systemic Fibrosis),約在2000年左右,陸陸續續發現一些這樣的患者,此病的特徵為全身皮膚、皮下組織的纖維化,許多內臟組織也都可能受影響的一個全身性疾病,分析這些患者的情況後發現,主要發生在末期腎臟病(慢性腎臟病第四期以及第五期)、尤其是已經進入透析的患者身上,而且與含有Gadolinium(釓)的核磁共振顯影劑,有強烈的相關性!
再進一步分析,含有Gadolinium(釓)的核磁共振顯影劑中,也分成比較危險的種類(class I,確定曾經導致數個病例),比較安全的種類(class II,可說幾乎沒有造成確定病例),以及尚未確定的種類(class III,累積經驗仍不算多,因此不確定安全性);另外,幾乎所有的病例都是腎絲球過濾率(eGFR) <30 ml/min/1.73 m2 (全世界文獻裡面只出現過 1、2 個 >30 的個案),就算是慢性腎臟病第四期(CKD stage IV)的患者,他們的 eGFR也是比較接近 15 ml/min/1.73 m2的。
因此,當要接受核磁共振影像檢查時,一定要確認腎功能(腎絲球過濾率,eGFR),如果數值小於 30,又或者最近腎臟功能急速惡化者(急性腎衰竭,AKI),如果真的得做核磁共振,放射科醫師會選擇用比較安全的class II顯影劑,可避免腎因性全身纖維化的產生。
當然,如果能夠改用電腦斷層來輔助診斷,就盡量照電腦斷層就好了,不過,核磁共振的解像力,在某些部位或器官是無法取代的,那就還是用核磁共振,放射科醫師都會把關選擇較安全的顯影劑。
那,為甚麼核磁共振之後,還是要盡快透析呢?
先澄清一個觀念:盡快透析,其實無法避免患者產生腎因性全身纖維化,所以還是要選安全的 class II 顯影劑。然而,血液透析確實能夠移除體內殘存的這些顯影劑,因此,理論上,越早透析,這些顯影劑積累於組織中的量就越少。綜上所述,盡快透析這個做法雖然證據薄弱,只有理論上的好處,但為了這個難纏的疾病,放射科學會仍然還是建議,可以的話,最好將透析時間挪近一點,盡快移除含有Gadolinium(釓)的核磁共振顯影劑(Contrast media manual v10.3, P.88)。
上一段所謂的“挪近一點”,並不是要腎友馬上立刻接受透析,只要在洗腎室可配合的情況下,將下一次的透析時間往前改近一點就可以了,畢竟,核磁共振的時間,不是那麼容易安排在剛好透析之前,有時候檢查排的進去就很偷笑了,如果只能安排在傍晚做檢查,而晚上洗腎室又沒辦法透析,那也沒有關係,將洗腎時間排在隔天早上或下午,都還算能接受。
各家醫院的建議可能不盡相同,提供一個國外的建議—舊金山大學醫學中心,建議血液透析患者接受核磁共振檢查之後,在24小時之內安排血液透析,是比較好的做法。
最後,再強調一次結論:
注射了核磁共振的顯影劑之後,盡早安排血液透析,理論上是較佳的做法。
再嘮叨一下,至於患有慢性腎臟病,但還沒開始洗腎的患者,做完檢查後,不需要為了移除顯影劑,而預防性的立刻接受血液透析,因為沒有好處。
PS. 感謝我的兩位好同學,協助我釐清觀念,特此向台中榮總放射科陳虹潔主治醫師、柳營奇美醫院放射科許文遠主治醫師致謝~!
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