最新的“美國腎臟病期刊(AJKD)”裡,有一篇剛好就在討論透析液裡的“鈣離子濃度”,因為之前已經寫過三篇和這個有關的文章了(什麼?還沒看過?連結在此:第一篇、第二篇、第三篇),但我在第三篇的結尾,留下了一個未解的問題,那就是……
Q:如果是副甲狀腺機能亢進的患者,使用鈣離子濃度 2.5 meq/L的透析液,會不會影響到副甲狀腺機能亢進的治療?
這個問題真的很無奈。
這篇文章,第一個段落就把這個問題做了很詳細的整理,有不少研究顯示,把患者的透析液鈣離子濃度調低(如:從 3.5 mEq/L調成 3.0 mEq/L,或從3.0 mEq/L調成 2.5 mEq/L),血鈣會因此而降低(當然),但是因為血中鈣離子降低 → 刺激副甲狀腺素增加 → 鹼性磷酸脢增加。而因為副甲狀腺濃度增加,會使醫師得開立更多的活性維他命D來壓制副甲狀腺,而增加的活性維他命D,會增加腸道吸收更多的磷,導致血中磷離子濃度上升,而血磷的上升又會增加磷結合劑(鈣片,或其他選擇)的使用劑量,如下表整理。
透析液鈣離子 | 血中鈣離子 | 副甲狀腺素 | 活性維他命D用量 | 血中磷離子 | 鹼性磷酸脢 |
↓ | ↓ | ↑ | ↑ | ↑ | ↑ |
因此,本篇這個部份的結語提到,當患者的副甲狀腺是功能亢進時,有兩種作法:
1. 用患者的血清游離鈣濃度(ionized calcium)當基準,使用比這個基準稍微高一點的透析液,可能比較合適。
2. 另一種做法,是維持透析液鈣離子於 2.5 mEq/L不變,但是增加活性維他命D的劑量,以及增加鈣片來降血中的磷,因為透析液的鈣離子濃度用的比較低,所以有本錢把鈣片增加,作者認為這樣的作法,控制副甲狀腺的效果應該差不多,只不過腸道磷的吸收增加,可能會是個問題。
2015.6.3補充:感謝蔡文欽朋友,磷結合劑並非只有鈣片而已,也有其他的選擇,之後會再專文介紹。
“透析液鈣離子濃度”雖然是個小細節,但能討論的還真多,念了這些文章之後會發現,這個細節,不只是看患者血中鈣濃度來決定,還要考慮患者的副甲狀腺情況、使用什麼種的磷結合劑、有沒有用活性維他命D等等,來綜合判斷;如果患者願意的話,自費測個血中的 ionized calcium(健保碼24007B,約400-500元),或許有幫助選擇最合適的透析液。
後記:這篇文章還有討論其他的面向,如:尿毒性動脈鈣化(calcific uremic arteriolopathy)、血管硬化(vascular stiffness)、心血管鈣化(cardiovascular calcification),可惜的是,為了這些情況,而去降低透析液的鈣離子,最低也是只能到 2.5 mEq/L,而且都沒有明顯的效果,最多只能建議“不能用太高的鈣濃度”而已。而如果是透析中很容易掉血壓的患者,用高一點的鈣濃度,可以改善生活品質,也比較容易達到脫水的目標。由於不是我想討論的重點,就不花版面贅述了。
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Langote A, Ahearn M, Zimmerman D. Dialysate Calcium Concentration, Mineral Metabolism Disorders, and Cardiovascular Disease: Deciding the Hemodialysis Bath.
Am J Kidney Dis. Published online May 7, 2015.
http://doi.org/10.1053/j.ajkd.2015.02.336