首先,先釐清“掉血壓(以下簡稱掉壓備註)”的發生,是不是和洗腎有關。
一般來說,請注意,我是說“一般來說”,並不是絕對喔,一般來說(很重要,所以要講三次),與洗腎相關掉壓的特徵為:
可能脫水速度太快、超速了。
發生時間通常在後半段。
如果有以上兩個特徵之一,就比較像是與洗腎相關。
為什麼會掉血壓?在前一篇文章有整理囉,節錄重點如下:
到了後半段,補水的速度變慢……慢到跟不上脫水的速度時,
又加上……防衛機制沒有啟動,就掉壓了。
要避免洗腎相關的掉壓,我們得矯正上面黃底的三個重點:
讓脫水的速度放慢
讓洗腎後半段時的補水速度增加
試著讓防衛機制恢復正常
怎麼做?
一、放慢脫水速度
方法一是請患者控制水分,液體類(開水、茶、湯、飲料等等)的食物盡量少喝,重的少,自然脫水量少,脫水速度就慢。
方法二是拉長透析時間,同樣脫水 3 公斤,4個小時脫完,和5個小時脫完,當然是5個小時脫水比較慢,速度差了 20%,就比較有機會把水脫完不掉壓。
脫水速度應該要控制在多少以下呢?這篇文章中有說,應該控制在每公斤每小時 10 cc以下,最多不能超過每公斤每小時 13 cc的速度,否則,會增加死亡率喔。
補水的速度,和身體組織剩多少水分有關係。
讓身體在洗腎的後半段還留有足夠的水量,就能讓補水的速度增加,講白話一點,就是不要洗那麼乾。把目標體重調高,就能讓體內的水量增加,補水的速度就會變快,就會減少掉壓的機會。
可是,目標體重不能無限制的一直往上增加,我們在解釋乾體重的文章中講過,腎友洗腎完應該保持越乾越好,在沒洗腎的那幾天所吃進去的水分,身體才有足夠的彈性空間來容納。這也是“乾體重”這個名詞的由來:洗完越乾越好,不要乾到不舒服就好。因此,是否該調高目標體重,一定要和醫師充分討論,再來調整。
三、改善防衛機制的啟動
影響防衛機制的因素有:體質(糖尿病、年紀大等等)、平常的血壓用藥、在洗腎中吃東西、透析液的溫度、透析液的鈉離子或鈣離子濃度等等。
體質是無法改變的,但我們如果把血糖盡量控制好,可以讓自律神經失調不再惡化下去。
血壓用藥是我們能夠調整的,在洗腎前幾個小時的這段時間,可以試著把血壓藥物減少,或者洗腎前不吃血壓藥,也能夠減少掉壓的發生。
在洗腎當中進食,會使得原本就已經抓襟見肘的血流,跑去腸胃消化食物,以致於重要器官(腦或心臟)的血流下降,就會使防衛機制反應變差。我知道不少腎友會在洗腎當中吃東西,也沒有掉壓的情況,但是“避免在洗腎當中進食”才是正確的做法喔。
升高血壓的方法就是要想辦法收縮血管,而收縮血管的方法有:降低透析液溫度(遇冷收縮嘛),使用升壓藥物-Midodrine等等。透析液的溫度是冷一點比較好,由於每個人體溫不盡相同,個人化的建議是設定在比體溫低0.5度。Midodrine或許有點效果,但是之後再以專文討論比較完整。
當透析液的鈉離子濃度或鈣離子濃度調高一點,也有助於讓血壓穩定,但是調高這兩種離子濃度的做法都有隱憂,調高鈉離子濃度會口渴(文章討論在此),調高鈣離子濃度會血管鈣化(文章討論在此),因此,透析液的這些離子濃度調整,需要更個人化的調整,還是要請腎友與醫師充分討論,再做決定。
有人嘗試用肉鹼(L-carnitine)來減少透析時的掉壓,可惜效果並不一致,無法建議,請參照之前肉鹼(L-carnitine)的文章。
節錄重點
1. 用發生掉壓的時間點,粗略區分是否與洗腎相關
2. 與洗腎相關的掉壓,可試著放慢脫水速度、調高乾體重、和改善身體防衛機制等等
另外,與洗腎無關的掉壓原因,常見的有:感染、心臟衰竭、體內大出血。當有相關的症狀的時候,則需針對這些原因做進一步治療。
備註:
透析中的掉壓有著嚴格的定義,1. 收縮壓(systolic blood pressure)下降 20 mmHg 或平均血壓(mean blood pressure)下降 10 mmHg,2. 出現症狀,3. 洗腎室醫護人員需要處理以改善的狀況,在設計研究的定義裡,三個同時都存在才算透析中的掉壓。說實在的,這和“低血糖”的定義很像。
不過臨床上,一般會用比較寬鬆的定義來看掉壓,這部分則由臨床醫師及護理師來做判斷。但需要澄清一點,每個人的血壓基準點不同,有的人本身就血壓比較低,如果沒有症狀,一般小心觀察來處理就可以了。
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