因為
洗腎時,會脫水。
六個字,打完收工。
是的!就這麼簡單,如果洗腎的時候不需要脫水,那洗腎本身就幾乎不可能掉血壓了。
從另一個角度來講,掉血壓(以下簡稱為:掉壓備註),有時候不是洗腎造成的,和洗腎沒有關係,然而,這些與洗腎無關的掉壓,背後的原因,都是非常嚴重的問題,一定要好好分辨:
1. 感染
只要是感染都有可能造成敗血症、進而休克,休克的意思就是血壓不夠,而使得身體一些重要器官罷工了。常見的感染包含血管(廔管)的感染、肺炎、腹腔內的感染等等。
2. 心臟衰竭
心律不整會使得心臟亂跳,血壓就會不穩定。心肌缺氧、或心肌梗塞都有可能引發心臟收縮不良,心臟力氣變差,身體的馬達故障了,當然血壓就掉下來了。
3. 體內大出血
當很嚴重的出血時,心臟的氧氣不足,力氣也會減弱,就像馬達油不夠,當然就沒力了。最常見出血的地方,是腸胃道,不管是胃潰瘍、十二指腸潰瘍、痔瘡、大腸病變等等,都可能會導致出血。
以上這三個是比較常見、和洗腎無關的掉壓原因,那與洗腎有關的掉壓,又是怎麼一回事呢?
回到文章開頭第一句話,洗腎會脫水,所以會掉血壓,照這麼說,那每次洗腎都會脫水,為什麼不是每次都會掉血壓呢?這才是最重要的核心問題!要繼續看下去之前,請先看一下“洗腎患者的血壓應該要多少”這篇文章,幫您歸納重點兩句話:
會影響血壓的種種因素,可以簡化成兩個:
血量、與血管阻力。
當洗腎的治療開始之後,身體中多餘的水分、與累積的毒素,就慢慢的清除掉,也就是開始脫水與脫毒素了。水量減少代表血量也跟著減少,而身體在血量減少的同時,會有兩種自然的反應(圖中的星星與紅十字),來保持住血壓不往下掉,以保護重要的器官(如心臟與腦部):
1. 防衛機制的啟動(圖中的星星處)
當身體偵測到血管裡的血量慢慢在減少,會使得血管收縮(增加血管阻力,能使血壓上升),心臟收縮力增強或者心跳加快(馬達轉強一點),以維持血壓不下降。
這裡的關鍵其實是“偵測”,患者可能會因為本身疾病的關係,而使得偵測能力變差,常見的原因有:糖尿病、年紀大、或尿毒本身等等因素,這些都有可能讓反應變鈍,因此,有的人就是比較不耐脫水,和體質有關係。
所以,和洗腎有關係的掉壓
較常發生在糖尿病或老年人
2. 從血管外面的組織補充血管內的水分(圖中的紅十字處)
當血引流到體外,而脫去水分的同時,身體中的組織也持續地給血液補充水分,一個脫水,一個補水,目的是使血量不變。然而,之前的文章就有講過脫水速度是不能太快的,追根究底其實就是因為補水的速度有其極限,當脫水的速度比補水的速度還要快時,血管中的血量就會下降,進而產生低血壓的種種症狀。
還要講很重要的一點觀念,身體組織補水的速度,和組織裡的水量多寡有關。講白話一點,當身體水很多時,組織補水速度快;身體水很少時(比較乾的時候,或者越接近乾重時),組織補水速度慢。
因此,洗腎的前半段,身體還有很多水,補水的速度和脫水速度差不多是相等,但是到了後半段,補水的速度變慢,假如慢到跟不上脫水的速度時,又加上前面所說的防衛機制沒有啟動,就掉壓了。
所以,和洗腎有關係的掉壓,
發生時間通常在後半段。
通常是脫水速度快的人。
可能要考慮調整乾體重。
理由在此。
那應該怎麼辦呢?下一篇“洗腎時會掉血壓,怎麼辦?”會告訴你~
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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