Case Discussion < Presentation of Case >　　 　　A 43-year-old man who had received the diagnosis of end-stage renal disease caused by chronic glomerulonephritis for 6 years was seen because of episodic intradialytic hypotension (IDH) for 2 weeks. He had been in his usual state of health and underwent regular maintenance hemodialysis (HD) through an arteriovenous fistula at another hospital 3 sessions a week, with each session lasting 4 hours. He had used the same dialyzer for years without problem. The blood flow rate and bicarbonate-based dialysate flow rate was 300 ml/min and 500 ml/min, respectively. His ideal dry weight was 52 kg for the past six months. The average ultrafiltration (UF) rate per session was less than or close to 1 liter/hour without causing any discomfort. The daily urine amount was 30 ml. The blood pressure was around 130/85 mmHg while he continued to receive atenolol 25 mg/day. He hiked on every weekend without any exercise intolerance. No atenolol was used on the day of dialysis. Because of hot weather recently, he consumed a plenty amount of cold soft drinks and shredded ice products. In late June, he started to experience excessive body weight gain (>6 kg) between HD sessions. Due to excessive weight gain, the UF was set at a higher rate (> 1 liter/hour) according to his weight gain at each presentation. Therefore, his ideal dry weight could not be achieved within a 4-hour HD session because of episodic IDH. 　　 The episodic IDH occurs at the latter stage of each HD session, especially in the first HD session of each week, associated with nausea, muscle cramps and yawning. The blood pressure during IDH episodes was around 90/60 mmHg. 　　 Before initiation of each HD session, he had clear consciousness without ill appearance. The blood pressure was 144/90 mmHg, the pulse rate 80 beats per minute, the respiration rate 24 breaths per minute, and temperature 36.8oC before each HD session. The pulse oximetry showed SpO2 96% while he was breathing ambient air. The conjunctiva was pink. Lungs were symmetrically expanded but with basal crackles. Examinations of the heart and abdomen were normal. There was mild to moderate pitting edema at both lower extremities. 　　While IDH occurred during HD, UF was immediately discontinued and blood flow was reduced to 150 ml/min. Patient was repositioned with legs elevation. Several times of normal saline 100 ml and 50% glucose bolus injection were given accordingly. Meanwhile, oxygen was supplied through nasal cannula and vital signs were monitored closely. The blood biochemistry tests and complete 12-lead EKG during IDH showed no significant changes in all aspects including cardiac enzymes. Echocardiography was normal. In subsequent HD sessions, HD duration was extended to 4.5 hours. Sequential UF and occasional Sodium modeling were adapted to lessen the drastic change of intravascular volume. He also received re-education on diet and fluid intake from dietitian. He gradually reduced his inter-session body weight gain to less than 4 Kg and no further IDH event was experienced. Later, he resumed the original HD settings. Results of laboratory tests and radiography Table 1. CBC and differential count Date WBC K/μL Hgb g/dL Hct (%) Plt (K/μL) Maintenance 6.56 11.8 33.7 365 During IDH 6.32 12.1 35.9 354 After adjustment 6.48 11.8 33.6 355 Table 2. Biochemistry   Pre-HD BUN (mg/dl) Post-HD BUN (mg/dl)   eKt/V   UF (L) Duration (Hour) Pre-HD BW (Kg) Pre-HD Cre (mg/dl) Na (mmol/l) K (mmol/l) AST (U/l) ALT (U/l) Bil (T) (mg/dL) Maintenance 88 30 1.20 4 4 56 8.8 136 4.6 20 18 0.9 During IDH 102 40 0.98 3 3.3 58.5 9.3 139 4.5 21 19 1.0 After adjustment 94 34 1.11 4.5 4.5 58 9.1 138 4.3 18 18 1.0 CXR (During IDH): Mildly enlarged heart size with cardiothoracic ratio 0.55. No costo-pleural angles blunting < 病例分析 > 　　Intradialytic hypotension (IDH)-透析中低血壓是病患在接受血液透析尤其是伴隨脫水(Ultrafiltration, UF)時相當常見的臨床表現。統計約15%至50%的血液透析療程會伴隨透析中低血壓的發生。透析中低血壓對臨床醫師重要之處，不僅在於要能預防，並且能處理其發生，也要能瞭解可能因低血壓而伴隨的急性及延遲性併發症對病患的影響。 　　 臨床上造成透析中低血壓發生的原因很多 (Table 1) ，通常不會是單一原因造成透析中低血壓。但不論是什麼原因，都會增加病患fistula thrombosis及cardiovascular diseases的發病率(morbidity)與死亡率(mortality)。會引起透析中低血壓的常見危險因子包括高脫水率(UF rate)，此尤其常見於在兩次透析療程間體重增加過多或dry weight設定過低的病患、罹患心血管疾病導致cardiac reserve不足、糖尿病病患伴隨 autonomic neuropathy、透析前或透析中飲食及透析當天未停用降血壓藥物等。 　　 大部份病患發生透析中低血壓時， 會伴隨一些不具特異性的症狀，如頭暈、頭重、打哈欠、抽筋、噁心、嘔吐或喘。依據這些症狀，有經驗的血液透析病患大概都知道自己發生透析中低血壓，但透析中定時的血壓測量也能幫助醫師及早警覺與處理。但若是初進入透析之病患或緊急透析病患就更需要醫師的高度警覺心。 　　 雖然造成透析中低血壓的原因很多，但基本處理方法都是類似的，一旦病患發生透析中低血壓，第一步要做的就是停止脫水及降低blood flow rate，並將病患安置成頭低腳高或Trendelenburg姿勢，並視需要給予氧氣，mannitol或normal saline注射。臨床實務上常以normal saline bolus infusion為第一線治療方法。另外，50% glucose bolus injection也時常被使用，因為50% glucose bolus injection被研究證實能增加血中arginine vasopressin的濃度，進而改善透析中低血壓。其他後續的處理方法則須依據造成透析中低血壓的原因採個別處理。 　　透析中低血壓其實是可以預防的。在血液透析過程中，針對可能發生透析中低血壓的高風險病患，我們可以事前採用一些預防方法或利用特殊的透析設定來減低透析中低血壓的發生機會(Table 2)。使用低脫水率是預防透析中發生低血壓最直接的方法，停止脫水也適用於任何原因造成的透析中低血壓，但在如兩次透析療程間體重增加過多的病患，則會造成脫水量不足的結果，此時就必須考慮延長透析時間及增加次數，並加強飲食控制，否則有可能發生pulmonary edema。此外也要考慮病患dry weight是否過低導致相對高脫水率，而引起透析中低血壓。罹患心血管疾病導致cardiac reserve不足的病患，根本方法還是以處理心血管疾病為主，其它為輔。透析前或透析中減少進食或透析當天停用降血壓藥物，也都是常採用的方法。若這些方法並不適合，如病患拒絕配合延長透析時間或次數時，就必須考慮採用特殊的透析設定如sequential UF、sodium modeling、降低透析液溫度，甚至居家夜間透析來達成目的。 < References > 1. Hemodynamic instability during hemodialysis: Overview. UpToDate (www.uptodate.com) 2. Am J Kidney Dis. 2008;52(2):294-304 3. Curr Opin Nephrol Hypertens 2012,21:593-599   Table 1. Etiology of intradialytic hypotension (Modified from UpToDate) Rapid reduction in plasma osmolality Rapid fluid removal Inaccurate dry weight setting Autonomic neuropathy Diminished cardiac reserve, cardiac arrhythmia, ischemic heart disease and pericardiac effusion or tamponade Acetate-based dialysate Adenosine release due to organ ischemia Meal ingestion during dialysis Anaphylactic reaction to dialyzer membrane Excessive synthesis of endogenous vasodilator (e.g. nitric oxide) High magnesium concentration in dialysate Inadequate vasopressin synthesis   Table 2. Intervention to prevent or treat intradialytic hypotension (Modified from Curr Opin Nephrol Hypertens 2012,21:593-599) Limit interdialytic weight gain: restrict sodium intake Optimal dry weight adjustment Avoid food intake during HD Sequential ultrafiltration Sodium modeling Bicarbonate-based dialysate Lower dialysate temperature Switch to hemodiafiltration Increased HD duration or frequency Suspend anti-hypertension medication on HD day Use of midodrine or carnitine 繼續教育考題 1. (C) 臨床上會發生於透析時併發症，並不包括？ A Intradialytic hypotension B Intradialytic hypertension C Increased urine output D Acute coronary syndrome 2. (D) 發生透析中低血壓時常見的症狀，包括？ A Fatigue B Muscle cramping C Dizziness D All of above 3. (D) 常見造成透析中低血壓的原因為？ A High ultrafiltration rate B Inappropriate dry weight setting C Poor cardiac reserve D All of above 4. (B) 預防透析中低血壓的一般原則，不包括？ A Suspend anti-hypertensive medication on the HD days B Encourage food intake during HD C Optimal dry weight adjustment D All of above 5. (C) 臨床上處理透析中低血壓的基本原則，不包括？ A Suspend ultrafiltration B High osmotic fluid infusion C Decrease dialysate flow D Decrease blood flow 6. (D) 臨床上於兩次透析療程間體重增加過多的病患，一般需採用何方法以避免透析中低血壓，但又避免造成脫水量不足? A Increased HD duration or frequency B Sequential ultrafiltration C Sodium modeling D All of above

答案解說 ( C ) 臨床上會發生於透析時的併發症，包括常見的intradialytic hypotension，而少數病患會出現血壓越來越高的paradoxical phenomenon (intradialytic hypertension)。若病患cardiac reserve不足，則可能發生acute coronary syndrome。一般長期透析病患的尿量是與透析時間成反比。 ( D ) 透析中低血壓時常見的症狀包括大部份病患發生透析中低血壓時，會伴隨一些不具特異性的表現，如頭暈、頭重、打哈欠、抽筋、噁心、嘔吐或喘。 ( D ) 常見造成透析中低血壓的原因包括如Table 1所述。 ( B ) 預防透析中低血壓的一般原則如Table 2所述，但不包括增加飲食。 ( C ) 臨床上處理透析中低血壓的基本原則如Table 2所述，但不包括降低透析液流速。透析液流速與毒素清除關連較大，而非血壓。 ( D ) 臨床上於兩次透析療程間體重增加過多的病患，一般需採用降低脫水率、延長透析時間、次數並加強飲食控制以避免體重增加過多。其他原則如Table 2所述，也常一起併用。