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🫀 生理适应 · 第1课，共10课 · 7 min

钾：能让心脏停跳的电解质

Potassium: The Electrolyte That Stops Hearts

🍌 Potassium 是唯一在过高和过低两端都有致命范围的电解质。过低时心脏颤动；过高时心脏停跳。考试会考查这两种情况，而且通常放在同一位患者身上。

🍌 Potassium is the one electrolyte with a lethal range on both ends. Too low and the heart quivers; too high and it stops. The exam asks about both, usually in the same client.

💡 核心要点

高钾：T 波高尖；calcium gluconate 保护心脏，insulin 和 dextrose 使钾转移，钾结合剂和透析将钾清除。低钾：T 波低平和 U 波，有 digoxin 中毒风险；缓慢补充，绝不能 IV 推注。

High potassium: peaked T waves; calcium gluconate protects the heart, insulin and dextrose shift it, binders and dialysis remove it. Low potassium: flat T and U waves, digoxin toxicity risk; replace slowly, never IV push.

🧠 为什么重要

钾的正常值是 3.5 至 5.0 mEq/L。HYPERKALEMIA（高钾血症，高于 5.0）源于肾衰竭、保钾利尿剂、ACE inhibitors、酸中毒、组织挤压伤、烧伤和输注库存较久的血液。ECG 显示 T 波高尖，随后 QRS 波群增宽，最后出现正弦波并发生心脏停搏；同时伴有肌无力和感觉异常。治疗包括 IV CALCIUM GLUCONATE 以稳定心脏（它并不降低钾），然后用 IV REGULAR INSULIN WITH DEXTROSE 和雾化吸入 albuterol 将钾转移到细胞内，酸中毒时使用 sodium bicarbonate，并用钾结合剂、袢利尿剂或透析将钾清除；同时停止一切钾摄入。HYPOKALEMIA（低钾血症，低于 3.5）源于袢利尿剂和噻嗪类利尿剂、呕吐、腹泻、鼻胃管吸引和 insulin；ECG 显示 T 波低平和 U 波，并伴有肌无力、痉挛、便秘、肠梗阻，以及对 DIGOXIN 的敏感性危险地升高。口服补充 potassium chloride 时应随餐服用并喝一整杯水，以减少胃肠道刺激；或经 IV 用泵稀释输注，外周静脉速度不超过约 10 mEq/hr，绝不能静脉推注，且要先确认患者有足够的尿量。教导患者多吃富含钾的食物：香蕉、橙子、土豆、西红柿、菠菜、鳄梨和干果。

Normal potassium is 3.5 to 5.0 mEq/L. HYPERKALEMIA (above 5.0) comes from kidney failure, potassium-sparing diuretics, ACE inhibitors, acidosis, crushed tissue, burns and transfusions of older blood. ECG shows tall PEAKED T WAVES, then a widened QRS and finally a sine wave and arrest; muscle weakness and paresthesias accompany it. Treatment: IV CALCIUM GLUCONATE to stabilize the heart (it does not lower potassium), then IV REGULAR INSULIN WITH DEXTROSE and nebulized albuterol to shift potassium into cells, sodium bicarbonate if acidotic, and potassium binders, loop diuretics or dialysis to remove it; stop all potassium intake. HYPOKALEMIA (below 3.5) comes from loop and thiazide diuretics, vomiting, diarrhea, nasogastric suction and insulin; ECG shows FLATTENED T waves and U WAVES, with muscle weakness, cramps, constipation, ileus and a dangerously increased sensitivity to DIGOXIN. Replace orally with potassium chloride supplements taken with food and a full glass of water to limit GI irritation, or IV diluted by pump at no more than about 10 mEq/hr peripherally, never by push, and check that the client has adequate urine output first. Teach high-potassium foods: bananas, oranges, potatoes, tomatoes, spinach, avocados and dried fruit.

🏥 真实场景

📈 一位肾衰竭患者漏做了一周透析，到院时虚弱，钾为 7.1，监护仪上显示 T 波高尖。护士先输注 calcium gluconate，然后用 insulin 加 dextrose，同时安排透析。Calcium 争取到的是分钟，insulin 争取到的是小时，透析解决的是根本问题。考试会问哪一步最先做，答案是让心脏继续跳动的那个药物。

📈 A client with kidney failure misses dialysis for a week and arrives weak with a potassium of 7.1 and peaked T waves on the monitor. The nurse hangs calcium gluconate first, then insulin with dextrose, while dialysis is arranged. Calcium buys minutes, insulin buys hours, dialysis fixes the problem. The exam asks which comes first, and the answer is the drug that keeps the heart beating.

📌 要点总结

  • 正常值 3.5 至 5.0；两个方向都会引起心律失常Normal 3.5 to 5.0; both directions cause arrhythmias
  • 高钾血症：calcium gluconate、insulin 加 dextrose、钾结合剂、透析Hyperkalemia: calcium gluconate, insulin plus dextrose, binders, dialysis
  • 低钾血症：注意服用 digoxin 的患者；用泵补充，绝不能推注Hypokalemia: watch digoxin clients; replace by pump, never push

📖 本课术语

高钾血症 (Hyperkalemia): 钾高于5.0 mEq/L，表现为高尖T波，并可使心脏停跳。

低钾血症 (Hypokalemia): 钾低于3.5 mEq/L，表现为T波平坦和U波，并增加digoxin中毒的风险。

MURDER（高钾血症征象） (MURDER (hyperkalemia signs)): Muscle weakness（肌无力）、Urine output low（尿量减少）、Respiratory distress（呼吸窘迫）、Decreased cardiac contractility（心肌收缩力下降）、ECG changes（ECG变化，高尖T波）、Reflexes abnormal（反射异常）：钾高于5.0 mEq/L的征象。

钾（K+） (Potassium (K+)): 正常3.5至5.0 mEq/L；低会带来T波平坦、U波和digoxin中毒，高会带来高尖T波和心脏停跳，低于2.5或高于约6.0至6.5是危急值。

✅ 自我测试

一位患者钾水平为 6.8 mEq/L，并有 T 波高尖。护士预计首先给予哪种药物？A client with a potassium level of 6.8 mEq/L has peaked T waves. Which medication does the nurse expect to give FIRST?
  1. 口服 furosemideOral furosemide
  2. IV calcium gluconate
  3. 皮下 insulinSubcutaneous insulin
  4. 口服钾结合剂Oral potassium binder

答案: B · IV calcium gluconate

Calcium gluconate 立即稳定心肌细胞膜，在其他措施降低钾的同时预防心律失常。皮下 insulin 降低钾的速度太慢，而且不像第一种药物那样紧急地保护心脏。

Calcium gluconate stabilizes the cardiac membrane immediately, preventing arrhythmias while other measures lower the potassium. Subcutaneous insulin lowers potassium too slowly and does not protect the heart as urgently as the first medication does.

一位服用 furosemide 和 digoxin 的患者钾为 2.9 mEq/L。为什么这个发现特别危险？A client taking furosemide and digoxin has a potassium of 2.9 mEq/L. Why is this finding especially dangerous?
  1. 低钾会增强 digoxin 的作用Low potassium potentiates digoxin
  2. 低钾会导致高血糖Low potassium causes hyperglycemia
  3. 低钾没有临床意义Low potassium is not clinically significant
  4. 低钾会阻断 furosemide 的作用Low potassium blocks the effect of furosemide

答案: A · 低钾会增强 digoxin 的作用

低钾血症会增强 digoxin 的作用，即使 digoxin 水平正常也会增加中毒风险。低钾不会阻断 furosemide；它是 furosemide 把钾排出后产生的结果，而这正是造成 digoxin 危险的原因。

Hypokalemia potentiates digoxin, raising toxicity risk even at normal digoxin levels. Low potassium does not block furosemide; it is a result of the potassium furosemide washes out, which is what sets up the digoxin danger.

哪种 ECG 改变最能体现低钾血症？Which ECG change is most characteristic of hypokalemia?
  1. T 波低平伴 U 波Flattened T waves with U waves
  2. T 波高尖Tall peaked T waves
  3. QRS 波群增宽Widened QRS complex
  4. QT 间期缩短Shortened QT interval

答案: A · T 波低平伴 U 波

T 波低平和 U 波的出现是低钾的经典表现；T 波高尖提示高钾。

Flattened T waves and the appearance of U waves are classic for low potassium; peaked T waves indicate high potassium.

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