- 期刊
老年人抗利尿素分泌異常症
Syndrome of Inappropriate Secretion of Antidiuretic Hormone in the Elderly
摘要
抗利尿分泌異常症(SIADH)爲老年人常見之病患。抗利尿素(ADH)是在下視丘產製，經神經纖維運輸到腦下垂體後葉貯藏，其乃受血漿滲透壓與血量的調節而分泌。如果ADH的分泌過多已非血漿滲透壓與血量所需的生理反應，則謂之抗利尿素分泌異常症。ADH的生理功能主要是（一）促使水由腎小管的重新吸收；（二）促使微小動脈的收縮。老年人基礎的ADH分泌與受血漿滲透壓刺激的分泌都有增加的現象；但對血量減少刺激之反應則減少。在一般生理情況下ADH的分泌主要是受血漿滲透壓的調節，所以老年人的血漿ADH的濃度長期處在比較高的狀態下，因此之故腎臟對ADH刺激的反應變得比較遲鈍。老年人各種電解質不平衡的病況以低血鈉症爲最多（約佔老年病患的9%），而低血鈉症中又有大約30%是由SIADH所引起者。會引起SIADH最多的原因是（一）各種腦神經的疾病、（二）各種肺部疾病、（三）各種癌病、（四）各種藥物；這些情況在老年人都是常見者，這也難怪SIADH會常見於老年人。SIADH會促使體內水份增加與鈉離子的減少而引起低血鈉症，而低血鈉症又會經由低血滲透壓而傷害腦神經。老年人本來腦神經就比較脆弱易受傷害，甚至輕微的低血鈉症在老年人都會引起注意力、心智、步伐不穩，易生意外；嚴重者會發生痙攣、昏迷、永久性腦部傷害、呼吸終止、腦幹疝脫甚至死亡等。診斷處置上是先確定病人的體液量是正常的，而且病人須不存在有腦下垂體、腎上腺、甲狀腺等疾病。然後病人的情況如果能符合下面的條件，即可以確定診斷：血漿鈉離子的濃度小於135mEq/L、血漿滲透壓小於275mOs/kg、尿液的滲透壓大於150mOs/kg、尿液的鈉離子濃度大於30mEq/L、同時限水可以減緩低血鈉症。但是老年人有些之獨特處：（一）ADH的分泌已和年輕人不一樣、（二）可能合併有其它疾病狀況、（三）可能正在服用一些藥物，所以臨床表徵可能不是那麼典型，可能影響對SIADH的判斷，診斷評估上應特別小心斟酌。治療上：（一）在嚴重血鈉過低的情況下可以補充3%的NaCl，但速度要很慢（小於0.05mL/kg/min），血鈉上升太快有嚴重的副作用，甚至可造成死亡。（二）限水乃爲非常有效的方法。（三）亦可增加鹽與蛋白質的攝取量。（四）當然根本原因的治療是最重要的方法。（五）以上都無法控制病情時，可以用藥物來幫助：fludrocortisone、democlocycline、lithium carbonate與vasopressinV2 antagonists。或有所助益。
並列摘要
SIADH is a common disorder in the elderly. ADH is produced in the hypothalamus, transported through the nervous fibers to the posterior pituitary gland. ADH scertion is regulated by plasma osmolality and blood volume. If ADH excessive secretion is out of proportion to the physiological responses to plasma osmolality and plasma volume, it is the SIADH. The physiological functions of ADH are (1) to increase water reabsorption from the renal tubules and (2) to increase arteriole constriction. In the elderly, the basal and osmolality stimulated ADH secretion is increased, but ADH response to volume depletion is decreased. Because kidneys in the elderly are under higher ADH stimulation, the renal response to ADH is blunted. Hyponatremia is the most common electrolyte imbalance in the elderly (9% of geractric patients). About 30% of geriatric hyponatremia is due to SIADH. The most common causes of SIADH are: (1) nervous diseases; (2) pulmonary diseases; (3) cancers and (4) drugs or medication. In geriatric patients, mild hyponatremia may cause poor attention, mentation and gait, leading to accidents. Severe hyponatremia may cause seizure, coma, permanent brain damage, respiratory arrest, brain stem herniation and even death. Diagnostically, we have to firstly make sure that the patient is normovolemic and does not have pituitary, adrenal and thyroid disorders. Then, if the patient's conditions fulfilled the following criteria, he/she has SIADH: plasma osmolality is less than 130 mEq/L, plasma osmolality is less than 275 mOsm/kg, urine osmolality is more than 150 mOsm/kg, urine sodium concentration is less than 30 mEq/L and water restriction can relive hyponatremia. In the elderly, (1) ADH secretion and regulaion have been altered; (2) SIADH may accompany other disorders; (3) patients may take other medications; so the clinical and laboratory findings may be atypical. Therapeutically; (1) severe hyponatremia may be ameliorated by intravenous 3% NaCl and the infusion rate should be slow (less than 0.05 mL/kg/min); (2) water restriction is a very effective measure; (3) salt and protein intake may be increased; (4) treatments of the underlying disorders are the basic and important measures; (5) if all in vain, the following drugs may be used: fludrocortisone, demeclocycline, lithium carbonate and vasopressin V2 antagonists.