A patient presents with hyponatremia, low serum osmolality, and high urine osmolality.
What is the most likely diagnosis?
SIADH.
Hyperthyroidism.
Diabetes insipidus.
Addison's disease.
The Correct Answer is A
Choice A rationale
The Syndrome of Inappropriate Antidiuretic Hormone (SIADH) is characterized by the excessive release of ADH, leading to water retention and dilutional hyponatremia. Serum sodium is typically less than 135 mEq/L, and serum osmolality is low, often less than 280 mOsm/kg. Despite the diluted blood, the kidneys continue to excrete concentrated urine with a high osmolality, usually greater than 100 mOsm/kg. This triad of findings is the classic presentation for SIADH in a clinical setting.
Choice B rationale
Hyperthyroidism involves an overproduction of thyroid hormones, which increases the metabolic rate and can lead to symptoms like tachycardia, weight loss, and heat intolerance. While it can affect fluid and electrolyte balance indirectly through increased perspiration or changes in renal blood flow, it does not typically present with the specific combination of hyponatremia, low serum osmolality, and inappropriately high urine osmolality that defines a primary disorder of water metabolism like SIADH.
Choice C rationale
Diabetes insipidus is the functional opposite of SIADH, characterized by a deficiency of ADH or a lack of response to it. This leads to the excretion of large volumes of very dilute urine, resulting in high serum osmolality and hypernatremia, where serum sodium exceeds 145 mEq/L. Patients with diabetes insipidus have a low urine osmolality, often less than 200 mOsm/kg, because they cannot concentrate their urine effectively, which contradicts the high urine osmolality seen in the patient.
Choice D rationale
Addison's disease is characterized by adrenal insufficiency, leading to low levels of cortisol and aldosterone. While this can cause hyponatremia and hyperkalemia due to the loss of sodium and retention of potassium in the kidneys, it is usually accompanied by hypovolemia and hypotension. The primary mechanism of hyponatremia in Addison's is sodium wasting, whereas in SIADH, the hyponatremia is dilutional. Addison's would typically present with a different clinical picture including high potassium.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Choice A rationale
Inflammation limited to the external ear, known as otitis externa, is a relatively benign condition compared to the severe risks associated with mastoiditis. While it causes localized pain and edema, it does not involve the bony structures of the skull. Mastoiditis represents an extension of infection from the middle ear into the mastoid air cells. The nurse's concern must focus on the potential for deeper, life-threatening structural involvement rather than simple external canal irritation.
Choice B rationale
Cerumen production is a physiological process of the external auditory canal designed to protect the ear from debris and infection. Increased earwax may cause temporary discomfort or minor hearing changes, but it is not a complication of a bacterial infection in the mastoid bone. Focusing on cerumen during a mastoiditis assessment would ignore the critical signs of systemic infection or intracranial involvement. This choice does not address the serious nature of the client's current pathology.
Choice C rationale
The mastoid air cells are located in close proximity to the temporal lobe of the brain and the sigmoid sinus. If mastoiditis is left untreated, the infection can erode through the thin bony partitions, leading to life-threatening complications such as meningitis, brain abscess, or dural sinus thrombosis. This represent the most significant risk because it involves the central nervous system. Early recognition of neurological changes or severe headaches is vital in preventing permanent disability or death.
Choice D rationale
While conductive hearing loss is a common finding in middle ear infections and mastoiditis due to fluid and debris blocking sound waves, it is typically manageable and often reversible. It does not carry the same level of acuity or mortality risk as an intracranial infection. The nurse prioritizes complications that threaten the client's life or basic neurological function. Temporary hearing loss, though concerning for the client, remains a secondary priority compared to the risk of brain infection.
Correct Answer is D
Explanation
Choice A rationale
Hypophosphatemia is a condition where serum phosphorus levels fall below the normal range of 2.5 to 4.5 mg/dL. While phosphorus levels can be affected by various metabolic processes and insulin administration, it is not the primary electrolyte concern during prolonged vomiting and metabolic alkalosis. The shifts associated with alkalosis specifically target cations rather than anions like phosphate. Therefore, while monitoring is important in complex cases, it is not the highest risk associated with this specific acid-base disturbance.
Choice B rationale
Hyponatremia involves a sodium level below 135 to 145 mEq/L. Vomiting does cause the loss of sodium and water, but the body often compensates through the renin-angiotensin-aldosterone system, which promotes sodium retention to maintain volume. While sodium levels may fluctuate, the hallmark of metabolic alkalosis from upper gastrointestinal loss is the specific depletion of hydrogen and chloride. Potassium imbalances usually present a more acute and life-threatening risk than the moderate sodium fluctuations seen in simple vomiting.
Choice C rationale
Hypocalcemia is defined as a total serum calcium level below 9.0 to 10.5 mg/dL. In an alkalotic state, the decrease in hydrogen ions causes more calcium to bind to albumin, which reduces the amount of ionized, physiologically active calcium in the blood. While this can cause symptoms like tetany, it is often a functional deficiency rather than a total body deficit. Potassium depletion is generally more severe in vomiting because it involves both direct loss and significant renal excretion.
Choice D rationale
Hypokalemia, where potassium is less than 3.5 to 5.0 mEq/L, is the highest risk. During vomiting, potassium is lost directly in gastric secretions. Furthermore, in metabolic alkalosis, hydrogen ions move out of cells to compensate for the high extracellular pH, forcing potassium to move into the cells to maintain electrical neutrality. Additionally, the kidneys excrete more potassium in exchange for retaining hydrogen ions. These three mechanisms work together to rapidly and severely deplete serum potassium levels.
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