An 83-year-old woman is brought to the emergency department from her nursing home due to poor appetite, fatigue, diarrhea, and confusion. The patient has a history of moderate dementia, hypertension, mild intermittent asthma, and bilateral knee osteoarthritis. She was recently hospitalized with pneumonia for which she was treated with broad-spectrum antibiotics. The patient was discharged to the nursing home in stable condition and had normal laboratory values 2 weeks ago. Since that time, she has had worsening diarrhea. The diarrhea is foul-smelling but does not contain any blood. She has mild abdominal discomfort. Temperature is 37.6 C (99.7 F), blood pressure is 96/54 mm Hg, pulse is 112/min, and respirations are 14/min. She has poor skin turgor. There is no peripheral edema. The patient's lungs are clear to auscultation. The abdomen is soft, but she has mild generalized tenderness without rebound or guarding. Laboratory results are as follows: A stool specimen tests positive for Clostridium difficile toxin. Which of the following is most likely present in this patient?

Question

An 83-year-old woman is brought to the emergency department from her nursing home due to poor appetite, fatigue, diarrhea, and confusion.  The patient has a history of moderate dementia, hypertension, mild intermittent asthma, and bilateral knee osteoarthritis.  She was recently hospitalized with pneumonia for which she was treated with broad-spectrum antibiotics.  The patient was discharged to the nursing home in stable condition and had normal laboratory values 2 weeks ago.  Since that time, she has had worsening diarrhea.  The diarrhea is foul-smelling but does not contain any blood.  She has mild abdominal discomfort.  Temperature is 37.6 C (99.7 F), blood pressure is 96/54 mm Hg, pulse is 112/min, and respirations are 14/min.  She has poor skin turgor.  There is no peripheral edema.  The patient's lungs are clear to auscultation.  The abdomen is soft, but she has mild generalized tenderness without rebound or guarding.  Laboratory results are as follows:  A stool specimen tests positive for Clostridium difficile toxin.  Which of the following is most likely present in this patient?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d4e5_f613_bc81_35005740047a_MD0003_00 An assessment of volume status is essential in diagnosing and treating hyponatremia (serum sodium <135 mEq/L). This patient's recent history of poor oral intake and diarrhea due to Clostridium difficile infection, laboratory evidence of prerenal azotemia (eg, blood urea nitrogen/creatinine ratio >20), and examination findings of tachycardia, hypotension, decreased skin turgor, and absence of peripheral edema strongly suggest hypovolemia (depletion of salt and water). Hypovolemic hyponatremia occurs due to a multiple-pathway mechanism that illustrates the body's priority to restore euvolemia at the risk of developing hypotonicity: Decreased renal perfusion leads to decreased renal tubular sodium delivery, which stimulates the renin-angiotensin-aldosterone system and increases sodium reabsorption. (Angiotensin II also stimulates thirst, which leads to increased water intake.) Nonosmotic stimulation of antidiuretic hormone (ADH) occurs in response to angiotensin II, hypovolemia (stimulates stretch receptors in the left atrium), and hypotension (stimulates baroreceptors in the carotid arteries). Consequent salt and water retention help correct the hypovolemia. However, in the setting of ongoing ADH secretion, hypotonic hypovolemic hyponatremia can develop due to retention of a relative excess of total body water. ADH levels will remain high (not low) until hypovolemia is corrected (Choice C). Infusion of normal saline is the treatment of choice for hypovolemic hyponatremia as it replenishes the body's depleted salt stores, restores euvolemia, and shuts off nonosmotic stimuli for ADH release. (Choices A and E) High ADH and high urine sodium are characteristic of the syndrome of inappropriate ADH secretion, which is a common cause of euvolemic hyponatremia. Low renin and low aldosterone would also be expected. This patient has hypovolemic, rather than euvolemic, hyponatremia and would be expected to have low urine sodium. (Choice D) Low ADH and low urine sodium may be observed in a patient with central diabetes insipidus, which typically presents with polyuria, polydipsia, and normal to high serum sodium levels. Educational objective: Hypovolemic hyponatremia occurs due to nonosmotic stimulation of antidiuretic hormone (ADH) secretion in response to hypovolemia, hypotension, and decreased renal perfusion (via angiotensin II). Restoration of blood volume shuts off nonosmotic stimulation of ADH and corrects the hyponatremia. References: Hyponatremia: a prospective analysis of its epidemiology and the pathogenetic role of vasopressin. (http://www.ncbi.nlm.nih.gov/pubmed/3966753) Diagnosis and management of hyponatremia in hospitalised patients. (http://www.ncbi.nlm.nih.gov/pubmed/19769706)

An 83-Year-Old Woman Is Brought to the Emergency Department from Her