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Chapter 2: Disorders of Extracellular Volume: Hypovolemia and Hypervolemia

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A localized outbreak of cholera occurs after severe flooding in the Gulf States. Patients are suffering a spectrum of gastrointestinal losses, but the fluid (“rice-water” stools) has a [Na] of 135–140 mM, a [Cl] of 100 mM, and a [HCO3] of 25 mM. There are many patients, but, fortunately, most have mild-moderate losses and can be treated with standard oral rehydration solutions (ORS). A smaller number of patients suffering more severe losses (based on physical examination) will require intravenous fluid (IVF) therapy.

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Which behavior/physical examination findings would most support the use of IVF therapy?

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A. Restless/irritable

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B. Thirsty and drinks eagerly

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C. Poor skin turgor

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D. Urinary fractional excretion of Na (FENa) less than 1%

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E. Lethargic/obtunded

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The answer is E. Determination of clinical volume status hinges on extracting key historical information and a skillfully performed physical examination, yet an accurate assessment of ECF volume status remains a challenge in clinical medicine. Choices A and B are more characteristic of mild-moderate losses, and these patients can be treated with ORS. All patients would be expected to have poor skin turgor and a FENa less than 1%, so these do not discriminate. Patients who have a decreased level of consciousness, however, are more likely to have suffered more losses that may still be ongoing and probably will be unable to drink. Such patients should be diagnosed as having more severe and probably life-threatening hypovolemia and should receive prompt and aggressive IVF therapy.

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Which of the following is the best choice of IV solution to administer?

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A. 5% dextrose in water

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B. 0.45% (half-isotonic) saline

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C. 0.9% (isotonic) saline

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D. 0.45% saline with 75 mM bicarbonate added

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E. 3% (hypertonic) saline

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The answer is D. Patients who are hypovolemic need to always receive isotonic solution, which excludes all choices except C and D. Recent literature has suggested that using high [Cl] solutions in large volume resuscitation may increase the probability of acute kidney injury, so giving the half NaCl/half Na-bicarbonate solution may be the better choice of isotonic saline. Importantly, the rate of volume repletion needs to be commensurate with the volume already lost and exceed the rate of ongoing losses. Therapy should be monitored by following the physical examination. For example, as volume is repleted, blood pressure should increase, tachycardia should slow, and orthostasis should improve along with skin ...

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