Chapter 26
Fluid, Electrolyte, and Acid-Base Balance
Related Clinical Terms
An agent that counteracts acidity, such as sodium
bicarbonate, aluminum hydroxide gel, and magnesium trisilicate.
Commonly used to manage heartburn.
Hyperaldosteronism (Conn’s disease)
A condition of hypersecretion of
aldosterone by adrenal cortical cells accompanied by excessive loss
of potassium and generalized muscular weakness, hypernatremia,
and hypertension. Usual cause is adrenal tumor; usual treatment is
adrenal-suppressing drugs prior to tumor removal.
Renal tubular acidosis
A metabolic acidosis resulting from impaired
renal reabsorption of bicarbonate; the urine is alkaline.
Syndrome of inappropriate ADH secretion (SIADH)
A group
of disorders associated with excessive ADH secretion in the
absence of appropriate (osmotic or nonosmotic) stimuli.
Characterized by hypotonic hydration (hyponatremia, fluid
retention, and weight gain) and concentrated urine. Usual
causes are ectopic secretion of ADH by cancer cells (e.g., small
cell lung cancers) and brain disorders or trauma affecting the
ADH-secreting hypothalamic neurons. Temporary management
involves restricting water intake.
Mr. Heyden, a somewhat stocky
72-year-old man, is brought in to the
emergency room (ER). The paramedics
report that his left arm and the left
side of his body trunk were pinned beneath some wreckage, and
that when he was freed, his left hypogastric and lumbar areas
appeared to be compressed and his left arm was blanched and
without sensation. On admission, Mr. Heyden is alert, slightly
cyanotic, and complaining of pain in his left side; he loses
consciousness shortly thereafter. His vital signs are taken, blood
is drawn for laboratory tests, and Mr. Heyden is catheterized and
immediately scheduled for a CT scan of his left abdominal region.
Analyze the information that was subsequently recorded on Mr.
Heyden’s chart:
Vital signs: Temperature 39°C (102°F); BP 90/50 mm Hg and
falling; heart rate 116 beats/min and thready; 30 respirations/
Given the values above and his attendant cyanosis, what would
you guess is Mr. Heyden’s immediate problem? Explain your
CT scan reveals a ruptured spleen and a large hematoma in
the upper left abdominal quadrant. Splenic repair surgery is
scheduled but unsuccessful; the spleen is removed.
Rupture of the spleen results in massive hemorrhage. Explain
this observation. Which organs (if any) will compensate for the
removal of Mr. Heyden’s spleen?
Hematology: Most blood tests yield normal results. However,
renin, aldosterone, and ADH levels are elevated.
Explain the cause and consequence of each of the hematology
Urinalysis: Some granular casts (particulate cell debris) are noted,
and the urine is brownish-red in color; other values are normal,
but urine output is very low. An order is given to force fluids.
(a) What might account for the low volume of urine output?
(Name at least two possibilities.) (b) What might explain the
casts and abnormal color of his urine? Can you see any possible
relationship between his crush injury and these findings?
The next day, Mr. Heyden is awake and alert. He says that he
now has feeling in his arm, but he still complains of pain. However,
the pain site appears to have moved from the left upper quadrant
to his lumbar region. His urine output is still low. He is scheduled
once again for a CT scan, this time of his lumbar region. The order to
force fluids is renewed and some additional and more specific blood
tests are ordered. We will visit Mr. Heyden again shortly, but in the
meantime think about what these new findings may indicate.
(Answers in Appendix H)
Case Study
Urinary System
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