C h a p t e r 8
Disorders of Fluid, Electrolyte, and Acid–Base Balance
203
R E V I EW E X E R C I S E S
1.
A 40-year-old man with advanced acquired
immunodeficiency syndrome (AIDS) presents with
an acute chest infection. Investigations confirm
a diagnosis of
Pneumocystis carinii
pneumonia.
Although he is being treated appropriately, his
serum sodium level is 118 mEq/L. Tests of adrenal
function are normal.
A.
What is the likely cause of his electrolyte
disturbance?
B.
What are the five cardinal features of this
condition?
2.
A 70-year-old woman who is taking furosemide
(a loop diuretic) for congestive heart failure
complains of weakness, fatigue, and cramping of
the muscles in her legs. Her serum potassium is
2.0 mEq/L and her serum sodium is 140 mEq/L.
She also complains that she notices a “strange
heartbeat” at times.
A.
What is the likely cause of this woman’s
symptoms?
B.
An ECG shows a depressed ST segment and
low T-wave changes. Explain the physiologic
mechanism underlying these changes.
C.
What would be the treatment for this woman?
3.
A 50-year-old woman presents with symptomatic
hypercalcemia. She has a recent history of breast
cancer treatment.
A.
How do you evaluate this person with increased
serum calcium levels?
B.
What is the significance of the recent history of
malignancy?
C.
What further tests may be indicated?
4.
A 34-year-old woman with diabetes is admitted to
the emergency room in a stuporous state. Her skin
is flushed and warm, her breath has a sweet odor,
her pulse is rapid and weak, and her respirations
are rapid and deep. Her initial laboratory tests
indicate a blood sugar of 320 mg/dL, serum HCO
3
–
of 12 mEq/L (normal, 24 to 27 mEq/L), and a pH
of 7.1 (normal, 7.35 to 7.45).
A.
What is the most likely cause of her lowered pH
and bicarbonate levels?
B.
How would you account for her rapid and deep
respirations?
C.
How would you explain her warm, flushed skin
and stuporous mental state?
5.
A 16-year-old girl is seen by her primary care
provider because her parents are concerned about
her binge eating and their recent discovery that she
engages in self-induced vomiting. Initial laboratory
tests reveal a serum K
+
of 3.0 mEq/L and Cl
–
of 93.
A.
Explain her low K
+
and Cl
–
.
B.
What type of acid–base abnormality would you
expect her to have?
6.
A 65-year-old man with chronic obstructive lung
disease has been using low-flow oxygen therapy.
He has recently developed a severe respiratory
tract infection and has trouble breathing. He
is admitted to the emergency room because his
wife is having trouble arousing him. She relates
that he had “turned his oxygen way up” because
of difficulty breathing. His respirations are 12
breaths/minute. Arterial blood gases, drawn on
admission to the emergency room, indicated a
PO
2
of 85 mm Hg (normal, 90 to 95 mmHg)
and a PCO
2
of 90 mm Hg (normal, 40 mm Hg).
His serum HCO
3
–
was 34 mEq/L (normal, 24 to
48 mEq/L). What is his pH?
A.
What is the most likely cause of this man’s
problem?
B.
How would you explain the lethargy and
difficulty in arousal?
C.
What would be the main goal of treatment for
this man in terms of acid–base balance?
D.
Explain the concurrent respiratory and
metabolic acidosis that often occurs in persons
with chronic respiratory acidosis.
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