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Sx Pretest Questions and Correct
Answers/ Latest Update / Already
Graded
A 48-year-old woman develops constipation postoperatively and
self-medicates with milk of magnesia. She presents to clinic, at which
time her serum electrolytes
are checked, and she is noted to have an elevated serum
magnesium level. Which of the following represents the earliest
clinical indication of hypermagnesemia?
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Ans: *loss of deep tendon reflexes*
The earliest clinical indication of hypermagnesemia is loss of deep tendon
reflexes. States of magnesium excess are
characterized by generalized neuromuscular depression. Clinically, severe
hypermagnesemia is rarely seen except in those patients with advanced
renal failure treated with magnesium-containing antacids. However,
hypermagnesemia is produced intentionally by obstetricians who use
parenteral magnesium sulfate (MgSO4) to treat
preeclampsia. MgSO4 is administered until depression of the deep tendon
reflexes is observed, a deficit that occurs with modest hypermagnesemia
(over 4 mEq/L).
Greater elevations of magnesium produce progressive weakness, which
culminates in flaccid quadriplegia and in some cases respiratory arrest
due to paralysis of the
chest bellows mechanism. Hypotension may occur because of the direct
arteriolar relaxing effect of magnesium. Changes in mental status occur in
the late stages of the
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syndrome and are characterized by somnolence that progresses to
coma.
A previously healthy 55-year-old man undergoes elective right
hemicolectomy for a stage I (T2N0M0) cancer of the cecum. His
postoperative ileus is somewhat
prolonged, and on the fifth postoperative day his nasogastric tube is
still in place. Physical examination reveals diminished skin turgor, dry
mucous membranes, and
orthostatic hypotension. Pertinent laboratory values are as follows:
Arterial blood gases: pH 7.56, PCO2 50 mm Hg, PO2 85 mm Hg.
Serum electrolytes (mEq/L):
Na+ 132, K + 3.1, Cl− 80; HCO3− 42.
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Urine electrolytes (mEq/L): Na+ 2, K+ 5, Cl− 6.
What is the patient's acid-base abnormality?
Ans: *Metabolic alkalosis with respiratory compensation*
The patient has a metabolic alkalosis secondary to gastric losses of HCl,
with compensatory hypoventilation as reflected by the elevated arterial
pH and PCO2 and supported by the absence of clinical lung disease. The
PCO2 would be normal if the metabolic alkalosis was uncompensated.
A 65-year-old man undergoes a technically difficult abdominal-
perineal resection for a rectal cancer during which he receives 3
units of packed red blood cells. Four
hours later, in the intensive care unit (ICU), he is bleeding heavily
from his perineal wound. Emergency coagulation studies reveal
normal prothrombin, partial
Sx Pretest Questions and Correct
Answers/ Latest Update / Already
Graded
A 48-year-old woman develops constipation postoperatively and
self-medicates with milk of magnesia. She presents to clinic, at which
time her serum electrolytes
are checked, and she is noted to have an elevated serum
magnesium level. Which of the following represents the earliest
clinical indication of hypermagnesemia?
,2 | Page
Ans: *loss of deep tendon reflexes*
The earliest clinical indication of hypermagnesemia is loss of deep tendon
reflexes. States of magnesium excess are
characterized by generalized neuromuscular depression. Clinically, severe
hypermagnesemia is rarely seen except in those patients with advanced
renal failure treated with magnesium-containing antacids. However,
hypermagnesemia is produced intentionally by obstetricians who use
parenteral magnesium sulfate (MgSO4) to treat
preeclampsia. MgSO4 is administered until depression of the deep tendon
reflexes is observed, a deficit that occurs with modest hypermagnesemia
(over 4 mEq/L).
Greater elevations of magnesium produce progressive weakness, which
culminates in flaccid quadriplegia and in some cases respiratory arrest
due to paralysis of the
chest bellows mechanism. Hypotension may occur because of the direct
arteriolar relaxing effect of magnesium. Changes in mental status occur in
the late stages of the
,3 | Page
syndrome and are characterized by somnolence that progresses to
coma.
A previously healthy 55-year-old man undergoes elective right
hemicolectomy for a stage I (T2N0M0) cancer of the cecum. His
postoperative ileus is somewhat
prolonged, and on the fifth postoperative day his nasogastric tube is
still in place. Physical examination reveals diminished skin turgor, dry
mucous membranes, and
orthostatic hypotension. Pertinent laboratory values are as follows:
Arterial blood gases: pH 7.56, PCO2 50 mm Hg, PO2 85 mm Hg.
Serum electrolytes (mEq/L):
Na+ 132, K + 3.1, Cl− 80; HCO3− 42.
, 4 | Page
Urine electrolytes (mEq/L): Na+ 2, K+ 5, Cl− 6.
What is the patient's acid-base abnormality?
Ans: *Metabolic alkalosis with respiratory compensation*
The patient has a metabolic alkalosis secondary to gastric losses of HCl,
with compensatory hypoventilation as reflected by the elevated arterial
pH and PCO2 and supported by the absence of clinical lung disease. The
PCO2 would be normal if the metabolic alkalosis was uncompensated.
A 65-year-old man undergoes a technically difficult abdominal-
perineal resection for a rectal cancer during which he receives 3
units of packed red blood cells. Four
hours later, in the intensive care unit (ICU), he is bleeding heavily
from his perineal wound. Emergency coagulation studies reveal
normal prothrombin, partial
