The answers to the electrolyte quiz from April 5, 2012 are B and E (explanations are below).
1. A 24-year-old man is found unconscious in the street and brought into the emergency room. No medical history is available. His blood pressure is 110/70 mm Hg, respiratory rate 13 per minute. He appears disheveled and is comatose and responsive only to pain. His pupils are reactive to light and he has a non-focal neurological examination. No fetor is noted. He is intubated, undergoes gastric lavage, and activated charcoal is administered via a nasogastric tube.
Laboratory Studies
Serum sodium 130 mEq/L
Serum potassium 3.2 mEq/L
Serum chloride 94 mEq/L
Serum bicarbonate 11 mEq/L
Blood urea nitrogen 56 mg/dL
Serum creatinine 1.8 mg/dL
Serum glucose 72 mg/dL
Serum ethanol 6 mg/dL
Acetest Negative
Serum 0.02 mmol/L β-hydroxybutyrate
Serum lactate 2 mmol/L
Serum salicylate None detected
Serum creatine kinase 25 mU/mL
Serum osmolality 315 mOsm/kg
Arterial blood studies on room air:
pH 7.29
PCO229 mm Hg
The most appropriate first step in the management of this patient is:
A. Dopamine
B. Fomepizole
C. Hemodialysis
D. Forced alkaline diuresis
E. Thiamine
2. A 21-year-old college student who had a seizure at a party is brought into the emergency room by his friends. They report that he used PCP. On examination, he is unresponsive and smells of urine.
Laboratory Studies
Serum sodium 138 mEq/L
Serum potassium 3.7 mEq/L
Serum chloride 95 mEq/L
Serum bicarbonate 8 mEq/L
Blood urea nitrogen 14 mg/dL
Serum creatinine 1.0 mg/dL
Serum glucose 65 mg/dL
Serum creatine kinase 95 mU/mL
Serum osmolality 288 mOsm/kg
Serum toxicology Negative screen
Urine toxicology Positive for PCP screen
Urine ketones Negative
Arterial blood studies on room air:
pH 7.25
PCO226 mm Hg
The most appropriate first step in the management of this patient is:
A. Fomepizole
B. Alkaline diuresis
C. Hemodialysis
D. Ethanol infusion
E. None of the above
Explanation
1. (B) This patient has an anion gap metabolic acidosis and an osmolar
gap of 31 mOsm/kg (normal <10). The differential diagnosis of an anion gap
metabolic acidosis with an osmolar gap is intoxication with ethanol
(accompanied by alcoholic ketoacidosis), ethylene glycol, methanol and
propylene glycol (a vehicle in certain intravenous medications such as
lorazepam). In this case, the serum ethanol and ketone levels are negligible.
Ethylene glycol and methanol intoxication can sometimes be distinguished if one
finds evidence of visual impairment, loss of pupillary light reflexes or
papilledema (suggesting methanol poisoning), or inebriation without fetor,
hypocalcemia, calcium oxalate crystalluria, or urine
fluorescence under a Wood’s light (all favoring the diagnosis of ethylene glycol
poisoning). Confirmation of an elevated serum level of ethylene glycol or
methanol requires specialized techniques such as gas chromatography or mass
spectrometry that are not readily available in most hospital laboratories, and
therefore may take considerable time to obtain. Fortunately, the initial
treatment of both types of intoxications is the same and should therefore be
initiated as soon as either diagnosis is suspected. The treatment should
include gastric decontamination, sodium bicarbonate if necessary to correct
severe acidemia (pH <7.0-7.2), and inhibition of hepatic alcohol
dehydrogenase with either ethanol or fomepizole to delay or prevent metabolism
of the alcohols to their toxic metabolites. Hemodialysis and hemofiltration are
very effective at removing the toxic alcohols and their metabolites, but
placement of dialysis access, followed by several hours of treatment, are required
to achieve significant clearance. Thus, fomepizole or ethanol should always be
initiated first, even if subsequent dialysis is contemplated. Thiamine and
pyridoxine are cofactors for alternative pathways for the metabolism of
glyoxylic acid (a toxic metabolite of ethylene glycol), but their efficacy is
unknown and they should be considered only as optional, adjunctive therapy.
Forced alkaline diuresis is useful in the management of salicylate
intoxications, but has no role in toxic alcohol ingestions.
2. (E) This patient has a mixed metabolic and respiratory acidosis. The
severe metabolic acidosis is associated with an elevated anion gap and no
osmolar gap. In this clinical setting it is most likely lactic acidosis due to
the PCP-induced seizure. This usually resolves spontaneously and no specific
treatment is necessary.
(Questions and answers courtesy of Dr. Alan Yu, Director, Kidney Institute and Professor of Medicine, UKMC, Kansas)
