Transcript The Osmolar Gap

Amazing, Amusing & Awesome
Acidosis Anecdotes
. . . And Gnarly Mnemonics
Kent R. Olson, MD
Medical Director
California Poison Control System
Clinical Professor of Medicine
UC San Francisco
 Case 1: An Acidic Alcoholic
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A 44 yo man was found unconscious,
with a suicide note and a half-empty
bottle of Jim Beam.
BP 110/80 HR 110 RR 24
pH 7.47
pCO2 22
pO2 88
Na 140 K 3.8 Cl 106 HCO3 18
ETOH 0.18 gm/dL
 Causes of Metabolic Acidosis:
“MUDPILES”
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Methanol
Uremia
DKA
Phenformin, Paraldehyde
INH, Iron
Lactic acid
Ethylene glycol
Salicylate
 Salicylate Intoxication:
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Typical mixed acid-base abnormality:
– Respiratory alkalosis
– Metabolic acidosis
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May be acute or chronic
Large OD may cause delayed peak
Treatment:
– Alkalinize urine, restore serum pH
– Hemodialysis
 Case 2: A Gapped Gipper
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30 yo M found comatose
Temp 86F, pH 6.9
Na 147, K 4.9, Cl 105, Bicarb 5
– Anion gap 37
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Glu 166, BUN 16, Cr 1.5
Measured Osm 331
– Osm gap 23
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Ethanol “zero”
 The Osmolar Gap:
Osm = 2 (Na) + BUN/2.8 + Glucose/18
Gap = Measured - Calculated Osm = 0 + 5
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Causes of Osm Gap:
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Ethanol
Isopropyl alcohol & Acetone
Methanol & Ethylene glycol
Other alcohols & glycols
Erroneous results:
– Wrong tube; Different specimen times
– Falsely normal gap with vaporization
method
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Methanol poisoning
METHANOL
ELEVATED
OSMOLAR GAP
FORMALDEHYDE
FORMIC ACID
ANION GAP
ACIDOSIS
 Ethylene Glycol & Methanol:
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Osmolar gap
Anion gap
– Lactate low, does not account for gap
– Early in the intoxication, anion gap may
be absent
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Additional clues: (may be unreliable)
– EG: urine crystals, fluorescence
– Methanol: visual disturbance
 Ethylene Glycol & Methanol:
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Main DDx: Alcoholic Ketoacidosis
– Anion and Osmolar gaps
– Low lactate
– AKA clues:
• GETS BETTER over a few hrs with fluids and
dextrose
• Ketone levels +/- (beta-hydroxybutyrate)
 Case 3: Not on the List
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A 15 year old young woman was
found comatose (GCS 7)
BP 92/34 mm Hg HR 120/min
RR 24/min pulse ox 94% (room air)
pH 7.16 pCO2 27 pO2 127
Anion gap 20
– Salicylate negative
– Methanol, EG negative
 Case 3, cont.
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She became more obtunded and was
intubated
Treated with IV fluids
Received bicarbonate 50 mEq x 1
Recovered, extubated in 12 hours
Admitted to ingesting 500 ibuprofen
tablets (200 mg size)
Seifert SA et al: J Tox Clin Tox 2000; 38:55-7
 Ibuprofen
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Common NSAID
Propionic acid derivative
– Contributes to acidosis
– (Naproxen is also a PA derivative)
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Moderate OD: GI upset
Severe OD:
– Coma, seizures
– Hypotension, renal failure
– ARDS
 Case 4: A Surprising Finding
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28 yo F found comatose in a hotel
room, 2 empty bottles of Extra
Strength Tylenol (total about 150 gm)
BP 120/50, HR 130, pupils midrange
pH 7.03, HCO3 4, anion gap 25
ASA negative, APAP 850 mg/L
AST 70
Lactate >11 mmol/L
 Acetaminophen
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Case (continued):
– ETOH, Methanol, Ethylene Glycol tests
all negative
– Patient later developed liver, renal
failure
 Acetaminophen
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Massive ingestion:
– Rare cause of early onset metabolic
acidosis
– Mechanism unknown, probably acute
metabolic dysfunction in liver cells
– Can also cause coma, hypotension
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Different mechanism than hepatic
injury
 Cases 5-6: Metabolic Madness
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Ataxic 2 yo child
– Na 152
– HCO3 12, pH 7.24
– Ammonia 80
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Obtunded 25 yo F
– BP 60s systolic
– pH 7.16, pCO2 37, pO2 66
– Hypoglycemia (glucose = 50s)
– Calcium 6.6
 Valproic acid (Depakote)
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Common anticonvulsant
Increasing use in psychiatry
Metabolic dysfunction
– Hypoglycemia
– Hypocalcemia
– Elevated ammonia
– Encephalopathy
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Coma and rarely cerebral edema
Consider hemodialysis if VPA>1000
 Cases 7-8: Caustic Cocktails
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A sulfuric anion gap:
33 yo M ingested "Hot Shot Drain
Cleaner" containing 9% sulfuric acid
BP 110-120/palp, drooling, in pain
ET intubated shortly after arrival
Initial Na 143, K 8.1, Cl 97, HCO3 <5,
– Anion gap >40
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Lactate 2.1
 Caustic Cocktails, continued...
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Not an anion gap:
43 yo F ingested Lysol Toilet Bowl
Cleaner (HCl 8.5-9.5%, pH <1)
Pain! Serum CPK 26,812
pH 7.19, CO2 24
Na 144 Cl 121 HCO3 18.6
– Anion gap = 4.4
 A Final Stumper:
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A 5 year old Laotian immigrant girl
was brought to the ED at 3 AM very
lethargic
History of nausea and vomiting
starting at 1 AM
BP 89/42 HR 103 R 16 T 97
Pupils 4 mm, skin normal
Mouth dry, active peristalsis
 Case 9 Continued...
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According to the father, at 6 pm the
previous evening the family had
eaten a meal of steamed wild root
They collected it near the Berkeley
Marina and considered it a tasty
substitute for bamboo shoots
At 1 AM all 5 family members
experienced nausea and vomiting;
the 5 yo also had diarrhea
 Case 9, Continued...
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Shortly after admission, the child's
pupils were noted to be dilated and
poorly reactive
Respirations were shallow, and the
HR was 65/min
pH 6.8 pCO2 21 pO2 220
Shortly after, the child had a tonicclonic seizure
 Case 9, Continued...
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Further Hx:
The family said a brother was taking
some type of “chest medicine”
A family member was sent home to
retrieve the bottle….
 Common causes of seizures
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Cocaine/amphetamines
Tricyclic antidepressants
Bupropion
Diphenhydramine
Tramadaol
Isoniazid (INH)
Phenothiazines & antipsychotics
 Case, continued
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The bottle contained erythromycin
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A blood cyanide level was 6 mg/L
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The wild root was identified as
pampas grass; although usually nontoxic, at certain times of
the year it elaborates
cyanogenic (cyanideproducing) glycosides.
 “MUDPILES” revised?
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Methanol or metformin
Acetaminophen or AKA (“maudespil?”)
Uremia
DKA or Depakote
Phenformin or paracetamol
INH, Iron or ibuprofen
Lactic acid
Ethylene glycol
Salicylate or syanide?
 A Shorter Mnemonic:
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SALAD:
Lab Test:
– Salicylate
ASA
– Alcohols
Osm
– Lactic acid
Lactate
– Anuria
BUN/Cr
– DKA
Glucose
California Poison Control System
Public Hotline:
Medical Consult:
1-800-876-4766
1-800-411-8080
Nationwide:
1-800-222-1222