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Flashcards in topic 26 Deck (18):

Why do standard chemistries help when treating a toxin? What standard chemistries can be obtained?

• The evaluation of a suspected poisoned patient may require obtaining standard chemistries to determine physiological effects of the toxin:
– Electrolytes, BUN, creatinine

– Blood glucose

– hepatic transaminases

– calcium, magnesium, etc.


What are 3 types of fluid loss related to toxins and what causes them?

• Fluid resuscitation may be necessary after toxin exposure depending upon the site of fluid loss:

– fluid losses from GI tract
• corrosives
• cathartics
• Methylxanthines (e.g., caffeine, theophylline)
• cholinergic overdose

– fluid losses from the skin
• chemical burns
• Diaphoresis (excessive sweating)

– redistribution of volume
• iron
• snake envenomation
• vasodilators
• vasodilating drugs (ethanol, nitrites, opiates)

• Electrolyte losses or disturbances
– hyponatremia (e.g., diuretics, chronic use of

lithium) – hypokalemia (e.g., beta-adrenergics, loop

diuretics, salicylates, methylxanthine

overdose) – hyperkalemia (e.g., digoxin overdose,

fluorides) – hypocalcemia (e.g., Ethylene glycol,

hydrofluoric acid, NH4HF2 )


What are 3 types of electrolytes losses or disturbances related to toxins and what causes them?

• Electrolyte losses or disturbances
– hyponatremia (e.g., diuretics, chronic use of lithium)
– hypokalemia (e.g., beta-adrenergics, loop
diuretics, salicylates, methylxanthine overdose)
– hyperkalemia (e.g., digoxin overdose, fluorides)
– hypocalcemia (e.g., Ethylene glycol, hydrofluoric acid, NH4HF2 )


What are 11 things that could cause an anion gap acidosis?

• A Alcohol (ethanol)
• M Methanol
• U Uremia
• D Diabetic ketoacidosis (DKA)
• P Paraldehyde, phenol (other phenol derivatives)
• I Iron, INH, inborn errors of metabolism (organic acids)
• L Lactic acidosis (numerous causes including CAD’s)
• E Ethylene glycol, diethylene glycol
• C Carbon monoxide, cyanide
• A Aspirin (salicylates) and acetaminophen (massive OD)
• T Toluene


What is measured in a blood gas analysis?

Blood gas analysis: – measuring pH, partial pressure CO2, & O2
• calculates O2saturation (not measured)

– co-oximetry actually measures normal and abnormal oxygen species

• oxyhemoglobin

• carboxyhemoglobin

• methemoglobin (Fe3+ valence)


How is an anion gap measured? What is an abnormal anioin gap?

• Anion Gap = [Na+] - [Cl-+ HCO3-]

Abnormal is above 14


How is the osmolar gap obtained? What is normal osmolality? How is osmolality calculated?

• Osmolar Gap: – measured by freeze point depression– estimated (calculated) osmolality

– normal osmolality varies (average ~290 to 300 mOsm/kg H2O).

Calc. osmolality = (2 x Na+) + BUN/2.8 + BS/18


How is the osmolar gap calculated? How is the blood level of the toxin estimated?

Osmolar Gap: – “normal” is dependent upon substance

– Osmolar Gap ( Osm) = [ Measured Osm ] - [ Calculated Osm ].

• Estimate blood level of toxin: – Level (mg/dL) =

(osmolar gap X MW)/10


What are some toxocologic causes of an increased osmolar gap?

– Methanol (MW=32)
– Ethanol (MW=46)
– Ethylene glycol (MW = 62)
– Isopropanol (MW = 60)
– Acetone (MW = 58)


When is determining acid/base status important for toxic exposures? When is determining the true oxygen saturation important?

• Determining acid/base status is important in many toxic exposures:
– Metabolic acidosis with toxic alcohols/glycols
– Metabolic acidosis and respiratory failure with
tricyclic antidepressants

• Important to determine true oxygen saturation
by co-oximetry for a variety of toxic conditions:
– Carboxyhemoglobin in CO poisoning
– Methemoglobin


How can tricyclics affect the heart?

Tricyclics affect the sodium and potassium channels. In overdose, the blockade of these channels, especially the Na+ channel may lead to
decrease in strength and prolong depolarization with
widened QRS and the effect on K+ channels may lead to delayed repolarization and prolonged QT.
This may lead to serious arrhythmias such as VTach.


When is Enzyme Multiplied Immunoassay Test (EMIT) used? How does it work?

• Used for common meds & drugs of abuse

• Principle based on labeled vs. unlabeled drug to compete for drug antibody. Label is an enzyme loosely attached to known drug.
• Patient’s serum is added that may or may not have the same drug to be tested.
• If no drug is present in patient’s sample it does not compete with the antibody sites.
• Antibody stays attached to known enzyme labeled drug & enzyme is not free (i.e., not displaced) to catalyze chemical reaction.
• If patient drug is present, it attaches to ab & displaces enzyme  color change, etc.


When is urine immunoassay used? How does it work?

• Based on monoclonal antibodies to classes of drugs.

• Detect drugs of abuse and tricyclics


How does Radioimmunoassay (RIA) work?

• Principle- competition between known amounts radioactive labeled drug mixed with known amounts drug specific ab and unknown drug in patient’s serum.

• High amount drug in patient’s serum competes with known labeled drug for ab

• Precipitate = pt. drug + ab, hence  counts


How does gas chromatography work?

• Uses capillary column through which liquids

or solids are injected after vaporization.

• Inert gases carry specimen out of column and

time of exit from column (retention time) is

recorded by chemical detectors.

• The unknown’s retention time and abundance

of peak are compared to standards for I.D.


How does mass spectrophotometry (GC-MS) work?

• Combined with GC=gold standard tox test

• Costly, but specificity is high

• Principle-high energy electrons bombard test substance and fragment molecule into separate parts with measurable MW.

• Each drug has its own recognizable pattern.


How does Atomic Absorption Spectrophotometry

(AAS) work? When is it used?

Costly, very specific, quant. I.D. metals

• Principle: flame excites outer shell electrons, they emit characteristic wavelength of light when returning back to stable orbit.

• Used to assay for arsenic, mercury, iron,
selenium, thallium, and cadmium.


When is diagnostic imaging useful?

• Radiopacity of pharmaceuticals / substances

– C C oated pills (enteric coated)
– H H eavy metals (e.g., lead)
– I I llicit drugs (e.g., cocaine packs) or I ron pills
– P P henothiazines
– S S ustained release

• Chest radiographs in overdose patients

• Neuroimaging in toxic cases