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Flashcards in topic 26 Deck (18):
1

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.

2

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 )

3

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 )

4

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

5

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)

6

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

• Anion Gap = [Na+] - [Cl-+ HCO3-]

Abnormal is above 14

7

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

8

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

9

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)

10

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

11

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.

12

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.

13

When is urine immunoassay used? How does it work?

• Based on monoclonal antibodies to classes of drugs.

• Detect drugs of abuse and tricyclics

14

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

15

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.

16

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.

17

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.

18

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