topic 26 Flashcards
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.
