Flashcards in Unit 2 - Dyshemoglobinemia Deck (39):
explain what hemoglobin is and its purpose
conjugated protein (64,500 D)
-two pairs of polypeptide chains (4 heme molecules attached total)
-for tissue perfusion
what is heme's structure?
Fe complexed at the center of a porphyrin ring
-ferrous state (2+) of the Fe carries O2, CO
-globin chain protects Fe moiety from inappropriate oxidation
difference between carboxyhemoglobin, oxyhemoglobin, and methemoglobin?
carboxy = CO
oxy = O2
met = O2, but heme Fe in +3 form
what are sources of CO?
1. incomplete combustion of carbon containing material
-gasses: methane VS coal VS gasoline
2. internal production (minimal, only if ingest/inhale methyline Cl)
explain the entry/exit of CO (pharmacokinetics)
-CO gains entry through respiration
-methylene cloride is converted to CO in vivo only
-via hemoglobin, myoglobin, etc.
explain CO pharmacology?
binds to Hb (200-250 x O2)
-shifts O2 dissociation curve to the left
-decrease in RBC 2,3-DPG
explain the mechanism of CO?
1. mitochondrial cytochrome oxidase binding
-increased with hypoxia and hypotension
2. NO displaced from platelets from peroxynitrites
explain the mild, moderate, and severe effects of CO?
mild: HA, nausea/vomiting, dizziness
moderate: cheset pain, blurred vision, dyspnea on exertion, tachycardia, tachypnea, cognitive deficits, myonecrosis, ataxia
severe: seizures, coma, dysrhythmias, hypotension, MI/ischemia, skin bullae
what are "late/chronic effects" of CO? when do they occur?
-dementia, psychosis, amnesia
-parkinsonism, paralysis chorea, cortical blindness, apraxia, agnosias, peripheral neuropathy, incontinence
these are preceded by a "lucent" period of 2-40 days, meaning it can seem like a patient got better, but then has these effects
what is the theory behind the mechanism of late effects of CO?
-during recovery, WBC are attracted and adhere to brain microvasculature due to cyclooxygenase dysfunction (?)
-WBCs release proteases, convert xanthine dehydrogenase to xanthine oxidase, promoting FR formation, leading to delayed lipid peroxidation
at what ages are adults at greatest risk?
how should one evaluate CO poisoning?
look for end-organ manifestations of toxicity
-CNS, cardiac, perfusion
-CO level is of relative importance
what is pulse oximetry in CO poisoning?
-carboxyhemoglobin is read as oxyhemoglobin
what is arterial blood gas in CO poisoning?
co-oximeter will be appropriate
calculation will be falsely normal b/c pO2 is not affected
what is treatment for CO poisoning?
1. ABC's, O2 to shorten CO half-life (from 2-7 hr to 30-150 min)
2. hyperbaric O2 under pressure (HBO)
-shortens half-life to 4-86 minutes, increases O2
-prevents lipid peroxidaiton in animal models
what are indications for HBO?
1. loss of consciousness
-syncope, coma, seizures
2. GCS < 15 on presentation
3. CO level > 10%
4. MI, ventricular dysrhythmias
5. neurologic signs 2-4 hours out
what are some neuroanatomical side effects of CO?
bilateral low density areas of globus pallidus, putamen, and caudate nuclei
how does one "pick out" cyanide poisoning?
1. lactate > 10 mmol/L
2. patient doesn't respond to supportive care
what are the forms of cyanide?
1. gas (usually chemical warfare/industrial accidents)
2. crystal (requires mucous membranes or po exposure)
-jewelers, electroplating, other industries, house fires
where does cyanide bind?
cytochrome A3 on ETC
-rapid onset of multi-system organ failure (no ATP)
what is treatment for cyanide?
1. ABCs, supportive care, ACLS, largely not successful
2. cyanide antidote kit/package (sodium/amyl nitrite)
-binds with cyanide to make cyanocobalamin (B12)
4. HBO +/0
when and how should one treat with hydroxocobalamin?
1. any smoke-inhalation victim that is NOT improving despite supportive care including O2
2. any intentional cyanide exposure
-5 g dose, can be repeated x1
-give concurrently with sodium thiosulfate
-may cause increased BP
what is the mechanism of sodium/amyl nitrite in cyanide poisoning?
sodium/amyl nitrite makes met-Hb, so the CN (and H2S, if any) bind to met-Hb instead of cytochromes
-these cyanomet-Hb or SHmet-Hb are then excreted
--cyanometHb needs thiosulfate to be excreted
define what methemoglobin is?
heme Fe oxidized to ferric (+3) form
-normal amounts 1-3%
what is the mechanism of methemoglobinemia?
1. rate of heme oxidation increases
2. reduction of heme is limited
3. structural abnormalities of heme
what are causes of methemoglobinemia?
2. infantile disposition
3. external causes
how does methemoglobin exert its toxicity?
1. incapacitates O2 transport
2. shifts O2 dissociation curve to left
what are symptoms of methemoglobin at:
10-20% apparent cyanosis
20-50% dizziness, fatigue, HA, exertional dyspnea
what is pulse oximetry in methemoglobin?
falsely and aberrantly lowered
-measured as both oxy and deoxyhemoglobin, will fall rapidly into high 80s
what is arterial blood gas in methemoglobin?
1. co-oximeter will be appropriate
2. calculation will be falsely normal b/c pO2 is not affected
what are drugs that give methemoglobinemia?
1. nitrites (major)
2. nitrates in infants (major)
6. local anesthetics
these cause oxidant stress
what are toxins that give methemoglobinemia?
1. nitrites (major)
2. nitrates in infants (major)
3. aniline dye
4. potassium chlorate
5. diarrheal illness in infants (make nitrites; major)
what is treatment for methemoglobinemia?
3. methylene blue (tetramethyl tionine chloride; specific antidote)
-minor antidotes and in non-responders to methylene blue
explain the mechanism of methylene blue
used in treatment of methemoglobinemia
-cofactor of NADPH reductase
-gains electron, then donates directly to methemoglobin
-methemoglobin reduction to (Fe 2+)
when is methylene blue treatment indicated?
if methemoglobin level >20-30%, or symptoms
what are cautions in using methylene blue?
1. hemolytic anemia from weak oxidizing capability
2. painful at injection site (dysuria)
3. higher doses can cause dyspnea, restlessness, tremor, precordial pain, apprehension
what are possible reasons for methylene blue non-responders?
1. hemoglobin M disease
2. G6PD deficiency - lack generation of NADPH dependent methemoglobin reducase
3. CL salts inactivating G6PD
-more benign, levels up to 10 g/dL don't cause cyanosis
5. wrong diagnosis
what is sulfhemoglobinemia?
symptoms similar to methemoglobinemia
-methemoglobin levels will be elevated
-laboratory can "tease out" by adding cyanide to blood
-treatment is supportive only