Dyshemoglobinemias Flashcards

1
Q

What is the basic structure of hemoglobin?

A
  • conjugated protein- MW 64,500 daltons
  • two pairs of polypeptide chains- four heme molecules attached
  • purpose: tissue perfusion
  • heme contains an iron complexed at the center of a prophrin ring- Ferrous state (2+) of the Fe atom carries O2
  • the globin chain protects the iron moiety from inappropriate oxidation
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2
Q

Redox Reactions

A
  • redox reactions: always occur together
  • reduction- transfer of electons to a substrate, a substrate is reduced if it gains an electron
  • oxidation- extraction of electrons from a substrate, a substrate is oxidized if it loses an electron
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3
Q

Carbon monoxide

A
  • gas
  • source: incomplete combustion of carbon containing material: methane vs. coal vs gasoline gasses (generators, house fires)
  • internal production (minimal- only methyline chloride furniture stripper)
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4
Q

Pharmacokinetics of CO

A
  • absorption/excretion- CO gains entry through respiration, methylene chloride is converted to CO in vivo
  • distribution- hemoglobin/myoglobin/other
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5
Q

Risk of Exposure to CO

A
  • proximity

- those that breathe faster- babies, pregnant women

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6
Q

CO Pharmacology

A
  • binds to hemoglobin (200-250x oxygen)
  • shifts the oxygen dissociation curve to the left (tighter tissue binding)
  • decrease in erythrocyte 2,3 diphosphoglycerate
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7
Q

CO Mechanism

A
  • mitochondria cytochrome oxidase binding- increased with hypoxia and hypotension
  • nitric oxidase displaced from platelets forms peroxynitrites
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8
Q

CO Effects

A
  • mild- HA, N/V, dizziness
  • moderate- chest pain, blurred vision, dyspnea on exertion, tachycardia, tachypnea, cognitive deficits, myonecrosis, ataxia
  • severe- seizures, coma, dysrhymthmias, hypotension, MI/ischemia, skin bullae
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9
Q

Late/Chronic Effects of CO Poisoning

A
  • cognitive dysfunction
  • dementia, psychosis, amnesia
  • parkinsonism, paralysis chorea, cortical blindness, apraxia, agnosias, peripheral neuropathy, incontinence

-preceded by a lucent period of 2-40 days

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10
Q

Mechanism of Late effects of CO

A
  • reperfusion injury- during recovery, WBCs are attracted and adhere to the brain microvasculature (? due to cyclooxygenase dysfunction)
  • WBCs release proteases, converts xanthine dehydrogenase…promoting free radical formation…leading to delayed lipid peroxidation
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11
Q

Risk of late effects of CO poisoning

A
  • incidence varies in the literature from 3%-14%-33%-43% at various times of follow-up and severity of illness
  • adults (>30) appear to be at greater risk
  • most cases of overt signs involved a loss of consciousness
  • look for end organ manifestations of toxicity- CNS, cardiac, perfusion; CO level- relative importance
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12
Q

Oxygen saturation in CO poisoning

A
  • pulse oximetry- falsely normal (carboxyhemoglobin is read as oxyhemoglobin
  • arterial blood gas- co-oximeter- will be appropriate
  • calculation- will be faslsely normal because P)2 is not affected
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13
Q

Treatment of CO

A
  • ABCs, oxygen- shortens CO T1/2 (2-7 hr to 30-150 min)
  • consider hyperbaric oxygen treatment: shortens T1/2 (4-86 min), increased O2- prevents lipid peroxidation in animal models
  • 12-43% neurologic impairment with 100% oxygen alone, 0-4% treated with HBO
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14
Q

Indications of hyperbaric oxygen

A
  • loss of consciousness- syncope, coma, seizures
  • GCS < 15 on presentation
  • CO level: >10%
  • myocardial ischemia, ventricular dysrhythmias
  • neurologic signs 2-4 hours out
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15
Q

Brain findings of CO exposure

A

-bilteral low density areas of the globus pallidus, putamen, and caudate nuclei are seldom seen

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16
Q

How do you pick out Cyanide exposure?

A
  • lactate > 10 mmol/L was associated with significant CN levels
  • patient does not respond to supportive care..If CO alone, oxygen should make it “go away” and the patient will get better…especially with acid/base, if CN…NO response
17
Q

What are the basics of Cyanide?

A
  • found in many forms
  • gas (chemical warfare/industrial accidents)
  • crystal (requires mucous membrane or po exposure): jewelers, electroplating, other industries..house fires
  • binds to cytochrome A3 on the electron transport chain…rapid onset of multi-system organ failure…no ATP
18
Q

Cyanide treatment

A
  • ABCs, supportative care, ACLS, largely not successful
  • cyanide antidote kit/packages
  • hydroxocobalamin- binds with cyanide to make cyanocobalamin (B12)
  • Hyperbariac oxygen +/-
19
Q

Hydroxycobalamin

A
  • hydroxocobalamin (Vit B12a) + Cyanide —> cyanocobalamin (Vit B12)
  • any smoke-inhalation victim that is NOT improving despite supportive care including O2
  • any intentional cyanide exposure- 5 gram dose, can be repeated x1
  • give concurrently with sodium thiosulfate