dyshemoglobinemias

Question 1

CO (mechanism, O2 sats, tx)

Answer 1

• gains entry/exit through respiration; no metabolism
• binds Hb and myoglobin with greater affinity than O2 –> hypoxemia
• binds mitochondrial cytochrome oxidase –> inhibits cellular respiration
• displaces NO from platelets –> peroxynitrites –> free radical damage
• late/chronic nuerologic effects due to reperfusion injury and lipid peroxidation
• pulse ox falsely normal (can’t distinguish between oxy Hb and carboxy Hb)
• arterial blood gas falsely normal bc pO2 isn’t affected
• tx: hyperbaric O2 prevents lipid peroxidation and neurologic sequelae
• HBO indications = loss of consciousness, CO level >10%, GCS <15, MI, ventricular dysrhythmias

Question 2

CN poisoning (mechanism, tx)

Answer 2

• identified by lactate levels (> 10 mmol/L) or PT unresponsive to O2 tx
• binds to cytochrome A3 on electron transport chain
• tx: nitrites, sodium thiosulfate, hydroxycobalamin (vit B12a)

**note: O2 tx doesn’t help CN poisoning like it does for CO poisoning!

Question 3

sodium nitrite

Answer 3

• used to treat CN poisoning
• CN likes Fe3+
• turn Hb into Met-Hb –> CN moves from Fe3+ on cytochromes to those in RBCS (but then you need to treat Met-Hb with methylene blue)
• dangerous in concurrent CO poisoning

Question 4

sodium thiosulfate

Answer 4

• used to treat CN poisoning
• enhances normal metabolism of CN via rhodanase

Question 5

hydroxycobalamin

Answer 5

• used to treat CN poisoning
• binds with CN to make cyanocobalamin
• give concurrently with sodium thiosulfate
• indications: any smoke inhalation victim that is NOT improving despite supportive care and O2, any intentional CN exposure

Question 6

Methemoglobinemia (mechanism, causes, O2 sats, tx)

Answer 6

• heme iron oxidized to Fe3+ form
• shifts O2 disassociation curve to the left –> less O2 unloading to tissues
• causes: congenital or acquired via drugs/toxins(nitrites, nitrates in infants)
• O2 sats: pulse ox in mid 80’s (falsely low because it can’t read MetHb), arterial blood gas falsely normal bc pO2 isnt affected
• tx: methylene blue

Question 7

Methylene blue

Answer 7

• cofactor of NADPH reducatse, gains electron and donates directly to reduce MetHb to Hb
• indications: MetHb >20-30% or symptoms
• adverse side effects: hemolytic anemia because of weak oxidizing capabilities –> RBC oxidative damage –> hemolysis
• non-responders: Hb M disease, G6PD deficiency (lack generation of NADPH-dependent MetHb reductase), sulfhemoglobinemia, wrong dx