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N935 Advanced Pathophysiology > hematologic - hemoglobin disorders > Flashcards

hematologic - hemoglobin disorders Flashcards

1
Q

Hemoglobin makeup

A

large molecule
made up of proteins and iron
4 folded chains of globin

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2
Q

an individual erythrocyte may contain about

A

300 million hemoglobin molecules

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3
Q

Normal hemoglobin beta chain made up of which amino acids

A

the first 6 amino acids

valine, histidine, leucine, thre, proline, glutamic acid

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4
Q

which amino acid is substituted in sickle cell hemoglobin beta chain

A

glutamic acid

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5
Q

synthesis of hemoglobin begins in the

A

proerythroblast and continues through the reticulocyte stage

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6
Q

2 succinyl CoA + 2 glycine yields

A

pyrrole molecule

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7
Q

4 pyrrole molcules combine to form

A

protoporphyrin which combines with iron to make heme

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8
Q

hemoglobin A has which subunits?

A

2 alpha and 2 beta subunits

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9
Q

the type of hemoglobin chain in the hemoglobin molecule determines

A

the binding affinity for oxygen

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10
Q

the oxygen combining capacity is directly related to

A

hemoglobin concentration and not on the number of RBCs

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11
Q

in the lungs hemoglobin picks up oxygen which binds to the iron forming

A

oxyhemoglobin

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12
Q

when oxygen molecules are released at the tissues oxygenated hemoglobin becomes

A

deoxyhemoglobin

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13
Q

oxygen release depends on

A

the need for oxygen in the surrounding tissues

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14
Q

shape of the oxy-hemoglobin dissociation curve is ___ and why

A

sigmoidal due to cooperative binding of oxygen to hemoglobin

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15
Q

RBC lifespan

A

120 days

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16
Q

how is hemoglobin destroyed?

A

liver kupffer cell phagocytose the hemoglobin and iron is released back into the blood and carried by transferrin to the bone marrow for production of new RBCs or to the liver to be stored

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17
Q

the porphyrin portion (pyrrole rings) of hemoglobin is converted to

A

biliverdin and then unconjugated bilirubin is conjugated by hepatocytes and secreted in bile

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18
Q

hemoglobin disorder that has altered affinity

A

methemoglobin

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19
Q

hemoglobin disorder that is a quantitative disorder of the globin chain

A

thalaseemia

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20
Q

hemoglobin disorder that is a qualitativev disorder of globin sturctures

A

sickle cell

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21
Q

methemoglobin is formed when the iron in hemoglobin is

A

oxidized from the ferrous (Fe2+) to the ferric (Fe3+) state

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22
Q

can methemoglobin bind oxygen?

A

no so oxygen cannot be carried to tissues

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23
Q

the NADH-dependent enzyme, methemoglobin reductase, is responsible for

A

converting MHgb back to Hgb

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24
Q

methemoglobin reductase pathway

A

uses nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase in the erythrocyte from anaerobic glycolysis to maintain heme iron in its ferrous state

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25
Q

how does methemoglobin move the oxy-hgb dissociation curve?

A

moves the curve markedly to the left and therefore delivers little oxygen to the tissues (Left Loves)

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26
Q

symptoms of oxygen deprivation

A

muscle weakness, nausea, tachycardia

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27
Q

methemoglobin levels >50% leads to

A

coma and death

28
Q

3 mechanisms of methemoglobinemia

A

congenital
1. globin chain mutation
2. methemoglobin reductase system mutation
Acquired
3. toxic exposure to substance that oxidizes normal hgb iron that exceeds the normal capacity

29
Q

globin chain mutation definition

A

mutations that stabilize heme iron in the Ferric (Fe3+) state, making it relatively resistant to reduction by the methemoglobin reductase system

30
Q

globin chain mutation presentation/manifestation

A

patient’s blood will be brownish/blue color and cyanotic appearance
patient is usually asymptomatic d/t their levels rising >30%

31
Q

impaired reductase system definition

A

mutations impairing the NADH and cytochrome b methemoglobin reductase system usually result in methemoglobinemia levels below <25%

32
Q

impaired reductase system manifestation/presentation

A

exhibit slate-gray pseudocyanosis despite normal PaO2 levels

33
Q

exposure to agents that oxidize Hgb can produce

A

a life threatening methemoglobinemia

34
Q

acquired methemoglobinemia definition

A

rare, life threatening amounts of methemoglobin accumulate exceeding its rate of reduction

35
Q

infants have ____ levels of methemoglobin reductase in their erythrocytes

A

lower levels which puts them at great susceptibility to oxidizing agents

36
Q

chemical exposure to ____ in well water can lead to methemoglobinemia

A

nitrates

37
Q

nearly all _____ have been associated with methemoglobinemia ____ being the most common

A

topical anesthetic preparations, benzocaine being the most common

38
Q

anesthesia considerations for methemoglobinemia

A

avoid tissue hypoxia, administering oxygen does not correct low oxygen saturation levels, pulse oximetry is unreliable, need an aline, blood sample may be chocolate color, correct acidosis, monitor for hypoxic ischemia, avoid oxidizing agents

39
Q

examples of oxidizing agents

A

Local anesthetics, nitrates, and nitric oxide

40
Q

toxic methemoglobinemia treatment

A

supplemental oxygen
1-2mg/kg methylene blue infused over 3-5minutes
may need to repeat after 30 minutes

41
Q

where does methylene blue act?

A

through the methemoglobin reductase system and requires the activity of G6PD

42
Q

methylene blue acts as an

A

electron donor for the nonenzymatic reduction of methemoglobin

43
Q

what enzyme converts methylene blue to leukomethylene blue

A

NADPH methemoglobin reductase (requires G6PD)

44
Q

if someone has G6PD deficiency can you give them methylene blue?

A

no

45
Q

B thalassemia definition

A

inherited defect in globin chain synthesis

can be a carrier, have mild anemia, or severe anemia

46
Q

B0 vs B+ allele in B thalassemia

A

B0 - produce no B globin

B+ - produce reduced amounts of B globin

47
Q

the defective synthesis of B globin contributes to anemia in 2 ways

A
  1. inadequate formation of HbA = microcytic, poorly hemoglobinized red cells
  2. excess unpaired a-globin chains form toxic precipitates that damage the membranes of erythroid precursors that die by apoptosis
48
Q

where is B thalassemia predominant?

A

african mediterranean area

49
Q

where is A thalassemia predominant?

A

southeast asia/india

50
Q

definition of A thalassemia

A

deletion of one or more of the a globin genes

disease severity is proportional to the number of a globin genes that are deleted

51
Q

thalassemia major

A

life threatening

requires transfusions during 1st few years of life

52
Q

what are the 3 defects that depress oxygen carrying capacity in thalassemia major

A

ineffective erythropoiesis
hemolytic anemia
hypochromia and microcytosis

53
Q

mortality in someone with thalassemia major is usually from

A

arrhythmias and CHF

54
Q

treatment of thalassemia major

A

transfusions, chelation therapy
splenectomy
bone marrow transplantation

55
Q

anesthesia management in mild thalassemia

A

consider preop transfusion to Hgb >10

56
Q

anesthesia management/considerations in severe forms of thalassemia

A

patients can have splenomegaly, hepatomegaly, skeletal malformations, CHF, intellectual disability, iron overload
risk for infection, need DVT prophylaxis, risk for difficult intubation d/t oro-facial malformations, make sure the blood bank is aware

57
Q

sickle cell disease

A

the amino acid valine is substituted for glutamic acid at one point in each of the 2 beta chains

58
Q

sickle cell trait

A

only 1 beta chain is affected

59
Q

exposure of a sickled cell to low oxygen causes

A

crystals to form inside and elongate the RBC

60
Q

sickle cell trait (does/does not) increase perioperative morbidity and mortality

A

does not

61
Q

sickle cell disease (does/does not) increase perioperative morbidity and mortality

A

does

62
Q

risk factors for sickle cell perioperative morbidity and mortality

A

age, frequency of sickle crisis’, elevated creatinine, cardiac conditions, surgery type

63
Q

what is the transfusion goal for patients with sickle cell

A

increase ratio of normal Hgb to sickle Hgb

64
Q

sickle cell disease anesthetic management/considerations

A

avoid the 3 H’s! (hypothermia, hypoxia, hypovolemia)
avoid stress (give versed)
high narcotic requirements
current T&C
Tourniquet - controversial could increase risk of crisis potentially

65
Q

Acute chest syndrome looks like ___ on cxray

A

pneumonia

66
Q

When does acute chest syndrome develop and what kind of treatment do they need?

A

develops 2-3 days postop

treatment for hypoxemia, analgesia, blood transfusions, nitric oxide therapy

67
Q

incidence of acute chest syndrome is decreased if

A

preop Hct is >30%

N935 Advanced Pathophysiology (15 decks)

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