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Pathophys II > Hematologic Pathophysiology Hemoglobin Disorders > Flashcards

Hematologic Pathophysiology Hemoglobin Disorders Flashcards

1
Q

Hemoglobin is a large molecule made up of

A

proteins & iron

four folded chains of a protein called globin

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2
Q

An individual erythrocyte may contain about

A

300 million hemoglobin molecules

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3
Q

Hemoglobin A is most common & made up of

A

2 alpha and 2 beta

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4
Q

Describe the formation of hemoglobin:

A

synthesis begins in the proerythroblast & continues through the reticulocyte stage
2 succinyl-CoA (formed in the Kreb cycle) + 2 glycine–> pyrrole molecule
4 pyrrole molecules combine to form protoporphyrin which combines with iron to make heme
Heme + globin combine
4 subunit chains possible (alpha, beta, gamma, and delta)

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5
Q

In the lungs, hemoglobin picks up

A

oxygen, which binds to the iron ions, forming oxyhemoglobin

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6
Q

The bright red, oxygenated hemoglobin travels to the body tissues, where it

A

releases some of the oxygen molecules, becoming darker red deoxyhemoglobin

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7
Q

Oxygen release depends on the need for

A

oxygen in the surrounding tissues

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8
Q

Each hemoglobin chain has a heme prosthetic group containing an atom of

A

iron

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9
Q

There are _________ in each hemoglobin and therefore _____ in each hemoglobin molecule

A

4 hemoglobin chains; 4 iron atoms

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10
Q

Each of the irons can bind loosely with

A

oxygen (O2) making a total of 8 oxygen atoms

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11
Q

The type of hemoglobin chain in the hemoglobin molecule determines the

A

binding affinity for oxygen

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12
Q

The oxygen combining capacity is directly related to

A

hemoglobin concentration and not on the number of RBCs

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13
Q

The shape of the hemoglobin O2 dissociation curve is

A

sigmoidal due to cooperative binding of oxygen to hemoglobin

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14
Q

Lifespan of the RBC is

A

120 days

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15
Q

When the RBC dies, _____ is released

A

hemoglobin

liver Kupffer cells phagocytose the hemoglobin

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16
Q

Describe the destruction of hemoglobin.

A 
hemoglobin opens up--> releases iron & heme
iron is released back into the blood & carried by transferrin to bone marrow for production of new RBCs or to the liver to be store
Porphyrin portion (pyrrole rings) of hemoglobin are converted to biliverdin & then unconjugated bilirubin
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17
Q

Disorders of hemoglobin that are commonly clinically significant include:

A

methemoglobin- altered affinity
thalassemia- quantitative disorder of globin chain
sickle cell disease- qualitative disorder of globin structure

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18
Q

Methemoglobin is formed when the

A

iron in hemoglobin is oxidized from the ferrous (Fe2+) to the ferric (Fe3+) state
ic=ick= it’s not a good state

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19
Q

Methemoglobin cannot bind

A

oxygen and therefore cannot carry oxygen to the tissues

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20
Q

Normally <1% of a person’s hemoglobin in

A

methemoglobin

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21
Q

In situations of excess methemoglobin, the blood becomes

A

dark blue/brown

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22
Q

The NADH dependent enzyme_______ is responsible for converting Mhgb back to Hgm

A

methemoglobin reductase

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23
Q

The methemoglobin reductase pathway uses

A

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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24
Q

How does methemoglobin move the oxyhemoglobin dissociation curve?

A

moves the curve markedly to the left & therefore delivers little O2 to the tissues
increased affinity in the remaining heme sites that are in the ferrous state

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25
Q

Patients can tolerate methemoglobin up to

A

30%

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26
Q

Between 30-50% of methemoglobin,

A

30-50% symptoms of oxygen deprivation occur- muscle weakness, nausea, tachycardia

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27
Q

> 50% of methemoglobin leads to

A

coma & death

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28
Q

Describe the three mechanisms of methemoglobinemia:

A

Congenital:
1. globin chain mutation (HbM)
2. methemoglobin reductase system mutation
Acquired
3. toxic exposure to substance that oxidizes normal Hb iron that exceeds the normal capacity

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29
Q

For patients with the globin chain mutation, the patient’s blood will

A

be a brownish blue color & will have a cyanotic appearance

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30
Q

Describe how the globin chain mutation causes methemoglobinemia.

A

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

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31
Q

Patients who have globin chain mutation are often

A

asymptomatic as their methemoglobin levels rarely exceed 30% of total Hb unless exposed to a toxic dose of oxidizing agent

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32
Q

For patients with impaired reductase system methemoglobinemia, exposure to

A

agents that oxidize hemoglobin can produce a life-threatening methemoglobinemia

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33
Q

Patients affected with impaired reductase system methemoglobinemia may exhibit

A

slate-gray pseudocyanosis despite normal PaO2 levels

34
Q

Impaired reductase system methemoglobinemia occurs when

A

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

35
Q

Acquired methemoglobinemia is a

A

rare, life-threatening accumulation of methemoglobin that exceeds its rate of reduction

36
Q

Nearly all _______ have been associated with methemoglobinemia

A

topical anesthetic preparations

benzocaine is the most common

37
Q

Infants & relation to acquired methemoglobinemia

A

Infants have lower levels of methemoglobin reductase in their erythrocytes–> greater susceptibility to oxidizing agents

38
Q

What exposures for infants can lead to methemoglobinemia?

A

chemical exposure to nitrates in well water- new parents are advised to have well water tested or use bottle water if not breastfeeding

  • infants drink more water per body weight than children & adults
  • orajel
39
Q

For patients experiencing toxic methemoglobinemia, treatment includes

A

supplemental oxygen
1-2 mg/kg methylene blue infused over 3-5 minutes
-single treatment is usually effective- may need repeated after 30 minutes

40
Q

Methylene blue acts through

A

methemoglobin reductase system and requires the activity of G6PD

41
Q

Anesthesia considerations for the patient with methemoglobinemia include

A

avoid tissue hypoxia
administration of supplemental oxygen does not correct low oxygen saturation levels
pulse oximetry is unreliable- cannot detect methemoglobin
arterial line- frequent ABGs and co-oximetry
blood sample- chocolate color
correct acidosis
EKG- monitor for hypoxic ischemia
avoid oxidizing agents- local anesthetics, nitrates, nitric oxide

42
Q

Methylene blue acts as an

A

electron donor for the nonenzymatic reduction of methemoglobin

43
Q

Methylene blue is contraindicated in someone with

A

G6PD deficiency

44
Q

Which enzyme converts methylene blue to reduced form?

A

NADPH methemoglobin reducatse

45
Q

A distinct enzyme, NADPH methemoglobin reductase, converts methylene blue to

A

leukomethylene blue (the reduced form), using NADPH which requires G6Pd

46
Q

B- thalassemia is an

A

inherited defect in globin chain synthesis

47
Q

Types of B-thalassemia include:

A

minor- carrier of the trait, asymptomatic
intermedia- variable severity, mild anemia
major- severe anemia, transfusion dependent

48
Q

Beta thalassemia is predominant in

A

African, Mediterranean areas

49
Q

Alpha thalassemia is predominant in

A

Southeast Asia & India

50
Q

Alpha thalassemia is due to

A

deletion of one or more of the alpha globin genes

51
Q

The disease severity of alpha thalassemia is proportional to

A

the number of alpha globin genes that are deleted

52
Q

In alpha thalassemia, ______ are less pronounced than in Beta thalassemia however, ineffective

A

erythropoiesis & hemolysis

oxygen tissue delivery to the tissues remains

53
Q

The defective synthesis of beta globin contributes to anemia in two ways:

A

1) the inadequate formation of HbA results in microcytic, poorly hemoglobinized red blood cells &
2) the excess unpaired a-globin chains form toxic precipitates that damage the membranes of erythroid precursors, most of which die by apoptosis

54
Q

Beta thalassemia is the result of

A

two types of alleles with different single-base mutations:
betaO alleles which produce no B- globin
beta+ alleles, which produce reduced amounts of beta globin

55
Q

Mortality with thalassemia major is often due to

A

arrhythmias & CHF

56
Q

Thalassemia major is a

A

life-threatening condition- requires transfusions during 1st few years of life

57
Q

3 defects which depress oxygen carrying capacity in thalassemia major include:

A

ineffective erythropoiesis
hemolytic anemia
hypochromia & microcytosis

58
Q

In thalassemia major, unpaired globin

A

aggregate & precipitate which damage the RBC

59
Q

In thalassemia major, some defective RBCs die within

A

the bone marrow & cause bone hyperplasia

60
Q

In thalassemia major, altered morphology accelerates

A

clearance- producing splenomegaly

61
Q

Treatment of thalassemia major includes:

A

transfusion
splenectomy
bone marrow tranplantation

62
Q

Transfusions used to treat thalassemia major are at the cost of

A

iron overload & patient’s often need chelation therapy

63
Q

Having a splenectomy for thalassemia major

A

reduces transfusion requirements
deferred until >age 5
risk of post-splenectomy sepsis

64
Q

Anesthesia management for the patient with thalassemia include:

A

determine the severity & amount of end-organ damage
mild forms- chronic compensated anemia- consider preoperative transfusion to hgb >10
severe forms- splenomegaly, hepatomegaly, skeletal malformations, CHF, intellectual disability- iron overload leads to cirrhosis, right-sided heart failure
risk for infection- broad-spectrum abx
DVT prophylaxis
risk for difficult intubations due to oro-facial malformations
blood bank alerted that patient has thalassemia

65
Q

Sickle cell disease is when

A

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

66
Q

The sickle cell trait is when

A

only 1 beta chain is affected by substitution

67
Q

Exposure of the sickle cell to low oxygen causes

A

crystals to form inside & elongate the RBC

68
Q

The elongation of the RBC in sickle cell makes it impossible for the

A

RBC to pass through many small capillaries & the spiked end of the crystals are likely to rupture the membrane

69
Q

Sickle cell-hemoglobin S is most common in

A

African Americans

70
Q

Sickle cell hemoglobin S results in

A

severe anemia, RBCs of different shapes & sizes, recurrent painful episodes due to ischemia

71
Q

With sickle cell, the precipitated hemoglobin also damages the

A

cell membrane leading the sickling crisis of rupture cells, further decrease in oxygen tension, more sickling, & RBC destruction

72
Q

In terms of perioperative morbidity & mortality, the sickle cell trait

A

does not increase M&M

73
Q

In terms of perioperative morbidity & mortality, sickle cell disease

A

does increase M&M

74
Q

Risk factors for morbidity & mortality for patients with sickle cell disease include:

A

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

75
Q

Sickle cell preop transfusion is

A

controversial as to how much, when, & what

76
Q

The transfusion goal for the sickle cell patient undergoing preop transfusion is

A

increase ratio of normal hemoglobin to sickle hemoglobin

77
Q

Anesthetic management for the patient with sickle cell disease includes:

A 
avoid 3 H's: hypothermia, hypoxia, & hypovolemia
good premed- avoid stress
high narcotic requirements
Current T&C
tourniquet use is controverisal
78
Q

Acute chest syndrome looks like

A

pneumonia on a chest XR

79
Q

Acute chest syndrome develops

A

2-3 days into the postop period

80
Q

Acute chest syndrome demands treatment for

A

hypoxemia, analgesia, & blood transfusions

possible nitric oxide therapy

81
Q

The incidence of acute chest syndrome is decreased if

A

preop hematocrit is >30%

Pathophys II (43 decks)

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