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DA > Sickle Cell > Flashcards

Sickle Cell Flashcards

1
Q

Define Sickle Cell Anaema

A

Hereditary hemolytic anaemia resulting from the formation of abnormal haemaglobin: HbS

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2
Q

How does HbS differ from HbA

A

Valine substituted for glutamic acid at the 6th position of the beta chain

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3
Q

How does oxygen affinity for HbS differ from HbA (P50)

A

HbA P50 = 3.5 kPa

HbS P50 = 4.1 kPa (right shifted) –> lower O2 affinity

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4
Q

How is RBC survival decreased in Sickle cell disease

A

From 120 days normal RBCs to 12 days

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5
Q

What is the difference between Sickle cell anaemia and sickle cell trait

A

When the genetic defect is on both maternally and paternally derived chromosomes (11) - the patient is homozygous for sickle cell anaemia HbSS.

When only one has it - the patient is heterozygous and has sickle cell trait HBAS.

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6
Q

Describe the phenotype of a patient with sickle cell trait

A

HbA - 60%
HbS - 40%

Asymptomatic
No anemia
Normal life expectancy

  1. Sickling occurs only under extreme hypoxemia
    - -> occurs in renal medulla –> impaired renal concentrating ability
  2. Splenic infarcts
  3. Pulmonary infarcts
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7
Q

Which populations are at risk for HbSS and HbAS

A

Central African ancestry

Mediterranean ancestry

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8
Q

List 5 conditions that favour the formation of deoxyhaemoglobin and hence sickling

A 
Hypoxaemia
Acidosis
Dehydration (intracellular hypertonicity)
Increased 2.3-DPG levels
Increased/decreased temperature
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9
Q

Describe the pathophysiology in sickle cell anaemia

A

Formation of deoxyHb –> intracellular polymerization of HbS –> ‘sickle’ shape RBCs: more sticky and less pliable –> increased blood viscosity –> Formation of red cell aggregates –> obstruction of microcirculation –> circulatory stasis –> localized hypoxia –> more sickling

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10
Q

How can the clinical features of Sickle Cell Disease be classified

A
  1. Acute episodic crises
    - Vasoocclusive crises
    - Aplastic crises
    - Splenic sequestration crises
  2. Chronic and progressive features
    - Children: failure to thrive and recurrent infections
    - Recurrent infections (splenic infarction and atrophy)
    - Kidney failure
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11
Q

How do vasoocclusive crises present

A
  1. Microinfarctions
    - Acute abdominal/chest/back/joint pain
    - Differentiate between surgical and non-surgical abdo pain is difficult
  2. Macroinfarctions
    - Splenic/Cerebral/pulmonary/hepatic/renal/myocardial infarction
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12
Q

What is an aplastic crisis and why does this occur in sickle cell disease

A 
Profound anemia (Hb 2 - 3 g/dL) 
- Infections or folate deficiency --> bone marrow exhaustion/supression --> red cell prodcution fails --. sudden severe anaemia
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13
Q

What is a splenic sequestration crisis and why does it occur

A

Sudden pooling of blood in the spleen due to occlusion of venous drainage from the spleen leading to life-threatening hypotension

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14
Q

How is Sickle cell disease diagnosed

A

HbS in RBCs readily sickle when exposed to oxygen consuming agent (metabisulfite) or a hypertonic ionic solution (solubility test).

Confirmation requires haemoglobin electrophoresis

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15
Q

What are the preoperative options with regard to preparing a patient with sickle cell disease for theatre

A
  1. Hydration
  2. Control of infections
  3. Partial exchange transfusion
    - Reduce blood viscosity
    - Increase O2 CC
    - Decrease likelihood of Sickling
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16
Q

What are the intraoperative considerations for a patient with sickle cell anaemia

A
  1. AVOID Hb desaturation (FiO2 > 0.5 and High FGF)
  2. Avoid sickling precipitants
    - Hypothermia
    - Hyperthermia
    - Acidosis
    - Hypoxaemia
    - Hypovolaemia
    - Hypotension
    - Dehydration
  3. Monitor and maintain CO
    - A - line: goal directed haemodynamic monitoring
    - Arterial SVV analysis
    - Esophageal dopplar/transesophageal echo
    - CVP
    - PAWP with mixed venous SaO2 monitoring
17
Q

What are the postoperative considerations for a patient with sickle cell disease

A
  1. Prevent hypoxaemia (FiO2 > 0.5)
  2. Hemodynamic monitoring and management
  3. Aggressive Pain Rx
  4. Pulmonary physiotherapy
  5. Early ambulation
18
Q

What is G6PD deficiency/abnormality

A

There are 400 different variants of G6PD deficiency/malfunction –> hemolysis after exposure to virus/bacteria/certain drugs.

Red cells are protected from oxidising agents by glutathione. NADPH regenerates glutathione via the HEXOSE MONOPHOSPHATE SHUNT (HMS) which requires the enzyme Glucose-6-Phosphate Dehydrogenase (G6PD).

Abnormality of G6PD –> oxidation and precipitation of Hb in red cells, Heinz boies and hemolyisis

19
Q

Are males or females more commonly affected by G6PD

A

Males - X linked trait

20
Q

Why are episodes of hemolysis self limited in G6PD deficiency

A

Because only the older population of RBCs are destroyed

DA (50 decks)

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