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Primary FRCA > Physiology 4 > Flashcards

Physiology 4 Flashcards

1
Q

Outline the pathophysiology of the thalassaemias

A

Heterogeneous group of genetic disorders which affect rate of globin gene expression.
α-thalassaemias usually involve gene deletion
β-thalassaemias usually involve abnormal processing

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2
Q

How many functioning α and β genes are present in the erythroid precursor?

A

4x α and 2x β due to replication of the α gene

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3
Q

What are the α-thalassaemia traits?

A

α0 trait: Loss of both α genes from one chromosome (α0 α0 / α+ α+)

α+ trait: Loss of one α gene on one chromosome (α+ α0 / α+ α+)

homozygous α+ trait: Loss of one α gene on each chromosome (α+ α0 / α+ α0)

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4
Q

What clinical picture do the α-thalassaemia traits produce?

A

Similar
Usually not anaemic
Hypochromic, microcytic RBCs, raised RBC count
Hb electropheresis normal, HbA2 level normal

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5
Q

What is HbH disease?

A 
3x α gene deletions
Causes anaemia (Hb 70-110)
Microcytic, hypochromic RBCs.
Splenomegaly
HbH can be detected byh electropheresis
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6
Q

What happens if all four α globin chain genes are lost?

A

Hydrops foetalis

Death in utero

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7
Q

What causes β-thalassaemia?

A

DNA mutation resulting in absent (β0) or reduced (β+) β globin production.

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8
Q

How does β-thalassaemia major present?

A

As severe, transfusion-dependent anaemia (hpyochromic, microcytic) with onset around 3-6 months.
This is the time when the switch from γ to β globin takes place.
Serum electropheresis reveals reduced or absent HbA

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9
Q

Complications of β-thalassaemia?

A

If untreated by transfusion:
Bone marrow hyperplasia in skull and other haematopoeitic areas. Cortical thinning leading to fractures.
Hepatosplenomegaly
‘Hair on end’ appearance of skull x-ray

With transfusion: Iron overload after first decade.

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10
Q

What storage solution is used for red cells in Europe?

A 
SAG-M
Saline
Adenine
Glucose
Mannitol
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11
Q

Explain why each component of SAG-M storage solution is included

A

Saline: solvent and osmotic agent
Adenine: Increases intracellular ATP levels, prolonging RBC survival (though at the cost of decreased 2,3-DPG levels)
Glucose: Prolongs cell life
Mannitol: Osmotic stabiliser reducing storage-related haemolysis

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12
Q

How are packed red cells presented?

A

150-200ml concentrated RBC solution suspended in 100ml storage solution.
Single donor.
Haematocrit 50-70%

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13
Q

What is the shelf-life of packed RBCs?

A

35 days at 2-6°C (if adenine-containing solution used)

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14
Q

How are platelets presented?

A

Units of 250-300ml

Combined pool of several donors

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15
Q

What is the shelf life of pooled platelets?

A

3 days at 22°C
Risk of bacterial proliferation beyond this
Storage below 18°C damages platelet function

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16
Q

How is fresh frozen plasma presented?

A

Units of 200-300ml
Single donor
Rapidly frozen to -25°C after donation
Once thawed must be used within 6h

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17
Q

What is the shelf life of FFP?

A

1 year at -25°C

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18
Q

How is ABO group inherited?

A

Mendelian dominant inheritance

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19
Q

What is an agglutinin?

A

An antibody to ABO antigens

20
Q

How are ABO antigens created?

A

All have a common precursor - the H antigen
H-gene codes for fructose transferase which adds fructsose to end of the H oligosaccharide
Addition of a terminal sugar defines the ABO type of the antigen

Group A antigens have an N-acetyl galactosamine added to the H antigen

Group B antigens have a galactose molecule added to the H-antigen

21
Q

Where are ABO antigens found in the body?

A

Many tissues (including surface of erythrocytes)

22
Q

Where are Rhesus antigens found in the body?

A

Only on the surface of erythrocytes

23
Q

What is the most antigenic Rhesus antigen?

A

Rhesus D

24
Q

How prevalent is the Rhesus D antigen?

A

85% of caucasians +ve

99% of Asians +ve

25
Q

Do Rhesus D negative people constitutionally have anti-D antibodies?

A

No, they are acquired following exposure to Rhesus D +ve blood

26
Q

How may a person become sensitised to Rhesus D?

A

Blood transfusion

Childbirth

27
Q

Contrast antibodies to ABO antigens and Rhesus D antigen

A

Anti-ABO immunoglobulins are usually IgM

Anti-Rhesus D immunoglobulins are always IgG and can cross the placenta

28
Q

What are the possible immediate complications of blood transfusion?

A 
Acute haemolytic reaction (AHR)
Non-haemolytic febrile transfusion reaction (NHFTR)
Transfusion related acute lung injury (TRALI)
Allergic reaction
Bacterial contamination
Fluid overload
Electrolyte disturbance
Hypothermia
29
Q

What are the possible early complications of blood transfusion? (within days)

A 
Delayed transfusion reaction
Immune sensitisation (eg. RhD)
30
Q

What are the possible late complications of blood transfusion? (within weeks)

A

Iron overload

Blood-borne infection

31
Q

What is the pathophysiology of Acute Haemolytic Reaction?

A

Usually ABO incompatibility
Anti-ABO IgM fixes complement, lysing RBCs and causing cytokine release and mast cell degranulation leading to symptoms of severe reaction

32
Q

What is the pathophysiology of non-haemolytic febrile transfusion reactions?

A

Recipient Abs reacting against donor leucocyte antigens

33
Q

Which pyrogens are released in NHFTRs?

A

IL-1
IL-6
TNF-α

34
Q

What is the putative pathophysiology of TRALI?

A

Reaction between donor Abs and recipient leucocyte antigens

Activated neutrophils lodge within pulmonary vasculature, damaging the endothelium

35
Q

What type of RBC donor is often implicated in TRALI?

A

Multiparous women

36
Q

What is the most common cause of death or major morbidity following transfusion?

A

TRALI

37
Q

What types of allergic transfusion reactions can occur?

A

IgE-mediated

Anaphylactic reactions in patients with hereditary IgA deficiency due to presence of anti-IgA Abs (these patients need ‘washed’ RBCs

38
Q

What is the pathophysiology of delayed transfusion reactions?

A

Haemolytic reactions due to non-ABO incompatibility (often Rh or Kidd)
IgG-mediated therefore haemolysis is extravascular and less severe than AHR

39
Q

How much elemental iron is present in one unit of PRCs?

A

Approx 250mg

40
Q

At what threshold does iron overload from transfusion become significant?

A

Around 12-20 units

41
Q

What are blood donations in the UK routinely tested for?

A 
Hep B sAg
Hep C Ab + RNA
HIV Ab
Human T-cell leukaemia virus Ab
Syphilis Ab
vCJD
42
Q

What is the definition of ‘massive transfusion?’

A

Replacement of the circulating volume within 24h

43
Q

What are the main types of problems associated specifically with massive transfusion?

A

Disorders of:

  • Coagulation
  • Biochemistry/electrolytes
  • Temperature
  • Acid-base physiology
44
Q

What are the main electrolyte disturbances associated with massive transfusion?

A
  • Hyperkalaemia due to K+ leak from older cells

- Hypocalcaemia due to binding with residual citrate, particularly with FFP/platelets

45
Q

How does residual citrate in transfused products affect acid-base balance in massive transfusion?

A

Citrate is metabolised in the liver to produce HCO3- which can theoretically cause a metabolic alkalosis

Primary FRCA (34 decks)

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