Red Cell Transfusion - key points

Question 1

Indication for rc transfusion

Answer 1

Rarely if Hb>9g/dl
Nearly always if Hb>6g/dl

Question 2

List the preservatives and their functions

Answer 2

Citrate - prevents coagulation by binding calcium

Sodium biphosphate prevents excessive drop in pH

Dextrose - supports ATP generation by the glycolytic pathway

Adenine - acts as a substrate for red cell ATP synthesis

mannitol - osmotic diuretic acts as a membrane stabiliser

Question 3

expiration of red cells

Answer 3

35 days in ireland
42 days in america - for use by military

Question 4

Red cell metabolism

Answer 4

Energy from breakdown of glucose to lactate or pyruvate (anaerobic)

Embden-Meyerhof pathway

Lactate acid causes a pH drop -> lower the pH the less red cell is delivering oxygen

2,3-DPG removes oxygen and pushes it into tissues, lower 2-3 DPG means less oxygen delivering capacity

Question 5

History in preservative and storage development

Answer 5

1914 Payton Rous in NY combined citrate and glucose to yield a shelf life of 9 days

1937 the first blood bank was set up in Cook County Hospital in USA

In 1940s Acid citrate dextrose was introduced by Mollison

Blood was sotred in glass bottles to allow for autoclaving etc

In 1960s CPD replaced ACD - shelf life up to 21 days

plastic bags in the 60s - facilitated component production

70s adenine introduced - 35 day shelf life

SAGM -> 42 days in America but 35 in Europe

Question 6

What are the effects of storage on red cells

Answer 6

Increase:
- Plasma Hb
- plasma K+

Decrease:
- plasma pH
- plasma Na+
- RBC ATP + 2,3 DPG

Question 7

Talk about the storage lesion

Answer 7

In two weeks the 2,3-DPG levels fall to zero

ATP levels fall to about 50%

Oxygen disocciation curve shifts to the left

This is restored within 12 to 14 hours of transfusion

Question 8

What happens to the rbcs when stored, physically?

Answer 8

Loss of membrane lipids thus haemolysis gradually occurs

Question 9

What causes increase in plasma K+ and decrease in Na

Answer 9

Poor performance of ATPase due to cool temperatures

Normally acts as a pump for NA and K

Question 10

What is lost from rbcs when stored for long

Answer 10

Loss of platelets
Loss of labile clotting factors

Rbcs become echinocytes and eventually spheres

Question 11

At what temperature are rbcs stored?

Answer 11

Between 2 and 6 degrees

Question 12

Define massive transfusion

Answer 12

Replacement approximating or exceeding the patient’s blood volume within a 24 hour period

An ongoing transfusion requirement in an adult of more than 150ml per minute

Replacement of more than 50% of blood volume in 3 hours or less

Replacement of one blood volume, or transfusion of 10 units or more of red cells in a 24 hour period

Question 13

What are the priorities of massive transfusion

Answer 13

Correct hypovolaemia with crystalloids

Optimise oxygen-carrying capacity

Maintain haemostasis: platlets and coagulation factors

Correct or avoid metabolic disturbances

Maintain intravascular volume with colloids

Question 14

What is the trauma triad of death

Answer 14

Hypothermia
Acidosis
Coagulopathy

Question 15

What are six coagulopathies of trauma

Answer 15

Dilutional
Hypothermic
Platelet dysfunction
Coagulopathy of acidosis
Consumptive coaguloapthy
Hyperfibrinolysis

Question 16

What is the main effect of hypothermia on platelet function

Answer 16

Platelet activation byt he vwf pathway is reduced by 50% in indivudals at 30 degrees and 75% in others

Question 17

How does uncontrolled fibrinolysis occur

Answer 17

Reduced rates of thrombin generation

Leads to thinner fibrin strands with greater surface area and reduced or absent activation of thrombin activatable finrinolysis inhibitor

Tranexamic acid now used to inhibit this by strengthening clots and preventing breakdown of fibres