BT_PO 1.113 Describe the physiological mechanisms of limiting and preventing thrombosis

My Mum sent me this photo recently whilst on holidays in Jordan. This little “dairy” was set up at the roadside.

When I think about blood clotting, I tend to think of the pathways which aid coagulation, rather than those which prevent thrombosis. Clearly in healthy individuals the pro and anti thrombotic systems are in a delicate, finely tuned balance.

I used Guyton and Hall Textbook of Medical Physiology as the reference text for today’s post

BT_PO 1.113 Describe the physiological mechanisms of limiting and preventing thrombosis

Smooth endothelium prevents exposure to collagen which stops the activation of the extrinsic coagulation pathway T/F

Thrombomodulin binds thrombin, increasing the risk of thrombosis T/F 

Heparin is released endogenously from basophils T/F

The muscle pump in the lower limbs plays a role in preventing thrombosisT/F

Endogenous anticoagulants include antithrombin III, protein C and protein S T/F

Endogenous activation of the coagulation cascade causes a concurrent activation of a thrombolytic process T/F

One of my children is studying year 12 biology this year – it is WAY more high tech than when I studied the subject 30 yrs ago. They have been studying genetics and she told me recently that transgenic goats have been created whom produce large quantities of human antithrombin III in their milk which is extracted for therapeutic use – wow! Not really relevant to today’s post, but there are also transgenic sheep who express α1-antitrypsin in their milk

BT_PO 1.117 Describe the changes that occur during blood storage and their clinical implications

T/F  during storage of a unit of packed cells, the potassium concentration progressively rises – it can reach 30 mmol/L at 28 days

T/F  during storage of a unit of packed cells, the 2,3-DPG concentration falls to almost zero, within 24 hours

T/F  as storage time increases, some red cells become spherical and rigid – 10-20% of these may be destroyed within 24 hours if transfused at the maximum storage time

T/F  during storage of a unit of packed cells, the calcium concentration progressively falls – it can reach 0.1 mmol/L at 28 days

T/F  to extend the storage time of packed cells (e.g. for use in remote areas), they can be frozen

T/F  once thawed, a unit of fresh frozen plasma (FFP) must be used within 24 hours


  1. Kam and Power 3rd edition, page 291-292
  2. Red Cross Transfusion Service website

BT_PO 1.115 Describe blood groups and methods of cross matching blood

I wish the weather here were a bit more like this today…..

I just noticed that there is no post for today – sorry. It may just be be that time of the year…

So you are not left high and dry, a quick one from me today. The Australian Red Cross has some excellent materials on this topic. Here is a section of pre transfusion compatibility testing. The Red Cross also has a good section on who can receive which products. This is clinically important stuff.

BT_PO 1.115 Describe blood groups and methods of cross matching blood

A serological crossmatch involves the patient’s serum being exposed to donor red blood cells T/F

Major ABO incompatibilities require only a short exposure between plasma and red cells to produce haemolysis T/F

In Australia, all crossmatching requires a sample of the patient’s serum to be exposed to the donor red blood cellsT/F

An O negative patient is a universal donor for red blood cellsT/F

An O negative patient is a universal donor for plasma components (eg FFP) T/F

The compatibility between donor platelets and the recipient is of no clinical significance T/F

BT_PO 1.111 Outline the major haemoglobinopathies and their clinical significance

T/F  methaemoglobin has the iron in the ferric (Fe3+) rather than the ferrous (Fe2+) state – this renders it completely unable to bind with oxygen

T/F methaemoglobin is normally present in trace amounts – but metHb can increase to toxic levels with certain drugs (e.g. prilocaine, nitrates) especially in people with methaemoglobin reductase deficiency

T/F  carboxyhaemoglobin (COHb) has CO bound to the terminal amino groups on each of the 4 globin chains – this renders the Hb unable to bind O2

T/F  CO binds to Hb with 250 times greater affinity than O2

T/F  the binding of CO to Hb instead of O2 is the sole mechanism by which carbon monoxide leads to hypoxia

T/F  sickle cell disease is a genetic disorder leading to a single nucleotide substitution on the B globin chain of Hb (valine instead of glutamic acid) – this reduces the affinity of HbS for O2

T/F  a sickle cell crisis can be treated with IV methylene blue

Guyton, Nunn

2018.2 SAQ 6 – massive transfusion

**You are in luck today; a bit of miscommunication resulted in two posts being written for this SAQ. They include different statements, so I thought you may as well enjoy them both. Have fun!!**

Outline the adverse effects that could occur following the rapid transfusion for ten (10) units of packed red cells.

It is not uncommon for us to have to give a massive transfusion. There are significant physiological consequences of this practice, in addition to the usual risks of red cell transfusion.

There is a lot you could write on this topic. It is covered comprehensively in Miller’s Anesthesia Ch 61 Patient blood management: transfusion therapy. This article from BJA Education has a lot of information not required to answer the question, but does have a good section of complication of massive transfusion.

BT_RT 1.9   Describe physiological consequences of massive transfusion

BT_PO 1.116  Outline the composition, indications and risks of use of  blood components and products including packed red cells

BT_PO 1.117  Describe the changes that occur during blood storage and their clinical implications

Hypothermia caused by the rapid infusion of cold blood may worsen any coagulopathy T/F

Provided haemoglobin is returned to normal levels, oxygenation at the tissue level  is unlikely to be compromised by a massive transfusion T/F

Immediate immune reactions to packed red cells include anaphylaxis T/F

Most people with normal liver function can metabolise the citrate in packed red cells, so citrate toxicity is uncommon T/F

Citrate binds calcium and thus citrate toxicity manifests with the signs of hypocalcaemia T/F

Metabolism of citrate produces bicarbonate and thus may induce a metabolic alkalosis T/F

Transfusion related lung injury (TRALI) may be minimised by only using packed cells from female donors T/F

TRALI is an acute reaction seen within the first hour or two of transfusion T/F

2018.2 SAQ 6 – massive red cell transfusion

Outline the adverse effects which could occur following the rapid transfusion of ten (10) units of packed red cells.

BT_PO 1.116  Outline the composition, indications, and risks of use of the following blood components and products …. packed red cells ….
BT_RT 1.9  Describe physiological consequences of massive transfusion

As anaesthetists, it is our responsibility to direct the volume resuscitation of patients with major haemorrhage. Doing this well requires a sound knowledge of physiology in a number of areas, including the consequences of ‘massive transfusion’.

In response to a number of adverse outcomes related to blood transfusions, an excellent e-learning resource is now available. In addition, Miller 8th edition Chapter 61 (Patient Blood Management – Transfusion Therapy), and Oh 7th edition Chapter 95 (Blood Transfusion) will provide all the basic science background needed to answer this SAQ. The Australian Red Cross website also has excellent information.

In answering this SAQ, you need to consider both (i) the complications of any PRC transfusion, and (ii) the complications of rapidly giving 10 units.

T / F  one definition of a “massive” transfusion is replacing the whole blood volume in 24 hours

T / F  using O negative packed cells will avoid the risk of any haemolytic transfusion reactions

T / F  the risk of transfusion-related acute lung injury (TRALI) correlates with the number of units of PRC given

T / F  one unit of PRC contains about 10% of the normal amount of platelets, and 50% of the normal amount of clotting factors

T / F  massive PRC transfusion can cause hyperkalaemia and hypercalcaemia

T / F  blood is stored at 4 degrees C, so rapid transfusion will cause hypothermia unless the blood is warmed

T / F  transfused red cells have a left shifted OHC causing impaired oxygen offloading due to depleted 2,3 DPG – it can take 24 hours for this to be corrected

T / F the risk of HIV transmission via a transfusion is estimated at less than 1 in 1 million in Australia

This is a good opportunity to remind yourself of the MTP in your hospital. How do you contact blood bank, and how do you activate the MTP? Are there wall charts in your OR’s reminding you of critical ratios of different blood products? Where do you get ‘Level 1’ pressure infusers and blood warmers? Have you observed a massive transfusion – what went well, and what didn’t?

BT_PO 1.74 Outline the constituents and functions of plasma

In my books, this is not a very exciting topic….

I have only included what I would consider reasonably core statements here so I think it would be reasonable that you knew them all

BT_PO 1.74 Outline the constituents and functions of plasma

Plasma accounts for approximately  60-70% of blood volume T/F

Albumin is almost exclusively confined to the plasma in normal physiological states T/F

The negative charge of albumin results in a higher concentration of cations in the plasma compared with interstitial fluid, due to the Donnan effect T/F

Plasma proteins hold fluid and electrolytes within the capillaries, resulting in little exchange of substances between the plasma and interstitial fluid T/F

Antibodies against red blood cell antigens are present in the plasma of all individuals  T/F

AB+ patients make universal plasma donors T/F ( the answer to this will give you the answer to the previous statement)


Blood volume


There are a few LO’s that pertain to blood volume but there is not one exclusively devoted to the topic as such.  As anaesthetists, it is obviously clinically useful to be able to calculate a patient’s blood volume to assist making clinical decisions regarding fluid therapy in the setting of perioperative blood loss. Although most of us have the basic formula of calculating blood volume deeply lodged in our hippocampi (70 mls/kg bodyweight), this formula is less accurate when applied to patients at the extremes of age and body habitus. I took the picture above during a tonsillectomy of a young child who weighed 20 kg. By the end of the operation 20% of their (calculated) blood volume was in the sucker. (You should be able to determine whether I took the picture half way through or towards the end of the procedure.)

Our estimation of blood loss is significantly less precise than our ability to estimate blood volume. If you are beginning to worry about how much blood your patient has lost you probably should be measuring their Hb objectively- they will invariably have  lost more than you think. If you are doing obstetrics they will definitely have lost more than you think.

Cote’s chapter on paediatric anaesthesia in Miller will give you most of the answers.

I think you should know the answers to all of the statements below.

The blood volume of men and women of the same weight is effectively the same  T/F

The blood volume of a term neonate is about 90 mls/kg  T/F

The blood volume of a premature infant is 100-120 mls/kg  T/F

The blood volume of a five year old is about 70 mls/kg  T/F

The blood volume of a seventy-five year old is about 70 mls/kg  T/F

The blood volume of a morbidly obese adult is about 60 mls/kg  T/F

The blood volume of a pregnant woman at term is about 80mls/kg  T/F

The haemoglobin concentration of a postmenopausal woman should be the same as that of a man*  T/F

*This last statement is possibly contentious, though it really shouldn’t be. Lab reference values are different for men and women and this reflects the population used to develop them. The gender difference in haemoglobin concentrations in healthy subjects is only present in women who are menstruating. There is no gender difference in children or the elderly although reference values perpetuate this (I may have given away the answer to the last statement). Some authorities believe# that this difference in menstruating women reflects untreated iron deficiency and that if properly supplemented there is in fact no difference in haemoglobin concentration between the sexes.  Interestingly other primates that menstruate don’t demonstrate a gender difference in haemoglobin concentrations.

see the paper here #



Blood Transfusion

BT_PO 1.115  Describe blood groups and the methods of cross matching blood

BT_PO 1.116 Outline the composition, indications and risks of the following blood components and products:- packed red cells, FFP, cryoprecipitate, platelets, FVIIa

BT_RT 1.7  Describe blood groups and the physiological basis of transfusion reactions

Sometimes, the importance and value of the basic sciences is highlighted when a critical incident occurs. It is not uncommon for errors in clinical judgement or patient management to occur because underpinning scientific knowledge was lacking.

NSW Health published a Safety Bulletin in July 2018, following 3 incidents where ABO incompatible plasma was given in emergencies.  Click here for the link.

T / F   a group A patient has A antibodies on their red cells

T / F  a group A patient has B antibodies in their plasma

T / F  group O negative packed red cells can be given to nearly all patients because the transfused cells have no antigen*

T / F  group O negative FFP can be given to nearly all patients because it contains no ABO antibodies

T / F  platelets also have ABO antigens – however, sometimes ‘cross group’ platelets have to be given due to supply shortages

T / F  ‘positive’ or ‘negative’ refers to the Rhesus antigen – giving Rh+ blood to an Rh- patient will cause a major haemolytic transfusion reaction

* there may be a caveat to this answer

BT_PO 1.110 Describe the physiological consequences of acute and chronic anaemia


The plant above (photo courtesy of Jonny’s Seeds) is Amaranthus, or Love-lies-a-bleeding. Interestingly the seeds are a edible and very high in iron. How neat – the cause and cure for anaemia in one!

When I was in Copenhagen recently, I went to a very interesting set of talks regarding anaemia in the elderly and the implications for peri-operative management of these patients. Peri-operative management of anaemia has received a lot of interest in the literature in recent years as part of a patient blood management strategy. If you are interested in the topic, then you can have a look at this International Consensus Statement on Peri-operative Anaemia.

However the focus of this LO is more on the basic (patho)physiological consequences of anaemia.

BT_PO 1.110 Describe the physiological consequences of acute and chronic anaemia

There is a good chapter on anaemia in Nunn’s Applied Respiratory Physiology Ch 23 and here  is an article from BJA Education which covers the basic concepts.

These first statements cover core and important concepts

Oxygen delivery to the tissues is determined by both haemoglobin concentration and cardiac output T/F

PaO2 would be lower in the same patient at a Hb of 60g/dL compared with 13g/dL T/F

An increase in FiO2 from 0.21 to 0.5 will increase the oxygen content of the blood significantly in an anaemic patient T/F

Chronic anaemia decreases blood viscosity thereby reducing cardiac afterload T/F

Have a think about the next one, it is both true and false. You may need a calculator, but see if you can find some conditions where it is true

A doubling of cardiac output will compensate for a halving of Hb, with respect to oxygen delivery

I think this one is interesting, but not core (the answer lies in the first article I linked to in the introduction)

Iron deficiency is only detrimental if associated with anaemia T/F