Kocian, et al - Haemoglobin oxygen carriers and perioperative organ perfusion Flashcards
There's a bunch of useful information on this article so I recommend skimming it. However, in these flashcards, I will focus on the findings and presentation of blood transfusion alternatives. (There is a section on blood oxygen delivery that I believe have been covered in other lectures in both physio and other courses).
Tolerance to anemia has been shown to better than previously expected with anemia-related deaths attributed to Hb levels significantly below 5g/dL. In what population of patients, however, do we still need to watch out for anemic conditions in (they have lower tolerance to anemia)?
Patients with cardiac disease in general are more susceptible to negative effects of anemia and have lower tolerance:
-Watch out esp with patients that have CAD (standard threshold for transfusions for them is 8 g/dL). Note that this threshold value is pretty variable though* and requires us to incorporate considerations of disease extent, age, and concurrent pathologies.
In what range of Hb do we see cardio-protective effects in CABG patients and what are these protective effects?
ANH (acute normavolemic anemia) - 28% Hb.
Fewer myocardial lesions, fewer arrhythmias, less need for inotropic support.
What are the two most common concerns with RBC transfusions?
Delayed haemolytic reactions (body reacts and tries to destroy foreign blood) and alloimmunization (auto-immune response).
Infections from the transfusions
What is the main aim of RBC transfusions?
Increase tissue oxygenation.
It’s not even really to increase Hb - remember that Hb count is a concern due to tissue oxygenation issues so if tissue oxygenation is fine (this is a bit difficult to be sure of though(, even at lower Hb values, RBC transfusion is not indicated.
At what lower Hb limit do we see an increased post-op morbidity and mortality?
6 g/dL (but remember correlation does not = causation)
What is a developing alternative to RBC transfusions?
Artificial oxygen carriers.
Note: In Dr. Altose’s basic sciences lecture on blood transfusions, he states that none are feasible at the moment, so these are still in development.
What are the potential advantages of using artificial oxygen carriers?
No need for blood group testing (ABO and Rh +/-), immediate availability in sufficient quantities, less risk of auto-immune response, decreased infection risk, long shelf life and IV half life.
Modified hemoglobin solutions: what is a significant problem with the use of extracellular human hemoglobin?
It dissociates from a 2 alpha, 2 beta tetramer into two alpha-beta dimers which nephrotoxic (bad for kidneys). –> Hence, we have to chemically/genetically modify these.
Although modified human hemoglobin solutions have been shown to have similar O2 carrying capacity and behavior (Sigmoid O2 dissociation curve) as intrinsic hemoglobin in animal studies, what are some undesired side effects of their administration?
- NO scavenging which causes vasoconstriction (increased in systemic and pulmonary resistance)
- Decrease in functional capillary density
- Possible iron overload which may compromise immune function
- Elevation of pancreatic enzymes and bilirubin
What hemoglobin based solutions have potential to actually undergo testing so far?
human polymerized hemoglobin
bovine polymerized hemoglobin-based O2 carrier
enzyme cross-linked polyhemoglobin
MP4, Hemospan
The rest listed in the article are abandoned or discontinued
Perfluorocarbon emulsions are another possible artificial O2 carrier. Describe what they are.
Innert carbon-fluorine cmds with low viscosity and high gas-dissolving capacity. They are NOT miscible in water, so they have to be emulsified for dissolution in plasma.
Small in size (good), but have a linear relationship with O2 binding (instead of the sigmoid shape of hgb). Hence, if used, will require higher FiO2 for same efficacy as RBCs.
