Anesthesia Keywords Defined - 2004
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DS027       NORMOVOLEMIC HEMODILUTION: PHYSIOLOGICAL RESPONSE

Normovolemic hemodilution refers to the removal of blood and replacement with asanguinous fluid to maintain normovolemia. This is accompanied by a decrease in arterial oxygen content, but oxygen delivery is usually unaffected due to increase in cardiac out put as a physiologic compensation. The primary factor responsible for the increased cardiac output is decreased viscosity, which is most pronounced between HCT values of 45 and 30%, and the effect is progressively less significant when the HCT is below 25%. Decreased viscosity results in increased venous return, decreased peripheral resistance, and reduced after-load. The reduced peripheral resistance may also be due to reflex vasodilatation or local regulatory factors, such as endogenous release of nitric oxide.

1. Stehling L. Autologous Transfusion. In Miller RD (ed.): Anesthesia. 5th edition. Churchill Livingstone, Philadelphia, PA. 2000:1651.

DS028       TRANSFUSION COMPATIBILITY

The ABO-Rh type, cross match and antibody screen are referred to as compatibility tests. These tests were designed to demonstrate harmful antigen-antibody reactions in-vitro so that harmful antigen-antibody reactions can be avoided in-vivo.

Donor blood must be tested for the correct ABO-Rh type, hemolytic anti -A and Anti-B antibodies, and screened for unexpected antibodies.

Similarly recipient blood must also undergo ABO-Rh-typing and testing for unexpected antibodies.

ABO-Rh typing alone results in a 99.8% chance of a compatible transfusion, the addition of an antibody screen increases the safety to 99.94%, and a cross match increases this to 99.95%.

1. Miller RD. Transfusion Therapy. In Miller RD (ed.): Anesthesia. 5th edition. Churchill Livingstone, Philadelphia, PA. 2000:1615-16.

DS035       SIDE EFFECTS: PROSTAGLANDINS

Prostaglandins predominantly found in the uterus are those of the E and F types. The side effects are due to their stimulatory effects on smooth muscle, causing diarrhea and vomiting. PGE2 and 15-methyl-PGF2-alpha may cause pyrexia due to its effect on the hypothalamus. In large doses PGF-2-alpha can cause hypertension through constriction of vascular smooth muscle, while PGE produces a fall in blood pressure due to vasodilatation. The effects are exaggerated in the hypertensive patients.

PGFs cause contraction of the bronchial smooth muscle, and asthmatic patients are particularly sensitive to PGF 2 alpha. PGEs produce relaxation of bronchial smooth muscles1.

A case of myocardial infarction associated with the use of PGF2 in an otherwise well young woman has been reported.

1. Warmington ADL Postpartum hemorrhage. In Birnbach DJ, Gatt SP, Datta S (Eds) Textbook of Obstetric Anesthesia. Churchill Livingstone. Philadelphia, PA 2000:423-424.

2. Fkiers E, Duren DR, van Zwieten PA: A prostaglandin analogue as a probable cause of myocardial infarction in a young woman. BMJ 1991;302:416.

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