Summary of study session II

In study session II you have learnt

• Anemia is defined as a reduction of the body’s total red cell mass or it be defined as a deficiency of hemoglobin in the blood, which can be caused by either too few red blood cells or too little hemoglobin in the cells. Clinical symptoms and signs include feel tired with minimal exertion to dyspnea at rest depending on severity, tachycardia, and pallor of nail beds, palmar creases, conjunctivae and tongue.
• Anemia in pregnancy defined as hemoglobin (Hgb) level of < 10 gm/dL, hematocrit level of 30 % or is a qualitative or quantitative deficiency of Hgb or red blood cells in circulation resulting in reduced oxygen carrying capacity of the blood.
• The major function of red blood cells, also known as erythrocytes, is to transport hemoglobin, which in turn carries oxygen from the lungs to the tissues and excrete carbon dioxide from the tissues to the lungs.
• Any condition (hemorrhage, high attitude, cardiac failure, lung disease) that causes the quantity of oxygen transported to the tissues to decrease ordinarily increases the rate of red blood cell production.
• Hemoglobin is the constituent of the red blood cell that combines with oxygen and consists of two parts, hem and globin. Hem contains iron in the ferrous (Fe2+) state. Iron is an essential part of hemoglobin and when deficiency occurs due to dietary inadequacy or loss through chronic hemorrhage, anemia results.
• The majority of oxygen is carried bound to hemoglobin; a very small amount is dissolved in the plasma. Under normal circumstances, in the arterial circulation, one gram of hemoglobin is around 98% saturated and contains 1.34ml of oxygen. Therefore 1gm of hemoglobin can combine with 1.34 ml of oxygen.
• The oxygen content of blood (ml/100ml) = Saturation of oxygen X Hgb X 1.34 + 0.03 So for example, if the Hgb is saturated 98% and the hemoglobin concentration is 14gm per 100ml = 0.98 X 14 X 1.34 + 0.03 =18.4 ml per 100 ml of blood.
• The physiologic response to acute anemia, most often a result of hemorrhage, will depend on the extent and rate of acute blood loss. Baroreceptor reflexes release of catecholamines, angiotensin II, and vasoactive hormones ( renin–angiotensin– aldosterone) tries to maintain blood pressure and cardiac output.
• The increase in catecholamines will also confer a positive inotropic (increase the force of myocardial contractility) and chronotropic (increase heart rate) effects on the heart that will further augment cardiac output.
• Decreased intravascular volume stimulates the, which contributes to increasing cardiac output and improving tissue oxygen delivery by water retention.
• Chronic anemia is associated with expansion of plasma volume, hyperventilation, and an increased cardiac output. The increased cardiac output in anemia partially offsets the reduced oxygen-carrying effect of the anemia, because even though each unit quantity of blood carries only small quantities of oxygen, the rate of blood flow may be increased enough so that almost normal quantities of oxygen are actually delivered to the tissues.
• The compensatory physiologic response to acute, unreplaced volume loss is reduced under general anesthesia, emphasizing the importance of maintaining intravascular volume. The extent of the sympathetic stimulatory response to acute anemia is impaired during general anesthesia in that the heart rate does not increase to the same degree as in unanesthetized patients and the systemic vascular resistance is lower.
• Spinal anesthesia is preferred for lower abdomen and limb surgery, if the acute volume status is corrected, as they are associated with reduced blood loss.
• The main anesthetic considerations in chronic anemia are to minimize factors interfering with O2 delivery, prevent any increase in O2 consumption (shivering, fever) and to optimize the partial pressure of O2 in the arterial blood.
• Intraoperative monitoring should be aimed at assessing the adequacy of perfusion and oxygenation of vital organs. It should include routine monitors like electrocardiogram, blood pressure, Temperature monitoring, pulse oximetry, urine output and serial Hgb and hematocrit values can guide us to monitor ongoing blood losses.