Blood volume reduced

Fig. 24.4 Starling curve of relationship between cardiac filling pressure and cardiac output. In phase A, reduction in blood volume (by diuretics) reduces filling pressure and cardiac output. In phase B, reduction in blood volume reduces filling pressure and increases cardiac output...

Secondary aldosteronism results in high blood levels of aldosterone in the absence of a primary adrenal defect. Secondary aldosteronism develops when one of the stimuli of aldosterone secretion is overactive. Consequently, at least three types of conditions can lead to secondary aldosteronism excess of renin, ACTH, or potassium. The condition encountered most often clinically is that in which renin is overproduced because of increased secretion by the juxtaglomerular apparatus or, more rarely, because of overproduction of precursors or extrarenal secretion (for example, by tumors). Renal secretion is stimulated when (1) arterial blood flow to the kidney is reduced (stimulation of baroreceptors), either as a result of the reduction in effective blood volume or renal artery obstruction or (2) osmoreceptors are stimulated as a result of hyponatremia. The arterial blood volume can be reduced by factors that decrease the blood volume (reduced water, sodium, or both), passage of fluid from the blood vessels to the extracellular compartment, and pregnancy (see Table 9-1). 

Nontraditional Hormones. Novel hormones identified ia cardiovascular tissue have profound effects on maintenance of blood pressure and blood volume ia mammals. Atrial natriuretic hormone (ANH) is a polypeptide hormone secreted from the atria of the heart. When the cardiac atrium is stretched by increased blood volume, secretion of ANH is stimulated ANH ia turn increases salt and water excretion and reduces blood pressure (6). Endothelin is a polypeptide hormone secreted by endothehal cells throughout the vasculature. Although endothelin is released into the circulation, it acts locally in a paracrine fashion to constrict adjacent vascular smooth muscle and increase blood pressure (7). 

In theory, one could utilise GC-A ligands to lower blood pressure and to reduce blood volume as they increase the excretion of water and salt. Nesiritide, human recombinant BNP, is the first member of this new class of drugs approved for the initial intravenous treatment of acutely decompensated congestive heart failure. Whether nesiritide can be a valuable addition to the standard therapy of decompensated heart failure remains to be demonstrated. 

Plasma protein fractions include human plasma protein fraction 5% and normal serum albumin 5% (Albuminar-5, Buminate 5%) and 25% (Albuminar-25, Buminate 25%). Plasma protein fraction 5% is an IV solution containing 5% human plasma proteins. Serum albumin is obtained from donated whole blood and is a protein found in plasma The albumin fraction of human blood acts to maintain plasma colloid osmotic pressure and as a carrier of intermediate metabolites in the transport and exchange of tissue products. It is critical in regulating the volume of circulating blood. When blood is lost from shock, such as in hemorrhage, there is a reduced plasma volume. When blood volume is reduced, albumin quickly restores the volume in most situations. 

Metabolic acidosis can also result when a person is severely burned. Blood plasma leaks from the circulatory system into the injured area, producing edema (swelling) and reducing the blood volume. If the burned area is large, this loss of blood volume may be sufficient to reduce blood flow and oxygen supply to all the body s tissues. Lack of oxygen, in turn, causes the tissues to produce an excessive amount of lactic acid and leads to metabolic acidosis. To minimize the decrease in pH, the injured person breathes harder to eliminate the excess C02. However, if blood volume drops below levels for which the body can compensate, a vicious circle ensues in which blood flow decreases still further, blood pressure falls, C02 excretion diminishes, and acidosis becomes more severe. People in this state are said to be in shock and will die if not treated promptly. 

This is, quantitatively, extremely important. One condition in which the liver fails to take up protons and lactate is when a considerable amount of blood has been lost (e.g. during or after an accident). To compensate for this, blood flow to the splanchnic area, including the liver, is severely reduced so that the liver becomes hypoxic, and not enough ATP can be generated to maintain gluconeogenesis. Consequently, lactate and protons accumulate in the blood and the pH falls a condition known as lactic acidosis. It is important, therefore, to maintain blood volume after an accident, which is usually done by infusion of fluid. 

Pregnancy Increased blood volume Increased renal blood flow and GFR Reduced plasma albumin Increased hepatic metabolism Altered drug distribution between protein bound and free forms Greater excretion of renally-cleared drugs May need increased dose to maintain effective Cp... 

Sodium retention and hypo albumin aemi a are constant features. The former appears consequent on disturbed blood volume distribution, withslanch-nic dilatation and reduced effective central arterial blood volume leads to sodium retention. Hypoalbu-minaemia associated with reduced hepatic albumin synthesis, and raised portal pressure associated with obstruction to flow, as well as active sodium retention all predispose to ascites. Hypoalbuminaemia is associated with reduced hepatic synthesis. 

Hormonal agents that inhibit the production or action of angiotensin reduce peripheral vascular resistance and possibly blood volume (e.g., ACE inhibitors such as enalapril (5.137), ATj antagonists) other hormones that influence blood pressure could also be targeted... 

Diuretics lower blood pressure by reducing blood volume and promoting sodium depletion (e.g., diuretics such as hydrochlorothiazide (5.153))... 

The pharmacologic actions of phenoxybenzamine are primarily related to antagonism of -receptor-mediated events. The most significant effect is attenuation of catecholamine-induced vasoconstriction. While phenoxybenzamine causes relatively little fall in blood pressure in normal supine individuals, it reduces blood pressure when sympathetic tone is high, eg, as a result of upright posture or because of reduced blood volume. Cardiac output may be increased because of reflex effects and because of some blockade of presynaptic k2 receptors in cardiac sympathetic nerves. 

Diuretics, which lower blood pressure by depleting the body of sodium and reducing blood volume and perhaps by other mechanisms. 

Agents that block production or action of angiotensin and thereby reduce peripheral vascular resistance and (potentially) blood volume. 

Diuretics lower blood pressure primarily by depleting body sodium stores. Initially, diuretics reduce blood pressure by reducing blood volume and cardiac output peripheral vascular resistance may increase. After 6-8 weeks, cardiac output returns toward normal while peripheral vascular resistance declines. Sodium is believed to contribute to vascular resistance by increasing vessel stiffness and neural reactivity, possibly related to altered sodium-calcium exchange with a resultant increase in intracellular calcium. These effects are... 

Thiazides Hydrochlorothiazide Block Na/CI transporter in renal distal convoluted tubule Reduce blood volume plus poorly understood vascular effects Hypertension, mild heart failure ... 

A common reason for diuretic use is for reduction of peripheral or pulmonary edema that has accumulated as a result of cardiac, renal, or vascular diseases that reduce blood delivery to the kidney. This reduction is sensed as insufficient effective arterial blood volume and leads to salt and water retention and edema formation. Judicious use of diuretics can mobilize this interstitial edema without significant reductions in plasma volume. However, excessive diuretic therapy may lead to further compromise of the effective arterial blood volume with reduction in perfusion of vital organs. Therefore, the use of diuretics to mobilize edema requires careful monitoring of the patient s hemodynamic status and an understanding of the pathophysiology of the underlying illness. 

Detailed chemical analysis of blood (for example, in hospital analyzers) is usually performed upon blood serum, the clear or yellowish liquid in which the red and white blood cells reside. (One obvious and important exception for which whole blood is required is the measurement of hematocrit, or fraction of blood volume occupied by red blood cells.) Removing the cells makes the tests more straightforward experimentally, both by reducing chemical interferents and by making colorimetric reactions easier to detect optically. Further filtering to remove large proteins can improve detection of minor constituents still more. 

In addition to these traditional vasodilators, nesir-itide (Natrecor) was developed as a newer method for producing arterial and venous dilation in people with heart failure.58 This substance was derived from human B-type natriuretic peptide (BNP) using recombinant DNA techniques. BNP is a naturally occurring substance that is released from the ventricles when the heart is subjected to increased blood volume and pressure.12 This substance dilates peripheral arteries and veins, thus reducing cardiac afterload and preload, respectively. Hence, nesiritide can be administered intravenously to reduce cardiac workload in certain patients with severe or acute heart failure.12,58... 

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