Effective Circulating Blood Volume Research Articles

Shock: mechanisms and therapy.

A Unitarian concept of shock has been proposed based upon theoretical physiologic grounds and supported by experimental and clinical data. This concept depicts shock as a defect in effective tissue perfusion, related to a decrease in cardiac output and organ blood flow and an increase in peripheral resistance. Restoration of cardiac output and organ blood flow by maintenance of effective circulating blood volume (central venous pressure, 10 cm. H2O, blood volume, 80 ml./kg. ) in association with digitalization when indicated will be effective in most patients in shock. In the remaining patients in which resistance in the cutaneous and visceral microcirculation remains elevated (pale, cool extremities and reduced urinary output), increased blood flow can be promoted in these areas by use of drugs which decrease vasoconstriction by blocking alpha-receptors ( phenoxybenzamine, phentolamine, chlorpromazine) or decrease resistance to flow by yet unknown means ( massive doses of glucocorticosteroids ) or decrease resistance by beta-receptor stimulation ( isoproterenol ) and consequent dilatation of the microcirculation of the muscles, while also stimulating the same receptors in the heart to increase the force and rate of cardiac contraction. In view of the dismal results obtained by vasopressors, alpha-receptor stimulators such as Levarterenol and Aramine, the use of these substances should be abandoned as the only form of treatment in shock.

Vasodilators in shock--when?

Concepts for the use of vasodilators in shock are presented which have proved effective in clinical practice. Excessive vasoconstriction has the extremely deleterious action of shifting blood volume centrally to cause pulmonary congestion and cardiac overload and of decreasing tissue perfusion which leads to progressive metabolic acidosis. Evidences of extreme vasoconstriction therefore are persistent elevation of central venous pressure low pulse pressure and/or absence of peripheral pulses in some instances. Given these clinical signs vasodilators are advocated but they must be used only when the effective circulating blood volume is normal or being returned to normal. The vasodilator that has been used most in laboratory and clinical experiments (particularly in endotoxin shock) is phenoxybenzamine (Dibenzylene) an effective alpha receptor blocker at the neuromuscular junction. Alpha stimulators increase cardiac rate and arteriolar tone while beta receptors have a positive ionotropic effect on the heart and act as mild vasodilators. Phenoxybenzamine also seems to have some antiserotonin and antihistaminic effects. It is given intravenously in a dose of 1 mg/kg of body weight. Other agents with salutary effect include: trimethaphan hydralazine hydrocortisone and cortisol.

Central venous pressure monitoring: A useful guide to fluid therapy during shock and other forms of cardiovascular stress

Important relationships between venous pressure, blood volume, and cardiac output were described over fifty years ago, but the clinical application of peripheral venous pressure measurements was limited by errors in methodology and by incomplete physiologic data on the function of the venous system. There has been a recent renewal of interest in the venous system due to the advent of open heart surgery and additional physiologic data indicating that central venous pressure could be measured more accurately and would have more clinical usefulness than peripheral venous pressures. The description of new technics for cannulation of the central venous system by Richards and associates, [19] Hughes and Magovern, [20] Aubainac, [22] Keeri-Szanto, [24] and Wilson, Grow, and Demong [25] made monitoring of CVP a simple bedside procedure. A further modification of Wilson's technic involves the use of a 15 gauge, 6 inch, Rochester needle, which is introduced percutaneously into either subclavian vein. The needle is removed, leaving the outer catheter in place. A Seldinger guide wire is used to thread the catheter into the superior vena cava without fluroscopic guidance. A total of 132 catheterizations of the superior vena cava have been carried out by this technic, with a 8.3 per cent complication rate, none of which were serious. None resulted in death of the patient. CVP is not a linear function of blood volume, except under special controlled conditions that rarely exist in clinical practice. Therefore, CVP cannot be used to estimate blood volume. CVP, on the other hand, is an expression of the rate of venous return compared with the myocardial competency (the ability of the heart to handle the venous return). Since the terms “rate of venous return” and “effective circulating blood volume” are functionally similar, CVP can be used as a measure of the effective circulating blood volume related to the competence of the heart. Isolated absolute CVP measurements are of little value unless they are unusally high or low. Continuous monitoring of CVP and correlation of changes in pressure with volume expansion or contraction are useful guides to fluid therapy. CVP monitoring is an adjunctive procedure that facilitates the diagnosis and treatment of abnormal circulatory states and is most useful when related to other data, such as history, physical findings, urinary output, systemic blood pressure, pulse pressure, blood volumes, and cardiac output.

THERAPY FOR HYPOTENSION INDUCED BY SPINAL ANESTHESIA DURING PREGNANCY: OBSERVATIONS ON GRAVID EWES.

During actual and simulated spinal anesthesia in 21 term gravid ewes, induced maternal hypotension was associated with a proportionate decrease in uterine blood flow (UBF). Under these circumstances, vasopressor drugs administered intravenously restored maternal blood pressure (MBP) to normal without improving uterine blood flow. However, rapid infusions of 5% dextrose or dextran solution significantly improved both MBP and UBF proportionately. These results indicate that the prophylactic or therapeutic use of vasopressor agents in conjunction with spinal or caudal anesthesia during pregnancy is contraindicated. Rather, therapy designed to increase effective circulating blood volume should be initiated. This includes a rapid intravenous infusion of dextrose solution, elevation of the legs, and displacement of the uterus to the left to reduce vena caval obstruction and increase venous return to the heart.

The homologous blood syndrome: III. Influence of plasma, buffy coat and red cells in provoking its manifestations ∗

1. 1. Rapid exchange of homologous blood in dog or man may precipitate a state of shock. The reaction is dose-related and becomes more pronounced with increasing duration. 2. 2. Severe hypovolemia (diminution of the effective circulating blood volume) results from sequestration of both plasma and cells. 3. 3. Eventual return of a portion of the trapped blood is evident from repetitive blood volume studies. 4. 4. Separate exchange of components of homologous blood did not eliminate the manifestations of the syndrome in the experimental animal. However, erythrocytes reconstituted in physiologic saline solution caused the least dynamic alterations. 5. 5. Data obtained during clinical exchange of homologous erythrocytes and saline are presented. 6. 6. Amelioration of the homologous blood syndrome during cardiopulmonary bypass has been obtained by (a) reduction of the extracorporeal priming volume, (b) substitution of electrolyte solutions for a portion of the homologous blood and (c) reutilization of blood collecting in pleural and precardial spaces during surgery. 7. 7. Possible etiologic mechanisms of the homologous blood syndrome are discussed.

Role of histamine in meperidine-induced hypotension

Summary The challenge of intact and histamine-depleted dogs with large doses of meperidine has clearly established the fact that this drug does not have any intrinsic hemodynamic effect. The circulatory changes that are induced by meperidine injection in the intact animals are entirely due to the release of endogenous histamine. Correlation of information from these experiments as well as from the work of others suggests that the mechanism of histamine-induced hypotension has at least two components. One of these is a reduction in effective circulating blood volume and the other a decrense in peripheral vascular resistance.

The role of ouabain in myocardial insufficiency during anesthesia and surgery ∗

The pathogenesis of myocardial insufficiency during anesthesia and surgery is shown to be related to alterations in effective circulating blood volume as well as the directly depressant effects of anesthetic drugs on the myocardium. Stress is laid upon considering myocardial insufficiency in any differential diagnosis of the cause of hypotension in an anesthetized subject. A rational method for treating this state with ouabain, relating the known pharmacology of the drug to known pathologic changes in “shock” states, is presented. The key to these concepts is found in presently available knowledge of the effects of drugs on energy release mechanisms of the myocardium.

The cardiohemodynamic effects of venous congestion of the legs or of phlebotomy in patients with and without congestive heart failure.

The purpose of this study was to clarify the cardiohemodynamic responses to acute reduction in the effective circulating blood volume in man. McMichael and Sharpey-Schafer found that the cardiac output in normal subjects fell during venous congestion of the extremities (1). They attributed this reduction in cardiac output to a decrease in the right atrial pressure. Their observation that right atrial pressure usually falls during such acute reductions in the effective circulating blood volume was confirmed by Warren, Brannon, Stead, and Merrill (2), but these latter workers did not usually find an associated decrease in cardiac output. They therefore suggested that the cardiac output response is independent of changes in right atrial pressure, at least within physiological limits. However, observations by Howarth, McMichael, and SharpeySchafer (3) on the effects of phlebotomy and of venous congestion of the extremities in patients with congestive heart failure supported the concept that the level of right atrial pressure is an important factor in determining cardiac output. The studies reported herewith differ in certain aspects from all those just mentioned.

Antidiuretic effect of non-renal venous congestion on renal water excretion by the hydrated rat.

Summary(1) Water excretion by hydrated rats has been studied to ascertain the alterations after ligation of the inferior vena cava at 3 levels in relationship to the renal veins. In addition, the effects of unilateral nephrectomy, hypophysectomy and thoracic lymph duct ligation, and various other control procedures have been observed. (2) The antidiuretic effect of inferior vena cava ligation in the hydrated rat is shown to be independent of increased renal venous pressure, and is also shown to occur in the absence of the pituitary gland. (3) The critical importance of the lymphatic pathway in maintaining an effective circulating blood volume in the presence of acute venous obstruction is demonstrated by showing the lethal effects of hydration in animals with combined caval and thoracic duct ligation, procedures which are separately tolerated by the rat.

SURGICAL APPROACH TO HYPERTENSION

IN A previous report from the University of Illinois College of Medicine, de Takats, Heyer and Keeton 1 presented the classification, the preoperative study, the selection of cases and the surgical procedures employed, together with the results of follow-up studies of hypertensive patients. Of the methods for splanchnic nerve section, the transdiaphragmatic method of Smithwick 2 gave by far the best results. The selection of patients with early hypertension and the use of this improved technic seemed to us the two important factors in the obtaining of good results. An attempt was also made to analyze the mechanism of relief in hypertensive patients after splanchnic section. Aside from the actual lowering of blood pressure, a slow, gradual improvement of cardiac and renal function, a postural hypotension with consecutive decrease in effective circulating blood volume and a decrease in reflex nervous irritability due to adrenal denervation were mentioned as contributing to