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Colloid solutions have been advocated for use in treating hypovolemia due to their expected effect on improving intravascular retention compared with crystalloid solutions. Because the ultimate desired effect of fluid resuscitation is the improvement of microcirculatory perfusion and tissue oxygenation, it is of interest to study the effects of colloids and crystalloids at the level of microcirculation under conditions of shock and fluid resuscitation, and to explore the potential benefits of using colloids in terms of recruiting the microcirculation under conditions of hypovolemia. This article reviews the physiochemical properties of the various types of colloid solutions (eg, gelatin, dextrans, hydroxyethyl starches, and albumin) and the effects that they have under various conditions of hypovolemia in experimental and clinical scenarios.

Background: Hyponatremia is often associated with, and worsens, the prognosis of severe aneurysmal subarachnoid hemorrhage (SAH). Several possible endocrine perturbations of variable severity and variable sodium and water intake have been described in SAH. However, a comprehensive study of the different hormonal systems involved in sodium and water homeostasis and circulating blood volume modifications is still needed. Our aim was to assess water and sodium regulation after severe SAH by investigating blood volume and several hormonal regulatory systems in the context of hyponatremia prevention by controlled sodium intake., Methods: Nineteen mechanically ventilated patients with severe SAH, were prospectively studied. Replacement of sodium was at least 4.5 mmol x kg(-1) x d(-1) and adjusted on natriuresis. Hormones involved in electrolyte and water homeostasis: vasopressin, renin, angiotensin, aldosterone, and natriuretic peptides were assessed every 3 days for 12 days. Red blood cell volume was measured by the isotopic method (technetium-labeled red blood cells), in the first 48 h after admission and at day 7. Cardiac function was assessed using electrocardiogram, transthoracic echocardiography, and troponin Ic (cTnI). Outcome was assessed at 3 mo., Results: After SAH onset, hyponatremia, but not decreased circulating blood volume, was prevented by high sodium and water infusion adapted to renal excretion. The hormonal profiles were characterized by an increase in renin, angiotensin II, natriuretic peptide concentrations associated with increased troponin Ic, stable low levels of vasopressin, and the absence of increased aldosterone concentrations. There were no correlations between hormone concentrations and natriuresis., Conclusion: After severe SAH, in the context of multiple clinical interventions, increased natriuresis and low blood volume are consistent with cerebral salt wasting syndrome, probably related to the sequence of severe SAH, highly increased sympathetic tone, hyperreninemic hypoaldosteronism syndrome, and increased natriuretic peptides release.

Unlabelled: We conducted an open, randomized, and prospective study to determine the effect of hypertonic saline on the secretion of antidiuretic hormone (ADH) and aldosterone in children with severe head injury (Glasgow coma scale <8). Thirty-one consecutive patients at a level III pediatric intensive care unit at a children's hospital received either lactated Ringer's solution (Ringer's group, n = 16) or hypertonic saline (Hypertonic Saline group, n = 15) over a 3-day period. Serum ADH levels were significantly larger in the Hypertonic Saline group as compared with the Ringer's group (P = 0.001; analysis of variance) and were correlated to sodium intake (Ringer's group: r = 0.39, R(2) = 0.15, P = 0.02; Hypertonic Saline group: r = 0.42, R(2) = 0.18, P = 0.02) and volume of fluids given IV (Ringer's group: r = 0.38, R(2) = 0.15, P = 0.02; Hypertonic Saline group: r = 0.32, R(2) = 0.1, P = not significant). Correlation of ADH to plasma osmolality was significant if plasma osmolality was >280 mOsm/kg (r = 0.5, R(2) = 0.25, P = 0.06), indicating an osmotic threshold for ADH release. Serum aldosterone levels were larger on the first day than during Days 2 and 3 in both groups and inversely correlated to serum sodium levels only in the Ringer's group (r = -0.55, R(2) = 0.3, P < 0.001). This group received a significantly larger fluid volume on Day 1 (P = 0.05, Mann-Whitney U-test) than did patients in the Hypertonic Saline group, indicating hypovolemia during the first day. Head-injured children have appropriate levels of ADH. They may be hypovolemic during the first day of treatment, especially if they receive lactated Ringer's solution., Implications: In head-injured patients, we recommend fluid restriction to avoid inappropriate secretion of antidiuretic hormone. In a prospective, randomized, and controlled study in 31 children, we were able to show that the antidiuretic hormone levels are appropriate in response to hypovolemia, sodium load, or both.