The kidney in health and disease: X. CNS manifestations of disordered salt and water balance

Effects of Multiple Courses of Antenatal Corticosteroids on Regional Brain and Somatic Tissue Water Content in Ovine Fetuses

OBJECTIVE

To study the effects of single and multiple courses of antenatal corticosteroids on tissue water content in ovine fetuses.

METHODS

After chronic catheterization of the ewes and fetuses, the ewes were randomly assigned to receive single or multiple courses of dexamethasone or placebo beginning at 104-106 or 76-78 days' gestation, respectively. In the single course groups, the ewes received dexamethasone (6 mg, n = 6) or placebo (n = 6) as four intramuscular injections every 12 hours over 48 hours. The fetal tissues were harvested for water content determination 66 hours after the first injection of dexamethasone or placebo was given. In the multiple-course groups, the ewes received the same treatment (dexamethasone, n = 10, or placebo, n = 8), once a week for 5 weeks starting at 76-78 days' gestation. In these groups, the tissues were harvested 66 hours after the first the injection of the fifth and last treatment course. In both groups, tissues were harvested at 106-107 days' gestation. Tissue water content was determined by wet-to-dry weight ratio in brain (cerebral cortex, caudate nucleus, cerebellum, midbrain, and medulla) and somatic tissues (kidney, liver, muscle, and skin).

RESULTS

Water content in the brain regions (cerebellum and medulla) was lower (P <.05) in fetuses of dexamethasone-treated ewes than placebo-treated ewes after the multiple course but not the single course. Water content of somatic tissue was lower (P <.05) in fetuses of dexamethasone-treated ewes than placebo-treated ewes after the multiple courses, and in the liver after a single course.

CONCLUSION

Dexamethasone treatment of ewes at 70% of gestation results in decreased regional brain water content in the fetuses after multiple but not single treatment courses, in somatic tissues (kidney, liver, muscle, and skin) after multiple courses, and in the liver after a single course.

New topics in vasopressin receptors and approach to novel drugs: research and development of conivaptan hydrochloride (YM087), a drug for the treatment of hyponatremia

Hyponatremia is the most common electrolyte disorder in hospitalized patients and is associated with the risk of intractable seizures and death. The effectiveness of conventional therapies for hyponatremia is inconsistent, and the rapid correction of plasma sodium levels is thought to result in the occurrence of neurological complications. Arginine vasopressin (AVP) is the primary regulator of renal electrolyte-free water reabsorption via AVP-receptor type 2 (V2-R), and inappropriate or excessive AVP secretion independent of serum osmolality frequently causes excessive water retention, which is the etiological basis of hyponatremia. Therefore, the use of V2-R antagonists as anti-hyponatremic drugs in the clinical setting is anticipated to be reliable and safe. Conivaptan hydrochloride (YM087) is a novel dual AVP-R antagonist for AVP-R types 1a (V1a) and V2-R. In vitro studies have shown that it possesses high affinity for V1a-R and V2-R without any species differences. It also potently inhibited AVP-induced intracellular signaling through human V2 and V1a receptors with no agonistic activity. Conivaptan hydrochloride improved the plasma sodium concentration and plasma osmolality in hyponatremic rats, and its effectiveness was demonstrated in hyponatremic patients. This drug has been approved for use in the United States, which will bring relief to patients with hyponatremia.

Hypertonic saline

A key feature in the successful resuscitation of dehydrated or endotoxemic ruminants is the total amount of sodium administered. Administration of small volumes of HS and HSD offer major advantages over large volumes of isotonic saline because HS and HSD do not require intravenous catheterization or periodic monitoring, and are therefore suitable for use in the field. Hypertonic saline and HSD exert their beneficial effect by rapidly increasing preload and transiently decreasing afterload. Contrary to early reports, HS and HSD decrease cardiac contractility and do not activate a pulmonary reflex. The osmolality of HS and HSD should be 2400 mOsm/L (7.2% NaCl solution, 8 times normal plasma osmolality). Use of HS and HSD solutions of different osmolality to 2400 mOsm/L should be avoided at all costs, as too low a tonicity removes the main advantages of HS (low cost, decreased infusion time), whereas too high a tonicity may cause rapid vasodilation and decreased cardiac contractility, resulting in death. Rapid administration (> 1 mL/kg-1/min-1) of HS (2400 mOsm/L) should be avoided, as the induced hypotension may be fatal when coupled with a transient decrease in cardiac contractility. For treating dehydrated adult ruminants, HS (2400 mOsm/L, 4-5 mL/kg i.v. over 4-5 minutes) should be administered through the jugular vein and the cow allowed to drink water. This means that 2 L of HS should be administered to adult cattle. HSD should be administered in conjunction with isotonic oral electrolyte solutions to all calves 8% or more dehydrated (eyes recessed > or = 4 mm into the orbit, cervical skin tent duration > 6 seconds) or calves with reduced cardiac output (fetlock temperature < 29 degrees C when housed at 10-24 degrees C). For treating dehydrated calves, HSD (2400 mOsm/L NaCl in 6% dextran-70, 4-5 mL/kg i.v. over 4-5 minutes) should be administered through the jugular vein and the calf allowed to suckle an isotonic oral electrolyte solution. This means that 120-200 mL of HSD of HSD should be administered to a calf. HSD should be routinely administered to severely depressed or comatose calves, as HSD provides the fastest method of resuscitation while rapidly reversing the effects of hyperkalemia.

Cerebral effects of resuscitation with hypertonic saline and a new low-sodium hypertonic fluid in hemorrhagic shock and head injury

OBJECTIVES

A 2400-mOsm/L hypertonic solution (isosal) with a lower sodium content, compared with conventional 7.5% hypertonic saline, was formulated using a mixture of sodium chloride, glucose, and mixed amino acids. This solution was developed to minimize hypernatremia during resuscitation. We assessed the effects of isosal on hemodynamics, brain edema, and plasma sodium concentration after head injury associated with hemorrhagic shock. DESIGN. Prospective, randomized laboratory study.

SETTING

University research laboratory.

SUBJECTS

Twenty-one adult female Suffolk sheep, weighing 39 to 49 kg.

INTERVENTIONS

Animals were subjected to a 2-hr period of hemorrhagic shock to a mean arterial pressure (MAP) of 40 to 45 mm Hg in the presence of a freeze injury to the cerebral cortex. The hemorrhagic shock/head injury phase was followed by 2 hrs of resuscitation with isosal, a new 2400-mosm/L low-sodium hypertonic fluid, 2400 mosm/L of 7.5% hypertonic saline, or lactated Ringer's solution. Initial resuscitation was with a bolus injection of 8 mL/kg of the study solution; subsequent resuscitation in all three groups was with lactated Ringer's solution as needed to maintain baseline cardiac output.

MEASUREMENTS AND MAIN RESULTS

Serial hemodynamics, intracranial pressure, electrolytes, and osmolarity were measured. AT the end of resuscitation, the animals were killed and brain water content (mL H2O/g dry weight) of the injured and uninjured areas was determined. Resuscitation volumes were significantly lower in the isosal (19 +/- 5 mL/kg) and 7.5% hypertonic saline (14 +/- 2 mL/mg) groups compared with the lactated Ringer's solution (35 +/- 5 mL/kg) group. Intracranial pressure after 2 hrs of resuscitation was significantly lower in the isosal (7 +/- 1 mm Hg) and hypertonic saline groups (4 +/- 1 mm Hg). Water content in all areas of the brain was significantly lower in the hypertonic saline group compared with the lactated Ringer's solution group. Brain water content in the isosal group was lower than in the lactated Ringer's solution group only in the cerebellum. Plasma sodium content was lower in the isosal group than in the hypertonic saline group.

CONCLUSIONS

After combined head injury and shock, isosal and 7.5% hypertonic saline have similar effects on hemodynamics and intracranial pressure. Hypertonic saline induces a greater degree of brain dehydration; isosal resuscitation results in smaller increases in plasma sodium.

Intraosseous resuscitation of hemorrhagic shock in a pediatric animal model using a low sodium hypertonic fluid

OBJECTIVE

To study the efficacy of a low sodium hypertonic resuscitation fluid for resuscitation of severe hemorrhage in a pediatric animal, using the intraosseous route.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University physiology laboratory.

SUBJECTS

Seventeen immature (6- to 9-wk-old) piglets, weighing 10.6 +/- 0.4 kg, were studied under anesthesia.

INTERVENTIONS

A new 2400 mosm/L hypertonic fluid, "Isosal" was formulated with reduced (3.45%) sodium content compared with a 2400-mosm/L (7.5%) hypertonic saline solution. This formulation was accomplished by substituting glucose and mixed amino acids for sodium. Piglets were subjected to 1 hr of hemorrhage, reducing the cardiac output to 50% of baseline value. Resuscitation was carried out through the intraosseous route with an initial 6 mL/kg bolus of either hypertonic saline, Isosal, or lactated Ringer's solution. After the initial bolus, additional test fluid was given to maintain the cardiac output at baseline value for a 2-hr period.

MEASUREMENTS AND MAIN RESULTS

Total resuscitation volumes, hemodynamic variables, and electrolytes were measured. Intraosseous vascular access was easily established in all animals, and fluid resuscitation was carried out effectively through this route. Resuscitation volumes were significantly lower for both of the hypertonic fluids (12.7 +/- 1.2 mL/kg for hypertonic saline, and 12.5 +/- 1.7 mL/kg for Isosal solution) compared with lactated Ringer's solution (75.3 +/- 11.6 mL/kg) (p = .01). Both hypertonic saline and Isosal solution resulted in an immediate supranormal response in cardiac output that lasted 20 mins. In contrast, when lactated Ringer's solution was used, multiple boluses were required over a 20-min period to normalize cardiac output. Serum sodium was significantly higher in the hypertonic saline group compared with the Isosal or lactated Ringer's groups (p = .001).

CONCLUSIONS

Isosal solution was as effective as hypertonic saline in "small volume" resuscitation of severe hemorrhagic shock in a pediatric animal model through the intraosseous route, and produced significantly less hypernatremia when compared with hypertonic saline.

Liver injury as a model of uncontrolled hemorrhagic shock: resuscitation with different hypertonic regimens

Using a standardized liver injury model of uncontrolled hemorrhage, we tested the effect of different hypertonic solutions on mortality, blood pressure, intra-abdominal bleeding, and circulating blood volume. After liver injury, rats were randomized to 4 groups: lactated Ringer's (LR, n = 10), Isosal (ISO, n = 10), hypertonic saline (HS, n = 10), and hypertonic sodium acetate (HA, n = 10). In all resuscitation groups, 4 mL/kg was infused at a rate of 0.4 mL/min. Blood volume was evaluated both directly and by estimation. Mortality was highest after HA resuscitation (40%) and lowest after HS resuscitation (0%), but this difference was not significant. Blood pressure was significantly higher after HS resuscitation, and this difference was sustained for 4 hours. The HA resuscitation did not increase blood pressure compared with LR resuscitation. Intraperitoneal blood volume was significantly higher with HS (25.5 +/- 0.7 mL/kg) and HA (26.8 +/- 1.2 mL/kg) than with LR (22.5 +/- 0.4 mL/kg). The HA resuscitation led to a significantly larger drop from baseline values of estimated terminal circulating blood volume than LR resuscitation. Nonparametric analysis combining survival time and directly measured change in blood volume demonstrated a significant advantage to HS, compared with LR. HA and HS resuscitations increased bleeding from uncontrolled solid viscus injury. The HS resuscitation restored blood pressure better than the other hypertonic solutions and maintained circulating blood volume in spite of increased bleeding. The HA and ISO resuscitations did not exhibit any advantage over LR in resuscitation of solid viscus injury.

Diagnostic approach to polydipsia and polyuria

A variety of metabolic disturbances account for the majority of cases of polydipsia and polyuria. This chapter presents guides to differential diagnosis as well as a discussion of the etiology and clinical features of the primary causes--central diabetes insipidus, nephrogenic diabetes insipidus, and psychogenic polydipsia.

Is continuous haemofiltration superior to intermittent dialysis and haemofiltration treatment?

1. Mortality in cases of acute renal failure has increased from roughly 30% to roughly 70% in recent decades. 2. The rise paralleled the creation of intensive care units. In such units, more seriously ill patients reach the stage of acute renal failure. Before the advent of intensive care units, these patients died before acute renal failure could occur. 3. From a theoretical viewpoint, continuous haemofiltration (CH) has substantial advantages as opposed to intermittent dialysis and haemofiltration treatment. 4. No clinical proof of the superiority of continuous haemofiltration to the intermittent techniques has yet been provided. 5. In our own patient group, total mortality for acute renal failure patients decreased following adoption of continuous haemofiltration. During a selected period of use of continuous haemofiltration for patients with an unfavourable prognosis, however, the mortality with continuous haemofiltration was higher than that with the intermittent methods.

Plasma expanders. An update

This review of the literature has revealed that isotonic fluids, such as 0.9 percent sodium chloride and Ringer's lactate, are effective plasma volume expanders. Despite the continued use of a variety of colloid solutions in resuscitation, there is no good evidence to document a benefit of these solutions over the crystalloid solutions. The additional cost of colloid compared with crystalloid is another argument against colloid use. The most interesting solution currently being assessed is hypertonic saline solution. Its major benefit is that a small volume of fluid can achieve effective resuscitation. The smaller weight gain and lower incidence of peripheral edema may also prove to be significant benefits. Further evaluations are needed to verify the efficacy of this therapy. Finally, a recent National Institute of Health consensus panel identified the appropriate indications for fresh frozen plasma. They concluded that there is no indication for the use of fresh frozen plasma as a volume expander.

Cerebral effects of isovolemic hemodilution with a hypertonic saline solution

In view of a growing interest in the resuscitative use of hypertonic saline solutions, the authors have examined the cerebral effects of isovolemic hemodilution carried out over 1 hour (hematocrit decreased from 40% to 20%, stable arterial and right arterial pressures), using a hypertonic lactated Ringer's solution (HT-LR: Na+ 252 mEq/liter, osmolality 480 mOsm/liter). Experiments were carried out in anesthetized ventilated rabbits. Measured variables included cerebral blood flow (using the H2 clearance method), intracranial pressure (ICP), the electroencephalogram, spinal cord and skeletal muscle water content (%H2O), and the specific gravity of small (10- to 30-mg) tissue samples taken from different areas of the left hemisphere (including the cortex, thalamus, internal capsule, and hippocampus). The changes produced by HT-LR were compared with those seen in both undiluted control animals and in rabbits hemodiluted with normal saline (Na+ 155 mEq/liter, osmolality 310 mOsm/liter). The results demonstrate that hemodilution with HT-LR leads to the expected increases in serum Na+ and osmolality (158 +/- 6 mEq/liter and 320 +/- 5 mOsm/kg, respectively, mean +/- standard deviation) and that these were accompanied by reductions in the %H2O of all cerebral and extracerebral tissues, increases in the specific gravity of all tissue regions studied, and a decrease in ICP (1.9 +/- 0.7 mm Hg). By contrast, rabbits with hemodilution by normal saline showed no changes in either %H2O or specific gravity, but had significant increases in ICP (3.3 +/- 1.3 mm Hg). Cerebral blood flow increased in all animals hemodiluted with either HT-LR or normal saline by a combined average of +29 ml/100 gm/min. Although these studies were performed in neurologically normal animals, the combination of cerebral changes seen with HT-LR (cerebral dehydration, less peripheral edema, decreased ICP but with increased cerebral blood flow) suggests that this approach may have some advantages over the use of isotonic fluids, and may have some utility in the resuscitation of head-injured patients.