Use of Urine Electrolytes and Urine Osmolality in the Clinical Diagnosis of Fluid, Electrolytes, and Acid-Base Disorders.

We discuss the use of urine electrolytes and urine osmolality in the clinical diagnosis of patients with fluid, electrolytes, and acid-base disorders, emphasizing their physiological basis, their utility, and the caveats and limitations in their use. While our focus is on information obtained from measurements in the urine, clinical diagnosis in these patients must integrate information obtained from the history, the physical examination, and other laboratory data.

L-lactic acidosis: pathophysiology, classification, and causes; emphasis on biochemical and metabolic basis.

L-lactic acidosis (L-LA) is the most common cause of metabolic acidosis in the critical care setting, which has been associated with a large increase in mortality. The purpose of this article is to provide clinicians with an overview of the biochemical and metabolic background required to understand the different pathophysiological mechanisms that may lead to the development of L-LA. We propose a classification based on whether the pathophysiology of L-LA is due predominantly to increased production or decreased removal of L-lactic acid.

Impact of Prolonged Fasting on the Risk of Calcium Phosphate Precipitation in the Urine: Calcium Phosphate Lithogenesis during Prolonged Fasting in a Healthy Cohort.

Purpose: Intermittent fasting and curtailing water intake for extended periods were likely common in Paleolithic times. Today it occurs for religious and dietary reasons. This restriction in intake should cause a decrease in the urine flow rate while raising the concentration of certain substances in urine to the point of precipitation.

Renal potassium physiology: integration of the renal response to dietary potassium depletion.

We summarize the current understanding of the physiology of the renal handling of potassium (K), and present an integrative view of the renal response to K depletion caused by dietary K restriction. This renal response involves contributions from different nephron segments, and aims to diminish the rate of excretion of K as a result of: decreasing the rate of electrogenic (and increasing the rate of electroneutral) reabsorption of sodium in the aldosterone-sensitive distal nephron (ASDN), decreasing the abundance of renal outer medullary K channels in the luminal membrane of principal cells in the ASDN, decreasing the flow rate in the ASDN, and increasing the reabsorption of K in the cortical and medullary collecting ducts. The implications of this physiology for the association between K depletion and hypertension, and K depletion and formation of calcium kidney stones are discussed.

Approach to the Treatment of Diabetic Ketoacidosis.

Diabetic ketoacidosis (DKA), a common cause of severe metabolic acidosis, remains a life-threatening condition due to complications of both the disease and its treatment. This Acid-Base and Electrolyte Teaching Case discusses DKA management, emphasizing complications of treatment. Because cerebral edema is the most common cause of mortality and morbidity, especially in children with DKA, we emphasize its pathophysiology and implications for therapy.

How Protective Mechanisms Interact to Prevent Overnight Calcium Phosphate Precipitation - An Observational Study to Determine Factors Against Calcium Phosphate Lithogenesis in a Healthy Cohort.

Background/aims: As restful, non-interrupted sleep is essential for normal mental and physical functioning, the urine flow rate (UFR) overnight remains low. Due to this reduced UFR, the kidneys produce a lower urine volume, which may lead to supersaturation of lithogens in the renal collecting system. The protective mechanisms that prevent the rise in the concentration of the lithogenic substances in urine, such as calcium phosphate, are explored.

Effect of improving the usability of an e-learning resource: a randomized trial.

Optimizing the usability of e-learning materials is necessary to reduce extraneous cognitive load and maximize their potential educational impact. However, this is often neglected, especially when time and other resources are limited. We conducted a randomized trial to investigate whether a usability evaluation of our multimedia e-learning resource, followed by fixing of all problems identified, would translate into improvements in usability parameters and learning by medical residents.

Integration of the response to a dietary potassium load: a paleolithic perspective.

Our purpose is to integrate new insights in potassium (K(+)) physiology to understand K(+) homeostasis and illustrate some of their clinical implications. Since control mechanisms that are essential for survival were likely developed in Paleolithic times, we think the physiology of K(+) homeostasis can be better revealed when viewed from what was required to avoid threats and achieve balance in Paleolithic times. Three issues will be highlighted.

Bolus administration of intravenous glucose in the treatment of hyperkalemia: a randomized controlled trial.

Background: Hyperkalemia is a common medical emergency that may result in serious cardiac arrhythmias. Standard therapy with insulin plus glucose reliably lowers the serum potassium concentration ([K(+)]) but carries the risk of hypoglycemia. This study examined whether an intravenous glucose-only bolus lowers serum [K(+)] in stable, nondiabetic, hyperkalemic patients and compared this intervention with insulin-plus-glucose therapy.

An efficient approach to improve the usability of e-learning resources: the role of heuristic evaluation.

Optimizing the usability of e-learning materials is necessary to maximize their potential educational impact, but this is often neglected when time and other resources are limited, leading to the release of materials that cannot deliver the desired learning outcomes. As clinician-teachers in a resource-constrained environment, we investigated whether heuristic evaluation of our multimedia e-learning resource by a panel of experts would be an effective and efficient alternative to testing with end users. We engaged six inspectors, whose expertise included usability, e-learning, instructional design, medical informatics, and the content area of nephrology.

Non-natriuretic doses of furosemide: potential use for decreasing the workload of the renal outer medulla with minimal magnesium wasting in the rat.

Background/aims: Since furosemide (FS) inhibits active Na(+) reabsorption by medullary thick ascending limb (mTAL) in the renal outer medulla, it may decrease its work during periods of low O2 supply to deep in the renal outer medulla. This study was designed to demonstrate that there may be a dose of FS would reduce its metabolic work while preventing the excessive loss of magnesium (Mg(2+)). Mg(2+) is important because the ATP needed to perform work must have bound Mg(2+) to it.

Hypokalemia during treatment of diabetic ketoacidosis: clinical evidence for an aldosterone-like action of insulin.

Objectives: To investigate whether the development of hypokalemia in patients with diabetic ketoacidosis (DKA) treated in the pediatric critical care unit (PCCU) could be caused by increased potassium (K(+)) excretion and its association with insulin treatment.

Study Design: In this prospective observational study of patients with DKA admitted to the PCCU, blood and timed urine samples were collected for measurement of sodium (Na(+)), K(+), and creatinine concentrations and for calculations of Na(+) and K(+) balances. K(+) excretion rate was expressed as urine K(+)-to-creatinine ratio and fractional excretion of K(+).

Response of the renal inner medulla to hypoxia: possible defense mechanisms.

Background/aims: Owing to the precarious blood supply to the renal medulla and the high metabolic requirement of the medullary thick ascending limb of Henle's loop, this nephron segment should be especially vulnerable when its supply of O(2) declines.

Methods: Rats were exposed to 8 or 21% O(2) at different time points up to 5 h, and samples were collected for urine flow rate, urine (U(osm)) and renal papillary (RP(osm)) osmolality, urinary excretion of Na(+), Cl(-), K(+) and Mg(2+), blood gases, erythropoietin and vasopressinase activity in plasma. Other groups of rats were pretreated with desmopressin acetate (dDAVP) or underwent bilateral nephrectomy (BNX) 1 h prior to the exposure.

Development and evaluation of a multimedia e-learning resource for electrolyte and acid-base disorders.

This article reports on the development and evaluation of a Web-based application that provides instruction and hands-on practice in managing electrolyte and acid-base disorders. Our teaching approach, which focuses on concepts rather than details, encourages quantitative analysis and a logical problem-solving approach. Identifying any dangers to the patient is a vital first step.

Intrarenal urea recycling leads to a higher rate of renal excretion of potassium: an hypothesis with clinical implications.

Purpose Of Review: This review aims to illustrate why urea recycling may play an important role in potassium (K⁺) excretion and to emphasize its potential clinical implications.

Recent Findings: A quantitative analysis of the process of intrarenal urea recycling reveals that the amount of urea delivered to the distal convoluted tubule is about two-fold larger than the quantity of urea excreted in the urine. As the number of osmoles delivered to the late cortical distal nephron (CCD) determines its flow rate when aquaporin 2 water channels have been inserted in the luminal membrane of principal cells, urea recycling may play an important role in regulating the rate of excretion of K⁺ when the distal delivery of electrolytes is not very high.

Is there escape from renal actions of vasopressin in rats with a hyponatremia for greater than 48 hours?

Escape from the renal actions of vasopressin is said to occur in rats with chronic hyponatremia. Our objective was to provide specific evidence to test this hypothesis. Hence the osmolality in the excised renal papilla and in simultaneously voided urine (U(Osm)) was measured in rats with and without hyponatremia.

Importance of Residual Water Permeability on the Excretion of Water during Water Diuresis in Rats.

When the concentration of sodium (Na(+)) in arterial plasma (P(Na)) declines sufficiently to inhibit the release of vasopressin, water will be excreted promptly when the vast majority of aquaporin 2 water channels (AQP2) have been removed from luminal membranes of late distal nephron segments. In this setting, the volume of filtrate delivered distally sets the upper limit on the magnitude of the water diuresis. Since there is an unknown volume of water reabsorbed in the late distal nephron, our objective was to provide a quantitative assessment of this parameter.

Monitoring of protein catabolism in neonates and young infants post-cardiac surgery.

Aims: To evaluate cell catabolism by balance of nitrogen and phosphate, and creatinine excretion in children post-cardiac surgery; to establish protein and energy requirements to minimize catabolism; and to assess nutritional therapy by following these parameters and serial anthropometric measurements.

Methods: A prospective observational study of children with congenital heart disease undergoing cardiac surgery. Blood samples and 24-h urine collections were obtained postoperatively for creatinine measurement and nitrogen and phosphate balance.