An acute infusion of lactic acid lowers the concentration of potassium in arterial plasma by inducing a shift of potassium into cells of the liver in fed rats.

BACKGROUND: Potassium (K(+)) input occurs after meals or during ischemic exercise and is accompanied by a high concentration of L-lactate in plasma (P(L-lactate)). METHODS: We examined whether infusing 100 µmol L-lactic acid/min for 15 min would lead to a fall in the arterial plasma K(+) concentration (P(K)). We also aimed to evaluate the mechanisms involved in normal rats compared with rats with acute hyperkalemia caused by a shift of K(+) from cells or a positive K(+) balance. RESULTS: There was a significant fall in P(K) in normal rats (0.25 mM) and a larger fall in P(K) in both models of acute hyperkalemia (0.6 mM) when the P(L-lactate) rose. The arterial P(K) increased by 0.8 mM (p < 0.05) 7 min after stopping this infusion despite a 2-fold rise in the concentration of insulin in arterial plasma (P(Insulin)). There was a significant uptake of K(+) by the liver, but not by skeletal muscle. In rats pretreated with somatostatin, P(Insulin) was low and infusing L-lactic acid failed to lower the P(K). CONCLUSIONS: A rise in the P(L-lactate) in portal venous blood led to a fall in the P(K) and insulin was permissive. Absorption of glucose by the Na(+)-linked glucose transporter permits enterocytes to produce enough ADP to augment aerobic glycolysis, raising the P(L-lactate) in the portal vein to prevent postprandial hyperkalemia.

Occult risk factor for the development of cerebral edema in children with diabetic ketoacidosis: possible role for stomach emptying.

The incidence of cerebral edema during therapy of diabetic ketoacidosis (DKA) in children remains unacceptably high-this suggests that current treatment may not be ideal and that important risk factors for the development of cerebral edema have not been recognized. We suggest that there are two major sources for an occult generation of osmole-free water in these patients: first, fluid with a low concentration of electrolytes that was retained in the lumen of the stomach when the patient arrived in hospital; second, infusion of glucose in water at a time when this solution can be converted into water with little glucose. In a retrospective chart review of 30 patients who were admitted with a diagnosis of DKA and a blood sugar > 900 mg/dL (50 mmol/L), there were clues to suggest that some of the retained fluid in the stomach was absorbed. To minimize the likelihood of creating a dangerous degree of cerebral edema in patients with DKA, it is important to define the likely composition of fluid retained in the stomach on admission, to look for signs of absorption of some of this fluid during therapy, and to be especially vigilant once fat-derived brain fuels have disappeared, because this is the time when glucose oxidation in the brain should increase markedly, generating osmole-free water.

Antenatal Bartter's syndrome: why is this not a lethal condition?

There are four themes in this teaching exercise for Professor McCance. The first challenge was to explain how a premature infant with Bartter's syndrome could survive despite having such a severe degree of renal salt wasting. Second, the medical team wanted to know why there was such a dramatic decrease in the natriuresis in response to therapy, despite the presence of a permanent molecular defect that affected the loop of Henle. Third, Professor McCance was asked why this patient seemed to have a second rare disease, AQP2 deficiency type of nephrogenic diabetes insipidus. The fourth challenge was to develop a diagnostic test to help the parents of this baby titrate the dose of indomethacin to ensure an effective dose while minimizing the likelihood of developing nephrotoxicity. The missing links in this interesting story emerge during a discussion between the medical team and its mentor.

Indicators of lean body mass catabolism: emphasis on the creatinine excretion rate.

BACKGROUND: The major stress response to critical illness leads to a catabolic state and loss of lean body mass. AIMS: To test whether an increased rate of creatinine excretion might provide unique and timely information to monitor cell catabolism; to relate this information to balances of cell constituents (nitrogen, potassium, phosphate and magnesium); to evaluate the effectiveness of nutritional therapy to reverse this catabolic process. DESIGN: Prospective observational study. METHODS: Children with severe traumatic brain injury admitted to the paediatric critical care units of The Hospital for Sick Children, Toronto, Canada and Hospital das Clínicas, Faculty of Medicine of Ribeirão Preto, University of São Paulo, Brazil were studied. Complete 24 h urine collections were obtained for measurement of creatinine excretion rate and daily balances of nitrogen, potassium, phosphate and magnesium. RESULTS: Seventeen patients were studied for 3-10 days. On Day 1, all had negative balances for protein and phosphate. Balances for these intracellular constituents became positive when protein intake was >/=1 g/kg/day and energy intake was >/=50% of estimated energy expenditure (P < 0.0001). Creatinine excretion rate was positively correlated with the urea appearance rate (r = 0.60; P < 0.0001), and negatively with protein balance (r = -0.45; P < 0.0001). Sepsis developed in four patients; before its clinical detection, there were negative balances for all intracellular markers and an abrupt rise in the excretion of creatinine. CONCLUSION: Negative balances of intracellular components and an increase in rate of creatinine excretion heralded the onset of catabolism.

Uncovering the basis of a severe degree of acidemia in a patient with diabetic ketoacidosis.

In this teaching exercise, the goal is to demonstrate how an application of principles of physiology can reveal the basis for a severe degree of acidaemia (pH 6.81, bicarbonate <3 mmol/l (P(HCO(3))), PCO(2) 8 mmHg), why it was tolerated for a long period of time, and the issues for its therapy in an 8-year-old female with diabetic ketoacidosis. The relatively low value for the anion gap in plasma (19 mEq/l) suggested that its cause was both a direct and an indirect loss of NaHCO(3). Professor McCance suggested that ileus due to hypokalaemia might cause this direct loss of NaHCO(3), and that an excessive excretion of ketoacid anions without NH(4)(+) in the urine accounted for the indirect loss of NaHCO(3). In addition, he suspected that another factor also contributing to the severity of the acidaemia was a low input of alkali. He was also able to explain why there was a 16-h delay before there was a rise in the P(HCO(3)) once therapy began. The missing links in this interesting story, including a possible basis for the hypokalaemia, emerge during the discussion between the medical team and Professor McCance.

A hyperglycaemic hyperosmolar state in a young child: diagnostic insights from a quantitative analysis.

This teaching exercise demonstrates how the application of principles of physiology can identify the cause of a severe degree of hyperglycaemia (plasma glucose concentration 80 mmol/l) in a very young patient with newly diagnosed diabetes mellitus, determine whether the patient has diabetic ketoacidosis, and highlight the potential risks for this patient on admission and during initial therapy. A consultation with Professor McCance was sought to determine whether this patient had an unusual degree of 'insulin resistance'. There were also uncertainties regarding the acid-base diagnosis. The patient did not appear to have an important degree of metabolic acidosis as judged from his pH of 7.39 and plasma bicarbonate concentration of 20 mmol/l in arterial blood; hence the diagnostic impression was that he had a hyperglycaemic hyperosmolar state. However, his plasma anion gap was significantly elevated, and remained so for 60 h, despite the administration of insulin. Issues in management concerning the basis for this severe degree of hyperglycaemia and how to minimize the risk of developing cerebral oedema are addressed. The missing links in this interesting story emerge during a discussion between the medical team and their mentor, Professor McCance.

The patient with a severe degree of metabolic acidosis: a deductive analysis.

This teaching exercise demonstrates how principles of physiology might help in identifying the cause of a particularly severe case of metabolic acidosis and making appropriate decisions about therapy. The patient's plasma pH was 7.00 and their plasma bicarbonate concentration was 2 mmol/l. Because the time course of the patient's illness was believed to be <24 h, this suggested that a large quantity of acid had been added to the body in this short time period, but the medical team managing the case could not identify any acid that could have been produced rapidly by endogenous processes, or was ingested by the patient. Moreover, there was a question about how such a very low arterial PCO(2) (8 mmHg) could be sustained. Even once the diagnosis was made, there were issues to resolve concerning therapy. These included questions about how much sodium bicarbonate to administer, and what dangers might arise during this therapy. The missing links in this interesting story emerge during a discussion between the medical team and their imaginary mentor, Professor McCance.

An improved approach to the patient with metabolic acidosis: a need for four amendments.

Clinicians should identify life-threatening issues in patients with metabolic acidosis. These threats may be present before therapy begins and/or anticipated after therapy commences. By adding four amendments, short-comings in the commonly used clinical approaches for the diagnosis of metabolic acidosis can be overcome. First, a definition of metabolic acidosis should consider not only the concentration of bicarbonate but also the content of bicarbonate in the extra cellular fluid compartment. The latter requires a quantitative estimate of the ECF volume, which can be obtained using the hematocrit and/or the total protein concentration in plasma. Second, to determine if the basis for metabolic acidosis was the addition of acids or the loss of NaHCO 3 , one must hunt for new anions, not only in plasma, but also in the urine. Third, it is important to measure the venous as well as the arterial PCO2 to assess the capacity to buffer H+ while minimizing H + binding to intracellular proteins. Fourth, to assess the role of the kidney in a patient with metabolic acidosis, the urine osmolal gap and the concentration of creatinine in the urine should be measured to provide an estimate of the rate of excretion of ammonium.

Unusual causes of hypokalaemia and paralysis.

We demonstrate how the application of physiological principles may help to identify unusual causes of a very low plasma potassium (K+) concentration (P(K)) and paralysis. In the two patients described, the short time course of the illness suggested that there was an acute shift of K+ into cells. The combination of a low rate of excretion of K+, the absence of a metabolic acid-base disorder, and the fact that the clinical findings occurred very soon after a large intake of carbohydrate supported this impression. Surprisingly, the P(K) remained low for many hours after these stimuli to shift K+ into cells had abated. The missing link in this story was eventually provided by the attending medical team with the help of their mentor, Professor McCance.

Acute and fatal hyponatraemia after resection of a craniopharyngioma: a preventable tragedy.

Central diabetes insipidus developed for the first time in a 14-year-old female during the resection of a craniopharyngioma. The water diuresis persisted until a vasopressin analogue (dDAVP) was given. Professor McCance was asked to explain why hypernatraemia developed, to anticipate dangers that might develop in the salt and water area with therapy, and to provide insights into why this patient died, due to the subsequent development of hyponatraemia that caused a lethal rise in intracranial pressure. The team specifically wanted Professor McCance's opinions as to why a PNa of 124 mmol/l was uniquely dangerous for this patient, and this was a particularly challenging conundrum. Nevertheless, with the aid of a mini-experiment, a careful chart review, and creative thinking, he was able to offer a novel solution, and to suggest ways to prevent its occurrence in other patients.

Diagnostic approach to a patient with hyponatraemia: traditional versus physiology-based options.

The usual diagnostic approach to a patient with hyponatraemia is based on the clinical assessment of the extracellular fluid (ECF) volume, and laboratory parameters such as plasma osmolality, urine osmolality and/or urine sodium concentration. Several clinical diagnostic algorithms (CDA) applying these diagnostic parameters are available to the clinician. However, the accuracy and utility of these CDAs has never been tested. Therefore, we performed a survey in which 46 physicians were asked to apply all existing, unique CDAs for hyponatraemia to four selected cases of hyponatraemia. The results of this survey showed that, on average, the CDAs enabled only 10% of physicians to reach a correct diagnosis. Several weaknesses were identified in the CDAs, including a failure to consider acute hyponatraemia, the belief that a modest degree of ECF contraction can be detected by physical examination supported by routine laboratory data, and a tendency to diagnose the syndrome of inappropriate secretion of antidiuretic hormone prior to excluding other causes of hyponatraemia. We conclude that the typical architecture of CDAs for hyponatraemia represents a hierarchical order of isolated clinical and/or laboratory parameters, and that they do not take into account the pathophysiological context, the mechanism by which hyponatraemia developed and the clinical dangers of hyponatraemia. These restrictions are important for physicians confronted with hyponatraemic patients and may require them to choose different approaches. We therefore conclude this review with the presentation of a more physiology-based approach to hyponatraemia, which seeks to overcome some of the limitations of the existing CDAs.

An approach to the patient with severe hypokalaemia: the potassium quiz.

The objective of this teaching session with Professor McCance is to develop an approach to the management of patients with a very low plasma potassium (K(+)) concentration (P(K)). The session begins with a quiz based on six recent medical consultations for a P(K) < 2 mmol/l. Professor McCance outlined how he would proceed with his diagnosis and therapy, using the synopsis that described each patient. This approach was then applied to a new patient, a 69-year-old woman who had a large volume of dependent oedema and developed a severe degree of weakness and hypokalaemia during more aggressive diuretic therapy that included a K(+)-sparing diuretic. The initial challenge for Professor McCance was to deduce why the K(+)-sparing diuretic was not effective in this patient. He also needed to explain why the P(K) was so low on admission.

Recurrent uric acid stones.

A 46-year-old female had a history of recurrent uric acid stone formation, but the reason why uric acid precipitated in her urine was not obvious, because the rate of urate excretion was not high, urine volume was not low, and the pH in her 24-h urine was not low enough. In his discussion of the case, Professor McCance provided new insights into the pathophysiology of uric acid stone formation. He illustrated that measuring the pH in a 24-h urine might obscure the fact that the urine pH was low enough to cause uric acid to precipitate during most of the day. Because he found a low rate of excretion of NH(4)(+) relative to that of sulphate anions, as well as a high rate of citrate excretion, he speculated that the low urine pH would be due to a more alkaline pH in proximal convoluted tubule cells. He went on to suspect that there was a problem in our understanding of the function of renal medullary NH(3) shunt pathway, and he suggested that its major function might be to ensure a urine pH close to 6.0 throughout the day, to minimize the likelihood of forming uric acid kidney stones.

Acidosis in a patient with cholera: a need to redefine concepts.

A patient presented with cholera and a severe degree of ECF volume contraction. Despite large losses of bicarbonate (HCO3-)-containing diarrhoeal fluid, laboratory acid-base values were remarkably close to normal. A detailed analysis emphasizing principles of physiology and a quantitative approach provided new insights and eventually better definitions of metabolic and respiratory acidosis. A shift in focus from HCO3- concentration to HCO3- content in the extracellular fluid (ECF) compartment revealed the presence of metabolic acidosis. Central to this analysis was an emphasis on the haematocrit to enable a more accurate estimate of the degree of ECF volume contraction. The latter also revealed 'contraction' metabolic alkalosis, which masked the underlying metabolic acidosis. The presence of a respiratory acidosis of the tissue type was evident from the raised venous PCO2, which was not surprising once the magnitude of the ECF contraction had been appreciated. 'Bad buffering', as defined by Professor McCance, was the immediate danger and prompted swift action to restore an effective circulation. The haematocrit and the venous PCO2 also contribute valuable information to monitor the response to therapy. Nevertheless, there were still dangers to be discovered when an in-depth analysis suggested that the administration of isotonic saline would introduce an unanticipated danger for the patient.

An unusual cause for ketoacidosis.

A 22-year-old male developed a severe degree of metabolic acidosis (plasma pH 7.20, bicarbonate 8 mmol/l), with a large increase in the plasma anion gap (26 mEq/l). Ketoacidosis was suspected because of the odour of acetone on his breath and a positive qualitative test for acetone in plasma (to a 1:4 dilution). Later, his plasma beta-hydroxybutyrate concentration was found to be 4.5 mmol/l. After receiving an infusion of 1 l of half-isotonic saline and 1 l of 5% dextrose in water over 24 h, as well as curtailing his large oral intake of sweetened beverages, all blood tests became normal. Diabetic ketoacidosis, alcoholic ketoacidosis, starvation ketosis and hypoglycaemic ketoacidosis were all ruled out, and his toxin screen was negative for salicylates. Finding another possible cause for ketoacidosis became the focus of this case.

Anorexia nervosa and chronic renal insufficiency: a prescription for disaster.

Our imaginary consultant, Professor McCance, is asked to explain the basis for four major acute electrolyte abnormalities in a young woman with long-standing anorexia nervosa. She has a severe degree of hypokalaemia (2.0 mmol/l) with renal potassium wasting, a contracted extracellular fluid volume with renal NaCl wasting, hyponatraemia (118 mmol/l) while excreting hypoosmolar urine, and metabolic acidosis with a normal plasma anion gap (pH 7.20, bicarbonate 9 mmol/l). McCance begins his discussion by considering the basis for hypokalaemia, as this electrolyte disorder is potentially life-threatening. Its pathophysiology is linked to the other major findings, using principles of integrative physiology together with a deductive and quantitative analysis. Nevertheless, to reach his final diagnosis, he requires information about newer molecular discoveries. Not only is he able to suggest a likely diagnosis, but he also devises a novel long-term plan for therapy.

Osmotic demyelination syndrome: a potentially avoidable disaster.

Osmotic demyelination of the brain (ODS) is a dreaded complication that typically occurs several days after aggressive therapy for chronic hyponatraemia, but is eminently avoidable. In this teaching exercise, Professor McCance, an imaginary consultant, is asked to explain how he would have treated a 28-year-old female who had hyperkalaemia, hypoglycaemia, hypotension and hyponatraemia (118 mM) to prevent the development of ODS. He begins with a review of the physiology, including his own landmark work on chronic hyponatraemia associated with a contracted extracellular fluid volume. Adding quantitative analysis, the cause of the excessive rise in plasma sodium concentration is revealed, and a better plan for therapy is proposed.

How to select optimal maintenance intravenous fluid therapy.

Hyponatraemia is the commonest electrolyte abnormality in hospitalized patients. If the plasma sodium concentration (P(Na)) declines to approximately 120 mM in <48 h, brain cell swelling might result in herniation, with devastating consequences. The volume and/or the composition of fluids used for intravenous therapy often contribute to the development of acute hyponatraemia. Our hypothesis is that the traditional calculation of the daily loss of insensible water overestimates this parameter, leading to an excessive daily recommended requirement for water. We offer suggestions to minimize the risk of iatrogenic hyponatraemia.

An integrative physiological approach to polyuria and hyponatraemia: a 'double-take' on the diagnosis and therapy in a patient with schizophrenia.

A patient with a history of schizophrenia was brought to the emergency department with extensive self-inflicted soft tissue injuries. Primary polydipsia was evident on admission, because he had a maximally dilute urine, a urine flow rate of 10 ml/min, and hyponatraemia (100 mmol/l). During an imaginary consultation with Professor McCance in which he applied basic principles of integrative physiology and a deductive analysis in quantitative terms, other reasons for the polyuric state were considered. Moreover, based on the very low value for the concentration of urea in plasma (< 0.7 mmol/l, BUN 1 mg /dl), the goals of therapy to prevent osmotic demyelination became evident. Applying this simple approach, a more comprehensive and accurate differential diagnosis, and a plan for therapy to avoid serious complications was compiled.