Life-threatening hyperkalemia induced by arginine

Metabolic Alkalosis in the Pediatric Patient: Treatment Options in the Pediatric ICU or Pediatric Cardiothoracic ICU Setting

Metabolic alkalosis is characterized by the primary elevation of the serum bicarbonate concentration with a normal or elevated partial pressure of carbon dioxide. Although there may be several potential etiologies in the critically ill patient in the pediatric or cardiothoracic intensive care unit, metabolic alkalosis most commonly results from diuretic therapy with chloride loss. In most cases, the etiology can be determined by a review of the patient's history and medication record. Although generally innocuous with limited impact on physiologic function, metabolic alkalosis may impair central control of ventilation, especially when weaning from mechanical ventilation. The following manuscript presents the normal homeostatic mechanisms that control pH, reviews the etiology of metabolic alkalosis, and outlines the differential diagnosis. Options and alternatives for treatment including pharmacologic interventions are presented with a focus on these conditions as they pertain to the patient in the pediatric or cardiac intensive care unit.

Safety and performance benefits of arginine supplements for military personnel: a systematic review

CONTEXT

Dietary supplements are widely used by military personnel and civilians for promotion of health.

OBJECTIVE

The objective of this evidence-based review was to examine whether supplementation with l-arginine, in combination with caffeine and/or creatine, is safe and whether it enhances athletic performance or improves recovery from exhaustion for military personnel.

DATA SOURCES

Information from clinical trials and adverse event reports were collected from 17 databases and 5 adverse event report portals.

STUDY SELECTION

Studies and reports were included if they evaluated the safety and the putative outcomes of enhanced performance or improved recovery from exhaustion associated with the intake of arginine alone or in combination with caffeine and/or creatine in healthy adults aged 19 to 50 years.

DATA EXTRACTION

Information related to population, intervention, comparator, and outcomes was abstracted. Of the 2687 articles screened, 62 articles meeting the inclusion criteria were analyzed. Strength of evidence was assessed in terms of risk of bias, consistency, directness, and precision.

RESULTS

Most studies had few participants and suggested risk of bias that could negatively affect the results. l-Arginine supplementation provided little enhancement of athletic performance or improvements in recovery. Short-term supplementation with arginine may result in adverse gastrointestinal and cardiovascular effects. No information about the effects of arginine on the performance of military personnel was available.

CONCLUSIONS

The available information does not support the use of l-arginine, either alone or in combination with caffeine, creatine, or both, to enhance athletic performance or improve recovery from exhaustion. Given the information gaps, an evidence-based review to assess the safety or effectiveness of multi-ingredient dietary supplements was not feasible, and therefore the development of a computational model-based approach to predict the safety of multi-ingredient dietary supplements is recommended.

Hyperkalemia: Disorders of Internal and External Potassium Balance

The serum potassium level is normally preserved de spite changes in potassium intake and output (the exter nal potassium balance) and changes in its distribution in the body (the internal potassium balance). External potassium homeostasis depends primarily on renal ex cretion of the daily exogenous potassium burden. Inter nal homeostasis depends on the extrarenal regulation of potassium. Skeletal muscle and liver are the dominant sites of that regulation. The two chief regulators of inter nal balance are insulin and catecholamines, the latter acting through β-adrenergic receptors. Acid-base bal ance and the cellular potassium content are other important regulators of internal balance. The major disorders of external balance are renal failure, hypo reninemic hypoaldosteronism, interstitial nephritis, and a variety of drugs that impair renal potassium excretion. The major disorders of internal balance are diabetes mellitus, acidosis, medications, and release of endoge nous potassium during vigorous exercise, traumatic muscle injury, or tumor lysis chemotherapy. These dis orders frequently result in troublesome elevations of serum potassium in the intensive care setting. Their re view in this article includes a thorough discussion of the evaluation and proper management of the hyperkalemic patient.

Metabolic Alkalosis

Metabolic alkalosis is a common acid-base disturbance in critically ill patients. In this review we discuss the approach to diagnosis and management of this disorder; particular emphasis is given to the causes most com monly responsible for alkalosis in critical care medicine. We present rules for (1) identifying the presence of metabolic alkalosis, ( 2 ) determining whether the disor der is simple or complicated by a second acid-base dis turbance, and (3) determining the cause: The causes are subdivided into three major groups: Chloride-respon sive, chloride-resistant, and alkali administration. The pathogenesis of each type of alkalosis is discussed sep arately, although we stress that more than one cause may be responsible in critically ill patients. The patho logical consequences of metabolic alkalosis and ap proaches to treatment are reviewed. The major issues relating to the critically ill patient are (1) identification and removal of exogenous sources of alkali, (2) iden tification and minimization of HCl losses or selective NaCl losses, and (3) maneuvers to reduce serum HCO 3 concentration without producing extracellular fluid volume overload.

Tissue-specific regulation of potassium homeostasis by high doses of cationic amino acids

The administration of l-arginine hydrochloride has been used for testing pituitary secretion in humans, and as an experimental model for induction of acute pancreatitis in rats and mice. Whereas in the first case, the administration of the amino acid is associated with hiperkalemia, in the model of acute pancreatitis no data are available on possible changes in potassium homeostasis. The present study shows that the acute administration to mice of l-arginine hydrochloride or other cationic amino acids almost duplicate plasma potassium levels. This effect was associated to a marked decrease of tissue potassium in both pancreas and liver. No changes were found in other tissues. These changes cannot be ascribed to the large load of chloride ions, since similar effects were produced when l-ornithine aspartate was administered. The changes in potassium levels were dependent on the dose. The displacement of intracellular potassium from the liver and pancreas to the extracellular compartment appears to be dependent on the entry of the cationic amino acid, since the administration of an equivalent dose of alfa-difluoromethyl ornithine HCl (DFMO), a non physiological analog of l-ornithine, which is poorly taken by the tissues in comparison with the physiological cationic amino acids, did not produce any change in potassium levels in pancreas and liver. The analyses of the expression of cationic amino acid transporters (CAT) suggest that the CAT-2 transporter may be implicated in the potassium/cationic amino acid interchange in liver and pancreas. The possible physiological or pathological relevance of these findings is discussed.

Treatment of Severe Metabolic Alkalosis with Continuous Renal Replacement Therapy: Bicarbonate Kinetic Equations of Clinical Value

Concomitant severe metabolic alkalosis, hypernatremia, and kidney failure pose a therapeutic challenge. Hemodialysis to correct azotemia and abnormal electrolytes results in rapid correction of serum sodium, bicarbonate, and urea but presents a risk for dialysis disequilibrium and brain edema. We describe a patient with Zollinger-Ellison syndrome with persistent encephalopathy, severe metabolic alkalosis (highest bicarbonate 81 mEq/L), hypernatremia (sodium 157 mEq/L), and kidney failure despite 30 hours of intravenous crystalloids and proton pump inhibitor. We used continuous renal replacement therapy (RRT) with delivered hourly urea clearance of ~3 L/hour (24 hour sustained low efficiency dialysis with regional citrate anticoagulation protocol at blood flow rate 60 ml/min and dialysate flow rate 400 ml/min). To mitigate a pronounced decrease in plasma osmolality while removing urea from this hypernatremic patient, dialysate sodium was set to start at 155 mEq/L then at 150 mEq/L after 6 hours. Serum bicarbonate, urea, and sodium were slowly corrected over 26 hours. This case demonstrates how to regulate and predict the systemic bicarbonate level using single pool kinetic modeling during convective or diffusive RRT. Kinetic modeling provides a valuable tool for systemic blood pH control in future combined use of extracorporeal CO2 removal and continuous RRT systems.

Effects of Arginine Supplementation on Amino Acid Profiles in Blood and Tissues in Fed and Overnight-Fasted Rats

Chronic arginine intake is believed to have favorable effects on the body. However, it might be hypothesized that excessive consumption of an individual amino acid exerts adverse effects on distribution and metabolism of other amino acids. We evaluated the effect of chronic intake of arginine on amino acid concentrations in blood plasma, liver, kidneys, and soleus and extensor digitorum longus muscles. Rats were fed a standard diet or a high-arginine diet (HAD) for two months. Half of the animals in each group were sacrificed in the fed state, and the other half after fasting overnight. HAD increased blood plasma concentrations of urea, creatinine, arginine, and ornithine and decreased most other amino acids. Arginine and ornithine also increased in muscles and kidneys; an increase of lysine was observed in both muscle types. Methionine, phenylalanine, threonine, asparagine, glycine, serine, and taurine decreased in most tissues of HAD fed animals. Most of the effects of HAD disappeared after overnight fasting. It is concluded that (i) enhanced dietary arginine intake alters distribution of almost all amino acids; and (ii) to attain a better assessment of the effects of various nutritional interventions, an appropriate number of biochemical measurements must be performed in both postprandial and postabsorptive states.

Postoperative hyperkalemia

Hyperkalemia occurs frequently in hospitalized patients and is of particular concern for those who have undergone surgery, with postoperative care provided by clinicians of many disciplines. This review describes the normal physiology and how multiple perioperative factors can disrupt potassium homeostasis and lead to severe elevations in plasma potassium concentration. The pathophysiologic basis of diverse causes of hyperkalemia was used to broadly classify etiologies into those with altered potassium distribution (e.g. increased potassium release from cells or other transcellular shifts), reduced urinary excretion (e.g. reduced sodium delivery, volume depletion, and hypoaldosteronism), or an exogenous potassium load (e.g. blood transfusions). Surgical conditions of particular concern involve: rhabdomyolysis from malpositioning, trauma or medications; bariatric surgery; vascular procedures with tissue ischemia; acidosis; hypovolemia; and volume or blood product resuscitation. Certain acute conditions and chronic co-morbidities present particular risk. These include chronic kidney disease, diabetes mellitus, many outpatient preoperative medications (e.g. beta blockers, salt substitutes), and inpatient agents (e.g. succinylcholine, hyperosmolar volume expanders). Clinicians need to be aware of these pathophysiologic mechanisms for developing perioperative hyperkalemia as many of the risks can be minimized or avoided.

Differential diagnosis of nongap metabolic acidosis: value of a systematic approach

Nongap metabolic acidosis is a common form of both acute and chronic metabolic acidosis. Because derangements in renal acid-base regulation are a common cause of nongap metabolic acidosis, studies to evaluate renal acidification often serve as the mainstay of differential diagnosis. However, in many cases, information obtained from the history and physical examination, evaluation of the electrolyte pattern (to determine if a nongap acidosis alone or a combined nongap and high anion gap metabolic acidosis is present), and examination of the serum potassium concentration (to characterize the disorder as hyperkalemic or hypokalemic in nature) is sufficient to make a presumptive diagnosis without more sophisticated studies. If this information proves insufficient, indirect estimates or direct measurement of urinary NH(4)(+) concentration, measurement of urine pH, and assessment of urinary HCO(3)(-) excretion can help in establishing the diagnosis. This review summarizes current information concerning the pathophysiology of this electrolyte pattern and the value and limitations of all of the diagnostic studies available. It also provides a systematic and cost-effective approach to the differential diagnosis of nongap metabolic acidosis.

Diagnosing growth hormone deficiency in adults

Adult growth hormone (GH) deficiency is a recognised syndrome associated with adverse phenotypic, metabolic, and quality-of-life features which improve in many patients when GH is substituted. The appropriate selection of patients at risk of growth hormone deficiency (GHD) is the crucial first step in arriving at a correct diagnosis. Although multiple diagnostic modalities are available including a 24-hour serum GH profile, stimulated GH levels, and insulin-like growth factor-1 (IGF-1) levels, the use of dynamic tests for GH reserves is required in most cases. This paper discusses the utility and drawbacks of the various testing modalities with reference to international guidelines. Regardless of the test chosen, clinical pitfalls including age and obesity must be taken into account. In addition, there is considerable analytical variation in the biochemical measurements of GH and IGF-1 which must be considered before making a diagnosis of GHD in adulthood.

Effect of amino acid infusion on potassium serum levels in neuroendocrine tumour patients treated with targeted radiopeptide therapy

PURPOSE

Administration of positively charged amino acids has been introduced to reduce the nephrotoxicity of targeted radiopeptide therapy (TRT). However, the amino acid solution may have side effects, including hyperkalaemia. The aim of this study was to evaluate the frequency and the magnitude of hyperkalaemia in neuroendocrine tumour (NET) patients undergoing TRT.

METHODS

Enrolled in the study were 31 patients with NET eligible for TRT with [(90)Y-DOTA(0),Tyr(3)]octreotide ((90)Y-DOTATOC). Their mean age was 54 ± 14 years. Of these 31 patients, 21 (67%) were referred for the first treatment cycle, while 10 (33%) were referred for a subsequent therapy cycle. Patients were treated with therapeutic doses of (90)Y-DOTATOC ranging from 7,030 to 35,520 MBq. To inhibit tubular reabsorption of (90)Y-DOTATOC, 1 l of physiological saline solution containing 25 g of arginine hydrochloride and 25 g of lysine hydrochloride was given over 4 h starting 1 h before (90)Y-DOTATOC injection. All patients underwent a standard biochemical blood analysis at baseline, and 4 h and 24 h after the beginning of the amino acid infusion.

RESULTS

ANOVA repeated measures showed a significant overall effect on K(+) levels over time (F = 118.2, df = 2, P < 0.0001). Mean serum levels of K(+) were 4.00 ± 0.33 mmol/l at baseline, 5.47 ± 0.57 mmol/l at 4 h, and 4.38 ± 0.63 mmol/l at 24 h after the beginning of the infusion. Post-hoc analysis showed that K(+) levels at 4 h were significantly (P < 0.05) higher than at baseline. K(+) levels at 24 h were significantly (P < 0.05) lower than at 4 h but they were still significantly (P < 0.05) higher than K(+) levels at baseline. On a subject-by-subject basis, none of the 31 patients had increased K(+) levels at baseline. At 4 h, 24 of the 31 patients (77%) had K(+) levels above the normal range, and 6 patients (19%) experienced severe hyperkalaemia (K(+) ≥ 6 mmol/l). All patients with increased K(+) levels were clinically asymptomatic. At 24 h, only 4 patients (13%) had increased K(+) serum levels. The magnitude of the increase in K(+) levels between baseline and 4 h was relatively homogeneous over the whole group (1.41 ± 0.50 mmol/l) and it was not related (linear regression, P>0.05) to baseline K(+) levels. Intravenous administration of 40 mg furosemide 1 h after the beginning of the amino acid infusion did not have a significant effect on K(+) levels (P>0.05). No clinical characteristic was predictive for the increase in K(+) levels (chi-squared test, P > 0.05).

CONCLUSION

Hyperkalaemia is a frequent, potentially life-threatening side effect of basic amino acid infusion during TRT. K(+) levels 4 h after the beginning of the infusion should be monitored in patients at risk of complications, such as those with heart disease and those with risk factors for nephrotoxicity.

Kidney protection during peptide receptor radionuclide therapy with somatostatin analogues

This review focuses on the present status of kidney protection during peptide receptor radionuclide therapy (PRRT) using radiolabelled somatostatin analogues. This treatment modality for somatostatin receptor-positive tumours is limited by renal reabsorption and retention of radiolabelled peptides resulting in dose-limiting high kidney radiation doses. Radiation nephropathy has been described in several patients. Studies on the mechanism and localization demonstrate that renal uptake of radiolabelled somatostatin analogues largely depends on the megalin/cubulin system in the proximal tubule cells. Thus methods are needed that interfere with this reabsorption pathway to achieve kidney protection. Such methods include coadministration of basic amino acids, the bovine gelatin-containing solution Gelofusine or albumin fragments. Amino acids are already commonly used in the clinical setting during PRRT. Other compounds that interfere with renal reabsorption capacity (maleic acid and colchicine) are not suitable for clinical use because of potential toxicity. The safe limit for the renal radiation dose during PRRT is not exactly known. Dosimetry studies applying the principle of the biological equivalent dose (correcting for the effect of dose fractionation) suggest that a dose of about 37 Gy is the threshold for development of kidney toxicity. This threshold is lower when risk factors for development of renal damage exist: age over 60 years, hypertension, diabetes mellitus and previous chemotherapy. A still experimental pathway for kidney protection is mitigation of radiation effects, possibly achievable by cotreatment with amifostine (Ethylol), a radiation protector, or with blockers of the renin-angiotensin-aldosterone system. Future perspectives on improving kidney protection during PRRT include combinations of agents to reduce renal retention of radiolabelled peptides, eventually together with mitigating medicines. Moreover, new somatostatin analogues with lower renal retention may be developed. Furthermore, knowledge on kidney protection from radiolabelled somatostatin analogues may be expanded to other peptides.

Safety profile of L-arginine infusion in moderately severe falciparum malaria

BACKGROUND

L-arginine infusion improves endothelial function in malaria but its safety profile has not been described in detail. We assessed clinical symptoms, hemodynamic status and biochemical parameters before and after a single L-arginine infusion in adults with moderately severe malaria.

METHODOLOGY AND FINDINGS

In an ascending dose study, adjunctive intravenous L-arginine hydrochloride was infused over 30 minutes in doses of 3 g, 6 g and 12 g to three separate groups of 10 adults hospitalized with moderately severe Plasmodium falciparum malaria in addition to standard quinine therapy. Symptoms, vital signs and selected biochemical measurements were assessed before, during, and for 24 hours after infusion. No new or worsening symptoms developed apart from mild discomfort at the intravenous cannula site in two patients. There was a dose-response relationship between increasing mg/kg dose and the maximum decrease in systolic (rho = 0.463; Spearman's, p = 0.02) and diastolic blood pressure (r = 0.42; Pearson's, p = 0.02), and with the maximum increment in blood potassium (r = 0.70, p<0.001) and maximum decrement in bicarbonate concentrations (r = 0.53, p = 0.003) and pH (r = 0.48, p = 0.007). At the highest dose (12 g), changes in blood pressure and electrolytes were not clinically significant, with a mean maximum decrease in mean arterial blood pressure of 6 mmHg (range: 0-11; p<0.001), mean maximal increase in potassium of 0.5 mmol/L (range 0.2-0.7 mmol/L; p<0.001), and mean maximal decrease in bicarbonate of 3 mEq/L (range 1-7; p<0.01) without a significant change in pH. There was no significant dose-response relationship with blood phosphate, lactate, anion gap and glucose concentrations. All patients had an uncomplicated clinical recovery.

CONCLUSIONS/SIGNIFICANCE

Infusion of up to 12 g of intravenous L-arginine hydrochloride over 30 minutes is well tolerated in adults with moderately severe malaria, with no clinically important changes in hemodynamic or biochemical status. Trials of adjunctive L-arginine can be extended to phase 2 studies in severe malaria.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00147368.

Homespun remedy, homespun toxicity: baking soda ingestion for dyspepsia

A 68-year-old man presented to the Emergency Department with a severe metabolic alkalosis after ingesting large quantities of baking soda to treat his dyspepsia. His underlying pulmonary disease and a progressively worsening mental status necessitated intubation for respiratory failure. Laboratory studies revealed a hyponatremic, hypochloremic, hypokalemic metabolic alkalosis. The patient was successfully treated after cessation of the oral bicarbonate, initiation of intravenous hydration, and correction of electrolyte abnormalities.

Use of exogenous arginine in multiple organ dysfunction syndrome and sepsis

Given the multiple biological, metabolic, and pharmacologic effects of supplemental arginine, much effort has been devoted to defining its role in numerous clinical conditions. Herein, we review the multiple pathways of arginine metabolism with its various enzyme systems; the effect of arginine on nutrition, healing, and immune system; and its clinical use. Sepsis has been postulated to be an arginine-deficient state and/or a syndrome with elevated levels of nitric oxide. So-called immunonutritional formulations containing various nutritional components have been used most often, yet the effects often are attributed to arginine alone. Such conclusions led to guidelines recommending against the use of arginine-supplemented diets in critically ill patients. While caution in the face of a lack of evidence for benefit in sepsis is commended, well-defined studies examining arginine monotherapy in the context of full nutritional support should be carried out so as to define the possible clinical uses of arginine in critically ill and septic patients.

Hyperkalemia: a review

Potassium is the principal intracellular cation, and maintenance of the distribution of potassium between the intracellular and the extracellular compartments relies on several homeostatic mechanisms. When these mechanisms are perturbed, hypokalemia or hyperkalemia may occur. This review covers hyperkalemia, that is, a serum potassium concentration exceeding 5 mmol/L. The review includes a discussion of potassium homeostasis and the etiologies of hyperkalemia and focuses on the prompt recognition and treatment of hyperkalemia. This disorder should be of major concern to clinicians because of its propensity to cause fatal arrhythmias. Hyperkalemia is easily diagnosed, and rapid and effective treatments are readily available. Unfortunately, treatment of this life-threatening condition is often delayed or insufficiently attentive or aggressive.

Full-thickness skin necrosis after arginine extravasation--a case report and review of literature

The arginine test is highly useful in the evaluation of short-stature children and adolescents. Extravasation of arginine can cause full-thickness skin necrosis that requires serious surgical intervention with aesthetic and functional sequellea. The authors describe a case of distal forearm skin necrosis caused by arginine extravasation that was treated by wide debridement and a combination of groin flap and later with split-thickness skin graft. The authors emphasize the need for early and active management of arginine extravasation injuries.

High plasma arginine concentrations in critically ill patients suffering from hepatic failure

OBJECTIVE

In physiological conditions, the liver plays an important role in the regulation of plasma arginine concentrations by taking up large amounts of arginine from the hepatic circulation. When hepatic failure is present, arginine metabolism may be disturbed. Therefore, we hypothesized high arginine plasma concentrations in critically ill patients suffering from hepatic failure.

DESIGN

We prospectively collected blood samples from a cross-section of intensive care unit patients.

SETTING

Surgical intensive care unit of a Dutch university medical center.

SUBJECTS

A total of 52 critically ill patients with clinical evidence of dysfunction of more than two organs were recruited.

MEASUREMENTS

Plasma arginine concentrations were determined by HPLC. We identified correlations of arginine concentrations with organ failure scores and laboratory variables by univariate and multiple regression analyses.

RESULTS

High plasma arginine concentrations were found in critically ill patients developing organ failure. Patients who were in the highest quartile of plasma arginine concentrations had significantly lower fibrinogen concentrations, higher lactic acid concentrations, and longer prothrombin time. Stepwise multiple regression analysis showed that concentrations of arginine were independently associated with the presence of hepatic failure (P=0.03) and renal failure (P=0.048). In addition, lactic acid proved to be an independent determinant of plasma arginine concentration (P=0.014).

CONCLUSIONS

Critically ill patients who suffer from hepatic failure have elevated plasma arginine concentrations. Additional arginine in the treatment of these patients can be harmful, and therefore should not be used as a standard nutritional regimen until further evaluation.

Disorders of potassium homeostasis. Hypokalemia and hyperkalemia

This article reviews the diagnosis and management of clinical disorders of potassium balance, with particular attention to the critically ill patient. The normal regulation of potassium balance is reviewed as a background for understanding these disorders, followed by a discussion of the causes and management of hypo- and hyperkalemia. Practical guidelines are presented for acute and chronic management.

Assessment of the safety of glutamine and other amino acids

Glutamine is used to supplement intravenous and enteral feeding. Although there have been many human studies of its efficacy, there have been very few studies with safety as a primary goal. This article analyzes the literature on the safety of glutamine and also examines the available information on high intakes of total protein and other amino acids, so that additional indicators of potentially adverse effects can be suggested. Four studies that specifically addressed glutamine safety were identified, from which it was concluded that glutamine is safe in adults and in preterm infants. However, the published studies of safety have not fully taken account of chronic consumption by healthy subjects of all age groups. To help identify potential undetected hazards of glutamine intake, the literature on adverse effects of high dietary intake of protein and other amino acids was examined. High protein is reputed to cause nausea, vomiting and ultimately death in adults, and has been shown to result in neurological damage in preterm infants. Individual amino acids cause a variety of adverse effects, some of them potentially fatal, but neurological effects were the most frequently observed. Because glutamine is metabolized to glutamate and ammonia, both of which have neurological effects, psychological and behavioral testing may be especially important.

The clinical pharmacology of L-arginine

L-Arginine (2-amino-5-guanidinovaleric acid) is the precursor of nitric oxide, an endogenous messenger molecule involved in a variety of endothelium-mediated physiological effects in the vascular system. Acute and chronic administration of L-arginine has been shown to improve endothelial function in animal models of hypercholesterolemia and atherosclerosis. L-Arginine also improves endothelium-dependent vasodilation in humans with hypercholesterolemia and atherosclerosis. The responsiveness to L-arginine depends on the specific cardiovascular disease studied, the vessel segment, and morphology of the artery. The pharmacokinetics of L-arginine have recently been investigated. Side effects are rare and mostly mild and dose dependent. The mechanism of action of L-arginine may involve nitric oxide synthase substrate provision, especially in patients with elevated levels of the endogenous NO synthase inhibitor asymmetric dimethylarginine. Endocrine effects and unspecific reactions may contribute to L-arginine-induced vasodilation after higher doses. Several long-term studies have been performed that show that chronic oral administration of L-arginine or intermittent infusion therapy with L-arginine can improve clinical symptoms of cardiovascular disease in man.

Therapeutic modification of the L-arginine-eNOS pathway in cardiovascular diseases

L-Arginine is the substrate for nitric oxide production. Endothelium dysfunction could be attributed to L-arginine deficiency or the presence of L-arginine endogenous inhibitors. This hypothesis leads to the assumption that provision of L-arginine could be the key for endothelial function improvement. Many studies have proven that L-arginine has a beneficial effect on endothelium dependent vasoreactivity, as well as on the interaction between vascular wall, platelets and leucocytes. Therefore, individuals with risk factors for atherosclerosis and patients with coronary artery disease or heart failure, could benefit from therapy with L-arginine.

Drug-induced hyperkalemia: old culprits and new offenders

Prescribed medications, over-the-counter drugs, and nutritional supplements are used by many patients. Although most of these products are well tolerated, drug-induced hyperkalemia may develop in patients with underlying renal impairment or other abnormalities in potassium handling. Drug-induced hyperkalemia most often occurs from impaired renal potassium excretion. However, disturbed cellular uptake of a potassium load as well as excessive ingestion or infusion of potassium-containing substances may also occur. Physicians must be aware of medications that can precipitate hyperkalemia, how these drugs induce alterations in potassium homeostasis, and the patient characteristics that increase the risk of hyperkalemia.

Metabolic alkalosis in the critically ill

Metabolic alkalosis is the commonest form of acid-base disorder seen in critically ill patients. Although the effects of acidosis have long been known, those of severe metabolic alkalosis are only slowly being recognized. Metabolic alkalosis is itself associated with an increased mortality and a knowledge of the causative factors and treatment options is important. In one study, around 50% of general surgical patients developed postoperative metabolic alkalosis, whereas other acid-base disturbances were uncommon. Metabolic alkalosis results from an accumulation of alkali or a loss of acid. Clinical signs are nonspecific but dehydration may be prominent because of a contraction of the extracellular fluid volume due to loss of chloride. Metabolic alkalosis leads to hypoventilation in patients both with and without lung disease, although in the latter, the effect is relatively transient. In patients with chronic obstructive lung disease, however, the development of metabolic alkalosis leads to prolonged hypoventilation and the establishment of a mixed acid-base disorder that may cause difficulty in weaning in the ventilated patient. This is an often forgotten cause of prolonged stay in the intensive care unit with consequent cost and morbidity implications.

Hyperkalemia in patients infected with the human immunodeficiency virus: involvement of a systemic mechanism

BACKGROUND

The appearance of hyperkalemia has been described in human immunodeficiency virus (HIV)-positive patients treated with drugs with amiloride-like properties. Recent in vitro data suggest that individuals infected with HIV have alterations in transcellular K+ transport.

METHODS

With the objective of examining the presence of alterations in transmembrane K+ equilibrium in HIV-positive patients, we designed a prospective, interventional study involving 10 HIV-positive individuals and 10 healthy controls, all with normal renal function. An infusion of L-arginine (6%, intravenously, in four 30-min periods at 50, 100, 200, and 300 ml/hr) was administered, and plasma and urine electrolytes, creatinine, pH and osmolality, total and fractional sodium and potassium excretion, transtubular potassium gradient, plasma insulin, renin, aldosterone, and cortisol were measured.

RESULTS

A primary disturbance consisting of a significant rise in plasma [K+] induced by L-arginine was detected in only the HIV patients but not in the controls (P < 0.001 between groups). A K+ redistribution origin of the hyperkalemia was supported by its rapid development (within 60 min) and the lack of significant differences between HIV-positive individuals and controls in the amount of K+ excreted in the urine. The fact that the HIV-positive individuals had an inhibited aldosterone response to the increase in plasma K+ suggested a putative mechanism for the deranged K+ response.

CONCLUSIONS

These results reveal that HIV-infected individuals have a significant abnormality in systemic K+ equilibrium. This abnormality, which leads to the development of hyperkalemia after the L-arginine challenge, may be related, in part, to a failure in the aldosterone response to hyperkalemia. These results provide a new basis for understanding the pathogenesis of hyperkalemia in HIV individuals, and demonstrate that the risk of HIV-associated hyperkalemia exists even in the absence of amiloride-mimicking drugs or overt hyporeninemic hypoaldosteronism.

Acute hyperkalemia associated with intravenous epsilon-aminocaproic acid therapy

Epsilon-aminocaproic acid (Amicar) is used to treat severe hemorrhage refractory to usual medical management. This antifibrinolytic drug has been associated with a number of renal complications. However, there are no descriptions of this medication causing hyperkalemia. This report describes the development of hyperkalemia in a patient with underlying chronic renal insufficiency treated with intravenous epsilon-aminocaproic acid. The patient, who underwent coronary artery bypass grafting, had no other obvious cause for the acute increase in serum potassium concentration. Based on data in animals and humans, the cationic amino acids lysine and arginine have been shown to enter muscle cells in exchange for potassium and lead to hyperkalemia through a shift of potassium from the intracellular to the extracellular space. Epsilon-aminocaproic acid, a synthetic amino acid structurally similar to lysine and arginine, also has been noted to cause an acute increase in serum potassium in anephric dogs infused with this medication. It is probable that the mechanism underlying the increase in serum potassium with epsilon-aminocaproic acid is also based on the shift of potassium from the intracellular to the extracellular space. Hence, it appears that intravenous epsilon-aminocaproic acid can also cause hyperkalemia in humans.

Pharmacological nutrition after burn injury

Burn patients develop pathophysiological alterations, which include extensive nitrogen loss, malnutrition, markedly increased metabolic rate and immunologic deficiency. This predisposes burn patients to frequent infections, poor wound healing, increased length of hospitalization and increased mortality. The nutritional support requires high protein and high energy diets preferably administered enterally soon after injury. The effects of increased dietary components such as glutamine, arginine and (n-3) fatty acids and related compounds have been evaluated in burn victims. These components, when supplied in quantities two to seven times of those in normal diets of healthy persons, appear to have beneficial pharmacological effects on the pathophysiological alterations associated with burns. However, the efficacy of immune-enhancing diets remains to be convincingly shown.

A fatal overdose of arginine hydrochloride

CASE REPORT

Arginine hydrochloride is used both diagnostically to test for growth hormone deficiency and therapeutically for treatment of metabolic alkalosis. We describe a 21-month-old girl who developed cardiopulmonary arrest following an accidental overdose of arginine hydrochloride. The patient developed acute metabolic acidosis and transient, but severe, hyponatremia. Thirty-six hours after successful resuscitation, she developed fatal central pontine and extrapontine myelinolysis. Unlike previous reports of arginine-toxicity, our patient showed no evidence of hyperkalemia. This case illustrates a previously unreported mechanism of arginine hydrochloride toxicity.

Dietary supplementation with L-arginine fails to restore endothelial function in forearm resistance arteries of patients with severe heart failure

OBJECTIVES

We sought to examine the efficacy of dietary supplementation of L-arginine on endothelium-dependent vasodilation in patients with congestive heart failure.

BACKGROUND

Endothelial dysfunction, as evidenced by a diminished response to such vasodilators as acetylcholine, is well defined in patients with heart failure. These responses are improved by intraarterial infusion with L-arginine. Because L-arginine is a semi-essential amino acid, we investigated the effects of dietary L-arginine on endothelium-dependent vasodilation in these patients.

METHODS

Twenty patients with heart failure (New York Heart Association functional class III/IV, mean [+/- SE] age 51.3 +/- 1.7 years) and seven healthy control subjects (mean age 52.6 +/- 3.3 years) were studied. All patients continued taking their usual treatment. Responses to acetylcholine and sodium nitroprusside were determined using forearm plethysmography. Patients with heart failure received either L-arginine (20 g/day every day for 28 days) or placebo (vehicle syrup in equal amounts) in a double-blind protocol. The calculated power of the study was between 62% and 80% to detect a 30% to 40% change in area under the dose-response (forearm vascular resistance) curve.

RESULTS

Responses to acetylcholine, but not to sodium nitroprusside, were significantly attenuated in patients with heart failure compared with control subjects (mean area under curve [AUC], control subjects vs. patients with heart failure: 1,125.4 +/- 164.5 vs. 617.3 +/- 116.6 U, p < 0.05, by Student t test). A significant increase in urea and aspartate transaminase levels in patients receiving active L-arginine treatment was observed. Responses to acetylcholine (AUC; before vs. after L-arginine: 641.5 +/- 126.7 vs. 695.9 +/- 151.9 U) and sodium nitroprusside were not affected by either L-arginine or placebo.

CONCLUSIONS

Endothelial dysfunction was apparent in patients with heart failure despite rigorous vasoactive treatment. Oral administration with L-arginine was ineffective in influencing endothelial function in these patients.

Acid-base disorders in medicine

The practice of internal medicine involves daily exposure to abnormalities of acid-base balance. A wide variety of disease states either predispose patients to develop these conditions or lead to the use of medications that alter renal, gastrointestinal, or pulmonary function and secondarily alter acid-base balance. In addition, primary acid-base disease follows specific forms of renal tubular dysfunction (renal tubular acidosis). We review the acid-base physiologic functions of the kidney and gastrointestinal tract and the current understanding of acid-base pathophysiologic conditions. This includes a review of whole animal and renal tubular physiologic characteristics and a discussion of the current knowledge of the molecular biology of acid-base transport. We stress an approach to diagnosis that relies on knowledge of acid-base physiologic function, and we include discussion of the appropriate treatment of each disorder considered. Finally, we include a discussion of the effects of acidosis and alkalosis on human physiologic functions.

Recent advances: parenteral nutrition support

Even though there is an abundance of research related to the clinical and physiologic effects of parenteral nutrition and specific nutritional substrates, few new products have been released for clinical use. This review illustrates some of the directions being taken in the future development of parenteral nutrition products and some new perspectives related to the current effects (or lack of effects) of TPN. When considering the individual effects of specific nutrient substrates (arginine, glutamine, LCTs, MCTs, SCFAs) as reviewed here, it becomes apparent that the infusion of parenteral nutrition has the potential to produce a variety of metabolic responses that could be both beneficial and harmful. These effects depend on the type and quantity of substance infused as well as the disease and clinical condition of the patient. This also is true for those substances (GH, IGF-1) being evaluated to direct the effects of TPN infusions in a manner that improves protein accretion and supports the immunologic response of the body. At best, these investigations are producing a great amount of new and more specific information about the metabolic response to illness and the effects of TPN and individual substrate on that response.

Acid dialysate correction of metabolic alkalosis in renal failure

Severe metabolic acidosis may occur during hemodialysis when the incorrect acid dialysis concentrate from a two-part bicarbonate dialysis system is used in an acetate dialysis machine. We deliberately applied this technique to correct severe metabolic alkalosis in a patient with chronic renal failure. Rapid correction of the metabolic alkalosis was achieved and the procedure was well tolerated.

Hyperkalemia in diabetes mellitus

Potassium filtered at the glomerulus is almost completely reabsorbed before the distal tubule; it must therefore be secreted into the collecting duct. The rate of potassium secretion is determined by a number of factors, notably aldosterone, distal sodium delivery, and serum potassium. Normal serum potassium is maintained by the interplay of passive leak of potassium from the cells and its active return to the cells. Transmembrane potassium distribution is influenced largely by acid-base equilibrium and hormones including insulin and catecholamines. In the diabetic with ketoacidosis hyperkalemia, in the face of potassium depletion, is attributable to reduced renal function, acidosis, release of potassium from cells due to glycogenolysis, and lack of insulin. Chronic hyperkalemia in diabetics is most often attributable to hyporeninemic hypoaldosteronism but other conditions including urinary tract obstruction may also contribute. A variety of clinical situations (e.g., volume depletion) and drugs (e.g., nonsteroidal antiinflammatory agents, and heparin) may acutely provoke hyperkalemia in susceptible individuals.

The effects of arginine, dextran and Haemaccel infusions on urinary albumin, beta 2-microglobulin and N-acetyl-beta-D-glucosaminidase

Male volunteers were infused with L-arginine dextran and Haemaccel. Arginine (0.5 g/kg body weight infused over 30 min) resulted in transient highly significant increases in urinary albumin (p less than 0.001), beta 2-microglobulin (p less than 0.001) and N-acetyl-beta-D-glucosaminidase [NAG] (p less than 0.001). These effects lasted less than 120 min. Dextran 40 and 70 (500 ml infused over 2 h) did not affect urinary albumin, beta 2-microglobulin or NAG excretion. Haemaccel (8 ml/kg body weight infused over 2 h) resulted in significant increases in urinary albumin (p less than 0.05) and beta 2-microglobulin (p less than 0.01) during the second hour of the infusion. It also caused a biphasic increase in urinary NAG excretion, the initial peak (p less than 0.05) coinciding with the peak of albumin and beta 2-microglobulin excretion. The second peak which was more defined (p less than 0.01) occurred 21-24 h after the beginning of the infusion. Neither arginine or Haemaccel have been reported to be nephrotoxic whereas dextran infusions are a well recognised cause of acute tubular necrosis. These data indicate that increases in urinary beta 2-microglobulin and NAG are not always reliable indicators of nephrotoxicity or renal tubular cell damage.

Drug-induced electrolyte disorders

A wide variety of pharmacologic agents have been implicated in a number of electrolyte disorders. The present review focuses on abnormalities of sodium, potassium, calcium, magnesium, and phosphate. Several mechanisms are involved in the pathogenesis of these disorders. These involve stimulation and modulation of other hormones (e.g., antidiuretic hormone, renin-angiotensin system, parathyroid hormone), damage to renal tubules, and, in some cases, a combination of factors. Recognition of these abnormalities is important because their presence may be life threatening or may aggravate the side effects of the drug itself.

Disorders of body fluids, sodium and potassium in chronic renal failure

A stable volume and composition of extracellular fluid are essential for normal functioning of the body. Since the kidney is primarily responsible for regulating extracellular fluid, loss of kidney function should have catastrophic consequences. Fortunately, even with loss of more than 90 percent of renal function, a remarkable capacity to regulate body fluid volumes and sodium and potassium persists. Nevertheless, this capacity is limited to chronic renal disease and this has important consequences for clinical management of these patients. How can sodium and potassium homeostasis be assessed? Methods for evaluating the steady-state regulation of sodium include measurement of body fluids and their distribution in different compartments and measurement of exchangeable and intracellular sodium. Short-term regulation of body sodium can be assessed from measurement of sodium balance during changes in dietary salt. Potassium is predominantly contained within cells and thus the assessment of its regulation requires special emphasis on measurement of steady-state body stores and potassium distribution across cell membranes. However, the methods used to make all of these measurements require assumptions that may not hold in the altered state of uremia. This raises problems in interpretation requiring critical analysis before conclusions can be made regarding sodium and potassium homeostasis in patients with chronic renal failure. This review focuses on abnormalities of body fluids, sodium and potassium in patients with creatinine clearances of less than 20 ml/min due to chronic renal failure and the impact of conservative therapy, dialysis and renal transplantation on these patients.

Effects of loop diuretics on carbohydrate metabolism and electrolyte excretion

The effects of two loop diuretics, bumetanide and furosemide, on carbohydrate metabolism and electrolyte balance were assessed in 11 normal male subjects in a double-blind manner. Glucose, insulin, glucagon, and growth hormone responses to 5-hour glucose tolerance test and arginine infusion were measured during the control and drug treatment periods. Three other non-insulin-dependent diabetic subjects, receiving diuretic drug for six weeks, underwent a similar protocol. Kaliuresis and natriuresis due to diuretic administration were significant only on day 1 of treatment. There were no significant changes in total body potassium by 40K counting; net potassium loss by balance study was minimal in both the acutely treated subjects and the chronically treated patients. Effects of bumetanide and furosemide on water and electrolyte excretion did not differ. Glucose tolerance was significantly improved with bumetanide but not with furosemide. Plasma insulin, glucagon, and growth hormone levels during the oral glucose tolerance test were unaffected by either drug. Insulin levels with arginine infusion were significantly increased, and growth hormone levels decreased with bumetanide but not with furosemide. No evidence of impaired carbohydrate metabolism in the three chronically treated diabetic subjects was seen. It is concluded that the effects of bumetanide and furosemide on potassium balance and glucose utilization were minimal in this experimental setting.