Adrenergic modulation of extrarenal potassium disposal

Pharmacotherapy in congestive heart failure: aldosterone receptor antagonism: interface with hyperkalemia in heart failure

Aldosterone receptor antagonism (ARA) is an increasingly well-accepted element of heart failure therapy. The experimental underpinnings for the use of ARA in heart failure are strong being linked to a variety of tissue-based cardiac effects characteristic of drugs in this class. However, the benefits of ARA therapy do not come without some risk since drugs in this class are potent inhibitors of renal potassium (K+) elimination. Thus, some increment in serum K+, up to and including the development of overt hyperkalemia (typically defined as a serum K+ value in excess of 6.0 mEq/L), is to be expected whenever they are used. Hyperkalemia attributable to ARA relates to several factors including ARA dose, patient predisposition to hyperkalemia, as in the case of renal failure, and dietary intake of K+. The risk of some change in serum K+ with ARA should not be a deterrent to use of drugs in this class but, rather should prompt careful surveillance for the onset of this potentially life-threatening electrolyte disturbance. The frequency of such scrutiny should be patient-specific and based on the constellation of risk factors for hyperkalemia.

Aldosterone biosynthesis, regulation, and classical mechanism of action

Circulating aldosterone is principally made in the glomerulosa zone of the adrenal cortex by a series of enzyme steps leading to the conversion of cholesterol to aldosterone. Uniquely, aldosterone's production is regulated at two critical enzyme steps: (1) early in its biosynthetic pathway (the conversion of cholesterol to pregnenolone cholesterol side chain cleavage enzyme) and (2) late (the conversion of corticosterone to aldosterone by aldosterone synthase). A variety of factors modify aldosterone secretion--the most important are angiotensin II (AngII), the end-product of the renin-angiotensin system (RAS), and potassium. However ACTH, neural mediators and natriuretic factors also contribute at least over the short run. Aldosterone's classical epithelial effect is to increase the transport of sodium across the cell in exchange for potassium and hydrogen ions. Although still controversial, there is an increasing body of data that supports the hypothesis that aldosterone can be synthesized in tissues outside of the adrenal cortex, specifically in the heart and the vasculature. Aldosterone's biosynthesis appears to be regulated in these tissues similar to what occurs in the adrenal cortex. The role of this extra adrenal aldosterone production in health and disease is as of yet undetermined.

Hyperkalemia, congestive heart failure, and aldosterone receptor antagonism

Hyperkalemia is a common occurrence in patients with congestive heart failure, particularly when renal failure coexists. The level of renal function in congestive heart failure is often difficult to ascertain because good measurement tools for estimation of renal function are not available. Serum creatinine values have often been offered as a good gauge of renal function, although in most cases true renal function is appreciably lower than the estimate derived from a specific serum creatinine value. Thus, patients with congestive heart failure very commonly, particularly in the advanced stages of the disease, have moderate renal insufficiency, either due to specific heart failure-related renal perfusion changes or as the result of renal involvement from the same processes having caused the heart failure, as is the case with diabetes. It is in this setting of mild-to-moderate levels of renal failure that therapies, such as angiotensin-converting inhibitors, angiotensin-receptor blockers, and aldosterone-receptor antagonists, are administered either individually or collectively. Each of these drug classes reduces the homeostatic ability to eliminate ingested potassium loads by the renal route and increase the tendency to evolve into a hyperkalemic state. This is noteworthy because aldosterone-receptor antagonists are increasingly considered as important therapies in the long-term management of heart failure. Spironolactone has been employed in this capacity and a new aldosterone-receptor antagonist, eplerenone, will become available in the near future, which further increases the importance of evaluating and treating the hyperkalemia risk in a timely manner.

Experimental hyperkalaemia in rabbits: effects of salbutamol and norepinephrine treatments on blood biochemistry and electrocardiography

The effects of salbutamol and norepinephrine on the electrocardiogram (ECG), serum potassium level and enzyme activities were studied in rabbits with hyperkalaemia; norepinephrine and salbutamol may be therapeutically useful. For induction of hyperkalaemia, 300 mM KCl solution was used and then isotonic saline solution containing 6 microg salbutamol and 3.9 microg norepinephrine per ml were administered. Norepinephrine and salbutamol decreased the serum potassium from 7.36 +/- 0.26 and 7.21 +/- 0.31 mmol/L to 5.62 +/- 0.27 and 4.35 +/- 0.33 mmol/L, respectively, and caused the ECG changes (flatness of P wave, widening of QRS complex and bradycardia) to return to the control conditions (time 0). Norepinephrine, but not salbutamol, decreased the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) to the control levels. These results suggest that monitoring of the enzyme activities might be useful as it yields indexes suitable for evaluating the therapeutic approach with norepinephrine in hyperkalaemia.

Treating interdialytic hyperkalemia with fludrocortisone

Hyperkalemia is a frequent and dangerous problem in dialysis patients. Many factors contribute to potentially life-threatening potassium elevation and most remedies used to treat hyperkalemia are handicapped by the consequences of the separate pools of intra- and extracellular potassium. Besides the kidney, the colon has the ability to excrete potassium, which can help lower total body potassium. Several prior authors have addressed the colon's ability to up-regulate potassium secretion, including the effect of aldosterone on fecal potassium content. Potentially dangerous intradialytic maneuvers to lower potassium levels may be avoidable with the use of the mineralocorticoid agonist fludrocortisone.

Efficacy of albuterol inhalation in treatment of hyperkalemia in premature neonates

OBJECTIVE

To evaluate the efficacy of inhaled albuterol for treatment of hyperkalemia in premature neonates by conducting a prospective, randomized placebo-controlled and double-blinded clinical trial.

STUDY DESIGN

Neonates <2000 g receiving mechanical ventilation with central serum potassium > or =6.0 mmol/L (6.0 mEq/L), were randomly assigned to treatment or placebo groups. Albuterol (400 microg) or saline was given by nebulization. The dose was repeated every 2 hours until the potassium level fell below 5 mmol/L (maximum 12 doses) or there were signs of toxicity.

RESULTS

Nineteen patients completed the study (8 in the albuterol and 11 in the saline group). Serum potassium levels declined rapidly in the first 4 hours in the albuterol group, from 7.06 +/- 0.23 mmol/L to 6.34 +/- 0.24 mmol/L (P =.003) versus no significant change in the saline group (6.88 +/- 0.18 mmol/L to 6.85 +/- 0.24 mmol/L; P =.87). At 8 hours, the fall continued to be greater in the albuterol group versus the saline group (5.93 +/- 0.3 mmol/L and 6.35 +/- 0.22 mmol/L, respectively; P =.04).

CONCLUSION

Albuterol inhalation may be useful in rapidly lowering serum potassium levels in premature neonates.

Hyperkalemia in dialysis patients

Serious hyperkalemia is common in patients with end-stage renal disease (ESRD) and accounts for considerable morbidity and death. Mechanisms of extrarenal disposal of potassium (gastrointestinal excretion and cellular uptake) play a crucial role in the defense against hyperkalemia in this population. In this article we review extrarenal potassium homeostasis and its alteration in patients with ESRD. We pay particular attention to the factors that influence the movement of potassium across cell membranes. With that background we discuss the emergency treatment of hyperkalemia in patients with ESRD. We conclude with a review of strategies to reduce the risk of hyperkalemia in this population of patients.

Pharmacotherapy in congestive heart failure: Hyperkalemia in congestive heart failure

Hyperkalemia is not an uncommon occurrence in the congestive heart failure patient, particularly when renal failure coexists. Hyperkalemia in CHF is typically medication-related. Its occurrence is inevitably linked to the simultaneous ingestion of angiotensin-converting enzyme inhibitors and beta-blockers, and more recently, aldosterone receptor antagonists, such as spironolactone. The most devastating consequence of hyperkalemia is its cardiotoxicity that can be fairly insidious in its rate of development. The therapy of hyperkalemia in congestive heart failure can involve both acute and semiacute management phases. Acute hyperkalemia management includes measures that block the adverse membrane effects of hyperkalemia, such as intravenous calcium administration, and efforts to shift potassium intracellularly, such as occurs with intravenous bicarbonate and/or inhaled beta-agonists. Semiacute management of hyperkalemia includes measures to increase urinary potassium excretion and administration of binding resins, such as Kayexalate®. Prevention is the cornerstone of hyperkalemia management in the heart failure patient and requires that careful attention be directed to both identifying exogenous sources of potassium and pinpointing the maximum tolerable dose of either an angiotensin-converting enzyme inhibitor or an angiotensin-receptor blocker. (c)2001 by CHF, Inc.

Dynamics and consequences of potassium shifts in skeletal muscle and heart during exercise

Since it became clear that K(+) shifts with exercise are extensive and can cause more than a doubling of the extracellular [K(+)] ([K(+)](s)) as reviewed here, it has been suggested that these shifts may cause fatigue through the effect on muscle excitability and action potentials (AP). The cause of the K(+) shifts is a transient or long-lasting mismatch between outward repolarizing K(+) currents and K(+) influx carried by the Na(+)-K(+) pump. Several factors modify the effect of raised [K(+)](s) during exercise on membrane potential (E(m)) and force production. 1) Membrane conductance to K(+) is variable and controlled by various K(+) channels. Low relative K(+) conductance will reduce the contribution of [K(+)](s) to the E(m). In addition, high Cl(-) conductance may stabilize the E(m) during brief periods of large K(+) shifts. 2) The Na(+)-K(+) pump contributes with a hyperpolarizing current. 3) Cell swelling accompanies muscle contractions especially in fast-twitch muscle, although little in the heart. This will contribute considerably to the lowering of intracellular [K(+)] ([K(+)](c)) and will attenuate the exercise-induced rise of intracellular [Na(+)] ([Na(+)](c)). 4) The rise of [Na(+)](c) is sufficient to activate the Na(+)-K(+) pump to completely compensate increased K(+) release in the heart, yet not in skeletal muscle. In skeletal muscle there is strong evidence for control of pump activity not only through hormones, but through a hitherto unidentified mechanism. 5) Ionic shifts within the skeletal muscle t tubules and in the heart in extracellular clefts may markedly affect excitation-contraction coupling. 6) Age and state of training together with nutritional state modify muscle K(+) content and the abundance of Na(+)-K(+) pumps. We conclude that despite modifying factors coming into play during muscle activity, the K(+) shifts with high-intensity exercise may contribute substantially to fatigue in skeletal muscle, whereas in the heart, except during ischemia, the K(+) balance is controlled much more effectively.

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.

Salbutamol metered-dose inhaler with spacer for hyperkalemia: how fast? How safe?

OBJECTIVE

To determine the efficacy of inhaled salbutamol (rapidly delivered, using a metered-dose inhaler with a spacer device [MDI-S]) in lowering the serum potassium levels in patients with hyperkalemia.

DESIGN

A randomized, double-blind, placebo-controlled trial.

PATIENTS

Seventeen chronic renal failure patients referred to the Nephrology Unit between October 1, 1997 and March 31, 1998 for hemodialysis were randomized.

INTERVENTION AND RESULTS

Group 1 received salbutamol followed by a placebo. Group 2 received a placebo followed by salbutamol. Each patient inhaled 1,200 microg salbutamol or a placebo through an MDI-S within 2 min. Blood samples were obtained repeatedly before inhalation and after 1, 3, 5, 10, and 60 min. The pulse rate and blood pressure were repeatedly measured. Insulin levels were examined in a subset of patients (n = 10) before, and 1 and 5 min following inhalation. Salbutamol's known side effects, palpitation, tachycardia tremor, and headache, were recorded. Potassium levels rose after 1 min following the completion of treatment and then decreased steadily thereafter. A rise of > or = 0.1 mEq/L was seen in 10 of 17 patients (59%) during the treatment period and there was no change (0%) seen during the placebo period (p < 0.0001). Within 3 min after inhalation of salbutamol, potassium levels declined as a function of time. Potassium levels in those patients taking the placebo did not change as a function of time (p < 0.001). The difference between the placebo and the salbutamol-treated periods reached significance after 5 min (p < 0.05). The serum glucose levels rose following inhalation of salbutamol, with a significant rise after 3 min. The heart rate rose significantly within the first 5 min following inhalation. Serum insulin levels remained unchanged 1 min after inhalation; however, after 5 min, a significant elevation was detected.

CONCLUSION

Salbutamol inhalation of 1,200 microg, using an MDI-S, has a relatively rapid onset of action that induces a consistent reduction in serum potassium levels, starting 3 to 5 min following delivery. Unexpectedly, a paradoxical elevation was detected in serum potassium levels in the first minutes following inhalation. This effect, although minor (0.15 mEq/L above baseline), may cast some doubt on the role of salbutamol inhalation as the first treatment for excessive hyperkalemia.

Torsade de pointes ventricular tachycardia during low dose intermittent dobutamine treatment in a patient with dilated cardiomyopathy and congestive heart failure

The authors describe the case of a 56-year-old woman with chronic, severe heart failure secondary to dilated cardiomyopathy and absence of significant ventricular arrhythmias who developed QT prolongation and torsade de pointes ventricular tachycardia during one cycle of intermittent low dose (2.5 mcg/kg per min) dobutamine. This report of torsade de pointes ventricular tachycardia during intermittent dobutamine supports the hypothesis that unpredictable fatal arrhythmias may occur even with low doses and in patients with no history of significant rhythm disturbances. The mechanisms of proarrhythmic effects of Dubutamine are discussed.

Hyperkalemia in the elderly: drugs exacerbate impaired potassium homeostasis

OBJECTIVE

To review the pathophysiology underlying the predisposition to hyperkalemia in the elderly; the medications that disrupt potassium balance and promote the development of hyperkalemia in the elderly; the prevention of hyperkalemia in elderly patients treated with potassium-altering medications; and the appropriate management of hyperkalemia when it develops.

METHODS AND MAIN RESULTS

A MEDLINE search of the literature (1966-1996) using the terms hyperkalemia, drugs, elderly, and treatment was conducted and pertinent review articles, textbooks, and personal files were consulted. Elderly subjects appear to be predisposed to the development of hyperkalemia on the basis of both innate disturbances in potassium homeostasis and comorbid disease processes that impair potassium handling. Hyperkalemia in the elderly is most often precipitated by medications that impair cellular uptake or renal disposal of potassium. This electrolyte disorder is best prevented by recognition of at-risk physiology in the aged, avoidance of therapy with certain high-risk medications, and monitoring of plasma potassium concentration and renal function at intervals appropriate for the medication prescribed. Management of hyperkalemia entails identification of the clinical manifestations of severe hyperkalemia, stabilization of cardiac tissue, promotion of cellular potassium uptake, and ultimately removal of potassium from the body.

CONCLUSIONS

Geriatric patients should be considered at risk of developing hyperkalemia, especially when they are prescribed certain medications. Potassium levels should be monitored at appropriate intervals when these patients are treated with potassium-altering medications. Appropriate management of hyperkalemia in the elderly can avoid life-threatening neuromuscular and cardiac complications.

Ritodrine- and terbutaline-induced hypokalemia in preterm labor: mechanisms and consequences

The effects of ritodrine and terbutaline on potassium homeostasis, renal function, and cardiac rhythm were assessed in women treated with these drugs for preterm labor. Timed blood and urine samples were obtained for two hours before and during six hours of intravenous ritodrine (N = 5) and terbutaline (N = 5) administered in pharmacologically equivalent doses. No differences were found in any parameters affecting potassium homeostasis or renal function between these drugs. A decrease in mean plasma potassium of 0.9 mEq/liter occurred after 30 minutes of drug infusion (4.2 +/- 0.1 to 3.3 +/- 0.1 mEq/liter, P < 0.005) before any significant changes in plasma glucose (75.0 +/- 4.7 to 93.7 +/- 6.1 mg/dl, P = NS) or plasma insulin (12.4 +/- 6.0 to 28.4 +/- 5.1 mU/ml, P = NS). The mean plasma potassium after four hours of drug infusion was 2.5 +/- 0.1 mEq/liter. Plasma insulin rose to a level known to induce cellular potassium uptake (39.2 +/- 7.7 mU/ml) after 60 minutes of drug therapy and remained at this level for four hours. Hyperlactatemia occurred at four hours (4.7 +/- 0.8 mmol/liter) and the plasma lactate/pyruvate ratio increased in a 10:1 ratio. Both drugs significantly reduced glomerular filtration rate, sodium, potassium, and chloride excretion and urinary flow rate. Changes in acid-base homeostasis, plasma aldosterone, or renal potassium excretion did not contribute to ritodrine-or terbutaline-induced hypokalemia. In 83 women with preterm labor randomly assigned to ritodrine (N = 42) or terbutaline (N = 41), the maximum decrease in plasma potassium occurred after six hours of drug infusion. During Holter monitoring, 3 of 14 women treated with ritodrine or terbutaline developed symptomatic cardiac arrhythmias at the lowest plasma potassium while no women treated with saline and morphine (N = 12) developed cardiac arrhythmias (P = 0.14). We conclude that ritodrine and terbutaline induce profound hypokalemia by stimulating cellular potassium uptake and both drugs cause significant renal sodium and fluid retention and cardiac arrhythmias. Careful monitoring of electrolytes, fluid balance, and cardiac rhythm should occur during tocolytic therapy with ritodrine or terbutaline.

Exercise-Induced Renal and Electrolyte Changes

In brief The metabolic stress of exercise brief can impair the kidneys' ability to maintain volume and electrolyte homeostasis. Minor abnormalities in renal function and plasma electrolyte composition, such as hypovolemia, electrolyte loss, hyperkalemia, and lactic acidosis, may result. In addition, direct and hormonal effects of exercise on the kidneys can lead to proteinuria or hematuria. Rarely, the effects of exercise on the kidneys can be life-threatening, as with heatstroke or rhabdomyolysis. Optimal care not only includes expedient diagnosis and treatment, but also educating the patient about adequate hydration and other preventive measures.

Treatment of hyperkalemia in children with intravenous salbutamol

The aim of this study is to investigate the efficacy and safety of intravenous salbutamol in hyperkalemia. Fourteen children with chronic renal failure, three with acute renal failure and hyperkalemia were treated by intravenous infusions of 4 micrograms/kg salbutamol. Reductions in the mean plasma potassium (K+) concentrations obtained at 40 to 120 min after therapy were statistically significant when compared with the mean plasma K+ concentration at the beginning of therapy (P < 0.01).

The effect of esmolol given during cardiopulmonary bypass

beta-Adrenergic antagonism decreases the size of myocardial infarction and provides myocardial protection during hypothermic arrest for cardiac surgery. However, concern regarding the negative inotropic and chronotropic effects of beta-adrenergic antagonism persisting after cardiopulmonary bypass (CPB) has impeded the use of esmolol for this purpose during cardiac surgery. This is a randomized, double-blind prospective study of the effects of esmolol infused during CPB and the effects of hypothermic CPB on esmolol. Patients scheduled for CPB were randomized to receive intravenous esmolol (300.micrograms.kg-1.min-1 during CPB after a bolus of 2 mg/kg prior to CPB) or placebo. Infusion was stopped at 10 min after release of aortic cross-clamp. Hemodynamics were measured, as well as serum esmolol, catecholamines, lactate, and potassium. Postoperative variables measured included electrocardiographic changes, creatine kinase (CK)-MB fractions, post-CPB dysrhythmias and drugs, hospitalization time and cost, and mortality. Esmolol was administered to 16 patients and placebo to 14. Esmolol levels reached a high of 10.5 +/- 0.9 micrograms/mL during CPB, but decreased to 0.1 +/- 0.02 microgram/mL within 30 min after stopping infusion. Cardiac indices (cardiac index, stroke volume index, left cardiac work index, left ventricular stroke work index, right cardiac work index, and right ventricular stroke work index) were higher in the esmolol group for the first hour post-CPB (P < 0.05). Systemic arterial lactate and coronary sinus lactate were lower in the esmolol group after CPB (P < 0.05), but myocardial lactate extraction was not significantly different between groups. After CPB, hemoglobin was lower in the esmolol group (P < 0.05) due to longer CPB and aortic cross-clamp time (P < 0.05), but oxygen consumption was less than in the control group (P < 0.05). Post-CPB serum potassium was higher in the esmolol group (P < 0.05). Results are confounded by more chronically beta-adrenergically blocked patients randomized to the esmolol group (P < 0.05). Esmolol infused during CPB in this series of patients was associated with high concentrations during CPB but did not result in any adverse clinical effects after CPB.

Plasma potassium response to acute respiratory alkalosis

Acute respiratory alkalosis (hyperventilation) occurs in clinical settings associated with electrolyte-induced complications such as cardiac arrhythmias (such as myocardial infarction, sepsis, hypoxemia, cocaine abuse). To evaluate the direction, magnitude and mechanisms of plasma potassium changes, acute respiratory alkalosis was induced by voluntary hyperventilation for 20 (18 and 36 liter/min) and 35 minutes (18 liter/min). The plasma potassium response to acute respiratory alkalosis was compared to time control, isocapnic and isobicarbonatemic (hypocapnic) hyperventilation as well as beta- and alpha-adrenergic receptor blockade by timolol and phentolamine. Hypocapnic hypobicarbonatemic hyperventilation (standard acute respiratory alkalosis) at 18 or 36 liter/min (delta PCO2-16 and -22.5 mm Hg, respectively) resulted in significant increases in plasma potassium (ca + 0.3 mmol/liter) and catecholamine concentrations. During recovery (post-hyperventilation), a ventilation-rate-dependent hypokalemic overshoot was observed. Alpha-adrenoreceptor blockade obliterated, and beta-adrenoreceptor blockade enhanced the hyperkalemic response. The hyperkalemic response was prevented under isocapnic and isobicarbonatemic hypocapnic hyperventilation. During these conditions, plasma catecholamine concentrations did not change. In conclusion, acute respiratory alkalosis results in a clinically significant increase in plasma potassium. The hyperkalemic response is mediated by enhanced alpha-adrenergic activity and counterregulated partly by beta-adrenergic stimulation. The increased catecholamine concentrations are accounted for by the decrease in plasma bicarbonate.

Hypokalemic effects of intravenous infusion or nebulization of salbutamol in patients with chronic renal failure: comparative study

To examine and compare the efficacy and safety of different routes of administration of salbutamol in treating hyperkalemia, 15 patients with chronic renal failure (blood urea nitrogen > 80 mg/dL, serum creatinine > 8.0 mg/dL) were enrolled to sequentially receive either intravenous infusion (0.5 mg) or nebulization (10 mg) of salbutamol. Five of these patients (33.3%) did not respond to the intravenous salbutamol and were excluded from the study. Both treatments significantly decreased plasma potassium in 10 patients and the decrease was sustained for at least 3 hours. After infusion, the maximal reduction in plasma potassium levels was 0.92 +/- 0.10 mEq/L and occurred after 30 minutes. On the other hand, the maximal reduction in plasma potassium after nebulization (0.85 +/- 0.13 mEq/L) was similar to that after infusion, but it occurred after 90 minutes. Insulin and blood glucose increased, whereas blood pH, PCO2, sodium, osmolality, and blood pressure did not change after either treatment. Heart rate increased significantly after both treatments, but less after nebulization than after infusion. It is concluded that both infusion and nebulization are simple, effective, and safe therapeutic modalities for the treatment of hyperkalemia in patients with chronic renal failure. Infusion should be used in patients requiring a rapid decrease in plasma potassium; nebulization, on the other hand, should be used in patients with coronary artery diseases.

An anaesthetic drug error: minimizing the risk

A medication error caused a near fatal cardiac arrest in a previously healthy patient undergoing elective surgery. Inadvertent epinephrine injection induced ventricular dysrhythmias, hypertension, hypotension and pulmonary oedema. The case was investigated using critical-incident technique and was reviewed by the Risk Management Team of the Department of Anaesthesia. The purpose of this report is to present the recommendations resulting from the investigation. These include: improved resident training in intravenous drug management, the use of anaesthetic drug ampoules with distinct labels, and the development of a standardized colour code system for labels on anaesthetic drug ampoules. Furthermore, it is recommended that all anaesthetic drug errors be reported to the Canadian agencies responsible for drug packaging in order to identify patterns in anaesthetic drug errors, and to facilitate the implementation of effective drug identification systems.

Treatment of hyperkalaemia using intravenous and nebulised salbutamol

In 11 children (aged 5-18 years) with end stage chronic renal failure, the effect on plasma potassium of two doses of salbutamol (separated by two hours) given intravenously (4 micrograms/kg) and on a separate date, of salbutamol administered by nebuliser (2.5 mg if the child weighed below 25 kg, 5 mg if above) was observed. Within 30 minutes of the first dose, the mean plasma potassium concentration fell significantly by 0.87 and 0.61 mmol/l after intravenous and nebulised administration respectively. Sixty minutes after the second dose the plasma potassium was significantly reduced by a further 0.28 and 0.53 mmol/l respectively. There was a significant difference between the two methods of administration at 300 minutes after the first dose favouring nebulisation. No major side effects were observed. Nebulised salbutamol should be the first choice emergency treatment of hyperkalaemia.

Coexistence of beta 2- and beta 3-adrenoceptors in plasma potassium control in conscious rabbits

1. In conscious rabbits the intravenous infusion of adrenaline (0.3 microgram kg-1 min-1), noradrenaline (1 microgram kg-1 min-1) or isoprenaline (1.25 micrograms kg-1 min-1) caused a significant decrease in plasma potassium levels. Propranolol (9 mg kg-1, s.c.) and ICI 118551 (30 micrograms kg-1, s.c.) reversed adrenaline-induced hypokalaemia and revealed a sustained hyperkalaemia. 2. Salbutamol (0.5 microgram kg-1 min-1, i.v.), beta 2-adrenoceptor agonist, evoked a biphasic response: an initial hyperkalaemia which was followed by a hypokalaemia; a higher dose (3 micrograms kg-1 min-1, i.v.) solely induced hypokalaemia. ICI 118551 blocked the salbutamol-mediated response. 3. Noradrenaline evoked hypokalaemia was blunted completely in the presence of bupranolol (0.1 mg kg-1, s.c.), a beta 1-, beta 2- and beta 3-adrenoceptor antagonist, but not in the presence of the beta 1-adrenoceptor antagonist CGP 207 12A (1 mg kg-1, s.c.). 4. BRL 37344 (0.15 microgram kg-1 min-1, i.v.), SR 58611A (0.26 microgram kg-1 min-1, i.v.), both full beta 3-agonists, and CGP 12177 (0,25 micrograms kg-1 min-1, i.v.), a partial agonist which also acting as a non-selective beta 1- and beta 2-antagonist, induced a significant hypokalaemia. Bupranolol, but not ICI 118551 or CGP 20712A, blocked the BRL 37344-mediated hypokalaemia. 5. Ouabain (1.7 micrograms kg-1 min-1, i.v.), an inhibitor of the Na,K-pumps, inhibited both salbutamol-and BRL 37344-mediated hypokalaemia. 6. These data suggest the coexistence of beta 2- and beta 3-adrenoceptor control of extrarenal potassium disposal; moreover both beta 2 and beta 3 hypokalaemic effects would be mediated by activation of Na,K-pumps.

Glucose modulation of the disposal of an acute potassium load in patients with end-stage renal disease

PURPOSE

Extrarenal potassium disposal plays an important role in the tolerance of an acute potassium load and is particularly critical in patients with renal failure. Insulin is known to stimulate this disposal by enhancing potassium uptake into the cells. Since dietary potassium is generally ingested in combination with carbohydrates, the predictable stimulation of endogenous insulin release may blunt the expected increase in plasma potassium. The goal of the current study was to evaluate the effect of oral glucose on the disposition of an acute oral potassium load in hemodialysis patients and in normal controls.

PATIENTS AND METHODS

Eight hemodialysis patients and eight normal control subjects were studied after an overnight fast. Each subject received an oral load of potassium chloride elixir (0.25 mmol/kg). Plasma potassium was measured at baseline and at 30-minute intervals for 3 hours. On a separate study day, the subjects underwent the identical protocol, with the addition of 50 g of oral glucose to the potassium load to stimulate endogenous insulin release. The identical two experimental protocols were repeated in each subject during concomitant beta blockade with propranolol.

RESULTS

The maximal increase in plasma potassium after the potassium load was significantly greater in the hemodialysis patients than in the controls (0.93 +/- 0.08 versus 0.52 +/- 0.04 mmol/L, p < 0.001). Concomitant oral glucose markedly blunted the maximal rise in potassium levels in both experimental groups (0.40 +/- 0.09 and 0.22 +/- 0.07 mmol/L, respectively, p < 0.005 versus potassium alone). With concomitant beta blockade, the maximal increase in plasma potassium after the potassium load was significantly greater in the hemodialysis patients than in the controls (1.11 +/- 0.12 versus 0.72 +/- 0.09 mmol/L, p = 0.02). Concomitant oral glucose again markedly blunted the maximal increase in potassium in both experimental groups (0.72 +/- 0.09 and 0.39 +/- 0.06 mmol/L, respectively, p < 0.01 versus potassium alone). The potassium load in the absence of glucose did not produce changes in plasma insulin concentration in either experimental group. The potassium load in combination with oral glucose load produced more sustained hyperinsulinemia in the dialysis patients than in the control subjects.

CONCLUSIONS

Exogenous glucose, by stimulating endogenous secretion of insulin, enhances extrarenal disposal of a potassium load. This protective effect of exogenous glucose against hyperkalemia is independent of adrenergic stimulation. The beneficial effect of exogenous glucose defends against the development of severe hyperkalemia after dietary potassium ingestion, and is critically important in hemodialysis patients, due to their negligible renal potassium excretion.

Potassium and anaesthesia

Potassium is the principle intracellular ion, and its concentration and gradients greatly influence the electrical activity of excitable membranes. Because anaesthesia is so intimately involved with electrically active cells, potassium concentrations in surgical patients have received considerable attention in diagnostic and therapeutic applications. With the ongoing evolution in the indications for potassium, it is important to review the role of potassium in cellular activity, in storage and regulation, in diseases that alter potassium homeostasis, and in the therapeutic implications of perioperative alterations of potassium concentration. A rational approach to abnormal potassium values and the use of potassium in the operating room is sought, based on a physiological understanding of risks and benefits.

Pathophysiology and management of self-poisoning with beta-blockers

The prognosis of self-poisoning with beta-blockers is excellent, especially if medical management is started immediately but the wide variety of clinical symptoms and proposed treatments complicate the therapeutic strategy. Beta-blockers that are liposoluble or have marked anti-arrhythmic activity are more lethal (e.g. propranolol, sotalol). Similarly, pre-existing cardiac pathology or co-ingestion of psychotropic or cardioactive drugs increases mortality. The first-line symptomatic treatment is administration of atropine and volume-expanding fluids to treat bradycardia and hypotension, respectively. However atropine is often unsuccessful in reversing beta-blocker-induced bradycardia and repeated doses can provoke atropine poisoning. If symptomatic treatment fails, then antidotes should be administered in a precise order: first, high doses of glucagon, followed by isoproterenol, epinephrine, and the new inhibitors of phosphodiesterases. Mechanical ventilation should be started at the same time as pharmacological treatment in cases of severe collapse or prolonged QRS.

The basis for common reference intervals for serum potassium

In order to investigate the relevance of the currently used lower reference limit for S-Potassium in Danish hospital laboratories, analytical bias in the measurement of S-Potassium was compared with the lower reference limit in each of 52 Danish hospital laboratories. The acceptable bias range was estimated according to Gowans et al on the basis of the result of two different reference sample groups. The estimated acceptable 0.95 bias range was 0.24 mmol/L, so the observed bias range of 0.23 mmol/L was within this limit. As all preanalytical errors tend to increase the measured S-Potassium, all acceptable bias should be in the direction of decreasing the measured value. It can be concluded that analytical performance allows for more uniform (even common) reference interval(s) in all Danish and perhaps Nordic hospital laboratories, provided that preanalytical errors can be controlled.

The effect of acute hypothermia and serum potassium concentration on potassium cardiotoxicity in anesthetized rats

We examined the effects of hypothermia on serum K+ concentration and the interaction of body temperature and K+ load on cardiac toxicity in anesthetized rats. Serum K+ concentration significantly decreased to 2.61 +/- 0.13, 2.59 +/- 0.19 and 2.39 +/- 0.14 mmol/l at 31.0 degrees C, 28.0 degrees C and 25.0 degrees C, respectively, from the control value of 2.80 +/- 0.15 mmol/l at 37.0 degrees C. We used a 300% increase in baseline QRS duration as evidence of cardiac toxicity. Serum K+ concentrations of 4.95 +/- 0.12, 4.71 +/- 0.10, 4.45 +/- 0.14 and 4.07 +/- 0.14 mmol/l resulted in cardiac toxicity at 37.0 degrees C, 31.0 degrees C, 28.0 degrees C, and 25.0 degrees C, respectively. These data indicate that the level at which an elevation of serum K+ concentration causes cardiac toxicity diminishes with progressive hypothermia. We conclude that hypothermia induces hypokalemia, possibly through redistribution, and that the myocardium appears to be more sensitive to the toxic effects of K+ as hypothermia deepens.

Coronary revascularisation in insulin-dependent diabetic patients with chronic renal failure

Insulin-dependent diabetic patients found to have substantial coronary artery disease at the time of assessment for renal transplantation have 2-year survival of less than 50%. Because most of these patients have no angina symptoms their management is controversial. We tried to find out whether coronary artery revascularisation in such patients might decrease the combined incidence of unstable angina, myocardial infarction, and cardiac death. 151 consecutive insulin-dependent diabetic candidates for renal transplantation underwent coronary angiography. 31 had stenoses greater than 75% in one or more coronary arteries, atypical chest pain or no chest pain, and a left ventricular ejection fraction greater than 0.35. Of these, 26 agreed to be randomly assigned medical treatment (a calcium-channel-blocking drug plus aspirin) or revascularisation (angioplasty or coronary bypass surgery). 10 of 13 medically managed and 2 of 13 revascularised patients had a cardiovascular endpoint within a median of 8.4 months of coronary angiography (p < 0.01). 4 medically managed patients died of myocardial infarction during follow-up. Thus, revascularisation decreased the frequency of cardiac events in insulin-dependent diabetic patients with chronic renal failure and symptomless coronary artery stenoses. These findings suggest that diabetic renal transplant candidates should be screened for silent coronary artery disease, because revascularisation may decrease cardiac morbidity and mortality in this population.

Renal effect of dopexamine hydrochloride in patients with chronic renal dysfunction

Dopexamine hydrochloride, a dopamine analogue, has been reported, both experimentally and clinically, to increase renal blood flow (RBF) and improve renal function in normal kidneys. The availability of computer-enhanced radionuclide scintigraphy, which provides accurate non-invasive measurement of changes in RBF, enabled us to study the renographic effects of dopexamine hydrochloride in patients with chronic renal dysfunction (CRD). Ten patients suffering from CRD and ten normal kidney donors were the study population. Renography was performed, heart rate (HR) and blood pressure (BP) measured, and hematological and biochemical tests carried out before and after intravenous infusion of dopexamine 2 micrograms kg-1 min-1 for 60 min. The patient population displayed significant increases in total cortical and medullary RBF and renographic clearance rate (CR), while in kidney donors the RBF was increased in all kidney regions with no change in CR. HR increased in both groups, while BP showed no significant changes. The hematological and biochemical changes were transient and returned to preinfusion levels after 24 h. It is concluded that dopexamine hydrochloride 2 micrograms kg-1 min-1 increases RBF and CR in patients with CRD.

Metabolic effects of beta 2-agonists

Catecholamines produce a number of biochemical changes most of which result from stimulation of beta 2-receptors. Interest in these metabolic effects has increased recently as a consequence of the concern over the relatively high mortality from acute asthma attacks. In this review the data on the impact of beta 2-agonists on glucose production, insulin release and lipolysis are presented. Thereafter the subject of hypokalaemia, the mechanism for its production by beta 2-agonists and its relevance to cardiac arrhythmias are considered in detail. Finally the fall in plasma magnesium and the possible role of beta 2-agonists in the production of lactic acidosis are discussed.

Diltiazem enhances potassium disposal in subjects with end-stage renal disease

Seven subjects with end-stage renal disease (ESRD) who were anuric and dialysis-dependent were studied during a 28-hour interdialytic period to assess changes in plasma potassium. Plasma potassium, glucose, magnesium, aldosterone, and cortisol were measured every 4 hours. Eight normal subjects were similarly treated. Subjects with ESRD had a progressive increase in plasma potassium, in contrast to normal subjects who exhibited a characteristic diurnal variation. In ESRD, diltiazem significantly reduced the rate of increase in plasma potassium compared with placebo and resulted in a significantly lower net increase in potassium over the entire 28-hour period. Diltiazem did not affect plasma potassium in normal subjects. Diltiazem did not affect plasma aldosterone, cortisol, glucose, or magnesium. In conclusion, diltiazem reduced the rate of increase of plasma potassium during a 28-hour interdialytic period.

Effect of Bilateral Stellectomy on Electrical Instability of the Atrium in the Dog with Hypokalemia

To investigate the effect of sympathetic nerve activity on electrical instability of the atrium in the presence of hypokalemia, open chest electrophysiological study was performed before and after bilateral stellectomy (BS) in 15 dogs with hypokalemia (hypokalemia group) and in 15 dogs with normokalemia (control group). Hypokalemia was created by infusion of 5.0 g/kg of polystyrene sulfonic acid calcium into the colon. Serum level of potassium was significantly lower in the hypokalemia group (2.94 +/- 0.52 mEq/L) than in the control group (4.86 +/- 0.51 mEq/L, P less than 0.01) before BS. There was no significant change in serum level of potassium in the two groups after BS. Incidence of electrically induced atrial fibrillation (AF) was significantly higher in the hypokalemia group (80%) than in the control group (13%, P less than 0.001) before BS. It was significantly reduced in the hypokalemia group (40%, P less than 0.05), but not in the control group (6%) after BS. Dispersion of effective refractory period of the atrium (delta ERP) was significantly greater in the hypokalemia group (26.1 +/- 2.8 msec) than in the control group (22.0 +/- 3.3 msec, P less than 0.005) before BS. It was significantly decreased to 23.1 +/- 3.2 msec in the hypokalemia group (P less than 0.001) and to 20.6 +/- 2.5 msec in the control group (P less than 0.01) after BS. Maximum conduction delay in the atrium (MaxCD) was 36.1 +/- 3.5 msec before and 36.2 +/- 4.1 msec after BS in the hypokalemia group and 31.1 +/- 4.2 msec before and 32.3 +/- 4.9 msec after BS in the control group. There was a significant difference in MaxCD between the two groups before BS. Atrial fibrillation threshold (AFT) was significantly lower in the hypokalemia group (3.9 +/- 0.7 mA) than in the control group (13.8 +/- 3.1 mA, P less than 0.001) before BS. It was significantly increased both in the hypokalemia group (6.5 +/- 1.3 mA, P less than 0.001) and in the control group (15.0 +/- 2.7 mA, P less than 0.005) after BS. It is concluded that sympathetic nerve activity may play some role in the increase in electrical instability of the atrium in the presence of hypokalemia.

Hemodynamic and metabolic effects of intravenous clentiazem in hypertensive patients

To determine the hemodynamic and certain metabolic effects of clentiazem, a diltiazem congener, 10 untreated essential hypertensive patients were given the calcium antagonist in 3 successive doses totaling 1.0 mg/kg intravenously. Mean arterial pressure and total peripheral resistance progressively declined from 121 +/- 3 mm Hg and 47 +/- 2 U (mean) to 110 +/- 3 mm Hg and 33 +/- 1 U, respectively (p less than 0.05); heart rate remained unchanged. Cardiac output increased as a result of augmented cardiopulmonary volume (p less than 0.05) produced by peripheral venoconstriction and norepinephrine release (from 258 +/- 41 to 319 +/- 42 pg/ml; p less than 0.01). Surprisingly, there was an immediate reduction in plasma aldosterone (10.4 +/- 1.2 to 6.5 +/- 1.0 ng/dl; p less than 0.01), serum potassium (4.3 +/- 0.1 to 3.6 +/- 0.1 mEq/dl; p less than 0.001) and calcium (9.5 +/- 0.1 to 8.8 +/- 0.1 mg/dl; p less than 0.001) concentrations, whereas epinephrine increased (21.2 +/- 3.3 to 45.8 +/- 5.9 pg/ml; p less than 0.002). Previous studies with diltiazem, conducted similarly, did not show these changes. Therefore, clentiazem reduced mean arterial pressure through a decrease in total peripheral resistance, and released epinephrine was associated with intracellular potassium influx (urinary potassium did not change). The inhibited aldosterone release was not compensated by altered renal blood flow, glomerular filtration or increased plasma renin activity. These findings underscore the concept that calcium antagonists are a remarkably heterogeneous antihypertensive group.

Normal renin-aldosterone-insulin and potassium interrelationship in FMF patients and amyloid nephropathy

The renin-aldosterone system and plasma insulin were studied in 19 patients with familial Mediterranean fever (FMF). Their relationships to serum potassium level at rest and before and after oral glucose loading are described. An interesting finding is the occurrence of hyperkalemia in the absence of oliguria, in the advanced stages of renal failure. No differences were found in the activity of the renin-angiotensin-aldosterone system to explain these variations in serum potassium found in some of the patients. The response of the renin-aldosterone system to glucose loading showed no abnormality, and the regular relationship between serum potassium, plasma renin activity (PRA), aldosterone, insulin, and plasma pH is maintained. Levels of insulin, potassium, and bicarbonate in serum or plasma pH were found similar in FMF patients with normal renal function with and without proteinuria. Further decrease in renal function due to the progression of the underlying disease is manifested by an increase in FENa+ and FEK+ and a hyperchloremic metabolic acidosis, as is the case in other patients with chronic renal failure.

Salbutamol infusion to treat neonatal hyperkalaemia

Salbutamol infusion, 4 micrograms/kg in 5 ml of water infused for 20 minutes, was given to treat hyperkalaemia (potassium level > 6.0 mmol/l) in 10 critically ill preterm infants (median gestational age 26 weeks). Seven infants had acute renal failure, two had persistent metabolic acidosis without renal failure and the remaining infant had a combination of acute renal failure and persistent metabolic acidosis. No infant developed a tachycardia or became hyperglycaemic in response to the infusion. Seven of the 10 infants ultimately died but this was at a mean of 9 days following the infusion and as a consequence of complications due to their extreme prematurity or major congenital abnormality. In response to the infusion the potassium level fell in 7 infants with acute renal failure by a median of 1.1 mmol/l (range 0.7-1.8) at one hour but in the three infants with a persistent metabolic acidosis, the potassium level continued to rise. We conclude that salbutamol infusion achieves, without side-effects, at least a temporary reduction in hyperkalaemia in preterm infants with renal failure, but not metabolic acidosis. Its effect is of sufficient duration to allow ample time for definitive therapy to be instituted and thus may be a useful alternative for infants in whom the possible hypoglycaemic side-effects of glucose and insulin should be avoided.

Potassium homeostasis with indomethacin therapy in normal subjects

In an attempt to delineate effects of prostaglandin (PG) synthesis inhibition on potassium metabolism in normal subjects, we challenged 13 young, healthy volunteers with a potassium chloride infusion before and after a 4-day course of indomethacin (25 mg orally, three times a day). The plasma potassium level was monitored at 10-minute intervals throughout the 50-minute infusion and for a total of 180 minutes. The maximal increment in plasma potassium level was 0.82 +/- 0.07 mmol/L (mEq/L) in the untreated state, and 0.86 +/- 0.08 mmol/L with indomethacin treatment. The basal potassium level before infusion was higher in the indomethacin-treated than the control state (3.83 +/- 0.07 v 3.68 +/- 0.07 mmol/L; P less than 0.01). Urinary potassium excretion over the 3-hour study period equalled the potassium load administered, and was unaffected by indomethacin therapy. Indomethacin did not alter insulin or aldosterone levels during the study. PGE2 excretion over the 3 hours was lower in the indomethacin than the control phase, although it was higher than normal in both phases. In an additional experiment, the comparative effects of a saline versus saline-potassium infusion on PG excretion were studied. No differences were seen between the excretion patterns of PGE2 or 6-keto-PGF1a with the two infusions. We conclude that (1) although basal serum potassium level is slightly higher in healthy young people during indomethacin treatment, there is little effect on handling of an acute potassium load; (2) the aldosterone response to hyperkalemia is PG-independent; (3) urinary PG excretion increases in response to a saline-based infusion, but the effect is not enhanced by acute potassium loading.

Adrenergic modulation of extrarenal potassium disposal in men with end-stage renal disease

In normal subjects, beta-adrenergic stimulation lowers the serum potassium, whereas alpha-stimulation raises it. Epinephrine, a mixed alpha and beta agonist, acutely lowers the blood potassium in normal subjects, but not in patients with end-stage renal disease. This study was designed to determine whether the resistance to the hypokalemic effect of epinephrine in dialysis patients is due to a blunted beta-adrenergic response, or to an augmented alpha-adrenergic response. The infusion of epinephrine at low doses (0.01 microgram/kg/min) produced a significant increase in serum potassium in hemodialysis patients (+0.21 +/- 0.07 mmol/liter, P less than 0.05), as compared to a nonsignificant decrease (-0.06 +/- 0.04 mmol/liter) in normal subjects. Epinephrine at high physiologic doses (0.04 microgram/kg/min) failed to significantly change the serum potassium in the dialysis patients (-0.10 +/- 0.14 mmol/liter), but substantially lowered serum potassium in the controls (-0.64 +/- 0.10 mmol/liter, P less than 0.001). There was no significant correlation (r = 0.03) between the baseline serum potassium concentration and the magnitude of change during epinephrine infusion. Epinephrine infusion (0.04 microgram/kg/min) during beta-blockade with propranolol produced a greater rise in serum potassium in the dialysis patients as compared to the controls (+0.69 +/- 0.11 vs. +0.32 +/- 0.11 mmol/liter, P less than 0.05). Epinephrine infusion (0.01 microgram/kg/min) during alpha-blockade with phentolamine resulted in similar changes in serum potassium in dialysis patients and in normal control (-0.10 +/- 0.12 vs. -0.10 +/- 0.06 mmol/liter). Moreover, phentolamine reversed the increase in serum potassium observed in dialysis patients during the infusion of epinephrine following beta-blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Extrarenal potassium tolerance in chronic renal failure: implications for the treatment of acute hyperkalemia

The role of extrarenal potassium homeostasis is well recognized as a major mechanism for the acute defense against the development of hyperkalemia. The purpose of this report is to examine whether or not the various mechanisms of extrarenal potassium regulation are intact in patients with end-stage renal disease (ESRD). The available data suggest that with the development of ESRD and the uremic syndrome there is impaired extrarenal potassium metabolism that is related to a defect in the Na,K-adenosine triphosphatase (ATPase). The responsiveness of uremic patients to the various effector systems that regulate extrarenal potassium handling is discussed. Insulin is well positioned to play an important role in the regulation of plasma potassium concentration in patients with impaired renal function. The role of basal insulin may be even more important than previously appreciated, since somatostatin infusion causes a much greater increase in the fasting plasma potassium in rats with renal failure than in controls. Furthermore, stimulation of endogenous insulin by oral glucose results in a greater intracellular translocation of potassium in uremic rats than in controls. Under at least two common physiologic circumstances, feeding and vigorous exercise, endogenous catecholamines might also act to defend against acute increments in extracellular potassium concentration. However, it is important to appreciate that the response to beta 2-adrenoreceptor-mediated internal potassium disposal is heterogeneous as judged by the variable responses to epinephrine infusion. Based on the evidence presented in this report, a regimen for the treatment of life-threatening hyperkalemia is outlined. Interpretation of the available data demonstrate that bicarbonate should not be relied on as the sole initial treatment for severe hyperkalemia, since the magnitude of the effect of bicarbonate on potassium is variable and may be delayed. The initial treatment for life-threatening hyperkalemia should always include insulin plus glucose, as the hypokalemic response to insulin is both prompt and predictable. Combined treatment with beta 2-agonists and insulin is also effective and may help prevent insulin-induced hypoglycemia.

Potassium, glucose, insulin interrelationships during adrenaline infusion in normotensive and hypertensive humans

1. Significant increases in arterial noradrenaline (NA) of similar magnitude were seen in normotensive (NT) and hypertensive humans (HT) during adrenaline (ADR) infusion. 2. Significant falls in plasma potassium (K+) were observed in both NT and HT during ADR infusion, even at rates equivalent to minor stress. Levels achieved were significantly lower in HT than in NT. 3. Plasma glucose increased significantly in HT at all ADR infusion rates but only at higher rates of infusion in NT. 4. Basal insulin levels were significantly higher in NT than in HT. After cessation of infusion, insulin increased three-fold in HT and two-fold in NT. 5. Infusion of ADR to produce levels seen during mild to moderate stress resulted in significant increases in plasma NA, falls in plasma K+ and increases in plasma glucose. The expected large insulin response to rising glucose was not seen until after ADR was ceased, confirming the inhibitory effect of ADR on glucose stimulated insulin release.

Treatment of hyperkalaemia with intravenous salbutamol

Thirteen children with hyperkalaemia were treated by intravenous infusions of salbutamol, 4 micrograms/kg over 20 minutes. Reductions in the mean (SD) plasma potassium concentrations, of 1.48 (0.5) and 1.64 (0.5) mmol/l were obtained at 40 and 120 minutes, respectively, after completion of the infusions. No side effects were noted.

[Simplified strategy for anesthesia of pheochromocytoma]

The only curative treatment of phaeochromocytoma consists in surgical removal. This carries a high risk due to the acute release of catecholamines. General anaesthesia cannot by itself prevent haemodynamic disturbances during surgical manipulation of the tumour. Careful preparation, based on intravascular volume repletion as well as alpha-, and, if required, beta-adrenergic blockade, has been shown to reduce morbidity and mortality. However, this protocol is often cumbersome, and does not prevent totally the haemodynamic instability as a decrease in blood pressure at the start of treatment, or after removal of the tumour. Since voltage-dependent calcium channels are involved in both secretion and action of catecholamines, calcium-channel antagonists might be an interesting therapeutic alternative. In fact, short-term treatment by dihydropyridines may attenuate blood pressure variability during the preoperative period. During surgery, a dose-dependent reduction in systemic vascular resistances has been shown with intravenous nicardipine. However, dihydropyridines do not control cardiac adrenergic stimulation, which causes tachycardia or persistently increased blood pressure in spite of low or normal systemic vascular resistances. Such an acute cardiac hyperactivity, which can only be assessed by continuous haemodynamic monitoring, is electively sensitive to a beta-adrenergic blocker rather than a calcium channel antagonist with high cardiac affinity (diltiazem, verapamil). Esmolol is available for intravenous administration. It is an ultra-short acting agent, ensuring a selective dose-related cardiac beta 1-blockade. Combining esmolol with nicardipine gives control over almost all episodes of haemodynamic worsening during phaeochromocytoma resection. Preoperative medical treatment no longer aims to suppress adrenergic stimulation completely, but to prevent acute haemodynamic changes.(ABSTRACT TRUNCATED AT 250 WORDS)