On the mechanism by which chloride corrects metabolic alkalosis in man

Inpatient Diuretic Management of Acute Heart Failure: A Practical Review

The inpatient treatment of acute heart failure (AHF) is aimed at achieving euvolemia, relieving symptoms, and reducing rehospitalization. Adequate treatment of AHF is rooted in understanding the pharmacokinetics and pharmacodynamics of select diuretic agents used to achieve decongestion. While loop diuretics remain the primary treatment of AHF, the dosing strategies of loop diuretics and the use of adjunct diuretic classes to augment clinical response can be complex. This review examines the latest strategies for diuretic management in patients with AHF, including dosing and monitoring strategies, interaction of diuretics with other medication classes, use adjunctive therapies, and assessing endpoints for diuretic. The goal of the review is to guide the reader through commonly encountered clinical scenarios and pitfalls in the diuretic management of patients with AHF.

Case in Point: Correction of Dialysis-Induced Metabolic Alkalosis

Normal saline solution infusion with concurrent removal by ultrafiltration successfully corrected pretreatment metabolic alkalosis when other measures were inadequate for a patient on dialysis.

Metabolic Alkalosis: A Brief Pathophysiologic Review

Metabolic alkalosis is a very commonly encountered acid-base disorder that may be generated by a variety of exogenous and/or endogenous, pathophysiologic mechanisms. Multiple mechanisms are also responsible for the persistence, or maintenance, of metabolic alkalosis. Understanding these generation and maintenance mechanisms helps direct appropriate intervention and correction of this disorder. The framework utilized in this review is based on the ECF volume-centered approach popularized by Donald Seldin and Floyd Rector in the 1970s.  Although many subsequent scientific discoveries have advanced our understanding of the pathophysiology of metabolic alkalosis, that framework continues to be a valuable and relatively straightforward diagnostic and therapeutic model.

Ammonia Transporters and Their Role in Acid-Base Balance

Acid-base homeostasis is critical to maintenance of normal health. Renal ammonia excretion is the quantitatively predominant component of renal net acid excretion, both under basal conditions and in response to acid-base disturbances. Although titratable acid excretion also contributes to renal net acid excretion, the quantitative contribution of titratable acid excretion is less than that of ammonia under basal conditions and is only a minor component of the adaptive response to acid-base disturbances. In contrast to other urinary solutes, ammonia is produced in the kidney and then is selectively transported either into the urine or the renal vein. The proportion of ammonia that the kidney produces that is excreted in the urine varies dramatically in response to physiological stimuli, and only urinary ammonia excretion contributes to acid-base homeostasis. As a result, selective and regulated renal ammonia transport by renal epithelial cells is central to acid-base homeostasis. Both molecular forms of ammonia, NH₃ and NH₄⁺, are transported by specific proteins, and regulation of these transport processes determines the eventual fate of the ammonia produced. In this review, we discuss these issues, and then discuss in detail the specific proteins involved in renal epithelial cell ammonia transport.

Implications of Serum Chloride Homeostasis in Acute Heart Failure (from ROSE-AHF)

Lower serum chloride (Cl) levels are strongly associated with increased long-term mortality after admission for acute heart failure (AHF). However, the therapeutic implications of serum Cl levels during AHF are unknown. We sought to determine the short-term clinical response and postdischarge outcomes associated with serum Cl levels in AHF. Serum Cl was measured at randomization (n = 358) and during hospitalization from patients with AHF in the Renal Optimization Strategies Evaluation in Acute Heart Failure trial. Outcomes included diuretic response and renal function at 72 hours and death and rehospitalization at 60 and 180 days. Baseline Cl tertiles were 84 to 98; 99 to 102; and 103 to 117 meq/l. Baseline Cl level was associated with diuretic efficiency (p <0.001) but not change in cystatin C (p = 0.30) at 72 hours and was associated with 60-day death (hazard ratio [HR] 0.86, p = 0.029), 60-day death and rehospitalization (HR 0.90, p = 0.01), and 180-day death (HR 0.91, p = 0.049). These associations were attenuated with additional adjustment for loop diuretic dose (p >0.05). Chloride change correlated with weight change (ρ 0.18, p = 0.001), cystatin C change (ρ -0.35, p <0.001), and cumulative sodium excretion (ρ -0.21, p <0.001) but was not associated with any clinical outcomes (p >0.05 for all). In conclusion, serum Cl levels in AHF were inversely associated with loop diuretic response and were prognostic. However, changes in Cl levels were associated with parameters of decongestion but not with clinical outcomes.

Chloride transport

Chloride transport along the nephron is one of the key actions of the kidney that regulates extracellular volume and blood pressure. To maintain steady state, the kidney needs to reabsorb the vast majority of the filtered load of chloride. This is accomplished by the integrated function of sequential chloride transport activities along the nephron. The detailed mechanisms of transport in each segment generate unique patterns of interactions between chloride and numerous other individual components that are transported by the kidney. Consequently, chloride transport is inextricably intertwined with that of sodium, potassium, protons, calcium, and water. These interactions not only allow for exquisitely precise regulation but also determine the particular patterns in which the system can fail in disease states.

Chloride: the queen of electrolytes?

BACKGROUND

Channelopathies, defined as diseases that are caused by mutations in genes encoding ion channels, are associated with a wide variety of symptoms and have been documented extensively over the past decade. In contrast, despite the important role of chloride in serum, textbooks in general do not allocate chapters exclusively on hypochloremia or hyperchloremia and information on chloride other than channelopathies is scattered in the literature.

STUDY DESIGN

To systematically review the function of chloride in man, data for this review include searches of MEDLINE, PubMed, and references from relevant articles including the search terms "chloride," "HCl," "chloride channel" "acid-base," "acidosis," "alkalosis," "anion gap" "strong anion gap" "Stewart," "base excess" and "lactate." In addition, internal medicine, critical care, nephrology and gastroenterology textbooks were evaluated on topics pertaining the assessment and management of acid-base disorders, including reference lists from journals or textbooks.

CONCLUSION

Chloride is, after sodium, the most abundant electrolyte in serum, with a key role in the regulation of body fluids, electrolyte balance, the preservation of electrical neutrality, acid-base status and it is an essential component for the assessment of many pathological conditions. When assessing serum electrolytes, abnormal chloride levels alone usually signify a more serious underlying metabolic disorder, such as metabolic acidosis or alkalosis. Chloride is an important component of diagnostic tests in a wide array of clinical situations. In these cases, chloride can be tested in sweat, serum, urine and feces. Abnormalities in chloride channel expression and function in many organs can cause a range of disorders.

It is chloride depletion alkalosis, not contraction alkalosis

Maintenance of metabolic alkalosis generated by chloride depletion is often attributed to volume contraction. In balance and clearance studies in rats and humans, we showed that chloride repletion in the face of persisting alkali loading, volume contraction, and potassium and sodium depletion completely corrects alkalosis by a renal mechanism. Nephron segment studies strongly suggest the corrective response is orchestrated in the collecting duct, which has several transporters integral to acid-base regulation, the most important of which is pendrin, a luminal Cl/HCO(3)(-) exchanger. Chloride depletion alkalosis should replace the notion of contraction alkalosis.

Acid-base disturbances in gastrointestinal disease

Disruption of normal gastrointestinal function as a result of infection, hereditary or acquired diseases, or complications of surgical procedures uncovers its important role in acid-base homeostasis. Metabolic acidosis or alkalosis may occur, depending on the nature and volume of the unregulated losses that occur. Investigation into the specific pathophysiology of gastrointestinal disorders has provided important new insights into the normal physiology of ion transport along the gut and has also provided new avenues for treatment. This review provides a brief overview of normal ion transport along the gut and then discusses the pathophysiology and treatment of the metabolic acid-base disorders that occur when normal gut function is disrupted.

Chronic neutral phosphate supplementation induces sustained, renal metabolic alkalosis

The aim of the present study was to test whether intravenous neutral phosphate supplementation, recently shown in our laboratory to acutely stimulate proton secretion in the distal nephron, was able to induce a sustained metabolic alkalosis. Neutral Na and K phosphate supplementation for seven days, with equivalent reduction in chloride supply and unchanged intake of sodium and potassium, in ADX rats receiving fixed physiological doses of aldosterone and dexamethasone (group 1, N = 7), was responsible for a severe metabolic alkalosis (MA; delta [HCO3] 11 +/- 1.3 mM, and delta pH 0.11 +/- 0.06 unit). Metabolic alkalosis was at least in part of renal origin, since net acid excretion (NAE) transiently increased, principally due to an increment in titratable acid excretion rate. Balances were equilibrated for sodium and negative for chloride and potassium, which may have contributed to the severity of the MA. Chronic i.v. neutral Na phosphate, without change in potassium and chloride supply, in ADX rats receiving the same doses of steroids (group 2, N = 5), was responsible for a less severe MA (delta [HCO3] 7.5 +/- 0.9 mM, and delta pH 0.07 +/- 0.01 unit), also of renal origin. In this group, balances were positive for chloride and sodium and equilibrated for potassium. Finally, neutral Na and K phosphate supplementation with reduction in chloride supply in intact rats (group 3, N = 4) was also able to induce a MA (delta [HCO3] 5.5 +/- 1.8 mM, and delta pH 0.06 +/- 0.01 unit) of renal origin, with balances negative for chloride and equilibrated for potassium and sodium. In all groups, the generation and maintenance of MA probably resulted from stimulated proton secretion in the distal nephron, as suggested by the observed increase of PCO2 over HCO3 concentration ratio in the urine and a fall in urine pH despite augmented urinary buffer content throughout the phosphate infusion period. Glomerular filtration rate did not significantly vary in any group. In conclusion, chronic supplementation of neutral phosphate appears to stimulate per se proton secretion in the distal nephron, independently of sodium, chloride, and potassium balances, and adrenal steroid secretion. Thus neutral phosphate supplementation should be added to the previously known factors able to induce MA.

Gastric conduit urinary diversion in normal dogs. Part II, Hypochloremic metabolic alkalosis

Gastric conduit urinary diversion was performed in 10 dogs after complete cystectomy. Four dogs were euthanatized on day 30 because of hypochloremic metabolic alkalosis and renal failure. Hematologic and biochemical changes in six dogs evaluated for 120 days were compatible with hypochloremic metabolic alkalosis. The continuous loss of hydrochloric acid from the gastric conduit resulted in significant increases in arterial blood pH, PaCO2, anion gap, TCO2, and the concentration of HCO3-. There were significant decreases in PaO2 and the serum concentrations of chloride and potassium. Deterioration of renal function resulted in all dogs. It was concluded that hypochloremic metabolic alkalosis makes gastric conduit urinary diversion unsatisfactory for clinical use in dogs.

Chloride-depletion metabolic alkalosis induces ECF volume depletion via internal fluid shifts in nephrectomized dogs

We recently reported that chloride-depletion metabolic alkalosis (CDMA) results in renal losses of Na, K, and water. In these studies we investigated whether CDMA (induced using a new model that avoids external changes in Na and water balance) was also associated with internal Na and water shifts out of the ECF. CDMA was induced using haemofiltration in functionally nephrectomized dogs. Plasma ultrafiltrate was substituted quantitatively with a solution duplicating each dog's plasma electrolyte composition in control animals, and with a solution containing HCO3 as the sole anion in CDMA animals. ECF volume was estimated as the space of distribution of [3H]-mannitol. Plasma composition and [3H]-mannitol distribution space were unchanged in control dogs. In CDMA dogs metabolic alkalosis developed; despite the absence of external changes in Na and water balance, the space of distribution of [3H]-mannitol decreased by 335 +/- 46 ml (equivalent to 8% of baseline ECF volume), calculated chloride space fell by 304 +/- 50 ml, and haematocrit increased from 45.6 to 48.5 vol%. We conclude that CDMA causes an internal shift of fluid out of the ECF. The resulting ECF volume contraction appears to be an inherent feature of CDMA.