Varying role of extracellular electrolytes in metabolic acidosis and alkalosis

Plasma potassium response after tromethamine (THAM) or sodium bicarbonate in the acidotic rabbit

The purpose of this study was to evaluate the plasma potassium (K+) response after administration of tromethamine (THAM) or sodium bicarbonate (NaHCO3) in an acidotic rabbit model. Eighteen healthy, adult female New Zealand White rabbits were subjected to severe hypoxia until a base deficit of -10 mEq/L resulted. Rabbits were then randomized to receive THAM solution, NaHCO3, or no drug (control). The drug was administered over 2 min in quantities calculated to correct a base deficit of 10 or greater. Plasma K+ and sodium (Na+) were measured for 45 min after drug administration. No difference in K+ response was noted after THAM, NaHCO3, or no drug. In contrast, THAM resulted in significantly lower Na+ concentrations when compared to the NaHCO3 or the control group (P < 0.05). In this rabbit model, alkalinization after THAM administration results in K+ changes similar to those after NaHCO3. THAM should be considered when treating acidosis in patients where hypernatremia is a concern.

Potassium chloride improves the thermotolerance of chickens exposed to acute heat stress

Experiments were designed to test the hypothesis that chicks that drank an electrolyte solution containing K prior to and during an acute exposure to heat would have greater thermotolerance than chicks that consumed only water. In three experiments, 5- or 7-wk-old male chickens drank distilled water (control), or .3, .6, or .9% KCl solutions (Experiments 1 and 2), and .6 or .9% KCl or .8% KHCO3 solutions (Experiment 3) for 48 h before acute heat stress (HS) and during HS. Body temperature (Tb), blood pH, partial pressure of blood carbon dioxide (pCO2), ionized Ca (Ca2+), plasma Na, K, Cl, total Ca, inorganic P (Pi), and osmolality (Osm), and water consumption were determined. Water intake increased with the concentration of KCl. Before HS, .6% KCl increased plasma K and Ca2+, whereas .9% KCl resulted in a marked increase in K, Ca2+, Na, Cl, and Osm and a decrease in pH. During HS, .6% KCl-birds had lower hyperthermic Tb and pH values and higher Ca2+ and K concentrations than controls. Plasma Na and Osm of .6% KCl birds decreased whereas those of the control birds remained unchanged. Providing K as KHCO3 aggravated respiratory alkalosis and failed to influence either Tb or plasma electrolytes, suggesting that the beneficial effect of .6% KCl may in part be attributed to the accompanying Cl. Hyperthermic Tb and Ca2+ values were highly correlated. The results showed that .6% KCl solution reduced HS-related responses and indicated a relationship among supplemental KCl, blood Ca2+, and Tb.

A model of the hyperkalemia produced by metabolic acidosis

In both humans and animals, mineral acids predictably result in hyperkalemia, whereas plasma K+ remains normal or may even decrease during organic acidosis. The purpose of these studies was to define the mechanism for these effects in the opossum kidney cell, an established epithelial cell line derived from the renal cortex of the opossum. This cell was chosen because the acid/base transport pathways in this cell type are well defined and because it is one of the few cells known to express K/H antiport, the transport pathway that has been proposed to mediate the hyperkalemia of acidosis. Cell K+ at pH 7.4 averaged 988 +/- 48 nmol/mg protein. Relative to this value (100%), cell K+ increased when buffer pH was increased to pH 8.4 with NaOH (108% +/- 3%) and decreased when buffer pH was acidified with HCl to pH 6.4 (93% +/- 4%), producing a highly significant correlation of cell K+ with buffer pH: cell K+ (% of baseline at pH 7.4) = 6.9 (cell pH) + 49 (r = 0.5, P < 0.004). In contrast, acidification of the buffer to pH 6.4 with either butyric or lactic acid increased cell K+ (115% +/- 4% and 110% +/- 2%, respectively, both P < 0.05 v 7.4 or HCl value). Cell pH acidified in response to HCl at a rate of 0.0053 +/- 0.0007 pH U/s, a significantly slower rate than in response to lactic acid or butyric acid (0.0071 +/- 0.0007 and 0.0091 +/- 0.0007 pH U/s, respectively). Unidirectional ouabain-sensitive 42K+ influx was significantly inhibited by HCl acidosis and less so by the organic acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of diabetic ketoacidosis and non-ketotic hyperosmolar diabetic coma

Although mortality of diabetic ketoacidosis (KA) has decreased during the past 20 yr to 1-2%, hyperosmolar non-ketotic coma (HNC) is still lethal in 20-30% of cases due to severe underlying conditions or to complications. The most frequent causes of death are infections and thromboembolic disorders. The strategies of initial treatment of KA and HNC are similar; in KA, insulin, fluid and electrolyte replacement have first priority. In HNC, rehydration and electrolyte administration are of primary importance. It is now generally recognized that insulin therapy is best performed using low doses (4-8 units/h); after institution of insulin treatment and rehydration there are rapid changes of fluid and electrolytes from the extra- into the intravascular space. In this situation it is a major therapeutic challenge to avoid complications due to hypokalaemia, hypophosphataemia, hypomagnesaemia and hypovolaemia. These complications should be avoided by adequate replacement, and particularly by regular clinical and laboratory monitoring. When blood glucose concentrations decrease below 14 mmols/l, blood glucose concentrations should initially be maintained at this level because rapid lowering below this level may increase the risk of brain oedema. Too-vigorous fluid replacement with crystalline solutions also increases the risk that brain oedema or complications like the adult respiratory distress syndrome will develop. If hypovolaemia persists in spite of adequate crystalloid solutions, colloid-containing fluids such as albumin should be administered. It is not established whether replacements of phosphate and magnesium have clinical benefits. Nevertheless, it is probably justified to administer phosphate and magnesium when their serum concentrations are below the normal range, particularly if the clinical situation is critical. Mortality from diabetic coma in industrialized countries may only be decreased by prophylaxis, i.e. by education of all diabetic patients and physicians to detect metabolic decompensation early.

A patient with hyperkalemia and metabolic acidosis

Uptake of potassium by extrarenal tissues, primarily muscle and liver, represents a major defense mechanism in the maintenance of normokalemia following an acute elevation in the serum potassium concentration. Insulin, epinephrine, and aldosterone all play major roles in maintaining the normal distribution of potassium between the intracellular and extracellular environment. In addition to hormonal regulation, changes in blood pH and tonicity also exert a strong influence on extrarenal potassium metabolism. Last, the serum potassium concentration per se directly influences its own cellular uptake and this transport mechanism appears to be inhibited by uremia.

Hyperkalemia in diabetic ketoacidosis

Patients with diabetic ketoacidosis tend to have somewhat elevated serum K+ concentrations despite decreased body K+ content. The hyperkalemia was previously attributed mainly to acidemia. However, recent studies have suggested that "organic acidemias" (such as that produced by infusing beta-hydroxybutyric acid) may not cause hyperkalemia. To learn which, if any, routinely measured biochemical indices might correlate with the finding of hyperkalemia in diabetic ketoacidosis, we analyzed the initial pre-treatment values in 131 episodes in 91 patients. Serum K+ correlated independently and significantly (p less than 0.001) with blood pH (r = -0.39), serum urea N (r = 0.38) and the anion gap (r = 0.41). The mean serum K+ among the men was 5.55 mmol/l, significantly higher than among the women, 5.09 mmol/l (p less than 0.005). Twelve of the 16 patients with serum K+ greater than or equal to 6.5 mmol/l were men, as were all eight patients with serum K+ greater than or equal to 7.0 mmol/l. Those differences paralleled a significantly higher mean serum urea N concentration among the men (15.1 mmol/l) than the women (11.2 mmol/l, p less than 0.01). The greater tendency to hyperkalemia among the men in this series may have been due partly to their greater renal dysfunction during the acute illness. However, other factors that were not assessed, such as cell K+ release associated with protein catabolism, and insulin deficiency per se, may also have affected serum K+ in these patients.

Effect of various therapeutic approaches on plasma potassium and major regulating factors in terminal renal failure

PURPOSE

The development of life-threatening hyperkalemia poses a risk for patients with chronic preterminal renal failure. Various therapeutic options have been suggested for hyperkalemic emergencies in these patients; to date, however, no study has evaluated the relative efficacies of these measures in the presence of renal failure. Our goal was to examine the acute effects of a variety of therapeutic approaches, as well as those of hemodialysis, on plasma potassium levels in a hemodialysis population.

PATIENTS AND METHODS

Ten patients with terminal renal failure undergoing maintenance hemodialysis were enrolled in the study. Blood gas parameters and plasma sodium, potassium, glucose, osmolality, renin, aldosterone, epinephrine, norepinephrine, dopamine, and insulin were measured before, during, and after 60-minute infusions of bicarbonate, epinephrine, and insulin in glucose, and before, during, and after performance of regular hemodialysis for one hour.

RESULTS

Hypertonic as well as isotonic intravenous bicarbonate (2 to 4 mmol/minute) induced a marked rise in plasma bicarbonate and pH, but failed to lower the plasma potassium level (5.66 versus 5.83 mmol/liter before and after). Epinephrine, 0.05 microgram/kg/minute administered intravenously, decreased plasma potassium only slightly from 5.57 to 5.25 mmol/liter, and five patients showed no decline. On the other hand, insulin in glucose, 5 mU/kg/minute intravenously, effectively lowered plasma potassium levels from 5.62 to 4.70 mmol/liter, and hemodialysis induced the most rapid decline from 5.63 to 4.29 mmol/liter. Plasma aldosterone was elevated before treatment; it correlated with plasma potassium and dropped during intravenous bicarbonate administration or hemodialysis. Pretreatment plasma renin activity, insulin, epinephrine, norepinephrine, and dopamine levels were generally normal.

CONCLUSION

We conclude that in patients with terminal renal failure undergoing maintenance hemodialysis, intravenous bicarbonate is ineffective in lowering plasma potassium rapidly, and epinephrine is effective in only half the patients, whereas insulin in glucose is a fast and reliable form of therapy for hyperkalemic emergencies. Plasma aldosterone levels are appropriate in relationship to plasma potassium levels, and levels of other potassium-influencing hormones are generally normal.

The plasma potassium concentration in metabolic acidosis: a re-evaluation

The purpose of these investigations was to describe the mechanisms responsible for the change in the plasma [K] during the development and maintenance of hyperchloremic metabolic acidosis. Acute metabolic acidosis produced by HCI infusion resulted in a prompt rise in the plasma [K], whereas no change was observed during acute respiratory acidosis in the dog. After 3 to 5 days of acidosis due to NH4Cl feeding, dogs became hypokalemic; this fall in the plasma [K] was due largely to increased urine K excretion. Despite hypokalemia, aldosterone levels were not low, and the calculated transtubular [K] gradient was relatively high, suggesting renal aldosterone action. Thus, rather than anticipating hyperkalemia in patients with chronic metabolic acidosis due to a HCl load, the finding of hyperkalemia should suggest that the rate of urinary K excretion is lower than expected (ie, there are low aldosterone levels or failure of the kidney to respond to this hormone).

Role of the endocrine pancreas in the kalemic response to acute metabolic acidosis in conscious dogs

Metabolic acidosis due to organic acids infusion fails to elicit hyperkalemia. Although plasma potassium levels may rise, the increase is smaller than in mineral acid acidosis. The mechanisms responsible for the different effects of organic acid acidosis and mineral acid acidosis remain undefined, although dissimilar hormonal responses by the pancreas may explain dissimilar hormonal responses by the pancreas may explain the phenomena. To test this hypothesis, beta-hydroxybutyric acid (7 meq/kg) or hydrochloric acid (3 meq/kg) was infused over 30 min into conscious dogs (n = 12) with chronically implanted catheters in the portal, hepatic, and systemic circulation, and flow probes were placed around the portal vein and hepatic artery. Acid infusion studies in two groups of anesthetized dogs were also done to assess the urinary excretion of potassium (n = 14), and to evaluate the effects of acute suppression of renal electrolyte excretion on plasma potassium and on the release/uptake of potassium in peripheral tissues of the hindleg (n = 17). Ketoacid infusion caused hypokalemia and a significant increase in portal vein plasma insulin, from the basal level of 27 +/- 4 microU/ml to a maximum of 84 +/- 22 microU/ml at 10 min, without changes in glucagon levels. By contrast, mineral acid acidosis of similar severity resulted in hyperkalemia and did not increase portal insulin levels but enhanced portal glucagon concentration from control values of 132 +/- 25 pg/ml to 251 +/- 39 pg/ml at 40 min. A significant decrease in plasma glucose levels due to suppression of hepatic release was observed during ketoacid infusion, while no changes were observed with mineral acid infusion. Plasma flows in the portal vein and hepatic artery remained unchanged from control values in both acid infusion studies. Differences in renal potassium excretion were ruled out as determinants of the disparate kalemic responses to organic acid infusion compared with HCl acidosis. Evaluation of the arteriovenous potassium difference across the hindleg during ketoacid infusion demonstrates that peripheral uptake of potassium is unlikely to be responsible for the observed hypokalemia. Although the tissue responsible for the different kalemic responses could not be defined with certainty, the data are compatible with an hepatic role in response to alterations in the portal vein insulin and/or glucagon levels in both acid infusion studies. We propose that cellular uptake of potassium is enhanced by hyperinsulinemia in ketoacid infusion, and release of potassium results from increased glucagon levels in HCl acidosis. Whether the changes in plasma potassium that other types od organic acid acidosis produce are accounted for by a similar hormonal mechanism remains to be determined.

Natural history of lactic acidosis after grand-mal seizures. A model for the study of an anion-gap acidosis not associated with hyperkalemia

To define the time course of the metabolic acidosis that follows a single grand-mal seizure, we obtained serial blood samples from eight consecutive patients. Immediately after a seizure, the mean (+/- S.E.M.) venous lactate concentration was 12.7 +/- 1.0 meq per liter, the mean carbon dioxide content 17.1 +/- 1.1 mmol per liter, and the mean arterial pH 7.14 +/- 0.06. Sixty minutes later their values were 6.6 +/- 0.7 meq per liter (P less than 0.005), 23.6 +/- 1.1 mmol per liter (P less than 0.005) and 7.38 +/- 0.04 (P less than 0.005) respectively. The spontaneous resolution of the acidosis was due, in large part, to the metabolism of lactate and to the concomitant removal of hydrogen ion. There was no change in the serum potassium concentration, despite the development of a severe systemic acidemia and the subsequent return to normal of the pH. We suggest that the patient with seizures may serve as a unique model of lactic acidosis.

Potassium and intracellular pH

Recent work has clarified some of the complex interrelationships between cell pH and potassium. These studies have been limited by the techniques available for accurately measuring cell pH. At present it is obvious that intracellular pH is a major regulator of the cellular potassium concentration, but the precise relationship between these two is still uncertain. It has become increasingly clear, however, that no simple relationship exists between the intracellular to extracellular hydrogen ion and potassium ion ratios. Many experiments do demonstrate that the extracellular metabolic alkalosis of potassium depletion is accompanied by a decrease in skeletal muscle pH in rat, rabbit, and probably dog. The response of cardiac and renal tubular cell pH to potassium depletion is less clear, although most evidence indicates that there is also a reduction in the pH of these tissues. This effect on cell pH appears to be independent of chloride. By contrast, hyperkalemia seems to raise muscle cell pH at the same time it induces an extracellular metabolic acidosis. The metabolic and physiologic consequences of potassium-induced alterations in cell pH have yet to be fully elucidated.