THE MECHANISM OF ACIDOSIS PRODUCED BY HYPEROSMOTIC INFUSIONS

Hypertonicity: Pathophysiologic Concept and Experimental Studies

Disturbances in tonicity (effective osmolarity) are the major clinical disorders affecting cell volume. Cell shrinking secondary to hypertonicity causes severe clinical manifestations and even death. Quantitative management of hypertonic disorders is based on formulas computing the volume of hypotonic fluids required to correct a given level of hypertonicity. These formulas have limitations. The major limitation of the predictive formulas is that they represent closed system calculations and have been tested in anuric animals. Consequently, the formulas do not account for ongoing fluid losses during development or treatment of the hypertonic disorders. In addition, early comparisons of serum osmolality changes predicted by these formulas and observed in animals infused with hypertonic solutions clearly demonstrated that hypertonicity creates new intracellular solutes causing rises in serum osmolality higher than those predicted by the formulas. The mechanisms and types of intracellular solutes generated by hypertonicity and the effects of the solutes have been studied extensively in recent times. The solutes accumulated intracellularly in hypertonic states have potentially major adverse effects on the outcomes of treatment of these states. When hypertonicity was produced by the infusion of hypertonic sodium chloride solutions, the predicted and observed changes in serum sodium concentration were equal. This finding justifies the use of the predictive formulas in the management of hypernatremic states.

Hypertonicity: Pathophysiologic Concept and Experimental Studies

Disturbances in tonicity (effective osmolarity) are the major clinical disorders affecting cell volume. Cell shrinking secondary to hypertonicity causes severe clinical manifestations and even death. Quantitative management of hypertonic disorders is based on formulas computing the volume of hypotonic fluids required to correct a given level of hypertonicity. These formulas have limitations. The major limitation of the predictive formulas is that they represent closed system calculations and have been tested in anuric animals. Consequently, the formulas do not account for ongoing fluid losses during development or treatment of the hypertonic disorders. In addition, early comparisons of serum osmolality changes predicted by these formulas and observed in animals infused with hypertonic solutions clearly demonstrated that hypertonicity creates new intracellular solutes causing rises in serum osmolality higher than those predicted by the formulas. The mechanisms and types of intracellular solutes generated by hypertonicity and the effects of the solutes have been studied extensively in recent times. The solutes accumulated intracellularly in hypertonic states have potentially major adverse effects on the outcomes of treatment of these states. When hypertonicity was produced by the infusion of hypertonic sodium chloride solutions, the predicted and observed changes in serum sodium concentration were equal. This finding justifies the use of the predictive formulas in the management of hypernatremic states.

Abnormalities of serum potassium concentration in dialysis-associated hyperglycemia and their correction with insulin: a unique clinical/physiologic exercise in internal potassium balance

The absence of significant losses of potassium in the urine makes dialysis-associated hyperglycemia (DH) a model for the study of the internal potassium balance. Studies of DH have revealed that hyperkalemia is frequent at presentation, insulin infusion is usually the only treatment required, and the magnitude of the decrease in serum potassium concentration (K(+)) during treatment of DH with insulin depends on the starting serum K(+) level, the decreases in serum glucose concentration and tonicity, and the increase in serum total carbon dioxide level. We present an analysis of these findings based on previously studied actions of insulin. Calculations of transcellular potassium shifts based on the combined effects of insulin-the increase in the electrical potential differences (hyperpolarization) of the cell membranes and the correction of the hyperglycemic intracellular dehydration through decrease in serum glucose concentration-produced quantitative predictions of the decrease in serum K(+) similar to the reported changes in serum K(+) during treatment of DH with insulin. The lessons from analyzing serum K(+) changes during treatment of DH with insulin are applicable to other conditions where internal potassium balance is called upon to protect serum K(+), such as the postprandial state. The main questions related to internal potassium balance in DH that await clarification include the structure and function of cell membrane potassium channels, the effect of insulin on these channels, and the mechanisms of feedforward potassium regulation.

[Hyperchloremic acidosis druing plasma volume replacement]

OBJECTIVES

Review of the physiological and clinical consequences of hyperchloraemic acidosis observed during plasma volume replacement using crystalloids and colloids.

DATA SOURCES

Data were searched in the Medline database after 1990 using the following key words: metabolic acidosis, crystalloids, colloids, albumin, gelatin, hydroxyethyl starch.

DATA EXTRACTION

Publications before 1990 were selected for their historical value. Most of articles published after 1990 and all types including case report were accepted.

DATA SYNTHESIS

Large volume infusion of isotonic solution can cause hyperchloraemic acidosis. Colloid plasma substitutes using saline solvent may be responsible for the same kind of acidosis with acidaemia. The anion gap is not modified in this case because of chloride increase. Physiological mechanism may be described using the Henderson-Hasselbach equation or the strong ion difference decrease (Stewart concept). Excessive chloride infusion is a major factor in this acid-base disorder and the term hyperchloraemic acidosis should be preferred to dilutional acidosis. When perioperative acidosis occurs, careful and complete analysis of acid-base disturbance should be made. The association of a normal anion gap, normal lactatemia, hyperchloraemia and acidaemia does not need specific treatment. Acidosis corrects spontaneously and slowly following chloride normalization. But any factor that may increase acidosis should be avoided.

CONCLUSION

The use of balanced solution like lactated-Ringer solution instead of isotonic saline solution for fluid resuscitation, except for specific contra-indication as intracranial hypertension, may avoid hyperchloraemic acidosis. Potential risk of this acidosis led to the conception of a new colloid using balanced crystalloids solution as the solvent (Hextend).

Anesthetic formulation of tumescent solutions

There is no standard or official recipe for the tumescent anesthetic solutions. The actual concentrations of lidocaine and epinephrine should depend on the areas to be treated and clinical situation. This article discusses the safe usage of tumescent solutions and the proper procedures and precautions to take when mixing these solutions.

An evidence-based evaluation of the use of sodium bicarbonate during cardiopulmonary resuscitation

The use of bicarbonate is rooted in three decades of clinical experience and observational studies. For many years, bicarbonate passed the tried and true test for clinical therapies; however, administration of sodium bicarbonate during cardiac arrest and hypoxic acidosis has become increasingly controversial. The controversy provides an excellent opportunity to evaluate the impact an evidence-based approach might have on a common clinical practice. Is bicarbonate efficacious in the treatment of the severe acidosis that accompanies cardiac arrest during cardiopulmonary resuscitation (CPR)? Are the deleterious effects of bicarbonate clinically relevant? What is the evidence upon which a rational decision may be based? This review evaluates and ranks the evidence supporting the use of sodium bicarbonate in the therapy of acidosis associated with cardiac arrest during CPR.

Osmotherapy. Basic concepts and controversies

Osmotherapy with compounds such as mannitol has become a mainstay of neurologic and neurosurgical intensive care. Elevated intracranial pressure is the most common indication. A substantive debate remains as to the appropriate timing of administration and the optimal fluid management protocol, and experts disagree about the clinically relevant mechanisms of action of osmotic diuretics. This article briefly summarizes the basic literature on the physical actions of mannitol, addresses commonly asked questions, and highlights some of the controversies that arise at the bedside.

Reduction of post-traumatic intracranial hypertension by hypertonic/hyperoncotic saline/dextran and hypertonic mannitol

Cerebral injury is seen in one of three patients with multiple traumas; thus efficient shock treatment is a most important measure against the development of secondary brain damage. Small-volume resuscitation in severe hemorrhagic shock by hypertonic/hyperoncotic saline/dextran has been shown to instantaneously normalize cardiac output and to raise systemic blood pressure. In this study, the fluid regimen was compared with hypertonic mannitol to investigate their therapeutic efficacy in intracranial hypertension. The experiments were performed in rabbits subjected to a focal lesion of the brain to induce acute, vasogenic brain edema. The resulting intracranial hypertension was enhanced in a standard manner by inflation of an epidural balloon until an intracranial pressure (ICP) of 17 mm Hg was obtained. Intravenous administration of either 7.2% saline/10% dextran-60 or of 20% mannitol rapidly decreased the elevated ICP. After the first injection, ICP lowering was maintained longer by the mannitol than by the hypertonic saline/dextran, whereas no differences in duration of ICP lowering were found when the infusions of these solutions were repeated. The systemic blood pressure increased after injection of the saline/dextran solution, but it tended to decrease after injection of the mannitol. Transient increases in plasma osmolality, colloid-osmotic pressure, and plasma-Na+ were more pronounced after administration of the saline/dextran solution than after the administration of the mannitol. No difference in the tissue water content between the traumatized and contralateral hemisphere was observed in the animals receiving mannitol; however, after saline/dextran infusion, the water content was somewhat increased in the exposed hemisphere but decreased in the nonexposed, contralateral hemisphere (decreased to a point even below the corresponding level of animals who received the mannitol). The increase of the cerebral water content of the traumatized hemisphere was associated with a respective increase of the cerebral Na+ content and a (nonsignificant) decrease of the K+ content. The present findings demonstrate that the hypertonic/hyperoncotic saline/dextran was as efficient as the mannitol in reducing ICP that had been increased by a cerebral lesion and a space-occupying mass; the underlying mechanisms responsible for the reduction might differ. Because of the powerful hemodynamic properties of the saline/dextran in circulatory shock, administration of the solution in patients with multiple traumas and head injury might be particularly advantageous for the prevention of secondary ischemic brain damage.

Hypertonic saline infusion induces activation of the lymphocyte Na+/H+ antiport and cytosolic alkalinization in healthy human subjects

The Na+/H+ antiport is a membrane transport protein that extrudes intracellular protons in exchange for extracellular sodium. Some details of its physiological and pathophysiological role remain poorly defined. Experimental evidence suggests that the antiporter is involved in the regulation of cell volume. In the present study, we therefore investigated the activity of the lymphocyte Na+/H+ antiport in nine healthy volunteers following acute hypertonic (2.5%) saline infusion (4 mmol NaCl/kg over 120 min). Antiport activity was measured after acidifying the cells with Na+ propionate (5-40 mM) using the fluorescent dye bis-carboxyethyl carboxyfluorescein. Hypertonic saline induced significant increases in plasma osmolality (308.4 +/- 2.3 vs. 293.5 +/- 2.7 mOsm/kg; P < 0.01), serum Na+ (150.8 +/- 3.7 vs. 138.9 +/- 0.5 mmol/kg; P < 0.01), and Cl- concentrations (118.0 +/- 3.9 vs. 101.1 +/- 1.0 mmol/kg; P < 0.01). Extracellular hypertonicity was followed by a stimulated activity of the lymphocyte Na+/H+ antiport with an increase in the apparent Vmax values from 2.44 +/- 0.16 to 3.27 +/- 0.34 10(-3) s-1 (P < 0.01) and a slight rise in pK, from 6.81 +/- 0.03 to 6.87 +/- 0.03 (P < 0.05) after hypertonic saline. In addition to antiport activation, cytosolic alkalinization was observed with cytosolic pH values averaging 6.90 +/- 0.02 before and 6.99 +/- 0.02 (P < 0.01) after hypertonic saline. Our results show for the first time that acute extracellular hypertonicity in man due to hypertonic NaCl loading is associated with a stimulated lymphocyte Na+/H+ antiport activity and cytosolic alkalinization.

Acid-base disturbance and ventilatory response to changes in plasma osmolality in Pekin ducks

The effects of acute changes in plasma osmolality on blood acid-base status and ventilation were investigated in the Pekin duck, Anas platyrhynchos. Hyperosmolality due to intravenous infusion of hypertonic NaCl or sucrose caused a prolonged acidosis (so-called dilution acidosis), which was attributable to a decrease in estimated strong ion difference due to a fall in the plasma [Na+]:[Cl-] ratio. Ventilation did not increase in response to the acidosis, and was actually depressed in some birds. PaCO2 increased by 3.5 +/- 1.5 Torr and PaO2 decreased by 4 +/- 2 Torr over the 2 h experimental period in all animals. It is suggested that the extracellular acidosis due to hyperosmolality is accompanied by an intracellular alkalosis which may suppress chemoreceptor stimulation, resulting in no ventilatory increase. Hyposmolality had no effect on acid-base status or respiration.

Acute increase in plasma osmolality as a cause of hyperkalemia in patients with renal failure

These studies were performed in patients with chronic renal failure to understand the mechanism(s) of hyperkalemia secondary to hypertonic NaCl infusion. In 10 patients, after intravenous infusion of either 5% or 2.5% NaCl (6 mEq per kg body wt for 120 minutes in both solutions), the maximum increase in plasma potassium averaged 0.6 (range 0.3 to 1.3) mmol/liter (P less than 0.01) or 0.3 (range 0.2 to 0.6) mmol/liter (P less than 0.01), respectively. The rise of both plasma potassium and osmolality was significantly higher during 5% NaCl than during 2.5% NaCl infusion (P less than 0.01). A significant linear correlation (P less than 0.01) between plasma potassium and osmolality was observed. Urinary potassium excretion was increased to a similar extent by 5% NaCl and 2.5% NaCl infusion. The observed hyperkalemia, secondary to NaCl infusion, was independent of venous pH, plasma bicarbonate, anion gap, insulin levels, and urinary norepinephrine and epinephrine excretion, and was associated with a fall in plasma aldosterone concentration. In separate studies, nine patients were treated with desoxycorticosterone acetate (DOCA; 20 mg i.m. for three days) before receiving saline (5%) infusion. DOCA did not prevent the level increase in plasma potassium that remained significantly correlated with plasma osmolality (P less than 0.01). In conclusion, hypertonic NaCl infusion in patients with renal failure causes a clinically relevant hyperkalemia despite increased renal excretion of potassium. This hyperkalemia is independent of acid-base or hormonal mechanisms known to regulate extrarenal homeostasis of potassium, and is strictly correlated with a rise in plasma osmolality.

The effect of high-dose mannitol on serum and urine electrolytes and osmolality in neurosurgical patients

The effect of mannitol on serum and urine electrolytes and osmolality was investigated intraoperatively in neurosurgical patients. Patients in Group A (n = 7) received 1 gm . kg-1 of 20 per cent mannitol ("low"-dose) and in Group B, (n = 7) 2 gm . kg-1 ("high"-dose). There was a significant decrease in serum sodium and bicarbonate, and a significant increase in serum osmolality in both groups after mannitol administration. The decrease in serum sodium and the increase in serum osmolality were significantly greater in patients receiving the larger dose of mannitol. The infusion of low-dose mannitol resulted in a slight decrease in serum potassium. In contrast, after high-dose mannitol there was a significant rise in serum potassium reaching a maximum mean increase of 1.5 mmol . l-1. Urine electrolyte concentration and osmolality showed a similar decrease in both groups. The significant changes that occurred with the administration of mannitol were of short duration in these patients with normal cardiac and renal function. The clinically most important change is the increase in serum potassium with high-dose mannitol. The exact mechanism of this increase remains unclear.

Non-radioisotopic estimate of body water and its spaces in hypertonic expansion

Mathematically rigorous formulae of apparent sodium volume of distribution for body water and of stable sodium chloride space for extracellular volume were derived and applied to data from five anuric dogs infused with hypertonic saline. The error of the formula used in the past to compute apparent sodium volume of distribution was also computed and the errors introduced in the calculation of sodium chloride space by the experimental methods applied were corrected. Apparent sodium volume of distribution, computed from a correct formula, is a measure of body water and corrected estimates of sodium chloride space agree with radio-sulphate space estimates of extracellular volume.

Studies in acid-base balance. I. Effect of alkali therapy in newborn dogs with mechanically fixed ventilation

The effect of rapid or slow infusion of hypertonic sodium bicarbonate on acid-base balance and serum osmolality was studied in 36 acidotic newborn dogs. Respiratory acidosis and hypoxia were produced by mechanically fixed hypoventilation. One group of animals breathed 100% O2 to prevent hypoxemia. Rapid infusion of HCO3- in acidotic and hypoxic animals resulted in only a transient (1 minute) and small (0.05 pH units) elevation of arterial pH followed by a continuous fall, resulting in a lower pH and a worsened metabolic condition than in the nontreated controls. In nonhypoxic acidotic animals, rapid infusion of HCO3- had little effect on arterial pH. PaCO2 increased suddenly by 17 Torr in hypoxic and, by 13 Torr, in nonhypoxic animals. There was a concomitant fall in PaO2 (15 Torr). Serum osmolality rose rapidly after rapid infusion of HCO3-. Rapid infusion of hypertonic bicarbonate into an animal or infant whose ventilation is fixed thus results in a less than predicted elevation of arterial pH. PaCO2 rises, PaO2 falls, and serum osmolality rises. The net result may be a worsening rather than an improvement in the animals' metabolic state.

The effects of single infusion of hypertonic sodium bicarbonate on body composition in neonates with acidosis

Acid-base equilibrium and plasma and red blood cell water and solute were evaluated in a group of asphyxiated, acidotic neonates prior to and following infusion of hypertonic NaHCO3. The dose was calculated to correct the deficit of base in a bicarbonate space of 400 ml/kg and was given at a rate of 0.3 mM NaHCO3/kg/minute. All of the infants with RDS and two of the five with other forms of asphyxia received ventilatory assistance during the infusion. The quantity of base infused was sufficient to alter acid-base balance and shift whole blood and red blood cell pH values toward normal. The changes in body composition 3 minutes following the infusion indicate that the osmotic load imposed by the hypertonic NaHCO3 caused a shift of solute-free water into the interstitial and intravascular fluids. During the period from 3 to 30 minutes following the infusion there was redistribution of extracellular water and solute so that plasma volume and [Na]PL decreased. Since there was no evidence of an intracellular shift of solute, we hypothesize that the changes in body composition between 3 and 30 minutes postinfusion were in part the consequence of gradual penetration of transcellular fluids by Na. Osmotic inactivation of ECF Na by sequestration with connective tissue polyelectrolytes may also play a role. These studies' do not provide an answer to the clinical problem of whether the beneficial effects of prompt correction metabolic acidosis outweigh the potenially harmful effect of the osmotic alterations that accompany rapid infusion of hypertonic NaHCO3.

The effect of fructose infusions in the course of labor upon parturient and fetus

Fructose infusions were administered to parturients with healthy term fetuses at a speed of 1 g/min for 106 on the average. The results confirm that fructose has the expected properties. The blood glucose and FFA levels show that a substantial part of the infused fructose is indeed stored and that only a small portion is used to cover immediate energy needs. This positive result is predominant by a considerable degree of acidosis arising in the parturient in spite of the fact that fructose was infused at a slower rate than in the majority of papers published so far. Since the fructose infusions were intended for premature fetuses, which already have an increased tendency toward acidosis, the results confirm the unsuitability of such a treatment.

Arterial and mixed venous PCO2 and hydrogen ion, bicarbonate and base excess concentrations in water-depleted dogs

The arterial (a), mixed venous (v), and arterial-mixed venous differences (A-V) of hydrogen ion concentration ([H+]), PCO2, HCO-3 and base excess (BE) were measured during 3 h in control (C), water-depleted (WD) and water- and salt-depleted (WSD) dogs. In WD animals the difference in hydrogen ion concentration between venous and arterial blood increased because the [H+] increased more in venous than in arterial blood. In WSD animals (A-V) [H+] remained unchanged since both [H+]a and [H+]v increases were parallel. [H+] variations seem to represent the changes in fixed-acid concentration of blood. The difference between both groups of animals in (A-V) [H+] changes could be ascribed to PCO2 variations. [HCO-3] values changed inconsistently. Arterial samples from the experimental groups showed a continuous decrease at the same rate of change. The mean values in WSD were lower than in WD. [HCO-3]v of WSD decreased slowly during the experiment. The rate of decrease of (A-V) [HCO-3] was higher in WD than in WSD. The different behavior of of [HCO-3] between both arterial and mixed venous samples and among experimental groups disappeared if [HCO-3] changes were corrected for bicarbonate generation due to PCO2 variation (respiratory bicarbonate). Thus [HCO-3] corrected for PCO2 variation represents metabolic changes, in good agreement with both [H+] and BE variations. The metabolic acidosis cannot be explained only on the basis of the increase in blood lactate; it is suggested that other fixed acids might contribute to the decrease in blood bicarbonate. In both experimental groups PvCO2 increased continuously. The (A-V) PCO2 showed the same rate of change. There is a good relationship between this increase and the degree of plasma volume change. It therefore might be that PvCO2 increase is a direct consequence of hemodynamic impairment. In WD and WSD, BE decreased progressively in both arterial and mixed venous samples. BEa values were lower than BEv values after the experiment began. (A-V) BE decreased in an exponential manner in both experimental groups; this change could be ascribed to the increased level of deoxygenated hemoglobin in mixed venous blood, thus giving rise to a decrease in fixed acid concentration.

Rapid infusion of sodium bicarbonate and albumin into high-risk premature infants soon after birth: a controlled, prospective trial

We conducted a controlled, prospective trial to evaluate the effectiveness of rapidly infusing sodium bicarbonate (NaHCO3) and salt-poor albumin into high-risk, premature infants in the first 2 hours of life. Fifty-three infants, randomized into one of four treatment groups, received 8 ml. per kilogram of a solution containing either (A) glucose in water, (B) salt-poor albumin, (C) NaHCO3, or (D) a combination of albumin and NaHCO3. After the initial infusion, the babies received no colloid or alkali solutions until 4 hours of age. We managed them supportively with warmth, appropriate oxygen administration, isotonic fluid infusion, and close monitoring. Among the infants who received alkali, 14 of 26 acquired the respiratory distress syndrome (RDS), 11 died, and four had intracranial hemorrhage. Among babies who received no alkali, RDS occurred in 11 of 27, 5 died, and none had intracranial hemorrhage. These results do not support the common practice of rapidly infusing NaHCO3 into high-risk, premature infants, and they suggest that the early management of such infants needs renewed critical evaluation.

The pH and titratable acidity of intravenous infusion solutions

The acidic nature of infusion solutions may contribute to local thrombophlebitis or systemic acidosis. The pH of four commercially available solutions ranged from 4·55 to 6·40 and titratable acidities (to pH 7·4) ranged from 0·18 to 1·08 meq acid/litre. When equilibrated in vitro at PCO2of 40 mm Hg the pH ranged from 4·5 to 6·0 and titratable acidity ranged from 20 to 26 meq acid/litre. Two solutions prepared from commercial solutions and containing 28 meq/litre sodium bicarbonate had a pH of 7·5 and a titratable acidity of 4–5 meq base/litre when equilibrated at a PCO2of 40 mm Hg. Systemic acidosis due to some infusions may be prevented by the addition of sodium bicarbonate to the infusion solutions to produce a pH of 7·4 at PCO2of 40 mm Hg.

Biochemical changes associated with the use of haemodilution with 5 per cent dextrose in water and mannitol for open-heart surgery

Many advantages are gained from the use of haemodilution in open-heart surgery. There is a lessened post-operative morbidity from bleeding, renal failure, and serum hepatitis. However, dilution with 5% dextrose in water is associated with a greater metabolic acidosis and a higher incidence of serious dysrhythmias than is pure blood. In order to elucidate the causes of these complications, 26 patients were studied using different degrees of haemodilution. The metabolic acidosis appeared to be mainly due to the dilution of blood buffer. Changes in electrolyte balance were more marked with greater dilution. The effects on serum sodium and chlorides were transient. The serum potassium level fell markedly during the post-operative phase and was associated with dysrhythmias. We believe that variation in potassium concentration is due to redistribution of potassium between the intracellular and extracellular phase as well as to an increased urinary excretion of potassium. The acidosis and hypokalaemia can be rapidly corrected by the administration of sodium bicarbonate and potassium. The changes in acid-base metabolism and electrolyte balance can possibly be prevented by suitably modifying the priming fluid.