Lactic acidosis: current concepts

Lactic Acidosis: An Update

Lactic acidosis is an etiologically and biochemically heterogeneous disorder that is due to the overproduc tion of lactic acid or the underutilization of lactate. It occurs with disorders in which tissue oxygenation is impaired (Type A) and with disorders in which it is not (Type B). Lactic acidosis is an anion-gap metabolic acidosis in which the lactate concentration is greater than or equal to 5 mM and the systemic pH is less than 7.30. Treatment is largely empiric and generally unsatis factory. The use of sodium bicarbonate in lactic acidosis is currently controversial. The adverse effects of bicar bonate and the beneficial effects of dichloroacetate in experimental models of lactic acidosis are reviewed.

Type B lactic acidosis and insulin-resistant hyperglycemia in an adolescent following cardiac surgery

OBJECTIVE

To report the presence of type B lactic acidosis and insulin-resistant hyperglycemia following cardiopulmonary bypass in a pediatric patient.

DESIGN

Case report.

SETTING

Tertiary referral children's hospital pediatric intensive care unit.

PATIENT

Fourteen-year-old child with hyperlactatemia and hyperglycemia following cardiac surgery.

INTERVENTIONS AND RESULTS

We report a patient who following cardiopulmonary bypass for repair of his congenital heart disease developed type B lactic acidosis and hyperglycemia resistant to insulin therapy. Resolution of his hyperlactatemia and hyperglycemia occurred approximately 24 hrs postoperatively without apparent ill effect.

CONCLUSIONS

Type B lactic acidosis is a phenomenon that may occur in the pediatric population in conjunction with insulin-resistant hyperglycemia. We observed that its resolution corresponded to improvement in the patient's hyperglycemia.

Blood lactate: biochemistry, laboratory methods, and clinical interpretation

With the renewed awareness of blood lactate as an indicator of circulatory impairment, there has been much interest in the use of lactate measurements to determine the overall state of oxygenation of patients in critical care. This review begins by covering the areas of lactate homeostasis and biochemistry, both of which are essential for fully understanding the interpretation of lactate measurements. Then, the clinical interpretation of lactate measurements includes sections on the causes and treatments of hemodynamic deficits leading to lactic acidosis, the classification of lactate abnormalities, and the use of lactate measurements in critical care monitoring, including surgery. Both the principles and the latest developments in lactate methodology are covered, including the new whole blood analyzers. This review concludes with reference intervals and guidelines to the interpretation of results.

Metabolic and neurologic effects of an intravenous medium-chain triglyceride emulsion

These studies were undertaken to investigate the relationship between medium-chain fatty acid availability, medium-chain fatty acid oxidation, and central nervous system toxicity during infusion of medium-chain triglycerides in dogs. Six dogs received a sequential, stepwise infusion of trioctanoin at three different rates for 80 min each, providing calories below and equal to resting energy expenditure in the species. Ketone body production rates (using a 14C beta-hydroxybutyrate tracer) and plasma concentrations of lactate and octanoate were monitored. Three animals were infused with saline to serve as controls. Blood-brain barrier integrity was assessed with Evans blue dye, and brain samples were taken at the end of the study to quantify brain water. Three animals were studied under anesthesia to obtain good quality EEG and intracranial pressure measurements. Results were (1) plasma octanoate increased to 0.37 +/- 0.13, 0.78 +/- 0.2, and 1.44 +/- 0.41 mmol/liter during the three infusion intervals; (2) emesis, somnolence, and coma were observed at the two highest trioctanoin rates; (3) ketone body concentrations and production increased from 102 +/- 15 to 859 +/- 54 mumol/liter and 3.6 +/- 0.43 to 18.5 +/- 1.7 mumol/kg/min, respectively, at the highest trioctanoin infusion rate; and (4) plasma lactate also increased from 1.3 +/- 0.1 to 4.3 +/- 0.9 mmol/liter at the highest infusion rate. EEG changes were also observed, consisting of high amplitude slowing and reduction in amplitude of faster components. There was no extravasation of Evans blue dye, nor change in brain water or intracranial pressure. The conclusion--medium-chain triglycerides have significant dose-related central nervous system toxicity in dogs. Therefore, caution should be exercised in clinical studies with MCTs, including careful measurement of medium-chain fatty acid concentrations.

The pharmacology of dichloroacetate

Dichloroacetate (DCA) exerts multiple effects on pathways of intermediary metabolism. It stimulates peripheral glucose utilization and inhibits gluconeogeneis, thereby reducing hyperglycemia in animals and humans with diabetes mellitus. It inhibits lipogenesis and cholesterolgenesis, thereby decreasing circulating lipid and lipoprotein levels in short-term studies in patients with acquired or hereditary disorders of lipoprotein metabolism. By stimulating the activity of pyruvate dehydrogenase, DCA facilitates oxidation of lactate and decreases morbidity in acquired and congenital forms of lactic acidosis. The drug improves cardiac output and left ventricular mechanical efficiency under conditions of myocardial ischemia or failure, probably by facilitating myocardial metabolism of carbohydrate and lactate as opposed to fat. DCA may also enhance regional lactate removal and restoration of brain function in experimental states of cerebral ischemia. DCA appears to inhibit its own metabolism, which may influence the duration of its pharmacologic actions and lead to toxicity. DCA can cause a reversible peripheral neuropathy that may be related to thiamine deficiency and may be ameliorated or prevented with thiamine supplementation. Other toxic effects of DCA may be species-specific and reflect marked interspecies variation in pharmacokinetics. Despite its potential toxicity and limited clinical experience, DCA and its derivatives may prove to be useful in probing regulatory aspects of intermediary metabolism and in the acute or chronic treatment of several metabolic disorders.

Metabolic and hemodynamic consequences of sodium bicarbonate administration in patients with heart disease

PURPOSE

The use of sodium bicarbonate (NaHCO3) in cardiopulmonary arrest has been questioned, but the effects of NaHCO3 in patients with heart disease are not known. We therefore prospectively evaluated the effects of NaHCO3 in patients with congestive heart failure.

PATIENTS AND METHODS

Ten patients received NaHCO3 and control infusions of equimolar sodium chloride (NaCl). Measurements were made of blood gases, 2,3-diphosphoglyceric acid (2,3-DPG), glucose, lactate, cardiac hemodynamics, and oxygen consumption.

RESULTS

The arterial oxygen tension (pO2) fell an average of 10 mm Hg after NaHCO3 administration in patients with congestive heart failure, whereas it rose with NaCl (p less than 0.005). Myocardial oxygen consumption decreased by 17% (p less than 0.002) without an accompanying change in oxygen demand. Systemic oxygen consumption fell by 21%. Red blood cell 2,3-DPG levels were elevated at baseline, but did not change with NaHCO3 administration. The oxygen pressure at 50% hemoglobin saturation (P50) was correspondingly elevated at baseline in these patients and decreased significantly with NaHCO3 (Bohr effect) (p less than 0.003). The arterial and mixed venous carbon dioxide tensions increased with NaHCO3 but decreased with NaCl administration (p less than 0.05). Blood glucose concentrations fell by 1.7 mmol/L with NaHCO3 (p less than 0.003) and blood lactate concentrations increased uniformly (p less than 0.001). Three patients developed net myocardial lactate generation during NaHCO3 administration; two of these three developed symptoms of angina. Coronary blood flow did not change with NaHCO3 but increased with NaCl (p less than 0.04). Two patients developed transient pump failure.

CONCLUSION

These data demonstrate that NaHCO3 impairs arterial oxygenation and reduces systemic and myocardial oxygen consumption. The decrease in oxygen utilization is associated with anaerobic metabolism, enhanced glycolysis, and elevation of the blood lactate level, and may lead to transient myocardial ischemia in some patients. Thus, the use of NaHCO3 in such patients warrants re-evaluation.

Post-convulsive lactic acidosis in diabetic patients

Diabetic patients have an increased risk of developing epileptic convulsions compared with the non-diabetic population. Generalised seizures may cause a severe, but self-correcting, lactic acidosis for which specific treatment is both unnecessary and potentially hazardous. Two cases of post-convulsive lactic acidosis occurring in diabetic patients are reported. The cause of the acidosis was confirmed only in retrospect in each case.

Pathophysiology of type A hypoxic lactic acidosis in dogs

Hypoxic lactic acidosis (HLA) was induced in dogs by ventilating them with a hypoxic gas mixture of 8% O2-92% N2. The animals were studied both in the control state and after development of HLA, where arterial lactate was above 5 mM, pH was below 7.2, bicarbonate was below 12 mM, and arterial PO2 was between 26 and 30 Torr. After hypoxia had been present for 90 min, most of the increase in arterial lactate vs. control was due to increased lactate production from gut and carcass in the presence of a decreased capacity of the liver to extract lactate. The capacity of the liver to extract lactate in the normoxic state was evaluated in another group of six dogs after infusion of L-lactic acid such that arterial pH, lactate, and bicarbonate were similar to hypoxic values. In these experiments it was found that the capacity of the liver to extract lactate was 14.8 +/- 1.7% of the delivered load vs. 4.9 +/- 1.3% observed in hypoxic animals. The decreased liver lactate extraction in HLA was probably secondary to both a decrease in liver oxygen uptake and a decrease in liver intracellular pH and was paralleled by an increase in liver tissue lactate levels. Cardiac output, in contrast to other forms of lactic acidosis, was increased by 40% vs. control and femoral artery flow by 35%, whereas liver blood flow was unchanged and renal blood flow decreased. Hypoxic lactic acidosis thus is the consequence of overproduction of lactate by both gut and carcass, in the presence of impaired utilization of lactate by the liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Bicarbonate haemodialysis: an adequate treatment for lactic acidosis in diabetics treated by metformin

Lactic acidosis in diabetics on metformin therapy is rare but still associated with poor prognosis. The authors report here five cases. Three patients were initially with a cardiovascular collapse and all had an acute renal failure. Sodium bicarbonate haemodialysis therapy led to a dramatic improvement. Consciousness and hemodynamic status recovered rapidly. Severe metabolic and blood gases derangements were also rapidly corrected. Plasma metformin removal, appreciated by repeated blood samplings in 3 cases, was satisfactory. All patients survived. However, blood metformin levels remained abnormally high at the end of the dialytic therapy. In conclusion, (1) bicarbonate dialysis is an adequate treatment of lactic acidosis observed in diabetic patients treated with metformin since it rapidly corrects the acid-base disorders and partially removes metformin; (2) the sole accumulation of metformin is not sufficient to explain lactic acidosis since this latter might be corrected in spite of persisting high levels of blood metformin.

Lactic acidosis as a predictor of downtime during cardiopulmonary arrest in dogs

Studies have shown that over 50% of cardiovascular deaths occur before hospitalization. A major factor associated with survival in cases of out-of-hospital cardiac arrest is the time from cardiovascular collapse to the initiation of cardiopulmonary resuscitation (CPR) or "downtime." The purpose of this study was to determine whether blood lactate levels could be used to predict downtime in the canine cardiac arrest model. Femoral arterial and Swan-Ganz catheters were placed in 22 mongrel dogs, and ventricular fibrillation was electrically induced. The dogs remained in ventricular fibrillation without ventilation for 5, 10, 15, 30, or 60 minutes. After the predetermined fibrillation time, a left anterolateral thoracotomy was performed, and open-chest cardiac massage was begun. Arterial and mixed venous lactate levels were determined for every 5 minutes during 30 minutes of cardiopulmonary resuscitation. The correlation coefficient between the mixed venous and arterial lactate levels was 0.96 or greater during all stages of resuscitation. Peak serum lactate level increased linearly in relation to downtime. The increase in lactate level was not evident until after CPR was begun, and it remained at peak levels or decreased insignificantly, despite optimal open-chest CPR. Linear regression analysis revealed that 84% of the variability in serum lactate levels could be explained by downtime differences. In this model, blood lactate level is a reliable and objective measure of downtime and may be a useful indicator of the adequacy of CPR if levels decrease or remain stable. The clinical implications of this study lie with the use of blood lactate levels in the emergency department to guide the aggressiveness of resuscitative efforts.

Metabolic effects of bicarbonate in the treatment of diabetic ketoacidosis

The effect of intravenous bicarbonate on the changes in intermediary metabolites during the initial treatment of diabetic ketoacidosis was examined in 16 patients. The results were compared with the changes seen in 16 patients receiving intravenous saline. Infusion of 150 mmol (mEq) bicarbonate significantly delayed the fall in blood lactate, lactate:pyruvate ratio, and total ketone bodies observed in the saline treated group. No difference in the rate of fall of blood glucose concentration was found. There is no metabolic indication for the use of intravenous bicarbonate in the treatment of diabetic ketoacidosis.