Lactic acidosis and the cardiovascular system in the dog

Biguanides Metformin and Phenformin Generate Therapeutic Effects via AMP-Activated Protein Kinase/Extracellular-Regulated Kinase Pathways in an In Vitro Model of Graves' Orbitopathy

BACKGROUND

It was hypothesized that the biguanides metformin and phenformin, which are anti-hyperglycemic drugs used for diabetes mellitus, would have therapeutic effects in an in vitro model of Graves' orbitopathy (GO). Because adipogenesis, hyaluronan production, and inflammation are considered important in the pathogenesis of GO, this study aimed to determine the therapeutic effects and underlying mechanisms of biguanides on these parameters.

METHODS

In vitro experiments were performed using primary cultured orbital fibroblasts from patients with GO. Orbital preadipocyte fibroblasts were allowed to differentiate into adipocytes and were treated with various concentrations of metformin or phenformin. Oil Red O staining was performed to evaluate lipid accumulation within the cells. Western blot analysis was used to measure the expression of adipogenic transcription factors and the phosphorylation of AMP-activated protein kinase and mitogen-activated protein kinase signaling proteins. Hyaluronan production was measured using enzyme-linked immunosorbent assay, and mRNA levels of proinflammatory molecules were determined using real-time polymerase chain reaction after interleukin (IL)-1β stimulation with or without biguanide treatment.

RESULTS

Lipid accumulation during adipogenesis in GO orbital fibroblasts was dose-dependently suppressed by both metformin and phenformin. Adipocyte differentiation was attenuated, and the adipogenic transcription factors peroxisome proliferator-activated receptor γ and CCAAT-enhancer-binding proteins-α/β were downregulated. Furthermore, metformin and phenformin increased the phosphorylation of AMP-activated protein kinase and suppressed extracellular-regulated kinase activation. The IL-1β-induced hyaluronan production and mRNA expression of IL-6, cyclooxygenase-2, and intercellular adhesion molecule-1 were also significantly suppressed after metformin or phenformin co-treatment.

CONCLUSIONS

The present study indicates that the biguanides metformin and phenformin exert an anti-adipogenic and inhibitory effect on hyaluronan production and expression of pro-inflammatory molecules in GO orbital fibroblasts, suggesting that they could potentially be used for the treatment of GO.

Association between mortality and replacement solution bicarbonate concentration in continuous renal replacement therapy: A propensity-matched cohort study

BACKGROUND

Given the known deleterious effects seen with bicarbonate supplementation for acidemia, we hypothesized that utilizing high bicarbonate concentration replacement solution in continuous venovenous hemofiltration (CVVH) would be independently associated with higher mortality.

METHODS

In a propensity score-matched historical cohort study conducted at a single tertiary care center from December 9, 2006, through December 31, 2009, a total of 287consecutive adult critically ill patients with Stage III acute kidney injury (AKI) requiring CVVH were enrolled. We excluded patients on maintenance dialysis, those who received other modalities of continuous renal replacement therapies, and patients that received a mixed of 22 and 32 mEq/L bicarbonate solution pre- and post-filter. The primary outcome was in-hospital and 90-day mortality rates.

RESULTS

Among enrollees, 68 were used 32 mEq/L bicarbonate solution, and 219 received 22mEq/L bicarbonate solution for CVVH. Patients on 32 mEq/L bicarbonate solution were more often non-surgical, had lower pH and bicarbonate level but had higher blood potassium and phosphorus levels in comparison with those on 22 mEq/L bicarbonate solution. After adjustment for the baseline characteristics, the use of 32 bicarbonate solution was significantly associated with increased in-hospital (HR = 1.94; 95% CI 1.02-3.79) and 90-day mortality (HR = 1.50; 95% CI 1.03-2.14). There was a significant increase in the hospital (p = .03) and 90-day (p = .04) mortality between the 22 vs. 32 mEq/L bicarbonate solution groups following propensity matching.

CONCLUSION

Our data showed there is a strong association between using high bicarbonate solution and mortality independent of severity of illness and comorbid conditions. These findings need to be evaluated further in prospective studies.

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.

Severe metabolic or mixed acidemia on intensive care unit admission: incidence, prognosis and administration of buffer therapy. A prospective, multiple-center study

Introduction

In this study, we sought describe the incidence and outcomes of severe metabolic or mixed acidemia in critically ill patients as well as the use of sodium bicarbonate therapy to treat these illnesses.

Methods

We conducted a prospective, observational, multiple-center study. Consecutive patients who presented with severe acidemia, defined herein as plasma pH below 7.20, were screened. The incidence, sodium bicarbonate prescription and outcomes of either metabolic or mixed severe acidemia were analyzed.

Results

Among 2, 550 critically ill patients, 200 (8%) presented with severe acidemia, and 155 (6% of the total admissions) met the inclusion criteria. Almost all patients needed mechanical ventilation and vasopressors during their ICU stay, and 20% of them required renal replacement therapy within the first 24 hours of their ICU stay. Severe metabolic or mixed acidemia was associated with a mortality rate of 57% in the ICU. Delay of acidemia recovery as opposed to initial pH value was associated with increased mortality in the ICU. The type of acidemia did not influence the decision to administer sodium bicarbonate.

Conclusions

The incidence of severe metabolic or mixed acidemia in critically ill patients was 6% in the present study, and it was associated with a 57% mortality rate in the ICU. In contradistinction with the initial acid-base parameters, the rapidity of acidemia recovery was an independent risk factor for mortality. Sodium bicarbonate prescription was very heterogeneous between ICUs. Further studies assessing specific treatments may be of interest in this population.

Lactic acidosis induced by metformin: incidence, management and prevention

Lactic acidosis associated with metformin treatment is a rare but important adverse event, and unravelling the problem is critical. First, this potential event still influences treatment strategies in type 2 diabetes mellitus, particularly in the many patients at risk of kidney failure, in those presenting contraindications to metformin and in the elderly. Second, the relationship between metformin and lactic acidosis is complex, since use of the drug may be causal, co-responsible or coincidental. The present review is divided into three parts, dealing with the incidence, management and prevention of lactic acidosis occurring during metformin treatment. In terms of incidence, the objective of this article is to counter the conventional view of the link between metformin and lactic acidosis, according to which metformin-associated lactic acidosis is rare but is still associated with a high rate of mortality. In fact, the direct metformin-related mortality is close to zero and metformin may even be protective in cases of very severe lactic acidosis unrelated to the drug. Metformin has also inherited a negative class effect, since the early biguanide, phenformin, was associated with more frequent and sometimes fatal lactic acidosis. In the second part of this review, the objective is to identify the most efficient patient management methods based on our knowledge of how metformin acts on glucose/lactate metabolism and how lactic acidosis may occur (at the organ and cellular levels) during metformin treatment. The liver appears to be a key organ for both the antidiabetic effect of metformin and the development of lactic acidosis; the latter is attributed to mitochondrial impairment and subsequent adenosine triphosphate depletion, acceleration of the glycolytic flux, increased glucose uptake and the generation of lactate, which effluxes into the circulation rather than being oxidized further. Haemodialysis should systematically be performed in severe forms of lactic acidosis, since it provides both symptomatic and aetiological treatment (by eliminating lactate and metformin). In the third part of the review (prevention), the objective is to examine the list of contraindications to metformin (primarily related to renal and cardiovascular function). Diabetes is above all a vascular disease and metformin is a vascular drug with antidiabetic properties. Given the importance of the liver in lactate clearance, we suggest focusing on the severity of and prognosis for liver disease; renal dysfunction is only a prerequisite for metformin accumulation, which may only be dangerous per se when associated with liver failure. Lastly, in view of metformin's impressive overall effectiveness profile, it would be paradoxical to deny the majority of patients with long-established diabetes access to metformin because of the high prevalence of contraindications. The implications of these contraindications are discussed.

Physiological effects of hyperchloraemia and acidosis

The advent of balanced solutions for i.v. fluid resuscitation and replacement is imminent and will affect any specialty involved in fluid management. Part of the background to their introduction has focused on the non-physiological nature of 'normal' saline solution and the developing science about the potential problems of hyperchloraemic acidosis. This review assesses the physiological significance of hyperchloraemic acidosis and of acidosis in general. It aims to differentiate the effects of the causes of acidosis from the physiological consequences of acidosis. It is intended to provide an assessment of the importance of hyperchloraemic acidosis and thereby the likely benefits of balanced solutions.

Disorders of acid-base balance

BACKGROUND

Intensivists spend much of their time managing problems related to fluids, electrolytes, and blood pH. Recent advances in the understanding of acid-base physiology have resulted from the application of basic physical-chemical principles of aqueous solutions to blood plasma. All changes in blood pH, in health and in disease, occur through changes in three variables: carbon dioxide, relative electrolyte concentrations, and total weak acid concentrations. However, while this quantitative approach has enjoyed widespread use among researchers, clinicians are reluctant to employ it. Recent advances have brought a measure of parity between the newer and the older, descriptive approach to acid-base physiology.

DATA SYNTHESIS

Case-based review of the literature.

CONCLUSION

Both quantitative and traditional approaches can be easily combined to result in a powerful tool for bedside acid-base analysis.

Flumazenil—Treatment or Toxin

Flumazenil is frequently administered to the poisoned patient. Seizures may be precipitated and resedation may occur in patients who awakened following flumazenil administration. Seizures may increase morbidity and mortality of the overdose. Benefit:Risk ratio of administering flumazenil should be determined in each overdose patient. Indications for flumazenil are limited.

Lactic acidosis in metformin therapy

The biguanide drugs metformin and phenformin have been linked in the past to lactic acidosis, a metabolic condition associated with high rates of mortality. Although concern over the hyperlactataemic effect of phenformin led to the withdrawal of this drug from clinical practice in the 1970s, the situation with metformin has been less clear. Retrospective data indicate that, in metformin-treated patients with lactic acidosis, neither the degree of hyperlactataemia nor accumulation of metformin is of prognostic significance. Furthermore, the lowest rates of mortality were seen in patients with high plasma concentrations of metformin, which has led to the hypothesis that the drug may confer some benefit, linked to an increase in vasomotility, in such cases. Overall, it appears that mortality in patients receiving metformin who develop lactic acidosis is linked to underlying disease rather than to metformin accumulation, and that metformin can no longer be considered a toxic drug in this respect. These findings are likely to be of considerable relevance to the management of patients with type 2 (non-insulin-dependent) diabetes mellitus, especially where such patients are elderly.

Natural history and course of acquired lactic acidosis in adults. DCA-Lactic Acidosis Study Group

STUDY OBJECTIVE

To determine the pathogenesis and clinical course of lactic acidosis in adults receiving standard medical care.

DESIGN

Placebo arm of a 5-year prospective, randomized, blinded study comparing placebo and dichloroacetate as specific lactate-lowering therapy. Each patient received intravenous saline placebo in addition to conventional therapy.

SETTING

Intensive care units of 10 tertiary care hospitals in North America.

PATIENTS

One hundred twenty-six patients with lactic acidosis, defined as arterial blood lactate greater than or equal to 5 mmol/L and either arterial pH of less than or equal to 7.35 or base deficit greater than 6 mmol/L. Patients were followed for up to 6 months.

MEASUREMENTS AND MAIN RESULTS

Mean +/- SD demographic entry data for 126 patients included: age 56 +/- 17 years, lactate 10.4 +/- 5.5 mmol/L, pH 7.24 +/- 0.14, calculated base deficit 14.1 +/- 5.4, arterial systolic blood pressure 103 +/- 29 mm Hg, Glasgow Coma score 7.9 +/- 4.9, and APACHE II score 19.2 +/- 8.1. Despite fluids and pressors, 32% of patients had systolic blood pressures of less than or equal to 90 mm Hg in association with sepsis (59%), cardiac failure (18%), or hemorrhage (18%). The most common causes of lactic acidosis in the absence of shock were sepsis (49%), liver disease (15%), and respiratory failure (12%). The median survival was 38.5 hours. Survival at 24 hours was 59%. Arterial pH predicted 24-hour survival better than base deficit or bicarbonate level. Percent survival was 41% at 3 days and 17% at 30 days. Only 21% of patients survived to leave the intensive care unit, and 17% were discharged from the hospital. In patients receiving sodium bicarbonate, neither acid-base nor hemodynamic status improved.

CONCLUSIONS

In this first prospective study of the clinical course of acute lactic acidosis in adults, nearly all subjects had both hemodynamic and nonhemodynamic (metabolic) underlying causes, many of which independently predicted survival and most of which were refractory to standard care.

Bicarbonate does not increase left ventricular contractility during L-lactic acidemia in pigs

Lactic acidosis decreases left ventricular contractility, but whether bicarbonate increases left ventricular contractility during lactic acidosis in vivo is controversial. Therefore, we measured hemodynamics and left ventricular mechanics before and after bicarbonate administration during L-lactic acid infusion in 15 anesthetized pigs. The pigs were beta-blocked and atrially paced to minimize indirect effects of acidosis on contractility. We measured mean arterial pressure, left ventricular end-diastolic pressure, thermodilution cardiac output, left ventricular pressure (Miller catheter), and left ventricular volume (three orthogonal pairs of ultrasonic crystals). Left ventricular contractility was assessed primarily using the slope (Emax) of the end-systolic pressure-volume relationship. While PCO2 was kept constant, 0.2 M L-lactic acid was infused, which reduced arterial pH to 7.05 +/- 0.06. Animals were then randomized to receive either 1 M NaHCO3 (n = 8), which increased pH to 7.45 +/- 0.11, or an equivalent amount of 1 M NaCl (n = 7). Bicarbonate decreased mean arterial pressure (105 +/- 20 to 95 +/- 39 mm Hg, p < 0.05) but did not increase cardiac output. These effects were not significantly different from the effects of saline. Bicarbonate did not significantly increase Emax (4.2 +/- 0.8 to 4.9 +/- 0.8 mm Hg/ml) and was indistinguishable from saline (5.0 +/- 0.7 to 5.2 +/- 0.7 mm Hg/ml). We conclude that bicarbonate infusion does not directly increase left ventricular contractility during lactic acidemia in pigs within this pH range.

Plasmodium berghei: lactic acidosis and hypoglycaemia in a rodent model of severe malaria; effects of glucose, quinine, and dichloroacetate

Fulminant malaria infections are characterised by hypoglycaemia and potentially lethal lactic acidosis. In young adult Wistar rats (n = 26) infected with Plasmodium berghei (ANKA strain), hyperparasitaemia (greater than 50%), anaemia (PCV 19.6 +/- 5.3%; mean +/- SD) hypoglycaemia (1.04 +/- 0.74 mmol/litre), hyperlactataemia (13.2 +/- 2.20 mmol/litre), hyperpyruvicaemia (0.51 +/- 0.12 mmol/litre) and metabolic acidosis (arterial pH 6.96 +/- 0.11) developed after approximately 14 days of infection. Hypoglycaemia was associated with appropriate suppression of plasma insulin concentrations. In a second series of experiments the metabolic effects of treatment with glucose (500 mg/kg/hr), quinine (5 mg/kg bolus followed by 10 mg/kg over 1 hr) and a potent activator of pyruvate dehydrogenase, dichloroacetate (300 mg/kg) were studied over a 1-hr period. In control animals quinine had no measurable effects, but dichloroacetate significantly reduced arterial blood lactate (74%) and pyruvate (80%). In infected animals, glucose infusion attenuated the rise in lactate (38% compared with 82%; P less than 0.01) but quinine had no additional metabolic effects. Dichloroacetate further attenuated the rise in lactate (14%; P less than 0.01).

Lactic acidosis

An understanding of the pathophysiology of lactic acidosis is crucial in facilitating the optimal care of critically ill patients. The relevant biochemistry of lactic acidosis is reviewed, and the more controversial aspects relating to the genesis of the acidosis are highlighted. The current system of classification of lactic acidosis divides etiologies on the basis of the presence or absence of clinical signs of tissue hypoperfusion. Several types of lactic acidosis in which clinical evidence of tissue hypoperfusion is lacking demonstrate hemodynamic evidence of occult hypoperfusion. The diagnostic and therapeutic implications of this observation are discussed. Current diagnostic criteria for lactic acidosis include a pH less than 7.35 and blood lactate concentration greater than 5 to 6 mM/L. An important issue relates to the implications of lactate values that are greater than normal but below this diagnostic range. The use of the oxygen flux test may be valuable in the diagnosis of occult tissue hypoperfusion in patients with low-grade elevations in lactate levels. The current therapy for lactic acidosis involves addressing the primary cause and supportive management. The use of bicarbonate in the therapy for lactic acidosis is controversial due to potential adverse effects on cardiac function. The specifics of this controversy are outlined, and newer therapeutic alternatives are reviewed. The use of blood lactate concentration as a prognostic index may be more useful in patients with shock than without shock.

Comparison of sodium bicarbonate with dichloroacetate treatment of hyperlactatemia and lactic acidosis in the ischemic rat

Serum lactic acidosis is characterized by a pH less than 7.25 and lactate greater than 5 mEq. Although sodium bicarbonate (NaHCO3) is standard treatment for this condition, clinical and experimental studies suggest that high doses of NaHCO3 may be ineffectual or even detrimental to brain, cardiovascular, and respiratory function, as well as survival. For this reason, low dose therapy with NaHCO3 has been recommended. Sodium dichloroacetate (NaDCA) has been used successfully to treat clinical and experimentally-induced lactic acidosis. The present study was designed to compare the effects of low dose NaHCO3 with NaDCA on blood pressure, blood chemistries and brain metabolites in rats with a low flow-induced (Type A, the most common type) lactic acidosis. Fasted male Wistar rats were subjected to cerebral ischemia and systemic hypotension for 30 min at which time, if the pH or HCO-3 fell to 7.2 or 10, respectively, the rat was treated with NaHCO3, NaDCA, or an equal volume of sterile water. Over the 30 min of recirculation that followed ischemia, treatment had no effect on blood pressure or glucose or on brain glucose or glycogen. NaHCO3 had no effect on lactate but appeared to stabilize pH and increase HCO3- more than in sham- or NaDCA-treated rats. Although NaDCA caused a greater increase in HCO3- than sham treatment, pH continued to decline. However, lactate decreased more in NaDCA- than in sham- or NaHCO3- treated rats. These results suggest that low dose NaHCO3 is not detrimental in this model; however, although NaHCO3 stabilized pH, it did not rapidly correct the acidosis. NaDCA at this dose had no effect on the acidosis but was effective in decreasing lactate. Since serum lactate has previously correlated with survival and since higher doses of NaDCA have corrected lactic acidosis in other studies, future evaluation of postischemic treatment with higher doses of NaDCA is warranted.

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)

Evidence for a detrimental effect of bicarbonate therapy in hypoxic lactic acidosis

Lactic acidosis, a clinical syndrome caused by the accumulation of lactic acid, is characterized by lactate concentration in blood greater than 5 mM. Therapy usually consists of intravenous sodium bicarbonate (NaHCO3), but resultant mortality is greater than 60 percent. The metabolic and systemic effects of NaHCO3 therapy of hypoxic lactic acidosis in dogs were studied and compared to the effects of sodium chloride or no therapy. Sodium bicarbonate elevated blood lactate concentrations to a greater extent than did either sodium chloride or no treatment. Despite the infusion of NaHCO3, both arterial pH and bicarbonate concentration decreased by a similar amount in all three groups of dogs. Additional detrimental effects of NaHCO3 were observed on the cardiovascular system, including decreases in cardiac output and blood pressure that were not observed with either sodium chloride or no treatment. Thus there is evidence for a harmful effect of NaHCO3 in the treatment of hypoxic lactic acidosis.