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Lactic acidosis

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Lactic acidosis

Lactic acidosis
Classification and external resources
ICD-10 E87.2
ICD-9-CM 276.2
DiseasesDB 29145
MedlinePlus 000391
eMedicine article/768159
MeSH D000140

Lactic acidosis is a physiological condition characterized by low pH in body tissues and blood (acidosis) accompanied by the buildup of lactate, especially L-lactate, and is considered a distinct form of metabolic acidosis. Lactic acidosis is characterized by lactate levels >5 mmol/L and serum pH <7.35.

The condition typically occurs when cells receive too little oxygen (hypoxia), for example, during vigorous exercise. In this situation, impaired cellular respiration leads to lower pH levels. Simultaneously, cells are forced to metabolize glucose anaerobically, which leads to lactate formation. Therefore, elevated lactate is indicative of tissue hypoxia, hypoperfusion, and possible damage.

Contents

  • Signs and symptoms 1
  • Causes 2
  • Pathophysiology 3
  • Classification 4
  • Treatment 5
  • Other animals 6
    • Reptiles 6.1
    • Ruminants 6.2
  • References 7

Signs and symptoms

Lactic acidosis is commonly found in people who are unwell for one of various reasons, such as severe heart and/or lung disease, a severe infection with sepsis, the systemic inflammatory response syndrome (SIRS) due to another cause, severe physical trauma, or severe depletion of body fluids.[1] Symptoms in humans include all those of typical metabolic acidosis (nausea, vomiting, generalized muscle weakness, rapid breathing).[2]

Causes

The several different causes of lactic acidosis:

Pathophysiology

Most cells in the body normally metabolize glucose to form water and carbon dioxide in a two-step process. First, glucose is broken down to pyruvate through glycolysis. Then, mitochondria oxidize the pyruvate into water and carbon dioxide by means of the Krebs cycle and oxidative phosphorylation. This second step requires oxygen. The net result is ATP, the energy carrier used by the cell for metabolic activities and to perform work, such as muscle contraction. When the energy in ATP is used during cell work via ATP hydrolysis, hydrogen ions, (positively charged protons) are released. The mitochondria normally incorporate these free hydrogen nuclei back into ATP, thus preventing buildup of unbound hydrogen cations, and maintaining neutral pH.

If oxygen supply is inadequate (hypoxia), the mitochondria are unable to continue ATP synthesis at a rate sufficient to supply the cell with the required ATP. In this situation, glycolysis is increased to provide additional ATP, and the excess pyruvate produced is converted into lactate and released from the cell into the bloodstream, where it accumulates over time. While increased glycolysis helps compensate for less ATP from oxidative phosphorylation, it cannot bind the hydrogen cations that result from ATP hydrolysis. Therefore, hydrogen cation concentration rises and causes acidosis.[7]

The excess hydrogen cations produced during lactic acidosis are widely believed to actually derive from production of lactic acid. This is incorrect , as cells do not produce lactic acid; pyruvate is converted directly into lactate, the anionic form of lactic acid. When excess intracellular lactate is released into the blood, maintenance of electroneutrality of the blood requires that a cation be released into the blood, as well. This can reduce blood pH. Glycolysis coupled with lactate production is neutral in the sense that it does not produce excess hydrogen cations, however, pyruvate production does produce them. Lactate production is buffered intracellularly, e.g. the lactate-producing enzyme, lactate dehydrogenase, binds one hydrogen cation per pyruvate molecule converted. When such buffer systems become saturated, cells will transport lactate into the bloodstream. Hypoxia certainly causes both a buildup of lactate and acidification, and lactate is therefore a good "marker" of hypoxia, but lactate itself is not the cause of low pH.[8] There is a view that during exercise and critical illness, lactate production is not generated by lack of oxygen but by catecholamine-driven glycolysis, and that the lactate serves as an energy source for other tissues.[9]

Lactic acidosis sometimes occurs without hypoxia, for example, in rare inborn errors of metabolism where mitochondria do not function at full capacity. In such cases, when the body needs more energy than usual, for example during exercise or disease, mitochondria cannot match the cells' demand for ATP, and lactic acidosis results. Also, muscle types that have few mitochondria and preferentially use glycolysis for ATP production (fast-twitch or type II fibers) are naturally prone to lactic acidosis.

Lactic acidosis is also a consequence of the processes causing rigor mortis. In the absence of oxygen, tissue in the muscles of the deceased carry out anaerobic metabolism using muscle glycogen as the energy source, causing acidification. With depletion of muscle glycogen, the loss of ATP causes the muscles to grow stiff, as the actin-myosin bonds cannot be released. (Rigor is later resolved by enzymatic breakdown of the myofibers.)

Classification

The Cohen-Woods classification categorizes causes of lactic acidosis as follows:[10]

  • Type A: Decreased perfusion or oxygenation
  • Type B:

Treatment

Direct removal of lactate from the body (e.g. with hemofiltration) is difficult, and there is limited evidence for benefit.[11] In type A lactic acidosis, treatment consists of effective management of the underlying cause, and there is limited evidence to support the use of sodium bicarbonate solutions to improve the pH (which is associated with increased carbon dioxide generation and may reduce the calcium levels).[12]

In lactic acidosis produced by medication, withdrawal of the medication may be necessary.

Lactic acidosis in the context of mitochondrial disorders (type B3) may be treated with a ketogenic diet and possibly with dichloroacetate (DCA),[13] although this may be complicated by peripheral neuropathy and has a weak evidence base.[14]

Other animals

Reptiles

Reptiles, which rely primarily on anaerobic energy metabolism (glycolysis) for intense movements, can be particularly susceptible to lactic acidosis. In particular, during the capture of large crocodiles, the animals' use of their glycolytic muscles often alter the blood's pH to a point where they are unable to respond to stimuli or move.[15] There are recorded cases in which particularly large crocodiles who put up extreme resistance to capture later died of the resulting pH imbalance.[16]

Certain turtle species have been found to be capable of tolerating high levels of lactic acid without suffering the effects of lactic acidosis. Painted turtles hibernate buried in mud or underwater and do not resurface for the entire Winter. As a result they rely on anaerobic respiration to provide the majority of their energy needs.[17] Adaptations in particular in the turtle's blood composition and shell allow it to tolerate high levels of lactic acid accumulation. In the anoxic conditions where anaerobic respiration is dominant, calcium levels in the blood plasma increase.[17] This calcium serves as a buffer, reacting with the excess lactate to form the precipitate calcium lactate. It is suggested that this precipitate is reabsorbed by the shell and skeleton thereby removing it from the bloodstream; studies examining turtles who have been subjected to prolonged anoxic conditions have up to 45% of their lactate stored within their skeletal structure.[17]

Ruminants

In ruminant livestock, the cause of clinically serious lactic acidosis is different from the causes described above.

In domesticated

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  2. ^ MedlinePlus Encyclopedia Lactic acidosis
  3. ^ Fimognari, F. L.; Pastorelli, R.; Incalzi, R. A. (2006). "Phenformin-Induced Lactic Acidosis in an Older Diabetic Patient: A recurrent drama (phenformin and lactic acidosis)". Diabetes Care 29 (4): 950–1.  
  4. ^ Yang, Por-Wen; Lin, Kuan-Hung; Lo, Su-Huey; Wang, Lee-Ming; Lin, Hong-Da (2009). "Successful Treatment of Severe Lactic Acidosis Caused by a Suicide Attempt with a Metformin Overdose". The Kaohsiung Journal of Medical Sciences 25 (2): 93–7.  
  5. ^ McKenzie, Robin; Fried, Michael W.; Sallie, Richard; Conjeevaram, Hari; Di Bisceglie, Adrian M.; Park, Yoon; Savarese, Barbara; Kleiner, David; Tsokos, Maria; Luciano, Carlos; Pruett, Timothy; Stotka, Jennifer L.; Straus, Stephen E.; Hoofnagle, Jay H. (1995). "Hepatic Failure and Lactic Acidosis Due to Fialuridine (FIAU), an Investigational Nucleoside Analogue for Chronic Hepatitis B". New England Journal of Medicine 333 (17): 1099–105.  
  6. ^ "Truvada". 
  7. ^ Hochachka, P. W.; Mommsen, T. P. (1983). "Protons and anaerobiosis". Science 219 (4591): 1391–7.  
  8. ^ Robergs, Robert A.; Ghiasvand,, Farzenah; Parker Daryl (2004). "Biochemistry of exercise-induced metabolic acidosis". American Journal of Physiology: Regulatory, Integrative and Comparative Physiology 287 (3): R502–16.  
  9. ^ Gladden, LB (Mar 2008). "Current trends in lactate metabolism: introduction". Medicine and science in sports and exercise 40 (3): 475–6.  
  10. ^ Woods, Hubert Frank; Cohen, Robert (1976). Clinical and biochemical aspects of lactic acidosis. Oxford: Blackwell Scientific.  
  11. ^ Cerdá, J; Tolwani, AJ; Warnock, DG (Jul 2012). "Critical care nephrology: management of acid-base disorders with CRRT.". Kidney international 82 (1): 9–18.  
  12. ^ Boyd, JH; Walley, KR (Aug 2008). "Is there a role for sodium bicarbonate in treating lactic acidosis from shock?". Current opinion in critical care 14 (4): 379–83.  
  13. ^ Stacpoole, PW; Kurtz, TL; Han, Z; Langaee, T (2008). "Role of dichloroacetate in the treatment of genetic mitochondrial diseases". Advanced drug delivery reviews 60 (13–14): 1478–87.  
  14. ^ Pfeffer, G; Majamaa, K; Turnbull, DM; Thorburn, D; Chinnery, PF (2012). Chinnery, Patrick F, ed. "Treatment for mitochondrial disorders". The Cochrane database of systematic reviews 4: CD004426.  
  15. ^ http://compphys.bio.uci.edu/bennett/pubs/80.pdf
  16. ^ [2]. Accessed 31 January 2009.
  17. ^ a b c Jackson, Donald C. (2002). "Hibernating without oxygen: physiological adaptations of the painted turtle". The Journal of Physiology 543 (3): 731–737.  
  18. ^ a b c d e Kimberling, C. V. 1988. Jensen and Swift's diseases of sheep. 3rd Ed. Lea & Fibiger, Philadelphia. 394 pp.
  19. ^ a b c Pugh, D. G. 2002. Sheep and goat medicine. Saunders. 468 pp.
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  24. ^ Nagaraja, TG; Avery, TB; Bartley, EE; Galitzer, SJ; Dayton, AD (1981). "Prevention of lactic acidosis in cattle by lasalocid or monensin". Journal of Animal Science 53 (1): 206–16.  
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  26. ^ Kaufmann, W. 1976. Influence of the composition of the ration and the feeding frequency on ph-regulation in the rumen and on feed in-take in ruminants. Livestock Prod. Sci. 3: 103-114.

References

Treatment of lactic acidosis in ruminants may involve intravenous administration of dilute sodium bicarbonate, oral administration of magnesium hydroxide, and/or repeated removal of rumen fluids and replacement with water (followed by reinoculation with rumen organisms, if necessary).[18][19][20]

Measures for preventing lactic acidosis in ruminants include avoidance of excessive amounts of grain in the diet, and gradual introduction of grain over a period of several days, to develop a rumen population capable of safely dealing with a relatively high grain intake.[18][19][20] Administration of lasalocid or monensin in feed can reduce risk of lactic acidosis in ruminants,[24] inhibiting most of the lactate-producing bacterial species without inhibiting the major lactate fermenters.[25] Also, using a higher feeding frequency to provide the daily grain ration can allow higher grain intake without reducing the pH of the rumen fluid.[26]

Because of the high solute concentration of the rumen fluid under such conditions, considerable water is translocated from the blood to the rumen along the osmotic potential gradient, resulting in dehydration which cannot be relieved by drinking, and which can ultimately lead to hypovolemic shock.[18] As more lactate accumulates and rumen pH drops, the ruminal concentration of undissociated lactic acid increases. Undissociated lactic acid can cross the rumen wall to the blood,[23] where it dissociates, lowering blood pH. Both L and D isomers of lactic acid are produced in the rumen;[18] these isomers are metabolized by different metabolic pathways, and activity of the principal enzyme involved in metabolism of the D isomer declines greatly with lower pH, tending to result in an increased ratio of D:L isomers as acidosis progresses.[22]

[21] of lactic acid is low, about 3.9, versus, for example, 4.8 for acetic acid; this contributes to the considerable drop in rumen pH which can occur.pKa The [22]

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