Metabolic acidosis

55,992views

00:00 / 00:00

High Yield Notes

8 pages

Flashcards

Metabolic acidosis

of complete

Questions

USMLE® Step 1 style questions USMLE

of complete

A 62-year-old man comes to his primary care physician for a routine visit. The patient has no acute complaints, but he feels out of breath after walking 3-4 blocks. The patient has a 50-pack-year smoking history and consumes one pack of cigarettes per day. His temperature is 37.0°C (98.6°F), pulse is 77/min, blood pressure is 159/83 mmHg, and respirations are 12/min. Physical exam reveals a barrel shaped chest, bilateral wheezing, and a prolonged expiratory phase. Routine labs are ordered. Which of the following sets of findings would be expected given this patient’s clinical presentation?

External References

First Aid

2024

2023

2022

2021

Acetazolamide p. 251, 568, 624

metabolic acidosis p. 610

Addison disease p. 353

metabolic acidosis in p. 610

Diabetic ketoacidosis (DKA) p. 355

metabolic acidosis p. 610

Diarrhea

metabolic acidosis from p. 610

Ethylene glycol

metabolic acidosis p. 610

Hyperventilation

metabolic acidosis p. 610

Iron

metabolic acidosis p. 610

Lactic acidosis

metabolic acidosis p. 610

Metabolic acidosis p. 610

adrenal insufficiency p. 353

neonatal respiratory distress syndrome p. 679

renal failure p. 621

symptoms of p. 610

Renal tubular acidosis

metabolic acidosis p. 610

Salicylates

metabolic acidosis p. 610

Spironolactone p. 627, 663, 673, 676

metabolic acidosis p. 610

Uremia

metabolic acidosis p. 610

Transcript

Watch video only

With metabolic acidosis, “acidosis” refers to a process that lowers blood pH below 7.35, and “metabolic” refers to the fact that it’s a problem caused by a decrease in the bicarbonate HCO3− concentration in the blood.

Normally, blood pH depends on the balance or ratio between the concentration of bases, mainly bicarbonate HCO3−, which increases the pH, and acids, mainly carbon dioxide CO2, which decrease the pH.

The blood pH needs to be constantly between 7.35 and 7.45, and in addition the blood needs to remain electrically neutral, which means that the total cations, or positively charged particles, equals the total anions, or negatively charged particles.

Now, not all of the ions are easy or convenient to measure, so typically the dominant cation, sodium Na+, which is typically around 137 mEq/L and the two dominant anions, chloride Cl−, which is about 104 mEq/L, and bicarbonate HCO3−, which is around 24 mEq/L, are measured.

The rest are unmeasured. So just counting up these three ions, there’s usually a difference, or “gap” between the sodium Na+ concentration and the sum of bicarbonate HCO3− and chloride Cl− concentrations in the plasma, which is 137 minus 128 (104 plus 24) or 9 mEq/L.

This is known as the anion gap, and normally it ranges between 3 and 11 mEq/L. The anion gap largely represents unmeasured anions like organic acids and negatively charged plasma proteins, like albumin.

So, basically, metabolic acidosis arises either from the buildup of acid in our blood, which could be because it’s produced or ingested in increased amounts, or because the body can’t get rid of it, or from excessive bicarbonate HCO3− loss from the kidneys or gastrointestinal tract.

The main problem with all of this is that they lead to a primary decrease in the concentration of bicarbonate HCO3− in the blood.

They can be broken down to two categories, based on whether the anion gap is high or normal. So, the first category of metabolic acidosis is a high anion gap metabolic acidosis.

In this case, the bicarbonate HCO3− ion concentration decreases by binding of bicarbonate HCO3− ions and protons H+, which results in the formation of H2CO3 carbonic acid, which subsequently breaks down into carbon dioxide CO2 and water H2O.

These protons can come from organic acids which have accumulated in the blood, but they can also come from increased production in our body.

One such example is lactic acidosis, which is where decreased oxygen delivery to the tissues leads to increased anaerobic metabolism and the buildup of lactic acid.

Summary

Metabolic acidosis is a condition in which the body produces too much acid (e.g. acetic acid or ketones), or excessively loses bicarbonate ions (e.g. diarrhea or renal failure). In metabolic acidosis, the respiratory center is stimulated in order to compensate for the acidosis and the individual hyperventilates, leading to dyspnea. Other associated symptoms are related to the underlying cause, for example, in diabetic ketoacidosis there's nausea and vomiting.

Sources

  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Metabolic acidosis: pathophysiology, diagnosis and management" Nature Reviews Nephrology (2010)
  6. "Metabolic acidosis" Acta Med Indones (2007)
  7. "Management of the Metabolic Acidosis of Chronic Kidney Disease" Advances in Chronic Kidney Disease (2017)
  8. "Respiratory Acid–Base Disorders in the Critical Care Unit" Veterinary Clinics of North America: Small Animal Practice (2017)
  9. "Respiratory acidosis" Respir Care (2001)
Elsevier

Copyright © 2024 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.

RELX