Metabolic Medicine Made Simple : Metabolic Acidosis with raised Anion Gap

Causes of Metabolic Acidosis with raised Anion Gap include :

Aspirin Ingestion
Ethylene Glycol Poisoning
Methyl Alcohol Ingestion
Uremic Acidosis
Lactic Acidosis








Normal Anion Gap is 6 - 12
pH less than 7.35 is indicative of Metabolic Acidosis.

In patients with markedly elevated anion gap and if frank uremia is not present,the osmolar gap should be calculated to assess for ethanol,methanol or ethylene glycol intoxication.




The serum Osmolality is calculated by using the following formula :

Serum Osmolality = 2 (Na + Glu / 18 + BUN /2.8 )

The Osmolar gap is calculated by the following formula :

Osmolar Gap = Observed Osmolarity - Calclated Osmolarity.





Osmolar Gap metabolic acidosis is seen in :

Acute Methanol
Ethanol or
Ethylene glycol.

Ethylene Glycol Poisoning

This occurs following antifreeze ingestion.
It is characterized by presence of rectangular envelope shaped calcium oxalate crystals in the urine.
Serious sequelae of this poisoning include :

Acute Respiratory Distress Syndrome
Heart failure
Renal failure

Aspirin / salicylate toxicity causes :

Mixed Anion gap metabolic acidosis and respiratory alkalosis with no osmolar gap.


Methyl Alcohol poisoning :

This causes visual changes ( snowfield vision ) and acute pancreatitis.
It doesnot cause renal failure or urine crystals.

Uremia / Renal failure :

It can cause anion gap metabolic acidosis due to failure to excrete acids.


Lactic Acidosis 

can  result from numerous causes including poor delivery of oxygen to the tissues and poor oxygen utilization by the tissues.

The result is an anion gap metabolic acidosis.

Metabolic Medicine Made Simple : Mixed Metabolic and Respiratory Acidosis

pH would be below 7.35.

HCO3- would be reduced suggestive of Metabolic Acidosis.

PaCO2 would be reaised or inapprprately normal.

Winter formula is used to calculate what PaCO2 ought to be in order to compensate for the metabolic acidosis and that PaCO2 is inappropriately normal.

Winter formula is as follows :

PaCO2 = 1.5 (HCO3-) + 8

Metabolic Medicine Made Simple : Metabolic Alkalosis

}()); Metabolic Alkalosis :

Human blood pH is maintained between 7.35 - 7.45.

This is done by various mechanisms the most significant being regulation of CO2, carbonate and hydrogen atoms by the lungs and the kidneys.





A pH of more than 7.45 is considered alkalosis and a pH of less than 7.35 is considered acidosis.




The pCO2 and HCO3- values can then be used to differentiate between a respiratory or a metabolic cause of acid base disturbance.

The normal HCO3- is 24 meq/l and the normal PCO2 is 40 mmHg.



Any deviation from these normal values is indicative of an acid base disorder.

Metabolic acid base disorders are due to a primary change in concentration of HCO3 while respiratory acid base disorders are due to a primary change in PCO2.


Main causes of Metabolic Alkalosis includes :

Exogenous administration of an alkali.

Removal of acidic gastric secretions due to vomiting or NG tube aspiration.

Renal Hydrogen ion loss due to mineralocorticoid excess

Contraction Alkalosis.

Electrolytes & Metabolic Medicine Made Simple : Metabolic Acidosis

Metabolic Acidosis :

Metabolic acidosis is indicated by a low pH < 7.4 and low serum bicarbonate < 24 meq / l.

There are different causes of metabolic acidosis :


Acute Renal Failure :

It occurs due to failure of the kidneys to excrete acids generated during normal protein metabolism namely inorganic phosphates and sulfates.

It may have various causes such as acute hypovolemia due to vomiting and diarrhoea , GI bleed leading to hypotension and ischemia.

Type I Renal Tubular Acidosis :

It is characterized by low tubular Ammonium production.
The primary defect in this disease is failure to excrete sufficient hydrogen ions in urine.
Without sufficient hydrogen ions in tubular fluid,ammonium cannot be produced.


Type 2 Renal tubular Acidosis :

This is characterized by defective tubular bicarbonate reabsorption .
It is often inherited and may be a components of Fanconi Syndrome.
Type II RTA can also occur with use of drugs like Carbonic Anhydrase Inhibitors.

Causes of Decreased Anion Gap Metabolic Acidosis include :

Plasma cell Dyscrasias

Lithum intoxication.

Paraproteinemias.






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Metabolic Medicine Made Simple : Post ictal Metabolic Acidosis

Post seizure metabolic acidosis is usually the result of a grand mal / tonic clonic seizure.

Seizures result in an accelerated production of lactic acid in the muscle and reduced hepatic lactate uptake.

This post - ictal lactic acidosis is transient and usually resolves within 60 - 90 minutes.

In such patients,the most appropriate treatment is observation and repeating the chemistry panel after 2 hours to see if the acidosis has improved /resolved on its own.

If it has not resolved,it is better to look for other potential causes of metabolic acidosis.
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The common causes of ketosis include :

Diabetes

Alcoholism

Starvation

The use of bicarbonate in the treatment of lactic acidosis or ketoacidosis is very contraversial.

It is only recommended in severe acute acidosis pH < 7.2

Full correction with bicarbonate should not be sought.

Only a sufficient amount of bicarbonate should be given to correct the ph to 7.2.

In lactic acidosis,bicarbonate treatment may paradoxically depress cardiac performance and worsen the acidosis by enhancing lactate production.

Serum lipase levels are generally used to assess for pancreatic disease but may also be elevated in DKA and other conditions making the test poorly specific for any one disease process.