how to read an abg

1. METABOLIC ACIDOSIS
Dr Pragyan Pattnaik
1st year pg resident
General surgery
Unit 3.

3. METABOLIC ACIDOSIS
• Metabolic acidosis is a condition that occurs when the body produces
excessive quantities of acid or when the kidneys are not removing
enough acid from the body. If unchecked, metabolic acidosis leads
to acidemia, i.e., blood pH is low (less than 7.35) due to increased
production of hydrogen ions by the body or the inability of the body to
form bicarbonate (HCO −) in the kidney. Its causes are diverse, and its
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consequences can be serious, including coma and death. Together
with respiratory acidosis, it is one of the two general causes of
acidemia.

5. A: High Anion-Gap Acidosis
1. . Ketoacidosis
• Diabetic ketoacidosis
• Alcoholic ketoacidosis
• Starvation ketoacidosis
2. . Lactic Acidosis
• Type A Lactic acidosis (Impaired perfusion)
•Type B Lactic acidosis (Impaired carbohydrate met
abolism)
3. . Renal Failure
• Uraemic acidosis
• Acidosis with acute renal failure
4. . Toxins
• Ethylene glycol
• Methanol
Causes of Metabolic Acidosis
(classified by Anion Gap)

6. B : Normal Ani on-Gap Acidosis (or Hyper chloraemic acidosis)
1. Renal Causes
• Renal tubular acidosis
• Carbonic anhydrase inhibitors
2. GIT Causes
• Severe diarrhoea
• Uretero-enterostomy or ileal obstruction
• Drainage of pancreatic or biliary secretions
• Small bowel fistula
3. Other Causes
• Recovery from ketoacidosis
• Addition of HCl, NH4Cl

7. ANION GAP
-
• Na+ + Unmeasured cations = Cl- + HCO3 + Unmeasured anions.
• Or Unmeasured anions – Unmeasured cations = Na+ - Cl- + HCO3-
• Definition:
• Anion gap is quantity of anions not balanced by cations
• Usually due to negatively charged plasma proteins as the charges of the
other unmeasured cations and anions tend to balance out.

8. TESTS FOR METABOLIC ACIDOSIS
• Tests to diagnose metabolic acidosis :
• Arterial blood gas
• pH, pO2 , pCO2 , HCO3 (bicarbonate)
• Venous blood sample
• Sodium, potassium, chloride, bicarbonate
• Glucose
• Serum lactose
• Measured serum osmolarity
• Serum ketones
• Osmolar gap
• Urine
• Urine pH, urine ketones
• Calculations
• Anion gap
• Sodium concentration minus the sum of chloride
concentration and bicarbonate concentration.
• Measured osmolar gap minus calculated osmolar gap.
• Appropriate pCO2 change based on serum
bicarbonate.

9. DIAGNOSIS OF METABOLIC ACIDOSIS
• Determine the main acid – base problem.
1. pH lower than 7.35
• Acidosis
• Metabolic or Respiratory.
2. Bicarbonate lower than 20 meq/L
• MetabolicAcidosis
• Determine the main acid – base problem.
1. CalculateAnion Gap
• AG : Sodium – (Chloride +
Bicarbonate)
• NormalAG : 8 to 16 meq/L ( 5 to 7
meq/L using newer lab analyzers)
2. Determine if patients history and physical
fits the proposed diagnosis of type and
causes of metabolic acidosis.

10. LOW ANION GAP
A low anion gap is frequently caused by hypoalbuminemia.
Albumin is a negatively charged protein and its loss from
the serum results in the retention of other negatively char
ged ions
such as chloride and bicarbonate. As bicarbonate and chlor
ide anions are used to calculate the anion gap, there is a
subsequent decrease in the gap.
In hypoalbuminaemia the normal anion gap is decreased
with
2.5 to 3 mmol/L per 1 g/dL decrease in serum
albumin.Common conditions that reduce serum albumin in
the clinical setting are hemorrhage nephrotic syndrome, int
estinal obstruction and liver cirrhosis.
The anion gap is sometimes reduced in multiple myeloma,
where there is an increase in plasma IgG (paraprot
einaemia).

11. HIGH ANION GAP
• An anion gap is usually considered to be high if it is over 12 mEq/L.
• The most common cause for high anion gaps are:
LacticAcidosis.
Ketoacidosis (diabetic ketoacidosis).

12. LACTIC ACIDOSIS.
• Lactic acidosis is a form of metabolic acidosis due to the inadequate
clearance of lactic acid from the blood.
• Lactic acidosis occurs when the body's buffering systems are
overloaded.
• Lactic acids are produced during anaerobic metabolism in the
muscle cells gets cleared from the blood through kidney.
• There are two types of lactic acid: L-lactate and D-lactate.
• Most forms of lactic acidosis are caused by too much L-lactate

13. CAUSES
• Lactic acidosis has a wide range of underlying causes.
Carbon monoxide poisoning.
Cholera.
Malaria.
Heart disease.
Cancer.
Intense exercise or physical activity.

14. DIABETIC KETO ACIDOSIS
• Diabetic ketoacidosis is a serious complication of diabetes that occurs
when our body produces high levels of blood acids called ketones.
• Ketoacidosis is a high anion gap metabolic acidosis due to an excessive
blood concentration of ketone bodies (keto-anions).
• Ketone bodies released into the blood are acetoacetate, beta-
hydroxybutyrate, acetone.

15. CAUSES
• Diabetic ketoacidosis occurs when a person with diabetes becomes dehydrated.
• In diabetic ketoacidosis, the body shifts from its normal metabolism (using
carbohydrates for fuel) to a fasting state (using fat for fuel).
• The resulting increase in blood sugar occurs, because insulin is unavailable to
transport sugar into cells for future use.
• As blood sugar levels rise, the kidneys cannot retain the extra sugar, thereby increasing
urination and causing dehydration.
• Causes may include such as diarrhea, vomiting, and/or high fever, heart
attack, stroke, trauma, stress, and surgery.Alow percentage of cases have no
identifiable cause.

16. NORMAL ANION GAP
• Normal anion gap is when the number of bicarbonate ions (HCO3-)
decreases.
• To compensate the amount of lost bicarbonate ions our body starts
absorbing chloride ions (Cl-).
• As a result the anion gap remains normal but the amount of
chloride ions in our body increases.
• This is also known as hyperchloremic acidosis.

17. HYPERCHLOREMIC ACIDOSIS
• This occurs basically because of two major
diseases:
• 1: severe diarrhea
• 2: renal tubular acidosis

18. SEVERE DIARRHEA
• It is when the bowel movement occurs more than 5 times a day.
• The person loses a great amount of bicarbonate ions in the stool
and therefore the amount of anions decreases.
• Bicarbonate ions are important for the blood buffer system.
• Due loss of these ions the buffer system cannot work properly thus
making the blood acidic.

19. RENAL TUBULAR ACIDOSIS
• Renal tubular acidosis (RTA) is a condition charac
terized by too much acid in the body due to a defe
ct in kidney function.
• The person’s blood becomes too acidic.
• Leads to growth retardation, kidney stones, bone
disease, chronic kidney disease, and possibly total
kidney failure.

20. • Kidneys maintain acid-base balance by excreting the acid ions and
reabsorbing the bicarbonate ions (base) into the body.
• This base neutralizes the acid produced by the body for the
digestion of food.

22. SIGNS AND SYMPTOMS
• Most common symptoms for
metabolic acidosis:

23. SIGNS AND SYMPTOMS
LacticAcidosis Renal tubular acidosis
• Back pain
• Lower abdominal pain
• Painful urination
• Cloudy urine
• Nausea/vomiting
• Muscle weakness
• Muscle cramping in the back and abdomen

24. SIGNS AND SYMPTOMS
Ketoacidosis Hyperchloremic acidosis
• Weakness
• Headache
• Nausea
• Severe dehydration
• Cardiac arrest

25. • ApH under 7.1 is an emergency, due to the risk of abnormal
heart rhythms, and may warrant treatment with intravenous
bicarbonate. Bicarbonate is given at 50-100 mmol at a time under
scrupulous monitoring of the arterial blood gas readings. This
intervention, however, has some serious complications in lactic
acidosis, and in those cases, should be used with great care.
• If the acidosis is particularly severe and/or intoxication may be
present, consultation with the nephrology team is considered
useful, as dialysis may clear both the intoxication and the
acidosis.
TREATMENT

26. • Intravenous fluid to promote circulation
• Oxygen, delivered with a face mask or another way
• positive pressure ventilation to deliver oxygen to the lungs
• Vitamin therapy
• Hemodialysis with bicarbonate
• Individuals who experience lactic acidosis while exercising can stop what
they are doing, rehydrate by drinking water, and rest.

27. TREATMENT FOR DIABETIC KETOACIDOSIS
• Fluid replacement
• Electrolyte replacement.
• Insulin therapy.

28. TREATMENT FOR RENAL TUBULAR
ACIDOSIS
• Treatment consists of correction of pH and electrolyte balance
with alkali therapy. Failure to treat RTAin children slows
growth.
• Alkaline agents such as sodium bicarbonate, potassium
bicarbonate, or sodium citrate help achieve a relatively normal
plasma bicarbonate concentration
• Potassium citrate can be substituted when persistent
hypokalemia is present

29. TREATMENT
The ECLS Appr oach to Management of MetabolicAcidosis
1. Emergency: Emergency management of immediately life-threatening
conditions always has the highest priority. For example, intubati on and
ventilation for airway or ventilatory control; CPR ( cardiopulmonary
resuscitation ); severe hyperkalemia.
2. Cause: Treat the underlying disorder as the primary therapeutic goal
Consequently, accur ate diagnosis of the cause of the metabolic acidosis is
important.

30. 3. Loss -Replace loss (e.g. of fluids and
electrolytes) where appropriate. Other
supportive care (oxygen administration) is
useful.

31. 4. Specifics there are often specific
Problems or complications associated with specific
causes or specific cases which require specific
management . for example: ethanol blocking treat
ment with methanol ingestion; haemodialysis can
remove some toxins.

32. WHOS AT RISK FOR METABOLIC
ACIDOSIS ??
• Ahigh-fat diet, low in carbohydrates
• Kidney failure
• obesity
• Dehydration
• Aspirin or methanol poisoning
• diabetes
• Smoking
• Chronic alcohol abuse

33. Thank you…
Good doctors help in replacing the fear of illness with trust in recovery!