BLOOD GAS ABNORMALITY😊

Lactic Acidosis

Types of Lactic acidosis	Notes
Type A	• Hypoperfusion / hypoxia Examples • Shock • Cardiac failure • Severe anemia • Carbon monoxide toxicity • Cyanide toxicity
Type B	• metabolic causes with normal oxygenation Examples • Malignancy • Renal failure • Hepatic failure • Drugs: metformin, ethanol, ethylene glycol, methanol • Diabetes mellitus • Seizures • Severe malaria / cholera

Renal Tubular Acidosis (RTA)

NOTE: Different Fanconis

ㅤ	ㅤ
Fanconi disease/syndrome	• Proximal tubular reabsorption problem → Type 2 RTA • Glycosuria, aminoaciduria
Fanconi anemia (Not syndrome)	• Pancytopenia + radial ray
Fanconi Bickel syndrome	• Mutation in GLUT-2   • Bickel → Bi → 2 (GLUT 2) Defect in glucose sensing → ↓ insulin release • Postprandial Hyperglycemia. • Fasting Hypoglycemia • Glycogen accumulation disorder

Stranger things characters

• Dustin (Cleido cranial dysplasia)

• Robin (Cock robin position)

• Ray (Radial Ray) Hopper (Holt Oram ASD)

BLOOD GAS ABNORMALITY

Anion Gap Correction in Hypoalbuminemia

• Normal AG: 10 mmol/L (with albumin 4.5 g/dL)

• Correction:
• For every ↓ 1 g/dL albumin below 4.5 → add 2.5 mmol/L to AG

• Example: Albumin 2.5 g/dL (↓2 g/dL), AG = 15
• Correction = 2 × 2.5 = 5
• Corrected AG = 15 + 5 = 20 mmol/L

All About ABG Interpretation

• MCQ Question: Identify the acid-base disorder in a patient with the given values.
• Blood pH: 7.2
• PO2: 90 mmHg
• pCO2: 80mmHg
• Plasma HCO3: 35mEq/L
• A. Respiratory acidosis,
• B. Respiratory alkalosis,
• C. Metabolic acidosis,
• D. Metabolic alkalosis.
ANS
A

Interpretation

• Normal ranges:
• Blood pH: 7.36-7.44.
• pCO2: 36-44 mmHg.
• HCO3: 21-27 mEq/L.

Formulae for Compensation

a. Metabolic disorders

• Metabolic acidosis
• Compensation: Reduce PCO2.
• Expected pCO2 = [ 1.5 x HCO3 ]+ 8 (Winters formula)

• Metabolic alkalosis
• Compensation: Increase PCO2.
• Expected pCO2 = [0.9 x HCO3 ] + 16

• Inference
• If actual pCO2 = expected pCO2,
• compensated.
• If actual pCO2 > expected pCO2
• uncompensated OR
• If actual pCO2 < expected pCO2
• hidden acid-base disorder.

• Important:
• Body never overcompensates.

b. Respiratory disorders

• Study the table

• Respiratory acidosis
• For every 10 mmHg rise in pCO2,
• HCO3 elevates by:
• Acute: 1 mEq/L.
• Chronic: 3.5 mEq/L.

• Respiratory alkalosis
• For every 10 mmHg decline in pCO2,
• HCO3 reduces by:
• Acute: 2 mEq/L.
• Chronic: 5 mEq/L.

MCQ Question:

• Interpret the ABG report
• Blood pH: 7.30
• pCO2: 29mmHg
• Plasma HCO3: 14 mEq/L
Explanation:
• Expected pCO2 = 1.5 x 14 + 8 = 29mmHg.
• Step 1: Acidosis (Low pH).
• Step 2: Primary metabolic disorder (low HCO3).
• Step 3: Compensation is present (actual pCO2 matches expected).
• Step 4: Calculate Anion gap for Metabolic acidosis.

Anion gap

• Interpret the ABG report with electrolytes
• Blood pH: 7.30
• pCO2: 29mmHg
• Plasma HCO3: 14 mEq/L
• Na+: 130mEq/L
• Cl-: 90mEq/L
• A. Compensated increased anion gap metabolic acidosis,
• B. Uncompensated increased anion gap metabolic acidosis,
• C. Compensated normal anion gap metabolic acidosis,
• D. Uncompensated normal anion gap metabolic acidosis.
ANS
Compensated increased anion gap metabolic acidosis

• Anion gap
• = Unmeasured anion - Unmeasured Cations
  = [Na+] - [(Cl-) + (HCO3-)].

• Normal anion gap:
• 12 ± 2 mEq/L.

• Reflects
• Laws of Electroneutrality.

• Unmeasured anions:
• Sulfate,
• Protein anions,
• Lactate,
• Salicylate.

• Metabolic acidosis is from:
• Increased utilization of HCO3
• Loss of HCO3.

1. Increased utilization of HCO3

• HAGMA

• Abnormal acids use up HCO3.

• Unmeasured anion (UMA) increases.

• Causes of increased anion gap (abnormal acids):
• Ketoacidosis
• DKA, Starvation
• Lactic acidosis.
• Uric acidosis.
• Alcohol poisoning
• Methanol,
• Ethanol,
• Ethylene glycol
• Kidney failure.

2. Loss of HCO3

• NAGMA.

• Loss is via GIT or kidney.
• GIT loss: Diarrhea.
• Renal loss: Renal tubular acidosis.

• Hyperchloremic Metabolic Acidosis.
• The body reclaims chloride anions to maintain balance.

MCQ Question:

• Interpret the ABG report (Final Calculation)
• Blood pH: 7.30,
• pCO2: 29mmHg,
• HCO3: 14 mEq/L,
• Na+: 130mEq/L,
• Cl-: 90mEq/L
Explanation:
• Anion gap = 130 - (90 + 14) = 26 mEq/L.
• 26 > 14, so it is an increased anion gap.

Question:

• Q. A 60-year-old diabetic patient with repeated vomiting following a recent dine-out. Her blood pressure was 90/60 mmHg
• pH: 7.3
• HCO3: 18mEq/L
• pCO2: 35mmHg
• Identify the acid-base disorder
• A. Metabolic Acidosis
• B. Metabolic Alkalosis
• C. Respiratory Alkalosis
• D. Respiratory Acidosis
Explanation:
• Vomiting causes metabolic alkalosis.
• pH indicates acidosis.
• A diabetic with stress can develop DKA (metabolic acidosis).

Question:

• Q. A 7-week-old baby was brought by the mother with complaints of repeated projectile vomiting and pellet stools. The probable metabolic disturbance is:
• A. Normal anion gap metabolic acidosis
• B. Hypochloremic hypokalemic metabolic alkalosis
• C. Hyperchloremic hypokalemic metabolic alkalosis
• D. Respiratory acidosis
ANS
• B. Hypochloremic hypokalemic metabolic alkalosis

Question:

• Q. The interpretation of the following ABG value is?
• pH-7.34
• Na-135meq/L
• Cl 93 meq/L
• HCO3 20meq/L
Explanation:
• C. Increased anion gap metabolic acidosis
• Anion gap = 135 - (93 + 20) = 21.
• This is a High anion gap.

Question:

• Q. The interpretation of the following ABG value is:
• pH: 7.5
• pCO2: 50mm Hg
• HCO3: 30meq/L
Answer:
B. Metabolic alkalosis + Respiratory Acidosis

Question:

• Q. A hyperventilating hysterical woman presents with carpopedal spasm. The cause is:
• A. High total calcium
• B. Low total calcium
• C. Alkalosis
• D. Acidosis
Explanation:
• Hyperventilation causes respiratory alkalosis (high pH).
• Plasma proteins become more negatively charged to buffer the pH.
• These proteins bind more calcium.
• Free calcium concentration is reduced.
• Neurons become hyperstimulated, causing carpopedal spasm.

Hypocalcemic tetany

• H+ and Ca2+ competitively bind to albumin.

• Mechanism: 
• ↓H+ (e.g., in respiratory alkalosis) → 
• ↑ Ca2+ binding to albumin → ↓ free Ca2+ 

IMPORTANT NOTES

Limiting pH:

• pH at which PCT stops excretion of H+ = 4.5

• Never seen in PCT due to strict buffering.

• Seen in collecting duct, where urine is acidified.

Normal Values: