**Question:** Aerial blood gas analysis of a patient reveals - pH 7.2, HCO3 36 mmol/L pCO2 70 mmHg. The abnormality is

A. Hypercapnia
B. Hypocapnia
C. Hyperchloremia
D. Hyperventilation

**Correct Answer:** **Option B: Hypocapnia**

**Core Concept:**
Blood gas analysis is an essential tool in assessing respiratory and acid-base balance in patients. The normal ranges for pH, HCO3, and pCO2 are:

- pH: 7.35-7.45 (slightly alkaline)
- HCO3: 22-28 mmol/L
- pCO2: 35-45 mmHg

**Why the Correct Answer is Right:**
The patient's blood gas analysis shows the following values: pH 7.2, HCO3 36 mmol/L, and pCO2 70 mmHg.

- A pH of 7.2 is significantly acidic (normal range is slightly alkaline, i.e., 7.35-7.45). This indicates respiratory acidosis due to reduced CO2 levels in the blood.
- A HCO3 level of 36 mmol/L is within the normal range (22-28 mmol/L), ruling out the contribution of acidosis from this parameter.
- A pCO2 of 70 mmHg is elevated (normal range is 35-45 mmHg), suggesting reduced CO2 levels in the blood, which is consistent with respiratory acidosis.

**Why Each Wrong Option is Incorrect:**

**Option A: Hypercapnia (Hyperventilation)**
- Hyperventilation refers to increased respiratory rate to remove excessive CO2 from the blood. However, the patient's pCO2 is elevated (70 mmHg), indicating reduced CO2 levels and not increased CO2 levels.

**Option C: Hyperchloremia (Hypokalemia)**
- Hyperchloremia (elevated serum chloride levels) is unrelated to the pH, HCO3, and pCO2 values provided. The patient's respiratory acidosis is not caused by altered chloride levels.

**Option D: Hypoventilation (Hypocapnia)**
- Hypoventilation refers to reduced respiratory rate to increase CO2 levels in the blood. In this case, the patient's pCO2 is elevated, confirming increased CO2 levels and not decreased levels.

**Core Concept Explanation:**

Respiratory acidosis is a condition where the pH of the blood is acidotic, indicating a decrease in the partial pressure of carbon dioxide (pCO2). This occurs due to insufficient ventilation, leading to accumulation of CO2 in the blood and causing respiratory acidosis.

**Why Each Wrong Option is Incorrect:**

**Option A: Hypercapnia (Hypoventilation)**
- Hypoventilation (increased pCO2) is not the cause of respiratory acidosis, as it would result in respiratory alkalosis