Understanding ABGs and Compensation

Which of the following pH values indicates acidosis?

• 7.48

• 7.32

• 7.40

• 7.46

Answer explanation

A pH value below 7.35 indicates acidosis. Among the options, 7.32 is the only value that falls below this threshold, confirming it as the correct choice for indicating acidosis.

• Normal

• Low

• High

• Unmeasurable

Answer explanation

A PaCO₂ value of 50 mmHg indicates hypercapnia, which is elevated carbon dioxide in the blood. Normal values range from 35 to 45 mmHg, making 50 mmHg a high value.

• 20 mEq/L

• 24 mEq/L

• 28 mEq/L

• 22 mEq/L

Answer explanation

A HCO₃⁻ level of 28 mEq/L indicates metabolic alkalosis, as normal levels range from 22 to 26 mEq/L. Values above this range suggest an alkalotic state, making 28 mEq/L the correct choice.

• Respiratory acidosis

• Metabolic acidosis

• Respiratory alkalosis

• Metabolic alkalosis

Answer explanation

The pH of 7.48 indicates alkalosis. The low PaCO2 of 32 mmHg suggests hyperventilation, leading to respiratory alkalosis. HCO3- is normal at 24 mEq/L, confirming the diagnosis.

Which of the following is a primary cause of metabolic acidosis?

• Vomiting

• Diuretics

• Diabetic ketoacidosis (DKA)

• Anxiety

Answer explanation

Diabetic ketoacidosis (DKA) is a primary cause of metabolic acidosis due to the accumulation of ketone bodies, which lower blood pH. In contrast, vomiting and diuretics typically lead to metabolic alkalosis.

What is the expected compensatory mechanism for respiratory acidosis?

Answer explanation

In respiratory acidosis, the lungs cannot effectively remove CO2, leading to increased acidity. The kidneys compensate by retaining bicarbonate (HCO3-) to help neutralize the acid, making 'Kidneys retain HCO3-' the correct answer.

• Respiratory acidosis

• Metabolic acidosis

• Respiratory alkalosis

• Metabolic alkalosis

Answer explanation

The patient has a low pH (7.30) indicating acidosis. The HCO3- level is also low (18 mEq/L), which confirms metabolic acidosis. The PaCO2 is normal, ruling out respiratory causes.

Which of the following ABG results indicates fully compensated respiratory acidosis?

Answer explanation

The correct choice, pH 7.38, PaCO2 48, HCO3 28, indicates fully compensated respiratory acidosis as the pH is near normal (7.35-7.45) with elevated PaCO2 and HCO3, showing compensation by metabolic alkalosis.

• Uncompensated

• Partially compensated

• Fully compensated

• Not enough information

Answer explanation

The pH is low (acidosis), and PaCO2 is elevated, indicating respiratory acidosis. HCO3- is slightly low, suggesting partial compensation. Since pH is still abnormal, this is classified as partially compensated.

Which of the following conditions is most likely to cause respiratory alkalosis?

• COPD

• Opioid overdose

• Hyperventilation due to anxiety

• Diabetic ketoacidosis

Answer explanation

Hyperventilation due to anxiety leads to excessive breathing, causing a decrease in carbon dioxide levels and resulting in respiratory alkalosis. In contrast, COPD and opioid overdose typically cause respiratory acidosis.