The arterial blood gas below indicates that the primary acid-base imbalance is:

pH - 7.25

PaCO2 - 20 mm Hg

HCO3- - 10 mEq/L

Select all that apply:

Normal range:

pH = 7.35-7.45

PaCO2 = 36-44 mmHg

HCO3- = 22-26 mEq/L

Choice A Reason:

Acidosis is indicated by a pH lower than the normal range of 7.35-7.45. In this case, the patient’s pH is 7.3, which confirms acidosis. Acidosis can be caused by either respiratory or metabolic factors, but the low pH alone confirms the presence of acidosis.

Choice B Reason:

Compensation refers to the body’s attempt to return the pH to normal by adjusting the levels of CO2 or HCO3-. In this case, the HCO3- level is within the normal range (22-26 mEq/L), indicating that there is no metabolic compensation occurring. Therefore, this choice is incorrect.

Choice C Reason:

Respiratory acidosis is indicated by an elevated PaCO2 level, which is higher than the normal range of 36-44 mmHg. The patient’s PaCO2 is 48 mmHg, suggesting that the acidosis is due to respiratory factors. This is consistent with the patient’s history of smoking and symptoms of respiratory distress.

Choice D Reason:

Alkalosis is indicated by a pH higher than the normal range of 7.35-7.45. Since the patient’s pH is 7.3, which is below the normal range, this indicates acidosis, not alkalosis. Therefore, this choice is incorrect.

Choice E Reason:

Metabolic acidosis is indicated by a low HCO3- level. In this case, the patient’s HCO3- level is within the normal range (25 mEq/L), indicating that the acidosis is not metabolic. Therefore, this choice is incorrect.

Choice A Reason:

To determine how much of the medication remains in the body after a certain period, we need to understand the concept of half-life. The half-life of a medication is the time it takes for the concentration of the drug in the bloodstream to reduce by half. For Medication A, the half-life is 3 hours. After 12 hours, which is four half-lives, the amount of medication remaining can be calculated step by step.

Choice B Reason:

Let’s break down the calculation. Initially, the patient receives 400 mg of Medication A. After the first half-life (3 hours), the amount of medication remaining is 400 mg ÷ 2 = 200 mg. After the second half-life (6 hours), the amount remaining is 200 mg ÷ 2 = 100 mg. After the third half-life (9 hours), the amount remaining is 100 mg ÷ 2 = 50 mg. Finally, after the fourth half-life (12 hours), the amount remaining is 50 mg ÷ 2 = 25 mg. Therefore, 375 mg is not a correct answer.

Choice C Reason:

Similarly, 150 mg is not correct. As shown in the detailed calculation, the amount of medication decreases by half every 3 hours. After 12 hours, the remaining amount is 25 mg, not 150 mg. This choice does not align with the half-life calculation.

Choice D Reason:

This is the correct answer. The step-by-step calculation shows that after 12 hours, which is equivalent to four half-lives, the amount of Medication A remaining in the patient’s body is 25 mg. This demonstrates the principle of half-life and how the concentration of a drug decreases over time.