A female student is driving to school when another driver nearly hits her. Her heart begins beating hard and fast as she becomes scared and aroused. Which of the following stages of the general adaptation syndrome is she experiencing?

Choice A: Metabolic Acid Deficit (Metabolic Alkalosis)

Vomiting or continuous nasogastric suctioning leads to the loss of gastric contents, which are rich in hydrochloric acid (HCl)1. This loss results in a decrease in the body’s acid levels, leading to a condition known as metabolic alkalosis2. Metabolic alkalosis is characterized by an increase in blood pH due to the loss of hydrogen ions (H+) and an increase in bicarbonate (HCO3-) levels. This condition can cause symptoms such as muscle twitching, hand tremors, and light-headedness.

Choice B: Carbonic Acid Excess (Respiratory Acidosis)

Carbonic acid excess, or respiratory acidosis, occurs when there is an accumulation of carbon dioxide (CO2) in the blood, leading to a decrease in blood pH3. This condition is typically caused by respiratory issues such as hypoventilation, chronic obstructive pulmonary disease (COPD), or severe asthma. It is not directly related to vomiting or nasogastric suctioning, which primarily affect the metabolic component of acid-base balance.

Choice C: Metabolic Acid Excess (Metabolic Acidosis)

Metabolic acidosis is characterized by a decrease in blood pH due to an accumulation of metabolic acids or a loss of bicarbonate. Common causes include renal failure, diabetic ketoacidosis, and severe diarrhea. Vomiting or nasogastric suctioning, which result in the loss of gastric acid, do not lead to metabolic acidosis but rather to metabolic alkalosis.

Choice D: Carbonic Acid Deficit (Respiratory Alkalosis)

Respiratory alkalosis occurs when there is a decrease in carbon dioxide levels in the blood, leading to an increase in blood pH. This condition is often caused by hyperventilation due to anxiety, fever, or high altitude. It is not related to the loss of gastric contents through vomiting or nasogastric suctioning, which primarily affect the metabolic component of acid-base balance.

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.