Regarding the cardiovascular effects of halothane on blood pressure, the following statements are given: 1. A drop of 20–30 mmHg in blood pressure is commonly observed 2. The fall in blood pressure begins early and is proportional to the depth of Anaesthesia 3. The fall in blood pressure reduces as the depth of Anaesthesia 4. The baroreceptor reflex mechanism is activated in response to the fall in blood pressure Which of the above statements are correct?

1. A

   A. 1, 2, and 3 only

2. B

   B. 2, 3, and 4 only

3. C

   C. 1, 2, and 4 only

4. D

   D. 1, 3, and 4 only

Appeared in: INI-CET EXAM -2026

Explanation

• Halothane causes a dose-dependent decrease in mean arterial pressure, primarily through myocardial depression which reduces cardiac output. This aligns with statements 1 and 2.
• The fall in blood pressure begins soon after administration and its magnitude is directly proportional to the alveolar concentration (depth of anesthesia).
• Statement 4 is included in the correct option, but it's crucial to understand that halothane significantly blunts the baroreceptor reflex. This means that despite the drop in blood pressure, there is little to no compensatory increase in heart rate, a key clinical characteristic of halothane.

Why Other Options Were Wrong

• Option A: This option includes statement 3, which is factually incorrect. The fall in blood pressure is directly proportional to the depth of anesthesia, meaning it becomes more severe, not less, as anesthesia deepens.
• Option B: This option includes the incorrect statement 3. Deeper anesthesia with halothane leads to a greater, not a reduced, fall in blood pressure.
• Option D: This option includes the incorrect statement 3. The hypotensive effect of halothane is exacerbated, not lessened, by increasing the depth of anesthesia.

Related Visual

Clinical Relevance

• Nursing practice connection: Knowing Pharmacology of Inhaled Anesthetics helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
• When a patient is under halothane anesthesia, nurses must continuously monitor blood pressure. A drop in BP without a corresponding rise in heart rate is expected and indicates the blunting of the baroreceptor reflex by the drug.
• This knowledge is critical for patient safety. An anesthetist might misinterpret hypotension without tachycardia as a sign of stability, when in fact it is a direct, and potentially dangerous, effect of the anesthetic.
• What if? If a patient under halothane anesthesia develops severe hypotension and the team decides to administer a sympathomimetic agent like epinephrine, there is a high risk of inducing ventricular arrhythmias. This is because halothane sensitizes the myocardium to the effects of catecholamines.

How to Approach the Question

• First, read the question stem and analyze each of the four statements independently based on your knowledge of pharmacology.
• Identify statement 2: 'proportional to the depth of Anaesthesia'. This describes a dose-dependent effect, which is a core principle for most anesthetics.
• Identify statement 3: 'reduces as the depth of Anaesthesia'. This is the direct opposite of statement 2. If one is true, the other must be false. Since dose-dependent effects are standard, statement 3 is highly likely to be incorrect.
• Eliminate all answer options that include the definitively incorrect statement (3). In this case, options A, B, and D all contain statement 3.
• This process of elimination leaves only option C as the possible answer, even if one of its components (statement 4) is clinically nuanced or partially incorrect.

Concept Tested & Keywords

• Concept Tested: Pharmacology of Inhaled Anesthetics
• Stem keywords: halothane, cardiovascular effects, blood pressure, depth of Anaesthesia, baroreceptor reflex
• Lead-in keywords: Which of the above statements are correct?

Question ID

QCgp3ZpJ7UwJQ3yXtXn7UM

Copy ID

Reference Book

E6 Pharmacology Katzung 16e p. 699-701