## Core Concept
Cushing's Triad is a physiological nervous system response to increased intracranial pressure (ICP) that results in three primary signs: increased blood pressure, irregular breathing, and a reduction in heart rate (bradycardia). This triad is a compensatory mechanism to maintain cerebral perfusion in the setting of raised ICP.

## Why the Correct Answer is Right
The classic components of Cushing's Triad are:
- **Hypertension**: A compensatory increase in blood pressure to ensure continued cerebral perfusion in the face of raised ICP.
- **Bradycardia**: A reflex decrease in heart rate in response to the increased blood pressure, attempting to normalize the cerebral blood flow.
- **Irregular breathing (or respiratory irregularity)**: Changes in respiratory pattern, which can range from Cheyne-Stokes respiration to other abnormal breathing patterns.

## Why Each Wrong Option is Incorrect
- **Option A:** Bradycardia is indeed a component of Cushing's Triad, making it an incorrect choice for "all except."
- **Option B:** Hypertension is a key component, so it's also incorrect as an "all except" option.
- **Option C:** Irregular breathing patterns are part of the triad, which means this option is incorrect for the same reason.

## Why the Correct Answer is Actually Correct
- **Option D:** Typically, Cushing's Triad consists of hypertension, bradycardia, and irregular breathing. **Tachycardia** is not a component of Cushing's Triad; instead, bradycardia is. Therefore, tachycardia is the correct "all except" option.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that Cushing's Triad is a late sign of raised intracranial pressure and indicates impending brain herniation. Early recognition and intervention are critical. Remember, the presence of Cushing's Triad signifies a severe and potentially life-threatening elevation in ICP.

## Correct Answer: D. Tachycardia