Regarding the pharmacological properties of intravenous induction agents, all of the following statements are correct EXCEPT:

Explanation

## Analysis of IV Induction Agent Properties ### Correct Statements (Options 0, 1, 3) **Option 0 — Propofol respiratory depression:** **Key Point:** Propofol causes profound dose-dependent respiratory depression and frequently induces apnea, especially at induction doses. Thiopentone, while also a respiratory depressant, is less likely to cause immediate apnea at standard induction doses. **Option 1 — Etomidate cardiovascular profile:** **Key Point:** Etomidate is the agent of choice when cardiovascular stability is critical (shock, sepsis, cardiac disease) because it maintains blood pressure and heart rate better than propofol or thiopentone. **Option 3 — Thiopentone context-sensitive half-time:** **Key Point:** Thiopentone has extremely high lipid solubility and undergoes rapid redistribution from the brain to peripheral tissues, but has slow hepatic metabolism. This results in a LONGER context-sensitive half-time (elimination half-life ~11 hours) compared to propofol (~40 minutes). Repeated doses lead to cumulative effects. ### The Incorrect Statement (Option 2 — Ketamine and ICP) **High-Yield:** Ketamine is one of the PREFERRED agents in head injury and elevated ICP because it: - Maintains or increases cerebral perfusion pressure (CPP) - Preserves airway reflexes - Does NOT increase ICP in most clinical scenarios (contrary to older teaching) - Maintains spontaneous ventilation **Warning:** The old teaching that "ketamine increases ICP" is now considered **incorrect**. Modern evidence and guidelines (including ASA and neurosurgical consensus) support ketamine use in head injury and neurosurgical patients. ### Comparative Table: IV Induction Agents | Property | Propofol | Thiopentone | Etomidate | Ketamine | |----------|----------|-------------|-----------|----------| | **Respiratory Depression** | Profound (apnea common) | Moderate | Minimal | Minimal | | **Cardiovascular Effect** | ↓ BP, ↓ HR | ↓ BP, ↓ HR | Stable | ↑ BP, ↑ HR | | **ICP** | ↓ (safe) | ↓ (safe) | ↓ (safe) | Maintained/↑ (but CPP preserved) | | **Airway Reflexes** | Abolished | Abolished | Preserved | Preserved | | **Context-Sensitive HT** | ~40 min | ~11 hours | ~5 hours | ~3 hours | | **Adrenal Suppression** | No | No | **Yes (single dose)** | No | **Clinical Pearl:** Ketamine's sympathomimetic effects (catecholamine release) offset its direct myocardial depression, making it ideal for hemodynamically unstable patients and head injury.