## IV Induction Agent Selection in Hemodynamically Unstable Patients ### Clinical Context: Septic Shock with Hypotension In a patient with septic shock and severe hypotension (BP 85/50 mmHg), the choice of induction agent is critical. Agents that cause myocardial depression or vasodilation are contraindicated because they risk cardiovascular collapse. ### Comparison of Hemodynamic Effects | Agent | BP Effect | HR Effect | SVR | Mechanism | Use in Shock | |-------|-----------|-----------|-----|-----------|-------------| | **Propofol** | ↓↓ (severe) | ↑ | ↓↓ | Myocardial depression + vasodilation | **Contraindicated** | | **Thiopentone** | ↓↓ (severe) | ↑ | ↓↓ | Myocardial depression + CNS depression | **Contraindicated** | | **Etomidate** | ↓ (mild) | ↔ | ↔ | Minimal CV effect | **Acceptable** | | **Ketamine** | ↑ or ↔ | ↑ | ↑ | Sympathomimetic (catecholamine release) | **Preferred** | ### Why Ketamine Is the Most Common Choice **Key Point:** Ketamine is the induction agent of choice in hemodynamically unstable patients (septic shock, hemorrhagic shock, cardiogenic shock) because it preserves or increases blood pressure through sympathomimetic effects. 1. **Sympathomimetic properties:** Ketamine causes catecholamine release from sympathetic nerve terminals, maintaining or increasing heart rate and blood pressure. 2. **Preserved airway reflexes:** Unlike propofol and thiopentone, ketamine maintains spontaneous ventilation and airway protective reflexes better. 3. **Preserved cerebral perfusion:** Maintains cerebral blood flow and intracranial pressure stability. 4. **Analgesic properties:** Provides analgesia in addition to hypnosis — a bonus in trauma/critical care. 5. **Bronchodilation:** Beneficial in patients with reactive airway disease. **High-Yield:** In any hemodynamically unstable patient (septic shock, hypovolemia, cardiogenic shock, anaphylaxis), ketamine is the induction agent of choice. This is tested frequently in NEET PG because it is clinically critical. ### Why Etomidate Is Second Choice Etomidate has minimal cardiovascular effects and is acceptable in unstable patients. However, it: - Lacks the sympathomimetic boost of ketamine - Causes adrenal suppression (single dose can impair cortisol response for 24 hours) - Does not provide analgesia **Clinical Pearl:** Etomidate is often reserved for patients with preserved baseline hemodynamics but relative contraindications to ketamine (e.g., uncontrolled hypertension, severe coronary artery disease). ### Mechanism Flowchart ```mermaid flowchart TD A[Hemodynamically Unstable Patient<br/>Septic Shock, Hypotension]:::outcome --> B{Choose Induction Agent}:::decision B -->|Propofol| C[Severe BP ↓↓<br/>Risk of Collapse]:::urgent B -->|Thiopentone| D[Severe BP ↓↓<br/>Risk of Collapse]:::urgent B -->|Etomidate| E[Minimal CV Effect<br/>Acceptable]:::action B -->|Ketamine| F[BP ↑ or ↔<br/>Sympathomimetic]:::action F --> G[Preferred Choice]:::outcome E --> H[Second Choice]:::outcome ``` **Warning:** Do NOT use propofol or thiopentone as induction agents in septic shock. Both cause profound vasodilation and myocardial depression, risking cardiovascular collapse and death. [cite:Stoelting & Miller Basics of Anesthesia 7e Ch 5; Harrison 21e Ch 296]
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