Volatile Anaesthetic Agents Medical Student Lecture.pptx

Volatile Anaesthetic Agents Medical Student

1. Volatile Anaesthetic Agents Medical Students Lecture Dr . Sulaiman Sani Bara Senior Registrar, Dept. of Anaesthesia & ICU ATBU Teaching Hospital, Bauchi 9/15/2025 1

2. Learning Objectives Define volatile anaesthetic agents and differentiate them from gaseous agents. Explain the physicochemical properties relevant to their clinical use. Discuss detailed pharmacokinetics (uptake, distribution, metabolism, elimination). Describe pharmacodynamics on various organ systems (CNS, CVS, RS, MSK). Explain the concept and clinical application of MAC and factors that alter MAC. Outline adverse effects, contraindications, and precautions. Review specific uses of Halothane, Isoflurane , Sevoflurane , Desflurane . Highlight occupational hazards and environmental concerns. 9/15/2025 2

3. Definition Volatile anaesthetic agents are liquids at room temperature that vaporize easily. Administered by inhalation using vaporizers in anaesthesia machines. They act mainly on the central nervous system to induce and maintain general anaesthesia . Distinct from gaseous agents (e.g., nitrous oxide, xenon). 9/15/2025 3

4. Physicochemical Properties Vapour pressure: Determines how readily a liquid vaporizes. Boiling point: Lower boiling point = easier vaporization. Blood:Gas partition coefficient: Indicates solubility in blood. Oil:Gas partition coefficient: Correlates with potency (Meyer-Overton rule). 9/15/2025 4

5. Pharmacokinetics - Uptake & Distribution Determined by: Inspired concentration (Fi). Alveolar ventilation (VA). Blood:gas partition coefficient (solubility in blood). Cardiac output (higher output slows induction). Alveolar-to-venous partial pressure difference. 9/15/2025 5

6. Pharmacokinetics - Elimination & Metabolism Elimination is primarily via exhalation (lungs). Minimal hepatic metabolism for most agents: Halothane : up to 20% (hepatotoxicity risk). Sevoflurane : 2–5% (Compound A in soda lime). Isoflurane / Desflurane : <0.2%. Context-sensitive half-time is short due to exhalation. 9/15/2025 6

7. Pharmacodynamics - CNS Effects Produce unconsciousness, amnesia, and immobility. Dose-dependent EEG changes: burst suppression at high concentrations. Increase cerebral blood flow (except low-dose Isoflurane ). Can increase intracranial pressure (important in neuro cases). 9/15/2025 7

8. Pharmacodynamics - Respiratory & Cardiovascular Respiratory system: Dose-dependent respiratory depression. Reduced tidal volume, increased respiratory rate. Blunted response to hypoxia and hypercarbia . Cardiovascular system: Vasodilation → ↓ systemic vascular resistance → hypotension. Myocardial depression (more with Halothane). Isoflurane , Sevoflurane , Desflurane : better preserved CO. 9/15/2025 8

9. Pharmacodynamics - Other Effects Musculoskeletal: Muscle relaxation (but not sufficient for surgery → use NMBDs). Renal: Reduced renal blood flow and GFR (dose-dependent). Hepatic: Reduced hepatic blood flow (Halothane hepatotoxicity). Trigger malignant hyperthermia in susceptible patients. 9/15/2025 9

10. Minimum Alveolar Concentration (MAC) Definition: Alveolar concentration at 1 atm that prevents movement in 50% of patients exposed to a surgical stimulus. Inverse of potency (lower MAC = higher potency). Factors decreasing MAC: age (elderly), hypothermia, opioids, pregnancy. Factors increasing MAC: hyperthermia, chronic alcohol, CNS stimulants. Typical MAC values: Halothane 0.75% Isoflurane 1.2% Sevoflurane 2% Desflurane 6% 9/15/2025 10

11. Specific Clinical Considerations Halothane : potent, non-irritant, but hepatotoxicity risk → rarely used. Isoflurane : inexpensive, stable, pungent (not for inhalation induction). Sevoflurane : non-irritant, ideal for paediatric induction, slight nephrotoxic risk. Desflurane : ultra-rapid onset/offset, airway irritation, requires heated vaporizer. 9/15/2025 11

12. Adverse Effects Cardiovascular depression, arrhythmias (Halothane). Respiratory depression, impaired hypoxic drive. Postoperative nausea and vomiting (PONV). Malignant hyperthermia (all agents except N2O). Hepatic dysfunction (Halothane hepatitis). Nephrotoxicity ( Sevoflurane compound A). 9/15/2025 12

13. Safety & Monitoring Use agent-specific vaporizers for accurate delivery. Continuous monitoring of end-tidal agent concentration. Ensure proper scavenging systems to reduce theatre pollution. Be vigilant for malignant hyperthermia – have dantrolene available. Avoid Halothane in repeated exposures (esp. children). 9/15/2025 13

14. Environmental & Occupational Concerns Volatile agents contribute to greenhouse effect. Desflurane has particularly high global warming potential. Scavenging systems and low-flow anaesthesia reduce exposure. Chronic occupational exposure linked to headaches, fatigue, miscarriage risks. 9/15/2025 14

15. Summary Volatile anaesthetics remain cornerstone of balanced general anaesthesia . Understanding their PK/PD is essential for safe and effective use. Agent choice depends on patient profile, surgery type, and safety considerations. Final year medical students should appreciate both clinical utility and hazards. 9/15/2025 15

16. Thank You Questions & Discussion 9/15/2025 16