Anaesthetics Series: Basic Anaesthetic Pharmacology | Ak Maheswaran

Summary

This on-demand teaching session is relevant to medical professionals who specialize in anaesthetic pharmacology. It will cover intravenous induction agents, inhalational anaesthetics, and muscle relaxants and delve into their pharmacodynamics, clinical rationale, pharmacokinetics, and uses. In addition, side effects and elimination of each drug will be discussed. Attendees will learn how to choose the right agents to induce, maintain, sedate, provide analgesia, and treat status epilepticus, asthmaticus, and more.

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Description

Introduction:

This guide provides a comprehensive overview of the pharmacological aspects of anesthesia, focusing on pharmacodynamics (effects of drugs on the body), pharmacokinetics (how the body processes drugs), and the clinical rationale for the use of specific agents.

1. Intravenous Induction Agents:

These agents are administered intravenously to induce anesthesia. Commonly used agents include:

Propofol:Uses: Induction, Maintenance, Sedation
Effects: Vasodilatation, decreased blood pressure, apnea, suppression of laryngeal reflexes, bronchodilatation, and anti-emetic properties.
Thiopental:Uses: Induction, Treatment of status epilepticus
Effects: Negative cardiovascular effects, prolonged respiratory depression, potential for bronchoconstriction, and anticonvulsant properties.
Etomidate:Uses: Induction
Effects: Relatively stable cardiovascular profile with a single dose, impaired steroid synthesis, and involuntary muscle movements.
Ketamine:Uses: Induction, Analgesia, Procedural Sedation
Effects: Increased heart rate, blood pressure, and sympathetic tone. Provides some analgesia and may cause emergence delirium and hallucinations.

2. Inhalational Anaesthetics:

These agents are inhaled to maintain anesthesia.

Common Effects: They generally cause myocardial depression, reduction in tidal volume, increased cerebral vasodilatation, and increased cerebral blood flow.
Types:Halothane: Noted for hepatic toxicity
Isoflurane, Enflurane, Sevoflurane, Desflurane: These have similar effects on the cardiovascular and respiratory systems, with some specific characteristics like bronchodilation or being airway irritants.

3. Muscle Relaxants:

These agents are used to paralyze muscles during surgery.

Suxamethonium:Uses: Rapid onset muscle paralysis
Side Effects: Bradycardia, myalgia, increased intragastric pressure, hyperkalemia, and potential for malignant hyperthermia.
Non-Depolarising Agents:Atracurium: Known for histamine release and is eliminated through Hoffman degradation.
Rocuronium: Increases heart rate and mean arterial pressure.
Vecuronium: Potential side effects include bronchospasm and hypotension.
Pancuronium: Known for causing tachycardia and arrhythmias.

Conclusion:

Anesthetic agents have specific pharmacological profiles that influence their use in clinical practice. It's imperative for clinicians to understand the pharmacodynamics and pharmacokinetics of these drugs to administer them safely and effectively. Whether used for induction, maintenance, or muscle relaxation during surgeries, each drug offers unique benefits and challenges. Proper understanding and application can significantly improve patient outcomes during surgical procedures.

Learning objectives

Learning objective: Understand and describe the basic mechanisms of action of intravenous induction agents.
Learning objective: Explain the key differences among the various intravenous induction agents in terms of their uses, chemical name, dose, and pharmacological effects.
Learning objective: Grasp the clinical rationale for propofol, thiopental, etomidate, and ketamine, including their cardiovascular, respiratory, and central nervous system (CNS) pharmacodynamic effects.
Learning objective: Demonstrate the uses, chemical name, dose, and pharmacokinetics/pharmacodynamics (PK/PD) of inhalational anesthetics, such as halothane, isoflurane, enflurane, sevoflurane, and desflurane.
Learning objective: Analyze the different muscle relaxants (suxamethonium, atracurium, rocuronium, vecuronium, and pancuronium), including their uses, dosing, pharmacological side effects, and elimination.

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BASIC ANAESTHETIC PHARMACOLOGY A Clinical GuideWhat are we going to cover? - IV induction Agents - Inhalational anaesthetics - Muscle relaxants Focus PHARMACODYNAMICS CLINICAL RATIONALE PHARMACOKINETICS (WHAT THE DRUG DOES (WHAT THE BODY DOES TO THE BODY) TO THE DRUG) - ONLY WHERE RELEVANTIntravenous Potpdftl l Induction Agents Propofol Thiopental Intravenous Induction Agents Etomidate Ketamine Propofol Thiopental Intravenous Induction Agents Etomidate Ketamine Propofol Uses: Chemical Name: Dose: Induction 2,6 di-isopropylphenol 1 – 2mg/kg Maintenance 50% dose in children Sedation This Photo by Unknown Author is licensed under CC BY-NC-ND Propofol CVS Respiratory CNS Vasodilatation Apnoea Smooth Induction  SVR Suppression of ICP  BP laryngeal reflexes Cerebral blood flow Bronchodilatation Anticonvulsant Anti-emetic This Photo by Unknown Author is licensed under CC BY-NC-ND Thiopental Uses: Chemical Name: Dose: Induction Thiobarbiturate IV 2 – 7mg/kg Status epilepticus Can be given rectally Thiopental CVS Respiratory CNS Negative inotrope Apnoea Smooth Induction  SVR Prolonger respiratory ICP  CO depression Cerebral blood flow  BP Can cause Anticonvulsant Bronchoconstriction Etomidate Uses: Chemical Name: Dose: Induction Carboxylated imidazole 0.3mg/kg Etomidate CVS Respiratory CNS Relatively stable with Transient Apnoea ICP single does Reduced rate and Cerebral blood flow volume Involuntary muscle Steroid Synthesis Coughing and hiccups movements impairment common Can get epileptiform activity on EEG Ketamine Uses: Chemical Name: Dose: Induction Phencylidine derivative IV 1.5 - 2mg/kg Analgesia Can be given IM or Procedural Sedation Orally Status asthmaticus Ketamine CVS Respiratory CNS  Heart rate Respiratory stimulant ICP  BP & CO Preservation of airway Amnesia  Sympathetic tone reflexes Some analgesia (not visceral) Emergence delirium & hallucinationsINHALATIONAL ANAESTHETICS Inhalation Agents Common Effects CVS Respiratory CNS Myocardial Depression Reduction in tidal Cerebral  SVR volume vasodilatation Cerebral blood flow Halothane Isoflurane Enflurane Sevoflurane Desflurane CNS Generic effects  CBF only > 1 Tonic-clonic muscle Generic effects Generic effects MAC activity and EEG changes CVS Bradycardia ?Ischaemic  Catecholamine Generic effects Generic effects  Catecholamine preconditioning sensitivity sensitivity (myocardium) (myocardium) RS Generic effects Airway irritant Bronchodilatation Bronchodilatation Airway irritant Bronchodilatation Slight  RR Other Hepatic toxicityMUSCLE RELAXANTSSuxamethonium Dose Onset: Offset 0.5 – 2 mg/kg IV 0.5 – 1 min 2 – 10 mins 2.5 mg/kg IMSuxamethonium – Side Effects Intragastric Bradycardia Myalgia pressure Hyperkalaemia Hypotension Tachyphylaxis Anaphylaxis Sux Apnoea Malignant hyperthermiaNon-Depolarising Atracurium Rocuronium Vecuronium Pancuronium • Dose • Dose • Dose • Dose • 0.5mg/kg • 0.6 – 1.2mg.kg • 0.1-0.2 mg/kg • 0.1mg/kg • Onset • Onset • Onset • Onset • 3 mins • 1.5 – 3 mins • 2 – 3 mins • 2 –3 mins • Side-Effects • Dose • Side effects • Side effects • Can cause dependent • Bronchospasm • Tachycardia histamine • Side effects • Hypotension • Arrythmia release • HR & MAP • Elimination Elimination • Elimination • Elimination • Hepatic • • Hoffman • Hepatic • Renal degradation • Duration • Duration • Duration • 45 mins 60 – 90 mins • Duration • 30 mins • • ~20 minsQUESTIONS