General Anesthesia Overview

General Anesthesia Overview

• General anesthesia involves systemic administration of drugs, rendering the patient unconscious during medical procedures.
• Safety, comfort, and minimal physiological disturbance to the patient are crucial for effective anesthesia.

Advantages

• No psychological burden on patients—completely unaware of surroundings.
• Ensures patient stillness for extended surgical periods.
• Allows for complete management of the airway, breathing, and circulation.
• Enables simultaneous surgery in multiple body areas.
• Useful for patients allergic to local anesthetics.
• Can be administered while the patient remains in a supine position.
• Easily adaptable to procedures with uncertain duration.
• Rapid administration is typically feasible.

Disadvantages

• Requires involvement from specialized healthcare providers.
• Necessitates complex and expensive medical equipment.
• Preoperative preparation for the patient is usually essential.
• Associated with physiological disturbances and risks of major complications (e.g., death, myocardial infarction, stroke).
• Minor complications can include nausea, vomiting, sore throat, headaches, shivering, and delayed mental recovery.
• Can trigger malignant hyperthermia—a serious reaction leading to rapid temperature increase, hypercapnia, hyperkalemia, and metabolic acidosis.

Determinants of Drug Choice and Dose

• Factors influencing drug selection include patient age and weight, physical condition, past drug reactions, anxiety levels, tolerance to depressants, allergies, and type of surgery (elective or emergency).

Modern Anesthetics

• General anesthesia commonly employs a mix of inhalational and intravenous agents.
• Total Intravenous Anesthesia (TIVA) can be administered alone via intravenous means or in combination with other drug classes (e.g., neuroleptics, opioids).

Characteristics of Ideal Anesthetic Drug

• Induces loss of pain sensation and noxious reflexes.
• Achieves muscle relaxation.
• Provides smooth induction and recovery.
• Causes anterograde amnesia without systemic toxicity or hazards to others.

Inhalation Anesthetics

• Early agents were volatile liquids or gases, including nitrous oxide, ether, and chloroform.
• Modern inhalation agents include halothane, isoflurane, and desflurane, used for maintaining anesthesia depth.

Indications for Inhalational Induction

• Common in young children and cases of upper airway obstruction (e.g., epiglottitis).
• Useful in lower airway obstruction contexts where intravenous access is difficult.

Disadvantages of Inhalational Induction

• Induction can be slower than intravenous methods.
• Risks of airway obstruction, bronchospasm, and laryngospasm.
• Potential issues include environmental pollution.

Minimum Alveolar Concentration (MAC)

• MAC refers to the concentration required to prevent movement in 50% of subjects in response to surgical stimuli; it quantifies anesthetic potency.

Nitrous Oxide (N2O)

• Commonly known as laughing gas; it is the least potent inhalational agent.
• Has a MAC of over 100%, typically used for analgesia with minimal side effects on respiration and cardiovascular stability.

Halothane

• Volatile liquid with a MAC of 0.7%, providing good control with smooth induction and recovery.
• Risks include cardiac sensitization to catecholamines, leading to dysrhythmias, vasodilation, and hypotension.