General Anesthesia

General Anesthesia

General Anesthesia Pharmacology

• Intravenous Anesthetic Agents

  • Barbiturates
  • Propofol
  • Etomidate
  • Ketamine
  • Benzodiazepines
  • Opioids
  • Neuromuscular Blocking Drugs

• Inhaled Anesthetic Agents

  • Volatile Anesthetics
  • Desflurane
  • Sevoflurane
  • Isoflurane
  • Halothane
  • Nitrous Oxide

Medication	Mechanism	Pharmacokinetics	Primary Effects/Uses	Advantages	Adverse Effects/Disadvantages
Barbiturates	Enhance GABAA receptor–mediated inhibition	Hepatic metabolism with redistribution; prolonged sedation with repeated doses	Induction of anesthesia; reduce CMRO₂, ICP, and CBF; anticonvulsant	Rapid onset via redistribution; potent anticonvulsant	Dose-dependent CNS depression, myocardial depression, cough/laryngospasm (esp. in asthmatics), histamine release
Propofol	Enhances GABAA receptor function	Hepatic & extrahepatic metabolism with fast redistribution	Rapid induction of unconsciousness; CNS depression; decreased ventilatory drive	Antiemetic; ideal for day-case surgery; no histamine release	Marked hypotension; respiratory depression
Etomidate	Enhances GABAA receptor function	Effect terminated by rapid redistribution	Induction of anesthesia particularly in cardiovascularly unstable patients	Short acting; CVS and RS stability in elderly/shocked patients	Nausea, vomiting; adrenal suppression (even after a single dose)
Ketamine	Noncompetitive NMDA receptor antagonist	IV onset within 30–60 s; redistribution halts effect in 15–20 minutes	Induction of general anesthesia & analgesia; preserves airway reflexes	Maintains CV stability in shock; bronchodilator; preserves respiratory drive	Increases HR and BP (not ideal in hypertensives); excess salivation; emergence agitation & hallucinations; contraindicated in head trauma
Benzodiazepines	Increase GABAA receptor affinity for GABA	Effects terminated by redistribution	Sedation, anxiolysis, amnesia, anticonvulsant effects; used in withdrawal protocols	Useful for managing insomnia, anxiety & CNS depressant withdrawal	Somnolence; cognitive deficits; tolerance; dependence; disinhibition (reversal possible with flumazenil)
Opioids	Bind opioid receptors (agonism)	Generally metabolized hepatically; varies by agent	Provide analgesia; modest CNS depression	Agents like fentanyl provide potent analgesia with cardiac stability; various options (fentanyl, alfentanil, etc.)	Respiratory depression; nausea/vomiting; sedation; miosis; hypotension (histamine release with morphine); agent-specific adverse effects
Neuromuscular Blocking Drugs	Block neuromuscular transmission	Varied (e.g., succinylcholine has rapid onset, others rely on metabolism and elimination)	Facilitate tracheal intubation; optimize surgical field through muscle relaxation	Rapid onset with certain agents (e.g., succinylcholine, rocuronium); various options for duration and reversal (anticholinesterases, sugammadex)	Depolarizing agents (e.g. succinylcholine): hyperkalemia, malignant hyperthermia, myalgia, anaphylaxis; nondepolarizing agents require reversal and may cause cholinergic side effects
All Decreases CNS, Heart, Lungs except ketamine and eto for heart only protective

Medication	Mechanism	Pharmacokinetics	Primary Effects/Uses	Advantages	Adverse Effects/Disadvantages
Inhaled Anesthetic Agents (General)	Modulate various CNS channels (GABAA, glycine, glutamate)	Low blood/tissue solubility → rapid onset; eliminated mainly by exhalation	Produce unconsciousness and amnesia; affect multiple organ systems	Noninvasive delivery; easy titration	Can cause dose-dependent respiratory & cardiovascular depression; some agents may trigger malignant hyperthermia; environmental concerns
Nitrous Oxide 104%	NMDA receptor antagonist	Minimal metabolism; rapid elimination via the lungs	Weak anesthetic producing analgesia; typically used as an adjunct	Mild CV and respiratory effects; rapid onset and offset	Nausea/vomiting; expansion of closed gas spaces; diffusion hypoxia; inhibits vitamin B12 metabolism
Desflurane 6%	Volatile agent acting via modulation of CNS ion channels	Very low solubility yields ultrarapid induction/recovery; negligible metabolism	Rapid induction and emergence suited for outpatient procedures	Minimal metabolism; very fast recovery	Pungent, irritating airway requiring special vaporizer; high concentrations may increase BP & HR
Sevoflurane 1.85%	Volatile agent acting via CNS ion channel modulation	Low blood solubility yields rapid induction/emergence; minimal metabolism	General anesthesia; particularly well tolerated in children	Pleasant odor; excellent bronchodilation; minimal HR effect	Degradation by CO₂ absorbents produces Compound A
Isoflurane 1.15%	Volatile agent modulating synaptic transmission	Moderate, leading to slower recovery than agents with low solubility	Maintenance of anesthesia with predictable control	Causes peripheral vasodilation and augments coronary blood flow	Slower recovery; may sensitize the myocardium to catecholamines
Halothane 0.75%	Volatile agent affecting multiple ion channels	High solubility leads to prolonged emergence	Historically used in children for induction (sweet odor); smooth induction	Pleasant odor; reduces BP effectively	Sensitizes myocardium to catecholamines; risk of halothane hepatitis; prolonged recovery

all increase icp

Steps of GA

2. Induction (hypnotic, analgesia, muscle relaxant)
3. Maintenance
4. Recovery (reversal)

Types of Induction of General Anesthesia

• Intravenous
• Inhalational

Physiological Changes During General Anesthesia

• Depress ventilatory control, depress ventilation and muscle movement, leading to hypercapnia and hypoxemia.
• Loss of airway reflex and gag response because of CNS depression, which may lead to aspiration of stomach contents.
• Patient needs immediate support of his airway and start controlled ventilation.
• Anesthesia agent leads to depress myocardial contractility and rate, leading to hypotension and organ hypoperfusion.
• It leads to either direct or indirect SVR reduction, which also leads to hypotension and organ injury.
• Patient will not move, this may lead to body injury if not monitored and protected by anesthesiologist during surgery.

Risks (Complications) of GA

Common Risks to General Anesthesia

5. Sore throat due to gas or tube used for breathing may notice difficulty in speaking but improves with time.
6. Temporary pain in the muscle.
7. Hypothermia for preterm and newborns leading to a drop in blood circulation and respiratory.
8. The risk of apnea in preterm infants aged less than 60 weeks, which requires the need to enter ICU.

Uncommon Risks of General Anesthesia / Sedation

9. Awareness of the operating room activity during surgery such as caesarean section, cardiac operations.
10. Eye contact may be accompanied by pain and may need medical treatment.
11. Damage to teeth, lips, and tongue.
12. Memory dysfunction.

Rare Risks of General Anesthesia That May Cause Brain Damage, Neurological Disability or Death

13. Airway obstruction that cannot be controlled quickly and difficulty intubation, leading to severe lack of oxygen.
14. Pulmonary aspiration causing pneumonia, hypoxia, and death. Risk is more with obesity and in pregnant women and in non-fasting patients.
15. Severe allergic reactions to anesthetics and other medications may cause difficulty breathing, skin rashes, hypotension, and cardiac arrest.

Risks increase with elderly patients, premature infants, and children under one year of age who suffer from chronic diseases such as heart disease, chest, arteries, pressure, diabetes, liver, and kidney disease, smokers, and obesity.

(ASA) Defines of (Level of Sedation / Analgesia)

Description	Minimal Sedation	Moderate Sedation / Analgesia	Deep Sedation / Analgesia	General Anesthesia
Responsiveness	Normal response to verbal stimulation	Purposeful response to verbal or tactile stimulation	Purposeful response following repeated or painful stimulation	Unarousable even with painful stimulus
Airway	Unaffected	No intervention required	Intervention may be required	Intervention often required
Spontaneous Ventilation	Unaffected	Adequate	May be inadequate	Frequently inadequate
Cardiovascular	Unaffected	Usually maintained	Usually maintained	May be impaired

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