What are the induction and maintenance agents used in general anesthesia, including their drug names, typical doses, and relevant contraindications or special considerations?

General Anesthesia: Induction and Maintenance Agents

For general anesthesia induction, use propofol 1.0-2.0 mg/kg IV combined with fentanyl 1-2 mcg/kg IV (or remifentanil 0.5-1.5 mcg/kg), followed by maintenance with either propofol infusion (75-150 mcg/kg/min) or volatile anesthetics (sevoflurane preferred over desflurane or isoflurane).

Induction Agents

First-Line: Propofol

• Dose: 1.0-2.0 mg/kg IV bolus 1, 2
• Onset: 30-45 seconds (one arm-brain circulation) 3
• Duration: 4-8 minutes 3
• Advantages:
  • Rapid, smooth induction with rapid clearance 4, 5
  • Reduced postoperative nausea/vomiting 2
  • Faster recovery times compared to midazolam 6
• Cautions:
  • Causes cardiovascular depression (decreased cardiac output, systemic vascular resistance, arterial pressure) 3
  • Avoid in hemodynamically unstable patients - associated with post-intubation cardiovascular instability in critically ill patients 7
  • Pain on injection in up to 30% of patients 3
  • Contraindicated in egg, soy, or sulfite allergies 3

Alternative: Etomidate

• Dose: 10-20 mg IV 1
• Advantages: Minimal cardiovascular effects, preferred for hemodynamically unstable patients 8
• Cautions: Recent evidence suggests potential mortality risk due to adrenal suppression 7 - use only when hemodynamic instability is severe

Alternative: Ketamine

• Dose: Variable (context-dependent)
• Advantages:
  • Sympathomimetic effects mitigate hemodynamic instability 9
  • Bronchodilation beneficial in asthma/COPD 8
  • Safest profile in critically ill patients - preferred over etomidate 7
• Cautions:
  • Increases upper airway secretions (use with atropine or glycopyrrolate) 8
  • Avoid in combination with sulfur mustard exposure 8

Benzodiazepines (Adjunct Only)

• Midazolam: 2-5 mg IV 1, 9
  • Use for inadequate sedation or when neuromuscular blockade required 9
  • Highly deliriogenic, causes delayed awakening 9
  • Active metabolite accumulates in renal dysfunction 9

Analgesic Co-Induction

Opioids (Essential Component)

• Fentanyl: 1-2 mcg/kg IV (100-150 mcg for adults) 1

  • Suppresses laryngeal reflexes, provides optimal intubation conditions 1
  • Duration: 1-4 hours 9

• Remifentanil: 0.5-1.5 mcg/kg bolus 9

  • Ultra-short duration (3-10 minutes) may hasten awakening 9
  • High risk of withdrawal and hyperalgesia after discontinuation 9

• Sufentanil: 10-15 mcg IV for adults 1

Maintenance Agents

Option 1: Total Intravenous Anesthesia (TIVA)

• Propofol infusion: 75-150 mcg/kg/min (or 20-60 mcg/kg/min) 2, 9
• Advantages:
  • Precise control with rapid recovery 4
  • No environmental greenhouse gas emissions 10
• Cautions:
  • Risk of propofol infusion syndrome at high doses 9
  • Hypertriglyceridemia 9
  • Ecotoxicity concerns (found in wastewater) 10

Option 2: Volatile Anesthetics (Preferred for Maintenance)

Sevoflurane (first choice) 10

• Lower environmental impact than desflurane or isoflurane 10
• Adequate potency with appropriate solubility 4
• Minimal hepatotoxicity risk 4

Desflurane (acceptable alternative)

• Faster emergence than isoflurane 11
• Highest greenhouse gas emissions - avoid when possible 10

Isoflurane (acceptable alternative)

• Adequate potency, minimal hepatotoxicity 4

Nitrous Oxide: DO NOT USE 2, 10

• High risk of PONV and delayed bowel function 2
• Strong recommendation against use 10

Adjunct Maintenance Agents

• Dexmedetomidine: Reduces opioid requirements 2
  • Caution: Higher incidence of hypotension and bradycardia 9
• Ketamine: May reduce chronic postoperative pain 2
• Magnesium, lidocaine infusions, gabapentinoids: For multimodal analgesia 2

Special Populations

Elderly Patients

• Reduce propofol dose by 30-50% - marked sensitivity in elderly 5
• Propofol-desflurane combination provides shortest induction/recovery times 11

Hemodynamically Unstable/Critically Ill

• First choice: Ketamine 7
• Avoid propofol - associated with cardiovascular instability 7
• Etomidate only if severe instability, despite mortality concerns 7

ASA Class III Patients

• Remimazolam (ultra-short-acting benzodiazepine): 6-12 mg/kg/h induction, up to 2 mg/kg/h maintenance 12
• Improved hemodynamic stability compared to propofol 12

Pediatric Patients (<6 months)

• Reduce amide local anesthetic doses by 30% 13

Critical Monitoring Requirements

• Depth of anesthesia monitoring (BIS or similar) recommended to reduce drug consumption 2, 10
• Neuromuscular monitoring mandatory when using muscle relaxants - train-of-four ratio ≥0.90 required before extubation 2
• Low tidal volume ventilation (6-8 mL/kg) with PEEP 6-8 cm H₂O reduces pulmonary complications 2

Key Contraindications Summary

Agent	Absolute Contraindications	Relative Contraindications
Propofol	Egg/soy/sulfite allergy	Hemodynamic instability, hypovolemia
Etomidate	None specific	Adrenal insufficiency concerns
Ketamine	Sulfur mustard exposure	Severe hypertension, increased ICP
Nitrous oxide	Avoid entirely [10]	All patients

3, 6, 1, 8, 6, 2, 9, 10, 7, 4