What are the medications used in General Anesthesia (GA), their doses, and mechanisms of action (MOA)?

Medications Used in General Anesthesia: Doses and Mechanisms of Action

Induction Agents

Propofol is the principal intravenous induction agent for general anesthesia, offering rapid onset and faster recovery times, administered at reduced doses of 25 mcg/kg/min in elderly patients (>60 years) or ASA III-IV status. 1

• Propofol acts via GABA-A receptor potentiation in the central nervous system, producing unconsciousness and amnesia 1, 2
• Standard induction dose: 1.5-2.5 mg/kg IV (reduce by 50% in elderly patients) 1, 3
• Maintenance infusion: 25-200 mcg/kg/min, titrated to effect 1

Etomidate (10-20 mg IV) can be used for hemodynamically unstable patients requiring induction, particularly in difficult airway scenarios 1

Ketamine serves dual roles as both an induction agent and analgesic adjunct through NMDA receptor antagonism 4, 5, 3

• Induction dose: 1-2 mg/kg IV 1
• Analgesic adjunct dose: 0.5 mg/kg IV bolus 4, 5, 3
• Continuous infusion: 0.1-0.2 mg/kg/h (maximum 0.4 mg/kg/h) 4
• Reduces opioid requirements by 30-50% when used as co-analgesic 3

Opioid Analgesics

Fentanyl (1-2 micrograms/kg) is the primary opioid for general anesthesia due to its rapid onset, predictable hemodynamic stability, and versatility across surgical procedures. 4, 5

• Fentanyl acts as a mu-opioid receptor agonist providing analgesia 5, 6
• Minor/ambulatory procedures: 1 microgram/kg 5
• Major/invasive procedures: 2 micrograms/kg 4, 5
• Pediatric dosing: 1-2 micrograms/kg (same weight-based dosing as adults) 4, 5
• Breakthrough pain in PACU: 0.5-1.0 micrograms/kg, titrated to effect 4

Remifentanil provides ultra-short acting analgesia via mu-opioid receptor agonism with rapid metabolism by nonspecific esterases 7

• Continuous infusion: 0.05-0.3 micrograms/kg/min 4, 7
• Particularly useful for procedures requiring rapid offset 7

Sufentanil offers potent analgesia through mu-opioid receptor agonism 4

• Bolus: 0.5-1 micrograms/kg 4
• Continuous infusion: 0.5-1 micrograms/kg/h after initial bolus 4, 5

Morphine provides longer-acting analgesia but should be avoided in renal insufficiency 4, 5

• Intraoperative: 25-100 micrograms/kg depending on age, titrated to effect 4
• Pediatric postoperative dosing varies by age: <3 months (25-50 mcg/kg), 3-12 months (50-100 mcg/kg), 1-5 years (100-150 mcg/kg) every 4-6 hours 4

Alfentanil: 10-20 micrograms/kg bolus 4

Piritramide: 0.05-0.15 mg/kg, titrated to effect 4

Benzodiazepines

Midazolam (0.02 mg/kg or 1-2 mg IV) provides anxiolysis and amnesia through GABA-A receptor potentiation, with relatively short half-life compared to other benzodiazepines 5, 1, 3

• Reduce dose by at least 20% in elderly (>60 years) or ASA III-IV patients 1, 3
• Can be used for sedation during spinal anesthesia, though use cautiously in very elderly due to postoperative confusion risk 4

Sedative-Hypnotics and Adjuncts

Dexmedetomidine acts as an alpha-2 adrenergic agonist providing sedation with less respiratory depression than benzodiazepines 1, 3

• Loading dose: 0.5-1 micrograms/kg IV 4, 3
• Continuous infusion: 0.2-0.7 micrograms/kg/h until end of procedure 4
• Caution: Risk of bradycardia and hypotension 3

Clonidine (alpha-2 agonist): 1-3 micrograms/kg IV bolus 4

Non-Opioid Analgesics

Acetaminophen provides analgesia through central COX inhibition 3

• IV loading dose: 15-20 mg/kg (10 mg/mL preparation) 4, 3
• Maintenance: 10-15 mg/kg every 6-8 hours 4
• Rectal loading: 20-40 mg/kg (15 mg/kg if <10 kg) due to poor bioavailability 4
• Maximum daily dose: 60 mg/kg 4

NSAIDs inhibit cyclooxygenase enzymes peripherally and centrally 3

• Ketorolac: 0.5-1 mg/kg (max 30 mg) single intraoperative dose; 0.15-0.2 mg/kg (max 10 mg) every 6 hours postoperatively (maximum 48 hours) 4, 3
• Ibuprofen IV: 10 mg/kg every 8 hours 4
• Ketoprofen IV: 1 mg/kg every 8 hours 4
• Diclofenac: 0.5-1 mg/kg every 8 hours 4

Metamizole (where available): 10-15 mg/kg every 8 hours IV, or 2.5 mg/kg/h continuous infusion (short-term hospital use only due to agranulocytosis risk) 4

Local Anesthetics

Lidocaine acts via sodium channel blockade providing systemic analgesic effects 4

• IV bolus: 1.5 mg/kg 4
• Continuous infusion: 1.5 mg/kg/h until end of procedure 4

Corticosteroids (Antiemetic/Anti-inflammatory)

Dexamethasone: 0.15-0.25 mg/kg (max 0.5 mg/kg) 4

Methylprednisolone: 1 mg/kg 4

Reversal Agents (Must Be Immediately Available)

Naloxone reverses opioid-induced sedation and respiratory depression through competitive mu-opioid receptor antagonism 4, 3

Flumazenil reverses benzodiazepine-induced sedation and respiratory depression through competitive GABA-A receptor antagonism 4, 3

Multimodal Opioid-Sparing Strategy

The optimal approach combines acetaminophen 1000 mg IV, ketorolac 15-30 mg IV, ketamine 0.5 mg/kg IV, and dexmedetomidine 0.5-1 mcg/kg loading dose, with propofol or midazolam for sedation, reserving low-dose fentanyl only for breakthrough needs. 3

This strategy minimizes opioid-related respiratory depression, postoperative nausea/vomiting, and ileus while maintaining adequate analgesia 3. The combination acts at different targets in the nociceptive system: acetaminophen (central COX inhibition), NSAIDs (peripheral/central COX inhibition), ketamine (NMDA antagonism), and dexmedetomidine (alpha-2 agonism) 3, 8.

Critical Monitoring Requirements

Continuous pulse oximetry, capnography (100% sensitivity/specificity for correct tracheal tube positioning), blood pressure, heart rate, and respiratory rate monitoring are mandatory during all general anesthesia cases. 4, 1, 3

• Capnography monitoring every 5-15 minutes until discharge criteria met 4
• Emergency equipment including suction, advanced airway equipment, and positive pressure ventilation must be immediately available 1
• Reversal agents (naloxone, flumazenil) must be present in the procedure room 4, 3

Special Population Considerations

Elderly patients (>65 years) require 50% dose reduction of all sedatives, with particular avoidance of benzodiazepines when possible. 4, 1, 3

Pediatric patients can receive the same weight-based dosing of fentanyl (1-2 micrograms/kg) as adults 4, 5

Patients with renal insufficiency (GFR <30) should receive fentanyl instead of morphine or meperidine 5, 3

Obese patients require dosing based on ideal body weight for most anesthetic agents 7

Common Pitfalls to Avoid

Respiratory depression occurs from inadequate titration and monitoring—use capnography for early detection and titrate all opioids and sedatives carefully 4, 3

Inadequate analgesia results from single-agent reliance—employ multimodal approach with ketamine (0.5 mg/kg) and non-opioid analgesics to enhance analgesia while minimizing opioid requirements 3, 8

Hemodynamic instability from excessive dosing in elderly or ASA III-IV patients—reduce all induction agent doses by 20-50% in these populations 1, 3

Postoperative confusion from benzodiazepine use in elderly—prefer dexmedetomidine or minimize benzodiazepine doses 4, 3