Pharmacology - Anesthetic Agents

Below is a summary of commonly used agents for induction and maintenancee of general anesthesia. Note that some agents are often used for multiple indications. Doses are IV, unless indicated. Also note that less common agents are detailed in the AFMS manual.

The agents are listed with the generic name followed by the trade name in brackets.

Propofol (Diprivan)

• Mechanism
• GABA receptor activation
• Indication
• Induction
• Dosing: 1-2.5 mg/kg
• Sedation
• Dosing: 25-75 mcg/kg/min
• Maintenance of general anesthesia
• Dosing: 50-150 mcg/kg/min
• Considerations
• Higher dose required for patients who are younger, drink excessively, smoke marijuana, or chronically use opioids or benzos
• Harder to assess awareness when used for maintenance, hence sedatives (e.g. benzo) often required
• Provides no analgesia, hence concurrent opioid administration or regional block required
• Stings on injection in most patients
• Up to 40% decrease in BP therefore avoid in severely hypovolemia
• Decreases respiratory drive to apnea
• Synergy with opioids & benzodiazepines
• Solution supports bacterial growth (discard after 6 hrs of opening)
• May help reduce post-op nausea and vomiting

Ketamine (Ketalar)

• Mechanism
• GABA receptor activation and NMDA receptor inhibition
• Indication
• Induction
• Dosing: 0.5-2 mg/kg
• Sedation
• Dosing: 0.2-0.8 mg/kg
• Analgesia
• Dosing: 0.2-0.8 mg/kg
• Considerations
• More often used for analgesia
• Infrequently used for induction unless in patients that would not tolerate propofol’s hypotension and/or respiratory depression
• Caution in CAD given increases sympathetic tone
• May cause dissociative state and restlessness/agitation on emergence in addition to hallucinations/nightmares post-op. May reduce with benzodiazepines
• May increase tracheobronchial secretions
• Minimal effects on respiration
• Good option in severe asthmatics (bronchodilates)

Etomidate (Amidate)

• Mechanism
• GABA receptor activation
• Indication
• Induction
• Dosing
• 0.2-0.6 mg/kg
• Considerations
• An alternative to propofol for patients that would not tolerate cardiac depression on induction
• Caution in sepsis given adrenal suppression
• Increases post-op nausea
• Stings on injection
• Post-op self-limited myoclonus

Sevoflurane (Ultane)

• Mechanism
• Unclear
• Indication
• Induction (Inhalational)
• Dosing: 4-8% inspired
• Maintenance of general anesthesia
• Dosing: ~2% inspired
• Considerations
• Least pungent volatile making it suitable for inhalational induction
• Reduce to the maintenance of 2% after induction to avoid cardiac depression
• Delivered in a mixture with O2 or N2O
• Risk of malignant hyperthermia

Desflurane (Suprane)

• Mechanism
• Unclear
• Indication
• Maintenance of general anesthesia
• Dosing
• ~6% inspired
• Considerations
• Most pungent volatile
• Delivered in a mixture with O2 or N2O
• May trigger elevated HD response on fast wash-in
• Risk of malignant hyperthermia
• Allows fastest awakening in obese patients and for operation >3hrs due to lower lipid solubility

Nitrous oxide (N2O)

• Mechanism
• Unclear
• Indication
• Maintenance of general anesthesia*
• Labour analgesia
• Dosing
• Variable mixture with volatile agent or O2
• Considerations
• * Cannot achieve 1 MAC, must be used with other gas
• Accelerates the wash in/out of second gas
• No risk of malignant hyperthermia
• Provides some labour analgesia as 50/50 mix with O2, does not affect uterine contraction
• Increases PONV and pulm HTN
• Easily expands air-filled cavities; caution in certain situations (e.g middle ear, vitreoretinal, neuro, and bowel surgery, pneumothorax)
• Combustible, hence avoided in laser surgery or cautery by gas-filled cavities
• Potential toxic cellular effects due to inactivation of vitamin B12

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