4) Anesthetic Agents

What are the common routes of administration of general anesthetics?

• Inhalation

• IV

How do you define general anesthesia? What are its 3 stages?

→ reversible state of CNS depression, which results in the loss of response to and perception of stimuli

1. Induction

2. Maintenance

3. Recovery

Why are inhaled anesthetics used only for maintenance?

→ b/c depth of anesthesia can be rapidly altered by simply changing the [inhaled gas]

• some agents have pungent odors or cause respiratory irritation, making them unsuitable for the induction stage (e.g., isoflurane & desflurane)

How is potency of inhalation anesthetics determined?

→ defined as minimum alveolar concentration (MAC)

• ↑ MAC = ↓ potency

How can blood solubility influence anesthetic action? Give an example.

→ Determines the induction and recovery speed, based on the blood:gas partition coefficient

• ↑ blood solubility gasses = dissolve more fully in the blood = sustained induction and recovery (e.g., isoflurane)

• ↓ blood solubility gasses = very rapid onset and recovery (e.g., desflurane)

Compare the action of nitrous oxide and isoflurane in terms of induction and recovery.

Compared to isoflurane, NO has:

• slower induction

• faster recovery

Give the receptors involved in action of general anesthetics.

• γ-aminobutyric acid (GABA_A​) receptors

• NMDA receptors

• inhibitory glycine receptors in spinal motor neurons

• nicotinic Ach receptors

What is malignant hyperthermia? In what category of patients is it commonly seen?

→ rare, life-threatening condition that can occur in a small % of patients exposed to halogenated hydrocarbons

• seen in burn victims, muscular dystrophy, myopathy, myotonia & osteogenesis imperfecta pt

How is malignant hyperthermia treated? How does the drug act?

Dantrolene - blocks Ca²⁺ from SR of muscle cells → heat production & relaxes muscle tone

How is thiopental useful as a anesthetic?

→ ultra-short-acting barbiturate with ↑ lipid solubility

• used for rapid induction

What are the concerns in using opioids along with general anesthetics?

• hypotension

• resp depression

• nausea

• vomiting

What is the concern in using Ketamine in young patients?

induce hallucinations in young adults

What are the common delivery routes for local anesthetics?

• topical administration

• infiltration

• perineural/neuraxial blocks (spinal, epidural, caudal)

How is the onset, potency and duration of local anesthetics influenced?

Onset: depend on pKa

• ↓ pKa = quicker onset

Potency and Duration: depend on lipid solubility

• ↑ lipid solubility = ↑ potency = longer duration of action

How are ester and amide local anesthetics metabolized?

Amides are biotransformed in the liver

Esters are biotransformed by plasma cholinesterase (pseudocholinesterase)

Compare the stability, onset and systemic toxicity of ester and amide local anesthetics.

Why are anesthetic adjuncts used along with anesthetics?

→ used to make the anesthetic experience safe and pleasant

• e.g., relieving anxiety, preventing nausea, providing extra analgesia, facilitating intubation

What are the 2 categories of skeletal muscle relaxants? How do they differ from each other?

What are the 2 categories of neuromuscular blocking agents? Give an example in each category.

1. NMBs

   • drugs interfere with transmission at the neuromuscular end plate

   • lack CNS activity

   • used during surgical procedures or in the intensive care unit to produce muscle paralysis and facilitate endotracheal intubation

   • e.g., Succinylcholine

2. Spasmolytics/antispasmodics

   • "centrally acting" muscle relaxants

   • used to reduce spasticity in various painful conditions (e.g., chronic back pain or fibromyalgic conditions)

   • e.g., Diazepam

What are the 2 categories of NMB agents? Give an example in each category.

1. Depolarizing Agents (e.g., succinylcholine)

2. Nondepolarizing Agents (e.g., tubocurarine, pancuronium, vecuronium)