Anesthesia Adjuncts and Balanced Anesthesia

Adjunct Anesthetics

• Also known as "helper drugs" that complement the use of general anesthetics
• Used simultaneously with general anesthetics for:
  • Anesthesia induction
  • Sedation
  • Reduction of anxiety
  • Amnesia

Types of Adjunct Anesthetics

• Neuromuscular blocking agents
• Sedative hypnotics or anxiolytics
  • Propofol, benzodiazepines, barbiturates, hydroxyzine, and promethazine
• Opioid analgesics
• Anticholinergics (atropine)
• Antiemetics (ondansetron)

Mechanism of Action and Drug Effects

• Fat-soluble drugs are stronger anesthetics than water-soluble drugs
• General anesthetics produce a progressive reduction of sensory and motor CNS functions
• The degree and speed of this process vary with the anesthetics and adjuncts used along with their dosages and routes of administration

Adverse Effects

• Sites primarily affected:
  • Heart (myocardial depression)
  • Peripheral circulation
  • Liver
  • Kidneys
  • Respiratory tract
• Malignant hyperthermia is an uncommon, but potentially fatal, adverse effect

Neuromuscular Blocking Drugs (NMBDs)

• Prevent nerve transmission in skeletal and smooth muscles, leading to paralysis
• Often used as adjuncts with general anesthetics
• Classified into two groups based on mechanism of action:
  • Depolarizing (e.g., succinylcholine)
  • Non-depolarizing (e.g., mivacurium, atracurium, rocuronium, vecuronium)

Indications for NMBDs

• Maintaining controlled ventilation during surgical procedures
• Endotracheal intubation (short-acting)
• Reducing muscle contraction in an area that needs surgery
• Diagnostic drugs for myasthenia gravis

Adverse Effects of NMBDs

• May cause:
  • Hypotension (blockade of autonomic ganglia)
  • Tachycardia (blockade of muscarinic receptors)
  • Hypotension (release of histamine)

Specific NMBDs

• Succinylcholine:
  • Metabolized more slowly than Ach
  • Most commonly used to facilitate endotracheal intubation
• Pancuronium:
  • Long-acting non-depolarizing NMBD
  • Most commonly employed for long surgical procedures that require prolonged muscle paralysis

Types of Local Anesthesia

• Central:
  • Spinal or intraspinal anesthesia
  • Intrathecal anesthesia: involves injection of anesthesia into the subarachnoid space
  • Epidural anesthesia: involves injection of anesthesia via a small catheter into the epidural space without puncturing the dura
• Peripheral:
  • Infiltration: small amounts of anesthetic solution are injected into the tissue that surrounds the operative site
  • Nerve block: anesthetic solution is injected at the site where the nerve innervates a specific area
  • Topical anesthesia: the anesthetic drug is applied directly onto the surface of the skin, eye, or any mucous membrane to relieve pain or prevent it from being sensed

Mechanism of Action and Drug Effects of Local Anesthetics

• Local anesthetics work by rendering a specific portion of the body insensitive to pain by interfering with nerve transmission in that area
• They block the generation and conduction of impulses through all types of nerve fibers by blocking the movement of certain ions important to this process

Adverse Effects of Local Anesthetics

• Possible systemic effects of the administration of local anesthetics include effects on circulatory and respiratory function
• The systemic adverse effects depend on where and how the drug is administered
• Such adverse effects are somewhat unlikely unless large quantities of a drug are administered

Specific Local Anesthetics

• Lidocaine:
  • One of the most commonly used local anesthetics
  • Available in several strengths, both alone and in different concentrations with epinephrine, and is used for both infiltration and nerve block anesthesia
  • Also available in topical form
  • Parenteral lidocaine is also used to treat certain cardiac dysrhythmias