Stages of General Anesthesia

 Clinical Notes

• Stage I is often brief due to rapid induction agents.

• Stage II is avoided or minimized with modern anesthetics to reduce risk of complications like laryngospasm.

• Stage III is carefully maintained during surgery.

• Stage IV is considered an overdose and must be prevented.

• Stage III Plane 3 → Surgical anaesthesia
• Most reliable indicator: Regular respiration

• Used for: Airway maintenance
• ❌ Contraindicated in gastric regurgitation risk
• “Brain mask” = LMA

Pain: sensory and emotional experience associated with actual or potential tissue damage

1. Components: sensory (objective characteristics of pain e.g., location, duration, intensity; thermal, mechanical, or chemical) and motivational/affective (associated with past experience, fear, suffering, anxiety, culture)

2. Anatomy and physiology: nociceptors specialized to convey noxious stimuli (mechanical, chemical, thermal) 

a. Hyperalgesia: exaggerated pain response to stimulus that was previously painful. 

i.  Primary: nociceptors in area of tissue damage fire or due to algesic chemicals (bradykinin, SP, etc.)

ii.  Secondary: absence of local causes so due to changes in CNS that result in nociceptor firing (e.g., referred pain due to convergence)

b. Allodynia: pain caused by stimulus that is normally innocuous (non-painful); e.g., abcess- just touch, hurts

c. Fiber types: local anesthetics target Ad and C fibers

i.  A-b: myelinated cutaneous mechanoreceptor (25-50 m/s); innervates Ruffini endings

ii.  A-d: myelinated nociceptor that mediates sharp, well-localized pain (10-30 m/s)

iii. C: have Schwan cells but no myelin; nociceptor that mediates dull, poorly-localized pain (<2.5 m/s)

d. Neurotransmitters:

i.  Excitatory: glutamate (most common, works on NMDA receptors), substance P (SP, p for pain; act at neurokinin, NK, receptors), calcitonin G-receptor peptide (CGRP; co-released with SP), prostaglandins (products of cyclooxygenase), and kinins

ii.  Inhibitory: GABA (amino acid; hyperpolarizes neurons so ¯ pain sensation), monoamines (e.g., seratonin, NE), and opioids (e.g., endorphins- give runner’s high; 3 made by body: 1) b-endorphin, 2) dynorphin, 3) enkephalins; 3 receptors: 1) mu- most important for pain, 2) delta, and 3) kappa)

Treatment:

a. Opioids: indicated for moderate to severe acute (post-op) pain, chronic cancer pain, or as sedative/pain reliever during general anesthesia.  A narcotic = sleep-inducing.

i.  Mechanism of action: bind opioid receptor in spinal cord and brainstem (mu, d, and kappa; found in periaqueductal grey- area in brain with tons of opioid receptors, when activated ® ¯ pain), inhibit peripheral nociceptors, activate descending pain control system, improve affective components of pain

ii.  Side-effects: euphoria, sedation, respiratory depression, nausea/vomiting, constipation (especially with elderly), addiction, tolerance (does not remain once drug removed)

b. NSAIDS (non-steroidal anti-inflammatory drugs): indicated for mild to moderate pain that has inflammatory component, fever.  Aspirin first made in 1853 from parts of willow bark.

i. Mechanism of action: inhibits cyclooxygenase (COX) which makes prostaglandins and other inflammatory agents.  Anti-pyretic (fever-reducing) actions mediated by effects on hypothalamus- center of brain that regulates body T.

ii. Side effects: since acidic- nausea, vomiting (rare), GI bleeding, prolonged bleeding time since inhibit platelets.  Warnings if ulcer history, combining NSAIDS (® ringing in ears), and flu/chicken pox in children ® risk of Rie syndrome (fatal brain inflammation)

c. Tylenol (acetaminophen): analgesic and anti-pyretic but no significant effect on inflammation.   OD kills liver.

d. Muscle relaxants: don’t act directly on muscles; indicated for myofascial pain (muscle/CT pain) but not analgesic (not good for pain control)

i. Mechanism of action: depends on drug but most ­ GABA-mediated signals in spinal cord

ii. Side-effects: sedation, weakness

e. Anti-depressants: low-doses indicated for chronic pain that is unresponsive to conventional analgesics, 1st choice for some types of neuropathic pain.  Side effects: sedation, xerostomia, CV effects.

i.  Mechanism of action: activate descending pain control systems ® pre-synaptic a-2 receptor to ­ monoamine (NE, seratonin) in brain ® inhibit SP, glutamate, etc. release from peripheral nociceptors.

4. Descending pain modulatory pathways: neuronal cell bodies in brainstem send projections to dorsal horn where release NT that inhibit incoming pain info or decrease sensitivity of neurons in dorsal horn to that info.  Opioids and antidepressants act in part by these pathways.

Emergency Drugs for Sedated Patients (AAPD Guidelines)

In the context of pediatric dentistry and sedation, it is crucial to be prepared for potential emergencies that may arise during or after sedation. The following is a list of emergency drugs that may be needed to rescue a sedated patient, along with their indications and uses.

Emergency Drugs

1. Albuterol for Inhalation

   • Indication: Bronchospasm or asthma exacerbation.
   • Use: Administered via nebulizer or metered-dose inhaler to relieve bronchospasm.

2. Ammonia Spirits

   • Indication: Syncope or fainting.
   • Use: Inhaled to stimulate respiration and increase alertness.

3. Atropine

   • Indication: Bradycardia or asystole.
   • Use: Increases heart rate by blocking vagal effects on the heart.

4. Diazepam

   • Indication: Seizures or severe anxiety.
   • Use: Administered intravenously or intramuscularly for rapid sedation or seizure control.

5. Diphenhydramine

   • Indication: Allergic reactions or anaphylaxis.
   • Use: Antihistamine for allergic symptoms; may also be used for sedation.

6. Epinephrine (1:1,000 and 1:10,000)

   • Indication: Anaphylaxis or severe asthma attack.
   • Use: 1:1,000 for intramuscular injection; 1:10,000 for intravenous administration in cardiac arrest.

7. Flumazenil

   • Indication: Benzodiazepine overdose.
   • Use: Reversal agent for sedation caused by benzodiazepines.

8. Fosphenytoin

   • Indication: Status epilepticus.
   • Use: Anticonvulsant for seizure control, administered intravenously.

9. Glucose (25% or 50%)

   • Indication: Hypoglycemia.
   • Use: Administered intravenously to rapidly increase blood glucose levels.

10. Lidocaine

    • Indication: Cardiac arrhythmias or local anesthesia.
    • Use: Antiarrhythmic agent for ventricular arrhythmias; also used for local anesthesia.

11. Lorazepam

    • Indication: Anxiety or seizures.
    • Use: Sedative and anticonvulsant, administered intravenously or intramuscularly.

12. Methylprednisolone

    • Indication: Severe allergic reactions or inflammation.
    • Use: Corticosteroid for reducing inflammation and managing allergic reactions.

13. Naloxone

    • Indication: Opioid overdose.
    • Use: Opioid antagonist to reverse respiratory depression and sedation caused by opioids.

14. Oxygen

    • Indication: Hypoxia or respiratory distress.
    • Use: Administered to improve oxygen saturation and support respiratory function.

15. Racemic Epinephrine

    • Indication: Croup or severe bronchospasm.
    • Use: Administered via nebulization to reduce airway swelling and improve breathing.

16. Rocuronium

    • Indication: Neuromuscular blockade for intubation.
    • Use: Non-depolarizing neuromuscular blocker for facilitating intubation.

17. Sodium Bicarbonate

    • Indication: Metabolic acidosis or hyperkalemia.
    • Use: Administered intravenously to correct acidosis and manage elevated potassium levels.

18. Succinylcholine

    • Indication: Rapid sequence intubation.
    • Use: Depolarizing neuromuscular blocker for quick intubation.

•  Contraindicated in: Jaundice, Pheochromocytoma, Obstetric cases.
•  Not contraindicated in: Previous Hepatitis A.
•  Associated complications:
  • Malignant Hyperthermia
  • Hepatotoxicity
  • ↑ Intracranial Tension
  • Predisposes to Arrhythmias
•  Stored: Amber bottles, colorless liquid.
•  Preservative: Thymol
•  Poor analgesic.
• Beta-blocker–like myocardial effects.
• Rapid, smooth induction.
• Dissolves in rubber.