Anesthesia Quiz: Planes and Agents

Anesthesia Types

• Anesthesia is a loss of feeling or sensation.
• An anesthesiologist is a physician with specialized training in administering anesthesia.
• Anesthesia is induced by various drugs, leading to partial or complete loss of sensation.
• Two types of anesthesia exist: local and general.

Local Anesthesia

• Provides pain-free state in a specific area (or region).
• Patients remain fully awake.
• Pain is absent in the anesthetized area.
• Some procedures necessitate sedation.
• Sedated patients can still hear their surroundings.

General Anesthesia

• Provides pain-free state for the entire body.
• Patients lose consciousness and feel no pain.
• Reflexes, such as swallowing and gag reflexes, are lost during deep general anesthesia.
• General anesthesia is critical in surgical practice, enabling analgesia, amnesia, and unconsciousness while relaxing muscles and suppressing undesirable reflexes.

Balanced Anesthesia

• A multidrug technique managing anesthetic needs.
• Optimizes beneficial drug effects while minimizing adverse qualities.
• Factors influencing anesthetic drug choice include patient's physical condition, surgical site/procedure, and anticipated length of procedure.

Stages of Anesthesia

• Anesthesia depth can be divided into four stages.
• Each stage exhibits increasing central nervous system (CNS) depression due to anesthetic drug accumulation in the brain.
• Stage I: Analgesia
• Stage II: Excitement/Delirium
• Stage III: Surgical Anesthesia
• Stage IV: Medullary Paralysis

Stage I Anesthesia

• Induction is part of Stage I anesthesia.
• It commences with the administration of anesthetic drugs and ends when consciousness is lost.
• Short-acting barbiturates can shorten this stage to 5-10 seconds.

Stage II Anesthesia

• Characterized by delirium and excitement.
• This stage is brief.
• Patients may move, mumble incoherently, display rigid muscles, and have no sense of pain.
• Noises are exaggerated and quiet sounds seem extremely loud during this stage.
• Surgical procedures should not be performed during this stage.

Stage III Anesthesia

• Stage of surgical analgesia.
• Divided into four planes (1-light to 4-deep).
• . Characterized by respiration, eye movement, reflexes, pupil size and other factors.
• Patients are ready for surgical procedures at planes 2 and 3.

Stage IV Anesthesia

• Characterized by respiratory paralysis, which is dangerous.
• Respiratory arrest and cessation of all vital signs can happen.

Intravenous Anesthetics

• Commonly used for inducing, supplementing, or short-term use in operative procedures.
• Rapid onset but metabolism is frequently slower, prolonging recovery time, especially in extended procedures.
• Several agents exist and have differing effects and recovery times.

Ultra-Short-Acting Barbiturates

• Three compounds (thiopental, thiopental, methohexital) are used for induction, supplemental drug use during short procedures, and maintenance hypnotics for short surgical procedures.

Benzodiazepines

• Midazolam (Dormicum, Versed), Diazepam (Valium), and Lorazepam (Ativan) are benzodiazepine derivatives used in anesthesia.
• Midazolam is most commonly used for induction due to its aqueous solubility and relatively quick action.

Etomidate

• Shares similar pharmacological properties with barbiturates but has less impact on the cardiovascular and respiratory systems.
• Notable for its quick elimination half-life (2.9 hours) making it suitable as a supplement for maintaining anesthesia, primarily in critically ill patients or as an induction agent.
• Rapidly metabolized in the liver

Propofol

• Primarily a hypnotic agent with strong cardiorespiratory depressive effects but no neuromuscular blocking properties.
• Rapid onset (50 seconds) and quick recovery (4-8 minutes) are its main characteristics.
• It is highly popular as an induction agent in outpatient procedures due to its rapid recovery time and antiemetic properties.
• Often used to supplement inhalational anesthesia in longer surgical procedures.
• Is used with opioids during cardiac surgeries.

Ketamine

• Its pharmacological actions differ significantly from other intravenous anesthetics.
• Produces a trance-like state of unconsciousness (eyes can stay open) and is characterized as dissociative.
• Used as induction, primarily in children, due to successful administration via intramuscular routes.

Disadvantages of Ketamine

• Has a tendency to trigger excitatory and hallucinatory phenomena during emergence from anesthesia.
• Patients may exhibit agitation, screaming, and vivid dreams in the recovery period.
• Other side effects are possible like vomiting, salivation, lacrimation, shivering, skin rashes and interactions with thyroid medications possibly leading to hypertension or tachycardia.

Neuroleptanesthesia

• Combining a neuroleptic drug with a strong narcotic agent creates neuroleptanalgesia.
• Introducing nitrous oxide and oxygen intensifies this effect, creating neuroleptanesthesia.
• Innovar (a mixture of fentanyl and droperidol) is a notable combination for preoperative use.
• Provides excellent preoperative sedation, with minimization of postoperative complications and reduced need for analgesics/antiemetics

Inhalational Anesthetics

• Classified based on physical properties.
• Nitrous oxide and cyclopropane are gaseous anesthetics stored in gas tanks, regulated by the anesthesia machine.
• Other inhalational anesthetics are liquid and volatile after receiving low heat that vaporizers offer as part of the anesthesia machine.
• Halogenated hydrocarbons are potent volatile anesthetics often used in combination therapy.

Partial Pressure Control

• Anesthesiologist controls partial pressure delivered to the lungs enabling manipulation of anesthetic gas concentration in the brain, thereby enabling adjustments in levels of unconsciousness.
• Anesthetic dose is determined experimentally and expressed as alveolar tension (MAC), determining the minimum concentration required for a defined anesthetic depth expressed as a percentage of the inhaled anesthetic gas at 1 atmosphere.
• Various agents need different amounts of partial pressure to reach the same depth of anesthesia.

Halogenated Hydrocarbons:

• Sevoflurane, isoflurane, enflurane, desflurane, halothane, and methoxyflurane fall into this category being potent anesthetics at low inhaled pressures.
• They do not exhibit all the optimal pharmaceutical characteristics needed for an anesthetic agent, thus are combined with other anesthetics and adjuncts for optimal effectiveness and safety.

Specific Agents: Halothane & Enflurane

• Halothane: A potent, non-flammable agent with a high blood-gas partition coefficient (prolongs induction/recovery). It is potentially harmful (arrhythmias, shivering during recovery common, vomiting, and liver damage are possible). It is an appropriate anesthetic option for children
• Enflurane: Though less potent than halothane, it has a rapid onset and recovery. It has lower arrhythmia incidence and stronger skeletal muscle relaxation compared to halothane but does potentially induce seizure activity.

Specific Agents: Isoflurane & Methoxyflurane

• Isoflurane: The dialkyl-halo ether considered the best choice. Unlike enflurane, it does not trigger seizures. It does not produce arrhythmias.
• Methoxyflurane: Is the most potent inhalation anesthetic due to its high lipid solubility.

Specific Agents: Diethyl Ether & Nitrous Oxide

• Diethyl Ether: Highly flammable and explosive, inducing salivary secretions, vomiting, and laryngospasm. Replaced by halogenated drugs.
• Nitrous Oxide (N2O): A powerful, well-tolerated yet gentle general anesthetic often paired with potent agents. It has a rapid onset and recovery.

Preanesthetic Medication

• Drugs given before the administration of anesthesia.
• Often a combination of drugs and medications
• Primary purpose is to prepare the patient for the anesthetic experience and potentially minimize unwanted after-effects. Specific uses:
• Relieve anxiety: Benzodiazepines
• Sedation: Barbiturates
• Prevent allergic/aspirational reactions: Antihistamines, antiemetics
• Analgesia: Opioids
• Decrease saliva secretions: Anticholinergics
• Minimizing nausea, vomiting, and other complications: Antiemetics

Adverse Effects

• Note undesirable reactions associated with these drugs.

Local Anesthesia

• Local anesthetic drugs block both sensory and motor nerve conduction, producing temporary loss of sensation without loss of consciousness.
• Mechanism: Suppresses action potentials in tissues by blocking voltage-gated sodium channels.
• Unlike general anesthetics, they don't usually cause CNS depression.
• Categorized structurally by a general resemblance to the alkaloid cocaine.
• Several administration methods exist: topical application, local infiltration, and regional anesthesia.

Topical Anesthesia

• Applying the anesthetic directly to the surface of the skin, open area, or mucous membrane to desensitize the surface.
• Helps lessen the need for deeper, more potent anesthetics for procedures.
• Can be applied in various ways, including cotton swabs and sprays.

Local Infiltration Anesthesia

• Involves injecting a local anesthetic directly into tissues.
• Often used for dental procedures, suturing small wounds, or creating small incisions to remove tissue samples (biopsy).

Regional Anesthesia

• Injecting a local anesthetic around nerves causing a wider anesthetized area compared to infiltration anesthesia.
• Prevents pain signals from reaching the brain by blocking nerve pathways.
• Two main types: Spinal anesthesia and Conduction blocks.

Spinal Anesthesia

• Injecting a local anesthetic into the subarachnoid space of the spinal cord, usually at the second lumbar vertebra.
• This causes a loss of feeling/movement in lower extremities, lower abdomen, and perineum.

Conduction Blocks

• Anesthetic injection near or into nerve trunks, creating a block in nerve signals.
• Examples include:
• Epidural block: Anesthetic injected into the space around the dura of the spinal cord, frequently used for obstetrics.
• Transsacral/Caudal block: injection into the epidural space of the sacrococcygeal notch (commonly in obstetrics)
• Brachial plexus block: Anesthetic injected into the brachial plexus, for arm or hand surgeries.

Specific Local Agents

• Cocaine, Procaine, Tetracaine, Lidocaine, Dibucaine, Pramoxine, Prilocaine, Etidocaine, Mepivacaine, Bupivacaine.
• Important notes: Specific dosages and uses vary widely, based on the agent. Always consult up-to-date medical texts or professionals.

Test your knowledge on the different planes of anesthesia and the agents used in anesthetic techniques. This quiz covers key characteristics and goals of general anesthesia, as well as comparisons between various anesthetic drugs. Get ready to enhance your understanding of this critical medical field!