Anesthesia Principles and Agents Quiz

Anesthesia

• Anesthesia is a loss of feeling or sensation.
• An anesthesiologist is a physician specializing in administering anesthesia.
• Anesthesia can be induced by various drugs causing partial or complete loss of sensation.
• Two types of anesthesia exist: local and general.

Local Anesthesia

• Local anesthesia provides a pain-free state in a specific area.
• Patients remain fully awake during local anesthesia, but the targeted area is numb.
• Some procedures may require sedation.
• Sedated patients can still hear surroundings.

General Anesthesia

• General anesthesia provides a pain-free state for the entire body.
• Patients lose consciousness when given a general anesthetic.
• Reflexes like swallowing and gagging are lost during general anesthesia.
• General anesthesia is crucial for surgical practice.
• General anesthesia acts on the CNS or ANS to render patients analgesic, amnesic, and unconscious, while causing muscle relaxation and suppressing undesirable reflexes.

Balanced Anesthesia

• Balanced anesthesia involves a multi-drug approach to manage a patient's anesthetic needs.
• The choice of anesthetic drug depends on various factors.
• These factors include patient condition, surgical procedure type, and anticipated length.
• Ideal general anesthetics induce anesthesia quickly and smoothly and allow for speedy post-procedure recovery.
• The proper depth of anesthesia is achieved through the use of various drugs, either alone or mixed.

Stages of Anesthesia

• The depth of anesthesia is divided into four stages characterized by progressively increasing CNS depression caused by anesthetic drug accumulation.
  • Stage I: Analgesia
  • Stage II: Excitement or delirium
  • Stage III: Surgical anesthesia (with varying planes of depth)
  • Stage IV: Medullary paralysis

Stage I Anesthesia

• Induction is a part of Stage I anesthesia.
• The administration of the anesthetic drug starts this stage.
• It lasts until consciousness is lost.
• Short-acting barbiturates may only take 5-10 seconds for consciousness to be lost.

Stage II Anesthesia

• This is the brief stage of delirium and excitement.
• Patient activity, incoherent speech, and muscle rigidity can be observed.
• Pain sensation is absent.
• Noises and sounds are exaggerated.

Stage III Anesthesia

• This is the stage of surgical analgesia, subdivided into four planes (or substages).
• Anesthesiologists differentiate planes based on respiration, eye movements, reflexes, pupil size, and other factors.
• Planes start from light (plane 1) to deep (plane 4).
• Patients are usually ready for surgery at planes 2 or 3.

Stage IV Anesthesia

• This is the dangerous stage of respiratory paralysis.
• It can easily result in respiratory arrest and loss of vital signs.

Intravenous (IV) Anesthetics

• IV anesthetics are used for induction and sometimes supplemental anesthesia.
• Recovery from some anesthetic drugs can be prolonged.
• Inhalational anesthetics are often used for longer anesthetic procedures.
• Recovery from an inhalational anesthetic is typically faster.

Ultra-Short-Acting Barbiturates

• These barbiturates are instrumental for induction and supplemental periods, particularly in short surgical procedures.
• Drugs include Pentothal, Surital, and Brevital sodium.

Benzodiazepines

• Important for anesthetic induction.
• Midazolam is the most popular.
• Its popularity results from aqueous solubility and short duration of action.

Etomidate

• Pharmacological properties are similar to barbiturates, but with a lessened effect on the cardiovascular and respiratory systems.
• Its relatively short half-life makes it suitable for supplementing anesthesia in critically ill patients, or induction.
• Rapidly hydrolyzed in the liver.

Propofol

• Primarily a hypnotic drug with cardiorespiratory depressant actions, not neuromuscular blockade.
• Propofol provides rapid anesthesia onset (50 seconds).
• Speedy recovery is attributed to redistribution and rapid metabolism.
• Used as induction agent, and as a supplement in longer surgical procedures.
• Suitable for outpatient anesthesia due to rapid recovery and antiemetic properties.
• Provides lower opioid doses in cardiac surgery.

Ketamine

• Ketamine's pharmacological actions differ significantly from other IV anesthetics.
• It induces a trance-like unconscious state with the patient appearing awake but unresponsive to stimuli.
• A useful anesthetic agent for children resistant to IV line insertion.
• Has risks including excitatory and hallucinatory side effects during recovery.

Neuroleptanesthesia

• Combining a neuroleptic (e.g., droperidol) with a potent narcotic (e.g., fentanyl) produces neuroleptanalgesia.
• Addition of nitrous oxide and oxygen leads to neuroleptanesthesia.
• Innovar is a combined fentanyl and droperidol product.
• It can deliver excellent sedation, analgesia and patient cooperation during surgery.
• Reduction in postoperative issues and doses of analgesics or antiemetics.

Inhalation Anesthetics

• Inhalational anesthetics are categorized by physical properties.
• Nitrous oxide and cyclopropane are gaseous anesthetics that are regulated by the anesthesia machine.
• Others are volatile liquids supplied by vaporizers attached to the machine.
• Halogenated hydrocarbons are the strongest volatile anesthetics.

Partial Pressure of Anesthetics

• Anesthesiologists regulate the partial pressure of the delivered anesthetic to control the anesthetic gas concentration in the brain, thus the level of unconsciousness.
• Anesthetic dose is expressed in terms of alveolar tension required for a defined level of anesthesia.
• Minimum alveolar concentration (MAC) is the minimum alveolar tension required to eliminate movement in 50% patients exposed to a standardized stimulus.

Halogenated Hydrocarbons

• Sevoflurane, desflurane, enflurane, isoflurane, halothane, and methoxyflurane are powerful halogenated hydrocarbons, producing surgical levels at low inspired partial pressures.
• None of them have all desired properties for anesthetic use, so they are often given with additional drugs.

Halothane

• Highly potent, non-flammable, with relatively high blood-gas partition coefficient.
• Induction and recovery times can be prolonged.
• Safe for children but has side effects such as arrhythmias, shivering, vomiting, and liver damage.

Enflurane

• Less potent than halothane but offers rapid induction and recovery.
• Lower incidence of arrhythmias and better skeletal muscle relaxation compared to halothane, but can trigger seizures.

Isoflurane

• One of the alkyl-haloethers, often preferred to others due to the lack of seizure activity and minimal induction of arrhythmias.
• Methoxyflurane is a highly potent inhalation anesthetic with strong lipid solubility.
• Sevoflurane is used for induction and maintenance of general anesthesia and has low pungency.
• Consequently, it is suitable for children, particularly in the induction phase.

Diethyl ether

• Highly flammable and explosive.
• Causes increased salivation, vomiting, and laryngospasm.
• Replaced by halogenated anesthetics.

Nitrous Oxide (N2O)

• Important and potent analgesic, well-tolerated as a weak general anesthetic.
• Often used for outpatient dental procedures.
• Rapid onset and recovery.
• Contraindicated in pregnant women, immunosuppressed patients, or those with anemia, due to its adverse effects.

Preanesthetic Medication

• Drugs given before anesthesia.
• This preparation is for inducing a calming state in patients before anesthesia, which leads to efficient and swift introduction into the anesthetic state.
• The intent is to lower anxiety, lessen stress, and prep the patient.

Preanesthetic Drugs

• Various drugs, acting as narcotics or anti-anxiety agents, aim to reduce anxiety and apprehension before surgery.
• This approach reduces pre-operative stress, speeds up the introduction into an anesthetic state, reduces the dosage of agents needed for anesthesia, and leads to smoother anesthesia recovery.
• Antiemetics reduce nausea and vomiting during immediate post-op recovery.

Anticholinergic

• Decreasing secretions of the upper respiratory track.
• Some anesthetic gases and volatile liquids are irritating to sensitive linings, hence increased mucous secretions.
• Loss of cough and swallowing reflexes during anesthesia can lead to mucous pooling, increasing risk of pneumonia and atelectasis (lung collapse).
• Anticholinergics, like glycopyrrolate, reduce these secretions and the possibility of these effects.

Other Preanesthetic Medications

• Barbiturates (like secobarbital and pentobarbital): preoperative sedatives.
• Opioids (like morphine and fentanyl): analgesia (pain relief).
• Phenothiazines and antihistamines (like promethazine and hydroxyzine): used with opioids; potentiate analgesic effect without significant additional side effects.
• Tranquilizers (like diazepam): pre-operative sedation.

Local Anesthetics

• Block sensory and motor nerve conduction to cause temporary loss of sensation without loss of consciousness.
• Mechanism of action: Suppress action potentials by blocking voltage-gated sodium channels, thus inhibiting pain impulse transmission.
• Local anesthetics are structurally similar to the alkaloid cocaine.
• Methods of administration include topical application, local infiltration, or regional anesthesia.

Topical Anesthesia

• Applying anesthetic to the surface of skin, mucous membranes, or open areas.
• Mostly used to desensitize the skin for injections of deeper local anesthetics.

Local Infiltration Anesthesia

• Injecting the local anesthetic directly into the tissue.
• Often used for dental procedures, suturing, or tissue biopsies.

Regional Anesthesia

• Injecting anesthetic around nerves, numbing the area supplied by those nerves.
• Larger affected area compared to local infiltration.
• Types include spinal anesthesia and conduction blocks.

Spinal Anesthesia

• Injecting the local anesthetic into the subarachnoid space of the spinal cord (typically around L2-L3).
• This type of regional anesthesia numbs the lower extremities, lower abdomen, and perineum.

Conduction Blocks

• Injection of local anesthetic near a nerve trunk or around a nerve.
• Types include epidural block (injecting anesthetic into the space surrounding the dura of the spinal cord) and trans-sacral (caudal) block, Brachial Plexus block.

Specific Local Anesthetics

• Cocaine: Topical nasal, pharyngeal, and tracheobronchial anesthesia (4%-10% concentrations and as crystals).
• Procaine: Available with and without epinephrine; epinephrine decreases bloodstream absorption, lengthening anesthetic duration for nerve blocks or infiltrations (1%-2% solutions). A 5%-20% solution is used for spinal anesthesia.
• Tetracaine: Topical use on mucous membranes (2% solution).
• Lidocaine: Rapid onset, minimal local irritation, higher potency and longer duration compared to procaine (0.5% for infiltration, 1%-2% topical mucosal, 5% spinal, and intravenously as an antiarrhythmic).
• Dibucaine, Pramoxine, Prilocaine, Etidocaine, Mepivacaine, and Bupivacaine: Also used as local anesthetics with varying applications.