WEEK 3: Anaesthesia Flashcards
Define anaesthesia.
It is the practice of medicine which involves using drugs to induce unconsciousness and prevent transmission of pain.
Anaesthesia is the practice of medicine in which drugs are given that block the sensation of pain or awareness [consciousness] and other sensations so that surgery and other procedures can take place without undue stress to the patient.
There are 5 types of anaesthesia currently recognized.
Discuss them.
- Procedural Sedation:
Definition: A state in which the patient remains awake and responsive during a medical procedure, but sedative medications are administered to help them tolerate discomfort or anxiety.
Characteristics: The patient maintains consciousness but may feel drowsy or relaxed. They can often follow simple commands.
Example: Administering a sedative to a patient undergoing a painful dental procedure to help them remain calm and cooperative.
- Conscious Sedation:
Definition: An induced state of decreased consciousness in which the patient is still able to respond purposefully to verbal commands.
Characteristics: The patient remains conscious but may experience a state of relaxation and reduced anxiety. They can follow instructions and cooperate with the procedure.
Example: Administering sedative medications to a patient undergoing a colonoscopy to help them relax and tolerate the procedure without discomfort.
- Analgesia:
Definition: The relief of pain without necessarily inducing loss of consciousness.
Characteristics: Analgesic drugs are used to alleviate pain by blocking pain signals or reducing the perception of pain.
Example: Applying a local anesthetic to numb a specific area before a minor surgical procedure or administering opioids through an epidural for pain relief during childbirth.
- Regional Anesthesia:
Definition: Anesthesia produced by blocking nerve transmission in a specific region of the body.
Characteristics: Sensory and motor functions are selectively blocked in the targeted area, allowing for pain-free surgery or procedures while maintaining consciousness.
Example: Injecting a local anesthetic around a nerve bundle in the wrist before hand surgery or administering a spinal anesthetic to block sensation in the lower body for a cesarean section.
- General Anesthesia:
Definition: A drug-induced state of unconsciousness in which the patient does not respond to painful stimuli or other external stimuli.
Characteristics: The patient is completely unconscious and unaware of their surroundings. Reflexes are suppressed, and muscle relaxation is achieved.
Example: Administering anesthetic gases or intravenous medications to induce unconsciousness for major surgery, such as open-heart surgery or abdominal procedures.
In the 200 years up to the 1840s, chemistry and anatomy had experienced a revolution.
Science and scientific method of thinking was beginning to enter the practice of medicine. People were synthesising drugs and experimenting with them.
Many drugs that later came to be known and used as anaesthetic drugs were developed in this period:
Name them.
Ether, nitrous oxide, chloroform, cocaine
When is World Anaesthesia Day?
World Anaesthesia Day: 16 October
Nitrous Oxide, ether, chloroform etc were already known. Many people had already tried to use them to demonstrate painless surgery, but they still did not know how to make them work or what equipment to use.
So, the demonstration of painless surgery by Morton (anaesthetist) on 16 October 1846 at Massachusetts General Hospital was a breakthrough long awaited. (picture)
The news spread round the world, and within weeks ether was being used in Europe, and the first ether anaesthetic in South Africa was in 1847.
The anaesthetic drug used on 16th October. It became the most widely used anaesthetic agent. Used to make most inhaled anaesthetic agents today.
Name the drug.
It was already well known and dentist often made it themselves for producing analgesia in their procedures. It had been widely used as ‘laughing gas’ for party games in Europe from the late 1700s. It was also used for obstetric analgesia. It is still with us today (less so).
Name the drug.
It was introduced in 1847, in Edinburgh. It was easier to use than ether and became widely used but caused dysrhythmias.
Halothane is a modern descendant of this drug.
Name the drug.
Ether
Nitrous Oxide
Chloroform
Traditionally, anaesthesia focused on, and was seen as producing the state of sleep.
Discuss how the drugs were classified.
What did anesthetists focus on in the post operative period?
As a result, the drugs were classed into those that:
- Induced sleep,
- Maintained sleep
- Reversed sleep.
In the post operative period, anesthetists focused on pain management.
Nowadays we talk about the whole perioperative period: from preoperative assessment to ‘surgical outcome’.
‘Outcome’ can be up to 30, 90 days or more after surgery.
State the 3 types of pre-operative drugs.
Preoperative drugs
-Analgesics
-Anxiolytics
-Chronic medication
Discuss the different types of analgesics used in anaesthesia.
It is good practice, which is supported by pathophysiology, to abolish any pain a patient may have preoperatively and to anticipate what pain patient is likely to have and treat before the patient experiences it (pre-emptive analgesia).
Analgesic drugs have side effects, some of which may be undesirable, such as nausea and vomiting (opiates), respiratory depression (opiates), bleeding (NSAID), etc.
Also, they may act at the site of injury (NSAID), peripheral pain transmission (local anaesthetic) and spinal cord (opioid), brain (opioid, paracetamol).
Combining analgesic drugs to control pain along the chain of transmission is called balanced analgesia.
Consider anaesthetic plan as a whole in choosing best approach to analgesia management and choice of analgesic drugs.
Analgesic
*Paracetamol
- Non-Steroidal Anti-inflammatory Drugs (NSAID)
*Acetates: diclofenac, indomethacin
*Fenamates: mefenamic acid
*Oxicams: piroxicam,
*Propionates: ibuprofen, ketofen
*Pyrazolones: phenylbutazone
*Salycylates: aspirin, - Opioids: a compound that binds to opioid receptors
-Strong: morphine, pethidine, fentanyl etc
Intermediate: buprenorphine, pentazocine
-Weak: codeine
- adjuvants
gabapentinoids
steroids
Magnesium
α2- agonists
Discuss anxiolytics as pre-operative drugs in anaesthesia.
Preoperative anxiety is to be expected. In the past this was managed with drugs. Patients have often come to terms with the surgery and surgeon before they come to theatre, but only meet the anaesthetist shortly before the operation.
Therefore, modern practice emphasizes the central role of the nurses and doctors (especially anaesthetists) in managing anxiety.
Talking, explaining to the patient, how their fears are to be managed is the best anxiolytic. Nowadays we want a patient who can be wide awake at the end of surgery (early recovery, early discharge), so do not want drugs that suppress them.
If patient is anxious about pain, we explain (how we will manage it). If they are afraid of not waking up (we explain). If they …. we explain.
It is important that people and patients know and understand that the anaesthetists are there to keep them safe and look after them while they undergo treatment, surgical or otherwise:
Many Anesthetic Associations emphasize this in their mottos:
ASA: Vigilance (1905)
CSA: We safeguard those who sleep (1930s)
AAGBI: Safe in Sleep (1932)
SASA: we guard with skill and wisdom (1970s)
RCoA: It is divine to alleviate pain
Discuss induction drugs.
State examples of Induction.
Outline characteristics of induction drugs.
Induction drugs are medications used to induce anesthesia, typically administered intravenously or via inhalation, to rapidly and smoothly transition a patient from consciousness to a state of unconsciousness during the initiation of general anesthesia.
Generally, ‘induction drugs’ refers to intravenous anaesthetic agents.
Historically they were used to produce sleep, then something else (anaesthetic gases) used to maintain sleep.
As after 1846, gases are used sometimes to induce sleep.
Nowadays, some ‘induction’ drugs’ such as propofol or ketamine can be used to maintain sleep as well. This is known as ‘total intravenous anaesthesia’, TIVA.
Induction Drugs
Thiopentone (1934-36)
Ketamine (1962-64)
Etomidate (1972)
Propofol (1989)
Induction Drug
-must produce ‘sleep rapidly’ [one arm-brain circulation time]
-Effect must be reversible
-Effect must be of short duration
-It should undergo minimal metabolism and excreted
Discuss maintenance drugs.
For almost 100 years, anaesthesia was induced with ether and chloroform (inhalational agents). The first modern inhalational agent was ‘halothane’ in the 1956 and (methoxyflurane -1960 and enflurane-1966: both not in use) Isoflurane (1979), sevoflurane (1990), desflurane (1990)
TIVA: propofol and ketamine are the main drugs used for intravenous maintenance (TIVA).
Modern surgery was able to be achieved through anaesthetists gaining better control of patient physiology.
One example of this is control of ventilation, which is achieved with muscle relaxation. First, there is need to pass an endotracheal tube (Suxamethonium/ Rocuronium), then keep the patient paralyzed (Atracurium), while mechanically ventilating them.
Analgesia can be achieved as described earlier, or through nerve blockade. Nerves can be blocked peripherally (e.g. wrist block), regionally (brachial plexus block) or axially (spinal/epidural).
Maintenance Drugs
- Inhalation Anaesthetics
Halothane
Isoflurane
Sevoflurane
Desflurane - Intravenous
Propofol
ketamine - Neuromuscular blocking drugs
Suxamethonium
Rocuronium
Vecuronium
Atracurium / cis-atracurium - Analgesics
- Regional anaesthesia drugs/techniques
Discuss the MOA of neuromuscular blocking drugs and give examples.
- Competitive Antagonism:
NMBDs exert their effects by competitively binding to nicotinic acetylcholine receptors (nAChRs) located on the motor endplate of skeletal muscle fibers.
These drugs compete with acetylcholine for binding to the alpha subunit of the nAChR, thereby preventing acetylcholine from activating the receptor and initiating muscle contraction.
By blocking access of acetylcholine to the neuromuscular receptor, NMBDs interrupt neuromuscular transmission, leading to muscle paralysis.
- Depolarizing vs. Non-Depolarizing Agents:
NMBDs can be classified into two main categories based on their mechanism of action: depolarizing and non-depolarizing agents.
**Depolarizing Agents:
Depolarizing NMBDs, such as succinylcholine (suxamethonium), initially activate the nAChR and cause depolarization of the motor endplate. However, they persistently stimulate the receptor, leading to sustained depolarization and desensitization of the neuromuscular junction, ultimately resulting in flaccid paralysis.
**Non-Depolarizing Agents: Non-depolarizing NMBDs, such as rocuronium, vecuronium, atracurium, and cisatracurium, competitively antagonize the action of acetylcholine at the nAChR without causing depolarization. These drugs bind reversibly to the receptor and block neuromuscular transmission, leading to muscle relaxation and paralysis.
Examples of Neuromuscular Blocking Drugs:
- Suxamethonium (Succinylcholine):
Depolarizing neuromuscular blocking agent.
Rapid onset of action and short duration of action.
Frequently used for rapid sequence induction and facilitation of endotracheal intubation. - Rocuronium:
Non-depolarizing neuromuscular blocking agent.
Intermediate onset and duration of action.
Often used for maintenance of muscle relaxation during surgery and mechanical ventilation. - Vecuronium:
Non-depolarizing neuromuscular blocking agent.
Intermediate onset and duration of action.
Commonly used for prolonged surgical procedures and in patients requiring prolonged muscle relaxation. - Atracurium / Cisatracurium:
Non-depolarizing neuromuscular blocking agents.
Intermediate onset and duration of action.
Metabolized spontaneously (Atracurium) or through Hofmann elimination (Cisatracurium), making them suitable for patients with hepatic or renal impairment.
These block access of acetylcholine to the neuromuscular receptor, causing muscle paralysis.
Neuromuscular blocking drugs
-Suxamethonium
-Rocuronium
-Vecuronium
-Atracurium / cis-atracurium
Discuss the MOA of Regional Anaesthesia and give examples.
By blocking nerve conduction, local anaesthesia blocks pain conduction.
*These local anesthetics work by reversibly binding to specific sodium channels located on the axonal membrane of peripheral nerves.
*By binding to these sodium channels, local anesthetics block the influx of sodium ions, which are necessary for the generation and propagation of action potentials along nerve fibers.
*As a result, nerve conduction is inhibited, leading to reversible loss of sensation (analgesia) and motor function (muscle paralysis) in the innervated area.
*The degree and duration of sensory and motor blockade depend on factors such as the type and concentration of the local anesthetic, the volume of drug injected, and the proximity of the nerve to the site of injection.
Early drugs were esters, like cocaine, and have many undesirable side effects, including allergic reactions. Newer drugs were developed, amino-amides.
Lignocaine, bupivacaine allowed regional anaesthesia to develop more widely. They are rapidly acting and long duration.
Regional anaesthesia drugs/techniques
Cocaine (1855) ester
Procaine (1904) ester
Tetracaine / Amethocaine (1932) ester
Lignocaine (1943) amide
Bupivacaine (1963) amide
Mepivacaine (1960s); (S(-)mepivacaine)- Ropivacaine (1996) amide
Discuss general anaesthesia, their different MOA and examples.
General anaesthesia
Anaesthesia of the whole patient
Patient unable to communicate, anaesthetist reliant on monitors.
Titrate general ‘wakefulness’ using sedation techniques.
Combine LA with GA
- GABAA is the receptor for an number of anaesthetic drugs. They cause influx of chloride ion which hyper-polarises the cell membrane and inhibits transmission / conduction. Different molecules attach to different sites on the GABA receptor. Relevant drugs are: intravenous drugs propofol, etomidate and thiopentone.
- NMDA receptors: these mediate the influx of Calcium. Ketamine and nitrous oxide block calcium influx.
- Inhalational drugs: halothane, isoflurane, sevoflurane and desflurane also act through GABAA, NMDA, and other potassium channel receptors.
- Local anaesthetics work through blocking sodium channels and preventing the generation of the nerve action potential.
Describe the process of Monitoring Depth of Anaesthesia: Clinical.
4 PHASES
1. Induction
2.Maintenance
3. Emergence: Stage 3-2
4. Recovery: Stage 2-1
STAGES
1. Induction, 2. Excitation: Phase 1
3. Surgical anaesthesia, 4. Overdose: Phase 2
STAGE 1: INDUCTION (Administration of anaesthetic agent)
Change in conscious level to LOC, regular breathing,
STAGE 2: EXCITATION
Excitation, Autonomic changes (respiration, heart rate, blood pressure, etc)
STAGE 3: SURGICAL STABILITY (Surgical Procedure)
Stability:
Autonomic stability
Loss of corneal reflex, laryngeal reflexes, eyes mid-line, Regular breathing (diaphragmatic), no movement to surgical stimulus (MAC).
STAGE 4: OVERDOSE
Autonomic instability (dysrhythmias, hypotension, decreased rate and depth of breathing, etc)
STAGE 3 TO 2: (End of surgery)
Excitation
Autonomic instability
STAGE 2 TO 1: (Recovery Room and post-surgical ward)
Return of consciousness
Return of stability
Effects of analgesics, surgery, physiological changes intraop. (eg hypothermia)
