General Anaesthesia

Question 1

Two main categories for anaesthesia

Answer 1

General anaesthesia – making the patient unconscious

Regional anaesthesia – blocking feeling to an isolated area of the body (e.g., a limb)

Question 2

meaning of anaesthesia

Answer 2

no sensation

parasthesia= altered sensation, anasthesia= no sensation

Question 3

what is a GA

Answer 3

A general anaesthetic involves putting the patient in a state of controlled unconsciousness. It is most often used so that a major surgical operation can be performed. During a general anaesthetic, the patient will be intubated or have a supraglottic airway device, and their breathing will be supported and controlled by a ventilator. The patient will be continuously monitored at all times immediately before, during and after general anaesthesia.

Question 4

fasting before anaesthetic

Answer 4

Before a planned general anaesthesic, the patient will have a period of fasting. The purpose of fasting is to make sure they have an empty stomach, to reduce the risk of the stomach contents refluxing into the oropharynx (throat), then being aspirated into the trachea (airway). Gastric contents in the lungs creates an aggressive inflammatory response, causing pneumonitis (inflammation of the lung tissue). The risk of aspiration is highest before and during intubation, and when they are extubated. Once the endotracheal tube is correctly fitted, the airway is blocked and protected from aspiration. Aspiration pneumonitis and pneumonia are major causes of morbidity and mortality in anaesthetics, although with planned procedures they are very rare.

Fasting for an operation typically involves:

6 hours of no food or feeds before the operation
2 hours of no clear fluids (fully “nil by mouth”)

In emergency situations the patient might not be fasted (rapid sequence induction is discussed below).

Question 5

preoxygenation

Answer 5

Preoxygenation
Before being put under a general anaesthetic, the patient will have a period of several minutes where they breathe 100% oxygen. This gives them a reserve of oxygen for the period between when they lose consciousness and are successfully intubated and ventilated (in case the anaesthetist has difficulty establishing the airway). This step may need to be skipped when an emergency general anaesthetic is required.

Question 6

premedication

Answer 6

Premedication
Medications are given before the patient is put under a general anaesthetic to relax them, reduce anxiety, reduce pain and make intubation easier. These may include:

Benzodiazepines (e.g., midazolam) to relax the muscles and reduce anxiety (also causes amnesia)
Opiates (e.g., fentanyl or alfentanyl) to reduce pain and reduce the hypertensive response to the laryngoscope
Alpha-2-adrenergic agonists (e.g., clonidine), which can help with sedation and pain

Question 7

what is RSI

Answer 7

rapid sequence induction/intubation

used to gain control over the airway as quickly and safely as possible where a patient is intubated in an emergency scenario and detailed pre-planning is not possible.

This is considerably more risky, as the patient has often not been fasted (risk of aspiration), and the anaesthetist has not had the chance to plan for individual factors and potential problems (e.g., a difficult airway). It is also used in non-emergency situations where the airway needs to be secured quickly to avoid aspiration, such as in patients with gastro-oesophageal reflux or pregnancy.

1. induction
2. ETT
   (risk of aspiration of stomach content so bed is positioned more upright).
3. . Cricoid pressure (pressing down on the cricoid cartilage in the neck) may be used to compress the oesophagus and prevent the stomach contents from refluxing into the pharynx (this is somewhat controversial and should only be done by someone trained and experienced).

Question 8

what is the triad of GA?

Answer 8

Hypnosis (unconsciousness)
Muscle relaxation
Analgesia

(not aware, can’t move, not in pain)

Question 9

hypnosis agents

Answer 9

Hypnotic agents are used to make the patient unconscious. They can be either given intravenously or by inhalation.

Intravenous options for a general anaesthetic include:
Propofol (the most commonly used)
Ketamine
Thiopental sodium (less common)
Etomidate (rarely used)

Inhaled options for a general anaesthetic include:
Sevoflurane (the most commonly used)
Desflurane (less favourable as bad for the environment)
Isoflurane (very rarely used)
Nitrous oxide (combined with other anaesthetic medications – may be used for gas induction in children)

Question 10

volatile anaesthetic agents

Answer 10

sevoflurane, desflurane, isoflurane

liquid at room temperature and need to be vaporised into gas to be inhaled. vaporiser devices are used for inhaled volatile agents. liquid meds are poured into the machine which turns it into vapour and mixes it with air in a controlled way. During the anaesthesia, the concentration of the vaporised anaesthetic medication can be altered to control the depth of anaesthesia.

Question 11

IV med as induction agent and inhaled med to maintain the GA

Answer 11

Commonly, an intravenous medication will be used as an induction agent (to induce unconsciousness), and inhaled medications will be used to maintain the general anaesthetic during the operation. Inhaled medications need to diffuse across the lung tissue and into the blood, where it takes a while for them to reach an effective concentration. IV agents have a head start, as they are infused directly into the blood and so can quickly reach an effective concentration.

Question 12

TIVA

Answer 12

total intravenous anaesthesia

involves using an intravenous medication for induction and maintenance of the general anaesthetic. Propofol is the most commonly used. This can give a nicer recovery (as they wake up) compared with inhaled options.

Question 13

Muscle Relaxation

Answer 13

blocks the neuromuscular junction from working.

Acetylcholine (the neurotransmitter) is released by the axon but is blocked from stimulating a response from the muscle.

Muscle relaxants are given to relax and paralyse the muscles. This makes intubation and surgery easier. There are two categories; Depolarising (e.g., suxamethonium)
Non-depolarising (e.g., rocuronium and atracurium)

Question 14

Muscle relaxation reversals

Answer 14

Cholinesterase inhibitors (e.g., neostigmine) can reverse the effects of neuromuscular blocking medications.

Sugammadex is used specifically to reverse the effects of certain non-depolarising muscle relaxants (rocuronium and vecuronium).

Question 15

Analgesia

Answer 15

Opiates are the most frequently used medication for analgesia (pain relief). Common agents used in anaesthetics are:

Fentanyl
Alfentanil
Remifentanil
Morphine

Question 16

Anti emetics

Answer 16

given at the end of the procedure to prevent post operative nausea and vomiting:

Ondansetron (5HT3 receptor antagonist) – avoided in patients at risk of prolonged QT interval
Dexamethasone (corticosteroid) – used with caution in diabetic or immunocompromised patients
Cyclizine (histamine (H1) receptor antagonist) – caution with heart failure and elderly patients

Question 17

Emergence

‘Twitching’

Answer 17

Before waking the patient, the muscle relaxant needs to have worn off. It is not good for the patient to regain consciousness whilst still paralysed (“awareness under anaesthesia”).

A nerve stimulator may be used to test the muscle responses to stimulation, to ensure the muscle relaxant effects have ended. This is often tested on the ulnar nerve at the wrist, watching for thumb movement (twitches). Alternatively, the facial nerve can be stimulated at the temple while watching for movement in the orbiculares oculi muscle at the eye. This involves a train-of-four (TOF) stimulation, where the nerve is stimulated four times to see if the muscle responses remain strong (indicating it has worn off) or whether they get weaker with additional stimulation (indicating it has not fully worn off). Medication can be used to reverse the effects of the muscle relaxants as discussed above (e.g., sugammadex).

Question 18

emergence (continued)

Answer 18

Once the muscle relaxant has worn off, the inhaled anaesthetic is stopped. The concentration of the anaesthetic in the body will fall, and the patient will regain consciousness. They are extubated at the point where they are breathing for themselves.

Question 19

risk of GA

Answer 19

Sore throat and post-operative nausea and vomiting are common adverse effects of general anaesthesia.

Significant risks of general anaesthesia include:

Accidental awareness (waking during the anaesthetic)
Aspiration
Dental injury, mainly when the laryngoscope is used for intubation
Anaphylaxis
Cardiovascular events (e.g., myocardial infarction, stroke and arrhythmias)
Malignant hyperthermia (rare)
Death

Question 20

malignant hyperthermia

Answer 20

a rare but potentially fatal hypermetabolic response to anaesthesia. The risk is mainly with:

Volatile anaesthetics (isoflurane, sevoflurane and desflurane) 
suxamethonium

*there are genetic mutations which increases the risk of malignant hyperthermia (These are inherited in an autosomal dominant pattern)

Question 21

causes of malignant hyperthermia

Answer 21

Increased body temperature (hyperthermia)
Increased carbon dioxide production
Tachycardia
Muscle rigidity
Acidosis
Hyperkalaemia

Question 22

treatment of malignant hyperthermia

Answer 22

dantrolene- interrupts the muscle rigidity and hypermetabolism by interfering with the movement of calcium ions in skeletal muscle.

Question 23

peripheral nerve blocks

Answer 23

a type of regional anaesthesia. The patient remains awake during the procedure. A local anaesthetic is injected around specific nerves, causing the area distal to the nerves to be anaesthetised. This usually involves making a limb numb so that a surgeon can operate without causing any pain. A screen is put up between the patient and the operating site so that they cannot see the operation taking place.

The injection is performed under ultrasound guidance, sometimes with the help of a nerve stimulator, so that it can be accurately applied to the area around the targeted nerve.

Regional anaesthesia will be performed where there are facilities available to quickly induce a general anaesthetic if it is not effective or the patient starts to experience pain. Patients are closely monitored. Sedation may be given to help the patient relax.

Sometimes a patient may have a combination of regional and general anaesthesia to reduce the physiological response during surgery and improve pain management post-operatively.

Question 24

central neuraxial anaesthesia

Answer 24

spinal anaesthetic or spinal block. It is a type of regional anaesthesia. The most common examples of when it is used for:

Caesarean sections
Transurethral resection of the prostate (TURP)
Hip fracture repairs

The patient remains awake during the procedure. A local anaesthetic is injected into the cerebrospinal fluid, within the subarachnoid space. It is only used in the lumbar spine, after the point where the spinal cord ends, to avoid damaging the spinal cord. In practice, the needle is usually inserted into the L3/4 or L4/5 spaces.

Neuraxial anaesthesia will cause numbness and paralysis of the areas innervated by the spinal nerves below the level of the injection. Cold spray applied to the skin is often used to test whether the anaesthetic has worked. It takes around 1-3 hours for the anaesthetic to wear off.

Question 25

epidural anaesthesia

Answer 25

most commonly used for analgesia in pregnant women in labour and post op after a laprotomy.

Question 26

difference between epidural and spinal block

Answer 26

epidural: insert a small tube catheter into the epidural space in the lower back, outside the dura mater, seperate from the spinal cord and CSF. local anaesthetic medications are infused through the catheter into the epidural space, where they diffuse to the surrounding tissues and spinal nerve roots, where they have an analgesic effect. This offers good pain relief during labour. Levobupivacaine is often used, with or without fentanyl.

Question 27

adverse effects of epidural

Answer 27

Headache if the dura is punctured, creating a hole for CSF to leak from (“dural tap”)
Hypotension
Motor weakness in the legs
Nerve damage (rare)
Infection, including meningitis
Haematoma (may cause spinal cord compression)

Question 28

risks of epidural

Answer 28

When used for analgesia in labour, the risks include:

Prolonged second stage
Increased probability of instrumental delivery

patients need an urgent anaesthetic review if they develop significant motor weakness (unable to straight leg raise). The catheter may be incorrectly sited in the subarachnoid space (and cerebrospinal fluid) rather than the epidural space.

Question 29

spinal block

Question 30

local anaesthesia

Answer 30

used to numb a very specific area where a procedure is being performed. The local anaesthetic (e.g., lidocaine) is usually injected by the person performing the procedure (rather than involving an anaesthetist). This is usually used for smaller operations and procedures.

Common examples of procedures performed using a local anaesthetic are:

Skin sutures in A&E after a skin laceration
Minor surgery to remove skin lesions
Dental procedures
Hand surgery (e.g., carpal tunnel syndrome surgery)
Performing a lumbar puncture
Inserting a central line
Percutaneous procedures (e.g., percutaneous coronary intervention)