Surgery - Anaesthetics Flashcards
There are two main categories of anaesthesia:
- General anaesthesia – making the patient unconscious
- Regional anaesthesia – blocking feeling to an isolated area of the body (e.g., a limb)
What is general anaesthetic
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.
Before a planned general anaesthesic, the patient will have a period of fasting. What is the purpose of this?
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.
___________ _______ and pneumonia are major causes of morbidity and mortality in anaesthetics, although with planned procedures they are very rare.
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”)
Before being put under a general anaesthetic, the patient will have a period of several minutes where they breathe 100% oxygen.
Why do they do this?
What is this called?
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.
Preoxygenation
What is the purpose of premedicating the patient before general anaesthetic?
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Medications are given before the patient is put under a general anaesthetic to relax them, reduce anxiety, reduce pain and make intubation easier.
Medications given before the patient is put under a general anaesthetic 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
When is Rapid Sequence Induction/Intubation used?
Rapid sequence induction/intubation (RSI) is 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.
Purpose of Rapid Sequence Induction/Intubation
The procedure is designed to ensure successful intubation with an endotracheal tube as soon as possible after induction (when the patient is unconscious) to protect the airway. The biggest concern during RSI is the aspiration of stomach contents into the lungs. The bed can be positioned so the patient is more upright to reduce the reflux of contents up the oesophagus. 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
There is a triad of general anaesthesia:
- Hypnosis
- Muscle relaxation
- Analgesia
Hypnotic agents are used to make the patient unconscious. They can be either given ________ or by _________.
Hypnotic agents are used to make the patient unconscious. They can be either given **intravenously **or by inhalation.
Hypnosis
Intravenous options for a general anaesthetic include:
- Propofol (the most commonly used)
- Ketamine
- Thiopental sodium (less common)
- Etomidate (rarely used)
Hypnosis
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)
Sevoflurane, desflurane and isoflurane are volatile anaesthetic agents. What is volatile agents
Volatile agents are liquid at room temperature and need to be vaporised into a gas to be inhaled.
Vaporiser devices are used for inhaled volatile agents. The liquid medication is poured into the machine. The machine then 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
Whats more common inhaled or intravenous medication as an induction agent?
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.
WHat is Total intravenous anaesthesia (TIVA
Total intravenous anaesthesia (TIVA) 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.
What is the function of Muscle Relation
Muscle relaxants block 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.
Muscle Relaxation
What are the two categories:
- Depolarising (e.g., suxamethonium)
- Non-depolarising (e.g., rocuronium and atracurium)
What can reverse the effects of neuromuscular blocking medications.
Cholinesterase inhibitors (e.g., neostigmine)
What can you use to specifically reverse the effects of certain non-depolarising muscle relaxants (rocuronium and vecuronium).
Sugammadex
Opiates are the most frequently used medication for analgesia (pain relief). Common agents used in anaesthetics are:
- Fentanyl
- Alfentanil
- Remifentanil
- Morphine
Antiemetics are often given at the end of the procedure by the anaesthetist to prevent post-operative nausea and vomiting. Common options for prophylaxis given at the end of the operation are:
- 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*
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 _____ _________ may be used to test the muscle responses to stimulation, to ensure the muscle relaxant effects have ended
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
What are the nerve simulator options?
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)
What is Train of Four (TOF)
a train-of-four (TOF) stimulation, is 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).
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 ________ at the point where they are breathing for themselves.
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.
Risks of General Anaesthesia
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
What is Malignant Hyperthermia
Malignant hyperthermia is 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 that increase the risk of malignant hyperthermia. These are inherited in an _______ _______ pattern.
There are genetic mutations that increase the risk of malignant hyperthermia. These are inherited in an** autosomal dominant **pattern.
Malignant hyperthermia causes:
- Increased body temperature (hyperthermia)
- Increased carbon dioxide production
- Tachycardia
- Muscle rigidity
- Acidosis
- Hyperkalaemia
How is Malignant Hyperthermia treated?
It is treated with dantrolene. Dantrolene interrupts the muscle rigidity and hypermetabolism by interfering with the movement of calcium ions in skeletal muscle.
Name other types of Anaesthesia
- Peripheral Nerve Blocks
- Central Neuraxial Anaesthesia
- Epidural Anaesthesia
- Local Anaesthesia
Peripheral nerve blocks are a type of ________ anaesthesia.
Peripheral nerve blocks are a type of regional anaesthesia.
What is Peripheral Nerve Blocks
Peripheral nerve blocks are 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
Central neuraxial anaesthesia is also known as a _____ _________ or ________ ________. It is a type of ________ anaesthesia.
Central neuraxial anaesthesia is also known as a spinal anaesthetic or spinal block. It is a type of regional anaesthesia.
Central Neuraxial Anaesthesia
The most common examples of when it is used for:
- Caesarean sections
- Transurethral resection of the prostate (TURP)
- Hip fracture repairs
What is Central Neuraxial Anaesthesia
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.
What is Epidural Anaesthesia
Epidural anaesthesia is most commonly used for analgesia in pregnant women in labour and post-operatively after a laparotomy (open abdominal surgery). Importantly, **an epidural is different from a neuraxial/spinal block. **
What does an epidural involve?
An epidural involves inserting a small tube (catheter) into the epidural space in the lower back. This is **outside **the dura mater, separate 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.
What are the Adverse effects Epidural
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)
Epidural
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.
What is Local Anaesthesia
Local anaesthesia is 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)
What is an endotracheal tube (ETT)
An endotracheal tube (ETT) is a flexible plastic tube with an inflatable cuff (balloon) at one end and a connector at the other. The tip of the endotracheal tube is inserted through the mouth, throat (pharynx), larynx and vocal cords into the trachea. Endotracheal tubes come in different sizes, with the diameter written in mm (e.g., 7-7.5mm for women, 8-8.5mm for men)
Once in the correct position, a syringe can be used to inflate the cuff via the pilot line. There is a pilot balloon towards the end of the pilot line, which inflates along with the cuff and allows the anaesthetist to roughly assess how inflated the cuff is (while it is out of sight in the trachea). The pressure in the cuff can be checked with a manometer (pressure sensor) to avoid over or under-inflation. There is a valve on the end of the pilot line that keeps the pilot balloon inflated.
The _________ _____ provides an extra hole on the side of the tip that gas can flow through in the event that the main opening at the tip of the ETT becomes occluded (blocked)
The Murphy’s eye provides an extra hole on the side of the tip that gas can flow through in the event that the main opening at the tip of the ETT becomes occluded (blocked)
What is a laryngoscope?
What is a McGrath Laryngoscope
A laryngoscope is a metal blade attached to a handle, with a light attached. It is inserted through the mouth and into the pharynx to visualise the vocal cords. An endotracheal tube can be guided along the blade into position in the trachea. A McGrath laryngoscope is a high-tech version of a standard laryngoscope, which has a camera and screen attached so that the vocal cords can be visualised via a live video feed.
What is a bougie
A bougie is a device to help with intubation, notably when the vocal cords cannot be visualised. The bougie is inserted into the trachea. The endotracheal tube slides along the bougie into the correct position in the airway. The bougie is then removed, and the endotracheal tube remains in place.
What is a stylet
A stylet is another device to help with intubation. It is a stiff metal wire (with a plastic coating) that is inserted into the endotracheal tube before intubation is attempted. It can be bent to hold the endotracheal tube in a specific shape. It is usually used to bend the tip of the endotracheal tube** anteriorly** towards the trachea (to avoid going posteriorly into the oesophagus).
What is Awake fibre-optic intubation
Awake fibre-optic intubation is a special procedure where the endotracheal tube is inserted with the patient awake, under the guidance of an endoscope (camera). A long thin tube with a camera on the end (endoscope) is inserted through the nose or mouth, down to a position below the vocal cords. The endotracheal tube is then inserted over the top of this tube into the correct position. Then the endoscope is removed, leaving the endotracheal tube in position. This is used where there is restricted mouth opening or difficult anatomy (e.g., after radiotherapy to the neck). Putting the patient to sleep prior to inserting the endotracheal tube is more risky, as a delay in intubation can lead to hypoxia.
What is Trismus
Trismus refers to pain and restriction when opening the jaw. This can make intubation more difficult and might need** awake fibre-optic intubation.**
What is Supraglottic Airway Devices
A supraglottic airway device (SAD) are an alternative to endotracheal intubation for ventilation. They are very commonly used in both elective and emergency scenarios. They are the first option if intubation fails in a difficult airway scenario.
The tip of the SAD will be located at the top of the oesophagus. The cuff will fit around the opening of the larynx, forming a seal between the device and the airway. The cuff can be inflatable or non-inflatable. SADs with inflatable cuffs are called laryngeal mask airways (LMA).
What is I-gel
I-gel is a type of non-inflatable SAD that uses a gel-like cuff that moulds to the larynx.
WHat are Oropharyngeal (Guedel) airways
Oropharyngeal (Guedel) airways are inserted into the oropharynx. They are rigid and create an air passage between in front of the teeth and the base of the tongue, maintaining a patent upper airway. They are inserted upside down, then rotated into position once the tip is past the tongue. These are most often used when ventilating the patient via a face mask and bag prior to inserting an SAD or ETT. The size is measured from the centre of the mouth to the angle of the jaw
What are Nasopharyngeal airways
Nasopharyngeal airways are slightly flexible tubes inserted through the nose. They create an air passage from outside the nostril to the pharynx (throat). The size is measured from the edge of the nostril to the tragus of the ear. They are often used in emergency scenarios, for example, in A&E or at cardiac arrests. They carry a risk of nosebleeds (epistaxis). A base of skull fracture is a contraindication for inserting a nasopharyngeal airway
What is a Tracheostomy
A tracheostomy refers to creating a new opening (-ostomy) in the trachea (trache-). A hole is made in the front of the neck with direct access to the trachea. A tracheostomy tube is inserted through the hole into the trachea and held in place with stitches or soft tie around the neck (trach tie). Tracheostomies may be temporary or permanent, depending on the indication.
Indications for a tracheostomy include
- Respiratory failure where long-term ventilation may be required (e.g., after an acquired brain injury)
- Prolonged weaning from mechanical ventilation (e.g., ICU patients that are weak after critical illness)
- Upper airway obstruction (e.g., by a tumour or head and neck surgery)
- Management of respiratory secretions (e.g., in patients with paralysis)
- Reducing the risk of aspiration (e.g., in patients with an unsafe swallow or absent cough reflex)
The Difficult Airway Society (DAS) have published guidelines on the steps to take in the case of unanticipated difficulty intubating a patient (DAS guidelines 2015).
There are four stages (summarised):
- **Plan A **– laryngoscopy with tracheal intubation
- Plan B – supraglottic airway device
- Plan C – face mask ventilation and wake the patient up
- Plan D – cricothyroidotomy
