ANAESTHETICS Flashcards
Broadly, what are the two types of airway management?
Simple airway
Advanced airway
Describe how a simple airway is maintained.
- Airway manoeuvre
- BVM
- OP/NP tube
Name two types of airway manoeuvre. What is the aim of airway manoeuvres?
Head tilt, chin lift
Jaw thrust
To lift the tongue and soft tissues of the pharynx anteriorly to open the airway.
When should you use a jaw thrust manoeuvre instead of head tilt?
Suspected trauma.
What is BMV?
Bag-mask-ventilation.
Facemask is used.
Which two airways can be used to aid BMV?
Oropharyngeal (OP) (guedel)
Nasopharyngeal (NP)
How do you insert an OP airway?
- Measure from the centre of the mouth to the angle of the jaw
- Insert into mouth and twist to advance
DO NOT USE IF GAG REFLEX PRESENT
How do you insert a NP airway?
- Measure from the tip of the nose to the tragus of the ear
- Through the nose
- Advance straight
DO NOT USE IN HEAD INJURY
Name two supraglottic airways?
LMA
iGel
How do you insert an LMA?
Insert blind
Inflate mask once situated
How do you insert an ET tube?
- Visualise with laryngoscope
- Sizing: 7 for women, 8 for men
- Inflate cuff to protect the airway
- 20-24cm markings should lie between the teeth
- Used in theatre and ICU
Elastic bougies can be used to aid ET tube placement.
How do you insert a tracheostomy?
• Needle (emergency) or surgical cricothyroidotomy
• Inserted from front of the neck
• Cuff to protect airway
Used in ITU
Which interventions protect the airway?
ET
Fibreoptic intubation
Cricothyroidotomy
What is a definitive airway?
Cuffed tube below the vocal cords to create a seal and prevent aspiration.
ET tube or tracheostomy.
(NOT LMA as this may not protect the airway and there is still risk of gastric aspiration).
Broadly, what are the two types of ventilation?
Non-invasive airway (NIV)
Invasive airway
When do we use NIV?
When supplemental O2 is failing e.g. respiratory failure.
What are the two types of NIV?
CPAP
BiPAP
How do we decide which type of NIV to use?
Depends on the type of respiratory failure.
Type I = CPAP
Type II = BiPAP
How does CPAP work?
Maintains a minimum airway pressure.
In alveolar collapse (pneumonia) –> keeps alveoli open
In pulmonary oedema (heart failure) –> pushes the fluid out
How does BiPAP work?
During inspiration, BiPAP gives extra IPAP (inspiratory positive pressure).
Increases lung expansion and ventilation.
AND during expiration, maintains minimum airway pressure with EPAP (same as CPAP):
Keeps alveoli open and pushes fluid out.
Give two examples of invasive ventilation.
ET tube.
Tracheostomy.
What two types of ventilation can be achieved with invasive management?
- Volume control - theatres.
2. Pressure control - theatres and ITU, protects lungs from too much pressure (ITU/children).
How does invasive ventilation work in terms of volume-control and pressure-control?
Volume-control:
- Pressure increases
- Target volume reached
- Ventilator stops
- Expiration occurs
Pressure-control:
- Pressure constant
- Target time reached
- Ventilator stops
- Expiration occurs
What is FiO2?
Fraction of inspired O2.
Molar/volumetric content of O2 in an inhaled gas.
What is the FiO2 for patients on air?
How does increasing the flow rate change the FiO2?
21%
Increases - 10L = 60%
Name four different methods of delivery O2?
Nasal cannula
Hudson mask
Reservoir mask (non-rebreather)
Venturi
What are the indications for the following type of O2 mask: Nasal cannulae? Hudson mask? Reservoir mask? Venturi mask?
NC - mild hypoxia.
Hudson mask - mild to moderate hypoxia
Reservoir mask - moderate to severe hypoxia
Venturi mask - COPD
What are some common issues with NC?
Irritate the nasal airway.
Don’t allow close control of FiO2.
What are some common issues with Hudson masks?
Risk of aspiration if the patient vomits whilst wearing the mask.
Don’t allow close control of FiO2.
What do you need to remember to do before fitting a reservoir mask?
Forgetting to fill the reservoir bag before attaching to the patient.
Doesn’t have a fixed seal so some air will leak out - it is not a fixed performance device.
What is humidified O2? Why is it used?
Oxygen is passed through a humidifying device producing a sterile vapour.
Reduces the drying effects of standard O2 and protects the airway mucosa.
What are the 3 components of anaesthesia?
Hypnosis
Muscle relaxation
Analgesia
What are the 3 levels of hypnosis? What class of drugs are used to achieve each level?
- Awake - local
- Sedated - sedatives
- Asleep - general
What types of local anaesthetic are there? What are they used for?
- Local - minor surgery, lacerations or wound repair.
- Regional - target specific nerves e.g. brachial plexus, usually for post-operative pain relief.
- Neuraxial - subarachnoid block (spinal) or epidural, for intra-operative and post-operative use.
What layers are found between the skin and CSF?
Skin –> fat –> supraspinous ligament –> Intraspinous ligament –> ligamentum flavum –> dura –> CSF
What is the difference between a spinal and epidural?
Spinal (subarachnoid block):
• Needle goes through ligament AND dura.
• Injected as a bolus, lasts about 2 hours.
• Smaller dose.
• Lumbar (below spinal cord) - same target as lumbar puncture.
Epidural: • Needle goes through ligament ONLY. • Catheter is passed. Local anaesthetic can be given as an infusion. • Larger doses can be given. Thoracic or lumbar.
What other drug is commonly mixed with epidural infusions?
Opioids - be careful not to prescribe opioids for these patients via other routes.
Below which dermatome can an incision be made following a spinal/epidural?
T10 - umbilicus (below the highest nerve root affected by the block).
An incision above this level will require general anaesthesia.
How do local anaesthetics work?
Reversibly block Na+ channels and inhibit the generation of action potentials.
Small diameter fibres and unmyelinated neurones are affected first.
Why are some local anaesthetics mixed with adrenaline?
Adrenaline acts as a vasoconstrictor:
• Reduces bleeding
• Prolongs effect by reducing perfusion to other tissues
Do not use adrenaline on end arteries e.g. fingers.
Name two commonly used local anaesthetics. What are they used for?
Lidocaine:
- Immediate onset, 15 mins duration
- Small procedures - laceration, chest drains, big cannulae
Bupivacaine:
- 10 mins onset, 2 hour duration (12-24 hour analgesia)
- Regional, spinal epidural
Why are neuraxial blocks preferred over GA?
Reduced affect on endocrine system
Reduced incidence of DVTs
Name a short-term sedative. What are its uses?
Midazolam IV
Endoscopy, regional anaesthesia
Name a long-term sedative. What are its uses?
IV propofol +/- alfentanil
ITU, intubated patients for theatre or transfer
Name 3 hypnotic drugs that can be inhaled.
- Isoflurane - cheapest
- Desflurane - wears off quickly
- Sevoflurane - used for induction
Name 3 hypnotic drugs that can be used intravenously.
- Propofol - quick onset, also antiemetic, fast redistribution
- Thiopenthal - quick, emergency
- Ketamine - CVS instability and analgesia
Name two ways the airway can be managed once sedation is achieved.
Spontaneous breathing - BVM or laryngeal mask (e.g. iGel)
OR
Controlled ventilation - intubating the trachea (requires muscle relaxant)
Why are muscle relaxants used?
- To aid intubation (relax the glottis)
- Muscles relaxed for surgery
- Patients do not ‘fight’ the ventilator