Anaesthesia Flashcards
ASA grading
Class I: completely healthy
Class II: mild systemic illness, no functional limitation
III: severe illness with end-organ damage (but still can work)
IV: incapacitating, constant threat to life
V: moribund patient not expected to live within 24h
Specific qns to ask in anaes hx
Past hx of anaesthesia
PMHx: Recent URTI, asthma, OSA, CVS diseases, severe GERD, severe motion sickness
Effort tolerance
Current medications
Last meal
Smoking hx
Fam hx of malignant hyperthermia
How long symptom free for URTI to qualify for GA?
6 weeks on paper, 2 weeks in practice
Why is smoking a problem in anaes?
- nicotine causes vasoconstriction, SVR increases; BP will plunge if given drugs causing vasodilation
- risk of laryngospasm, bronchospasm
- ideally quit smoking 4-6 weeks before op, at least 48-72h before op
How long to fast before op?
2 hr - clear fluids
light meal: 6 hours
heavy meal: 8 hours
What to do in pts with history of OSA?
pt to be discharged to HDU and not general ward. OSA worse at night due to effects of anaesthesia, need monitoring
Mnemonic for pre-op PE
LEMON-D
Look: craniofacial deformities, short/thick neck/beard, recessed chin
Evaluate: 3 finger inter-incisor, 3 finger thyromental distance , 2 finger mentum to hyoid bone
Mallampati score
Obesity
Neck ROM
Dentures/loose teeth
Mallampati scoring
Class I: complete visualisation of soft palate with tonsillar pillars
Class II: complete visualisation of uvula
Class III: visualise only base of uvula
Class IV: soft palate not visible at all
___ classification of laryngoscopic view grades
Cormack and Lehane
Grade 1: full view of glottis
Grade 2: partial view
Grade 3: only epiglottis seen
Grade 4: neither glottis nor epiglottis seen
Pre-op ix for patients according to ASA
ASA I >50yo: FBC, UECr, ECG
All others ix as needed: HbA1c, ABG, PT/PTT, LFT, trops
Most common peripheral nerve injury
Ulnar nerve
What 3 axis to align using what position?
oral axis
pharyngeal axis
laryngeal axis
sniffing morning air position - flexion at lower c spine, extension at upper c spine
*obese patients - stack pillows such that mouth is at level of sternum
How to size oropharyngeal and nasopharyngeal airway?
oral: corner of mouth to tragus of ear
nasal: anterior nares to tragus of ear to angle of mandible
Laryngeal mask airway sizing
How much air to cuff?
70-100kg: #5
Asian males: #4
Asian females: #3
30ml of air to cuff
5 point auscultation spots
Epigastrium
bilateral upper anterior chest
bilateral bottom mid-axillary
CO2 detector changes from __ to ___ when CO2 is detected
purple to yellow
Sizing of ETT
How much air to cuff?
Asian male: 8-8.5
Asian females: 7-7.5
Children: age/4 + 4
cuff with 4ml of air
5 ways to check correct ETT placement
1) direct visualisation of tube passing through vocal folds
2) equal, bilateral chest rise
3) auscultation bilateral lungs
4) misting of ETT tube
5) CO2 indicator purple to yellow
When is ETT preferred over LMA?
Higher risk of aspiration
- obesity, pregnancy, severe GERD
- surgery with pneumoperitoneum (eg. laparoscopic)
- intraabdominal surgeries
Nasal cannula FiO2 formula
(max O2 flow = 1/2L/min)
21% + (4 x oxygen flow rate)
eg. 1L/min, FiO2 = 25%
Every 1L increase, increases FiO2 by 4%
**Max FiO2 on nasal cannula is 40%
Hudson mask FiO2
(max O2 flow = 5-10L/min)
FiO2: 40-60% (max usually <50%)
Non-rebreather mask FiO2
(max O2 flow = 8-10L/min)
FiO2 usually max 80%
Highest FiO2 in variable performance masks
But can cause basal atelectesis
What is venturi mask?
Uses valves to mix O2 with ambient air - precise concentration
Components of general anaesthesia
1) *analgesia
2) *amnesia
3) *anesthesia - pt unconscious, asleep
4) reflex suppression
5) paralysis
__ classification on stages of anaesthesia
Guedel
Stage 1: amnesia (respi pattern regular), can still follow commands
Stage 2: uninhibited excitation, laryngospasm if airway manipulated, respiration irregular
Stage 3: surgical anaesthesia (respi pattern regular) - target depth
Stage 4: overdose, at risk for hypotension and cardiovascular collapse
pre-operative abx
Most: cefazolin
GI surgeries: ceftriaxone + metronidazole
purpose of pre-oxygenation
To replace nitrogen in functional residual capacity in lungs (that is usually in room air) with oxygen
allows 8 min of apnoea in 70kg adult without arterial o2 desaturation
**functional residual capacity = 2L
oxygen consumption = 250ml/min
usually, at 21% oxygen
FRC = 420mL
apneic time = 1.68min
at 100% oxygen
FRC time = 2000mL
apneic time = 8min**
Benzodiazepines work on the __ receptor
Used for ___, ___, ___ (but no ___)
GABA receptors
enhances GABA transmission (inhibitory neurotransmitter)
anxiolysis, amnesia, sedation
no analgesia
Reverse benzo overdose with ___
flumazenil
*not used in chronic benzo users, can cause seizures
Opioids act on ___ receptors
Used for ___ and ___, but no ___
mu, kappa, delta receptors
sedation, analgesia
no amnesia
Reverse opioid overdose with ___
naloxone
Types of induction agents
Inhalational: sevoflurane, isoflurane, desflurane
- used as main induction agent in children (problems with IV)
- can prolong stage 2 anesthesia, airway irritation, environmental pollution
Intravenous: ketamine, etomidate, propofol
- rapid, shortened stage 2
*adults usually TIVA or mixed inhaled/IV induction
Advantages of total intravenous anaesthesia (TIVA)
- avoid side effect of inhalational agents (hx of PONV, severe motion sickness)
- Environmentally friendlier
facts about propofol
- most common induction agent
- potent CVS and respi depressant
- decreases BP: decreases cardiac contractility & causes peripheral vasodilation
- works on GABA
Made from soybean??
Contains egg lecithin - contra in egg allergy
facts about etomidate
- minimal cardiac and respi depression
- works on GABA
good to use in pts with compromised haemodynamics
facts about ketamine
- cardiovascular STIMULANT
- minimal respi depression
- works on NMDA receptors (antagonist)
- potent analgesic and BRONCHODILATOR (good for asthmatics)
Side effects: hallucination, emergence delirium, increased salivation, increase ICP
Two types of ventilation in maintenance of general anaesthesia
1) spontaneous respiration
- no muscle paralysis
- patient determines RR and tidal volume
2) Intermittent positive pressure ventilation
- non-depolarising muscle relaxant used
- anaesthetist determines RR and tidal volume
Depolarising neuromuscular blocker example
Succinylcholine
- initially causes muscle fasciculations: depolarisation
- prolonged binding prevents repolarisation
- quick onset, shortest DOA
Non-depolarising neuromuscular blocker examples
rocuronium, pancuronium
- competes with acetylcholine at nicotinic receptors
- longer onset, longer duration of action
DOA: rocuronium < pancuronium
When reversing nondepolarising NMB, use ___. Must use ___ together to prevent ____.
neostigmine - acetylcholinesterase inhibitor to increase Ach - overwhelm blockade
glycopyrrolate (anticholinergic)
prevents overstimulation of muscarinic receptors by increased Ach (can cause bradycardia, bronchospasm)
What is minimum alveolar concentration?
concentration of inhaled anaesthetic agent at 1 atmospheric pressure which prevents reflex movement in response to surgical stimuli in 50% of subjects
Usually kept at 0.7-1.0
Examples of sympathomimetics and when to use what
Ephedrine
- act on both alpha and beta receptor
- vasoconstriction + increase HR
- good for low BP and low HR
Phenylephrine
- act on alpha receptor only
- vasoconstriction + reflex bradycardia
- good for low BP and high HR
How to check for reversal of neuromuscular block?
Train of four stimulation (muscle twitch 4 times similar strength with stimulation)
Using peripheral nerve stimulator
How do local anaesthetic drugs work?
Inhibits sodium channels on cell membrane of nerve axon - prevents conduction - membrane cannot depolarise, prevents generation of action potential
Examples of local anaesthetics
Amides: lidocaine, bupivacaine
esters: procaine, cocaine
LA blocks ___ nerve fibers more readily than ___ nerve fibers
myelinated > unmyelinated
LA works faster in ___ pH
__ is added to help LA work faster
higher pH (less acidic)
Sodium bicarbonate is added to increase pH to speed up onset of action
___ is added to LA to prolong LA action by causing ___
Adrenaline
causes local vasoconstriction, slows down absorption of LA from site of deposition -> prolong action
Toxicity effects of LA
CNS
- lightheadedness, perioral/tongue numbness, tinnitus, slurred speech, visual disturbances, anxiety
- CNS depression
CVS
- arrhythmia, cardiac arrest, hypotension
How to prevent LA toxicity?
How to manage toxicity?
- use lowest dose
- ultrasound guidance
- communicate with patient intraop and ask about symptoms
Mx: infuse lipid emulsion solution to remove from plasma
give BZD/propofol for seizures
Spinal cord end at __ in adults and __ in children
Adults - L1
Children - L3
Layers of dura and what is in between? Where does CSF flow?
Pia mater - adheres to spinal cord
Arachnoid mater - adheres to dura mater
CSF is between arachnoid and pia mater (subarachnoid space)
Anatomical landmark of spinal cord
Iliac crest/intercristal line indicates L4-L5 interspace when pt is in lateral flexed position
Layers of tissue LA needle goes through at spine
Skin -> subcutaneous tissue -> supraspinous ligament -> interspinous ligament -> ligamentum flavum -> epidural space -> subdural space -> arachnoid mater -> subarachnoid space
Spinal block given at ___ space. Catheter only placed in ___ space due to risk of infection.
subarachnoid space
epidural space
How to control flow of LA in the subarachnoid space?
Using baracity of solution
- Hyperbaric: LA + glucose/dextrose. Heavier than CSF, flows in direction of gravity and settles in dependent areas
- Hypobaric: LA + sterile water, rises in relation to gravity
___ dose is ___ higher than ___ as there are more layers of mater to traverse before acting on nerve roots
Epidural
10x
spinal
If LA blocks sympathetic nerves at ___ level, can cause bradycardia
T1-T4
What is post dural puncture headache?
CSF leaks through hole faster than it is being produced when dura mater is damaged
Downward displacement of brain structures
Pain worsened with sitting/standing. Relieved on lying down
RF: young, female, pregnant, big needle
Risk of doing spinals in pts with coagulopathy. How to manage?
Epidural/spinal haematoma. Need urgent MRI and surgical decompression of spine
Types of blocks for surgeries
- shoulder
- below elbow
- femoral fracture
Shoulder: interscalene block
anything below elbow: infraclavicular/axillary block
femoral fracture: femoral nerve
Minimum monitoring standards in anaesthesia
Non-invasive BP
ECG
Capnography
Inspired oxygen analyser
Pulse oximetry
(BECOP)
At what PaO2/SpO2 does hypoxemia occur?
60mmHg PaO2
91% SpO2
How does pulse oximetry work?
When is it limited?
measures transmission of light across vascular tissue bed
comparing spectra of oxygenated Hb over deoxygenated Hb
Limitations
- low SpO2 <70%
- Loss of pulsatile component: irregular blood flow, hypothermia, hypoperfusion, vasoconstriction
- nail polish
- dyes in circulation: methylene blue
How does automatic BP work?
Oscillometry - senses oscillations when cuff pressure falls below systolic pressure
peak amplitude of oscillations is read as mean BP
Intraarterial waveforms and what do they mean
Upstroke: ventricular contraction
Dicrotic notch: closure of AV valves
ECG monitoring in anesthesia usually ___, displays lead __.
___ leads required to display leads __ and __. Used for patients ____
3 leads: lead II
5 leads: lead II, V5. For pts with cardiac ischemia, cardiothoracic op
Phases of capnography
AB: exhale dead space
B: start expiration
BC: exhale dead space and alveolar air
CD: plateau, exhaled CO2 from alveoli
D: end of plateau phase. END TIDAL CO2 that corresponds to PaCO2 (~40mmHg)
E: start of inspiration
Different patterns on capnography and what they mean
Upward slope, slower rise = bronchospasm
Low ETCO2 = hyperventilation, airway obstruction, hypotension
High ETCO2 = hypoventilation, high production
Curare clefts - patient starting to wake up, tries to take a breath in
target number on bispectral index for adequate anaesthesia
40-60
Key components of PACU handover
- pt biodata: age, ASA, comorbids, PMHx, allergies, regular meds
- surgery, type of anaesthesia, intraoperative issues
- blood loss, urine output, transfusions
- problems expected post op
- pt current status
- post op instructions
respi cx at PACU
1) airway obstruction
- tongue falling back**
- laryngospasm, oedema
- secretions
- neck haematoma
2) hypoventilation
- residual effect of anaesthesia**
3) hypoxemia
haemodynamic issues at PACU
1) hypotension
- bleeding
- vasodilation
- cardiac dysfunction
2) hypertension
- pain
- ARU causing discomfort
- intracranial HTN: HTN + bradycardia
Shivering in the PACU
- causes
- effects
- how to stop?
cause
- hypothermia (<35deg)
- use of volatile agents
effect
- increased O2 consumption: can lead to cardiac ischemia
- coagulopathy (impairs plt function)
- delayed awakening
IV Pethidine can stop muscle contractions to stop shivering, but doesn’t mean pt not cold
Risk factors for post op nausea and vomiting (PONV)
pt factors
- young women, children
- obesity
- NON-smoker
- hx of motion sickness, hx of PONV
anaesthetic factors
- inhalational agents
- opioids
surgical factors
Mx of PONV
- Use less inhalational agents, use TIVA
- give more antiemetics (ondansetron, dexamethasone, droperidol, metoclopramide)
What medications to stop pre-op?
SGLT2 inhibitors (empagliflozin etc): stop 72hrs prior to surgery to prevent euglycemic DKA
all other meds: stop day of surgery
- OHGA
- insulin (do not stop basal insulin)
- ACEI/ARBs
