Anaesthetics - Pre-Operative Assessment Flashcards
What is general anaesthesia?
A state of total unconsciousness resulting from the use of centrally acting anaesthetic drugs
What are the three main types of GA?
IV induction w/ gas maintenance
Inhalation induction w/ gas maintenance
Total IV anaesthesia
Describe IV induction w/ gas maintenance
Pre-oxygenation/airway management
IV induction
Volatile gas maintenance
What are the most common IV induction agents?
Propofol
Thiopental
What are the most common volatile gas agents?
Sevoflurane
Isoflurane
in which patients is inhalation induction used?
Used in needle phobics/difficult intubation expected
Maintains spontaneous respiration
In which patients is TIVA used in?
Used in pts w/ PMH/FH of malignant hyperthermia
-volatile agents contraindicated
What are the advantages of TIVA?
Reduced post-op N/V
Predictability in bariatric pts
More control over depth of anaesthesia
What is rapid sequence induction (RSI)?
Delivery of rapidly acting muscle relaxant immediately after induction agent
-w/o waiting to see if resp can be assisted
What is the main risk of RSI?
Unable to intubate/ventilate unconscious pt
-difficult airway equipment should always be available
What is the purpose of RSI?
To rapidly produce optimum conditions for intubation in emergency situation
What is the triad of GA?
Narcosis (pt rendered unconscious)
Analgesia (lack of pain/suppression of phys reflexes)
Relaxation (reduction/absence of muscle tone)
What is the MoA of local anaesthetic?
Blockage of conduction of nerve impulses along nerve axons w/ lignocaine +/- adren
-adren causes vasoconstriction inc potency/duration of anaesthesia
How can local anaesthetic be used?
Topically
Local infiltration
Regional anaesthesia
Spinal anaesthesia/epidural
What is regional anaesthesia?
Local anaesthetic injected directly into minor/major nerves OR epidural space/CSF
What is the maximum safe dose of lignocaine?
3mg/kg
What is spinal anaesthesia?
Local anaesthetic solutions introduced via needle directly into CSF
What are the features of spinal anaesthesia?
Onset = Fast Duration = 1-4hrs Block = Complete block in affected area (T10-toes)
What is complete sensory block?
Loss of pain
Temperature
Positional sense
How should a pt be monitored when receiving spinal anaesthesia?
ECG
BP
RR
SpO2
What is the main complication of spinal anaesthesia?
Hypotension
-vasoconstrictors & fluids
What are the contraindications to spinal anaesthesia?
Raised ICP Hypovolaemia Surgery above thorax Local/systemic infection Procedures >2hrs duration
What is epidural anaesthesia?
Epidural catheter inserted into epidural space & local anaesthetic +/- analgesic delivered continuously via pump
What are the features of epidural anaesthesia?
Onset = 45mins
Duration = Longer, often combined w/ GA/spinal
Used as on demand pain relief
How should a patient be monitored when receiving epidural anaesthesia?
ECG
BP
RR
SpO2
What are the potential complications of epidural anaesthesia?
Hypotension Resp depression CSF/dural puncture -headache -total spinal paralysis
What are the general benefits of regional anaesthesia?
Less risk of
- chest infections
- cardiovascular complications
- PONV
- post-op pain
- DVT
What are the effects of GA on the cardiovascular system?
Decreased myocardial contractility
-decreased CO
-hypotension
Arrhythmias
What are the effects of GA on the resp system?
Resp depression
Decreased ventilator response to hypoxia/hypercapnia
Laryngospasm
What are the effects of spinal anaesthesia on the cardiovascular system?
Blockage of sympathetic nerves
-vasodilation
-bradycardia
Perioperative myocardial ischaemia/infarct
What are the effects of spinal anaesthesia on the respiratory system?
Resp depression
-if opiates used
What pre-op cardiovascular assessment should take place?
ECG +/- echo
What pre-op respiratory assessment should take place?
CXR
ABG
Pulmonary function
What are the common/major risks associated w/ GA?
PONV Anaphylaxis Awareness under GA Aspiration (use RSI if pt not starved) Cardio-respiratory issues
What are the common/major risks associated w/ spinal anaesthesia?
Neurological disorder (due to trauma) High spinal block (depression of brainstem) Urinary retention/bladder damage Cardio-resp issues Spinal headaches PONV
Describe the ASA classification
ASA 1 = normal healthy pt
ASA 2 = pt w/ mild systemic disease
ASA 3 = pt w/ severe systemic disease, restricting activity but not incapacitating
ASA 4 = pt w/ severe systemic disease representing constant threat to life
ASA 5 = moribund pt not expected to survive 24hrs w/o op
ASA 6 = brain-dead pt, organs being harvested
How can operative urgency be classified?
Immediate
Urgent
Expedited
Elective
Describe immediate operative urgency
To save life/limb/organ
- resus & surgery simultaneous
- pt in theatres w/i minutes
Describe urgent operative urgency
Acute onset/deterioration of condition threatening life/limb/organ
- surgery when resus complete
- w/i 6/24hrs
Describe expedited operative urgency
Stable pt requiring early intervention
-w/i days of decision to operate
Describe elective operative urgency
Surgery planned/booked in advance of admission
What investigations may be appropriate in pre-op assessment?
FBC, U&Es, LFTs, BM, clotting ECG, ECHO CXR Resp function tests C-spine XR
What is the purpose of pre-op starvation?
Minimise volume of gastric contents
-lowers risk of regurgitation & aspiration
What are the pre-op starvation times for food/clear fluids?
6-4-2: solid food, breast feeding, clear fluids Solid food (inc milk) = 6hrs Breast fed infants = 4hrs Formula fed infants = 2hrs Clear fluids (inc black tea/coffee) = 2hrs
What are the risks of increased pre-op starvation?
Dehydration
PONV
Anxiety
Discomfort
What are the principles of pre-op management of DM?
Minimise pre-op fasting times Comprehensive pre-op assessment Omit medication on day of surgery -if well controlled Sliding scale insulin infusion -if poorly controlled
What are the principles of peri-op management of DM?
Consider RSI (DM pts prone to aspiration)
Regular BM monitoring
-if >10mmol/L consider insulin/glucose
What are the principles of post-op management of DM?
Regular monitoring of BM & vital signs
What is the purpose of cricoid pressure
reduce risk of regurgitation
What is malignant hyperthermia?
condition often seen following administration of anaesthetic agents
What are the characteristics of malignant hyperthermia?
characterised by hyperpyrexia and muscle rigidity
What are the causes of malignant hyperthermia?
halothane
suxamethonium
What is the treatment of malignant hyperthermia?
Dantrolene
What are the benefits of an oropharyngeal airway?
Easy to insert and use
No paralysis required
Ideal for very short procedures
Most often used as bridge to more definitive airway
What are the benefits of a laryngeal mask airway?
Widely used
Very easy to insert
Device sits in pharynx and aligns to cover the airway
Paralysis not usually required
Commonly used for wide range of anaesthetic uses, especially in day surgery
What are the drawbacks of a laryngeal mask airway?
Poor control against reflux of gastric contents
Not suitable for high pressure ventilation (small amount of PEEP often possible)
What are the benefits of a tracheostomy?
Reduces the work of breathing (and dead space)
May be useful in slow weaning
Percutaneous tracheostomy widely used in ITU
What are the benefits of endotracheal tube?
Provides optimal control of the airway once cuff inflated
May be used for long or short term ventilation
Higher ventilation pressures can be used
What are the drawbacks of endotracheal tubes?
Errors in insertion may result in oesophageal intubation (therefore end tidal CO2 usually measured)
Paralysis often required
