Preoperative assessment Flashcards
Which 5 conditions confer a 1.5 x increase of perioperative death?
All 1.5 x risk
MI HF CVA PVD RF
To what extent does T1DM and T2 DM increase the risk of perioperative death
T1DM - 3 x risk
T2DM - 2 x risk
To what extent does SBP consistently above 160 mmHg increase perioperative mortality?
1.5 x
What effect does small reductions in high BP have on the perioperative morbidity and mortality risk?
They reduce stroke risk
They do not reduce MI or mortality risk
The reduction in stroke risk provided by pre-operative antihypertensive treatment should be weighed against the cost of delaying surgery
Compare the risk risk of dying the month before an MI with the month after an MI
Risk of dying in the month after MI is 50 x the risk of dying the month before and MI
What is the risk of dying at 12 months after an MI
1.5 - 3.0 times
How long should surgery be delayed post MI
3 - 6 months
How long after the placements of coronary stents/CABG is the perioperative risk of dying no longer elevated?
6 months
What is the risk of perioperative death 12 months after coronary artery stent placement if clopidogrel is stopped (for surgery) and what are the implications?
5 x increased risk of perioperative mortality
Implicaitons: Management of patient’s receiving anti-platelet medication should be jointly planned with the cardiologist
Compare the absolute risk of arterial thromboemboli for new biological Aortic valves not on warfarin with the absolute risk of arterial thromboemboli for new mechanical MITRAL valve on warfarin
Mechanical mitral valve on warfarin: 1:1000 monthly risk
Biological aortic valve NO warfarin: 1:2400 monthly risk
What should AF rate be prior to surgery?
< 100 bpm
What determines if patients on warfarin should be changed to heparin for the peri-operative period?
This depends on the nature of the surgery
Under what circumstances and when should aspirin be stopped prior to surgery
If aspirin is stopped, it should be stopped 5 days before surgery.
The risk of bleeding if aspirin is continued is exceeded by the risk of thrombosis except for surgeries: brain, spinal canal, prostate.
In what types of surgeries should aspirin be stopped ad why
Brain
Spinal cord
Prostate
Risk of bleeding exceeds risk of thrombosis in these surgeries
When should statins be stopped before surgery
DON’T STOP. reduce the risk of myocardial infarction, angina and heart failure,
When should CCB’s be stopped and why
DON’T STOP. reduce the risk of myocardial infarction, angina and heart failure,
When should BB be stopped and why
DON’T STOP. reduce the risk of myocardial infarction, angina and heart failure,
When should ACE I / ARB be stopped?
Stop ACE I in patients with major risk of haemorrhage or those planned for epidural anaesthesia.
Profound hypotensive episodes with regional and general anaesthesia
Should thiazide diuretics and spironolactone be stopped and why
DON’T STOP. reduce the risk of myocardial infarction, angina and heart failure,
When SHOULDN’T warfarin be stopped?
When the surgery can be performed with elevated INRs:
Eye,
dental,
endoscopies (bladder/bowel/uterus)
How long before surgery should warfarin be stopped?
The last does of warfarin should be taken 5 days before surgeries for which the risk of bleeding exceeds the risk of thrombosis.
When should warfarin be replaced by subcutaneous high dose LMWH
When the absolute risk of thrombosis is high
- a mechanical mitral valve or previous CVS events require LMWH
Example of a low risk patient: AF only (normal valves, no previous CVS events) –> in these circumstances LMWH not required
What is the priority with regard to oral diabetic drugs and insulin?
Avoiding peri-operative hypoglycaemia (many of the signs of hypoglycaemia are masked by anaesthesia)
Stop long acting drugs
Sliding scale if needed
What are the 4 mnemonics for the prediction of a difficult airway
Difficult BVM - BOOTS
Difficult ETT - MMAP
Difficult LMA - MOODS
Difficult FNA - FRONT
BOOTS Beard/Body piercings/Boobs Obese/Obstetrics Old age/Odd looking Toothless/Trauma Snoring/Stridor/Syndromes
MMAP Measure 3:3:1 (6 for Patil's and 12 for Savva) Malampati Class (1 - 4) Atlanto-occipital extension Pathology: upper airway
MOODS Mouth Opening Obstructed airway Disrupted pharynx/larynx Stiff Lungs
FRONT Fixed neck flexion Radiotherapy Obesity Neck mass Tracheal deviation
Which patients have a potentially unstable c-spine
Trauma/RA/Down’s syndrome
How often is facemask ventilation difficult and how often does it fail? Compare this to the same for intubation and back up techniques
BVM
Difficult 1 in 20
Fails 1 in 1500
ETT
Difficult: 1 in 50
Fails: 1 in 1500 (elective) ; 1 in 300 (emergencies)
Rescue techniques fail: 1 in 10 - 20
What does the ‘S’ in BOOTS mnemonic stand for?
Syndromes
Genetic syndromes and: Small mouth Receding chin High arched palate Large tongue Bull neck
Snoring: OSA
Stridor: UAO
What is the problem with tests for prediction of the difficult airway
Low specificity and low positive predictive value (large number of false positives)
Specificity: ± 10% prove to be actually difficult
Sensitivity: ± 50% of the difficult cases are predicted by the test
Why is predictive value of ‘airway difficulty’ challenging
Definitions of ‘airway difficulty’ vary widely
> 2 attempts > 10 min Requiring Bougie C-L 3 - 4 Failure
Describe the Cormack-Lehane classification
Grade 1: >50% glottis visible Grade 2: < 50% glottis visible Grade 2a: Glottis visible Grade 2b: Arytenoids visible Grade 3: Epiglottis only visible Grade 3a: Bougie possible Grade 3b: Bougie impossible Grade 4: No laryngeal structures visible
Describe Cook’s modified classification
Easy: No adjuncts required
Restricted: GEB required
Difficult: Advanced techniques required
How is the Mallampati test performed?
Open mouth as wide as possible
Stick tongue out without phonation
Describe the Mallampati classification
Class 1: Complete uvula (with faucial pillars and soft palate)
Class 2: Uvula masked by base of tongue (faucial pillars + soft palate visible
Class 3: Soft palate only
Class 4: Soft palate not visible
What is the Patil test
Thyromental distance < 6.0 cm is associated with difficult laryngoscopy
What is the specificity and sensitivity if the Mallampati test is combined with Patil’s test for prediction of a difficult airway
Specificity = 97% Sensitivity = 81%
Interpret the prognathism test
Grade A: Lower incisors can protrude > 1 cm beyond upper incisors
Grade B: Incisors align
Grade C: Lower incisors cannot align
B + C –> difficult laryngoscopy
What is the Savva test
Sternomental distance < 12.5% is associated with difficult laryngoscopy
How is upper neck movement objectively assessed
Pencil on vertex of forehead - movement should be ± 90 - 110º
OR
Finger on chin and occiput
After neck extension:
Occiput lower than chin - normal
Occiput and chin level - Moderate limitation
Chin lower than occiput - Severe limitation
When would radiographs be required in the assessment of a difficult airway?
Assess for C-spine stability in rheumatoid arthritis
When would CT/MRI be required for the airway assessment?
Partial airway obstruction at or below the glottis
What % of patients with normal airway difficulty assessment tests have Grade 3 - 4 laryngoscopy
5.8%
What is the likelihood of a difficult airway if prediction tests are positive?
3 - 6 fold
What is the likelihood of a easy airway if predictive tests are negative
1-2 fold
If Mallampati and Patil test are both positive, what is the likelihood of a difficult airway?
10 fold increase
What is the Han Scale?
Scale used to classify difficulty of mask ventilation
1 - Easy
2 - Airway adjuvant required ± NMB
3 - Requires 2 HCW ± NMB
4 - Impossible
What are the key statistics relevant to difficult mask ventilation
DMV occurs in 1 - 5%
< 20% DMV is predicted
Impossible DMV in 1:1500
What is the most important predictor of difficulty with AFOI (Awake Fibreoptic Intubation)
Lack of patient co-operation
Operator experience
Blood and secretions in the airway
Why test for pregnancy before surgery
EARLY
- Increased miscarriage risk
- Possible teratogenicity (no evidence for current agents in use)
LATE
- Increased preterm labour
- Regurg and aspiration risk
- Increased risk of failed intubation 1 in 300 (vs 1 in 2000)
Pre-op Rx of reflux
Weak evidence in the obstetric patient for Na Citrate (30ml) and PPI/H2RA
No evidence for these premedications in the non-obstetric patient but some anaesthetist give this regardless
What are the relevant questions to ask the patient with regards to previous anaesthetics
- Airway issues
- Drug issues
- Other complications - malignant hyperthermia
- Unpleasant experiences: PONV/Awareness - concil
- Repeat anaesthetics - If Halothane used at least 3 months between anaesthetics
If there was previous PONV - what pertinent details with regard to this can be sought
- Type of Surgery - Ophthalmic and gynae surgery -> PONV higher
- Analgaesics used (?opioids)
- Previous anti-emetics given for prophylaxis or Rx
If you elicit a history of a previous difficult intubation, which of the following is the single most important piece of information from the anaesthetic record?
Select one option from the list below.
Possible answers:
A. Size of endotracheal tube or laryngeal mask airway used
B. Any manoeuvres used to assist intubation
C. Ability to bag the patient with a face mask
D. Drugs used to assist endotracheal intubation
C. Correct.
All the points provide very useful information.
However, the ease of face mask ventilation of the patient is critical as it means that the patient can be kept safe and well-oxygenated while other methods are used to assist intubation.
If the patient is not easy to oxygenate with face mask ventilation, then the safest course is to plan for an awake fibreoptic intubation, providing you are skilled in the technique.
What are important inherited conditions related to anaesthesia
MALIGNANT HYPERTHERMIA
SUCCINYLCHOLINE APNOEA
INHERITED PORPHYRIA
Dystrophia myotonica (in close family members) - may only be mildly expressed in the patients - but underlying cardiac issues might be present which should be investigated
Other complications in family members important to elicit because patient will require reassurance
Apart from the related chronic illness, how does smoking affect anaesthetic management
Increased COHb (not usually significant)
Increased airway reactivity
Increase mucus production
but anaesthetic technique is not altered –> patients should be advised about cessation both for the longer term and immediately prior to the anaesthetic
Why is an alcohol history relevant in the pre-anaesthetic assessment
Increased tolerance to induction agent
Liver and cardiac disease (coagulation studies)
Hx delirium tremens in the mornings –> problems in the recovery period.
Regarding repeated anaesthetics:
Select true or false for each of the following statements.
A. It is advisable to avoid repeated halothane within three months
B. Repeated isoflurane anaesthetics are safe Missed answer
C. Repeated propofol anaesthetics are safe Missed answer
D. Repeated nitrous oxide anaesthetics are safe
E. Repeated anaesthetics with non-depolarising muscle relaxants are safe
A. True. However, as halothane is now hardly ever used in the UK, it is almost a historical restriction.
B. True. It is safe, but very rapid repeat anaesthetics (within 12 hours) may have a slower recovery due to incomplete excretion of the isoflurane.
C. True. Again, there is the issue of prolonged recovery with short intervals (within hours), but it is safe.
D. False. If repeat exposure within hours occurs, then the issue of inhibition of folate synthesis may be a problem. This is particularly the case if the combined length of exposure to this anaesthetic amounts to many hours.
E. True. The only issue is if reversal agents have been given in the last hour.
Does a history of PONV increase the risk of aspiration pneumonia
No
