Preoperative Care Flashcards
List the common medications that should be stopped prior to surgery
- COCP (4 weeks prior to major surgery)
- Tamoxifen (4 weeks prior to major surgery)
- HRT (4 weeks prior to major surgery)
- Antiplatelets (stop 7-14 days prior)
List the common drugs that should be held of the day of surgery
- ACE-i
- ARBs
- Diuretics
- Diabetic treatment (alternative should be arranged)
- Warfarin/Aspirin/Clopidogrel (unless coronary stent)
- Lithium
- NSAIDs
How should oral medications be given on the days of surgery
With a sip of water even if NBM
Which patients should receive perioperative steroid cover
- Adrenal insufficiency on steroids
- Undergoing pituitary or adrenal surgery
- On systemic steroid therapy >7.5mg/day for >1 week prior to surgery
- Those who have received >1 month steroid course in the past 6 months
What are the mineralocorticoid side effects of steroids
- Sodium and water retention
- Potassium loss
- Metabolic alkalosis
What are the Prednisolone and Dexamethasone equivalent doses of 100mg Hydrocortisone
- Prednisolone 25mg
- Dexamethasone 4mg
What does Warfarin inhibit
- Vitamin K-dependent clotting factors (2, 7, 9, 10)
- Protein C and S
How do you reverse warfarin:
A) >24 hours
B) Immediately
A) Vitamin K 10mg
B) FFP 15ml/KG
How should Warfarin be managed perioperatively
- Stop 3-5 days before
- Replace with heparin
INR targets for:
A) Open surgery
B) Invasive procedures
A) <1.2
B) <1.5
Mechanism of action of Heparin
- Binds to antithrombin 3
- Inhibits factors 2a, 9a, 10a, and 12a
How often should APTT be checked whilst on heparin infusion
6 hourly
How is LMWH reversed
Protamine 1mg per 100 units
Describe the Lee Index
Individual predictor of cardiac risk based on 6 parameters
- History of IHD
- History of CVA
- HF
- T1DM
- Impaired renal function
- High risk surgery
List the cardiac effects of general anaesthetic
- SVR decreases (20-30% at induction)
- Tracheal intubation reduces BP by 20-30mmHg
- Myocardial depression
- Increased cardiac irritability
What is the minimum interval between MI and elective surgery
6 months
How should T2DM be managed prior to surgery
Continue normal oral hypoglycaemics until the morning of surgery, except Metformin and Chlorpropamide which may need to be stopped earlier due to risk of lactic acidosis
Risk of MI if surgery performed within 3-6 months of previous MI
16%
What is the minimal accepted urine output guiding adequate renal perfusion
0.5ml/kg/hr
What is the best blood marker for assessing response to nutrition supplementation
Serum transferrin
Criteria for malnourishment
- BMI <18.5
- Unintentional weight loss >10% over 3-6 months
- BMI <20 and unintentional weight loss >5% over 3-6 months
List the risks associated with TPN
- Hyperosmolarity
- Lack of glycaemic control
- Micronutrient deficiencies
- Liver dysfunction
- Pancreatic atrophy
- Fluid overload
What scan should be performed prior to commencing home TPN
Bone densitometry
In whom should gastrostomy be considered for nutrition
If gastric feeding likely required for >4 weeks
How does pancytopenia occur when using TPN
B12/Folate deficiency
How many mg/ml in a 1% solution
10mg/ml
Maximum dose of Lidocaine with and without adrenaline
- Without = 3mg/kg
- With = 7mg/kg
Maximum dose of Bupivicaine with and without adrenaline
- Without = 2mg/kg
- With = 2mg/kg
Maximum dose of Prilocaine with and without adrenaline
- Without = 6mg/kg
- With = 9mg/kg
What are the symptoms of systemic local anaesthetic toxicity
- Perioral tingling
- Anxiety
- Tinnitus
- Drowsiness
- Seizures
- Coma
- Apnoea
- CV collapse
- Paralysis
What is the reversing agent for local anaesthetics
Lipid emulsion (intralipid 20%) at 1.5ml/kg over 1 minute
How is prilocaine toxicity treated
Methylene blue
How is a field block performed for inguinal hernia repairs
Direct infiltration of the ilioinguinal nerve above the ASIS
When should a heparin infusion be stopped prior to surgery
6 hours
What type of block should be used for the fingers and how is this performed
- Ring block
- NO ADRENALINE
- Inject either side of the digit at the level of the webspace
When might a sciatic block be used
Foot and ankle surgery
How is a sciatic block performed
Injection 2cm lateral to the ischial tuberosity at the level of the GT
Outline how a Bier’s block is performed
- IV access in both arms
- Exsaguinate limb with Eschmark bandage
- Apply double cuff touniquet
- Inflate upper cuff to 300mmHg
- Inject 40ml of 0.5% Prilocaine
- Inflate lower cuff
- Release upper cuff
Which dural space is used for spinal anaesthesia
Subarachnoid
What level is the needle inserted for spinal anaesthesia
L1-2
What dural space is used for epidural anaesthesia
Extradural space
What precautions must be taken with spinal catheters and anticoagulation
Catheters must not be removed whilst anticoagulated (remove 12 hours post low-dose LMWH and delay two hours before next dose)
What type of drug is Lidocaine
Amide local anaesthetic (also antiarrhythmic)
What is the primary precaution with Bupivacaine
Cardiotoxicity
What is the mechanism of action of Bupivicaine
Binds to the intracellular portion of sodium channels and blocks sodium influx into nerve cells to prevent depolarisation
Why is bupivicaine contraindicated in regional blockage
Due to its cardiotoxicity in the event that the tourniquet fails
What is the local anaesthetic of choice for IV regional anaesthesia
Prilocaine
At what pH do local anaesthetics become less effective
Acidic environments e.g. abscess
Which drugs contraindicate the use of adrenaline
- TCAs
- MAOIs
What is the major side effect of Prilocaine
Methaemoglobinemia
Why do spinal anaesthetics cause hypotension
Cause loss of sympathetic tone
Outline ASA grading
- Normal healthy individual
- Mild systemic disease
- Severe systemic disease that limits activity but is not incapacitating
- Incapacitating disease that is a constant threat to life
- Moribund patient not expected to survive
What are the aims of anaesthetic premedication
- Anxiolytic
- Enhances hypnotic effect of GA
- Amnesia
- Dries secretions
- Antiemetic effect
- Increases vagal tone
- Modifies gastric contents
Agent to reverse Benzodiazepines
Flumazenil
Side effects of Hyoscine
- Bradycardia
- Confusion
- Ataxia
What is the agent of choice for rapid-sequence induction
Sodium thiopentone
What is the agent of choice for induction of anaesthesia in those who are haemodynamically unstable and why
- Ketamine
- Produces little myocardial depression
What is the agent of choice for induction of anaesthesia in daycase surgery
Propofol
Which induction agents have antiemetic properties
Propofol
Which induction agent is associated with adrenal suppression
Etomidate
Why can thiopentate not be used with laryngeal airways
Sensitises the pharynx
What are the common depolarising neuromuscular blockers
Suxamethonium
What is the mechanism of action of Suxamethonium
Inhibits the action of acetylcholine at the neuromuscular junction
What is the fastest onset muscle relaxant
Suxamethonium
What are the adverse affects of suxamethonium use
- Hyperkalaemia
- Malignant hyperthermia
- Delayed recovery
Which anaesthetic agent is associated with dissociative anaesthesia
Ketamine
What anaesthetic agent is safe to use for sedation in the less monitored environment and why
Ketamine - maintains airway protection
What is suxamethonium metabolised by
Plasma cholinesterase
List the non-depolarising muscle relaxants
- Altracurium
- Vecuronium
- Pancuronium
Why does altracurium cause facial flushing, tachycardia, and hypotension
Causes generalised histamine release on administration
What is the reversal agent for altracurium, vecuronium, and pancuronium
Neostigmine
What is the incidence of malignant hyperthermia
1 in 15000
What is the inheritance pattern and gene defect associated with malignant hyperthermia
- Autosomal dominant
- Defect in gene on chromosome 19 encoding the ryanodine receptor
What are the clinical features of malignant hyperthermia
- Hyperpyrexia
- Muscle rigidity
What is the treatment of malignant hyperthermia
Dantrolene - prevents calcium release from the sarcoplasmic reticulum
What percentage of total volume does plasma make up
5% (3L)
In what physiological state should Hartmann’s solution be used cautiously and why
Alkalosis - as lactate is metabolised to bicarbonate
Where is a tracheostomy inserted
2cm below the cricoid cartilage
What is the background radiation rate
2.2msv per year
What is the CT scan attributable risk of cancer
1 in 2000
What is used to maintain anaesthesia
Inhalational anaesthetics
What are the side effects of Halothane
- Causes respiratory depression and CO2 retention
- Negative inotrope
- Mild muscle relaxant
Which inhalational anaesthetic should be avoided in epileptics
Enflurane
What condition is associated with isoflurane use
Coronary steal syndrome
What substance can be used to potentiate the effect of inhalational anaesthetics
Nitrous oxide
What are the risks of prolonged exposure to nitrous oxide
Suppresses methionine synthase which leads to myelosuppression and megaloblastic anaemia
What are the absolute contraindication to halothane
- History of pyrexia after admission
- Jaundice
What agents are associated with malignant hyperthermia
- Halothane
- Suxamethonium
- Antipsychotics
What is the treatment of Torsades de Pointes
IV Magnesium sulphate
What should be given to patients 2-3hrs before elective surgery
Carbohydrate-rich drinks
In whom do benzodiazepines reduce the incidence of post-operative delirium
Those already taking benzodiazepines
What is the postoperative concern in those with aortic stenosis
Cannot increase CO
What is the risk of using verapamil in VT
Can cause VF
What are the characteristics of stored blood
- High K+
- Low pH
- Decreased 2,3-DPG
- Less factor V and 8
Why does hypotension occur under spinal anaesthetic
Splanchnic vasodilatation
