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Principle components of Anaesthesia

1. Hypnosis
   • Three phases: (a) induction, (b) maintenance, (c) emergence
   • IV induction is faster than inhalational; most induction agents are assoicated with respiratory depression and vasodilation
   • Hypnotic agents are the same as those used for analgesia
2. Analgesia
   • Reduces somatic and autonomic response to pain
   • Usually opiate based - associated with respiratory depression
3. Muscle relaxation
   • Depolarising (suxamethonium): depolarise by binding and causing paralysis, fasiculation - last 5-15 minutes
   • Non-depolarising (vencuronium and rocuronium have no cardiovascular side effects): competitively bind with ACh receptors at the neuromuscular junction and last up to 60 minutes - reversed by neostigmine (anti-cholinesterase)

American Society of Anaesthestist (ASA) scoring system

1. Preparation

• Patients should be nil by mouth for 6-8 hours pre-operatively: allows for gastric emptying
• Airways assessment: Mallampati scoring system for predicting difficulty in intubation
• Pre-med: temazepam 10mg / lorazepam 2mg po 1hour before operation
• Identify patients at high risk of haemodynamic instability (therefore surgeon should be readily available)
  1. Tight LMS
  2. Severe AS or MS
  3. Tamponade or bleeding
  4. Poor LV
  5. Pregnancy

2. Commence

1. Sit patient up at 45'
2. Administer oxygen, apply oximeter and adjust oxygen
3. ECG
4. Place cannula in wrist (avoid left side if radial harvest is contemplated)
5. Insert arterial catheter

3. Induction

1. Patient placed flat
2. Pre-oxygenate with 100% oxygen by face mask (avoids pulmonary hypertension)
3. 1mg pancuronium during pre-oxygenation to avoid narcotic induced rigidity
4. INDUCTION: Fentanyl 5-10mcg/kg + etomidate 10-20mgiv
5. As soon as patient is unresponsive muscle relaxant is given
6. (May be necessary to give metaraminol and filling to counteract hypotension)
7. Trachea intubated and ETT secured
8. Table placed in trendelenburg position to facilitate insertion of central line
9. Urinary catheter inserted
10. Table leveled
11. Prophylactic antibiotics given
12. Patient shaved
13. Defibrillator leads attached
14. TOE inserted
15. Diathermy pads placed

4. Pre-bypass management & conduit harvesting

• Aimed at optimising haemodynamic parameters over the course of surgical activity
• Responds to variable levels of sympathetic stimulation

1. Deflate the lungs to facilitate sternotomy (risk of lacerating the right ventricle in redo surgery therefore the lungs are inflated)
2. Compression of the left subclavian artery by mammary retractors may mean that arterial pressure readings are not accurate
3. Occult blood loss may occur in the leg or pleura
4. For harvesting the IMA, the table needs to be raised and tilted away
5. Heparin administration 300Units/kg before the IMA is divided (avoid thrombosis) - check the ACT 3 minutes after the heparin is given
6. If the surgeon injects papaverine into the IMA it may be necessart ti give phenylephrine to counteract vasodilation and hypotension

5. Preparing to cannulate

• Hitching pericardium to sternal edges leads to hypotension (mechanical constriction, vagal stimulation)
• Dissection of aortic adventitia leads to high sympathetic stimulation
• Handling Right atrium whilst placing purse strings may result in AF
• Blood pressure should be <100mmHg systolic (reduce the risk of aortic dissection)

6. Before establishing bypass

• ACT must be >400 before bypass
• ACT must be >480 before hypothermic bypass
• Protamine must never be given whilst the patient is on bypass - to avoid catastrophic failure of the pump
• Volume can be given via the aortic cannula
• Blood loss can be drained by pump suckers directly back to the pump if the ACT is >400
• Once the venous cannula is connected, the patient can be put on bypass

7. During Cardiopulmonary bypass

• Drug concentrations are reduced due to priming volumes in the bypass circuit - additional may need to be given
• Patient can be disconnected from the ventilator

Checks during CPB

Challenges encountered during cardiopulmonary bypass

8. Post-bypass

Criteria for coming off bypass (TRAVEL)

• No conditions requiring the continuation of bypass
• Temperature 36.5 - 37.5'C
• Rate > 60, paced as necessary
• ABG: pO2 > 16kPa, pH 7.30 - 7.50
• Ventilation of lungs commenced
• Electrolytes: K+ 4.0 - 5.5
• Level table

1. Perfusionist begins re-warming during the last surgical anastomosis; anaesthetist can use warming blankets
2. Hand ventilate the lungs: ensure IMA graft not placed under tension by the lung
3. Place patient on the ventilator
4. Perfusionist allows heart to fill and eject by (a) slow occlusion of the venous pipe (b) and reducing arterial flow until pump flow is zero and "off bypass"
5. Rapid controlled transfusion by perfusionist via the arterial pipe
6. Inotropes, chronotropes, vasodilators / constrictors are started at this point
7. Protamine given 3mg/kg iv slow push to reverse heparinisation after bypass is termined*
8. Surgeon will spend time checking haemostasis while the protamine is being given
9. Surgeon decannulates the aorta once the heart is full or the pump is empty (aim systolic <110mmHg to avoid dissection)