FRCA Notes

Conduct of Anaesthesia

Resources

  • Induction
  • Vessel harvesting e.g. saphenous veins, radial arteries
  • Sternotomy ± conduit preparation
  • (IMA grafting)
  • Pericardial hitch
  • Heparinisation
  • Cannulation aorta & venous drainage
  • Cardiopulmonary bypass
  • Re-warming
  • Weaning from bypass
  • Reversal of heparin
  • De-cannulation
  • Wound closure
  • Transfer to CICU

  • AAGBI
  • 5-lead ECG
  • ± NIRS cerebral oxygen monitoring
  • Depth of anaesthesia monitoring

  • Large cannula(e)
  • A-line
  • CVC
  • ± PA introducer sheath

Induction

  • The aims are:
    1. Minimise the fall in SVR often seen with hypnotic agents, which reduces diastolic BP and therefore LV coronary perfusion
    2. Mitigate the increased sympathetic drive caused by laryngoscopy

  • High-dose opioids are typically used e.g. 250-500μg fentanyl, which provide cardiovascular stability and adequate anaesthetic depth
  • Remifentanil may be beneficial although its tendency to cause bradycardia may be a limiting factor
  • E.g. 350μg fentanyl + 5mg midazolam ± more fentanyl ± very very small amounts of propofol or etomidate

  • Historically pancuronium was used as the NMBA owing to its long duration and slight vagolytic action
  • The trend towards early extubation may make rocuronium a preferable agent
  • Atracurium's tendency to cause histamine release and hypotension makes it less suitable

Maintenance

  • Volatile agents may have myocardial protective properties via ischaemic preconditioning, which are more marked if used in the pre-bypass period
  • They can also be added to the oxygenator of the bypass system and therefore provided throughout the period of surgery
  • Whilst on bypass monitored via oxygenator exhaust concentrations

  • Some will run a propofol infusion during bypass to establish it prior to the post-bypass period, to help provide a smoother transition to the post-operative period
  • Seemingly no difference in outcomes whether propofol or volatile agents are used (BJA, 2024)

  • There's the potential for large swings in blood pressure during bypass, with periods of significant hypotension or hypertension
  • Generally one targets:
    • A MAP >60mmHg
    • Sinus rhythm

Hypertension

  • Laryngoscopy
  • Sternotomy is highly sympathetically stimulating and requires extra boluses of opioids
  • Aortic manipulation in preparation for cannulation leads to a baroreceptor response and profound hypertension

Hypotension

  • IMA and other vein harvesting are minimally stimulating, so there may be hypotension due to GA without stimulus
  • Pericardial hitch
    • In order to bring heart anteriorly for easier access, the pericardium is stretched to hitch the heart forward
    • This causes temporarily reduced preload, leading to profound hypotension (especially if patient has AS)
  • Dysrhythmia (often AF) caused by manipulation of the atria during venous cannulation
  • All normal intra-operative causes of hypotension

  • Aortic cannulation typically requires
    • An ACT >300s
    • An SBP <100mmHg to reduce the chance of iatrogenic aortic dissection

  • Full anticoagulation is typically achieved with 300 - 500units/kg heparin given at the end of the IMA harvesting period
  • The target ACT is 400 - 500s (3-4x baseline)
  • Although ACT is a reliable measure in the early stages, its efficacy wanes during longer procedures owing to variable activation of the clotting cascade

  • The latter is acheived through increasing volatile anaesthetic depth and reducing/ceasing vasoactive drug infusion

  • Drug pharmacokinetics and dynamics are altered whilst on cardiopulmonary bypass owing to:
    • Priming-induced haemodilution
    • Reduced plasma protein concentration
    • Hypothermia-induced altered drug clearance
    • Drug sequestration during lung isolation

  • This should be factored in to drug dosing
  • E.g. remifentanil dosing may be reduced by 30% once below 32°C, or 60% once below 27°C