What are the recommended anesthetic techniques, drug dosages, monitoring, methods to blunt the sympathetic response to laryngoscopy and sternotomy, and management of hypotension before cardiopulmonary bypass, during bypass, and during weaning in adult coronary artery bypass graft surgery?

Anesthetic Management for CABG Surgery

Induction and Drug Dosages

For induction of anesthesia in CABG surgery, use ketamine 2 mg/kg combined with midazolam and fentanyl 25 mcg/kg to provide superior hemodynamic stability compared to propofol, which causes significant hypotension. 1

• Ketamine-based induction (ketamine 2 mg/kg + midazolam + fentanyl) maintains mean arterial pressure and systemic vascular resistance better than propofol 0.5 mg/kg, which causes significant drops in MAP and SVR within one minute of induction 1
• Fentanyl 25 mcg/kg IV is the recommended induction dose, with additional boluses of 10-20 mcg/kg titrated when MAP increases >10% above baseline 2
• Add rocuronium for neuromuscular blockade as part of the standardized induction sequence 1
• Avoid propofol for induction if hemodynamic stability is the priority, as it causes significant hypotension requiring more vasopressor support pre-bypass 2

Blunting Laryngoscopy Response

Adequate opioid loading with fentanyl 25 mcg/kg before laryngoscopy is the primary method to blunt the sympathetic response, supplemented by the synergistic effects of ketamine and midazolam. 1, 3

• The combination of high-dose fentanyl with ketamine provides superior control of heart rate and blood pressure during laryngoscopy compared to other techniques 1
• Maintain MAP within 10% of baseline and heart rate within 20% of baseline values throughout intubation 2
• The ketamine-midazolam-fentanyl combination specifically prevents hypertensive responses during the intubation period 1

Blunting Sternotomy Response

Continue maintenance anesthesia with volatile agents (sevoflurane 0.25-2.0%) or additional fentanyl boluses (10-20 mcg/kg) titrated to maintain hemodynamic parameters within target ranges during sternotomy. 2

• Titrate maintenance anesthetic to keep MAP within 10% and HR within 20% of baseline specifically during the sternotomy stimulus 2
• The ketamine-based induction provides hemodynamic stability that extends through sternotomy without requiring excessive supplemental anesthesia 1
• Monitor for hypertensive responses and treat with additional volatile agent or opioid rather than allowing sustained elevations 2

Monitoring Requirements

Standard monitoring must include invasive arterial pressure, central venous pressure, pulmonary artery catheter with continuous cardiac output, and cerebral oximetry. 4, 1

• Measure and record: heart rate, MAP, CVP, pulmonary arterial pressure, pulmonary capillary wedge pressure, cardiac index, systemic and pulmonary vascular resistance indices, stroke work index, and left/right ventricular stroke work indices 1
• Cerebral oximetry monitoring is recommended during CPB to ensure adequate cerebral perfusion 4
• For aortic arch cases, add nasopharyngeal and core temperature (rectal/bladder) measurements 4
• Monitor oxygenator exhaust concentrations of volatile anesthetics during CPB 4
• Use quantitative neuromuscular monitoring to guide reversal agent administration, particularly for fast-track protocols 4

Managing Hypotension Pre-Bypass

Treat pre-bypass hypotension with vasopressors (phenylephrine or norepinephrine) rather than reducing anesthetic depth, as maintaining adequate anesthesia prevents dangerous hypertensive responses. 2

• Propofol and high-dose fentanyl regimens require vasopressor support more frequently (4/22 and 5/23 patients respectively) compared to other techniques 2
• Avoid reducing opioid doses to treat hypotension, as this risks inadequate anesthesia during surgical stimulation 2
• Target MAP >65 mmHg as the minimum acceptable threshold 2
• The ketamine-based technique requires less vasopressor intervention due to its sympathomimetic properties 1

Anesthetic Management During CPB

During CPB, administer IV anesthetics and opioids (except remifentanil) at doses at least as high as pre-bypass levels, accounting for hemodilution effects. 4, 5

Propofol on CPB:

• Reduce propofol dosing during CPB as lower doses achieve the same anesthetic effect due to increased free fraction from hemodilution 5
• TCI models (Schnider, Marsh, PGIMER) are inaccurate during CPB and should not be used 5

Opioid Management on CPB:

• Fentanyl and sufentanil: Give additional bolus before CPB initiation (plasma concentrations drop 25% at CPB start), then reduce maintenance dose as concentrations rise during CPB (sufentanil increases almost 50% post-CPB) 5
• Remifentanil: In normothermic CPB, maintain or increase dosing; under hypothermia, reduce infusion by 30% for every 5°C temperature decrease (60% reduction for moderate-deep hypothermia <28°C) 4, 5
• The Minto model for remifentanil may underestimate blood levels during normothermic/mild hypothermic CPB 4
• Alfentanil: No dose adjustment needed as free fraction remains stable 5

Volatile Agents on CPB:

• Volatile anesthetics may be used for maintenance during CPB using approved delivery equipment 4
• Do not use nitrous oxide immediately before or after CPB 4
• Monitor exhaust concentrations from the oxygenator 4

Vasopressor/Inotrope Requirements:

• Fentanyl-based techniques require vasoconstrictors more frequently during CPB (14/22 patients) compared to other regimens 2
• Thoracic epidural analgesia reduces catecholamine variability and provides better hemodynamic stability during CPB 6

Weaning from CPB

Prepare for weaning by ensuring adequate anesthesia, optimizing preload, and having inotropes/vasopressors immediately available for pharmacological support of low cardiac output syndrome. 4, 2

Inotropic Support:

• Positive inotropes and/or vasopressors are first-line treatment for low cardiac output syndrome during weaning 4
• Fentanyl-based anesthesia requires more inotropic support during weaning (14/22 patients) compared to propofol (7/23 patients) 2
• Consider levosimendan for patients with reduced LVEF undergoing isolated CABG to reduce risk of LCOS 4
• Levosimendan may improve survival in patients with poor LV function and perioperative LCOS 4

Hemodynamic Targets:

• Maintain MAP >65 mmHg and cardiac index >2.3 L/min/m² 2
• Thoracic epidural techniques provide higher MAP and SVR at lower heart rates during weaning 6

Circuit Management:

• Keep the CPB circuit functional until chest closure to allow emergency reinstitution if needed 4
• Ensure ECLS capability is available at all times 4

Neuromuscular Blockade:

• Use short-acting non-depolarizing agents (rocuronium, vecuronium) for fast-track protocols 4
• Protocolized reversal with sugammadex guided by quantitative monitoring is recommended for enhanced recovery 4

Common Pitfalls

• Avoid TCI models during CPB - they are inaccurate and lead to dosing errors 5
• Do not reduce opioid doses to treat pre-bypass hypotension - use vasopressors instead to maintain adequate anesthesia 2
• Remember to give additional fentanyl/sufentanil bolus before CPB initiation to compensate for the 25% drop in plasma concentration 5
• Reduce remifentanil significantly with hypothermia or risk prolonged sedation and delayed extubation 4, 5
• Propofol causes more hypotension at induction than ketamine-based techniques in cardiac patients 1, 2