| Advantages | Disadvantages |
| Protects against bypass-circuit-related complications | Potential for myocardial ischaemia without cold cardioplegia |
| Avoids risks of aortic & atrial cannulation esp. dissection | Unfavourable operating conditions due to beating heart |
| Avoids effects of cardioplegia | ↑ risk of anastomotic bleeding |
| Avoids risks of aortic cross-clamping esp. CVA | ↑ risk of suboptimal revascularisation & myocardial ischaemia |
| ↓ costs: no perfusionist | |
| ↓ costs: no bypass machine required | |
| ↓ costs: fewer ventilated days on CICU | |
| ↓ costs: shorter length of stay |
Off-Pump Coronary Artery Surgery
Off-Pump Coronary Artery Surgery
The curriculum asks for knowledge of the 'anaesthetic and surgical problems associated with “off pump” cardiac surgery'.
The topic was the subject of an SAQ in March 2017, with a roughly even split between advantages, causes of and methods to mitigate haemodynamic instability during off-pump surgery.
Resources
- Off-pump coronary artery bypass surgery carries the benefit of avoiding the complications associated with cardiopulmonary bypass
- Although the operations themselves aren't necessarily shorter, there is a shorter stay and accelerated post-operative recovery when using an off-pump technique
| Classification | Example |
| Non-modifiable risk factor | Advanced patient age |
| Respiratory | Chronic lung disease |
| Cardiovascular | Aortic disease precluding bypass Ventricular dysfunction e.g. LV systolic failure Previous stroke |
| Comorbidities | Advanced renal disease Diabetes |
Surgical technique
- Two techniques exist:
- A conventional mid-sternotomy approach
- A minimally invasive approach
- The key is to ensure effective local cardiac wall stabilisation to allow anastomotic suturing
- This is achieved via:
- Cardiac displacement to access posterior/lateral/inferior targets, either via pericardial retraction sutures or a stockinet sutured to the oblique sinus
- Stabilisers placed on the epicardium
- Intra-cardiac shunts may be used as they:
- Prevent bleeding from the arteriotomy site during anastomosis
- Maintain coronary perfusion, thus preventing ischaemia
- Are superior to the previous technique of proximal coronary artery occlusion (which involved ischaemic preconditioning for 5 mins, before 3 mins reperfusion then occlusion)
- The goals are largely similar to those of perioeprative care in other cardiac surgery:
- Provision of safe, maximally cardio-protective induction and maintenance techniques
- Maintenance of haemodynamic stability
- Early emergence and ambulation facilitated by excellent post-operative analgesia
- Beating-heart surgery requires stable cardiac rhythm and stable haemodynamics, which is naturally predicated on good communication with the surgical team
Monitoring and access
- AAGBI
- A conventional 5-lead ECG is routine
- Manipulation of the heart alters the heart-electrode positional relationship, leading to altered ECG traces
- This impairs the diagnostic accuracy of the ECG
- Thus a 12-lead ECG with monitoring of leads II, V4 and V5 increases efficacy of ischaemia detection
- Arterial line
- Cardiac output monitoring
- PA catheter use is commonplace, although vertical heart positioning can distort RA and PAWP
- TOE is used although again interpretation may be impaired by heart positioning
Haemodynamic management
- Haemodynamic changes occur during three phases:
- Lifting of the heart out of the pericardial sac to work on posterior and lateral surfaces
- Requires ventricular filling against gravity
- This reduces right heart pressures and thus reduces cardiac output
- Requires greater-than-normal filling pressures to maintain haemodynamics
- Pressure on the ventricular wall by the retractor
- This restricts wall motion locally, reducing ventricular dimensions
- Vertical position of the heart distorts mitral and tricuspid valve annuli
- Leads to significant MR/TR
- Maintenance of a high perfusion pressure (MAP >70mmHg) and low myocardial oxygen consumption are required, and achieved via:
- Fluids
- Trendelenburg position
- Vasopressors e.g. noradrenaline
- Atrial pacing to 60bpm
- Β-blockers such as esmolol to reduce HR (and therefore myocardial oxygen consumption)
Cardiac rate & rhythm managemnet
- Avoiding tachycardia remains key, aided by:
- Appropriate premedication
- Opioid-heavy induction techniques
- Rapidly-acting negative chronotropes such as: esmolol, verapamil or diltiazem
- Avoiding intra-operative arrythmias associated with cardiac displacement through use of magnesium and maintenance of K+ >4.5mmol/L
Other management
- There is some evidence that sevoflurane and isoflurane induce significant preconditioning, providing some myocardial protection against ischaemia
- Anticoagulation with heparin, but a lower ACT target of 250 - 300s
- Avoidance of hypothermia through conventional methods
- Slightly reduced risk-adjusted mortality vs. conventional CABG (debatable)
- Complication rate reduced
- Reduced need for transfusion of blood and blood products
- Reduces rates of stroke (30% reduction) and post-operative MI (marginal)
- Shorter duration of ventilatory support and ICU stay
- Shorter hospital stay
- Similar rates of post-operative AF
- Overall, the greatest benefit may be for elderly patients or those with poor LVSF, as they avoid the complications of CPB