Off-pump cardiac surgery refers to the performance of cardiac surgery without the patient going on cardiopulmonary bypass (CPB). Whilst initially developed in the 1960s, the improvement of the CPB approach appeared to make this the favoured approach. An increased appreciation of the benefits have allowed a further interest in the technique in certain scenarios. However, there has also be a more recent increased appreciation of the limitations of this approach
There is also no requirement for aortic cross-clamping, which may be hazardous in patients with extensive aortic disease.
More difficult surgical technique - possible impact on outcomes
More challenging anaesthetic technique
When thinking about the technique, we can think about some of the conditions that surgeons need for optimal operating. These can be neatly summarised as:
A bloodless field
A still operating site
The first two can be more challenging in off pump cardiac surgery and thus require modifications of the technique employed in on pump procedures.
Stabilisation The heart, or at least the section that is being operated on, needs to be fairly still in order to be able to perform to delicate stitching needed at the anastomotic sites. This is clearly the case during the cardiac standstill of CPB, but the heart is undergoing significant movement during its normal activities. A still section of wall is achieved through local wall stablisation through application of a specially designed stabliser. An example is the Octopus system which is widely used.
Bleeding Bleeding from the anastomotic sites would present an additional challenge to the surgeon. This is reduced through the use of shunts or clamps, depending on the nature of the vessel. Clamping of the native vessels would clearly induce ischaemia, and so would often be used with ischaemic preconditioning technique. A shunt technique allows distal blood flow to continue.
Differences from an on-pump technique include:
CVS The main differences in anaesthetic technique probably focuses around the CVS monitoring and support that may be needed due to the interactions with the heart during the surgical procedure - something that occurs with CPB in place in on-pump technique. The goals of the anaesthetic technique can be thought of as:
Control heart rate
Rhythm disturbances are more common during manipulation of the heart during surgery, and there will not be the ongoing support of the circulation from CPB. Optimising the electrolyte balance of the patient can help to minimise this risk.
Heart rate control through inducing bradycardia was once an important part of the surgical technique prior to effective stablisation. It is still important to minimise tachycardia, and this is acheived through beta blockers e.g. esmolol, or calcium channel blockers.
Coagulation The anticoagulation management is notably different from on-pump cardiac surgery. CPB requires significant anticoagulation and causes significant disruption of haemostasis physiology in itself. The haemostatic disruption is notably less from off-pump surgery, but some anticoagulation is still needed due to the vascular manipulation. An activated clotting time of 250-300s is usually targeted for before division of the internal mammary artery. This can usually be achieved with 1-2mg/kg heparin.
There is suggestion that with the off-pump technique there is:
A higher long-term mortality
A higher rate of need for repeat revascularisation
A lower rate of stroke
In a 2012 meta analysis of outcomes, the all cause long term mortality in the on-pump was 3.7% compared with 3.1% with an on-pump technique. This is a RR of 1.24 (95%CI 1.01-1.53). Similar trends were reported in the ROOBY trial, an RCT not included in the meta-analysis. This appears to be related to a lower level of graft patency over time.
However, the CORONARY trial did not appear to show any difference between the techniques. The UpToDate review notes that these patients were generally a higher risk group, and the surgeons were more familiar with the off-pump technique.
Some studies have suggested a reduced rate of stroke in the of--pump group. However, some more recent studies have suggested that there is no significant difference in neurologic dysfunction between the techniques.
Due to the limitations, as well as the advantages, a number of factors may play a role in deciding between off-pump or on-pump technique: