Patients undergoing major vascular surgery are at high risk of complications around the time of their surgery. This is because many of them have generalised arterial disease. During surgery blood flow is reduced at the site of surgery, which results in a lack of oxygen and nutrients being delivered to the body tissues (ischaemia). After the blood supply is restored, further damage can occur because of cellular responses and the blood flushing through the tissues. This is known as ischaemia-reperfusion injury.
Ischaemic preconditioning is a method where short periods of induced ischaemia (about 10 minutes) followed by reperfusion are used to protect against the prolonged periods of ischaemia required for surgery. Preconditioning can be carried out on the blood vessels where ischaemia will later occur or remotely, on different blood vessels. The clinical application of remote ischaemic preconditioning for patients undergoing open surgical or endovascular surgeries such as aneurysm repair, carotid endarterectomy, and revascularisation is not known.
We performed a systematic search of the literature to identify all the randomised controlled trials conducted on this topic. A total of 232 patients in four trials were randomised to remote ischaemic preconditioning or no preconditioning for three different operations on blood vessels. Based on the evidence from these small trials, there were too few data to be able to say whether remote ischaemic preconditioning has any beneficial or harmful effects. The studies varied in the surgical procedures, outcome measures and the way remote ischaemia was induced. The number of deaths around the time of surgery was not clearly different between the two groups. Heart attacks (myocardial infarction) may have been reduced in the remote ischaemic preconditioning group but this was apparent in only one trial and was not consistent across the trials. Unplanned critical care admissions tended to increase in the remote ischaemic preconditioning group. All the trials had a high risk of bias and the safety of this technique needs to be confirmed in trials with adequate numbers of participants.
Based on current evidence from small pilot trials, there are too few data to be able to say whether remote ischaemic preconditioning has any beneficial or harmful effects. The safety of this technique needs to be confirmed in adequately powered trials. Therefore, further randomised trials on this technique are required.
Despite advances in perioperative care, elective major vascular surgical procedures carry a significant risk of morbidity and mortality. Remote ischaemic preconditioning is initiated by brief, non-lethal periods of ischaemia in a vascular bed different from the one which will be subjected to ischaemic insult during surgery. It has the potential to provide local tissue protection from further prolonged periods of ischaemia.
The aim of this review was to compare the outcomes from vascular and endovascular surgical procedures with and without the use of remote ischaemic preconditioning.
The Cochrane Peripheral Vascular Diseases Group searched their Specialised Register (June 2011) and CENTRAL (2011, Issue 2). The authors searched MEDLINE via PubMed (July 2011), EMBASE (June 2011), and Science Citation Index Expanded (July 2011).
We considered for inclusion all randomised controlled trials that evaluated the role of remote ischaemic preconditioning in reducing mortality and systemic injury in patients undergoing open vascular or endovascular surgery.
We collected the data on characteristics of the trial, methodological quality, the remote ischaemic preconditioning stimulus used, mortality, morbidity, operating time and hospital stay from each trial. We analysed the data with both the fixed-effect and the random-effects models using RevMan analysis. For each outcome we calculated the risk ratio (RR) or mean difference with 95% confidence interval (CI) based on an intention-to-treat analysis.
We included four studies with a total of 115 patients randomised to undergo a vascular procedure with remote ischaemic preconditioning and 117 patients randomised to have the procedure without remote ischaemic preconditioning. None of the trials were of low risk of bias. There was no significant difference in mortality between the two groups (RR 1.70, 95% CI 0.51 to 5.72). Similarly, there was no statistically significant difference between the two groups for all other outcomes except reduced risk of myocardial infarction in the remote ischaemic preconditioning group, which was significant by the fixed-effect model (RR 0.31, 95% CI 0.10 to 0.90) but not by the random-effects model (RR 0.34, 95% CI 0.11 to 1.08). This positive effect was from the results of only one trial and was not consistently observed. Furthermore, it was noted that there was an observed trend of high incidence of unplanned critical care admission in the remote ischaemic preconditioning group, although this was not statistically significant (RR 2.15, 95% CI 0.87 to 5.33).