A recent paper published in the Lancet renewed our interest in preconditioning, specifically remote preconditioning (RIPC). 57 patients undergoing CABG were randomly assigned to receive three 5-min cycles of right upper arm ischemia, which was induced by an automated BP cuff with the idea that ischemia in one vascular bed will afford protection in another – in this case the heart. Troponin T levels were taken before surgery and at 6, 12, 24, 48, and 72 hours after surgery.
What did they find?
- A reduction in troponin T levels starting at 6 hour.
- 43% reduction in the area under the curve between control and treatment group.
- This study used a surrogate maker to try to predict clinical outcomes. Although, there is a reduction in the level of Troponin T in the treatment group does this translate to meaningful clinical outcomes (eg. Atrial fibrillation, length of stay, etc). The authors do not report these findings. Certainly, we are concerned about myocardial injury, but a difference between a Troponin of 0.4 vs 0.7 is that clinically significant?
Are there any concerns?
- The authors reported no ill outcome in the treatment group. However, there maybe ethical concerns with the study design. Numerous papers have demonstrated the cardioprotective effects of volatile anesthetic. In this study a total intravenous anesthetic technique was used to perhaps amplify the results.
What should the intensivist do?
- The skeptics will argue that we should do nothing until firm evidence emerges. In fact if firm evidence emerges, it is probably wrong!
- The zealots may argue that every ICU patient should have tourniquets applied to every limb, each of which (the tourniquets, not the limbs!) should be intermittently inflated. This may become a new market niche for MAST suits.
- The intellectual enthusiasts may argue that we MUST do a raft of randomized controlled studies with RIPC on the ICU.
- The pragmatists may argue that this is a benign intervention that should be used, unless there are specific contra-indications (eg. Vascular disease, fistula, etc.).