A systematic review pooled 79 randomised trials and 9,340 adults undergoing non-cardiac surgery, comparing remote ischaemic preconditioning — usually a blood pressure cuff inflated on the upper limb — with standard care or a sham. Most trials were single-centre; abdominal surgery was the commonest setting. The primary outcome was all-cause mortality at longest follow-up.
Overall, preconditioning did not reduce mortality (odds ratio 0.79, 95% CI 0.51 to 1.24, P = .30). In the subgroup that received it before induction of anaesthesia, it did (0.37, 0.17 to 0.81, P = .013). Exploratory outcomes favoured preconditioning: stroke (0.41, 0.22 to 0.78), hospital stay 0.84 days shorter, and peak postoperative NGAL, a renal injury biomarker, lower by 10.27 units.
A subgroup result that is positive when the overall result is not should be read as a hypothesis. There is a plausible mechanism — propofol has been argued to interfere with the protective signalling, which would explain why timing relative to induction matters — and that plausibility is exactly what makes this kind of finding seductive. Seventy-nine mostly single-centre trials with 9,340 patients across many operations is a heterogeneous pile, and the intervention is free, harmless and easy, which is why it keeps being tested and keeps not delivering. Do not adopt it. The specific question — preconditioning before induction — deserves one properly powered multicentre trial.
- Do not adopt remote ischaemic preconditioning as routine practice; the overall mortality result was null.
- If your unit already does it, doing it before induction rather than after is the version with any supporting signal.
- Treat the stroke and length-of-stay findings as exploratory; they were not the primary outcome.
- NGAL is a biomarker, not a clinical outcome — a lower value is not a kidney saved.
- Small single-centre trials dominate this literature and tend to overstate effects.
The statistics, in plain English
An overall interval of 0.51 to 1.24 crosses 1.0, so no effect is fully compatible with the data. Finding significance inside a subgroup of a null overall result is one of the commonest ways false positives enter the literature — the more subgroups examined, the more likely one appears. A biologically plausible explanation makes a subgroup finding worth testing; it does not make it true.
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