Description of the condition
Ischaemia reperfusion injury is defined as damage to an organ that occurs after a critical period of ischaemia, followed by restoration of blood supply. This can happen spontaneously, such as in stroke or myocardial infarction, or during transplantation and other types of surgery. Cells become deprived of oxygen in the ischaemic phase, and as a result, metabolism switches from aerobic to anaerobic glycolysis, leading to cell swelling, acidosis, ATP depletion, intracellular sodium (Na
Ischaemia reperfusion injury can lead to organ dysfunction or failure and is a significant clinical problem in transplantation, shock and major surgery. The high metabolism and vascular anatomy of the kidney is particularly sensitive to ischaemia reperfusion injury. The critical ischaemic period is organ-dependent: 15 to 20 minutes of ischaemia has been shown to cause irreversible damage to the kidney (Jaeschke 2002; Safian 2001; Schrier 2004).
Description of the intervention
Ischaemic preconditioning is a short and harmless period of deprivation of blood supply to particular organs or tissue, followed by a period of reperfusion (Chen 2009; Hausenloy 2009; Yin 1998). Preconditioning stimulus is applied before onset of ischaemia reperfusion injury to a target organ. In 1986 it was shown that ischaemic preconditioning on the heart can reduce ischaemia reperfusion injury, (local ischaemic preconditioning) (Murry 1986), and has since been reproduced in many other target organs. Later on, studies have shown that ischaemic preconditioning of remote organs and tissues at a distance can protect the target organ from ischaemia reperfusion injury as well (remote ischaemic preconditioning) (Przyklenk 1993). Use of the limbs as remote tissue offers many advantages, since skeletal muscle is less susceptible to ischaemia reperfusion injury than visceral tissues.
A typical schedule of four, five minute periods of ischaemic preconditioning, separated by five minutes of reperfusion, applied directly before the ischaemia reperfusion injury period of the target organ, is used in most clinical studies. Numerous variations to this schedule have been studied in animals and the efficacy of the ischaemic preconditioning has been shown to vary, depending on the preconditioned tissue volume, length of ischaemic preconditioning, reperfusion and time between ischaemic preconditioning and ischaemia reperfusion injury. The optimal schedule is still unclear and is probably different for different target organs and species (Alreja 2012; Cochrane 1999; Wever 2012).
How the intervention might work
Several endogenous molecules have been implicated in local and remote ischaemic preconditioning signalling, most of which are known to have cytoprotective effects. Downstream, the ultimate protective step in ischaemic preconditioning signalling appears to be inhibition of mitochondrial permeability transition pore opening, which prevents cell death. Remote and local ischaemic preconditioning appear to be similar in terms of invoking mitochondrial permeability transition pore inhibition, and many signalling molecules seem to be similar to those implicated in local ischaemic preconditioning signalling. However, remote ischaemic preconditioning requires transduction of the protective signal from the remote organ or tissue to the target organ.
The protective effects of ischaemic preconditioning are found both directly after application of the stimulus (early window of protection; EWOP), and in the days or weeks following (second window of protection). In animal models, both windows of protection have been shown to reduce renal ischaemia reperfusion injury (Wever 2012). Although there are similarities in the mechanisms underlying early and second windows of protection, the second window of protection has been found to require de novo protein synthesis of distal mediators such as iNOS and COX-2. However, remote ischaemic preconditioning signalling has been most extensively studied in the early window of protection, where three major pathways have been indicated in this process (Figure 1): the humoral route, the neurogenic pathway and alteration of immune cells. Signalling via the humoral route (upper route in Figure 1) requires release of signalling molecules such as adenosine or endorphins from the remote organ into the bloodstream, which are then carried to the target organ to exert their protective effects via their respective receptors.
|Figure 1. Remote ischaemic preconditioning signalling pathways|
The nervous system also appears to play a role in some models of remote ischaemic preconditioning: denervation or ganglion blockade inhibit the protective effect of remote ischaemic preconditioning (middle route). Activation of the neurogenic pathway by peptides released from the remote organ may cause systemic factor release (combined humoral-neurogenic route), lead to local factor release or activation of central reflexes. Both the humoral and the neurogenic pathways are thought to induce various kinase cascades and eventually prevent opening of the mitochondrial permeability transition pore in the target organ cells, thereby reducing cell death. Thirdly, remote ischaemic preconditioning has been shown to modulate gene and receptor expression on immune cells, which therefore pose a third signalling pathway that presumably reduces damage by altering the inflammatory response (lower route) (Tapuria 2008).
Why it is important to do this review
Despite that the efficacy of ischaemic preconditioning has been acknowledged since described by Murry 1986, the technique was introduced into clinical trials only relatively recently; however, results to date have not been consistently positive (Ali 2007; Choi 2011; Walsh 2008; Walsh 2010; Zimmerman 2011). Although experimental data show promise, the mechanism underlying ischaemic preconditioning signalling remains unclear and the optimal preconditioning protocol remains unknown (Wever 2012).
The kidney is very sensitive to ischaemia reperfusion injury, and therefore, is an organ system that can benefit from ischaemic preconditioning. Furthermore, kidney function and damage are very well documented and can be tested using robust endpoints. The kidney is therefore an ideal target organ to investigate the protective effects of ischaemic preconditioning on renal ischaemia reperfusion injury.
This review aims to look at the benefits and harms of local and remote ischaemic preconditioning to reduce ischaemia and reperfusion injury among people with renal ischaemia reperfusion injury.
Criteria for considering studies for this review
Types of studies
All randomised controlled trials (RCTs) looking at the role of ischaemic preconditioning versus no ischaemic preconditioning among patients undergoing interventions that result in ischaemic kidney damage.
There will be no restriction on publication status, language, or sample size. Quasi-RCTs (RCTs in which allocation to treatment was obtained by alternation, use of alternate medical records, date of birth or other predictable methods) will be excluded.
Types of participants
We will include all patients who undergo any intervention for any indication that result in ischaemic kidney damage (e.g. extracorporeal membrane oxygenation, endovascular aneurysm repair, coronary artery bypass grafting, aortic surgery and any other type kidney surgery). Liver, lung and peripheral bypass surgeries in which kidney injury is highly unlikely will be excluded. Studies investigating ischaemic preconditioning in kidney transplantation or patients at risk for contrast-induced nephropathy will be excluded.
Types of interventions
The ischaemic preconditioning protocol may consist of a remote or local ischaemic preconditioning stimulus applied before the intervention. Remote stimulus may be applied to any organ. Stimuli may be continuous (one continuous ischaemic pulse followed by reperfusion) or fractioned (two or more cycles of brief ischaemia and reperfusion). The ischaemic preconditioning stimulus may be applied directly before index ischaemia or some time, even days, before.
The control condition of no ischaemic preconditioning may consist of no intervention or mock Ischaemic preconditioning, that is, application of a tourniquet, blood pressure cuff or other means of occlusion without actually interrupting blood flow.
Types of outcome measures
- Serum creatinine level
- Complications and adverse effects related to ischaemic preconditioning
- Need for dialysis following kidney-related ischaemia
- Blood urea nitrogen
- Serum/urine neutrophil gelatinase-associated lipocalin (NGAL)
- Serum/urine kidney injury molecule-1 (KIM-1)
- Quality of life
- Length of hospital stay.
Search methods for identification of studies
We will search the Cochrane Renal Group's Specialised Register through contact with the Trials' Search Co-ordinator using search terms relevant to this review.
The Cochrane Renal Group’s Specialised Register contains studies identified from:
- Monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL)
- Weekly searches of MEDLINE OVID SP
- Handsearching of renal-related journals and the proceedings of major renal conferences
- Searching of the current year of EMBASE OVID SP
- Weekly current awareness alerts for selected renal journals
- Searches of the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov,
Studies contained in the Specialised Register are identified through search strategies for CENTRAL, MEDLINE, and EMBASE based on the scope of the Cochrane Renal Group. Details of these strategies, as well as a list of handsearched journals, conference proceedings and current awareness alerts, are available in the Specialised Register section of information about the Cochrane Renal Group.
See Appendix 1 for search terms used in strategies for this review.
Searching other resources
- Reference lists of review articles, relevant studies, and clinical practice guidelines.
- Letters seeking information about unpublished or incomplete studies to investigators known to be involved in previous studies.
Data collection and analysis
Selection of studies
The search strategy described will be used to obtain titles and abstracts of studies that may be relevant to the review. The titles and abstracts will be screened independently by two authors, who will discard studies that are not applicable; however studies and reviews that might include relevant data or information on studies will be retained initially. Two authors will independently assess retrieved abstracts and, if necessary the full text, of these studies to determine which studies satisfy the inclusion criteria.
Data extraction and management
Data extraction will be carried out independently by two authors using standard data extraction forms. Studies reported in non-English language journals will be translated before assessment. Where more than one publication of one study exists, reports will be grouped together and the publication with the most complete data will be used in the analyses. Where relevant outcomes are only published in earlier versions these data will be used. Any discrepancy between published versions will be highlighted.
Assessment of risk of bias in included studies
- Was there adequate sequence generation (selection bias)?
- Was allocation adequately concealed (selection bias)?
- Was knowledge of the allocated interventions adequately prevented during the study (detection bias)?
- Participants and personnel
- Outcome assessors
- Were incomplete outcome data adequately addressed (attrition bias)?
- Are reports of the study free of suggestion of selective outcome reporting (reporting bias)?
- Was the study apparently free of other problems that could put it at a risk of bias?
Measures of treatment effect
For dichotomous outcomes (e.g. need for dialysis, death) results will be expressed as risk ratio (RR) with 95% confidence intervals (CI). Where continuous scales of measurement are used to assess the effects of treatment (e.g. serum creatinine), the mean difference (MD) will be used, or the standardised mean difference (SMD) if different scales have been used.
Dealing with missing data
Any further information required from the original author will be requested by written correspondence (e.g. e-mailing or writing to corresponding author/s) and any relevant information obtained in this manner will be included in the review. Evaluation of important numerical data such as screened, randomised patients as well as intention-to-treat, as-treated and per-protocol population will be carefully performed. Attrition rates, for example drop-outs, losses to follow-up and withdrawals will be investigated. Issues of missing data and imputation methods (for example, last-observation-carried-forward) will be critically appraised (Higgins 2011).
Assessment of heterogeneity
Heterogeneity will be analysed using a Chi² test on N-1 degrees of freedom, with an alpha of 0.05 used for statistical significance and with the I² test (Higgins 2003). I² values of 25%, 50% and 75% correspond to low, medium and high levels of heterogeneity.
Assessment of reporting biases
If possible, funnel plots will be used to assess for the potential existence of small study bias (Higgins 2011).
Data will be pooled using the random-effects model but the fixed-effect model will also be used to ensure robustness of the model chosen and susceptibility to outliers.
Subgroup analysis and investigation of heterogeneity
Subgroup analysis will be used to explore possible sources of heterogeneity (e.g. preconditioning site, continuous versus fractionated ischaemic preconditioning, early versus late windows of protection). Heterogeneity among participants could be related to age and gender. Heterogeneity in treatments could be related to the type of intervention such as major aorta surgery or coronary artery bypass surgery. Adverse effects will be tabulated and assessed with descriptive techniques, as they are likely to be different for the various agents used. Where possible, the risk difference with 95% CI will be calculated for each adverse effect, either compared to no treatment or to another agent.
We will perform sensitivity analyses to explore the influence of the following factors on effect size.
- Repeating the analysis excluding unpublished studies
- Repeating the analysis taking account of risk of bias, as specified
- Repeating the analysis excluding any very long or large studies to establish how much they dominate the results
- Repeating the analysis excluding studies using the following filters: diagnostic criteria, language of publication, source of funding (industry versus other), and country.
We would like to acknowledge the referees for their assessments and suggestions.
Appendix 1. Electronic search strategies
Appendix 2. Risk of bias assessment tool
Contributions of authors
- Draft the protocol: TPM, KEW, MCW, MMR
- Study selection: TPM, KEW
- Extract data from studies: TPM, KEW
- Enter data into RevMan: TPM, KEW
- Carry out the analysis: TPM, KEW, MCW, MMR
- Interpret the analysis: KEW, MCW, MMR
- Draft the final review: TPM, KEW, DJAvdV, MMR, MCW
- Disagreement resolution: EJH
- Update the review: TPM, KEW
Declarations of interest