ischaemic heart disease is the commonest cause of death in many countries , including iran and coronary artery bypass grafting surgery ( cabg ) is one of the few treatment options for these patients ( 1 ) . for on - pump coronary artery bypass grafting surgery we cross - clamp the ascending aorta and consequently deprive cardiomyocytes of oxygenated blood , after surgical procedure releasing the cross - clamp induce abrupt tissues re - oxygenation and can cause ischemia / reperfusion injury ( 2 ) . this process can initiate an inflammatory response and produce oxygen free radicals , resulting a microvascular and endothelial cell dysfunction , increase risk of vasospasm , vascular thrombosis and accelerated atherosclerosis ( 3 , 4 ) . it may also induce cerebrovascular accidents , myocardial dysfunction and arrhythmias , multi - organ system dysfunction such as respiratory renal or gastrointestinal dysfunction ( 5 - 7 ) . to reduce ischemia - reperfusion organ injury , various treatment modalities have been used , such as leukocyte depletion therapy , anti - oxidant therapy , and complement therapy ( 8) . one of the effective measures used in this regard is ischaemic preconditioning , in which a brief periods of ischemia followed by reperfusion adapts the cardiac tissue to a longer ischaemic time and protects myocardium against adverse effects of ischaemic / reperfusion injury ( 9 , 10 , 15 ) . although the exact mechanism of ripc is not clearly identified , some factors such as nitric oxide ( no ) or adenosine release seems to play a fundamental role in this phenomenon ( 3 ) . some authors have proposed that the effect of ischaemic preconditioning may be transient , but animal studies have indicated that the protective role of ripc can last 24 hours after surgery ( 3 , 11 ) . in ripc , ischemia is induced through limb tourniquet ( 12 - 14 ) and has been used in various surgical procedures and even in patients undergoing percutaneous coronary intervention ( 15 ) . there is still controversy regarding the beneficial effects of ripc , on duration of hospital stay rate of mortality , myocardial infarction , stroke and renal dysfunction . as renal and cardiomyocyte dysfunction are the most important adverse effects of cabg , role of ripc on reducing renal complications and myocardial dysfunction has been addressed in the present study . this double - blind randomized clinical trial was conducted in mazandaran heart centre a tertiary referral university hospital on patients who underwent cabg from march 2013 to february 2015 . the protocol of the study was approved by mazandaran university of medical sciences research council and ethical committee and was registered at www.irct.ir ( irct138903123646n3 ) . the design and objectives of the study were explained to all participants and written informed consent was obtained . the consort ( consolidated standards of reporting trials ) recommendations for reporting randomized controlled clinical trials were followed ( figure 1 ) . consolidated standards of reporting trials ( consort ) diagram of patient flow through the trial we included patients undergoing non - emergency on - pump cabg surgery with ejection fraction ( ef ) higher than 35% . exclusion criteria were under age under 18 years , cabg with valve surgery , pregnancy , advanced liver disease ( inr > 2.0 ) , severe renal impairment ( creatinine clearance < 50 ml / min ) , respiratory failure ( o2 sat < 90 % ) , acute myocardial infarction up to 14 days before surgery , advanced lower limb vascular disease , and patients using sulfonamide or nicorandil . we used a combinations of midazolam , sufentanil and pancuronium bromide for induction of anesthesia . invasive arterial blood pressure , central venous pressure , o2 saturation , end tidal co2 , five leads ecg and nasopharyngeal temperature were monitored continuously . intravenous glyceryl trinitrate was administered during anesthesia ( 2070 g / min ) only when clinically indicated , since it may interfere with ripc . the surgical procedure was started with median sternotomy , after preparing left internal thoracic artery patients were put on bypass draining the right atrium and returning to the ascending aorta . the initial dose for heparin was 300 iu / kg to achieve an activated clotting time ( act ) of > 480 s. heparin was reversed using a full dose of protamine chloride returning activated clotting time ( act ) to or < 120 s. we used a non - pulsatile cpb circuit with uncoated tubes , a membrane oxygenator , and an open reservoir . for priming the cbp circuit we used a colloid based ( voluven ) solution with no blood or even blood products . with a moderate hypothermia ( 32 c ) we maintained a mean arterial pressure of 60 to 80 mmhg during cpb . after induction of anesthesia and before skin incision , remote ischaemic preconditioning was induced by 3 cycles ( each cycle 5-minutes ) of a tourniquet cuff inflation applied to upper thigh ( 20mmhg higher than the resting systolic arterial pressure ) followed by 5-minute reperfusion . for the sham or control group , the tourniquet was placed on the upper thigh , manipulated but inflated for the same period of time . at this period of time the lower limb was covered by a sterile sheath and inflation of tourniquet was done by one individual registered nurse responsible for randomization . serum creatinine , and troponin i level were measured at times 0 , 6 , 12 , 24 and 48 h postoperatively measured with the elecsys 2010 chemistry analyzer ( hitachi corp . , normal value for troponin i was equal or less than (  0.3 ng.ml-1 ) . aki was measured using acute kidney injury network ( akin ) criteria : stage 1 : serum creatinine rise of 0.3 mg / dl or 150%200% of baseline and/or urine output < 0.5 ml / kg / h for > 6 contiguous hours . stage 2 : serum creatinine rise of 200%300% of baseline and/or urine output < 0.5 ml / kg / h for > 12 contiguous hours . stage 3 : serum creatinine rise of > 300% of baseline or serum creatinine 4 mg / dl with an acute rise of at least 0.5 mg / l and/or urine output < 0.3 ml / kg / h for > 24 h or anuria for 12 h. serum troponin - i level , dialysis , serum crp and inotrope requirement ( measured before and at 6 , 12 , 24 and 48 hours after surgery ) , ventilator time , length of icu stay , in - hospital mortality also were considered as secondary outcomes . based on the assumptions of a 25% incidence for post - cabg aki and myocardial damage and 80% effect size for ripc we calculated a sample size of 50 for our study group . we used ( graphpad statmate ; graphpad software inc ; san diego , ca , usa ) software for computer randomization by means of sequentially - numbered sealed envelopes . one registered nurse who did the randomization , treatment allocation and delivering ripc was aware of patient group , other investigator , data collector , statistician , patients and doctors were blinded to study group . we compared the two groups with students t - test for unpaired data or mann - whitney u test comparing medians with interquartile ranges , depending on the normality of the distribution . categorical data were expressed as frequencies and were compared using x or kruskall - wallis statistics . statistical analysis was performed using medcalc ( medcalc software bvba , acacialaan , belgium ) and in all cases p<0.05 was considered statistically significant . the ripc was administered to all patients in study group with no distal arterial or venous complications . the two groups were statistically comparable in respects of age , gender , body mass index , euro score , care score , nyha class , hypertension , hyperlipidaemia , diabetes mellitus and drug history ( table 1 ) . * kruskal - wallis test * * angiotensin converting enzyme inhibitor / angiotensin-2 antagonist peri - operative data such as cross clamp time , bypass time , number of grafts , and anesthetic drugs used were comparable in two groups . there was no need for renal dialysis and there was no peri - operative or 30 days mortality ( table 2 ) . , * kruskal - wallis test , * * akin criteria serum troponin - t level was higher in sham group which was statistically significant ( p0.001 ) ( figure 2 ) . creatinine clearance was slightly higher in study group , the gap between two group became wider after 24h but this was not statistically significant ( p=0.69 ) ( figure 2 ) . inotropic score was identical in two group ( p=0.81 ) but serum crp level was higher in study group ( p=0.004 ) ( figure 2 ) . serum troponin - t and crp levels , inotrope score and creatinine clearance in study and sham group the mean inotrope use was 3.2 ( g / kg / min ) started six hours after surgery , reducing 12 hours after surgery and returned to none after 48 hours ( figure 3 ) . there is no statistically different rate of inotrope use in two groups ( p=0.61 ) . creatinine clearance , serum crp level , serum troponin - t and inotropic score creatinine clearance was slightly higher in study group , the difference become higher after 12 hours and remained same up to the last sample but the difference between two groups was not statistically significant ( p=0.11 ) ( figure 3 ) . troponin i level was zero in the first sample in two groups made a peak six hours after surgery and returned to normal 48h after surgery . the difference between two groups was statistically significant ( p=0.001 ) ( figure 3 ) . our study indicate that remote ischaemic preconditioning can reduce cardiac and potentially reduce renal complications after cabg surgery . it showed a lower serum troponin - i levels in the group received ripc against control group , also showed a lower creatinine clearance 24 hours after surgery in control group but this was not statistically significant . previous studies had a contradictory results regarding the role of ripc on reducing cardiac and renal complications after cardiac surgery . they showed a lower serum troponin - i level and lower airway resistance in 37 children with congenital heart disease undergoing cardiac surgery receiving four cycles of 5-minutes lower limb ischemia ( cuff inflated 15 mm hg above systolic blood pressure ) ( 16 ) . venugopal and colleagues have assessed the effect of three 5-minute cycles of brachial artery occlusion ( cuff inflated up to 200 mm hg ) on reducing myocardial damage in 23 cabg patients comparing with 22 patients in control group by measuring troponin - t levels in these patients . thielmann and colleague have investigated effect of ripc on reducing myocardial damage on 27 patients in study group comparing with 26 patients in control group by applying 3 cycles of five minutes upper limb ischemia in study group on patients undergoing cabg using crystalloid cardioplegia . they also showed a lower serum troponin - i levels in study group ( 18 ) . karami and colleagues have examined the clinical efficacy of ripc by applying 3 cycles of five minutes upper or lower limb ischemia on patients undergoing elective cabg and showed troponin - i rise in study and control group . the finding of our study is similar to cheung , venugopal and thielmann but it is different in two important ways . we used the lower limb for ripc and our study was done on adult population of patients . regarding the renal - protective effect of ripc , venugopal and colleagues have reported lower acute kidney injury ( aki ) in patients receiving ripc before cardiac surgery ( 18 ) . zarbock and colleagues randomized 240 patients with high risk for aki to receive 3 cycles of 5-minute ischemia in one upper arm before cardiac surgery and have reported reduced rate of aki in the ripc group ( 37.5 vs 52.5% ) ( 19 ) . candilio and colleagues have also compared the effect of simultaneous arm and thigh cuff inflation in two groups of 90 patients undergoing elective cabg and have reported 48% reduction in the incidence of aki also showed lower serum troponin - t level in the ripc group ( 20 ) . they have reported reduction in the serum creatinine level 12 hour after surgery but in present study serum creatinine level dropped 24 hours after surgery . we have excluded concomitant valve surgery from our study population while candilio s have included them . pedersen randomized 105 children undergoing cardiac surgery for complex congenital disorders to receive ripc by 4 cycles of 5 minutes inflating a cuff on lower limb to 40 mm hg above the systolic pressure and showed no renal protection in ripc group ( 21 ) . gallagher also randomized 86 patients with pre - existing chronic kidney disease to receive three 5-minute cycles of forearm ischemia prior to cabg and have reported no difference in the incidence of aki in ripc group ( 22 ) . li l in a review study indicated that the main reason for the contradicting results in ripc studies is different definition for akia ( 23 ) . he indicated that as serum creatinine is the mostly used biomarker for detecting aki ( 23 - 25 ) , which might not change significantly in an acute setting . moreover , the different protocols of ripc causes difference in the results , as the upper limb may be less effective than the lower limb and the pressure of the inflated cuff and the frequency of courses also play a role in this difference . besides , the different surgical procedures also affect the results , as walsh and colleagues have indicated that renal protective effect of ripc is only positive in the presence of cardioplegia ( 26 ) . in addition , the difference in the demographic characteristics of patients , besides different inclusion and exclusion criteria also causes this diversity , as some studies have assessed children and some have assessed patients with existing renal risk , which affect the results profoundly . regarding the evident controversy in the role of ripc on renal and cardiac complications of cardiac surgery , more studies are needed to establish the exact effect and the possible adverse effect of ripc , but it s essential to use a standard definition for aki for the results of different studies to be comparable . moreover , the different methods of ripc have to be compared and a standard method should be introduced , as each study has used its own method , which has caused the results not to be easily comparable with each other . the strengths of the present study included randomizing subjects into two intervention and control groups that besides excluding many factors caused limitation in confounding factors . moreover , this issue has rarely been addressed in iranian studies . beside the strengths , this study was not also free of limitations . although the patients were randomized into the groups , it would be more optimal to select patients from different centers , in order to omit any bias and increase the generalizability of the data . besides , the surgical procedure has to be standardized or performed by one surgeon , which was not possible in our center . the results of the present study indicated decrease in the serum levels of creatinine 24 hours after cabg in the ripc group , which indicates the superiority of this non - invasive inexpensive intervention in controlling the important complications of cardiac surgery .
objective : to investigate efficacy of remote ischaemic preconditioning on reducing kidney injury and myocardial damage after coronary artery bypass grafting surgery ( cabg).background : ischaemic preconditioning of a remote organ reduces ischaemia - reperfusion injury of kidney and myocardium after cabg.method:to reduce myocardial damage and kidney injury by applying remote ischaemic preconditioning we recruited 100 consecutive patients undergoing elective coronary artery bypass grafting surgery . 
 we applied three cycles of lower limb tourniquet , inflated its cuff for 5 minutes in study group or left un - inflated ( sham or control group ) before the procedure . 
 the primary outcome was serum creatinine , creatinine clearance and troponin - i levels at time 0 , 6 , 12 , 24 and 48 h. secondary outcomes were serum c - reactive protein , inotrope score , ventilation time and icu stay . 
 data s were analyzed by medcalc ( medcalc software bvba , acacialaan , belgium ) . 
 we compared the two group by student t test , chi - square and mann - whitney tests.results:the two groups were not statistically different in terms of age , gender , smoking habits , drug use , hypertension , hyperlipidemia and diabetes mellitus . 
 this study showed a higher crp level in study group comparing with control group ( p=0.003 ) , creatinine clearance was slightly higher in study group specially 24 h after procedure but was not statistically significant ( p=0.11 ) . 
 troponin - 
 i level was significantly lower in study group ( p=0.001).conclusion : this study showed a lower troponin - i level in study group which suggest a cardio - myocyte protective function of ripc . 
 it also showed slightly lower creatinine clearance in control group , gap between two group increases significantly 24 hours after procedure which may suggest a potential kidney protection by ripc . 
 serum crp level was higher in study group . 
 a multi - center randomized controlled trial with a longer time for creatinine clearance measurement may show the potential effectiveness of this non - invasive inexpensive intervention on reducing kidney injury after cabg .