Therapy with insulin in cardiac surgery: controversies and possible solutions

In Vitro Investigation of Insulin Dynamics During 4 Hours of Simulated Cardiopulmonary Bypass

BACKGROUND

Hyperglycemia is common in patients undergoing cardiovascular surgery with cardiopulmonary bypass. We hypothesize that intraoperative hyperglycemia may be, at least partially, attributable to insulin loss due to adhesion on artificial surfaces and/or degradation by hemolysis. Thus, our primary aim was to investigate the loss of insulin in 2 different isolated extracorporeal circulation circuits (ECCs), that is, a conventional ECC (cECC) with a roller pump, and a mini-ECC (MiECC) system with a centrifugal pump. The secondary aim was to assess and compare the relationship between changes in insulin concentration and the degree of hemolysis in our 2 ECC models.

METHODS

Six cECC and 6 MiECC systems were primed with red packed blood cells and thawed fresh-frozen plasma (1:1). Four additional experiments were performed in cECC using only thawed fresh-frozen plasma. Human insulin (Actrapid) was added, targeting a plasma insulin concentration of 400 mU/L. Insulin concentration and hemolysis index were measured at baseline and hourly thereafter. The end points were the change in insulin level after 4 hours compared to baseline and hemolysis index after 4 hours. The insulin concentration and hemolysis index were analyzed by means of a saturated linear mixed-effect regression model with a random offset for each experiment to account for the repeated measure design of the study, resulting in mean estimates and 95% confidence intervals (CIs) of the primary end points as well as of pairwise contrasts with respect to ECC type.

RESULTS

Insulin concentration decreased by 63% (95% CI, 48%-77%) in the MiECC and 92% (95% CI, 77%-106%) in the cECC system that contained red blood cells. Insulin loss was significantly higher in the cECC system compared to the MiECC (P = .022). In the cECC with only plasma, insulin did not significantly decrease (-4%; 95% CI, -21% to 14%). Hemolysis index in MiECC increased from 68 (95% CI, 46-91) to 76 (95% CI, 54-98) after 4 hours, in cECC from 81 (95% CI, 59-103) to 121 (95% CI, 99-143). Hemolysis index and percent change of insulin showed an excellent relationship (r = -0.99, P < .01).

CONCLUSIONS

Our data showed that insulin levels substantially decreased during 4 hours of simulated cardiopulmonary bypass only in the ECC that contained hemoglobin. The decrease was more pronounced in the cECC, which also exhibited a greater degree of hemolysis. Our results suggest that insulin degradation by hemolysis products may be a stronger contributor to insulin loss than adhesion of insulin molecules to circuit surfaces.

Systemic glucose-insulin-potassium reduces skeletal muscle injury, kidney injury, and pain in a murine ischaemia-reperfusion model

Glucose-insulin-potassium (GIK) is protective following cardiac myocyte ischaemia-reperfusion (IR) injury, however the role of GIK in protecting skeletal muscle from IR injury has not been evaluated. Given the similar mechanisms by which cardiac and skeletal muscle sustain an IR injury, we hypothesized that GIK would similarly protect skeletal muscle viability. A total of 20 C57BL/6 male mice (10 control, 10 GIK) sustained a hindlimb IR injury using a 2.5-hour rubber band tourniquet. Immediately prior to tourniquet placement, a subcutaneous osmotic pump was placed which infused control mice with saline (0.9% sodium chloride) and treated mice with GIK (40% glucose, 50 U/l insulin, 80 mEq/L KCl, pH 4.5) at a rate of 16 µl/hr for 26.5 hours. At 24 hours following tourniquet removal, bilateral (tourniqueted and non-tourniqueted) gastrocnemius muscles were triphenyltetrazolium chloride (TTC)-stained to quantify percentage muscle viability. Bilateral peroneal muscles were used for gene expression analysis, serum creatinine and creatine kinase activity were measured, and a validated murine ethogram was used to quantify pain before euthanasia. GIK treatment resulted in a significant protection of skeletal muscle with increased viability (GIK 22.07% (SD 15.48%)) compared to saline control (control 3.14% (SD 3.29%)) (p = 0.005). Additionally, GIK led to a statistically significant reduction in gene expression markers of cell death (CASP3, p < 0.001) and inflammation (NOS2, p < 0.001; IGF1, p = 0.007; IL-1β, p = 0.002; TNFα, p = 0.012), and a significant reduction in serum creatine kinase (p = 0.004) and creatinine (p < 0.001). GIK led to a significant reduction in IR-related pain (p = 0.030). Systemic GIK infusion during and after limb ischaemia protects murine skeletal muscle from cell death, kidneys from reperfusion metabolites, and reduces pain by reducing post-ischaemic inflammation.

Glucose-insulin-potassium correlates with hemodynamic improvement in patients with septic myocardial dysfunction

BACKGROUND

Glucose-insulin-potassium (GIK) demonstrates a cardioprotective effect by providing metabolic support and anti-inflammatory action, and may be useful in septic myocardial depression. The aim of this study was to examine the relationship between GIK and hemodynamic outcomes in septic shock patients with myocardial depression.

METHODS

Between October 2012 and March 2014, 45 patients in the intensive care unit who fulfilled the criteria for severe sepsis/septic shock and were treated with GIK were recruited. Patients were divided into two groups according to echocardiographic findings: hypodynamic (27%) and non-hypodynamic (36%).

RESULTS

Baseline vasopressor requirements did not differ between both groups. In 12 patients with hypodynamic septic shock with myocardial depression, mean arterial pressure (MAP) increased with the median [interquartile range (IQR)] area under the curve of 16 (8 to 29) mmHg, and the heart rate (HR) decreased with the median (IQR) area under the curve of -9 (-20 to 2)/min during the first 72 h. The total insulin dose correlated with improvement in MAP (r=0.61, P=0.061) and the cardiovascular Sequential Organ Failure Assessment score (r=-0.64, P=0.045) at 72 h, although this phenomenon was not observed in patients with non-hypodynamic septic shock. Serum glucose and potassium levels were within the target ranges in both groups during the 72-h study period.

CONCLUSIONS

Short-term improvement in hemodynamics correlated with GIK administration in septic shock patients with myocardial depression. The use of GIK was well tolerated in all patients. Further studies are required to demonstrate the role of GIK in septic myocardial dysfunction.

Glucose and Insulin Influences on Heart and Brain in Cardiac Surgery

The elective global ischemia of on-pump coronary artery bypass surgery contributes to the incidence of postoperative mortality, complications, and use of resources. In addition to cardiopulmonary bypass and techniques for myocardial protection such as aortic cross clamp, ventricular fibrillation, and cardioplegia, the administration of systemic glucose-insulinpotassium (GIK) in the perioperative period may act as both a metabolic modulator and potential inodilator. GIK may therefore serve to protect the myocardium and promote adequate cardiac and hemodynamic performance that would improve patient recovery. Cell, tissue, and animal experiments have determined a number of mechanisms of action by which this may be achieved, with increasing focus on insulin as the key component. The original concepts centered on GIK during or after ischemia switching metabolism away from that based on nonesterified fatty acids toward a more favorable glucose-based metabolism and thus improving the efficiency of adenosine triphosphate production and glycogen preservation. Insulin's ability to reduce intracellular fatty acid metabolism may also reduce cellular membrane damage. More recently other mechanisms have also been suggested, including osmotic, oxygen free radical scavenging, and antiapoptotic and anti-inflammatory effects. However, trials that have examined the role of GIK in cardiac surgery have been small, open label, and involved a wide variety of regimens. They have demonstrated improved glycogen preservation, reduced infarct size, reduced incidences of dysrhythmias, need for inotropic agents, and low cardiac output state, and overall reduced lengths of stay. The perceived need to achieve strict blood glucose control to reduce neurologic injury and improve overall mortality have conflicted with its practical difficulties, particularly during cold cardiopulmonary bypass, and the exact role of supplemental glucose administration and resulting hyperglycemia require re-examination.

Effect of glucose-insulin-potassium on hyperlactataemia in patients undergoing valvular heart surgery: A randomised controlled study

BACKGROUND

Hyperlactataemia represents oxygen imbalance in the tissues and its occurrence during cardiac surgery is associated with adverse outcomes. Glucose-insulin-potassium (GIK) infusion confers myocardial protection against ischaemia-reperfusion injury and has the potential to reduce lactate release while improving its clearance.

OBJECTIVES

The objective of this study is to compare the effect of GIK on the incidence of hyperlactataemia in patients undergoing valvular heart surgery.

DESIGN

A randomised controlled study.

SETTING

Single university teaching hospital.

PATIENTS

One hundred and six patients scheduled for elective valvular heart surgery with at least two of the known risk factors for hyperlactataemia.

INTERVENTION

Patients were randomly allocated to receive either GIK solution (insulin 0.1 IU kg(-1) h(-1) and an infusion of 30% dextrose and 80 mmol l(-1) potassium at 0.5 ml kg(-1) h(-1)) or 0.9% saline (control) throughout surgery.

MAIN OUTCOME MEASURES

The primary outcome was the incidence of hyperlactataemia (lactate ≥ 4 mmol l(-1)) during the operation and until 24 h after the operation. Secondary outcomes included haemodynamic parameters, use of vasopressor or inotropic drugs, and fluid balance until 24 h postoperatively. Postoperative morbidity endpoints were also assessed.

RESULTS

The incidences of hyperlactataemia were similar in the groups (32/53 patients in each of the control and GIK groups, P > 0.999). There were no intergroup differences in haemodynamic parameters, use of vasopressor and inotropic drugs, or fluid balance. The incidences of postoperative morbidity endpoints were similar in both groups.

CONCLUSION

Despite its theoretical advantage, GIK did not provide beneficial effects in terms of the incidence of hyperlactataemia or outcome in patients undergoing valvular heart surgery.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT01825720.

Insulin/NFκB protects against ischemia-induced necrotic cardiomyocyte death

In the heart, insulin controls key functions such as metabolism, muscle contraction and cell death. However, all studies have been focused on insulin action during reperfusion. Here we explore the cardioprotective action of this hormone during ischemia. Rat hearts were perfused ex vivo with an ischemia/reperfusion Langendorff model in absence or presence of insulin. Additionally, cultured rat cardiomyocytes were exposed to simulated ischemia in the absence or presence of insulin. Cytoprotective effects were measured by myocardial infarct size, trypan blue exclusion, released LDH and DNA fragmentation by flow cytometry. We found that insulin protected against cardiac ischemia ex vivo and in vitro. Moreover, insulin protected cardiomyocytes from simulated ischemia by reducing necrotic cell death. Protective effects of insulin were dependent of Akt and NFκB. These novel results show that insulin reduces ischemia-induced cardiomyocyte necrosis through an Akt/NF-κB dependent mechanism. These novel findings clarify the role of insulin during ischemia and further support its use in early GIK perfusion to treat myocardial infarction.

Safe and effective use of a glycemic control protocol for neonates in a cardiac ICU

OBJECTIVE

To investigate the safety and efficacy of a hyperglycemia protocol in neonates with critical cardiac illness. Neonates are often regarded as high risk for hypoglycemia while receiving continuous insulin infusions and thus have been excluded from some clinical trials.

DESIGN

A retrospective review.

SETTING

A pediatric cardiac ICU in a tertiary academic center.

INTERVENTIONS

Neonates with critical cardiac illness who developed hyperglycemia were placed on an insulin-hyperglycemia protocol at the attending physician's discretion. Insulin infusions were titrated based on frequent blood glucose monitoring.

MEASUREMENTS

Critical illness hyperglycemia was defined as a blood glucose less than 140 mg/dL. Hypoglycemia was defined as moderate (≤ 60 mg/dL) or severe (≤ 40 mg/dL). Initiating blood glucose, lowest blood glucose during insulin infusion, doses of insulin, duration of insulin, and time to blood glucose greater than 140 mg/dL were evaluated.

MAIN RESULTS

A total of 44 patients were placed on the protocol between January 2009 and October 2011. The majority of insulin infusions were initiated in the early postoperative period (33 of 44, 75%). Moderate hypoglycemia occurred in two patients (4.5%), with blood glucose levels of 49 and 53 mg/dL. No episodes of severe hypoglycemia occurred. A total of 345 discrete blood glucose levels were analyzed; two of these being greater than 60 mg/dL (0.58%). Mean blood glucose prior to starting insulin was 252 ± 45 mg/dL and time until euglycemia was 6.1 ± 3.9 hours. The mean duration of insulin infusion was 24.6 ± 38.7 hours, mean peak dose was 0.10 ± 0.05 units/kg/hour, and mean insulin dose was 0.06 ± 0.02 units/kg/hour. For postoperative patients, mean time after bypass until onset of hyperglycemia was 2.2 ± 2.6 hours.

CONCLUSIONS

A glycemic control protocol can safely and effectively be applied to neonates with critical cardiac disease. Neonates with critical cardiac illness should be included in clinical trials evaluating the benefits of glycemic control.

The effects of an insulin-glucose-potassium (IGK) pretreatment on the bupivacaine cardiotoxicity

BACKGROUND

The purpose of this study is to evaluate the effect of an IGK pretreatment on the cardiotoxicity of bupivacaine.

METHODS

Twenty-one anesthetized mongrel dogs were randomly divided into the following three groups: the control group (CG, n = 7), the treatment group (TG, n = 7) and the pretreatment group (PTG, n = 7). For the 30 min of pretreatment period, CG and TG received normal saline, while PTG received an IV bolus of insulin 2 U/kg, followed by an IGK infusion (2 U/kg/hr of insulin, 0.5-1.5 g/kg/hr of glucose, 1-2 mEq/kg/hr of KCl). The bupivacaine infusion was started at the rate of 0.5 mg/kg/min in all groups after the pretreatment period. CG received normal saline only. In TG, insulin (2 U/kg) was injected simultaneously with bupivacaine infusion, followed by the IGK infusion as with PTG. The hemodynamic variables and the time duration to reach the mean arterial pressure (MAP) of 60 mmHg were compared.

RESULTS

The bupivacaine infusion decreased the cardiac index, MAP, and heart rate in all three groups. Although insulin concentration was higher in TG than in PTG during bupivacaine infusion, the hemodynamic variables in PTG decreased at the slowest rate. The time taken to reach MAP of 60 mmHg in PTG, TG, and CG was 51.4 ± 8.5, 36.4 ± 9.6, and 27.1 ± 8.7 min, respectively (P < 0.05).

CONCLUSIONS

IGK delays the bupivacaine-induced cardiac depression. However, a pretreatment with IGK is more effective in delaying the bupivacaine-induced hypotension than simultaneous administration, regardless of insulin concentration.

An increase in the redox state during reperfusion contributes to the cardioprotective effect of GIK solution

This study aimed at determining whether glucose-insulin-potassium (GIK) solutions modify the NADH/NAD(+) ratio during postischemic reperfusion and whether their cardioprotective effect can be attributed to this change in part through reduction of the mitochondrial reactive oxygen species (ROS) production. The hearts of 72 rats were perfused with a buffer containing glucose (5.5 mM) and hexanoate (0.5 mM). They were maintained in normoxia for 30 min and then subjected to low-flow ischemia (0.5% of the preischemic coronary flow for 20 min) followed by reperfusion (45 min). From the beginning of ischemia, the perfusate was subjected to various changes: enrichment with GIK solution, enrichment with lactate (2 mM), enrichment with pyruvate (2 mM), enrichment with pyruvate (2 mM) plus ethanol (2 mM), or no change for the control group. Left ventricular developed pressure, heart rate, coronary flow, and oxygen consumption were monitored throughout. The lactate/pyruvate ratio of the coronary effluent, known to reflect the cytosolic NADH/NAD(+) ratio and the fructose-6-phosphate/dihydroxyacetone-phosphate (F6P/DHAP) ratio of the reperfused myocardium, were evaluated. Mitochondrial ROS production was also estimated. The GIK solution improved the recovery of mechanical function during reperfusion. This was associated with an enhanced cytosolic NADH/NAD(+) ratio and reduced mitochondrial ROS production. The cardioprotection was also observed when the hearts were perfused with fluids known to increase the cytosolic NADH/NAD(+) ratio (lactate, pyruvate plus ethanol) compared with the other fluids (control and pyruvate groups). The hearts with a high mechanical recovery also displayed a low F6P/DHAP ratio, suggesting that an accelerated glycolysis rate may be responsible for increased cytosolic NADH production. In conclusion, the cardioprotection induced by GIK solutions could occur through an increase in the cytosolic NADH/NAD(+) ratio, leading to a decrease in mitochondrial ROS production.

Avoiding stroke during cardiac surgery

The life saving benefits of cardiac surgery are frequently accompanied by negative side effects such as stroke, that occurs with an incidence of 2%-13% dependent to type of surgery. The etiology is most likely multifactorial with embolic events considered as main contributor. Although stroke presents a common complication, no guidelines for any routine use of pharmacological substances or non-pharmacological strategies exist to date. Non-pharmacological strategies include monitoring of brain oxygenation and perfusion with devices such as near infrared spectroscopy and Transcranial Doppler help. Epiaortic and transesophageal echocardiography visualize aorta pathology, enabling the surgeon to sidestep atheromatous segments. Additionally can the use of specially designed aortic cannulae and filters help to reduce embolization. Brain perfusion can be improved by using antero- or retrograde cerebral perfusion during deep hypothermic circulatory arrest, by tightly monitoring mean arterial blood pressure and hemodilution. Controlling perioperative temperature and glucose levels may additionally help to ameliorate secondary damage. Many pharmacological compounds have been shown to be neuroprotective in preclinical models, but clinical studies failed to confirm these results so far. Remacemide, an NMDA-receptor-antagonist showed a significant drug-based neuroprotection during cardiac surgery. Other substances currently assessed in clinical trials whose results are still pending are acadesine, an adenosine-regulating substance, the free radical scavenger edaravone and the local anesthetic lidocaine. Stroke remains as significant complication after cardiac surgery. Non-pharmacological strategies allow perioperative caregivers to detect injurious events and to ameliorate stroke and its sequelae. Considering the multi-factorial etiology though, stroke prevention will likely have to be addressed with an individualistic combination of different strategies and substances.

Glucose-transporter-mediated positive inotropic effects in human myocardium of diabetic and nondiabetic patients

Insulin causes inotropic effects via Ca(2+)-dependent and Ca(2+)-independent pathways. The latter one is potentially glucose dependent. We examined inotropic responses and signal transduction of insulin in human atrial myocardium of diabetic and nondiabetic patients to test for the role of glucose transporters. Experiments were performed in isolated atrial myocardium of 88 patients undergoing cardiac surgery and 28 ventricular muscle samples of explanted hearts. Influence of insulin (0.02 micromol/L) on isometric twitch force was examined with and without blocking glucose transporter (GLUT) 4 translocation (latrunculin), sodium-coupled glucose transporter (SGLT) 1 (phlorizin, T-1095A), or PI3-kinase (wortmannin). Experiments were performed in Tyrode solution containing glucose or pyruvate as energetic substrate. Messenger RNA expression of glucose transporters (GLUT1, GLUT4, SGLT1, SGLT2) was analyzed in atrial and ventricular myocardium of both diabetic and nondiabetic patients. Developed force increases after insulin (to 117.8% +/- 2.4% and 115.8% +/- 1.9%) in trabeculae from patients with and without diabetes. Inotropic effect was reduced after displacing glucose with pyruvate as well as after PI3-kinase inhibition (to 103% +/- 2%) or inhibition of glucose transporters GLUT4 (to 105% +/- 2%) and SGLT1 (phlorizin to 106% +/- 2%, T-1095A to 105% +/- 2%), without differences between the 2 groups. In glucose-free pyruvate-containing solution, only inhibition of PI3-kinase but not blocking glucose transporters resulted in further inhibitory effects. Messenger RNA expression did not show significant differences between patients with or without diabetes. Insulin exerts positive inotropic effects in human atrial myocardium. These effects are mediated via a PI3-kinase-sensitive and a glucose-transport-sensitive pathway. Differences in functional effects or messenger RNA expression of glucose transporters were not detectable between patients with and without diabetes.

Drugs mediating myocardial protection

The occurrence of myocardial ischaemia will result in either reversible or irreversible myocardial dysfunction. Even when revascularization is successful, some reperfusion injury may occur that transiently impairs myocardial function. Therefore, treatment should not only be directed towards prompt restoration of myocardial blood flow but measures should also be taken to prevent or alleviate the consequences of myocardial reperfusion injury. Over the years, various strategies have been developed. The present contribution reviews a number of these strategies focusing on pharmacological treatments that have been developed to address myocardial reperfusion injury.

Drugs and pharmaceuticals: management of intoxication and antidotes

The treatment of patients poisoned with drugs and pharmaceuticals can be quite challenging. Diverse exposure circumstances, varied clinical presentations, unique patient-specific factors, and inconsistent diagnostic and therapeutic infrastructure support, coupled with relatively few definitive antidotes, may complicate evaluation and management. The historical approach to poisoned patients (patient arousal, toxin elimination, and toxin identification) has given way to rigorous attention to the fundamental aspects of basic life support--airway management, oxygenation and ventilation, circulatory competence, thermoregulation, and substrate availability. Selected patients may benefit from methods to alter toxin pharmacokinetics to minimize systemic, target organ, or tissue compartment exposure (either by decreasing absorption or increasing elimination). These may include syrup of ipecac, orogastric lavage, activated single- or multi-dose charcoal, whole bowel irrigation, endoscopy and surgery, urinary alkalinization, saline diuresis, or extracorporeal methods (hemodialysis, charcoal hemoperfusion, continuous venovenous hemofiltration, and exchange transfusion). Pharmaceutical adjuncts and antidotes may be useful in toxicant-induced hyperthermias. In the context of analgesic, anti-inflammatory, anticholinergic, anticonvulsant, antihyperglycemic, antimicrobial, antineoplastic, cardiovascular, opioid, or sedative-hypnotic agents overdose, N-acetylcysteine, physostigmine, L-carnitine, dextrose, octreotide, pyridoxine, dexrazoxane, leucovorin, glucarpidase, atropine, calcium, digoxin-specific antibody fragments, glucagon, high-dose insulin euglycemia therapy, lipid emulsion, magnesium, sodium bicarbonate, naloxone, and flumazenil are specifically reviewed. In summary, patients generally benefit from aggressive support of vital functions, careful history and physical examination, specific laboratory analyses, a thoughtful consideration of the risks and benefits of decontamination and enhanced elimination, and the use of specific antidotes where warranted. Data supporting antidotes effectiveness vary considerably. Clinicians are encouraged to utilize consultation with regional poison centers or those with toxicology training to assist with diagnosis, management, and administration of antidotes, particularly in unfamiliar cases.

How does glucose insulin potassium improve hemodynamic performance? Evidence for altered expression of beta-adrenoreceptor and calcium handling genes

BACKGROUND

Glucose insulin potassium (GIK) improves hemodynamic performance after coronary artery surgery (CABG). We investigated whether this is associated with changes in gene expression of beta1-adrenergic receptor (ADRB1) or other calcium handling proteins.

METHODS AND RESULTS

During a randomized double-blind placebo-controlled trial, 48 patients undergoing on-pump CABG, allocated to receive pre-ischemic placebo (5% dextrose) or GIK (40% dextrose, K+ 100 mmol.L(-1), insulin 70 u.L(-1); 0.75 mL.kg(-1).h(-1)) continued for 6 hours after the removal of the aortic cross-clamp (AXC), underwent left ventricular biopsy for analysis of specific mRNAs immediately before AXC, before release of AXC, and 10 minutes after reperfusion (placebo n=24, GIK n=24). GIK or placebo was infused for a mean of 79+/-21 minutes or 79+/-18 minutes pre-ischemia respectively. Serial hemodynamic measurements were performed. Biopsy samples were snap-frozen and stored at -80 degrees C, mRNA was extracted and TaqMan real-time polymerase chain reaction was performed to investigate expression of ADRB1, sarcoplasmic reticulum Ca-ATPase (SERCA2a), and phospholamban (PLB). GIK significantly increased cardiac index versus placebo (P=0.037). TaqMan reverse-transcriptase polymerase chain reaction showed significantly greater ADRB1 mRNA expression at all time points (4.9-fold, 7.4-fold, and 15.6-fold increase, respectively; P<0.001), significantly greater SERCA2a mRNA expression after reperfusion (13.2-fold; P<0.001), and increased PLB mRNA expression at pre-ischemia and reperfusion (P<0.001 for both time-points) in GIK groups versus placebo.

CONCLUSIONS

The beneficial hemodynamic effects of GIK therapy are associated with increased ADRB1 and SERCA2a mRNA expression. Further work is therefore warranted to investigate these mRNA effects at the protein level.

Glucose-insulin-potassium and tri-iodothyronine individually improve hemodynamic performance and are associated with reduced troponin I release after on-pump coronary artery bypass grafting

BACKGROUND

Both glucose-insulin-potassium (GIK) and tri-iodothyronine (T3) may improve cardiovascular performance after coronary artery surgery (CABG) but their effects have not been directly compared and the effects of combined treatment are unknown.

METHODS AND RESULTS

In 2 consecutive randomized double-blind placebo-controlled trials, in patients undergoing first time isolated on-pump CABG between January 2000 and September 2004, 440 patients were recruited and randomized to either placebo (5% dextrose) (n=160), GIK (40% dextrose, K+ 100 mmol.L(-1), insulin 70 u.L(-1)) (0.75 mL.kg(-1) h(-1)) (n=157), T3 (0.8 microg.kg(-1) followed by 0.113 microg.kg(-1) h(-1)) (n=63) or GIK+T3 (n=60). GIK/placebo therapy was administered from start of operation until 6 hours after removal of aortic cross-clamp (AXC) and T3/placebo was administered for a 6-hour period from removal of AXC. Serial hemodynamic measurements were taken up to 12 hours after removal of AXC and troponin I (cTnI) levels were assayed to 72 hours. Cardiac index (CI) was significantly increased in both the GIK and GIK/T3 group in the first 6 hours compared with placebo (P<0.001 for both) and T3 therapy (P=0.009 and 0.029, respectively). T3 therapy increased CI versus placebo between 6 and 12 hours after AXC removal (P=0.01) but combination therapy did not. Release of cTnI was lower in all treatment groups at 6 and 12 hours after removal of AXC.

CONCLUSIONS

Treatment with GIK, T3, and GIK/T3 improves hemodynamic performance and results in reduced cTnI release in patients undergoing on-pump CABG surgery. Combination therapy does not provide added hemodynamic effect.

Signalling via the reperfusion injury signalling kinase (RISK) pathway links closure of the mitochondrial permeability transition pore to cardioprotection

Post-ischemic interventions that activate phosphatidylinositol-3-OH kinase (PI3K)-Akt or ERK1/2 pro-survival kinases (the so-called "reperfusion injury signalling kinase (RISK) pathway") during the first few minutes of reperfusion protect against lethal reperfusion-induced injury. We have previously shown that insulin protects against reperfusion-induced injury via activation of the PI3K-Akt pathway. In addition, opening of the mitochondrial permeability transition pore (mPTP) at the time of reperfusion is a major determinant of lethal reperfusion-induced injury, and pharmacologically inhibiting it is cardioprotective. In this study, we examined the relationship between the pro-survival kinase pathways and mPTP opening. Specifically, we tested the hypothesis that activation of the pro-survival kinase pathway by insulin protects cardiomyocytes by reducing the probability of mPTP opening upon reperfusion. Laser illumination of the fluorophore, tetramethyl rhodamine methyl ester (TMRM), was used to induce oxidative stress in the preparation of adult rat ventricular cardiomyocytes. Maintained illumination ultimately induces mPTP opening, detected as a global mitochondrial depolarization, followed by ATP depletion and rigor contracture. Insulin significantly delayed mPTP opening by a factor of approximately 1.7-fold (P<0.001). The effect of insulin was prevented by Wortmannin and by LY-294002, inhibitors of the PI3K pathway, by SH-6, a selective inhibitor of Akt, and by L-NAME, an inhibitor of nitric oxide production. The expression of a dominant negative construct of Akt eliminated the effect of insulin in delaying mPTP opening in a cardiac cell line. Furthermore, the overexpression of constitutively active Akt was sufficient to maximally delay mPTP opening. These results indicate that activation of the PI3K-Akt pro-survival kinase pathway inhibits opening of the mPTP, and demonstrate an important link between the survival kinases and the mPTP.

Hyperglycemia during cardiopulmonary bypass is an independent risk factor for mortality in patients undergoing cardiac surgery

BACKGROUND

Hyperglycemia is commonly present in the perioperative period in patients undergoing cardiac surgery, even during administration of insulin. A direct relationship between postoperative hyperglycemia and mortality has been established in diabetic patients undergoing cardiac surgery. However, this relationship might be confounded because patients with poor outcome receive more glucogenic drugs postoperatively. We assessed the influence of hyperglycemia (highest glucose level) during cardiopulmonary bypass on perioperative morbidity and mortality in diabetic and nondiabetic patients.

METHODS

We performed a multivariate logistic regression analysis on all diabetic (n = 1579) and nondiabetic (n = 4701) patients undergoing cardiac surgery at the Toronto General Hospital between 1999 and 2001. Boluses of insulin were given during cardiopulmonary bypass when the glucose level exceeded 15 mmol/L, when the serum potassium level exceeded 6.0 mmol/L, or both.

RESULTS

Overall mortality was 1.8% (n = 115). A high glucose level during cardiopulmonary bypass was an independent predictor of mortality in both diabetic (odds ratio, 1.20; confidence interval, 1.08-1.32) and nondiabetic (odds ratio, 1.12; confidence interval, 1.06-1.19; per millimole per liter increase in glucose) patients. A high glucose level during cardiopulmonary bypass was also an independent predictor of all major adverse events in both patient groups (odds ratio, 1.06; confidence interval, 1.03-1.09). A high glucose level was not closely related to cardiopulmonary bypass (r = 0.3) or aortic crossclamp times (r = 0.4).

CONCLUSIONS

A high peak serum glucose level during cardiopulmonary bypass is an independent risk factor for death and morbidity in diabetic patients and unexpectedly also in nondiabetic patients.

Insulina: efeitos cardiovasculares e aplicações terapêuticas

Vários estudos têm sugerido benefício do uso de insulina após o infarto do miocárdio e em pacientes criticamente doentes, diabéticos e não diabéticos. No entanto, não se estabeleceu rotineiramente o uso das infusões de insulina e glicose, pela ausência de estudos randomizados de grande porte, entendimento precário dos mecanismos pelos quais estas infusões seriam efetivas, complexidade para administrá-las e principalmente pela mudança cultural que é exigida dos profissionais de saúde para aplicá-las na sua prática. A insulina tem efeitos benéficos no coração, tais como a otimização do uso de substratos pelos cardiomiócitos, o aumento do fluxo coronariano, efeito anti-inflamatório e também ações diretas anti-apoptóticas nas células miocárdicas. Dentro deste contexto, são revisados os resultados clínicos das infusões de insulina e glicose após infarto e cirurgia cardíaca, possíveis mecanismos fisiopatológicos responsáveis por estes benefícios e, finalmente, uma proposta de um protocolo padrão para o uso em unidades de terapia intensiva e de pós-operatório de cirurgia cardíaca.

Glucose-Insulin-Potassium in Cardiac Surgery: A Meta-Analysis

BACKGROUND

Glucose-insulin-potassium therapy (GIK) has been suggested to reduce mortality and improve postoperative recovery after cardiac surgery. We performed a meta-analysis of all randomized studies using GIK in cardiac surgery.

METHODS

A systematic Medline search for all GIK studies in cardiac surgery was carried out. Randomized studies investigating the recovery of contractile function as a primary endpoint were included in the meta-analysis.

RESULTS

Thirty-five GIK trials were identified. Twenty-four studies were excluded because of lack of randomization, supplementary administration of other substances, or due to other primary endpoints. Eleven studies were included with a total of 468 patients who underwent either coronary artery bypass grafting or heart valve replacement. Six studies noted a significant improvement in postoperative recovery. One study demonstrated no effect. In four studies, no comparable statistical analysis was available. GIK patients required similar or lesser doses of catecholamines. From the available data we estimated a weighted mean of relative improvement in postoperative recovery of cardiac index for GIK patients versus controls of 11.4%. Five of 11 studies reported the incidence of postoperative atrial fibrillation (AF). AF occurred in 23% (20/86) in GIK versus 42% (36/86) in control patients (p = 0.009).

CONCLUSIONS

The findings indicate that GIK may considerably improve postoperative recovery of contractile function and reduce the incidence of atrial arrhythmias after cardiac surgery. However, several factors limit the power of this analysis and large, randomized multicenter trials are needed to fully assess the efficacy of GIK after cardiac surgery.

Intensive Insulin Therapy for Critically III Patients

OBJECTIVE:

To evaluate the clinical outcomes of glycemic control of intensive insulin therapy and recommend its place in the management of critically ill patients.

DATA SOURCES:

Searches of MEDLINE (1966—March 2004) and Cochrane Library, as well as an extensive manual review of abstracts were performed using the key search terms hyperglycemia, insulin, intensive care unit, critically ill, outcomes, and guidelines and algorithms.

STUDY SELECTION AND DATA EXTRACTION:

All articles identified from the data sources were evaluated and deemed relevant if they included and assessed clinical outcomes.

DATA SYNTHESIS:

Mortality among patients with prolonged critical illness exceeds 20%, and most deaths are attributable to sepsis and multisystem organ failure. Hyperglycemia is common in critically ill patients, even in those with no history of diabetes mellitus. Maintaining normoglycemia with insulin in critically ill patients has been shown to improve neurologic, cardiovascular, and infectious outcomes. Most importantly, morbidity and mortality are reduced with aggressive insulin therapy. This information can be implemented into protocols to maintain strict control of glucose.

CONCLUSIONS:

Use of insulin protocols in critically ill patients improves blood glucose control and reduces morbidity and mortality in critically ill populations. Glucose levels in critically ill patients should be controlled through implementation of insulin protocols with the goal to achieve normoglycemia, regardless of a history of diabetes. Frequent monitoring is imperative to avoid hypoglycemia.

Insulin therapy in critically ill patients

PURPOSE OF REVIEW

The recent publication of the results of an aggressive approach to the treatment of hyperglycaemia in critically ill patients, and a rekindling of interest in the use of an infusion of glucose insulin and potassium as adjunctive therapy in a diverse group of patients with cardiovascular disease, warrants a review of the multiple effects of insulin and a review of laboratory and clinical studies.

RECENT FINDINGS

The use of an aggressive protocol to maintain normoglycaemia in critically ill patients has been demonstrated to be a beneficial technique in the critical care setting. Implementation of the protocol outside of a research setting appears to be feasible. Recent studies on the use of insulin in addition to glucose and potassium in patients with diverse cardiovascular diseases have also demonstrated positive results.

SUMMARY

This review will summarize some of the putative beneficial effects of insulin as a pharmacological agent, and review recent clinical data. Although the relative benefits of normoglycaemia in the critical care setting and the beneficial effects of insulin are difficult to differentiate, a substantial overlap exists. The extent to which these converging therapies (aggressive normoglycaemia and insulin pharmacotherapy) will be applicable to diverse clinical settings has yet to be determined.