EuroSCORE II and N-terminal pro-B-type natriuretic peptide for risk evaluation: an observational longitudinal study in patients undergoing coronary artery bypass graft surgery.

BACKGROUND: Postoperative heart failure remains the major cause of death after cardiac surgery. As N-terminal pro-B-type natriuretic peptide (NT-proBNP) is a predictor for postoperative heart failure, the aim was to evaluate if preoperative NT-proBNP could provide additional prognostic information to the recently launched EuroSCORE II. METHODS: A total of 365 patients with acute coronary syndrome (ACS) undergoing isolated coronary artery bypass graft (CABG) surgery were studied prospectively. Preoperative NT-proBNP and EuroSCORE II were evaluated with regard to severe circulatory failure after operation according to prespecified criteria. To assess what clinical outcomes are indicated by NT-proBNP levels in different risk categories, the patients were stratified according to EuroSCORE II. Based on receiver operating characteristics analysis, these cohorts were assessed with regard to preoperative NT-proBNP below or above 1028 ng litre(-1). The follow-up time averaged 4.4 (0.7) yr. RESULTS: Preoperative NT-proBNP≥1028 ng litre(-1) [odds ratio (OR) 9.9, 95% confidence interval (CI) 1.01-98.9; P=0.049] and EuroSCORE II (OR 1.24, 95% CI 1.06-1.46; P=0.008) independently predicted severe circulatory failure after operation. In intermediate-risk patients (EuroSCORE II 2.0-10.0), NT-proBNP≥1028 ng litre(-1) was associated with a higher incidence of severe circulatory failure (6.6% vs 0%; P=0.007), renal failure (14.8% vs 5.4%; P=0.03), stroke (6.6% vs 0.7%; P=0.03), longer intensive care unit stay [37 (35) vs 27 (38) h; P=0.002], and worse long-term survival. CONCLUSIONS: Combining EuroSCORE II and preoperative NT-proBNP appears to improve risk prediction with regard to severe circulatory failure after isolated CABG for ACS. NT-proBNP may be particularly useful in patients at intermediate risk according to EuroSCORE II. CLINICAL TRIAL REGISTRATION: NCT00489827.

Mixed venous oxygen saturation predicts short- and long-term outcome after coronary artery bypass grafting surgery: a retrospective cohort analysis.

BACKGROUND: Complications of an inadequate haemodynamic state are a leading cause of morbidity and mortality after cardiac surgery. Unfortunately, commonly used methods to assess haemodynamic status are not well documented with respect to outcome. The aim of this study was to investigate Sv(O2) as a prognostic marker for short- and long-term outcome in a large unselected coronary artery bypass grafting (CABG) cohort and in subgroups with or without treatment for intraoperative heart failure. METHODS: Two thousand seven hundred and fifty-five consecutive CABG patients and subgroups comprising 344 patients with and 2411 patients without intraoperative heart failure, respectively, were investigated. Sv(O2) was routinely measured on admission to the intensive care unit (ICU). The mean (sd) follow-up was 10.2 (1.5) yr. RESULTS: The best cut-off for 30 day mortality related to heart failure based on receiver-operating characteristic analysis was Sv(O2) 60.1%. Patients with Sv(O2) <60% had higher 30 day mortality (5.4% vs 1.0%; P<0.0001) and lower 5 yr survival (81.4% vs 90.5%; P<0.0001). The incidences of perioperative myocardial infarction, renal failure, and stroke were also significantly higher, leading to a longer ICU stay. Similar prognostic information was obtained in the subgroups that were admitted to ICU with or without treatment for intraoperative heart failure. In patients admitted to ICU without treatment for intraoperative heart failure and Sv(O2) ≥60%, 30 day mortality was 0.5% and 5 yr survival 92.1%. CONCLUSIONS: Sv(O2) <60% on admission to ICU was related to worse short- and long-term outcome after CABG, regardless of whether the patients were admitted to ICU with or without treatment for intraoperative heart failure.

Myocardial metabolism before and after valve replacement for aortic stenosis.

AIM: Post ischemic disturbances of myocardial metabolism that may contribute to postoperative heart failure and are accessible to metabolic treatment have been identified early after coronary surgery. Knowledge derived from these studies may not be applicable to other patient groups. Therefore we studied myocardial energy metabolism in patients operated for isolated aortic stenosis. METHODS: Twenty patients undergoing isolated aortic valve replacement (AVR) because of aortic stenosis without significant regurgitation were studied before and immediately after surgery. Myocardial uptake of oxygen and energy substrates was assessed with coronary sinus catheter technique. RESULTS: Free fatty acids (FFA) were the main source of myocardial energy before and after AVR. A significant uptake of lactate was only recorded preoperatively. A significant uptake of glutamate of the same magnitude as previously described in coronary patients was found pre- and postoperatively. Postoperatively a relative decrease of myocardial oxygen extraction ratio (P<0.001) and oxygen consumption (P=0.14) by approximately 20% was observed. CONCLUSION: Preoperative and postoperative metabolic adaptation with substantial uptake of glutamate, previously claimed to be due to chronic or repetitive ischemia, was demonstrated. The results indicate that oxidative metabolism had not fully recovered when the procedure was completed. However, the potentially unfavorable postoperative metabolic state with predominant reliance on FFA as energy source was out-balanced by the unloading effect of AVR with a reduction in myocardial oxygen extraction.

High-dose glucose-insulin-potassium after cardiac surgery: a retrospective analysis of clinical safety issues.

BACKGROUND: Metabolic treatment with insulin or glucose-insulin-potassium (GIK) has received attention in association with myocardial infarction, cardiac surgery and critical care. As a result of insulin resistance during neuroendocrine stress, doses of insulin up to 1 IU kg-1 b.w.*h are required to achieve maximal metabolic effects after cardiac surgery. The clinical experience with regard to safety issues of such a high-dose GIK regime in critically ill patients after cardiac surgery is reported. METHODS: Retrospective, observational study involving all patients treated with high-dose GIK after cardiac surgery during one year in a cardiovascular center at a University Hospital. RESULTS: Eighty-nine patients out of 854 adult patients undergoing cardiac surgery were treated with high-dose GIK. Mean age was 69 +/- 1 years, Higgins score 5.3 +/- 0.3. Preoperatively 31.4% had left ventricular function EF< or =0.35 and 32.5% had sustained a myocardial infarct during surgery. Mortality was 5.6% and the average ICU stay was 3.7 +/- 0.5 days. The main indication for GIK was intraoperative heart failure (69.7%). The average glucose infusion rate during the first 6 h was 4.22 +/- 0.15 and 4.91 +/- 0.14 mg kg-1 b.w.*min, respectively, in diabetic and non-diabetic patients (P = 0.023). Blood glucose and s-potassium control was acceptable. CONCLUSIONS: The high-dose GIK regime allowed substantial amounts of glucose to be infused both in diabetic and critically ill patients with maintenance of acceptable blood glucose control. Provided careful monitoring, this regime can be safely used in clinical practice and deserves further evaluation for treatment of critically ill patients following cardiac surgery.

Management of life-threatening haemoptysis.

Massive haemoptysis represents a major medical emergency that is associated with a high mortality. Here we present two cases of life-threatening haemoptysis, the first caused by rupture of an aortic aneurysm into the lung in a 37-yr-old woman with polyarteritis nodosa and the second caused by massive bleeding from an angiectatic vascular malformation in the right main bronchus in a 21-yr-old woman. Fibreoptic bronchoscopy played an essential role in the diagnostic process and management of the respiratory tract. Diagnosis in the first case was obtained by CT scan and the aneurysm was treated surgically. In the second case, bronchial arteriography contributed to both definitive diagnosis and treatment. Initial cardiorespiratory management, diagnostic procedures and definitive therapy are described and reviewed. Adequate early management of the cardiorespiratory system is essential to the outcome. Aggressive measures to elucidate the cause of haemoptysis and prompt therapy are warranted because of the high risk of recurrence.

Myocardial uptake and release of substrates in type II diabetics undergoing coronary surgery.

OBJECTIVE: Knowledge about myocardial metabolism in diabetic patients is limited, and even more so in association with myocardial ischaemia and cardiac surgery. This study investigates myocardial substrate utilization in type II diabetic patients after elective coronary artery bypass graft surgery (CABG). DESIGN: Myocardial substrate utilization in 10 type II diabetic patients was assessed during the first hours after elective CABG with the coronary sinus catheter technique. RESULTS: No significant myocardial uptake of carbohydrates was observed. Free fatty acids were extracted throughout the study period but uptake was not related to arterial levels. As arterial levels of beta-hydroxybutyric acid tended to increase a significant myocardial uptake emerged. The average extraction rate of beta-hydroxybutyric acid was 31% with a peak of 42%. A comparable extraction rate of glutamate was also found whereas alanine was released from the heart. CONCLUSION: Free fatty acids were the main source of energy for the heart whereas uptake of carbohydrates was restricted. The high extraction rates of beta-hydroxybutyric acid and glutamate suggest an adaptive role for these substrates during this unfavourable metabolic state for the post-ischaemic diabetic heart.

Effects of high-dose glucose-insulin-potassium on myocardial metabolism after coronary surgery in patients with Type II diabetes.

The effects of glucose-insulin-potassium (GIK) on cardiac metabolism have been studied previously in non-diabetic patients after cardiac surgery. Although patients with diabetes mellitus can be expected to benefit most from such treatment, the impact of GIK in diabetic patients undergoing cardiac surgery remains unexplored. Therefore the present study investigates the effects of high-dose GIK on myocardial substrate utilization after coronary surgery in patients with Type II diabetes. A total of 20 patients with Type II diabetes undergoing elective coronary surgery were randomly allocated to either post-operative high-dose GIK or standard post-operative care, including insulin infusion if necessary to keep blood glucose below 10 mmol/l. Myocardial substrate utilization was studied using the coronary sinus catheter technique. Haemodynamic state was assessed with the aid of Swan-Ganz catheters. High-dose GIK caused a shift towards carbohydrate utilization, with significant lactate uptake throughout the study period and significant uptake of glucose after 4 h. Arterial levels of non-esterified fatty acids and beta-hydroxybutyric acid decreased, and after 1 h no significant uptake of these substrates was found. Increases in the cardiac index and stroke volume index were found in patients treated with high-dose GIK. A decrease in systemic vascular resistance was found both in the control group and in the high-dose GIK group. We conclude that high-dose GIK can be used in diabetic patients after cardiac surgery to promote carbohydrate uptake at the expense of non-esterified fatty acids and beta-hydroxybutyric acid. This could have implications for treatment of the diabetic heart in association with surgery and ischaemia.

Neurological injury after surgery for ischemic heart disease: risk factors, outcome and role of metabolic interventions.

OBJECTIVES: Neurological complication remains a feared and increasing problem in association with cardiac surgery. The aim of this study was to analyze risk factors for neurological complications in a cohort of patients in whom inotropes for weaning from cardiopulmonary bypass was gradually replaced by metabolic treatment. METHODS: The records of 775 consecutive patients undergoing coronary artery bypass grafting (CABG) or combined CABG+valve procedures were examined. Forward stepwise multiple logistic regression analysis was used for statistical evaluation of independent risk factors. RESULTS: The incidence of neurological injury was 1.8% in patients undergoing isolated CABG and 5.4% after combined CABG+valve procedures. After cross-validation multivariate analysis identified history of cerebrovascular disease, advanced age and aortic cross-clamp time as independent risk factors for postoperative cerebral complications. Chronic obstructive pulmonary disease and number of bypasses also emerged as risk factors in the primary analysis. CONCLUSIONS: In general, markers for advanced atherosclerosis, with history of cerebrovascular disease as the most important, emerged as predictors for neurological injury. Although it did not enter the final risk model, the results also suggest that postoperative heart failure deserves further surveillance as a potential risk factor for neurological complications. However, no evidence for untoward neurological effects associated with glutamate or glucose-insulin-potassium treatment was found.

Predictors of atrial fibrillation in patients undergoing surgery for ischemic heart disease.

OBJECTIVES: Atrial fibrillation (AF) remains a common problem after cardiac surgery. AF increases the risk for stroke and is associated with increased length of hospitalization. The aim of this study was to analyze risk factors for postoperative AF in a uniformly managed cohort of patients. DESIGN: The records of 775 consecutive patients undergoing coronary artery bypass grafting (CABG) or CABG + valve procedures were examined. Forward stepwise multiple logistic regression analysis was used for statistical evaluation. RESULTS: Mean age was 64.6 +/- 8.7 years. The incidence of AF was 29.1% in patients undergoing isolated CABG and 48.6% after CABG + valve procedures. Multivariate analysis identified advanced age (p = 0.000003), low postoperative mixed venous oxygen saturation (p = 0.0018), hypertension (p = 0.0059), preoperative history of AF (p = 0.023) and the need for mechanical circulatory support (p = 0.030) as predictors for postoperative AF. CONCLUSIONS: In agreement with previous studies, advanced age was the most important predictor of AF. Hypertension, history of AF and signs of circulatory failure were also predictive of AF. Preventive measures against AF should preferably be tested in high-risk populations, such as elderly patients.

Routine SvO2 measurement after CABG surgery with a surgically introduced pulmonary artery catheter.

OBJECTIVE: It has been argued that the poor correlation between cardiac output and mixed venous oxygen saturation (SvO2) reduces the value of SvO2. Routine use of Swan Ganz catheters is also controversial in cardiac surgery. Here our clinical experience with a simplified method for routine hemodynamic monitoring and the short-term prognostic value of SvO2 after CABG surgery is presented. METHOD: Peroperatively an epidural catheter is routinely introduced through the outflow tract of the right ventricle into the pulmonary artery for monitoring of pressure and blood sampling. Clinical data were retrospectively retrieved from the records and related to SvO2 routinely obtained on admission to the ICU after 488 CABG procedures. RESULTS: Average SvO2 on arrival to ICU was 67+/-7%. The SvO2 value of 55% represented a cut off point below which a high incidence of complications were found. Outcome after 456 procedures with SvO2 > or = 55% compared with 32 procedures with SvO2 < 55%: mortality 0 vs. 9.4% (P = 0.0003), perioperative myocardial infarction 6.2 vs. 29% (P < 0.0001), ventilator treatment 8.9+/-10.1 vs. 25.7+/-54.9 h (P = 0.0074), ICU stay 1.4+/-1.2 vs. 2.1+/-1.7 days (P = 0.0010). CONCLUSIONS: SvO2 was of prognostic value and due to its specificity it seems particularly useful for telling which patients are unlikely to develop cardiorespiratory problems. Thus, this simple method for hemodynamic monitoring could contribute to cost containment as it seems that we can safely reserve Swan Ganz catheters for high-risk patients.

Metabolic intervention for the ischemic and post-ischemic heart.

There is increasing evidence that the availability of different metabolic substrates can influence post-ischemic functional recovery of the heart and the damage incurred during episodes of myocardial ischemia. Here we present the rationale for metabolic interventions, describe their mechanisms of action and suggest potential clinical applications. In cardiac surgery, basic research, studies of human myocardial metabolism after cardiac operations, and available experience with metabolic interventions provide a rationale for metabolic support with glutamate and/or high-dose glucose-insulin-potassium (GIK) in postoperative cardiac failure. In the treatment of acute myocardial infarction GIK deserves serious evaluation as recent randomized studies in diabetics with myocardial infarction and in patients undergoing reperfusion strategies demonstrate significant reductions in mortality. However, before large scale prospective randomized studies are undertaken, further studies of myocardial metabolism in acute myocardial infarction and the impact of different GIK regimes may be advisable in order to determine appropriate doses. A brief overview of metabolic modulation with pharmacological measures is given as it eventually may prove that we have to await the introduction of pharmacological agents which enhance full glucose oxidation at the expense of free fatty acids to create the commercial interest necessary to achieve widespread use of metabolic therapies.

Assessment of myocardial glutamate requirements early after coronary artery bypass surgery.

Glutamate is an important substrate for the intermediary metabolism of the heart, particularly in association with ischemia. Early after coronary artery bypass surgery (CABG) myocardial uptake of glutamate seems to be limited by substrate availability (arterial levels). However, glutamate is not an innocuous substrate. As arterial levels of glutamate are important both for myocardial uptake and adverse effects, an attempt was made to determine a minimum dose of glutamate sufficient to supply the needs of the heart after CABG. Ten patients received and infusion of 220-240 ml of 0.1 M L-glutamic acid solution at varying rates during two 30-min periods, starting 2 h after uncomplicated elective CABG. Intravenous glutamate infusion caused a dose-dependent linear increase in arterial glutamate and an increased myocardial uptake of glutamate. However, myocardial uptake of glutamate correlated with arterial levels only at lower infusion rates. Although maximal peak uptake in individual patients (6.6 +/- 1.1 mumol/min) occurred at an average increase of arterial whole blood glutamate of 172 +/- 34 mumol/L, the greatest impact on myocardial glutamate uptake was achieved by increasing arterial whole blood glutamate by less than 100 mumol/L. This implies that an infusion rate of 30-40 mg glutamate/kg BW/h could suffice to achieve a maximal or near maximal myocardial glutamate uptake in most patients after CABG. The adequacy of this dosage remains to be confirmed in high-risk patients.

Intravenous aspartate infusion after a coronary operation: effects on myocardial metabolism and hemodynamic state.

BACKGROUND: In a previous study glutamate infusion after coronary artery bypass grafting was associated with beneficial effects on myocardial metabolism and myocardial performance. It has been claimed that aspartate is more important than glutamate for the recovery of myocardial metabolism after cardioplegic arrest. Therefore, the metabolic and hemodynamic effects of aspartate were studied after coronary artery bypass grafting. METHODS: Fifty to 240 mL of a 0.1 mol/L aspartic acid solution was infused intravenously during 60 minutes in 10 patients early after coronary artery bypass grafting. Myocardial metabolism was studied using the coronary sinus catheter technique. RESULTS: Aspartate infusion caused a significant increase in the arterial levels of both aspartate and glutamate. This was associated with a significant increase in myocardial uptake of aspartate and a decrease in myocardial uptake of glutamate. Myocardial exchange of other substrates remained unaffected. There were no changes in hemodynamic state except an increase of heart rate and pulmonary vascular resistance. CONCLUSIONS: Interactions with glutamate metabolism, compatible with competitive inhibition of myocardial glutamate uptake, which may have outweighed potential effects of aspartate, were observed. Recognition of these amino acid interactions is important as they are used together as additives in cardioplegic solutions.

Postoperative myocardial ischemia caused by chest tube compression of vein graft.

Here we report an unexpected and possibly overlooked cause of postoperative myocardial ischemia: a chest tube compressing a vein graft. After the position of the chest tube was adjusted, graft flow was reestablished, right ventricular contractility returned, and myocardial infarction was probably prevented. The literature on chest tube complications is briefly reviewed and experience from our institution is reported.

Metabolic and hemodynamic effects of intravenous glutamate infusion early after coronary operations.

Amino acids, particularly glutamate, have been proposed to play an important role in the recovery of cardiac oxidative metabolism after ischemia. In this investigation, the metabolic and hemodynamic effects of glutamate infusion after coronary operations were studied. From 220 to 240 ml 0.1 mol/L l-glutamic acid solution was infused in 10 patients during 1 hour starting 2 hours after operation. A control group of 10 patients received an infusion of 240 ml saline solution. During glutamate infusion, there were significant increases in the uptake of glutamate (from 0.7 +/- 0.2 micromol/min in the basal state to a peak of 5.7 +/- 1.2 micromol/min at 20 minutes) and lactate (from 4.9 +/- 2.0 micromol/min in the basal state to 14.1 +/- 4.4 micromol/min at 60 minutes; p < 0.01), whereas the uptake and release of other substrates remained essentially unaffected. Arterial glutamate levels (in whole blood) increased from 103 +/- 10 micromol/L to 394 +/- 20 micromol/L at 60 minutes. Thirty minutes after discontinuation of the glutamate infusion, arterial levels had decreased to 129 +/- 17 micromol/L. The markedly improved utilization of lactate and the unchanged release of alanine together suggest that the oxidative metabolism of the heart was stimulated by glutamate. The metabolic changes were associated with improved myocardial performance. Left ventricular stroke work index increased from 26.8 +/- 2.1 gm x beat(-1) x m(-2) body surface area to 31.3 +/- 3.1 gm x beat(-1) x m(-2) body surface area during glutamate infusion. Metabolic support with amino acids may provide a means to improve recovery of metabolic and hemodynamic function of the heart early after cardiac operations.