Retrospective analysis of the impact of a low glycaemic index diet on hospital stay following coronary artery bypass grafting: a hypothesis

Prehabilitation of Cardiac Surgical Patients, Part 1: Anemia, Diabetes Mellitus, Obesity, Sleep Apnea, and Cardiac Rehabilitation

The concept of "prehabilitation" consists of screening for and identification of pre-existing disorders followed by medical optimization. This is performed for many types of surgery, but may have profound impacts on outcomes particularly in cardiac surgery given the multiple comorbidities typically carried by these patients. Components of prehabilitation include direct medical intervention by preoperative specialists as well as significant care coordination and shared decision making. In this two-part review, the authors describe existing evidence to support the optimization of various preoperative problems and present a few institutional protocols utilized by our center for cardiac presurgical care. This first installment will focus on the management of anemia, obesity, sleep apnea, diabetes, and cardiac rehabilitation prior to surgery. The second will focus on frailty, malnutrition, respiratory disease, alcohol and smoking cessation, and depression.

Pre-admission interventions (prehabilitation) to improve outcome after major elective surgery: a systematic review and meta-analysis

OBJECTIVE

To determine the benefits and harms of pre-admission interventions (prehabilitation) on postoperative outcomes in patients undergoing major elective surgery.

DESIGN

Systematic review and meta-analysis of randomised controlled trials (RCTs) (published or unpublished). We searched Medline, Embase, CENTRAL, DARE, HTA and NHS EED, The Cochrane Library, CINAHL, PsychINFO and ISI Web of Science (June 2020).

SETTING

Secondary care.

PARTICIPANTS

Patients (≥18 years) undergoing major elective surgery (curative or palliative).

INTERVENTIONS

Any intervention administered in the preoperative period with the aim of improving postoperative outcomes.

OUTCOMES AND MEASURES

Primary outcomes were 30-day mortality, hospital length of stay (LoS) and postoperative complications. Secondary outcomes included LoS in intensive care unit or high dependency unit, perioperative morbidity, hospital readmission, postoperative pain, heath-related quality of life, outcomes specific to the intervention, intervention-specific adverse events and resource use.

REVIEW METHODS

Two authors independently extracted data from eligible RCTs and assessed risk of bias and the certainty of evidence using Grading of Recommendations, Assessment, Development and Evaluation. Random-effects meta-analyses were used to pool data across trials.

RESULTS

178 RCTs including eight types of intervention were included. Inspiratory muscle training (IMT), immunonutrition and multimodal interventions reduced hospital LoS (mean difference vs usual care: -1.81 days, 95% CI -2.31 to -1.31; -2.11 days, 95% CI -3.07 to -1.15; -1.67 days, 95% CI -2.31 to -1.03, respectively). Immunonutrition reduced infective complications (risk ratio (RR) 0.64 95% CI 0.40 to 1.01) and IMT, and exercise reduced postoperative pulmonary complications (RR 0.55, 95% CI 0.38 to 0.80, and RR 0.54, 95% CI 0.39 to 0.75, respectively). Smoking cessation interventions reduced wound infections (RR 0.28, 95% CI 0.12 to 0.64).

CONCLUSIONS

Some prehabilitation interventions may reduce postoperative LoS and complications but the quality of the evidence was low.

PROSPERO REGISTRATION NUMBER

CRD42015019191.

Low glycaemic index diets for the prevention of cardiovascular disease

BACKGROUND

The glycaemic index (GI) is a physiological measure of the ability of a carbohydrate to affect blood glucose. Interest is growing in this area for the clinical management of people at risk of, or with, established cardiovascular disease. There is a need to review the current evidence from randomised controlled trials (RCTs) in this area. This is an update of the original review published in 2008.

OBJECTIVES

To assess the effect of the dietary GI on total mortality, cardiovascular events, and cardiovascular risk factors (blood lipids, blood pressure) in healthy people or people who have established cardiovascular disease or related risk factors, using all eligible randomised controlled trials.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase and CINAHL in July 2016. We also checked reference lists of relevant articles. No language restrictions were applied.

SELECTION CRITERIA

We selected RCTs that assessed the effects of low GI diets compared to diets with a similar composition but a higher GI on cardiovascular disease and related risk factors. Minimum trial duration was 12 weeks. Participants included were healthy adults or those at increased risk of cardiovascular disease, or previously diagnosed with cardiovascular disease. Studies in people with diabetes mellitus were excluded.

DATA COLLECTION AND ANALYSIS

Two reviewers independently screened and selected studies. Two review authors independently assessed risk of bias, evaluated the overall quality of the evidence using GRADE, and extracted data following the Cochrane Handbook for Systematic Reviews of Interventions. We contacted trial authors for additional information. Analyses were checked by a second reviewer. Continuous outcomes were synthesized using mean differences and adverse events were synthesized narratively.

MAIN RESULTS

Twenty-one RCTs were included, with a total of 2538 participants randomised to low GI intervention (1288) or high GI (1250). All 21 included studies reported the effect of low GI diets on risk factors for cardiovascular disease, including blood lipids and blood pressure.Twenty RCTs (18 of which were newly included in this version of the review) included primary prevention populations (healthy individuals or those at high risk of CVD, with mean age range from 19 to 69 years) and one RCT was in those diagnosed with pre-existing CVD (a secondary prevention population, with mean age 26.9 years). Most of the studies did not have an intervention duration of longer than six months. Difference in GI intake between comparison groups varied widely from 0.6 to 42.None of the included studies reported the effect of low GI dietary intake on cardiovascular mortality and cardiovascular events such as fatal and nonfatal myocardial infarction, unstable angina, coronary artery bypass graft surgery, percutaneous transluminal coronary angioplasty, and stroke. The unclear risk of bias of most of the included studies makes overall interpretation of the data difficult. Only two of the included studies (38 participants) reported on adverse effects and did not observe any harms (low-quality evidence).

AUTHORS' CONCLUSIONS

There is currently no evidence available regarding the effect of low GI diets on cardiovascular disease events. Moreover, there is currently no convincing evidence that low GI diets have a clear beneficial effect on blood lipids or blood pressure parameters.

The glycemic index and cardiovascular disease risk

Postprandial hyperglycemia is increasingly recognized as an independent risk factor for cardiovascular disease. Glycemic "spikes" may adversely affect vascular structure and function via multiple mechanisms, including (acutely and/or chronically) oxidative stress, inflammation, low-density lipoprotein oxidation, protein glycation, and procoagulant activity. Postprandial glycemia can be reliably predicted by considering both the amount and type of carbohydrate. In particular, the glycemic index (GI), a measure of postprandial glycemic potency weight for weight of carbohydrate, has provided insights that knowledge of the sugar or starch content has not. In prospective observational studies, dietary GI and/or glycemic load independently predict cardiovascular disease, with relative risk ratios of 1.2 to 1.7 comparing highest and lowest quintiles. In randomized controlled trials in overweight subjects, diets based on low-GI carbohydrates have produced better cardiovascular-related outcomes than conventional low-fat diets. Taken together, the findings suggest that health professionals may be able to improve cardiovascular outcomes by recommending the judicious use of low- GI/glycemic load foods.

State of the Art Reviews: Glycemic Index, Obesity, and Chronic Disease

There is increasing evidence that both the amount and type of carbohydrate play an important role in weight management and risk of chronic disease. Classifying carbohydrates according to their post-prandial glycemic effect (ie, the glycemic index of foods) has yielded more useful insights than the historical distinctions of simple versus complex chemical structure. Diets based on carbohydrate foods that are more slowly digested and absorbed (ie, low glycemic index diets) have been independently linked to reduced risk of type 2 diabetes, cardiovascular disease, and some types of cancer. In individuals with diabetes, intervention studies have shown improvements in insulin sensitivity and glycated hemoglobin concentration with low glycemic index diets. Research also suggests that low glycemic index diets may assist with weight management through effects on satiety and fuel partitioning. Although ongoing research is needed, the current findings, together with the fact that there are no demonstrated negative effects of a low glycemic index diet, suggest that the glycemic index should be an important consideration in the dietary management and prevention of obesity and chronic disease.

Considerations in prevention of surgical site infections following cardiac surgery: when your patient is diabetic

The incidence of surgical site infections among patients with diabetes continues to occur at a greater rate when compared with their nondiabetic counterparts. Preexisting vascular changes, delayed wound healing, and impaired immune factors contribute. Adult patients with diabetes likely possess comorbid coronary artery disease, thus increasing the need for cardiac surgery. The resultant potential for infection can be combated with supplementary interventions above those universally taken. Modifiable risk factors of hyperglycemia and obesity are targeted preoperatively. Glycemic control, adequate tissue perfusion, and adjunct use of nasal mupirocin are addressed intraoperatively. Lastly, focus is placed on nutrition, exercise, and continued glucose control postoperatively and beyond discharge.

Glycemic index, postprandial glycemia and cardiovascular disease

PURPOSE OF REVIEW

Several lines of evidence indicate that exaggerated postprandial glycemia puts individuals without diabetes at greater risk of developing cardiovascular disease. In large, prospective observational studies, including meta-analyses, higher 120 min post-load blood glucose and glycated hemoglobin (a measure of average blood glucose level over time) independently predict cardiovascular mortality and morbidity in individuals without diabetes. These findings imply that the glycemic nature of dietary carbohydrates may also be relevant. We aim to provide a clearer perspective on how the glycemic impact of carbohydrates may modulate development of cardiovascular disease.

RECENT FINDINGS

In ecological studies, average dietary glycemic index (a measure of the postprandial glycemic potential of carbohydrates) and glycemic load (average glycemic index x amount of carbohydrate) predicts coronary infarct and cardiovascular disease risk factors, including HDL cholesterol, triglycerides and C-reactive protein. In short-term intervention studies of overweight and hyperlipidemic patients, low glycemic index diets lead to improvements in cardiovascular disease risk factors, including reduced LDL cholesterol and improved insulin sensitivity, as well as greater body fat loss on energy-restricted diets. Molecular studies indicate that physiological hyperglycemia induces overproduction of superoxide by the mitochondrial electron-transport chain, resulting in inflammatory responses and endothelial dysfunction.

SUMMARY

Taken together, the findings suggest that conventional high-carbohydrate diets with their high glycemic index may be suboptimal, particularly in insulin-resistant individuals. Because around one in four adults has impairments in postprandial glucose regulation, the glycemic potential of carbohydrates warrants further investigation in cardiovascular disease prevention.

Low glycaemic index diets for coronary heart disease

BACKGROUND

The glycaemic index (GI) is a physiological measure of the ability of a carbohydrate to affect blood glucose. Interest is growing in the low GI carbohydrate concept for the clinical management of people at risk of, or with established coronary heart disease. There is a need to review the current evidence from controlled trials in this area.

OBJECTIVES

The primary objective is to review the current evidence from RCTs that assess the relationship between the consumption of low glycaemic index diets and the effects on coronary heart disease and on risk factors for coronary heart disease.

SEARCH STRATEGY

We searched CENTRAL (Issue 4, 2003), MEDLINE (1966 to 2003), EMBASE (1980 to 2003) and CINAHL (1982 to 2003). We also contacted experts in the field.

SELECTION CRITERIA

We selected randomised controlled trials that assessed the effects of low glycaemic index diets, over a minimum of 4 weeks, on coronary heart disease (CHD) and risk factors. Participants included were adults who carry at least one major risk factor for coronary heart disease such as abnormal lipids, diabetes or being overweight.

DATA COLLECTION AND ANALYSIS

Two of our research team independently assessed trial quality and extracted data. Authors of the included studies were contacted for additional information when this was appropriate.

MAIN RESULTS

Fifteen randomised controlled trials met the inclusion criteria. No studies found reported the effect of low glycaemic index diets on CHD mortality or CHD events and morbidity. All fifteen included studies report the effect of low glycaemic index diets on major risk factors for CHD. Meta-analysis detected limited and weak evidence of a relationship between low glycaemic index diets and slightly lower total cholesterol, compared with higher glycaemic index diets. There is also limited and weak evidence of a small reduction in HbA1c after 12 weeks on low glycaemic index diets but not at 4 to 5 weeks. There is no evidence that low glycaemic index diets have an effect on LDL cholesterol or HDL cholesterol, triglycerides, fasting glucose or fasting insulin levels.

REVIEWERS' CONCLUSIONS

The evidence from randomised controlled trials showing that low glycaemic index diets reduces coronary heart disease and CHD risk factors is weak. Many of the trials identified were short-term, of poor quality and conducted on small sample sizes. There is a need for well designed, adequately powered, randomised controlled studies, of greater than 12 weeks duration to assess the effects of low glycaemic index diets for CHD.