Careful managment of blood pressure and blood lipids is one of the cornerstones of care for type 2 diabetes patients, as Professor Allen Hutchinson and Aileen McIntosh explain


 

Type 2 diabetes is a relatively common condition, with an estimated 1.4 million sufferers in the UK.1 The number of individuals affected is increasing and it has been estimated that 3 million might have the condition by 2010.1

Serious microvascular and macrovascular complications are associated with type 2 diabetes, which can be thought of as a progressive condition. As with any chronic disease, management can be challenging; in type 2 diabetes effective management often requires increasingly intensive care on the part of healthcare professionals and ongoing self-care by patients.

Mortality and morbidity are higher in individuals with type 2 diabetes than in those of similar age and sex who do not have the condition. Coronary heart disease is the leading cause of death among patients with type 2 diabetes. It has been estimated that men with type 2 diabetes have a two- to three-fold increase in risk of coronary heart disease, and premenopausal women a four- to five-fold increase. The risk of stroke may be increased two- to three-fold.

A key goal, therefore, in the effective management of type 2 diabetes is the reduction of premature mortality and morbidity from coronary heart disease. Given the increased risks in patients with type 2 diabetes, the management of blood pressure and blood lipids is of vital importance.

Developing the guideline

Two separate guideline development groups were involved in producing the guidelines for blood pressure management and blood lipid management, to enable the evidence to be considered in full. The chairs of the two groups worked closely and attended both groups.

The guideline development process is detailed in the full guideline.2,3 For both groups the development process was difficult because of the complexity of the clinical issues, including the multiplicity of factors involved in type 2 diabetes and the lack of good research evidence specific to type 2 diabetes.

Both groups started with key clinical questions to be addressed by the research evidence. They decided that the evidence that was required to support clinical decisions was that which reported important clinical outcomes, i.e. all-cause mortality, cardiovascular disease mortality or events and coronary heart disease mortality or events.

This type of evidence was considered to be more useful in the development process than evidence reporting only intermediate outcomes, such as serum lipoprotein or blood pressure outcomes, because the relationships between these intermediate outcomes and changes in coronary events are complex and not necessarily a robust basis for treatment recommendations.

Assessing risk

Both guideline development groups were keen to take a risk-based approach to management to reduce coronary event risk. Assessing risk level enables clinicians to offer patients appropriate treatments and to decide when treatment needs to be stepped up as the patientÍs risk increases. However, this approach immediately presented some challenges.

While risk assessment tools are available, it was thought that many did not take into account the additional degree of risk associated with type 2 diabetes. Even those tools that took diabetes into account, it was felt, often underestimated risk. The development groups therefore took the widely used Joint British Societies Coronary Risk Prediction Charts, reproduced in the British National Formulary,4 as the basis for their recommendations (see Box 1, below).

Box 1: 10-year coronary event risk

For the purposes of the guideline, higher and lower 10-year coronary event risk are defined as follows:

An individual at higher risk is one:

  • Who has manifest cardiovascular disease (a history or symptoms of coronary heart disease, stroke or peripheral vascular disease) or
  • Whose 10-year coronary event risk is assessed as above 15%, taking into account the known limitations of the risk assessment charts

An individual at lower risk is one:

  • Who does not have manifest cardiovascular disease and
  • Whose 10-year coronary event risk is 15% or below, taking into account the known limitations of the risk assessment charts

see British National Formulary 2002; 44

The guideline development groups also recognised that setting risk thresholds for treatment is largely a value judgement, which involves considerations of clinical and cost effectiveness. However, they provide explicit starting points for discussions between healthcare professionals and patients.

How robust is the evidence?

The research evidence underwent extensive and systematic searching, sifting and appraisal. The results of this systematic review were presented to the guideline development groups for them to consider and develop recommendations. We took the usual approach to grading of evidence and recommendations (Tables 1 and 2, below).

Table 1: Levels of evidence
Table 2: Grading of evidence

There was limited research evidence reporting the required outcomes in individuals with type 2 diabetes, for either blood pressure or blood lipid studies. As a result, the group considered evidence on populations in general and extrapolated the findings to individuals with type 2 diabetes. Studies of patients with type 2 diabetes are underway, and due to report soon, on both blood pressure and lipid interventions and will be important in filling this considerable evidence gap.

The evaluation of extrapolated evidence and the potential disbenefits (such as adverse events) had to be carefully considered by the development groups. Box 2 (below) shows the types of evidence they considered. Because of the need to extrapolate evidence, many of the recommendations have lower gradings than might be expected. This does not mean that they are not clinically very important.

Box 2: Types of evidence considered

For blood pressure and lipid interventions

  • Randomised controlled trials of primary prevention of coronary heart disease in general populations, with end points of CHD events and all-cause mortality
  • Epidemiological and physiological evidence which supports extrapolation and synthesis of trial evidence in formulating treatment recommendations
  • Expert and practitioner opinion, especially in discussion about extrapolation from trial data

For lipid interventions

  • Randomised controlled trials of secondary prevention of coronary heart disease in general populations, with end points of CHD events and all-cause mortality
  • Subgroup analysis of subjects from trials who were known to have type 2 diabetes

Managing blood pressure

The management of blood pressure in individuals with type 2 diabetes can usually be considered a primary prevention task.

The development group defined the target blood pressure level for most individuals with type 2 diabetes as 140/80 mmHg. For patients with microalbuminuria, the target level was set at 135/75 mmHg.

The development group recognised the difficulties involved in achieving these targets, which were based on evidence from hypertension intervention trials as well as the United Kingdom Prospective Diabetes Study.

Again, there was a paucity of trials which studied specific populations of individuals with type 2 diabetes, so there was considerable discussion about the appropriateness and applicability of extrapolated findings. Profiles of individuals with type 2 diabetes and raised blood pressure differ from those with raised blood pressure but without diabetes, and this will have an impact on effectiveness of treatment.

Managing blood lipids

In developing the recommendations for managing lipid levels, the guideline development group was hampered by a lack of homogeneity in the trial evidence. Most trials had different entry criteria in terms of HDL cholesterol, LDL cholesterol and triglyceride levels, and used different outcomes and treatment doses. These differences meant that it was not possible to recommend specific drugs in classes such as the statins, an issue of key importance given the varying costs and possible impact on prescribing budgets.

The group also found a lack of long-term data on clinical effectiveness and safety of statins and fibrates, which meant that it was not possible to recommend some treatments; for example, sufficient data are not yet available to support the use of fibrates in primary prevention of coronary heart disease.

The difficulties presented by these considerations were exacerbated because lipid profiles in individuals with type 2 diabetes may differ from those of the general population, a factor which has implications for the effectiveness of some interventions.

Anti-platelet therapy

The guideline provides a useful reminder that anti-platelet therapy is an important part of management of type 2 diabetes, as with any patient at risk of coronary heart disease. Evidence from general population studies and subgroup analyses of individuals with diabetes provided the evidence base for this recommendation.

Key recommendations

Such complex care areas resulted in many key recommendations concerning assessment and management of overall cardiovascular risk; assessment of blood pressure and lipids; management of normal and high blood pressure; management of normal and adverse lipid profiles, including lifestyle and pharmacological management. The algorithms (Figures 1 and 2, below) capture these key recommendations and are useful tools in working through complex decisions.

Figure 1: Algorithm for the management of blood pressure in patients with type 2 diabetes
Figure 2: Algorithm for the management of blood lipids in patients with type 2 diabetes

How will the guideline improve patient care?

The blood pressure and lipids guideline is one of a series published by NICE,5 which also covers the early management of retinopathy, renal disease and blood glucose in type 2 diabetes. Foot care was covered in an earlier guideline published by the RCGP6 which is being updated by NICE for issue in late 2003. All the guidelines take a risk-based approach to the management of type 2 diabetes.

By placing the emphasis on risk and highlighting the impact of cardiovascular disease in individuals with type 2 diabetes, this guideline provides a framework of clear recommendations to enable healthcare professionals to manage the condition effectively. This should help prevent or delay the onset of many of the complications associated with type 2 diabetes, and lessen the burden of the condition for patients and the NHS.

The guideline also contains audit criteria, which may provide a useful starting point for improving delivery of care. Challenging as these criteria may be for many healthcare teams they should only be seen as a starting point. The aim should be to shift the emphasis from measuring process to considering – and importantly measuring – outcomes. The guideline also provides a list of key areas for future research (Box 3, below).

Box 3: Areas for future research

Blood pressure management

  • Is there an optimal screening interval for blood pressure in individuals with type 2 diabetes and if so, what is it?
  • Does the screening interval vary by group (for example, severity of diabetes, age, life expectancy, ethnicity, current treatment)? Does it differ for screening versus monitoring?
  • Are there any advantages for automated (including 24-hour ambulatory patient self-testing) over standard blood pressure measurement?
  • What thresholds versus risks should be used for deciding on therapy?
  • Do adequate UK data exist to define risk based on ethnic group, age, sex, smoking habit, and other cardiovascular risks (for example, left ventricular hypertrophy)?

Lipid management

  • How often should lipid profiles be measured in patients on lipid-modifying treatment?
  • Should any biochemical monitoring for adverse effects of lipid-modifying treatment be undertaken?
  • Should HDL-C be a criterion for statin or fibrate treatment?
  • Do fibrates decrease mortality and coronary events in patients with diabetes and dyslipidaemia? If they do, are they effective in patients without a history of cardiovascular disease?
  • In which patients is combined statin and fibrate therapy effective? What are the short and long term adverse effects of combination therapy?
  • What behavioural interventions in patients with type 2 diabetes can reduce coronary heart disease risk?
  • How can CHD risk be predicted more accurately in individuals with type 2 diabetes in the UK, taking into account recently identified risk factors (e.g. microalbuminuria) and differences in risk between ethnic groups?

A separate guideline has been produced for patients and carers, and is intended to assist the partnership between patient and healthcare professional, an essential element in delivering effective care.

Promoting best practice

The series of guidelines on diabetes has tried to emphasise that type 2 diabetes is not just a problem of blood glucose control, but a complex condition that can lead to premature morbidity and mortality, especially from cardiovascular disease.

However, the guidelines have also shown that, while management may be complex and challenging for healthcare professionals and patients, there are gains to be made and it is possible to improve the healthy-life expectancy of patients with type 2 diabetes.

National Institute for Clinical Excellence. Management of Type 2 Diabetes - management of blood pressure and blood lipids. Inherited Clinical Guideline H. London: NICE, 2002. Copies of the guideline can be downloaded from the NICE website: www.nice.org.uk

This work was undertaken by ScHARR, University of Sheffield, which received funding from the RCGP on behalf of NICE. The views expressed in this article are those of the authors and not necessarily those of either the RCGP or NICE.

References

  1. Audit Commission. Testing Times: a review of diabetes services in England and Wales. London: Audit Commission, 2000.
  2. McIntosh A, Hutchinson A, Feder G et al. Clinical guidelines and evidence review for Type 2 diabetes: lipids management. Sheffield: ScHARR, University of Sheffield: 2002. www.nice.org.uk
  3. Hutchinson A, McIntosh A, Griffiths C et al. Clinical guidelines and evidence review for Type 2 diabetes: Blood pressure management. Sheffield: ScHARR, University of Sheffield: 2002. www.nice.org.uk
  4. British National Formulary. 44th edition, London: British Medical Association and the Royal Pharmaceutical Society of Great Britain, 2002.
  5. Type 2 diabetes guidelines series available at: www.nice.org.uk
  6. Hutchinson A, McIntosh A, Feder G, Home PD et al. Clinical Guidelines for Type 2 Diabetes: Prevention and Management of Foot Problems. London: Royal College of General Practitioners, 2000.

Guidelines in Practice, March 2003, Volume 6(3)
© 2003 MGP Ltd
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