Strengths and limitations of the study
This study involved a large number of people with type 2 diabetes at 42 practices. Trial participants have been previously compared with non-participants from the same practices and participating and non-participating practices revealing that the study participants are representative of the type 2 diabetic population in Nottingham.18 Therefore, these results may be generalisable to the population with type 2 diabetes in Nottingham, and to other urban populations in the UK. The trial achieved a high follow-up rate. As data were collected by face-to-face contact between participants and researchers, very few data were missing.
From discussions with practice nurses and GPs who took part in the study it was recognised that the algorithm was not used in the same way in all practices. In some practices the intervention was predominantly used by the nurses with GPs only involved in prescribing. In others, patients were seen by both the nurse and the GP, while in some practices the practice nurse had minimal involvement with the doctor both monitoring BP and adjusting treatment. These differences were due to a number of factors including the level of experience and training of the practice nurses and GPs, practice organisation, and levels of staffing. This situation reflects the reality of service provision in primary care and is likely to reflect the way this algorithm would be applied in practice.
One possible explanation for this trial's failure to demonstrate improvements in BP control is that practice nurses and GPs may not have complied with the treatment algorithm. The study's findings of a higher rate of BP-related consultations and some evidence of a greater proportion of participants receiving more than 50% of the maximum dose of antihypertensive drugs in the intervention arm suggests that practice nurses and GPs did comply with the algorithm, at least to some degree.
However, full compliance would have resulted in the prescription of a greater number of antihypertensive drugs. Participants reaching the end of the treatment algorithm would receive six antihypertensive drugs, but only three intervention arm participants received this number of drugs. It is possible that nurses and GPs increased the dose of antihypertensives that were already prescribed in accordance with the algorithm, but did not prescribe additional classes of antihypertensive drugs, or that participants preferred increases in the dose of existing medications to taking additional drugs. Although the study intervention included training for practice nurses in the use of the algorithm and guidelines about its use, it did not include other elements which may have increased compliance, such as reminders and feedback.19 Similarly, the intervention did not include specific strategies aimed at educating patients or increasing their involvement in treatment decisions, and it is possible that such interventions could have resulted in better patient outcomes.19
There is concern that guidelines for managing hypertension will result in patients requiring up to four, or possibly more, classes of antihypertensive drugs to meet current targets,20,21 with diminishing benefits in terms of cardiovascular risk for additional drugs and increasing risks of side effects or interactions.21 The population in this study was already receiving prescriptions for a high number of antihypertensive drugs. At follow up one-third of those prescribed antihypertensive drugs were prescribed three or more drugs. For some participants the decision not to prescribe additional drugs may reflect a rational and deliberate decision by both patient and practitioner after considering the level of absolute risk of an adverse event against the inconvenience and risk of side effects and interactions. The algorithm was based on titrating drugs up to the maximum tolerated dose before adding an additional antihypertensive whereas the more recent BHS guidelines advocate combining drugs at lower doses.5 The finding that participants in the intervention arm did not receive additional antihypertensive drugs may indicate potential difficulties in compliance with the most recent BHS guidelines.
A post-hoc power calculation using data from the trial and an intracluster correlation coefficient of 0.035 for controlled BP, an average cluster size of 34, and 34% of control group participants having well controlled BP, indicate an 82% power to detect an absolute difference of 11% in the percentage with controlled BP at the 5% significance level. It was therefore considered unlikely that insufficient power can explain the study's findings. However, these findings do not exclude the possibility that the intervention increases the percentage of participants with controlled BP by a smaller percentage, which may be clinically important. While this may be true, the magnitude of effect that was powered to detect was much smaller than demonstrated by secondary care studies demonstrating the benefits of nurse-led hypertension clinics.10
Comparison with existing literature
These findings should be viewed in the context of two recent trials. The first demonstrated that a secondary care nurse-led clinic could result in significant reductions in BP10 compared with usual care. This trial achieved five follow-up visits for each participant over 6 months. The second trial of a nurse-led intervention, which failed to demonstrate significant reductions in blood pressure, but demonstrated improvements in other cardiovascular risk factors, achieved only a median of two follow-up visits over a 1-year period.11 It is therefore possible that the current study's negative findings may relate to either the intensity or the duration of the intervention. Despite a significantly higher rate of consultations among intervention arm participants than those in the control arm, some participants may not have reached the point at which additional antihypertensives were recommended, especially as treatment changes are likely to have been based on repeated BP measurements rather than single measurements. However, onethird of intervention arm participants had six or more consultations over the 1-year period and the feasibility, and acceptability to patients, of increasing the consultation rate further in primary care in the UK is unknown.
A further potential explanation for the contrasting findings between the current trial and those of the secondary care nurse-led clinic may be differences in baseline blood pressure. Baseline BP in both treatment arms in this trial (mean 158/87 mmHg and 161/88 mmHg in the control and intervention arms, respectively)10 was considerably higher than in the current trial. Consequently, there was greater potential for improvement.
Overall these data suggest that improving BP control in practice is not as easy as suggested by data extrapolated from large clinical trials, such as the UKPDS.6 It is likely that improvements in BP control would be more expensive than was suggested in the health economic analysis of UKPDS data.6
Implications for future research and clinical practice
This trial has demonstrated that improvements in BP control achieved by specialist nurse-led clinics in secondary care may not be translatable to people with type 2 diabetes in primary care settings. It is possible that strategies, such as feedback from health professionals and reminders, could enhance practitioner compliance with such an algorithm. A nurse-led intervention to improve patient medication compliance, or patient education and greater involvement in decision-making could also enhance patient compliance, but such strategies require further evaluation.22,23,24 Strategies aimed at getting practices to prescribe, and patients to take more antihypertensive drugs may have a limited effect as many patients are already prescribed three or more drugs. A considerable proportion of people with diabetes are not achieving recommended BP targets and the provision of guidelines and training in their use seem unlikely to substantially increase this in the near future.
