a Epidemiological and Health Services Research Department, Research Coordination, Mexican Institute of Social Security, Mexico.
b Health Promotion Research Unit, London School of Hygiene and Tropical Medicine, London, UK.
c Environmental Epidemiology Unit, London School of Hygiene and Tropical Medicine, London, UK.
d Medical Research Unit on Ageing, Research Coordination, Mexican Institute of Social Security, Mexico. Currently at University of Leicester.
e Research Coordination, Mexican Institute of Social Security, Mexico.
Dr Margaret Thorogood, Health Promotion Research Unit, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1 7HT, UK. E-mail: M.Thorogood{at}lshtm.ac.uk
Abstract
Background In Mexico, hypertension is a major cause of disability and death in the elderly, but the most effective way to promote behaviour change in old people is unknown. Low resource interventions that are effective in normal healthcare settings are urgently needed. We report the results of a randomized trial of nurse-provided health and lifestyle advice during home visits to elderly people with hypertension in Mexico City.
Methods Subjects were 718 people with hypertension aged 60 years, who were residents of Mexico City and were registered with the Family Medicine Clinics of the Mexican Institute of Social Security (IMSS). A randomized controlled trial was carried out in which the intervention group was offered nurse visits over 6 months with blood pressure checks and negotiated lifestyle changes. The control group continued to receive usual care.
Results After 6 months, 36.5% of the intervention versus 6.8% of the control group had a blood pressure of <160/90 mmHg. The difference in the mean change in systolic blood pressure was 3.31 mmHg (P = 0.03, 95% CI : 6.32, 0.29) and the same difference in diastolic blood pressure was 3.67 mmHg (P = 0.00, 95% CI : 5.22, 2.12). Weight and sodium excretion fell more in the intervention group, but the difference was not significant.
Conclusions Nurse home visits are effective in reducing blood pressure in hypertensive patients aged 60 years.
Keywords Hypertension, elderly, Mexico
Accepted 23 April 2001
Latin America has an ageing population and consequently a rapid increase in non-communicable diseases. In Mexico, hypertension is now a major cause of disability and death in the elderly.1,2 Lifestyle intervention trials indicate effective ways to reduce blood pressure in elderly people, and guidelines for the management of hypertension recommend lifestyle changes as well as pharmacological treatment.35 However, the most effective way to promote behaviour change in old people in Mexico is unknown. Lifestyle interventions that use considerable resources, such as nutritionists, physical therapists or provision of food69 have been evaluated in efficacy trials, but whether lower resource interventions are effective in normal healthcare settings remains to be tested.
The Mexican Institute of Social Security (IMSS) has been part of the Health and Social Security System of Mexico since 1942, and currently covers 53% of the population. The proportion of elderly people covered by IMSS is higher compared with the rest of the country, and hypertension represents a serious health burden. For this reason innovative strategies for the care of elderly people with hypertension are an urgent necessity.
We report here the results of a randomized trial of an intervention to provide health and lifestyle advice during home visits to elderly people with hypertension in Mexico City. The aims of the study were to assess the effectiveness of the intervention in reducing blood pressure and to analyse the consequences in terms of weight and salt reduction and increase in physical activity.
Participants and Methods
Participants were men and women insured by the IMSS, and registered with one of 12 Family Medicine Centres run by the Institute in Mexico City. Participants were selected by multistage random sampling, first by Family Medicine Centre, and then by age-stratified sampling within the population served by each Family Medicine Centre, representing the population in IMSS in Mexico City. They were aged 60 years and were found to have either a mean systolic blood pressure (SBP) of
160 mmHg or a diastolic blood pressure (DBP) of
90 mmHg, or both, at screening. Screening took place over 6 months, with home-based blood pressure measurements made by trained nurses not involved in the intervention stage of the trial. A detailed description of this screening process has been reported.10 After informed consent was obtained, participants were randomly allocated to an intervention or a usual care group. Randomization was carried out by computer and was concealed until screening and recruitment were complete.
Measurement of baseline and outcome variables
Reduction in blood pressure was the primary goal of the intervention. Secondary outcomes were reductions in weight and salt excretion and increase in reported physical activity.
Blood pressure at screening and at follow-up was measured with a mercury sphygmomanometer. Three blood pressure measurements were carried out, twice seated and once after standing for at least 2 minutes, using the techniques recommended by the British Hypertension Society.11 Weight was measured with a Seca scale. Height was measured with a plastic stadiometer, recording to the nearest millimetre. Sodium in urine was measured in single morning samples using the autoprocessor Beckman Syncron CX5, with the technique of selective ion in samples of 69UL.12 The technician was blinded to the allocation group of the participants. Level of physical activity was measured using an adapted questionnaire (Hillsdon M, personal communication) that was divided into three sections: housework, activities outside the home, and recreational activities. Participants reported number and duration of occasions of activity per week in the last 4 weeks. Data on pharmacological treatment, socio-demographic variables, co-morbidity, and risk factors were collected at baseline. Outcome measurements were made by the same group of nurses, who were not otherwise involved in the trial, and were not told the trial group allocation of participants. Data collection began in January 1998 and finished in June 1999.
The intervention
Participants in the intervention group received regular visits from a nurse over 6 months. The nurses were first given training about ageing, clinical aspects of hypertension, personal interviews, health behaviour change models, process of negotiation and ethical aspects of home visits. During visits, the nurse measured blood pressure and the nurse and patient reviewed information from the baseline health check, and discussed possible lifestyle changes. The nurses tried to guide their patients to a healthier lifestyle and suggested different alternative ways to achieve the changes and negotiated specific targets. The nurse also reviewed the pharmacological treatment and adherence was encouraged. The patient led the process of negotiation, while the nurse provided information about risks and benefits from lifestyle change. The visits took place between once a month and fortnightly, with the exact timing decided by the patient and nurse through discussion. Quality control was provided through tape and video recorded interviews. The control group received a mailed pamphlet about hypertension. All patients continued to receive usual care from family physicians in the Institute's clinics.
Statistical analysis
Statistical significance of differences in mean changes of numerical variables in intervention and control groups was assessed using t-tests, following verification that distributions were reasonably represented by the Gaussian model. The statistical significance of differences in changes in proportions reporting physical activity and pharmacological treatment was assessed by logistic regression of final reported exercise and treatment on intervention, allowing for initial exercise by inclusion in the model.
The associations of intermediate and baseline variables with change in blood pressure, and the modification of the treatment effect by other variables was investigated in multiple linear regression analyses.
Most analyses excluded subjects who dropped out before the final assessment, but intention-to-treat analyses including all subjects are also reported for key comparisons.
Ethics
The study was approved by the Research Committee of the IMSS and the Ethics Committee of the London School of Hygiene and Tropical Medicine.
Results
There were 911 subjects eligible for the trial at screening. Twenty-eight subjects (3.1%) died, 101 people (11.1%) moved away and 64 people (7%) refused to participate (Figure 1). Thus, 718 subjects were recruited and randomized; 364 (50.7%) were allocated to intervention and 354 (49.3%) to control. Nineteen intervention and 16 control participants did not complete the final evaluation (Figure 1
). Table 1
shows the baseline characteristics in the two arms. Differences between groups were small, except in the proportion of people living alone.
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Although the mean reduction in weight in the intervention group was small and not statistically significant (1.06, 95% CI : 2.18, 0.04), the difference between this and the small weight gain in the controls was on the borderline of statistical significance (P = 0.05). Sodium excretion showed a similar pattern, but the difference did not approach statistical significance (5.85, 95% CI : 14.1, 2.37, P = 0.16). Differences within and between groups are presented in Table 2.
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This pragmatic trial tested the effectiveness of an intervention (home visits by nurses) that could be introduced widely in the health services in Mexico. The intervention significantly reduced SBP and DBP levels, with a mean reduction of 3.3 mmHg and of 3.7 mmHg, respectively. Significantly more participants in the intervention group reported that they had taken up walking and the proportion of participants who began anti-hypertensive drug treatment, having not been on treatment, was also significantly greater.
It is unlikely that the differences in SBP and DBP between the intervention and control group were due to an accommodation effect since the baseline and final measurements were carried out by a separate group of nurses, who had not been involved in the intervention, and would have been unknown to the participants. All the baseline and final measurements were carried out in the same conditions. The initial intention to use random zero sphygmomanometers was abandoned because they proved to be easily decalibrated when carried around and also because of the effect of underestimation of the blood pressure.13 Mercury sphygmomanometers, the best equipment available in Mexico at the time of the trial, were used.
A meta-analysis of pharmacological trials in hypertension found a 15.8 mmHg reduction in SBP and 5.6 mmHg reduction in DBP.14 Trials of pharmacological treatment for isolated systolic hypertension have found falls in blood pressure of between 10 and 12 mmHg in SBP and 4 and 5 mmHg in DBP.15,16 The differences found in this trial were smaller compared with the pharmacological trials, but higher compared with trials using lifestyle change strategies.17,18
Our results are in accord with previous findings that blood pressure lowering can be achieved with moderate intensity exercise.6,14,19,20 However, the intervention effect was only partially explained in the regression analysis by measured intermediate variables and it may have had an impact through other mechanisms which were not measured. One such measure is the improvement in participants' drugs adherence. The trial also found some differences in drug prescriptions, so the information provided by the nurses to the family physician may have an effect on these patterns.
Changes in body weight and sodium excretion were not significant, but this may be because the duration of the intervention was too brief to see a substantial impact. There is some suggestion in the data that weight and sodium intake were falling in the intervention group (Table 2). A significant change in sodium excretion might have been detected through a more accurate measurement of 24-h urine collection, but that was not possible in this trial of elderly people. Future trials of behaviour change should be planned with a longer duration to improve the likelihood of detecting change and assessing long-term sustainability of blood pressure reductions.
The absolute levels of risk associated with hypertension are higher in older people, so the potential benefits of blood pressure reduction are greater. A meta-analysis21 found that an average reduction of 1213 mmHg in SBP (mean age = 64 years) was associated with a 21% reduction in coronary heart disease and a 37% reduction in stroke. If the reductions in blood pressure observed in this trial are sustainable long term, then they may result in a reduction in the risk of stroke of nearly 10%, and a reduction of the risk in coronary heart disease of 5%.
The IMSS is the biggest social security institution in Mexico. It covers workers in almost all the private sector, along with their families. Other social security systems and the Ministry of Health cover the remaining 37%. About 10% of the Mexican population do not have access to the health system. The IMSS covers a disproportionately high number of elderly people, and effective strategies for their care are urgently needed. The intervention evaluated in this study has been costed at 101 902 pesos (US$11 137), or 35 pesos (US$4) per patient, giving a cost effectiveness ratio of 10 pesos (95% CI : 1296) (US$1) per millimetre reduction in SBP (Wonderling D, personal communication). Whether this represents good value compared with other health interventions remains to be determined. Certainly if this intervention is reproduced and extended to an integral care plan for the elderly, the opportunity cost has to be considered and reallocation of financial resources will be necessary as well as reallocation of human resources.
Recognition that health can be promoted for the elderly, has increased in the last few years22 but the idea that health promotion strategies for the elderly will save money is simplistic. Such strategies will incur extra cost but if they are effective they will improve the quality of life for the elderly and decrease the prevalence of disability.23
KEY MESSAGES What is already known
What this trial adds
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Acknowledgments
Special thanks to all the participants and to the supervisor nurses, computer offices and administrative staff of the Medical Research Unit on Ageing, Mexican Institute of Social Security. This trial was funded (26125-M) by the National Council of Science and Technology, Mexico (CONACYT) and the Mexican Institute of Social Security (IMSS).
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