However, an absence of evidence, which can lead to the catchphrase “We just don’t know”, does not mean we can’t be rational and use the best evidence available in our approach to managing our patients’ blood pressure (BP).
The underlying principle is the greatest good to the greatest number.
Let’s get back to basics. Why do we treat elevated blood pressure?
We treat it to avoid target organ damage through direct effects such as hypertensive retinopathy and nephropathy, and atheroma-mediated acute adverse events such as heart attacks and strokes. High blood pressure in the absence of these manifestations is a risk factor and not a disease.
In secondary prevention, where disease is evident, then a person is at high risk of serious adverse events and warrants blood pressure lowering, even at levels usually considered normal, as long as hypotension does not become evident.
Target blood pressure levels are set where benefit has been shown, and benefit has not been shown at lower levels. As reported in MJA InSight last week, a recent meta-analysis underscores this, showing more intense BP lowering leads to better clinical outcomes. In recognition of the difficulty — nigh impossibility — of getting everyone to an ideal systolic blood pressure of 115 mmHg, higher levels are tolerated and targeted.
In primary prevention, which is the circumstance for the majority of individuals we treat, cardiovascular disease (CVD) is not evident but may be present in some. The latter are the individuals who are most likely to have a heart attack or stroke and, because there are more of them than of those with known disease, on a population basis, that is where most events can be prevented.
To identify who is most likely to have covert disease you have to consider not only their blood pressure but also the other major determinants of CVD risk such as smoking status, age, sex, blood lipids and diabetes status. This cannot be done intuitively but requires an absolute calculator such as the Australian risk calculator.
Who will most likely benefit from blood pressure-lowering (and other drug) therapy is best determined using this approach. It also means that those who are least likely to benefit from medication can avoid it.
Why many doctors don’t treat hypertension to the point where target blood pressure levels are reached and maintained is a complex interaction of doctor, patient and system factors. What we have best control over is our own behaviour.
We often start treatment but run out of puff as we approach target blood pressure levels. This has been known as therapeutic inertia but is perhaps better known as foregone therapeutic benefit: we would be likely to commence therapy if the patient presented de novo with these levels but we are willing to accept them in a patient who is already on treatment.
Our experience also makes us fear the adverse effects of blood pressure-lowering medication on our patients, particularly the elderly.
However, the HYVET (Hypertension in the very elderly) trial demonstrated in a randomised placebo-controlled study in the very elderly that the burden of adverse events lay in the placebo arm of the trial and that benefit therefore outweighs harm in treating blood pressure in this group.
Postural hypotension can be avoided by doing standing BPs in the clinic or asking the patient to check their BP with a home monitor if they are symptomatic and using standing BPs as targets if the condition is found.
Once a patient has been shown to warrant BP-lowering medication through overt disease or high-risk status, then treating for this and other risk factors remains a sound principle.
Professor Mark Nelson is the head of the discipline of general practice at the University of Tasmania.
Posted 3 September 2012