By Christopher Labos, MD, CM, MSc

Blood pressure. If you're a primary care provider trying to do right by your patients, you might be understandably confused by the current mishmash of guidelines with different blood pressure targets. But as chaotic as things are, at least it's not the 1930s, when you might hear John Hay give a lecture to the BMA and say, "The greatest danger to a man with high blood pressure lies in its discovery, because then some fool is certain to try and reduce it."

Yeah, he said that. But what happened in the 1930s stays in the 1930s. And now we can at least agree that we should be treating high blood pressure. But what's the goal we should be aiming for? This is On Second Thought.

We've come a long way since FDR was recording blood pressures of 200 and his doctor prescribed him barbiturates and massage therapy.

That s#$# don't fly no more. Over the past hundred years, we have become much more aggressive in treating blood pressure. Remember the Oslo study? It defined mild hypertension as a blood pressure between 150 and 180 mm Hg. Now, those numbers send people screaming to the emergency room. So, let's acknowledge that things are substantially better than they once were. Let's agree on that and we can start to heal this nation again.

Before we get into the numbers, when we're treating blood pressure, let's make a few points about measuring it. Obviously, to treat something, you have to measure it properly. Two recent trials have illustrated that these details matter a lot.

The Cuff(SZ) randomized crossover trial — and it took me a minute to realize that Cuff(SZ) meant cuff size, so bravo, Ishigami et al — showed that picking the wrong cuff size could affect BP measurements by 4.5 points if you were one size off. If you were two sizes too small, you overestimated BP by almost 20 points.

Add on here another recent study, the ARMS crossover randomized clinical trial, looking at how arm position affected BP measures. If the arm was resting on your lap or hanging by your side, that overestimated blood pressure by 4 and 6.5 points. So sometimes you have to remember the fundamentals: cuff size, arm position — it might make the difference between increasing or maintaining the patient's meds.

But on to the main show. What numbers should we be aiming for? We no longer live in the "BP 200, the president's going to have a stroke" world of the 1940s, and even a BP of 150 is considered quite high these days. Studies like the MRC trial, INVEST, and SPRINT have pushed BP targets ever lower. SPRINT, in particular, randomized patients to a blood pressure target under 120 systolic vs under 140 systolic, and the under-120 arm won out with fewer cardiovascular events and lower all-cause mortality.

Pretty definitive slam dunk. But the more intensive treatment came with more hypotension, syncope, and kidney injury, because there is no free lunch in medicine. And ditto with BPROAD, just published and presented at the AHA annual meeting. A diabetic population randomized to 120 vs 140 as a BP target showed that more aggressive treatment was better.

Fewer cardiovascular events, like stroke, but no mortality difference, and more hypotension. So a cardiovascular benefit at the cost of more side effects. Now, like all cardiologists, my motto is "Save the heart and screw the kidney." But if you do care about the other organs in this meat sack that we call a human body, the question you need to wrestle with is, how much do you value cardiovascular protection vs how willing are you to tolerate side effects?

Hypotension may not sound dangerous, but gravity is an unforgiving mistress. If you painstakingly compile the summary of the various BP guidelines for easy perusal, you would notice something critical: One, I have too much free time on my hands; two, the disagreements are not really all that profound.

Arguing about 120 vs 130 vs 140 is not the same as saying, "Drugs schmugs; a good massage will fix what ails you, and here are some addictive sleeping pills for good measure." Physicians from the 1930s were a little sketch. So much of this controversy is about how you define high-risk patients and what are the age cutoffs.

Basically, the cardiovascular guidelines say, "Treat them all and let God sort it out" because they care about cardiovascular events and are concerned about cardiovascular endpoints. Whereas general practice guidelines put more emphasis on potential side effects and admittedly tend to treat a not so high-risk population, so they have laxer targets.

A 2014 analysis from the Blood Pressure Lowering Treatment Trialists' Collaboration had a good mathematical way of explaining this problem. Now, lowering blood pressure is obviously a good thing. That prevents heart attacks, strokes, kidney failure, and all that. Please don't let hypertension denialism become a thing.

Let's start with the basics. Treating high blood pressure led to a 15% to 18% decrease in cardiovascular events, pretty consistently across all risk categories, and other analyses have found that every 5-point decrease in blood pressure gives you about a 10% decrease in major cardiovascular events on the relative-risk scale.

While the benefits are pretty consistent across all groups, that difference in baseline risk translates into different absolute benefits. In the paper, when the population was divided into four different groups based on their cardiovascular risk, the absolute risk reduction in the lowest-risk group was 14 fewer cardiovascular events if you treat 1000 patients for 5 years.

With each higher-risk group, it was 20 fewer, 24 fewer, and 38 fewer. At the lowest-risk group, the number needed to treat was 71, 50, 42, and 26 fewer cardiovascular events with 5 years of treatment.

And herein lies the secret to the disagreement: If you have a high-risk patient, there is a big benefit to bringing that blood pressure down from 135 to 130. Whereas for a low-risk patient, it probably doesn't matter as much. And the cardiovascular benefits are going to be offset by the side effects and the risks for hypotension.

Of course, there's a simple solution to this dilemma: Just speak to the patient in front of you. Treat high blood pressure, and if your patient's blood pressure drops or they get dizzy or have fainting spells, then just ease up on the meds. It's not rocket science; it's just cardiology.

Arguing about five millimeters of mercury of blood pressure is probably less important from the public health perspective than the fact that tens of millions of people in the United States are unaware that they have hypertension, and even those diagnosed are being inadequately treated.

So, let's all do better as a medical community. Nobody should have untreated hypertension in this day and age. It's not the 1930s.