A Cuff by Any Other Name

Sphyg. Cuff. Gauge. BP Instrument: These are just some of the alternative names used to describe the device technically known as a sphygmomanometer.

No matter what you call it, one of the most important components of a blood pressure instrument – whether it be a manual sphygmomanometer or an automated non invasive blood pressure (NIBP) monitor – is the cuff: the portion that wraps around the patient’s limb and occludes the artery. In automated NIBP, the cuff does double duty, not only imparting air pressure and occluding the artery, but also acting as the “sensor.” In other words, transmitting the vibrations – the pressure pulse wave form – that are the basis for automatic oscillometric measurement.

Regardless of technology, the cuff is so vital to accurate measurement that using the wrong size or positioning it incorrectly can lead to measurement errors. Sometimes, significant errors.

So let’s talk about positioning of the cuff. Remember, the purpose of the cuff is to occlude the artery. To ensure it does just that, AAMI and the AHA both recommend that the bladder (the inflatable bag, or segment inside the cuff) be centered over the brachial artery. As such, the cuff artery mark should be positioned over the bladder’s lengthwise midpoint. You’d be surprised how many imported cuffs have the artery mark mis-positioned.

Arm cuffs should be wrapped around the bicep about one inch above the antecubital fold (elbow crease). In manual instruments the tube or tubes should protrude towards the wrist (in automated instruments it depends on where the monitor is positioned). The cuff should be snug, but not tight; you should be able to get one to two fingers between the arm and the cuff. Cuffs should always be wrapped around a bare limb, though be careful when rolling up sleeves as they might impede blood flow and impact measurement accuracy.

But proper positioning isn’t everything: The cuff needs to be correctly sized for the patient. Although AAMI and AHA both provide guidance on sizing, they don’t actually delineate specific sizes. Instead they refer to length/width ratios and other complex recommendations. The result is that cuff sizes and the names used to describe them (such as adult) vary by manufacturer, much the way women’s clothing sizes vary. In other words, an ADC adult cuff might be sized differently than the adult cuff of a competing brand.

So how do you know which cuff you should use? Most manufacturers print both a size name and a limb range in centimeters. Because the limb range is absolute, that’s what you should go by when determining fit or the cuffs you should have in your collection.

In practice, of course, you’ll use the cuff’s marking system to show you if you have the right fit.

Most modern cuffs have an “index” line and two “range” lines to help determine fit. The range lines consist of an inner line delineating the smallest intended limb and an outer for the largest. When the cuff is properly sized, the index line will fall somewhere between the two range lines. If the cuff is too small, the index line will fall outside the outside range line. Too big and the index line falls inside the inside range line.

So, what about those cuff names? In the 1970s, market leaders assigned names to cover the ranges. The most popular names were newborn, infant, child, adult, large adult (originally termed obese), and thigh. With the development of neonatal cuffs in the late ’80s and early ’90s, manufacturers serving the acute care sector refined the names for the cuffs: infant, child, small adult, adult, large adult, and thigh. It is important to note that while the three smaller cuffs were renamed, their relative sizes remained about the same. Many imported sphygs still use the older naming system. ADC is one of the few globally sourced sphyg manufacturers to have updated its cuff naming for consistency with the acute care markets.

In any clinical setting, we recommend a minimum of three cuffs: the ones now called small adult, adult, and large adult, covering patient limbs from 19 cm to 50 cm. Of course, pediatric specialists need a smaller range (infant, child, small adult) and bariatric specialists a larger one (adult, large adult, and thigh, or our new bariatric). ER and EMS applications that might treat patients of any size/age group should have at least four sizes (child, small adult, adult, large adult) but would probably be advised to have all six. Below I’ve listed ADC’s Adcuff names and size ranges, along with the “industry standard” colors. We produce cuffs in up to a dozen colors and a number of prints to allow for size or departmental coding, or simply to suit personal taste.