The accurate, reproducible measurement of blood pressure in any patient is integral to making the diagnosis of hypertension and to determining when treatment is indicated. However, this core component of medical and nursing practice is frequently assigned to the least trained care provider and, even when done by the most experienced authors and researchers, is rarely performed correctly.^6,7 Training of all levels of clinicians to improve noninvasive blood pressure assessment skills is critical to avoid misdiagnosis of hypertension and to prevent over- or undertreatment.

Blood pressure assessment using an inflatable bladder placed over the brachial artery and listening for characteristics of sounds audible above the artery has been the mainstay of blood pressure measurements for over a century. In 1905, Nikolai Korotkoff described a procedure to auscultate the sounds emitted near the artery when it is occluded and subsequently allowed to slowly fill. He then correlated these findings with the associated readings on the sphygmomanometer. He termed the sounds “Korotkoff” sounds and identified five distinct characteristics or phases (Table 7-1). That the procedure has remained essentially unchanged for decades is a tribute to the simplicity of manual blood pressure measurement using mercury, but also may reflect the fallibility of even a simple technology to produce accurate results.

The mercury sphygmomanometer is considered the gold standard in noninvasive blood pressure technology and is superior to aneroid, digital, and/or oscillometric machines. Sphygmomanometers include an inflatable cuffed bladder, a bulb for inflating the bladder, a valve to control the amount of air in the bladder,
and a gauge from which blood pressure can be read and recorded. The inflated cuff occludes arterial blood flow and allows auscultation of the artery via stethoscope.⁸ The mercury sphygmomanometer is made by placing liquid mercury in a glass cylinder to create a vertical column. Mercury is displaced into the column when pressure is placed on the opposite side. The pressure required to move liquid mercury up the glass column against the force of gravity is measured in “millimeters of mercury” (mmHg), the internationally recognized standard unit of pressure employed when assessing and recording blood pressures.

Mercury is a stable metal at room temperature and when sealed from the atmosphere. It requires little maintenance as long as it remains encased in the glass cylinder and the cylinder has no damage or leaks. Because it is a heavy metal, mercury is toxic to the environment and can cause devastating neurologic damage in infants, children, and adults. Therefore, state and federal agencies have implemented programs to educate industries that use mercury to consider replacement alternatives. There is also a national movement to sequester existing mercury manometers and thermometers and to remove them from the environment to prevent toxic spills in patient care areas.
The down side of the replacement campaign is the removal of one of the most accurate methods for measuring blood pressure.

To replace mercury manometers, facilities may select from a number of available devices such as manual “dial” aneroid pressure manometers or automated oscillometric devices that inflate the cuff, deflate the cuff, and calculate pressures based on data derived from arterial pulsations and proprietary algorithms. Both substitutes are known for inherent inaccuracies, with aneroid devices more likely to have greater margins of error than automated blood pressure devices.^9,10 However, it is not possible to determine the exact range of pressure variance based on monitor type, because almost all classes of non-mercury devices have sources of error. The result is erroneous blood pressure values that may be significantly inaccurate.¹¹ Thus, when measuring blood pressure on a patient who is hypertensive or may require antihypertensive medications, the method for monitoring should be standardized in order to optimize the quality of the results. Common errors in blood pressure measurement can be found in Table 7-2. To reduce the contribution of human error and faulty technique to blood pressure assessment, a list of recommendations for practice can be found in Box 7-1. Further, it is not unreasonable to validate the competence of medical, nursing, and allied professional staff in measuring blood pressure using a variety of devices.

Systolic blood pressure is measured at the first Korotkoff sound, where the first beat of the heart is heard. Diastolic blood pressure is measured at the value point where the sound disappears, which is the fifth Korotkoff sound. In rare patients, the fifth Korotkoff sound may be zero due to the hyperdynamic state of pregnancy. In those cases, the fourth Korotkoff sound (muffling of the sounds) should be used as the diastolic
value and should be documented as the source of the diastolic reading.⁷

The parturient should be in a sitting position with her legs uncrossed and feet flat on the floor or supported by a footrest. The arm used for blood pressure measurement should be completely supported by a table or pad, with the brachial artery of the arm positioned at the level of the patient’s right atrium. This landmark is known as the phlebostatic axis and is located at the intersection of the fourth intercostal space at the mid-axillary line. It approximates the level of the aorta and is the same reference point used to zero-reference invasive hemodynamic pressure tubing. The patient is allowed time (minimum, 10 minutes) to sit quietly without talking or moving to try to achieve a relaxed state prior to evaluation. Blood pressure evaluation then begins with location of the maximal impulse of the brachial artery by palpation. A blood pressure cuff of the correct size is placed above the brachial artery according to the artery placement marks on the inside of the cuff. The correct size for the bladder (not the cuff) is at least 80 percent of the circumference of the arm. The ratio of length to width should be 1.5 to 1; in other words, the length should be 1.5 times the width of the bladder.^7,12 Ideally, the clinician assessing blood pressure is sitting so that his or her eyes are at the level of the mercury meniscus of a sphygmomanometer or the numbers and dial of an aneroid manometer.

The radial artery is palpated at the point of maximal impulse, and the blood pressure cuff is inflated to 70 mmHg. The cuff is then quickly inflated in increments of 10 mmHg until the pulse is no longer palpable. It is important to note the pressure reading at which this occurs and the reading at which arterial pulsations return during deflation of the cuff. The bell of the stethoscope is placed over the strongest pulsation of the artery. The cuff is rapidly inflated 20 to 30 mmHg above the level where the pulse was no longer felt. The cuff is then deflated at a rate of 2 mmHg/sec until the first Korotkoff sound is heard (systole). Deflation of the cuff at 2 mmHg/sec continues until the Korotkoff sounds disappear (Korotkoff 5), which is diastole.¹² After the last sound is identified, the clinician continues to listen for additional sounds as pressure decreases at least another 10 mmHg. If no sounds are audible, rapid and complete deflation of the cuff is the endpoint. Systolic and diastolic pressures should be recorded to the nearest 2 mmHg.¹² Wait at least 1 minute between blood pressure measurements to allow venous emptying from the limb.

Initially, blood pressure should be measured in both arms to assess for differences between them. The arm with the highest pressure should be used for the duration of care. When patients are in a recumbent position in a hospital bed, it is important to follow the same procedure as outlined for patients in a sitting position. It is critical that the artery where blood pressure is measured be positioned at the level of the heart.

The study of hypertension in pregnancy has been hindered by a lack of agreement on a set of definitions to define subsets of the disease. It is difficult to interpret research findings when investigators use different criteria to identify preeclampsia and other hypertensive disorders. In an attempt to standardize terminology, professional organizations develop and publish independent classification systems for hypertension in pregnancy. The World Health Organization (WHO), the United Kingdom’s Royal College of Obstetricians and Gynaecologists (RCOG), the Society of Obstetricians and Gynaecologists of Canada (SOGC), and the U.S. National High Blood Pressure Education Program Work Group on High Blood Pressure in Pregnancy (NHBPEPWG, commonly called the NHBP Group) are examples of professional organizations that have developed terminology to use in the diagnosis and management of hypertension in pregnancy. There is, however, no universal agreement among professional groups regarding terminology, which may perpetuate the lack of meaningful data to further the study of hypertension in pregnancy. This chapter uses terms recommended by the NHBP Group, which are also used by the American College of Obstetricians and Gynecologists (ACOG), as defined in Table 7-3.

Hypertension is defined as a systolic pressure of 140 mmHg or higher or a diastolic pressure of 90 mmHg or higher, measured on at least two occasions at least 6 hours but not more than 7 days apart. Only one pressure (systolic or diastolic) needs to be elevated to meet the definition of hypertension. The NHBP Group’s terms for hypertensive conditions of pregnancy are chronic hypertension, preeclampsia-eclampsia, chronic hypertension with superimposed preeclampsia, and gestational hypertension.¹³ In part, the definitions imply the time of onset of the disease state. For example, chronic hypertension is elevated blood pressure that occurs prior to pregnancy or before the 20th week of pregnancy. Hypertension that develops during pregnancy and does not resolve by the 12th postpartum week is also classified as chronic hypertension.¹³

Preeclampsia-eclampsia is diagnosed when hypertension develops after the 20th week of pregnancy and is accompanied by proteinuria. Superimposed preeclampsia-eclampsia on chronic hypertension is considered when new onset proteinuria is present. In patients who have proteinuria prior to pregnancy, worsening of the proteinuria or hypertension is considered
a marker for superimposed preeclampsia. Gestational hypertension is diagnosed when blood pressure is elevated after the 20th week of pregnancy, but proteinuria does not develop.

The NHBP Group recommends that the term pregnancy-induced hypertension no longer be used. Rather, terms should be used that more accurately describe the patient’s hypertensive state.

Chronic hypertension in pregnancy is defined as hypertension (systolic 140 mmHg or higher, diastolic 90 mmHg or higher) that occurs prior to pregnancy, before the 20th week of pregnancy, or more than 12 weeks after delivery.¹³ The rate of chronic hypertension in pregnancy has increased in part due to the number of women who delay childbirth until their 30s, 40s, and 50s, a time when many non-pregnant women will first be diagnosed. The rate is further elevated in African-American women, women with type 2 diabetes mellitus, and obese women (body mass index 30 or above).¹⁴

Chronic hypertension is classified as mild or severe based on systolic or diastolic blood pressure thresholds. Mild chronic hypertension is a systolic blood pressure of 140 to less than 160 mmHg or a diastolic pressure of 90 to less than 100 mmHg.¹⁵ Severe chronic hypertension is a systolic pressure of 180 mmHg or higher or a diastolic pressure of 110 mmHg or higher.

For counseling purposes for the parturient and family, chronic hypertension is based on the blood pressure and the presence of organ system involvement. Patients are considered at lower risk if their blood pressure is in the mild chronic hypertension range and there is no organ involvement or injury.¹⁴ Most women with mild chronic hypertension are counseled to discontinue antihypertensive medications prior to pregnancy. This reduces the risk of fetal exposure to potential teratogenic effects of some antihypertensive drugs (e.g., angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers) and decreases the risk of fetal compromise from hypoperfusion pressures.¹⁴

Chronic hypertension is also categorized as primary or secondary, based on the causative factor.² Primary (essential) hypertension is the presence of elevated blood pressure in the absence of a causative disease or condition. Primary hypertension accounts for more than 90 percent of chronic hypertension in pregnancy. Risk factors for primary hypertension include:

Secondary hypertension, in contrast, is elevated blood pressure caused by another condition, such as kidney disease, endocrine disorders, adrenal gland tumors, collagen vascular diseases, arteriosclerosis, coarctation of the aorta, and some medications (Box 7-2).

Patients with chronic hypertension who are pregnant are at increased risk for perinatal morbidity and mortality when compared with women without hypertension. Chronic hypertension diagnosed before pregnancy begins has worse perinatal and maternal outcomes than chronic hypertension diagnosed during pregnancy.^14,15 This finding may be related to preexisting vascular injury and compromised end-organ function in this
population. Women with chronic hypertension also are at increased risk for superimposed preeclampsia and placental abruption.