Korotkoff Phase Should Be Used as the Endpoint for the Measurement of Diastolic Blood Pressure During Pregnancy
Literature Selection and Identification
Critical Appraisal of Selected Literature
Five Korotkoff Phases
Conducting System of Human Heart
Two of the most common complicating problems seen during pregnancy are the appearance of gestational diabetes and of hypertension. Both of these conditions are more likely to occur during late pregnancy and both generally abate in the postpartum period. Nevertheless, both of these conditions represent an increased risk for future development of disease. There is a lack of agreement among clinicians concerning the optimum blood pressure measurement device and inconsistencies in practice with regard to the method in which blood pressure is measured. Blood pressure is created by a number of physical forces related to the heart and blood vessels and regulated by hormones and other substances in the human body. The blood pressure measurement is an important clinical area because raised blood pressure in pregnancy may have relatively acute and potentially serious consequences; consequently, accurate measurements throughout the pregnancy are essential. The sounds produced by small amounts of blood passing through a blood pressure cuff are called Korotkoff sounds, after the physician who first used this method in the early 1900s, and five Korotkoff phases are described in adults. A review of the relevant and scholarly literature is followed by a critical review of selected studies to identify the most efficacious method of measuring blood pressure during pregnancy. The results of the research are followed by a discussion, conclusions and recommendations.
An Investigation as to which Korotkoff Phase Should Be Used as the Endpoint for the Measurement of Diastolic Blood Pressure During Pregnancy
Researchers in the field of family systems medicine have long recognized the association between psychosocial stressors and the onset of various illnesses and their exacerbation (McDaniel, 1992). Psychosocial distress has been implicated in the etiology and/or exacerbation of such conditions as chronic idiopathic prostatitis, somatization disorder, and adverse pregnancy outcomes (Langer et al., 1996). In an international study of medically unexplained physical symptoms, the World Health Organization concluded that psychosocial stress may be specifically responsible for many of the multiple, persistent, and medically unexplained somatic symptoms seen by primary care physicians across multiple cultures and populations (Isaac et al., 1995). Two of the most common complicating problems seen during pregnancy are the appearance of gestational diabetes (Freinkel, 1980, 1985) and of hypertension (National High Blood Pressure Education Program, 1990).
Hypertension has been linked to poor fetal development and ensuing perinatal death (Mansfield, 1986). In their study of pregnancy over 40 years, Horger and Smythe (1977) determined that fully one-third of their sample, black women of very high parity suffering from hypertension, accounted for two-thirds of all the perinatal deaths occurring during the study. These researchers attributed the link to placental malfunction. Other researchers have reported a link between hypertension and stillbirth, resulting from impaired placental circulation caused by placental infarction or abruption (Mansfield, 1986). Further, the prematurity rate rises with increased blood pressure, related both to premature labor and premature termination of the pregnancy; in addition, higher incidences of low birthweight have been reported among hypertensive patients by researchers in the Collaborative Perinatal Project (Mansfield, 1986).
Both gestational diabetes and hypertension are more likely to occur during late pregnancy and both generally abate in the postpartum period. Nevertheless, both of these conditions represent an increased risk for future development of disease (Baum, McCabe, & Schneiderman, 1992). The course of both of these conditions is such that both may be attributed to arising as a consequence of the progressive insulin resistance characteristic of pregnancy that abates postpartum, but may have revealed an underlying predisposition to subsequent disease development. However, today, there is a lack of agreement among clinicians concerning the optimum blood pressure measurement device and inconsistencies in practice with regard to the method in which blood pressure is measured. The blood pressure measurement is an important clinical area because raised blood pressure in pregnancy may have relatively acute and potentially serious consequences; consequently, accurate measurements during pregnancies are essential. The precise definition of the research question/hypothesis is presented below clarifying the explicit link to the identified clinical area of inquiry.
Statement of Problem
In the United States, 50 million people are thought to have high blood pressure; about half are receiving treatment and half of the treated are successful at reducing their blood pressure to below 140/90. This leaves about 37 million people in the United States with persisting hypertension. The incidence of high blood pressure rises with age; more common in men under 50, but more common in women over age 65 years. Over age 70 years, the incidence of high blood pressure approaches two-thirds of the population. Hypertension is divided into two groups - primary or essential hypertension and secondary to a specific disease. Diseases of the kidney and blocked kidney arteries, for example, can produce high blood pressure as a secondary effect. While no specific cause is found in 90% of hypertensives, one explanation is that the population at risk is becoming more sedentary with an increase in obesity. Their food supply is clearly suspect and it is not just the fat in the diet; these arterial problems with different and complex origins link to the diets and lifestyles that are currently popular in Europe and North America and occur less often among physically active, vegetable-eating populations who seldom eat dairy products, meat, and other high-protein-fat foods (Kaplan, 1998).
Today, there are four major concerns about blood pressure diagnosis and treatment:
1) BP readings may be inaccurate or biased;
2) White coat syndrome - higher BP readings are obtained in the doctor's office; 3) Inadequate sample (numerous readings are required to obtain a meaningful average); and 4) Corrective action taken is inappropriate (Kaplan, 1998).
Blood pressure is a dynamic feature of pumping blood. Blood pressure readings also tend to vary (BP tends to be lowest in the morning and highest in the late afternoon), and BP will rise with exertion and may be very high briefly with vigorous exercise (Kaplan, 1998). Because the blood pressure rate can be affected by such a wide range of physiological and psychosocial factors, identifying the most efficacious means of measuring blood pressure, particularly during pregnancy, becomes all the more important.
Blood pressure is created by a number of physical forces related to the heart and blood vessels and regulated by hormones and other substances in the human body. The heart pumps blood throughout the body in blood vessels or tubes called arteries, which are similar to a garden hose carrying water from a faucet to the flower bed. Arteries branch into smaller tubes called arterioles that deliver oxygen and other nutrients to the tissues (Griffith & Wood, 1997). A number of common and uncommon factors can lead to secondary high blood pressure. The more common causes for secondary hypertension include the use of certain medications (e.g., birth control pills), hyperthyroidism, pregnancy induced hypertension, and renal artery disease (Griffith & Wood, 1997). The cause of pregnancy-induced hypertension is unknown; however, pregnancy places a greater demand on the heart to pump blood and is associated with hypertension in certain individuals. According to Griffith and Wood, pregnancy-induced hypertension (PIH) includes a spectrum of high blood pressure disorders ranging from toxemia to chronic hypertension (Griffith & Wood, 1997).
The increased prevalence among older women of hypertension, diabetes, and fibroid tumors, in particular, has been of special concern because of the link between these conditions and poorer reproductive outcomes; thyroid and kidney disorders have been implicated as well (Mansfield, 1986). Hypertension has been arbitrarily defined as a blood pressure of 140/90 or more, and has the potential for damage to vital organs such as the brain, heart, kidney, and placenta; therefore, the condition places the mother and fetus at risk for increased morbidity and mortality (Mansfield, 1986). Because blood pressure rises slowly with age, older women may be at greater risk for this disorder and its ensuing pregnancy complications.
Hypertension has also been associated with increased maternal morbidity and mortality rates in a number of studies. The intervening complications may be cerebral hemorrhage, placental abruption, heart failure, or preeclampsia. A 1982 study of maternal mortality rates found that disorders of the cardiovascular system were the predominant indirect obstetric cause of death in their sample. However, this risk is not a modern discovery. In fact, as early as 1886, Galabin reported in his treatise on midwifery that when heart disease was "grave," one could expect 55% of the cases to be fatal (p. 326 in Mansfield, 1986).
Furthermore, patients with essential hypertension have an increased likelihood of labor induction and cesarean section deliveries, with their ensuing complications (Mansfield, 1986). These are additional reasons why the hypertensive patient may be at additional risk for a number of pregnancy complications.
Electronic databases used included:
1) Cochrane Database of Systematic Reviews.
2) CINAHL. Cumulative Index of Nursing and Allied Health.