15.7: Blood Pressure
By the end of this section, you will be able to:
- Describe correlation in blood pressure readings with severity of hypertension
- Discuss the importance of blood pressure cuff and size
- Identify factors that affect blood pressure
Blood pressure is the pressure exerted by the blood on arterial walls and must be measured to ensure the pressure is adequate to perfuse the body and not too great to rupture the blood vessels. It consists of two numbers, a higher systolic and lower diastolic, and is reported as a fraction with the systolic on top and the diastolic on the bottom. Systole is the pressure of blood during contraction of the left ventricle. Diastole is the pressure of the blood when the ventricles are at rest and filling.
Variations in Blood Pressure
The normal adult blood pressure ranges between 90 to 120 systolic and 60 to 80 diastolic, but it can vary due to medical conditions and age. An elevated blood pressure is known as hypertension and a lowered one is called hypotension . Either of these conditions can lead to serious health consequences. Hypertension increases the pressure placed on the arterial walls leading to complications such as hemorrhagic stroke but also increases the risk of a myriad of health conditions if it occurs with other comorbidities, particularly myocardial infarction , heart failure , cerebrovascular accident , and end-stage renal disease. Hypotension also presents various dangers. Hypotension means that blood is not being circulated sufficiently, which can lead to ischemia, anoxic brain injury, and even death. Hypotension is a hallmark characteristic of shock, a life-threatening condition that develops from multiple medical causes.
The presence of hypertension is considered a modifiable risk factor for cardiac and neurological conditions. Because it is often due to lifestyle choices, blood pressure is monitored annually and then more frequently if hypertension begins to develop. As a patient’s trends begin to increase outside of normal ranges, blood pressure is further categorized based on its risk to the individual and the recommended treatments (Table 15.9). An elevated blood pressure requires more frequent monitoring because the risk of hypertension is present. Hypertension is classified as either stage one or the more severe stage two. These classifications can help guide the plan of care for the patient.
| Category | Blood Pressure Reading |
|---|---|
| Normal | 90 to 119/60 to 80 |
| Elevated | 120 to 129 systolic and ≤80 diastolic |
| Stage I hypertension | 130 to 139 systolic or 80 to 89 diastolic |
| Stage II hypertension | ≥140 systolic or ≥90 diastolic |
Blood Pressure Cuff and Size
Blood pressure cuffs are available in a variety of sizes and are meant to wrap around the upper arm. The nurse is responsible for obtaining a proper size cuff for the patient (Figure 15.26). Within the cuff is the inflatable bladder, which, when inflated, impedes the blood flow through the brachial artery . The edges of the cuff will encircle the upper arm and be secured with Velcro to ensure that the cuff does not pop off during inflation of the bladder.
The first step is selecting which arm to use, this can be patient preference or the need to avoid the arm with IVs, lymphedema , fistulas, and so on. The width of the cuff should cover approximately 80 percent of the upper arm from shoulder to elbow, and the bladder within the cuff should encircle about 40 percent of the arm. An improper blood pressure cuff size leads to an inaccurate reading. If a blood pressure cuff is too large, the reading will be lower. If it is too small, the reading will be higher. At times, hypertension has been missed by medical personnel simply due to improper equipment.
The individual’s position can also affect the blood pressure reading. It is important for the nurse to instruct the patient to remain seated with the hand at the level of the heart and feet flat on the floor. Simply crossing the legs or ankles can lead to an inaccurate reading. It is also important to instruct the patient not to talk; to avoid caffeine and smoking thirty minutes prior, if possible; and to try to sit quietly for five minutes before, if possible.
See the competency checklist for Vital Signs: Blood Pressure. You can find the checklists on the Student resources tab of your book page on openstax.org.
Korotkoff Sounds
To place the cuff, the nurse will align the cuff on the patient’s arm, aligning the artery with the artery position indicator label on the cuff. The valve of the inflation bulb should be fully closed, then the nurse will place the diaphragm of the stethoscope over the brachial artery and inflate the cuff by squeezing the bulb. The gauge will inform the nurse of the pressure as the cuff inflates. Once the cuff is inflated to pressures greater than normal ranges and those indicated by the patient’s blood pressure trends, the nurse will begin to slowly deflate the bladder while carefully listening for the return of the pulse. This is done by turning the knob on the valve counterclockwise approximately 2 mm/s while listening and watching the pressure indicated on the gauge. The pulsating, tapping sound heard with a stethoscope as blood flows through the brachial artery is known as a Korotkoff sound . The first Korotkoff sound is the systolic blood pressure reading, and the last Korotkoff sound is the diastolic reading. Once the diastolic number is obtained and there are no more Korotkoff sounds heard, the bladder can be quickly deflated and the cuff removed. Remember that if the blood pressure does not align with the patient’s previous trends, the nurse should recheck in the other arm, recheck with a manual cuff if the reading was taken using an electronic machine, or let the patient rest for five minutes and recheck.
A demonstration of what to listen for when listening for the Korotkoff sounds is presented in this video.
Pulse Pressure
The difference between the systolic and diastolic blood pressure is the pulse pressure , which should normally be about 40 mm Hg. The pulse pressure is directly related to the blood volume, meaning that a decrease in blood volume will cause a decrease in pulse pressure. The pulse pressure is indirectly related to arterial compliance, meaning that inelastic arteries will have a wider pulse pressure. Abnormal pulse pressures are defined as either narrowed or low or widened or high. A narrowed pulse pressure is defined as a pulse pressure less than 25 percent of the systolic blood pressure (i.e., 110/85). A widened pulse pressure is defined as more than 100 mm Hg (i.e., 174/69). In athletes or those with increased muscle mass, a widened pulse pressure may be normal, and as people age, the pulse pressure continues to widen due to the loss of arterial compliance. Widened pulse pressure is a sign of other health conditions such as aortic valve abnormalities (regurgitation or sclerosis), hyperthyroidism, arteriosclerosis, and iron deficiency anemia. In contrast, narrow pulse pressure is present when the ventricles are unable to fully contract. These conditions include heart failure, cardiac tamponade, and aortic stenosis. Blood loss, dysautonomia, and postural orthostatic tachycardia syndrome also cause a narrow pulse pressure.
The risk for heart disease and atrial fibrillation increases in individuals with a widened pulse pressure. Even a 10 mm Hg rise in the pulse pressure can increase the risk of cardiovascular disease by 20 percent. Because of this risk, the pulse pressure should be monitored and kept in a normal range. The only proven way to maintain a healthy pulse pressure is by aerobic exercises, as these increase the arterial elasticity (Homan, 2022).
Auscultatory Gap
When a manual blood pressure is obtained, the nurse listens carefully for the Korotkoff sounds, noting both the origin and the disappearance of these sounds to record as the systolic and diastolic blood pressure measurements. Between the origin and the disappearance of the Korotkoff sounds is the auscultatory gap , a brief absence in the sounds. The auscultatory gap may be confused with the diastolic blood pressure if the nurse does not continue to listen for a few more seconds, leading to an inaccurate measurement. The auscultatory gap can also be missed in individuals with elevated blood pressures if the cuff pressure is not pumped high enough (Rehman, 2022).
Factors Affecting Blood Pressure
Blood pressure is determined by the force of heart contractions, the diameter of the blood vessels, and the amount of circulating blood. If any of these factors are abnormal, blood pressure will be abnormal.
The force of heart contractions will determine the force that blood exerts on the arterial walls. During exercise, the heart will strongly contract, increasing the blood pressure temporarily during the activity. When the heart contractions are weak, blood pressure drops. If the heart is unable to contract and pump blood through the vasculature , it is known as cardiogenic shock . A primary cause of this is heart failure.
Nurse:
Sarah, RN
Clinical setting:
Outpatient clinic
Years in practice:
5
Facility location:
Bedford, New Hampshire
A 35-year-old male comes into the clinic for a routine preventive visit. Because it was the early afternoon, we were not busy and were able to call him back as soon as he arrived. The first thing I do is have him take a seat and apply the blood pressure cuff while I ask him some general questions. To our surprise, the blood pressure began alarming at 144/70. I checked his results from the previous year and noticed normal readings. I verified that his ankles were uncrossed, and the cuff was in the right position. He asked me if that was normal. I asked if he was nervous since white coat syndrome—anxiety in healthcare settings—can temporarily increase blood pressure. He denied any anxiety.
After a recheck with the blood pressure slightly lower but still elevated, we tried to figure out what may have caused it. Perhaps a family history, lifestyle change. Nothing. “I’m running around all the time. I was almost late to this appointment and had to run up the stairs since the elevator wasn’t working.” Then I realized his blood pressure was elevated because he was running up the stairs to make it to his appointment on time.
The diameter of the blood vessels also affects blood pressure. If the diameter increases, the blood pressure decreases. If the diameter decreases, the blood pressure increases. An increase in the diameter of the blood vessel is called vasodilation . A decrease in blood vessel diameter is called vasoconstriction . To illustrate this relationship, consider drinking water through a narrow coffee stirrer versus a wider smoothie straw. It takes more effort or pressure to suck the water through the coffee stirrer than it would through the smoothie straw because of the narrow diameter of the stirrer. The same concept applies to blood vessel diameter and blood pressure. Severe vasodilation, with resultant hypotension, occurs in cases of septic and anaphylactic shock and drug overdoses, such as with opioids and cardiac medications. Severe vasoconstriction, leading to life-threatening hypertension, occurs in cases of cocaine overdose. Vasoconstriction also occurs as a compensatory mechanism in cases of extreme blood loss or cold. The fight-or-flight response, also known as the activation of the sympathetic nervous system, triggers vasoconstriction. In emergency situations, explained further in Table 15.10, blood is shunted from the periphery to the heart, lungs, and brain to provide additional stores to the vital organs for the response, known as shock. Shock is fatal if left untreated. The amount of available blood also affects blood pressure. Even if heart contractility and vasculature are healthy, if blood volume decreases, blood pressure will decrease. This is observed in hypovolemic shock, which occurs with hemorrhage or severe dehydration.
| Types of Shock | Description | Causes |
|---|---|---|
| Cardiogenic | Heart unable to contract efficiently, which decreases the amount of circulating blood | Heart failure, myocardial infarction, arrhythmias, cardiomyopathy, cardiac tamponade |
| Distributive | Systemic vasodilation | Sepsis, anaphylaxis, burns |
| Hypovolemic | Loss of blood volume | Hemorrhage, dehydration |
| Neurogenic | Inability to maintain heart rate and blood pressure | Central nervous system injury (brain or spinal cord) |
A 19-year-old female visits the emergency department complaining of dizziness, vaginal pain and discharge, abdominal pain, nausea, and vomiting. She appears diaphoretic. The nurse obtains a set of vital signs.
- Temperature 103.3°F (39.6°C)
- Pulse 134 bpm
- Respiratory rate 28 breaths per minute
- Blood pressure 86/58 mm Hg
A vaginal specimen is obtained to determine the presence of a sexually transmitted infection. The culture is positive for gonorrhea.
Analyzing this information, the decreased blood pressure, increased pulse, and presence of dizziness would lead to a diagnosis of shock.
After obtaining all the data, the nurse contacts the healthcare provider immediately for further orders and may suspect septic shock from untreated gonorrhea.
Lifestyle factors can instigate the development of hypertension. An unhealthy diet and a sedentary lifestyle can lead to atherosclerosis, plaque buildup in the arteries. This plaque in the arteries decreases the diameter and elasticity of the blood vessels leading to hypertension. Obesity itself will increase the risk of hypertension because the distance that the blood must travel is increased. With this increased distance, the heart must work harder, increasing the blood pressure. A healthy diet and exercise can help maintain a healthy blood pressure.
As previously mentioned, an incorrect cuff size or even patient position could alter the reading and yield an inaccurate result.
It is well documented that those of certain ethnicity or descent are at an increased risk of hypertension. A multitude of hypotheses exist for why this group suffers disproportionately from this condition, such as genetic factors and lifestyle, but perhaps another explanation is relevant. Could healthcare inequality and social determinants of health, particularly finances and access to health care, affect the development of hypertension among ethnicities such as Black, Asian, and Hispanic? Researchers are beginning to ask this same question. Nurses should be aware of social determinants of health that may affect the timely identification and treatment of hypertension, such as unreliable transportation or unfavorable and inaccessible office hours. Noting these social determinants of health during the initial assessment can help provide cues into personalized treatment plans. It is the nurse's responsibility to be patient advocates and nurture equality in health care to help alleviate some of the health burdens placed on at-risk populations (Aggarwal et al., 2021)