Arterial blood pressure is a measure of the pressure exerted by the blood as it flows through the arteries.
Blood pressureis the force exerted on the walls of an artery by the pulsing blood under pressure from the heart.
The systolic pressure is the pressure of the blood as a result of contraction of the ventricles, that is, pressure of the height of the blood wave.
The peak of maximum pressure when ejection occurs
Diastolic Pressure is the pressure when the ventricles are at rest. It is the minimal pressure exerted against the arterial walls at all times.
Blood Pressure is measured in millimeters of mercury (mmHg) and recorded as a fraction: systolic pressure over the diastolic pressure.
A typical blood pressure for a healthy adult is 120/80 mm Hg
The difference between the systolic and diastolic pressure is the pulse pressure. For a BP of 120/80, the pulse pressure is 40.
Determinants of blood pressure:
Blood pressure is the result of several factors: the pumping action of the heart, the peripheral vascular resistance (the resistance supplied by the blood vessels through which the blood flows), and the blood volume and viscosity.
Pumping Action of the Heart:
When the pumping action of the heart is weak, less blood is pumped into arteries (lower cardiac output), and the blood pressure decreases. When the heart’s pumping action is strong and the volume of blood pumped into the circulation increases (higher cardiac output), the blood pressure increases.
Peripheral Vascular Resistance:
Peripheral resistance can increase blood pressure if the diastolic pressure is affected. The internal diameter or capacity of the arterioles and the capillaries determines in great part the peripheral resistance to the blood in the body. The smaller the space within a vessel, the greater the resistance. Normally, the arterioles are in a state of partial constriction. Increased vasoconstriction, such as occurs with smoking, raises the blood pressure, whereas decreased vasoconstriction lowers the blood pressure.
When the blood volume decreases (for example, as a result of a hemorrhage or dehydration), the blood pressure decreases because of decreased fluid in the arteries. Conversely, when the volume increases (for example, as a result of a rapid intravenous infusion), the blood pressure increases because of the greater fluid volume within the circulatory system.
Blood pressure is higher when the blood is highly viscous (thick), that is, when the proportion of red blood cells to the blood plasma is high. This proportion is referred to as the hematocrit. The viscosity increases markedly when the hematocrit is more than 60% to 65%.
Regulation of bp
· Neural Factors
The major action of the sympathetic nerves on the vascular system is to cause vasoconstriction which increases the BP.
The sympathetic center in the medulla of the brain is activated to cause vasoconstriction in many different circumstances.
E.g. When we stand up suddenly after lying down, the effect of gravity causes blood to pool in the vessels of the legs and feet and BP drops. This activates baroreceptors in the large arteries of the neck and chest. They send off warning signals that result in reflexive vasoconstriction, which increases blood pressure
When blood volume suddenly decreases E.g. Hemorrhage, blood pressure drops and the heart begins to beat more rapidly. In such cases, sympathetic nervous system causes vasoconstriction to increase the blood pressure so that venous return increases and circulation can continue
When we exercise vigorously or are frightened and have to make a hasty escape. Under these conditions there is a generalized vasoconstriction except in the skeletal muscles. The vessels of the skeletal muscles dilate to increase the blood flow to the working muscles.
· Renal Factors
The kidneys play a major role in regulating arterial blood pressure by altering blood volume. As BP increases beyond normal the kidneys allow more water to leave the body in the urine. Since the source of this water is the blood stream, blood volume decreases, which in turn decreases BP. However when arterial blood pressure falls, the kidneys retain body water, increasingly blood volume and blood pressure rises.
In addition when arterial blood pressure is low, certain kidney cells release the enzyme renin into the blood. Renin triggers a series of chemical reactions that result in the formation of angiotensin II, a potent vasoconstrictor chemical
Renin converts the plasma protein Angiotensinogen to Angiotensin I, which in turn is converted to Angiotensin II by enzymes (ACE)
Angiotensin also stimulates the adrenal cortex to release aldosterone, a hormone that erthances sodium ion reabsorption by the kidneys. As sodium, moves into the blood water follows. Thus, blood volume and blood pressure both rise.
The effects of chemical substances, many of which are drugs, on blood pressure are widespread. E.g.: Epinephrine increases both heart rate and blood pressure. Nicotine increases blood pressure by causing vasoconstriction. Both alcohol and histamine cause vasodilation and decrease the blood pressure.
Factors affecting blood pressure:
Newborns have a mean systolic pressure of about 75 mm Hg. The pressure rises with age, reaching a peak at the onset of puberty, and then tends to decline somewhat.
In elders, elasticity of the arteries is decreased—the arteries are more rigid and less yielding to the pressure of the blood. This produces an elevated systolic pressure. Because the walls no longer retract as flexibly with decreased pressure, the diastolic pressure may also be high
10 — 13 years
14 — 17 years
18 years and older
Physical activity increases the cardiac output and hence the blood pressure
Thus 20 to 30 minutes of rest following exercise is can be reliably assessed
Stimulation of the sympathetic nervous system increases cardiac output and vasoconstriction of the arterioles, thus increasing the blood pressure reading (E.g. Anxiety, Fear, Emotional Stress)
Severe pain can decrease blood pressure greatly by inhibiting the vasomotor center and producing vasodilatation
· Ethnicity/ Race
African American males over 35 years have higher blood pressures than European American males of the same age.
After puberty, females usually have lower blood pressures than males of the same age; this difference is thought to be due to hormonal variations. After menopause, women generally have higher blood pressures than before.
· Diurnal variation
Pressure is usually lowest early in the morning, when the metabolic rate is lowest. then rises throughout the day and peaks in the late afternoon or early evening.
Many medications, including caffeine, may increase or decrease the blood pressure.
Both childhood and adult obesity predispose to hypertension.
Smoking results in vasoconstriction a narrowing of blood vessels. BP rises when a person smokes and returns to baseline about 15 minutes after stopping smoking.
· Disease process
Any condition affecting the cardiac output, blood volume, blood viscosity, and or compliance of arteries has a direct effect on the blood pressure.
Assessment of Blood Pressure:
Arterial BP measurements are obtained either directly (invasively) or indirectly (noninvasively).
The direct method requires the insertion of a thin catheter into an artery (Brachial, Radial or Femoral). Tubing connects the catheter with electronic hemodynamic monitoring equipment.
The monitor displays a constant arterial pressure waveform and reading. Invasive BP monitoring is used only in intensive-care settings.
The common indirect method requires a blood pressure cuff, a sphygmomanometer and stethoscope. The blood pressure cuff consists of a rubber bag that can be inflated with air called the bladder. It is covered with cloth and has two tubes attached to it. One tube connects to a rubber bulb that inflates the bladder. A small valve on the side of this bulb traps and releases the air in the bladder.
The other tube is attached to a sphgmomanometer.
The sphygmomanometer indicates the pressure of the air within the bladder.
There are two types of sphygmomanometer: aneroid and digital.
The aneroid sphygmomanometer is a calibrated dial that points to the calibrations.
Digital (electronic) sphygmomanometer eliminate the need to listen for the sounds of the client’s systolic and diastolic blood pressures through a stethoscope. Electronic blood pressure devices should be calibrated periodically to check accuracy.
Doppler ultrasound stethoscopes are also used to assess blood pressure. These are of particular value when blood pressure sounds are difficult to hear, such as infants, obese clients, and clients in shock. Systolic pressure may be the only blood pressure obtainable with some ultrasound models
Auscultation or palpation with auscultation is the most widely used technique.
Palpating the radial artery at the wrist by placing middle 3 fingers over it.
Auscultating for sounds by placing the stethoscope on the brachial artery.
Korotkoff, a Russian surgeon first described the sounds heard over an artery during cuff inflation in 1905.
When taking a blood pressure using a stethoscope, the nurse identifies phases in the series of sounds called Korotkoffs.
First the nurse pumps the cuff up to about 30 mm Hg above the point where the pulse is no longer felt; that is the point when the blood flow in the artery is stopped. Then the pressure is released slowly (2 to 3 mm Hg per second) while the nurse observes the readings on the manometer and relates them to the sounds heard through the stethoscope. Five phases occur but may not always be audible
Phase 1: The pressure level at which the first faint, clear tapping or thumping sounds are hear These sounds gradually become more intense. The nurse should identify at least two consecutive tapping sounds. The first tapping sound heard during deflation of the cuff is the systolic blood pressure.
Phase 2: The period during deflation when the sounds have a muffled, whooshing, or swishing quality.
Phase 3: The period during which the blood flows freely through an increasingly open artery and the sounds become crisper and more intense and again assume a thumping quality but softer than in phase 1.
Phase 4: The time when the sounds become muffled and have a soft, blowing quality.
Phase 5: The pressure level when the last sound is heard. This is followed by a period of silence. The pressure at which the last sound is heard is the diastolic blood pressure in adults.
Blood Pressure Sites:
The blood pressure is usually assessed in the client’s upper arm using the brachial artery and a standard stethoscope.
Assessing the blood pressure on a client’s thigh is indicated in these situations:
· The blood pressure cannot be measured on either arm (e.g., because of burns or other trauma).
· The blood pressure in one thigh is to be compared with the blood pressure in the other thigh.
Procedure for checking Blood Pressure:
· To obtain a baseline measure of arterial blood pressure for subsequent evaluation
· To determine the client’s hemodynamic status (e.g., cardiac output: stroke volume of the heart and blood vessel resistance)
· To identify and monitor changes in blood pressure resulting from a disease process or medical therapy (e.g., presence or history of cardiovascular disease, renal disease, circulatory shock, or acute pain; rapid infusion of fluids or blood products)
· Signs and symptoms of hypertension (e.g., headache, ringing in the ears, flushing of face, nosebleeds, fatigue).
· Signs and symptoms of hypotension (e.g., tachycardia, dizziness, mental confusion, restlessness, cool and clammy skin, pale or cyanotic skin)
· Factors affecting blood pressure (e.g., activity, emotional stress, pain, and time the client last smoked or ingested caffeine).
· Some blood pressure cuffs contains latex. Assess the client for latex allergy and obtain a latex-free cuff if indicated.
· Stethoscope or DUS.
· Blood Pressure cuff of the appropriate size.
Introduce self and verify the client’s identity.
Perform hand hygiene and observe appropriates infection control procedure.
Provide for client privacy
Position the client appropriately:
The adult client should be sitting unless otherwise specified. Both feet should be flat on the floor.
The elbow should be slightly flexed with the palm of the hand facing up and the forearm supported at heart level. Readings in any other position should be specified. The blood pressure is normally similar in sitting, standing, and lying positions
Expose the upper arm.
Legs crossed at the knee result in elevated systolic and diastolic pressures.
The blood pressure increases when the arm is below heart level and decreases when the arm is above heart level.
Wrap the deflated cuff evenly around the upper arm. Locate the brachial artery. Apply the center of the bladder directly over the antecubital space.
The bladder inside the cuff must be directly over the artery to be compressed if the reading is to be accurate.
For an adult, place the lower border of the cuff approximately 2.5 cm (1 in.) above the antecubital space.
Perform a preliminary palpatory determination of systolic pressure. The initial estimate tells the nurse the maximal pressure to which the manometer needs to be elevated in subsequent determinations. It also prevents underestimation of the systolic pressure or overestimation of the diastolic pressure should an auscultatory gap occur.
· Palpate the brachial artery/ radial artery with the fingertips.
· Close the valve on the bulb.
· Pump up the cuff until you no longer feel the brachial pulse.
· At that pressure the blood cannot flow through the artery. Note the pressure on the sphygmomanometer at which pulse is no longer felt.
· Release the pressure completely in the cuff, and wait 1 to 2 minutes before making further measurements.
This gives an estimate of the systolic pressure.
A waiting period gives the blood trapped in the veins time to be released. Otherwise, false high systolic reading will occur.
Position the stethoscope appropriately.
· Cleanse the earpieces with antiseptic wipe.
· Insert the ear attachments of the stethoscope in your ears so that they tilt slightly forward.
· Ensure that the stethoscope hangs freely from the ears to the diaphragm.
· Place the bell side of the amplifier of the stethoscope over the brachial pulse site.
· Place the stethoscope directly on the skin, not on clothing over the site.
Sounds are heard more clearly when the ear attachments follow the direction of the ear canal.
If the stethoscope tubing rubs against an objects, the noise can block the sounds of the blood within the artery.
Because the blood pressure is a low-frequency sound, it is best heard with the bell shaped diaphragm.
Hold the diaphragm with the thumb and index finger.
Auscultate the client’s blood pressure:
· Pump up the cuff until the sphygmomanometer reads 30 mm Hg above the points where the brachial pulse disappeared.
· Release the valve on the cuff carefully so that the pressure decreases at the rate of 2 to 3 mm Hg per second.
· As the pressure falls, identify the manometer reading at korotkoff phases I, IV, and V.
· Deflate the cuff rapidly and completely.
If the rate is faster or slower, an error in measurement may occur.
There is no clinical significance to phases II and III.
This permits blood trapped in the veins to be released.
· Wait 1 to 2 minutes before making further determinations.
Repeat the above steps to confirm the accuracy of the reading – especially if it falls outside the normal range.
Remove the cuff.
Wipe the cuff with an approved disinfectant.
Cuffs can become significantly contaminated.
Many institutions use disposable blood pressure cuffs.
Document and report pertinent assessment data according to agency policy.
Taking a Thigh Blood Pressure:
· Help the client to assume a prone position. If the client cannot assume this position, measure the blood pressure while the client is in a supine position with the knee slightly flexed. Slight flexing of the knee will facilitate placing the stethoscope on the popliteal space.
· Expose the thigh, taking care not to expose the client unduly.
· Locate the popliteal artery
· Wrap the cuff evenly around the mid thigh with the compression bladder over the posterior aspect of the thigh and the bottom edge above the knee. Rationale: The bladder must be directly over the posterior popliteal artery if the reading is to be accurate.
· If this is the client’s initial examination, perform a preliminary palpatory determination of systolic pressure by palpating the popliteal artery.
· In adults, the systolic pressure in the popliteal artery is usually 20 to 30 mm Hg higher than that in the brachial artery because of use of a larger bladder; the diastolic pressure is usually the same.
Blood pressure is not measured on a particular client’s limb in the following situation:
· The shoulder, arm, or hand (or the hip, knee, or ankle) is injured or diseased.
· A cast or bulky bandage is on any part of the limb.
· The client has had surgical removal of lymph nodes on axilla (or hip), such as for cancer,
· The client has an intravenous infusion in that limb.
· The client has an arteriovenous fistula (e.g., for renal dialysis) in that limb.
Selected Sources of Error in Blood Pressure Assessment:
· Bladder cuff too narrow
· Bladder cuff too wide
· Arm unsupported
· Insufficient rest before the assessment Repeating assessment too quickly Cuff wrapped too loosely or unevenly
· Deflating cuff too quickly
· Deflating cuff too slowly
· Failure to use the same arm consistently
· Arm above level of the heart
· Assessing immediately after a meal or while client smokes or has pain
· Failure to identify auscultatory gap
· The client should be mentally and physically relaxed.
· The size of the cuff should be proportionate to the arm circumference.
· The zero reading of the manometer should be kept at the level of the heart
· Blood pressure should be recorded by palpated method before the Auscultatory method.
· Pressure must be raised 30 mm Hg above the Palpatory level
· The cuff pressure should be decreased to zero level between the trials
· Size selected is proportional to the circumference of the limb being assessed. 40 % of the circumference of the mid arm.
· Bladder enclosed by the cuff encircles at least 80% of the arm of an adult, the entire arm of a child.
Alterations in bp
A blood pressure that is persistently above normal is called hypertension.
An elevated blood pressure of unknown cause
An elevated blood pressure of known cause
Classification of Hypertension :
Systolic BP mm Hg
Diastolic BP mm Hg
120 – 139
80 – 89
Hypertension, stage 1
90 — 99
Hypertension stage 2
· Salt intake
· Saturated fat
· Physical activity
· Environmental stress
· Socio economic status
· Other factors
· Age (B.P. Rises with age)
· Sex (At adolescence men display a higher average level)
· Ethnicity (more in black communities)
Signs and syisotoms:
· Vision disorders
Hypotension is a blood pressure that is below normal, that is, a systolic reading consistently between 85 and 110 mm Hg in an adult whose normal pressure is higher than this.
Orthostatic hypotension is a blood pressure that falls when the client sits or stands. It usually the result of peripheral vasodilatation in which blood leaves the central body organs, especially the brain, and moves to the periphery, often causing the person to feel faint.
Hypotension occurs when:
· arteries dilate
· peripheral vascular resistance decreases
· circulating blood volume decrease
· heart fails to provide adequate cardiac output
Symptoms of hypotension:
· Skin mottling
· Chest pain, increased heart rate
· Decreased urine output