Session 5Vital Signs – Blood Pressure

Session 5Vital Signs – Blood Pressure

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Learning Objectives

Learning Objectives

By the end of this session, students are expected to be able to:

Define blood pressure and other related terms

Describe determinants of blood pressure

Describe factors affecting blood pressure

Identify abnormalities of blood pressure

Describe important considerations when assessing blood pressure

Describe five phases of Korotkoff’s sounds

Describe common errors and effects when assessing blood pressure

Describe the procedure for assessing blood pressure

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Definition of Terms

Definition of Terms

Blood pressure: A measure of the pressure exerted by the blood as it flows through the arteries.

Systolic pressure: The highest point of pressure in the arteries and occurs when the left ventricle of the heart contracts.

Diastolic pressure: The lowest point of pressure in the arteries and occurs when the ventricle muscles of the heart relax between beats.

Pulse pressure: The difference between systolic and diastolic pressure.

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Determinants of Blood Pressure

Determinants of Blood Pressure

All normal individuals are expected to have the same measure of blood pressure.

Normal blood pressure is 120 mmHg Systolic, and 80mmHg diastolic.

However, there are few differences in the measure of blood pressure depending on a number of factors.

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These include:

These include

Salt sensitivity: High dietary sodium has been found as a cause of hypertension

Genetic factors

Sex: Females usually have lower blood pressure than males of the same age.

Race/ethnicity

Age: Average normal blood pressure for older people tend to be a little bit high

Body mass: High body mass index is associated with high blood pressure

Diet: (overall diet quality, macro- and micronutrient content)

Exercise: Physical activity increases the cardiac output and hence the blood pressure, thus 20-30 minutes of rest following exercise is indicated before checking blood pressure.

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Medications: Many medications may increase or decrease blood pressure.

Stress: Increases blood pressure however; severe pain decreases blood pressure by inhibiting vasomotor centre and producing vasodilatation.

Medications: Many medications may increase or decrease blood pressure.

Diurnal variations: Pressure is usually lowest early in the morning, when the metabolic rate is lowest, then rises throughout the day and speaks in the late afternoon or early evening.

Associated disease states, e.g. hypertension, diabetes and renal dysfunction.

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Factors Affecting Blood Pressure

Factors Affecting Blood Pressure

Peripheral resistance

Vessel elasticity

Blood volume

Cardiac output

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Peripheral Resistance

Peripheral Resistance

Blood cells and plasma encounter resistance when they contact blood vessel walls.

If resistance increases, then more pressure is needed to keep blood moving.

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Three main sources of peripheral resistance:

Three main sources of peripheral resistance

Blood vessel diameter

As the diameter of a tube gets smaller, a greater proportion of the fluid is in contact with the wall of the tube.

Therefore resistance to flow is increased and pressure rises.

Larger diameter, same volume, less pressure.

Smaller diameter, same volume, more pressure.

Constriction of blood vessels raises blood pressure.

Vessel diameter is actively regulated by vasomotor fibers, sympathetic nerve fibers that innervate the vessel's smooth muscle layer.

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Vasomotor fibers release norepinephrine, a powerful vasoconstrictor.

Vasomotor fibers release norepinephrine, a powerful vasoconstrictor.

A vasoconstrictor is a substance that causes blood vessels to constrict.

Blood vessel diameter is also regulated by blood-borne vasoconstrictors.

Record the effect of each of these chemicals on the blood vessel

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Blood viscosity

Blood viscosity

Viscosity is related to the thickness of a fluid.

The greater the viscosity, the less easily molecules slide past one another and the more difficult it is to get the fluid moving and keep it moving.

Because of this greater resistance to flow, a greater pressure is required to pump the same volume of viscous fluid.

The hematocrit is the percentage of red blood cells in the total blood volume.

The hematocrit affects blood viscosity and therefore resistance to flow.

The more viscous the blood, the greater resistance it encounters and the higher the blood pressure.

The hematocrit can increase when there are more red blood cells or less plasma in the blood.

The hematocrit can decrease when there are fewer red blood cells or more plasma.

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Total vessel length

Total vessel length

Total vessel length affects peripheral resistance.

Increased fatty tissue requires more blood vessels to service it and adds to the total vessel length in the body.

The longer the total vessel length, the greater the resistance encountered, and the greater the blood pressure

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Vessel Elasticity

Vessel Elasticity

Besides peripheral resistance, blood vessel elasticity also affects blood pressure.

A healthy elastic artery expands, absorbing the shock of systolic pressure.

The elastic recoil of the vessel then maintains the continued flow of blood during diastole.

When an individual has arteriosclerosis, arteries become calcified and rigid, so they can't expand when the pulse wave of systolic pressure passes through them.

Thus the walls of the artery experience higher pressures and become weaker and weaker.

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Blood Volume

Blood Volume

Blood volume affects blood pressure.

When there is a greater volume of fluid, more fluid presses against the walls of the arteries resulting in a greater pressure.

When there is less volume there is less pressure.

Reduced blood volume (for example due to excessive sweating) reduces blood pressure short term.

Long term homeostatic mechanisms compensate, bringing blood volume and blood pressure back up to normal levels.

Increased blood volume (for example due to water retention from excessive salt intake) increases blood pressure short term.

Long term homeostatic mechanisms compensate, bringing blood volume and blood pressure back up to normal levels.

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Cardiac Output

Cardiac Output

Anything that decreases cardiac output also decreases blood pressure, because there is less pressure on the vessel walls.

An increase in cardiac output results in increased blood pressure.

Cardiac Output = Heart Rate X Stroke Volume.

Anything that affects heart rate or stroke volume affects cardiac output and thus blood pressure.

If less blood is ejected from the heart with each beat, then blood pressure will be lower because there will be less blood pressing against the vessel walls.

Blood volume affects end diastolic volume and therefore stroke volume.

With decreased stroke volume, due to decreased venous return volume there is a decreased cardiac output and a decreased blood pressure.

With increased stroke volume, due to increased venous return and/or increased contractility, there is an increased cardiac output and increased blood pressure.

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Abnormalities of Blood Pressure

Abnormalities of Blood Pressure

Hypertension

It is the term used to describe the abnormally high blood pressure.

One abnormally high reading does not necessarily indicate pathological condition.

Hypertension without a known cause is called ‘Primary’ or ‘Essential’ hypertension.

Stage I hypertension is when the diastolic blood pressure is 90 mm Hg or higher or when the systolic blood pressure is higher than 140 mm Hg.

Condition associated with hypertension include: Intracranial pressure, arteries sclerosis, polycythaemia Hyperthyroidisms, some renal diseases congenital narrowing of the aorta.

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Hypotension

Hypotension

Hypotension is a blood pressure which is lower than 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.

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Important Considerations when Assessing Blood Pressure

Important Considerations when Assessing Blood Pressure

Blood Pressure Sites

The blood pressure is usually assessed in the client’s arm using the brachial artery and a standard stethoscope.

Assessing the blood on a client’s thigh is usually indicated in case of burns or trauma on both arms.

Methods

Blood pressure can be accessed directly or indirectly.

Direct (invasive monitoring) measurement involves the insertion of a catheter into the brachial, radial or femoral artery.

Two non-invasive indirect methods of measuring blood pressure are the auscultator and palpatory methods.

The auscultatory method is most commonly used in hospitals.

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Lifespan Considerations

Lifespan Considerations

Infants

Use a paediatric stethoscope with small diaphragm.

The lower edge of the blood pressure cuff can be closer to the antecubital space of an infant.

Arm and thigh pressures are equivalent in children under 1 year of age.

One quick way to determine the normal systolic blood pressure of a child is to use the following formula.

Normal systolic BP = 80 + (2 x child’s age in years)

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Children

Children

Take blood pressure prior to other uncomfortable procedures so that the blood pressure is not artificially elevated by the discomfort.

Elders

Do not allow cuff pressure to remain high any longer than necessary.

Determine if the client is taking antihypertensive and, if so, when the last dose was taken.

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Home Care Considerations

Home Care Considerations

If the client takes blood pressure readings at home, use the same equipment or calibrate it against a system known to be accurate.

Observe the client family member taking the blood pressure and provide feedback if further instruction is needed.

If the client is in a chair or low bed, the health care provider/family member should position in a way to maintain the client’s arm at heart level and so that reading the sphygmomanometer is at eye level.

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Phases of Korotkoff’s Sound

Phases of Korotkoff’s Sound

The Korotkoff Sounds

The Korotkoff sounds are the sounds heard through the stethoscope as the pressure cuff deflates.

The sounds are first heard when the cuff pressure equals the systolic pressure, and cease to be heard once the cuff has deflated past the diastolic pressure.

It is generally accepted that there are five phases of Korotkoff sounds.

Each phase is characterised by the volume and quality of sound heard.

The figure below illustrates these phases.

In this example, the systolic and diastolic pressures are 120mmHg and 80mmHg respectively.

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Phases of Korotkoff’s Sound

Phases of Korotkoff’s Sound

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Phase One

Phase One

With the pressure cuff inflated to beyond the systolic pressure, the artery is completely occluded and no blood can flow through it.

Consequently, no sounds are heard above the systolic pressure.

At the point where cuff pressure equals the systolic pressure, a sharp tapping sound is heard.

We recall that the blood pressure oscillates between systolic and diastolic pressure.

At systolic, the pressure is great enough to force the artery walls open and for blood to spurt through.

As the pressure dips to diastolic, however, the artery walls bang shut again.

It is the closing shut of the artery walls that results in the tapping sound.

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Phase Two

Phase Two

This phase is characterised by a swishing sound, caused by the swirling currents in the blood as the flow through the artery increases.

Sometimes, if the cuff is deflated too slowly, the sounds vanish temporarily.

This happens when the blood vessels beneath the cuff become congested, and is often a sign of hypertension.

The congestion eventually clears, and sounds resume.

The intervening period is called the auscultatory gap.

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Phase Three

Phase Three

In this phase, there is a resumption of crisp tapping sounds, similar to those heard in Phase 1.

At this stage, the increased flow of blood is pounding against the artery walls.

Phase Four

At this point, there is an abrupt muffling of sound.

The blood flow is becoming less turbulent. Some medical practitioners choose to record this point as the diastolic pressure.

Phase Five

This is the point at which sounds cease to be heard all together.

The blood flow has returned to normal and is now laminar.

The pressure cuff is deflated entirely and removed.

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Common Errors in Assessing Blood Pressure and their Effect

Common Errors in Assessing Blood Pressure and their Effect

Error

Effects

Bladder cuff too narrow

Erroneously high BP

Bladder cuff too wide

Erroneously low

Arm unsupported

Erroneously high

Insufficient rest before the assessment

Erroneously high

Repeating assessment too quickly

Erroneously high systolic and high diastolic readings

Cuff wrapped too loosely or unevenly

Erroneously high

Deflating cuff too slowly

Erroneously high diastolic reading

Failure to use the same arm consistently

Inconsistent measurements

Arm above the level of the heart

Erroneously low

Assessing immediately after a meal or while client smokes, or has pain

Erroneously high

Failure to identify auscultatory gap

Erroneously low systolic pressure and erroneously low diastolic pressure.

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Procedure for Assessing Blood Pressure

Procedure for Assessing Blood Pressure

Assess

Signs and symptoms of hypertension such as nose bleeds, headache, ringing in the ears, flushing of face, and fatigue.

Signs and symptoms of hypotension such as tachycardia, dizziness, mental confusion, restlessness, cool and clammy skin, pale or cyanotic skin.

Factors affecting blood pressure such as activity, emotional stress, pain, and the time the client last smoked or ingested caffeine.

Planning

Equipment

Stethoscope

Blood pressure cuff of the appropriate size

Sphygmomanometer

A container with tissue wipes with alcohol

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Technique (procedure)

Technique (procedure)

Explain to the client what you are going to do, why it is necessary and how he or she can cooperate.

Discuss how the results will be used in planning further care or treatments.

Wash hands and observe appropriate infection control procedures.

Provide client privacy

Position the client appropriately.

The adult client should be sitting unless otherwise specified.

Both feet should be flat on the floor since legs crossed at the knee result in elevated systolic and diastolic blood pressures.

The elbow should be slightly flexed with the palm of the hand facing up and the forearm supported at heart level.

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The blood pressure is normally similar in sitting, standing, and lying positions.

The blood pressure is normally similar in sitting, standing, and lying positions.

The blood pressure increases when the arm is below the heart level and decreases when the arm is above the heart level.

Wrap the deflated cuff evenly around the upper arm.

Locate the brachial artery.

Apply the centre of the bladder directly over the artery.

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.

If this is the client’s initial examination, perform a preliminary palpatory determination of systolic pressure.

The initial estimate tells the health care provider the maximum pressure to which the manometer needs to be elevated in subsequent determinations.

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It also prevents under estimations of the systolic pressure should an auscultatory gap occur.

It also prevents under estimations of the systolic pressure should an auscultatory gap occur.

Palpate the brachial artery with the fingertips.

Close the valve on the pump by turning the knob clockwise.

Pump up the cuff until you no longer feel the brachial pulse.

At that pressure the blood cannot flow through the artery.

Note pressure on the sphygmomanometer at which pulse is no longer felt.

This gives an estimate of the maximum pressure required to measure the systolic pressure.

Release the pressure completely in the cuff, and wait 1 to 2 minutes before making further measurements.

Awaiting period gives the blood trapped in the veins time to be released.

Otherwise, false high systolic readings will occur.

Position the stethoscope appropriately.

Clean the earpieces with alcohol or recommended disinfectant.

Insert the ear attachments of the stethoscope in your ears so that they tilt slightly forward.

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Sounds are heard more clearly when the ear attachments follow the direction of the ear canal.

Sounds are heard more clearly when the ear attachments follow the direction of the ear canal.

Ensure that the stethoscope hangs freely from the ears to the diaphragm.

Rubbing the stethoscope against an object can obliterate the sounds of the blood within an artery.

Place the bell side of the amplifier of the stethoscope over the brachial pulse.

Auscultate the client’s blood pressure.

Pump up the cuff until the sphygmomanometer reads 30mm Hg above the point where the brachial pulse disappeared.

Release the valve on the cuff carefully so that the pressure decreases at the rate of 2 to 3mm Hg per second. If the rate is faster or slower an error in measurement may occur.

As the pressure falls, identify the manometer reading at each of the five phases, if possible.

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Deflate the cuff rapidly and completely.

Deflate the cuff rapidly and completely.

Wait 1 to 2 minutes before making further determinations.

Repeat the above steps once or twice as necessary to confirm the accuracy of the reading.

If this is client’s initial examination, repeat the procedure on the client’s other arm. The difference between arms should not be more the 10 mm Hg.

The arm found to have the higher pressure should be used for subsequent examinations.

Record the blood pressure readings in the patient’s chart. Report any abnormalities noted.

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Key Points

Key Points

Blood pressure reflects cardiac output, peripheral vascular resistance, blood volume, and blood viscosity.

Factors influencing blood pressure are age, exercise, stress, gender, medications, obesity and diurnal variations, and disease processes.

Increases in peripheral resistance, blood volume, and cardiac output result in higher blood pressure.

Conversely decreases in any of these factors lead to lower blood pressure.

Three main sources of peripheral resistance: Blood vessel diameter, blood viscosity, and total vessel length.

If arteries lose their elasticity and become more rigid, blood pressure increases.

In taking blood pressure one has to assess, plan and carry out the measure making sure patient is comfortable

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Evaluation

Evaluation

What is pulse pressure?

Mention the common sites for assessing blood pressure.

For client with a previous blood pressure of 138/74 and pulse of 64, approximately how long should the health care provider take to release the blood pressure cuff in order to obtain an accurate reading?

What are the factors affecting blood pressure?

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References

References

Franco, V., & Oparil, S. (2006). Salt Sensitivity, a Determinant of Blood Pressure, Cardiovascular Disease and Survival: Journal of the American College of Nutrition, Vol. 25, No. 90003, 247S-255S

Kozie, B. et al. (2004). Fundamentals of Nursing, Concepts Process and Practice. (7th ed.), New Jersey: Pearson Education Inc.

Margret, F.’ & Alexander, (2008). Nursing Practice Hospital and Home. (3rd ed.). London: Architect Inc.

MOHSW (2008). Basic Nursing Procedures: A Manual for Nursing Practice in Tanzania. (3rd ed.).Dar es Salaam, Tanzania: Ministry of Health and Social Welfare.

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BELIEVE IN WHAT YOU DO

BELIEVE IN WHAT YOU DO

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