Blood Pressure

Subject: Fundamentals of Nursing

Overview

Blood Pressure

Blood pressure may be defined as the force exerted by blood against the walls of the vessels in which it is contained. The term blood pressure usually refers to the pressure of blood on the arterial wall. The force exerted by blood is of two types- the systolic and the diastolic blood pressure.

Systolic blood pressure: It is the highest degree of force exerted by blood on the arterial wall. This occurs when the left ventricle contracts to pump out blood into the large arteries. The normal range of systolic pressure is 110 mm of Hg to 140 mm of Hg.

Diastolic blood pressure: It is the lowest degree of force exerted by blood on the arterial wall when the heart is resting often contraction of the left ventricles. The normal range of diastolic blood pressure is 60 to 90 mm of Hg.

Pulse pressure: The difference between the systolic and diastolic blood pressure is called the pulse pressure. It indicates the volume output of the left ventricle. A pulse pressure of 20 to 50 mm of Hg is considered normal.

Factors Influencing Blood Pressure

Pumping action of the heart: Pascal's law operates in the pumping actions of the heart. This law states that any pressure applied to any part of enclosed fluid at rest is transmitted to all parts of the body. The circulatory system in the body is an enclosed system. The pressure caused by the contraction of the left ventricle is transmitted to the blood in the arteries. So a strong pumping action of the left ventricle results in high blood pressure whereas, a weak pumping action results in low blood pressure.

The volume of the circulating blood: The volume of the blood circulating in the vascular system affects the blood pressure. When the volume increases in an enclosed space such as a blood vessel, the pressure in that space rises and when volume is less, blood pressure is lowered. Thus, as cardiac output increases, more blood is pumped against arterial walls, causing the BP to rise e.g. when blood and fluid are lost from the body, blood pressure is lowered. When blood and intravenous infusion are given, the blood volume is increased thereby increasing the blood pressure.

Viscosity of blood: The more viscous the blood, the higher the blood pressure. The thickness or viscosity of blood affects the ease with which blood flows through small vessels. When the hematocrit rises and blood flow slows, arterial BP increases. The heart contracts more forcefully to move the viscous blood through the circulatory system.

The condition of the arterial wall: Normally, the walls of an artery are elastic and easily distensible. As pressure within the arteries increases, the diameter of vessel walls increases to accommodate the pressure change. Arterial distensibility prevents wide fluctuations in BP. In certain diseases such as arteriosclerosis, the vessels walls lose their elasticity and are fibrous tissue that cannot stretch well. The less the elasticity of the arterial wall, the greater is the resistance to blood flow. As a result when the left ventricle ejects its stroke volume, the vessels no longer yield to pressure. Increased resistance of arterial wall causes increased blood pressure. 

Peripheral resistance: BP depends on peripheral vascular resistance. Arteries and arterioles are surrounded by smooth muscle that contracts or relaxes to change the size of the lumen. The size of the arteries and arterioles changes to adjust blood flow to the needs of local tissues. For example, when major organ needs more blood, the peripheral arteries constrict, decreasing their supply of blood. More blood becomes available to the major organs because of the resistance change in the periphery. Normally arteries and arterioles remain partially constricted to maintain a constant flow of blood. Peripheral vascular resistance is the resistance to blood flow determined by the tone of vascular musculature and diameter of blood vessels. The smaller the lumen of a vessel, the greater is the peripheral vascular resistance to blood flow. When the peripheral blood vessel is constricted, the peripheral resistance increases, thereby increasing blood pressure. When the peripheral blood vessel dilates, peripheral resistance decreases thereby decreasing blood pressure

Age: As age increases, blood pressure also increases. Blood pressure in infants is around 80/50 mm of Hg whereas in old age it may be 140/90 mm of Hg.

Stress: Anxiety, fear, pain and emotional stress result in sympathathetic stimulation, which increases heart rate, cardiac output and vascular resistance, increase blood pressure.

Medication: Narcotic and analgesics lower down blood pressure.

Exercise: Exercise will increase blood pressure.

Sex: In male, it is higher than in female.

Position: Blood pressure is lower in lying down than sitting or standing.

Smoking: smoking results in vasoconstriction, a narrowing of blood vessels. BP rises when person smokes.

Diet: High sodium containing diet increases blood pressure, low calcium containing diet increases blood pressure.

Time: Blood pressure is usually low in early morning and high in early evening.

Scientific Principles

  • Exercise, emotion, anxiety, fear, tension and worry cause a temporary rise in blood pressure. So take BP when the patient is in relax.
  • The brachial artery in superficial in the antecubital area which is a convenient place for taking BP.
  • A twisted cuff may produce unequal pressure and can cause inaccurate reading so wrap cuff around the arm smoothly. 78 od pol 18 the
  • Use the appropriate size of cuff according to the age of the patient. Too narrow or too wide cuff may produce error in blood pressure reading.
  • A noisy environment and parallax error interfere with correct reading on manometer.
  • Air light system of cuff and tubing facilitates accurate reading.
  • Accurate reading is possible only when the stethoscope is directly over the artery.
  • The rubber tube attached to the compression bag should not be allowed to cross or touch each other as this may interfere in the sound used to determine the BP.
  • Sufficient pressure in the cuff obliterates the flow of blood through the brachial artery. The cuff should not be inflated too much as this causes unnecessary discomfort to the patient.
  • The patient's arm should not be placed above the level of the patient's heart as it may cause low blood pressure reading up to 10 mm of Hg.
  • The instrument should be in the eye level.

Sites for Taking Blood Pressure

  •  Upper extremity
  • Lower extremity

Purposes

  • To obtain baseline data for diagnosis and treatment.
  • To monitor change in condition of the patient.
  • To assess response to medical therapy.
  • To compare with subsequent changes that may occur during care of patient.
  • To determine patient's hemodynamic status.

Methods of Taking Blood Pressure

S.N. Nursing Action Rationale
1

 Identify patient.

Check the physicians' order, nursing care plan performed for right patient.

 

Ensures that right procedure is performed for right patient.
2 Assess for factors that may alter blood pressure. Ensure that patient has not smoked ingested caffeine or involved in strenuous physical activity within 30 minutes prior to procedure. Allows nurse to accurately assess for presence and significance of respiratory alteration. Smoking and ingestion of caffeine can increase blood pressure.
3 Explain the procedure and reassure the patient. Obtains patient's cooperation and reduces anxiety.
4 Wash and dry hands. Prevents cross infection.
5 Collect and check equipment (Sphygmomanometer, stethoscope, cotton swabs, disinfecting solution, pen, note pad.) Arranging articles aids for smooth functioning. Ascertains evidence of malfunction.
6

Assist the patient to either sitting or lying down position.

 So that can easily take the patients pulse.
7

Position the sphygmomanometer at appropriately heart level of the patient ensuring that mercury level is at zero.

Select a cuff of appropriate size.

Helps in obtaining accurate reading.
8 Expose the arm to make sure that there is no constrictive clothing above the placement of cuff.  Ensures accurate reading.
9 Apply the cuff appropriately 2.5 cm above the point where brachial artery can be palpated. The cuff should be applied smoothly and  firmly with the middle of the rubber bladder directly over the artery. Wrapping the cuff too tightly will impede circulation and wrapping the cuff very loosely will lead to false elevation of pressure.
10 Secure the cuff by tucking the end under or by fixing the Velcro fastener.  Prevents unwrapping of the cuff. 
11 Place the entire arm at the patient's heart level. Keep the arm well rested and supported. Obtains accurate reading. Ensures comfort of the client thereby enabling an accurate reading.
12 Connect the cuff tubing to the manometer tubing if needed and close the value of the inflation bulb.  
13 Palpate the radial pulse and inflate the cuff until pulse is obliterated. Inflate the compression bag a further 20-30 mm of mercury and then deflate cuff slowly. Note the point at which the pulse reappers, then release the valve. This is the palpatory method of taking systolic BP. Taking the systolic pressure by using palpatory method, gives an idea of how much the cuff should be inflated for taking blood pressure by listening with the stethoscope.
14

After taking palpatory systolic blood pressure, palpate brachial artery and place diaphragm of the stethoscope lightly over the brachial artery. Ensure that ear pieces of the stethoscope are placed correctly.

Close the air valve and inflate the cuff. Raise mercury level 20-30 mm mercury above the point of systolic pressure obtained by means of palpatory method.

Ensures accurate reading.
15 Release the valve of the inflation bulb, so that mercury column falls at the rate of 2-3 mm of  mercury/sec.  Prevents erroneous reading due to faster rate of deflation.
16 When first sound is heard, the mercury level is noted; this denotes systolic pressure. Frist sound is heard when the blood begins to flow through brachial artery.
17

Continue to deflate the cuff. When the sound disappears, note the mercury level. This is diastolic pressure.

  
18 Deflate the cuff completely and remove the cuff from the patient's arm. Occlusion of artery during the pressure reading causes venous congestion in the forearm.
19 Repeat the procedure after one minute if there is any doubt about the reading. Waiting time of one minute allows venous blood to drain completely.
20

Remove the equipment and clean ear pieces with a sprit swab.

Wash hands

Prevents chance of cross infection. with a sprit swab.
21 Ensure that the patient is comfortable.  
22 Document the reading in an appropriate observation chart or flow chart. Report any abnormal findings.  Maintains records.

 

Special Precautions

Do not take blood pressure on a patient's arm if:

  • The arm has an intravenous infusion on it.
  • The arm is injured/diseased.
  • The arm has a shunt/fistula for renal dialysis.
  • On the same side of the patient, he has had a radical mastectomy.
  • The arm is paralyzed.

Abnormality in Blood Pressure

Hypertension: When blood pressure is above the normal level, it is called hypertension. When diastolic reading is above 90 mm of Hg and the systolic reading is above 140 mm of Hg, the person is said to have hypertension.

Orthostatic hypertension: It is low BP associated with weakness or fainting when rising to n erect position. It is result of peripheral vasodilation without a compensatory increase in cardiac output.

Hypotension: When the pressure is below the normal level, it is called hypotension. When the systolic BP is below 110 mm of mercury or the diastolic BP is below 70 mm mercury, the person is said to have hypotension.

Pascal's Law and Blood Pressure

Pascal's law states that "A change in the pressure of an inclosed imcompressible fluid is conveyed undiminished to every part of the fluid and to the surfaces of its container." or pressure exerted on liquid will be equally distributed throughout the whole compartment. The same principle applies in our blood circulation. The circulatory system in the body is an enclosed system. When the left ventricle contracts it causes a pressure on the arteries which is equally transported throughout the whole system.

 

 

 

 

 

 

 
Things to remember

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