Arterial Blood Pressure and Shock

Definition of Blood Pressure

It is the pressure of the column of blood in the arterial system

Hypertension

Increase in blood pressure

Hypotension

Decrease in blood pressure

Components of Blood Pressure

Systolic blood pressure (SBP)

• It is the maximum pressure exerted during systole
• Normal value: 100-130 mmHg, Average: 120 mmHg

Diastolic blood pressure (DBP)

• It is the minimum pressure exerted during diastole
• Normal value: 70-75 mmHg, Average: 80 mmHg

Pulse pressure (PP)

• It is the difference between SBP and DBP (SBP-DBP)
• Average: 40 mmHg

Mean blood pressure (MBP):

• It is the average ofpressure throughout the cardiac cycle
• It can be calculated as DBP+1/3pp
• Normal value 95-100 mmHg, Average: 96 mmHg

Blood Pressure: Functions

• To maintain sufficient pressure head to keep the blood flowing through the blood vessels.
• To provide the motive force of filtration at the capillary bed, thus assuring nutrition to the tissue cells, formation of urine, lymph etc.

Factors affecting Blood Pressure

Age

• Both SBP and DBP increase with age

Gender

• During menopause SBP in females is less than males

Body built

• Obese individuals have high blood pressure

Climate

• Exposure to cold increases the BP
• Exposure to heat decrease the BP

Diurnal variation

• Lowest in the morning and peak values during afternoon

Exercise

• BP increases with severity of exercise

Emotions

• Excitement, fear and worry increase the SBP

Gravity

• Pressure in the vessel below the heart is more

Hereditary

• Familial tendencies of hypotension or hypertension are common

Meals

• SBP increases after meals

Sleep

• Sleep decreases the BP

Posture

• In standing posture DBP increases

Regulation of Blood Pressure

The aim of regulating the blood pressure is to maintain the normal Mean Blood Pressure within a narrow range

Different regulatory mechanism exists, which are

1. Rapidly acting regulatory mechanisms
2. Intermediate-acting regulatory mechanisms
3. Long-term regulatory mechanisms

Rapidly acting regulatory mechanisms

They begin to act within seconds to minutes after change in arterial blood pressure. It consists of following mechanisms

1. Baroreceptor reflex
2. Chemoreceptor reflex
3. CNS Ischaemic Response

Baroreceptor reflex

• Baroreceptors are receptors which are sensitive to pressure, i.e the stretch of the blood vessels
• They are present in carotid sinus and arch of aorta
• Raise in BP stimulates the baroreceptors
• The baroreceptors cause inhibition of the vasomotor center (VMC) and stimulation of cardiac vagal center (CVC) restoring the BP

Chemoreceptor reflex

• Chemoreceptors are receptors which are sensitive to change in the composition of blood
• They are present in carotid and aortic bodies
• Fall in BP decreases blood flow to the tissue which causes decrease in pO2 and increase in pCO2 to carotid and aortic bodies.
• The chemoreceptors cause stimulation of VMC and inhibition of CVC to restore the BP

CNS Ischaemic Response

Fall in BP → CNS ischaemia → CO2 accumulation in VMC → Stimulation of pressor area of VMC → Powerful sympathetic discharge throughout the body → Increase in HR and BP to maintain normal supply of blood to brain (last ditch stand to prevent the death of a person)

Intermediate acting regulating mechanisms

• They begin to act within few minutes and reach their full function within a few hours and remain functional from a few days to a month
• They primarily correct any change in the BP by changing the blood volume

Long term regulatory mechanisms

It is autoregulation of BP by kidneys

It takes 3-10 days for these mechanisms to come into act

The regulation is done by 2 ways

• Direct mechanism: It involves the control of blood volume by the kidneys
• Indirect mechanism: It involves the control of kidney functions indirectly via hormonal system

Application and implication in Nursing

Hypertension

It is defined as sustained increase of systemic arterial blood pressure above 140/90 mmHg

It is classified as

1. Primary or essential hypertension: Due to unknown cause
2. Secondary hypertension: Due to some underlying cause

Hypertension if untreated it can cause heart disease and stroke (paralysis)

Shock

It is a clinical syndrome characterized by inadequate tissue perfusion due to acute cardiac failure

Types of Shock

1. Hypovolemic shock
2. Cariogenic shock
3. Distributive
4. Obstructive

Characteristic features

• Hypotension (Low BP)
• Rapid and thready pulse
• Rapid, shallow breathing
• Cold, pale and moist skin
• Intense thirst
• Restless
• Nausea