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usually a doctor. It is good practice for the reviewer to document their interpretation of the ECG directly on to the ECG and to sign and date it. Once reviewed, the ECG should be filed in the patient’s medical notes. Nurses should document in the nursing notes when the ECG was recorded, who was asked to review it and the actual time the ECG was reviewed and indicate whether it was normal or, if abnormal, what further action was taken.

Blood pressure

Definition

Blood pressure may be defined as the force of blood inside the blood vessels against the vessel walls (Marieb and Hoehn 2010). Systolic pressure is the peak pressure of the left ventricle contracting and blood entering the aorta, causing it to stretch and therefore in part reflects the function of the left ventricle (Marieb and Hoehn 2010). Diastolic pressure is when the aortic valve closes, blood flows from the aorta into the smaller vessels and the aorta recoils back. This is when the aortic pressure is at its lowest and tends to reflect the resistance of the blood vessels (Marieb and Hoehn 2010).

Related theory

Blood pressure is determined by cardiac output and vascular resistance and can be described as:

Cardiac output is the volume of blood which flows out of the heart over a specified length of time (Marieb and Hoehn 2010). It is governed by the stroke volume of the heart (the amount of blood pumped out of the ventricles per beat) and the heart rate. The relationship is:

Therefore, if the two equations are combined, blood pressure could be seen as being:

In theory, anything which alters one of the above components (stroke volume, heart rate and resistance) will therefore produce a change in blood pressure. However, this is not always the case as a drop in one may be compensated for by an increase in the other (Patton and Thiobodeau 2009).

Normal blood pressure

Normal blood pressure ranges between 110–140 mmHg systolic and 70–80 mmHg diastolic at rest (Marieb and Hoehn 2010). However, it varies depending on age (increasing with age), activity and sleep, emotion and positioning (Levick 2010). It also varies depending on the time of day, being at its lowest while we sleep (Levick 2010). Blood pressure therefore reflects individual variations but an abnormal blood pressure should not be assumed to be the individual’s norm; rather, it will need to be assessed in relation to their previous results, general condition and other observations.

Hypotension

Hypotension is generally defined in adults as a systolic blood pressure below 100 mmHg (Marieb and Hoehn 2010). A low blood pressure may indicate orthostatic hypotension, that is, sudden drop in blood pressure when the patient rises from a supine or sitting position. This is usually compensated for by the baroreceptor reflex and the sympathetic nervous system but especially in older people, this may not work as efficiently (Marieb and Hoehn 2010). Hypotension can also be a symptom of many other conditions including shock, haemorrhage and malnutrition (Marieb and Hoehn 2010). Hypotension results in reduced tissue perfusion leading to hypoxia and an accumulation of waste products (Foxall 2009).

Hypertension

Hypertension is defined as sustained blood pressure greater than 140/90 mmHg (NICE 2006, Patton and Thiobodeau 2009). It can be either primary hypertension, with no single known cause, or secondary hypertension related to another factor such as kidney disease (Patton and Thiobodeau 2009). Factors leading to hypertension include gender, genetic factors and age, alongside risk factors such as obesity, lack of exercise, smoking and high caffeine and alcohol intake (Patton and Thiobodeau 2009). If hypertension is sustained, the heart will have an increased workload to maintain circulation; greater stress will be placed on the blood vessel walls and cardiac ischaemia can occur (Foxall 2009).

There are many illnesses and factors which can lead to changes in blood pressure (see Figure 12.9).

Figure 12.9 Factors that lead to an increase in blood pressure. Changes noted within green boxes increase