Chapter 3: Measuring and Recording the Vital Signs

Introduction

The measurement and recording of the vital signs is the first step in the process of physically examining a patient - that is, in collecting objective data about a patient's signs (i.e. what the nurse can observe, feel, hear or measure). This is a fundamental skill for nurses working in all clinical areas, but one which only develops with practice. This chapter introduces the knowledge and skills required by nurses to accurately measure and record a patient's vital signs - that is, their blood pressure (BP), pulse or heart rate (HR), temperature (T°), respiratory rate (RR) and blood oxygen saturation (SpO₂).

This chapter begins with an introduction to the importance of measuring the vital signs in nursing practice. It goes on to describe the measurement of each of the vital signs and the collection of other supporting data (e.g. height, weight, pain score), discussing key strategies and considerations. The chapter then reviews the processes involved in recording the data collected about the vital signs. Finally, the chapter discusses how a nurse should go about interpreting the data they have obtained, to build a clinical picture of the patient and plan for their care.

Important note

This section of the chapter assumes a basic knowledge of human anatomy and physiology. If you feel you need to revise these concepts, you are encouraged to consult a quality nursing textbook.

Measurement and recording of the vital signs

As described in the introduction of this chapter, the measurement and recording of the vital signs is a fundamental skill for nurses working in all clinical areas. The vital signs - blood pressure (BP), pulse or heart rate (HR), temperature (T°), respiratory rate (RR) and blood oxygen saturation (SpO₂) - provide baseline indicators of a patient's current health status. It is important to note that some nurses measure and record the vital signs at the commencement of the physical examination, while others integrate the collection of vital signs data into the physical examination; either approach is fine, provided the nurse is systematic in the way in which they approach their assessment, and so collects accurate and complete health data.

As you saw in the previous chapter of this module, health observation and assessment involves three concurrent steps:

The measurement and recording of the vital signs is the first step in the process of physically examining a patient. This step involves collecting objective data - that is, data about a patient's signs (i.e. what the nurse can observe, feel, hear or measure). Data collected during the physical examination, including measurements of the vital signs, is combined with that collected during the health history (as described in the previous chapter of this module), to build a complete picture of the clients' health status.

The normal parameters for each of the vital signs of healthy adults are listed following:

Nurses should become thoroughly familiar with the parameters for each of the vital signs. However, it is important for nurses to remember that these are average values for healthy adults. Some adults may have values which fall outside of these ranges. For example, very fit adults may have a pulse or heart rate which normally sits at or below 60 beats per minute; similarly, adults with respiratory conditions often have an oxygen saturation which normally sits well below 98%. Children and neonates have differing normal parameters for each of the vital signs; nurses who work with these patient groups must become familiar with these. When interpreting vital signs, it is important that nurses use critical thinking to interpret the entire clinical picture of the individual patient with whom they are working.

Measurement of blood pressure

Blood pressure is often abbreviated to 'BP'. Blood pressure uses two measurements, each recorded in millimetres of mercury (mmHg) - for example, 120mmHg / 80mmHg, often abbreviated to 120/80. Blood pressure is defined as the pressure of the blood against the arterial walls:

• When the heart contracts (systolic BP - the first measurement), and
• When the heart rests (diastolic BP - the second measurement).

Essentially, blood pressure is a measurement of the relationship between: (1) cardiac output (the volume of blood ejected from the heart each minute), and (2) peripheral resistance (the force that opposes the flow of blood through the vessels). Blood pressure also depends on factors such as the velocity of the blood, the intravascular blood volume and the elasticity of the vessel walls, etc.

The difference between the systolic and diastolic blood pressures is referred to as the pulse pressure. This normally ranges between 30mmHg and 40mmHg.

Blood pressure can be measured in a number of different ways. It is measured directly by inserting a small catheter into an artery - however, as a very invasive procedure, this strategy is typically only used for patients who are critically ill and for whom blood pressure is very difficult to measure accurately. In all other settings, blood pressure is measured indirectly using: (1) a sphygmomanometer and a stethoscope (a 'manual' measurement), or (2) a non-invasive blood pressure monitor (an 'automatic' measurement). This section of the chapter will teach both methods.

• Measuring blood pressure using a sphygmomanometer and a stethoscope (a 'manual' measurement): The client should be sitting or lying down. The arm used to take the blood pressure should be at the client's side, slightly flexed and with the palm turned upwards. The nurse should palpate the brachial pulse, in the antecubital space (i.e. the groove between the biceps and triceps muscles, in the bend of the elbow). A blood pressure cuff should be placed 2.5 centimetres above the site of the brachial pulse, with the bladder of the cuff (usually marked with a white stripe) centred over the artery. The cuff should be secured so it fits evenly and snugly around the arm.

The manometer - the device used to read the blood pressure measurement - should be positioned at the nurse's eye level. The valve on the pressure bulb should be closed by turning it clockwise. Avoid closing the valve too tightly, or it may be too difficult to release when the time comes to do so.

Place the stethoscope over the patient's brachial pulse, and hold it with your non-dominant hand. Place the binaurals (earpieces) of the stethoscope in your ears. Using your dominant hand, inflate the cuff to around 180mmhg (note that you may need to go higher if the patient's systolic blood pressure is >180mmHg, however this is rare). Then, release the valve to deflate the cuff, slowly and steadily (around 2 to 3mmHg per second to reduce measurement errors). You are listening for two things:

1. The first Korotkoff sound. This is a sharp thump or tap of the brachial pulse, which indicates the systolic blood pressure. Read the pressure (in mmHg) on the manometer at the point this occurs.
2. The disappearance of all Korotkoff sounds (i.e. all the noises related to the brachial pulse). This indicates the diastolic blood pressure. Read the pressure (in mmHg) on the manometer at the point this occurs.

Once these two measurements have been made, the cuff should be completely deflated and removed from the client's arm. The two blood pressure readings should be promptly recorded.

• Measuring blood pressure using a non-invasive blood pressure monitor (an 'automatic' measurement): This is achieved using the same principles as with the manual measurement, described above. However, it involves using an electronic monitoring device; this measures the circulating blood flow using an electronic sensor and, therefore, does not require the nurse to listen for Korotkoff sounds. The cuff of an automatic blood pressure monitor is applied in the same way as described above. The nurse then presses a 'start' button to instruct the machine to inflate the cuff, take a measurement and provide a reading.

It is important to highlight that although automatic blood pressure measurements are quick and convenient, they are not as accurate as manual blood pressure measurements. If a non-invasive blood pressure monitor returns a reading which is outside the expected parameters, it should always be checked with a manual measurement. Furthermore, it is worth noting that a cuff must fit correctly on a patient's arm, and be placed correctly so the bladder of the cuff is above the brachial artery, if a non-invasive blood pressure monitor is to return an accurate reading.

As described in the above section, the upper arm is the most common site to measure blood pressure; however, if this is not possible, blood pressure may also be measured from the thigh. Research suggests that the systolic blood pressure is slightly higher in the leg than in the arm, but the diastolic blood pressures are roughly similar. Blood pressure is taken on the thigh using the same technique described above.

In some cases, a patient may have their blood pressure taken a number of times in a number of positions (e.g. lying, sitting, standing). This is done to assess the client for orthostatic hypotension. This occurs when there is a 20 to 30mmHg drop in blood pressure when the client changes positions, and it may indicate health problems.

It is important for nurses to note that there are a number of common errors associated with blood pressure measurement. Errors may result if:

• The client's arm is positioned above or below the level of their heart.
• The cuff used is too large or too narrow for the client's arm.
• The cuff is wrapped too loosely or unevenly around the client's arm.
• The cuff is not deflated to a pressure higher than the patient's systolic blood pressure.
• The cuff is deflated at a rate slower or faster than 2 to 3mmHg per second.
• The cuff is reinflated (e.g. to check readings) before it is completely deflated.
• The stethoscope is pressed too firmly against the brachial artery.
• The nurse fails to wait 2 minutes before repeating the blood pressure measurement.

As described above, the majority of the common errors associated with blood pressure measurement are related to the size and position of the cuff. Blood pressure cuffs come in a variety of sizes, and it is essential that nurses select the correct size for the individual patient with whom they are working - if the cuff is too large, blood pressure will be underestimated, and if it is too small, blood pressure will be overestimated. Ideally, the width of the cuff should be 40% of the circumference of the limb from which the blood pressure is being measured, and the bladder within must encircle at least 80% of the limb.

As you saw in an earlier section of this chapter, the average blood pressure of a healthy adult is 120mmHg/80mmHg, typically written as 120/80. When measuring a client's blood pressure, a nurse may identify that it is high - a condition referred to as hypertension, or low - a condition referred to as hypotension. There may be a number of pathophysiological causes of hypertension (e.g. brain injury, systemic vasoconstriction, fluid retention, etc.)  and hypotension (e.g. fluid / blood loss, dehydration, etc.). It is important for nurses to recognise that there are also a number of physiological factors which affect blood pressure measurement; for example, recent exercise, feeling anxious or angry, experiencing pain, ingesting caffeine or tobacco, and obesity can all result in a patient recording higher than normal blood pressure. Remember: when interpreting vital signs, it is important that nurses use critical thinking to interpret the entire clinical picture of the individual patient with whom they are working.

Measurement of pulse or heart rate

Pulse or heart rate is often abbreviated to 'HR'. It is defined as the number of times a person's heart beats in a one-minute period. It is recorded at a rate of 'beats per minute'. Each contraction of the heart results in the ejection of blood into the vascular system, and this is felt in key locations of the body as a 'pulse'. In addition to assessing the rate at which a person's heart is beating, when measuring a person's HR, a nurse should also assess for the rhythm and quality of the pulse.

A patient's pulse may be measured using the same types of non-invasive, automatic monitors used to measure blood pressure, as described in the previous section of this chapter. However, it is generally preferred that heart rate is assessed by palpating a pulse, and it is this technique which will be taught in this chapter.

To measure a pulse, a nurse should place their fingers over an artery and feel for the pulse. Generally, pulses are palpated with the pads of the index and middle fingers. Firm pressure is applied to the pulse, but not so much pressure that the artery is occluded. There are a number of locations on the body in which a nurse may palpate an artery to feel for a pulse; the most common are:

• The radial artery, located on the outer edge of each wrist.
• The brachial artery, located in the antecubital space on each arm.
• The carotid artery, located on the inner sides of the sternocleidomastoid muscle in the neck.

It is important for nurses to note that a patient's heart rate can also be assessed by auscultating the heart. This is referred to as measuring the apical pulse.

When measuring the HR, a nurse may:

• Count the number of pulses for 60 seconds.
• Count the number of pulses for 30 seconds, and multiply by 2 - if the HR is regular.
• Count the number of pulses for 15 seconds, and multiply by 4 - if the HR is regular.

As described, it is important that a nurse assesses the pulse for regularity. If the pulse is irregular (i.e. the time between each beat varies, or beats are skipped, etc.), the pulse must be counted for one full minute (60 seconds). Additionally, an irregular pulse must be documented when recording the vital signs.

It is also important that the nurse assess the quality of the pulse - that is, its key characteristics. A patient's pulse may be described using terms such as thready (meaning the pulse is 'weak') or bounding (meaning the pulse is 'full' and 'strong'). This is important information that is used, along with HR and regularity of the pulse, to assess the health of the cardiovascular and other body systems.

The average pulse or heart rate for a healthy adult is 60 to 100 beats per minute. If a patient's pulse is >100 beats per minute, this is referred to as tachycardia; pain, infection, dehydration, stress, anxiety, thyroid disorder, shock, anaemia, certain heart conditions, etc. can all result in tachycardia. If a patient's pulse is <60 beats per minute, this is referred to as bradycardia; cardiac conduction defects, overdose (e.g. central nervous system depressants), head injury, severe hypoxia (with impending respiratory / cardiac arrest), shock, etc. can all result in bradycardia.

Measurement of temperature

Temperature is often abbreviated to 'T°'. This is defined as the temperature, in degrees Celsius (°C), of a person's body. Temperature is typically measured using a thermometer, which may be either automatic or manual. Temperature may be measured by one of several different routes:

• Orally, with the thermometer placed under the tongue (i.e. in the right or left sublingual pockets). This is the safest way of recording a patient's temperature, and also one of the most accurate. When taking an oral temperature measurement, nurses should take care to ensure the patient has not recently (within the last 10 minutes) ingested hot or cold foods or liquids, that the thermometer is covered by an appropriate shield (for hygiene purposes), and that the patient closes their mouth completely while the thermometer reads their temperature. Automatic thermometers can take up to 30 seconds to record a temperature reading.
• Via the tympanic membrane, with the thermometer placed onto the tympanic membrane within the ear. When taking a tympanic temperature measurement, nurses should take care to ensure that the thermometer is covered by an appropriate shield (for hygiene purposes), and that the sensor comes into contact with all sides of the ear canal.
• Via the axilla, with the thermometer placed under the arm. Although the axilla is a convenient location from which to record a temperature measurement, the accuracy of temperature measurements recorded here are uncertain (i.e. the axilla probably poorly reflects core body temperature).
• Rectally, with the thermometer inserted into the patient's rectum. This is both a safe and accurate way of recording a patient's body temperature, but it is both uncomfortable and invasive; therefore, it is not often used in most clinical settings.

When using an automatic or electronic thermometer to record a patient's temperature, the nurse should place the thermometer in the location on the patient's body at which the temperature is to be recorded, press 'start', and wait for an audible signal and the measurement to register on a display screen. If using a manual thermometer, the thermometer must be located on the patient's body as described, and the nurse must wait at least one full minute before reading the measurement on the gauge of the thermometer. It is worth noting that manual thermometers are rarely used in most clinical settings in the United Kingdom.

The average temperature for a healthy adult is 36.5°C to 37.5°C. If a patient's temperature is >37.5°C, they are said to have hyperthermia or a fever. If a patient's temperature is <36.5°C, they are said to have hypothermia. Causes of variations from normal temperature include infection, stress, dehydration, recent exercise, being in a hot or cold environment, drinking a hot or cold beverage, and thyroid disorders.

Measurement of respiratory rate

Respiratory rate is often abbreviated to 'RR'. This is defined as the number of times a person inhales and exhales in a 1 minute period. It is recorded at a rate of 'breaths per minute'.

Respiratory rate is typically measured by counting the number of times a patient completes a full ventilatory cycle (inhalation plus exhalation) in a 1 minute period. This can be measured by watching the rise and fall of the patient's chest and / or abdomen, or (though less commonly) the breath sounds may also be auscultated. It is best that nurses measure a patient's respiratory rate when the patient is unaware that they are doing so, as this will prevent the patient unconsciously (or even consciously!) changing the way they breathe.

When measuring the RR, a nurse may:

• Count the number of pulses for 60 seconds.
• Count the number of pulses for 30 seconds, and multiply by 2 - if the RR is regular.
• Count the number of pulses for 15 seconds, and multiply by 4 - if the RR is regular.

In addition to assessing a patient's heart rate, the nurse should assess:

• The rhythm, or pattern / regularity, of the patient's breathing.
• The depth of the patient's breathing, or level of lung expansion (normal, shallow, or deep).
• The effort associated with the patient's breathing, often evaluated by observing for accessory muscle use and tissue retractions, etc.

The average respiratory rate for a healthy adult is 10 to 16 breaths per minute. If a patient's RR is >16 breaths per minute, this is referred to as tachpynoea; this may result from cellular hypoxia, acidosis, conditions that interfere with gas exchange / ventilation / perfusion (e.g. pulmonary oedema, pneumonia, pulmonary embolism), shock, pain, anxiety, asthma, respiratory disease, cardiac disease, etc. If a patient's RR is <10 breaths per minute, this is referred to as bradypnoea; this may result from head injury, stroke, overdose (particularly of central nervous system depressants), respiratory failure, etc.

Measurement of blood oxygen saturation

Blood oxygen saturation is often abbreviated to 'SpO₂'. This is defined as the amount of oxygen present in a person's blood - specifically, bound to their haemoglobin - at a given time. It is measured as a percentage, using a non-invasive automatic measuring device called a pulse oximeter. The probe of a pulse oximeter is usually placed on the end of a patient's finger or toe or, less commonly, on their earlobe or their nose. A reading is given on the machine's screen after a period of approximately 15 seconds.

The blood oxygen saturation of a healthy adult is typically 98%-100%. A variety of problems, particularly those related to the respiratory and cardiovascular systems (refer to the information on HR and RR, above), can result in a patient's blood oxygen saturation reducing below this normal range.

Measurement of height, weight and body mass index (BMI)

Although not strictly vital signs, a patient's height, weight and - subsequently - their body mass index (BMI) can provide a nurse with important information about their overall health and physical condition. A patient's weight is measured using a scale, whilst their height is measured using a platform ruler or tape measure. Body mass index can then be calculated, using the following formula: BMI = Weight (kg) / Height (m)² It is worth noting that most clinical areas have charts which assist nurses to calculate BMI.

BMI is a useful, objective measurement of a person's body condition, based on their unique height and weight. A patient's BMI is interpreted as follows:

It is worth noting that the accuracy of the BMI measurement - and, therefore, its utility in the clinical context - is subject to much conjecture. As always, it is important that nurses use critical thinking to interpret the entire clinical picture of the individual patient with whom they are working.

Measurement of pain

In many clinical areas, pain is considered the sixth 'vital sign'. Pain is generally assessed using a strategy which can be remembered using the 'OPQRST' mnemonic

It is also important to highlight that there are a number of visual scales which can be used to assess pain in patients who are non-verbal. In patients who cannot describe their pain or communicate that they are experiencing pain, nurses should look for other signs of pain - such as restlessness, agitation, tachycardia, diaphoresis, pallor, etc.

Recording the vital signs

So far, this chapter has described in detail the processes involved in measuring a patient's vital signs. Once these have been measured, the information must be documented so that it can be used to: (1) assess the patient's condition, and (2) inform the care which is appropriate for that patient. As you saw in a previous chapter of this module, there are a variety of different ways that data can be recorded, and this generally differs between clinical settings and organisations; nurses are encouraged to familiarise themselves with the documentation strategies used in the organisation where they work. Regardless of how data is recorded, however, documentation must be complete, accurate, concise, legible and free from bias. You should revise the principles of documenting health observation and assessment data from the earlier chapter of this module, if required.

Often in the United Kingdom, a patient's vital signs are recorded using early warning score tools. These pieces of documentation allow a nurse to graphically represent a patient's vital sign measurements to identify changes over time, and to calculate simple scores which describe a patient's risk of deterioration into serious illness. Early warning score tools may also provide a nurse with information about how they should respond if they identify that a patient's vital signs are outside the expected ranges - for example, by increasing the frequency of monitoring, by requesting a medical review or by initiating an emergency call.

Interpreting the vital signs

Once you have measured and recorded a patient's vital signs, it is important that you are able to analyse and interpret the data you have collected. Essentially, this means attempting to understand and make sense of this data, based on the patient's physiological condition. Remember: it is important that nurses use critical thinking to interpret the entire clinical picture of the individual patient with whom they are working. Let's consider a case study example:

Example

Elizabeth is a graduate nurse working in the Accident and Emergency Department (A&E) of a large tertiary hospital in London. She is caring for a young man, Luke, who has been transported by road ambulance following a high-speed motor vehicle accident. Luke has an open, mid-shaft femoral fracture which is bleeding heavily.

Whilst receiving handover from the paramedics who attended the scene, Elizabeth measures Luke's vital signs, finding:

• A HR of 101 beats per minute (high).
• A RR of 18 breaths per minute (high).
• A BP of 60/110 (low).

The paramedics estimate that Luke has lost 1000mL of blood.

Elizabeth analyses and interprets this assessment data. She knows Luke has lost a significant amount of blood, which is likely to result directly in his low BP. Luke's high HR and RR are probably to compensate for his low blood pressure (i.e. his heart beats faster, and he breathes more rapidly, in an attempt to increase perfusion to his organs). Luke's high HR and RR may also be a response to the significant pain he is likely to be experiencing, and also shock at the situation in which he finds himself.

In analysing and interpreting her measurements of Luke's vital signs in this way, Elizabeth can plan effective care for Luke. She also has a baseline which she can use to evaluate the effectiveness of the care provided.

It is important to remember that learning to measure and record a patient's vital signs accurately, and to analyse and interpret the data collected, are skills which comes with practice. As a student and new graduate nurse, it is essential that you take every possible opportunity to practice collecting, recording and interpreting the vital signs of a variety of different patients, in a range of different clinical settings.

Conclusion

As you have seen in this chapter, the measurement and recording of the vital signs is the first step in the process of physically examining a patient - that is, in collecting objective data about a patient's signs (i.e. what the nurse can observe, feel, hear or measure). This chapter began with an introduction to the importance of measuring the vital signs in nursing practice. It went on to describe the measurement of each of the vital signs and the collection of other supporting data (e.g. height, weight, pain score), discussing key strategies and considerations. The chapter then reviewed the processes involved in recording data collected about the vital signs. Finally, the chapter discussed how a nurse should go about interpreting the data they have obtained, to build a clinical picture of the patient and plan for their care. In completing this chapter, you have become equipped with the knowledge and skills you require to accurately measure and record a patient's vital signs.

Reference list

Cox, C. (2009). Physical Assessment for Nurses (2nd edn.). West Sussex, UK: Blackwell Publishing, Ltd.

Jensen, S. (2014). Nursing Health Assessment: A Best Practice Approach. London, UK: Wolters Kluwer Publishing.

Wilson, S.F. & Giddens, J.F. (2005). Health Assessment for Nursing Practice (4th edn.). St Louis, MI: Mosby Elsevier.