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ObservationsChildren

Measuring blood pressure in infants, children and young people

Edited by Rose Mahoney, Lecturer in Children’s Nursing, London South Bank University

©2018 Clinical Skills Limited. All rights reserved

Arterial blood pressure is measured frequently throughout clinical practice. The readings provide part of an overall assessment of the patient’s condition and are vital in the monitoring and treatment of long-standing hypertension. Blood pressure is the pressure the blood exerts against the inner walls of the blood vessels, and it is the force that keeps blood circulating continuously even between heartbeats. The systolic component of blood pressure represents the pressure in the artery when the heart is contracting, whereas the diastolic phase is when the heart is at rest between beats (GOSH, 2015). Blood pressure varies throughout the vascular system: arterial systolic pressure is around 75 to 80 mmHg in an infant (ALSG, 2016). In a child aged between 1 and 10 years, you can calculate the expected systolic blood pressure using the formula: (age in years x 2) + 85, and for 10 years plus: age + 100 (ALSG, 2016). Blood pressure can be measured directly or indirectly. Direct measurement gives an accurate reading but is an invasive procedure involving cannulation and connection of a pressure transducer. Indirect measurement is performed using oscillometry via an automated electronic device, or by manual sphygmomanometry, using either a sphygmomanometer and a Doppler device, or a sphygmomanometer using auscultation with a stethoscope (GOSH, 2015). The latter is described here.

Blood pressure must be recorded in a standardised, reproducible manner. Many factors can influence the blood pressure recorded, including accuracy and efficiency of the equipment, use of correct technique and control of extraneous variables such as temperature, noise, crying, eating, exercise and movement (Dougherty & Lister, 2015). Children and young people are often unwilling to cooperate or remain still for a sufficient period of time (RCN, 2017). In older children, smoking may also be a factor.

Mercury sphygmomanometers were the mainstay of blood pressure recordings and management for many years. Although mercury devices are reliable and have formed the gold standard of measurement, they are being withdrawn internationally for health and safety reasons—notably the problem of dealing safely with mercury spillages and the ultimate disposal of mercury (see UKEA, 2012). NICE (2011) states that alternatives to mercury sphygmomanometers are now required for routine clinical use, but you are strongly advised to assess and evaluate published literature regarding the accuracy of the devices available. Aneroid devices may be less accurate than mercury sphygmomanometers and their alternatives, particularly over time (NICE, 2011).

Equipment

Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.

Electronic multifunction monitors that measure blood pressure, heart rate, temperature and oxygen saturations are common in healthcare settings. Such machines, if used, must be set up and calibrated using the manufacturer’s instructions and staff should be trained in their use. For more information on sphygmomanometers, see the Adults clinicalskills.net procedure: “Measuring blood pressure Part 1: Equipment”.

Doppler vascular flow detector and gel. (Although rare, a Doppler vascular flow detector is still used in some units.)

Electronic manual sphygmomanometer

Electronic multifunction monitor

Stethoscope

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Popliteal artery Position of cuff

Posterior tibial artery

Anterior tibial artery

This type of shunt diverts blood from the aorta to the pulmonary circulation. As a result, the blood volume in the pulmonary circulation rises, relieving the pressure in the right and left ventricles

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Measuring blood pressure in infants and children

Guide to cuff size: neonates to adolescents Ensure you are familiar with the cuff

Blalock-Taussig shunt

Measuring blood pressure in the lower leg (a)

Coarctation of the aorta: (a)

It is important to use a cuff of the appropriate size, according to the limb circumference (ALSG, 2016). Where reusable cuffs are used, it is important that they are cleaned between patients following local infection control policy. Cuffs for single-patient use are available and should be considered for infectious or immunocompromised patients. They are also used routinely in some wards and departments.

Check the cuff for signs of wear and tear (such as fluffing of the Velcro fastening). A loose cuff will not grip properly when inflated. Most cuffs have an expiry date; check that the cuff you are using has not gone past this date. The average life expectancy for a cuff is 18 months. Assess the quality of the tubing for cracks or any signs of perishing.

In a child with congenital heart disease who has a Blalock-Taussig shunt, the shunt will commonly affect readings on the right arm (although the shunt can be on the left or bilateral). If the shunt is bilateral, the blood pressure will need to be taken from the lower leg (Horrox, 2002).

The arm should be used for measuring blood pressure. If, however, this is not possible, the lower leg of an infant may be used, ensuring alignment of the centre of the bladder with the posterior tibial artery (RCN, 2017).

It is important to note that using the lower leg may give a higher systolic reading (Coyne et al., 2010). The limb used should always be documented to allow for consistent and accurate measurement (Dougherty & Lister, 2015).

In neonates suspected of having coarcation of the aorta, you should measure the blood pressure in all four limbs, as there may be a significant difference in blood pressure between the upper and lower limbs (South & Isaacs, 2012).

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(b) Document the limb used

Expiry dateRange finder

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When wrapped around the child’s arm, the end of the cuff must fall within the two lines that mark the range finder. If it does not, it is the wrong size.

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Indication Limb circumference/cuff size

Neonate 3–6 cm, 4–8 cm, 6–11 cm, 7–13 cm, 8–15 cm

Child 12–19 cm

Adolescent 17–25 cm

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(b) Using a Doppler device on an infant

Estimate the systolic pressure Position the stethoscope

Children with congenital heart disease who have had a subclavian flap repair for coarctation of the aorta should not have their blood pressure recorded on the left arm as it will be inaccurate (Horrox, 2002).

This method is used on some wards. If using a Doppler device, apply Doppler gel to the skin and place the Doppler, curved side against the patient’s skin. Ensure the Doppler device is free of the cuff to prevent muffled sounds or erroneous readings (Perry et al., 2014).

Place the stethoscope over the brachial artery and apply gentle pressure to ensure full contact with the skin; do not apply pressure too firmly as this can distort the Korotkoff sounds (Perry et al., 2014). Position the arm so that it is horizontal to the level of the heart (GOSH, 2015). Use a pillow or ask a colleague or the parent/carer to support the arm, as muscle tension can raise blood pressure (Dougherty & Lister, 2015). Steadily inflate the cuff to 30 mmHg above the estimated systolic pressure (Perry et al., 2014).

Estimate the systolic pressure by palpating the brachial artery: inflate the cuff and note the reading where the brachial pulse disappears (this is the estimated systolic pressure), then deflate the cuff (NICE, 2011).The bell of the stethoscope may allow you to hear the Korotkoff sounds better (see next page); however the diaphragm has a larger surface area and is therefore easier to hold in place (Dougherty & Lister, 2015).

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Measuring a child’s arm for cuff size Placing the cuff

Incorrect cuff size is a major source of error: an under-sized cuff can give a false high blood pressure reading and vice versa (RCN, 2017). Always use the biggest cuff that will fit comfortably (ALSG, 2016) and encircle 100 per cent of the arm (GOSH, 2015). The width of the cuff should be >80 per cent of the length of the upper arm and the bladder >40 per cent of the arm’s circumference (ALSG, 2016).

Expose the arm and ensure that clothes do not hinder the placement of the cuff or stethoscope; tight or restrictive clothing should be removed (GOSH, 2015). Locate the brachial artery and apply the cuff to the patient’s arm 2–3 cm above the antecubital fossa. The centre of the bladder must be over the artery (GOSH, 2015). The cuff should be tight enough to allow you to insert only one finger between the cuff and the patient’s arm.

Incorrect cuff size is a major source of error: an under-sized cuff can give a false high BP reading and vice versa (RCN, 2017). Always use the biggest cuff that will fit comfortably (ALSG, 2016) and encircle 100 % of the arm (GOSH, 2017). The width of the cuff should be >80% of the length of the upper arm and the bladder >40% of the arm’s circumference (ALSG, 2016).

Carotid arteries

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Deflate the cuff

Reduce the pressure

Repeated readings

If blood pressure is outside the normal limits, repeat the procedure, leaving 1–2 minutes between readings to allow for venous emptying (GOSH, 2015).

While continuing to hold the stethoscope in place, open the control valve slowly and carry on reducing the pressure at 2–3 mmHg per second. Once the first sound disappears, there is a silence. This is phase 2 of the Korotkoff sounds (K2). As you continue to reduce the pressure, the sounds return (K3). The pressure at the point where the sounds become distant represents diastole in children under 12 years (K4). The sound then completely disappears again. The pressure at this point represents diastolic blood pressure in children over 12 years (K5). Deflate the cuff slowly for a further 10–20 mmHg, checking that all sounds have disappeared, then deflate the cuff quickly for the patient’s comfort (Perry et al., 2014).

Slowly deflate at a rate of 2–3 mmHg per second: the point at which the first repetitive, clear tapping sounds (Korotkoff phase 1, or K1) appear for at least two consecutive beats gives the systolic pressure (NICE, 2011). Deflating a cuff too rapidly will underestimate systolic pressure and overestimate the diastolic reading (Frese et al., 2011).

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Korotkoff soundsCuff fully inflated

Artery completely occluded

Artery just opened

K1 – first two tapping sounds heard together; cuff at systolic pressure

Artery progressively opening

K4 – muffled sound, first diastolic reading; cuff at diastolic pressure

K5 – normal laminar blood flow, no sound; second diastolic reading

Artery completely open

Artery almost open

No sounds – cuff above systolic pressure

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K2 – blowing or swishing sound (tapping fadesor disappears); cuff between systolic and diastolic pressure

K3 – tapping sound reappears but softer than K1; cuff between systolic and diastolic pressure

When measuring the arterial blood pressure with sphygmomanometry and the use of a stethoscope (auscultation), the healthcare professional occludes the brachial artery with the inflated cuff. As the pressure is slowly released, a series of characteristic sounds—the Korotkoff sounds—can be heard, and noted against the graduated scale.

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measuring blood pressure in infants and children p1

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