A discussion on the skill of blood pressure measurement by the midwife during the antenatal period.
Hypertensive disorders are the second leading direct cause of maternal death (Lewis, 2007). The report “Saving Mother’s lives” (Lewis, 2007) highlighted the need for medical professionals, including midwives, to immediately recognise and act on the signs and symptoms of life threatening conditions such as pre-eclampsia. The report emphasised a lack of basic clinical skills being one of the leading causes of mortality and highlighted examples where healthcare professionals had misdiagnosed and failed to make routine measurements of blood pressure.
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The accurate and timely measurement of blood pressure throughout the antenatal period is a key midwifery skill. Whilst a routine practice, midwives need to be vigilant in their approach to ensure early detection of any anomalies and that subsequent management and referral is carried out (Macdonald, 2011). Throughout this essay we will examine the role of blood pressure measurement taking by the midwife, throughout the antenatal period, in identifying the onset of hypertensive disorders and pre-eclampsia. We will consider the importance of establishing a baseline blood pressure, the application of the skill in practice and factors, such as technique and equipment, which may affect the accuracy of the measurements taken. Minimising the impact of these factors will ensure that the measurements observed are as accurate as possible to enable clinical decision making and subsequent care.
Wilson (2005, p.29) defines blood pressure as “the pressure exerted by the blood on the vessel wall”. It is composed of two elements, systolic and diastolic pressure. Systolic pressure is the pressure within the brachial artery during ventricular systole (contraction of the ventricles). Diastolic pressure is the pressure within the artery during ventricular diastole (relaxation of the ventricles).
During pregnancy physiological changes occur in the body which have the direct result of affecting blood pressure. The cardiovascular system must meet the growing demands of the pregnant women and the fetus. As a result cardiac output increases by up to 40%. Changes in vascular activity occur as a result of increased levels of the hormone progesterone acting on the smooth muscle of the vessel walls causing vasodilation (Marshall, 2014). Due to this change during the first and second trimester of pregnancy there is a marked decrease in diastolic blood pressure and a minimal decrease in systolic blood pressure of approx 10mmHg. This can result in tiredness and light headedness for some women during early pregnancy and should be recorded by the midwife during antenatal appointments. Both diastolic and systolic blood pressures should however rise slowly throughout the third trimester to pre-pregnancy levels. Some women do not have the expected reduction in blood pressure during early pregnancy and this may be an early indicator of hypertensive disease in pregnancy (Coad, 2013).
During the antenatal period the Midwife is ideally placed to measure the woman’s blood pressure and confirm normality whilst detecting any unexpected deviations. NICE (2014a) best clinical practice advises that blood pressure measurement should be carried out at each antenatal visit in order to screen for pre-eclampsia. Increased frequency of blood pressure measurements should be considered for women who have additional risk factors for pre-eclampsia such as diabetes mellitus type I and obesity.
In order to correctly identify any complications developed during pregnancy, it is important for the midwife to establish a baseline measurement of the women’s blood pressure at the earliest opportunity. Mosby’s Medical dictionary (2008) defines a baseline as ‘the patient’s initial information at assessment against which later tests will be compared’. In the context of measurement of blood pressure the initial measurement taken at the booking appointment (or earlier appointment) will provide the midwife with a baseline of the women’s blood pressure for the duration of the antenatal period. Any unexpected deviations such as significant hypertension will also alert the midwife to the need for increased monitoring throughout the term of the pregnancy. The establishing of a baseline and monitoring over the ante natal period will also aid any other midwives and doctors that take over responsibility of the women’s care at the onset of labour.
The results yielded by accurate blood pressure measurement enable the midwife to effectively monitor and diagnose any potential complications throughout the antenatal period. They play a central role in the screening and management of hypotension and hypertension. The accuracy of these measurements is therefore critical due to the implications if not correct. There are two key factors which will affect the accuracy of blood pressure measurement; the equipment that is used and the technique in which the measurement is taken.
Blood pressure is measured through the use of a sphygmomanometer and these are either auscultatory (manual) or oscillatory (automated). Aneroid manometers (a form of auscultatory sphygmomanometer) are what is commonly used in the community setting due to being lightweight and compact. The method consists of the use of a combination of a stethoscope and an arm cuff which is used to take blood pressure readings. The midwife must listen for the sounds which correlate to systolic and diastolic pressure called Kortokoff sounds. This is a skill which requires training and practice. Automated oscillatory manometers are increasingly used within hospitals, partly due to their ability to be programmed to automatically take blood pressure at set intervals. Oscillatory manometers measure the vibration of blood travelling through the arteries and converts this movement into digital readings (OMRON, N.D). They do not require the use of a stethoscope. When using either type of devices it must be ensured that they have been appropriately validated, maintained and re-calibrated. Turner et al (2006) concluded that a failure to calibrate sphygmomanometers would result in the under and over detection of hypertension by up to 31%. The midwife therefore needs to be assured and is responsible for ensuring that any sphygmomanometer used has been appropriately calibrated and tested. To ensure comparable blood pressure measurements they should also record the type of sphygmomanometer used. Ensuring the use of the correct sized arm cuff when taking a measurement is also very important. Using standard size arm cuffs on obese patients may result in blood pressure’s being overestimated by up to 25% (Waugh & Smith, 2012).
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With both methods of measuring blood pressure there is a need to provide a relaxed setting, with the individual quiet and seated with their arm supported, palm up and stretched out. Ensuring that their clothing is not constricting the arm in any way. Once the arm is in the correct position the midwife should palpate the radial or brachial pulse before attaching the cuff to ensure correct positioning. Some automated devices will not measure blood pressure accurately if there is pulse irregularity (NCGC, 2011). By palpating the pulse first this will help identify any irregularity and allow for the midwife to switch to using a manual method, if not already, using direct auscultation over the brachial artery (NICE, 2014b). The cuff once in position should be inflated to 20-30 mmHG above the palpated systolic blood pressure and the stethoscope placed over the brachial artery. Deflation of the cuff should begin at a rate of 2 mmHG per second. Reindeers et al (2006) states that deflation of the cuff should not be any faster as this can result in an inaccurate measurement whereby systolic pressure is underestimated and diastolic pressure is overestimated. When clear tapping sounds first appear this is the systolic blood pressure. The diastolic blood pressure is measured at the point at which there is a disappearance of sounds. This is known as Korotkoff V (Bothamley & Boyle, 2008). Readings should be documented immediately and to the nearest 2mmHG. A difference in systolic blood pressure readings between right and left arms >10mmHg may be observed in antenatal women and is considered normal.
The midwife has an important role in screening women for hypertensive disorders during the antenatal period. At the booking appointment the midwife will complete a detailed assessment of the woman’s physical and mental wellbeing and at this stage is able to identify risk factors. To date no screening tests for pre-eclampsia have been recommended for routine use (UK National Screening Committee, 2010). Therefore the identification of risk factors coupled with routine blood pressure measurement and screening for proteinuria at every antenatal appointment are crucial to ensure effective screening for hypertensive disorders. The early diagnosis and referral of hypertension and hypotension reduces the risk of stroke and other complications during pregnancy and the onset of pre-eclampsia. This allows for management of the condition by both doctor and midwife.
Individual factors such as existing chronic hypertension, age or BMI put the woman at an increased risk of developing hypertension or pre-eclampsia during her pregnancy. The influence of these factors can be substantial, altering systolic readings as much as 20mmHg (NCGC, 2011). Maternal Body Mass Index (BMI) is a factor that has a significant influence on blood pressures levels during a woman’s pregnancy. Miller et al (2007) observed that trimester specific mean systolic blood pressures were between 10.7-12.0 mmHg higher and mean diastolic blood pressure between 6.9-7.4 mmHg higher, amongst obese women (BMI ≥ 30) v’s lean women (BMI ≤ 20). It is therefore important that maternal BMI is calculated at booking to identify any women classified as being obese. This is of relevance due to the increased incidence of pre-eclampsia and gestational hypertension amongst women with increased BMI (Bhattacharya et al, 2007).
The midwife is also able to identify and discuss additional non physical factors such as ethnic origin and a family history of hypertension. Lifestyle factors of the woman, such as if and how much she drinks, must also be given due consideration as alcohol inhibits the release of antidiuretic hormone (ADH) which leads to vasodilation and in turn will result in lowered BP (Marshall, 2014).
Antenatal appointments also allow for the monitoring of additional symptoms experienced by the women in pregnancy such as headaches, proteinuria, visual disturbances or epigastric pain which might suggest the onset of pre-eclampsia (Bothamley & Boyle, 2008). It is important to note that whilst an increase in blood pressure is often associated with pre-eclampsia it is not always a symptom of the condition.
Odent (2005) refers to the art of midwifery being in the ‘personality, the way of being, the background, the experience and the intuition’ of the midwife. Throughout this essay we have demonstrated that the skill of blood pressure measurement can be broken down to align with these fundamental components. At the heart of their practice midwives seek to provide women centred care and maintain the underpinning principles of continuity, choice and control. The midwife strives to remain compassionate and considerate of the impact of abnormal blood pressure measurement on the woman, her family and the unborn child. They recognise the need, and understand the reason, to undertake blood pressure measurement and establish a baseline for the women’s pregnancy. Utilising their ‘experience’ by ensuring that the procedure is carried out with equipment that has been correctly maintained and calibrated and that they remain highly skilled in the technique of blood pressure measurement. Key to this is ensuring that measurements are correctly recorded and that other antenatal observations are carried out as well as calling on basic ‘intuition’ to identify additional risk factors which might indicate a higher risk of hypertension. The early identification of a woman being at increased risk and the monitoring of blood pressure throughout the antenatal period by the midwife, will increase the possibility of any potential complications being diagnosed earlier. The midwife has all the competence and authority to recognise the warning signs of abnormality in the mother and this is key to her role in providing women centred care.
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