4. Assessment of maternal and neonatal vital signs
pulse measurement
CHAPTER CONTENTS
Factors influencing the heart rate36
Normal values36
Role and responsibilities of the midwife40
Summary40
Self-assessment exercises40
References40
LEARNING OUTCOMES
Having read this chapter, the reader should be able to:
• discuss the midwife’s role and responsibilities in relation to pulse assessment, identifying when, where and how it is undertaken
• identify the normal range for the childbearing woman and baby
• discuss factors that influence the heart rate.
The pulse is a direct indicator of the action of the heart; the midwife should recognise the significance of it as an assessor of wellbeing. From such a straightforward observation much information can be gained, and using the correct technique each time increases the reliability of the results. This chapter examines pulse assessment: what it is, how, when and why it is completed. Factors affecting heart rate are also discussed; other means of pulse assessment are discussed briefly. Assessment of the fetal heart is discussed in Chapter 1.
Definition
A pulse is a rhythmic expansion and recoil of the elastic arteries as the left ventricle ejects blood into the circulation (Jamieson et al 2002). The sinoatrial (SA) node is the heart’s pacemaker and ensures that the heart meets the body’s needs. The autonomic nervous system relays the cues which cause the heart to beat faster or slower to the SA node. The effects both extend to and come from the inter-relation of other body systems (e.g. the lungs). If, for example, running for a bus causes shortness of breath, one of the effects will be that the heart beats faster to supply more oxygen to the body tissues. Other factors affecting the heart rate are discussed below. These changes mean that it is necessary to assess a person’s pulse for its rate, rhythm and amplitude.
Factors influencing the heart rate
The following factors reduce the rate:
• rest and relaxation: calm, controlled breathing can reduce the heart rate
• insult or injury: myocardial infarction or other injury might cause the heart to slow or stop
• hypothermia
• good exercise tolerance: in athletes
• age: heart rate decreases with age.
Normal values
A healthy, non-pregnant female adult has a regular heart rate of approximately 65–85 beats per minute (bpm) (Docherty & Coote 2006), with the normal range between 60 and 100 bpm. Tachycardia refers to an abnormally fast pulse rate above 100 bpm and bradycardia is a slow heart rate, generally considered to be below 60 bpm, although Higgins (2008) suggests it should be considered bradycardic when the pulse rate is below 50 bpm.
The pulse rhythm should be regular; an irregular pulse reflects an irregular pumping action of the heart. The amplitude indicates changes in the amount of blood being pumped around the body, the pulse strength and elasticity of the arterial wall. It is subjectively described as ‘normal’, ‘weak’ or ‘thready’ (may be due to hypovolaemia), ‘rapid’, ‘full’ or ‘bounding’ (may be due to infection) (Trim 2005).
A newborn baby has a heart rate of 110–160 bpm, with the average being approximately 130 bpm. Heart rate varies noticeably with respiration in the newborn, hence it is important to count for 1 minute.
Changes related to childbirth
Pregnancy
During pregnancy the maternal heart rate increases from 7 weeks gestation by approximately 10–20 bpm, peaking by 32 weeks, due to changes in cardiac output and stroke volume, corresponding with an increase in total blood volume. The rate declines slightly during the third trimester, and positional changes are particularly obvious throughout pregnancy. The rate is higher in the sitting or supine position than the lateral recumbent position (Blackburn 2007).
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