16. Principles of elimination management
defecation
CHAPTER CONTENTS
Principles: promoting defecation126
Role and responsibilities of the midwife127
Summary127
Self-assessment exercises127
References127
LEARNING OUTCOMES
Having read this chapter the reader should be able to:
• describe the physiology of defecation
• discuss the factors that influence defecation
• discuss the ways in which the midwife can promote defecation.
Women experience a number of changes with their bowel habits during pregnancy and the postnatal period that might lead them to feel constipated or have loose stools, both of which can be uncomfortable and embarrassing. The midwife plays an important role in promoting normal bowel habits and preventing complications. This chapter focuses on defecation: the passage of faeces through the anal sphincter. Relevant physiology, factors influencing defecation and a discussion on how the midwife promotes defecation are all included.
Physiology
Faeces are normally semi-solid in consistency, containing 70% water. The remaining constituents are the end products of digestion, the residue of unabsorbed food, bile pigments, epithelial cells, mucus, bacteria, cellulose and some inorganic material. Faeces are propelled through the large intestine to the sigmoid colon by peristalsis, and water is absorbed from the faeces. The longer the faeces remain in the large intestine, the greater the amount of water absorbed, the harder the faeces become, and vice versa. Faeces usually stay in the sigmoid colon until the stimulus for defecation occurs.
The stimulus to defecate arises in response to the presence of faeces in the sigmoid colon, causing the faeces to pass from there to the rectum. This stimulus can vary from person to person and is often related to habit (Crisford 2008). The rectum is very sensitive to changes in pressure and, as the faeces enter the rectum, the pressure rises by 2–3 mmHg. As the rectal walls distend, the internal anal sphincter relaxes, reducing anal pressure – the inhibitory reflex – creating an awareness of the need to defecate. The puborectalis muscle contracts, decreasing the anorectal angle – the inflation reflex (Edwards 1997
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