The Pregnant Patient

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Obstetric anaesthesia requires detailed knowledge of the physiological changes associated with pregnancy. Whilst these are covered thoroughly in Section 2, Chapter 13, the salient points are outlined below to aid the reader.

As pregnancy progresses, the maternal blood volume increases and, although total haemoglobin increases, the haemoglobin concentration falls by dilution. The concentration of clotting factors increases causing a tendency to deep vein thrombosis exacerbated by pressure on the pelvic veins from the increasingly bulky uterus. Cardiac output increases throughout pregnancy due to increases in stroke volume and heart rate. Thoracic volume rises so that although tidal volume remains comparable to prepregnancy values, there becomes an impression of hyperinflation. At the end of pregnancy PaCO2 is reduced to 4 kPa. The hormonal changes of pregnancy cause relaxation of smooth muscle and ligaments, resulting in a reduction in lower oesophageal sphincter tone which, combined with increasing intraabdominal pressure, leads both to functional hiatus herniae and oesophageal reflux. Gastric contents are more voluminous than usual and gastric emptying is slowed. In labour, gastric emptying virtually ceases.

Patients in the third trimester of pregnancy should not be allowed to lie in the supine position for any reason without left lateral tilt to displace the uterus because the weight of the uterus compresses the inferior vena cava. The substantial reduction in venous return to the heart that follows may produce fainting. If compensatory vasoconstriction is abolished by epidural blockade, serious falls in cardiac output may result.

Analgesia in Labour

Pain in labour is the result of a hollow organ, the uterus, contracting against an obstruction, the foetus, in an attempt to expel it. The pain is the result of tension in the uterine wall. The patient's response to the pain of contractions is a psychological response that depends on culture, history and preparation; therefore, each patient must be taken on her own merits. The pain of labour is transmitted to the spinal cord via two routes, depending on the stage of labour. The impulses from the body and fundus of the uterus pass via the lower thoracic spinal roots, T10 to L1, while those from the cervix and birth canal pass via the sacral roots. The net result is that pain in the first stage of labour is perceived to be lower abdominal while in the second stage it changes focus to pelvis and perineum

Alierníitive potíi íol lowing

Alierníitive potíi íol lowing

Figure SC.1 Innervation of the birth canal

(see Figure SC. 1). Nocioceptive impulses pass up the spinal cord and are interpreted in the brain. The various methods of providing analgesia in labour are detailed in Figure SC.2.




Systemic analgesia

Nitrous oxide Inhalational agents IM opioids PCA

Epidural analgesia

Bolus Infusion

Figure SC.2

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Pregnancy And Childbirth

Pregnancy And Childbirth

If Pregnancy Is Something That Frightens You, It's Time To Convert Your Fear Into Joy. Ready To Give Birth To A Child? Is The New Status Hitting Your State Of Mind? Are You Still Scared To Undergo All The Pain That Your Best Friend Underwent Just A Few Days Back? Not Convinced With The Answers Given By The Experts?

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