Intrapartum nutrition and electrolytes

Chapter 8 Intrapartum nutrition and electrolytes



Paul Tomlinson, David T Y Liu



CHAPTER CONTENTS


Changes in labour 55

Nutrition in labour 56
Controversy 56

Management guidelines 56
Uncomplicated/spontaneous labour 56

Complicated labour: when fetal compromise/operative delivery more likely 56

Key points 56

Pregnant women approach labour with a mild degree of respiratory alkalosis and metabolic acidosis. Their capacity to use glucose is reduced. Defects in energy requirements are often met by increased lipolysis. This causes a small rise in plasma ketone levels throughout pregnancy. Ketonuria, however, is not observed unless plasma ketone concentration rises above 6–8 mmol/l. Gluconeogenesis does occur in the fetal liver and kidneys, but the main glucose supply is from the mother. This is provided by diffusion, across the placenta, down a concentration gradient. Fetal blood glucose levels are one-third to one-half that of the mother. As a result, fetal glucose rises and falls with changes in maternal nutritional state, and maternal starvation will reduce fetal plasma glucose. In labour, the fetal glucose requirement is 7–10 mg/kg per minute. Water diffuses freely across the placenta. Sodium and chloride concentrations are similar in maternal and fetal plasma, but potassium levels are higher in fetal than maternal blood, 6.4 mmol/l and 4.6 mmol/l, respectively. The likely mechanism of this is an active transport system.



CHANGES IN LABOUR


Labour further affects maternal metabolism and plasma electrolytes. Also, certain modern therapeutic measures employed in the management of specific problems in labour produce additional changes. The basic factors involved are:


• The energy of labour is provided predominantly by glucose, and most women enter labour with little reserve for sustained aerobic metabolism. Moderate accumulation of lactate causes a fall in maternal plasma pH to 7.34 and a fall in PaCO2 to 4–4.5 kPa.

• Oral intake of food and water is often discouraged to reduce the risk of regurgitation of stomach contents and aspiration pneumonia (Mendelson’s syndrome). This can occur in association with general anaesthesia, and abrupt changes in levels of consciousness produced by acute major pathology in labour or use of heavy sedation.

• Exertion, stress, and prolonged or high dose use of intravenous oxytocics (>16 mU/min Syntocinon) enhance antidiuretic hormone (ADH) production. This produces water retention and hyponatraemia.

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Mar 16, 2017 | Posted by in NURSING | Comments Off on Intrapartum nutrition and electrolytes

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