Summary

In study session I you have learnt

• Major physiological changes occur during pregnancy due to hormonal and mechanical factors from the enlarged uterus.
• Cardiovascular system changes include increase in blood volume, which progress throughout pregnancy.
• During pregnancy, there is an increase in the heart rate and stroke volume (the amount of blood pumped by the heart with each heart beat) producing raised cardiac out put(CO). CO increases further during labour.
• Between uterine contractions, the CO increases from pre-labour values by 10-25% during the first stage of labour, and 40% during the second stage of labour. The disproportionate increase in plasma volume over red cell volume in pregnancy causes a physiological anaemia, with a 15% drop in haemoglobin concentration and a decrease in blood viscosity.
• There is an increased demand for iron due to the increase in red cell volume and fetal requirements, and if iron stores are low, iron deficiency anaemia occurs.
• There is a relative hypercoagulable state during pregnancy in anticipation of haemorrhage at childbirth. Due to this there is an increased risk of thromboembolic disease in pregnancy.
• Aorto-caval compression occurs when the pregnant woman lies supine or semi-supine and the gravid uterus compresses the inferior vena cava (IVC) and aorta. This causes a decrease in venous return to the heart and a fall in CO and blood pressure, which can compromise the mother or fetus. Therefore, after the 20th week of gestation, a left lateral tilt should ALWAYS be maintained to prevent aorto-caval compression.
• In the respiratory system, hormonal changes result in capillary engorgement and swelling of the mucosa of the nose, oropharynx, larynx and trachea. As a result, smaller tracheal tubes may be required for intubation and bleeding may be precipitated by the use of nasal tubes, nasogastric tubes or oral/nasal airways.
• There is a progressive increase in oxygen consumption in pregnancy caused by the increased metabolic needs of the mother and fetus oxygen consumption increase by 20-30% at term.
• During Labour, it is increased by 60% as a result of the increased cardiac and respiratory workload.
• The functional residual capacity (FRC), which is the volume of air remaining in the lung at the end of a normal breath, decreases by 20% as pregnancy progresses due to the increased intra-abdominal pressure and upward displacement of the diaphragm. The combination of increased oxygen consumption and decreased FRC means that a pregnant mother who is rendered apnoeic at term, will desiderate much more quickly than her non-pregnant counterpart. Good preoxygenation is therefore essential in all pregnant women before general anesthesia.
• In the gastro intestinal system, anatomical changes and hormonal effects on smooth muscle tone promote gastric contents to reflux into the esophagus during pregnancy. Pulmonary aspiration of gastric contents can occur after vomiting or passive regurgitation, resulting in significant morbidity and mortality.
• All pregnancy women should be considerable to have a full stomach, with increased risk of aspiration from the end of the first trimester. During general anesthesia, the airway needs to be protected with a cuffed tracheal tube. A rapid sequence induction should be performed with pre-oxygenation, cricoid pressure, and avoiding positive pressure ventilation until the airway is secured with a tracheal tube.
• The use of regional anesthesia for caesarean section avoids the risks of aspiration associated with general anesthesia.
• Renal blood flow increases by 80% during pregnancy. Urea and creatinine levels are 40% lower than non-pregnant values. The normal values therefore need to be adjusted as values within the normal range for the non-pregnant state may indicate significant renal function impairment during pregnancy.
• During pregnancy the changes in central nervous system physiology include changes in pain threshold, susceptibility to general and local anesthetics (LA), and alterations in mood and cognitive function.