Blood Gas Changes
Observe the diagram on the right - 'Changes in maternal arterial blood gases in pregnancy' - note the fall in PaCO2 occurs early in pregnancy and is usually present in women anaesthetized in the first trimester for procedures such as termination of pregnancy and surgery for ectopic pregnancy.
What ventilator settings would you usually set for a term pregnant woman undergoing LSCS under general anaesthesia?
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A relatively increased tidal volume and respiratory rate, so that a ‘normal’ end-tidal CO2 for pregnancy (4.1 kPa) is maintained. If pressure-controlled ventilation is used, remember to check that ventilation is adequate. The numbers in the table below are a rough guide to initial settings and normal values for a woman weighing 55 kg.
|
Pregnant |
Non-pregnant |
|
| Respiratory rate |
15 |
12 |
|
Tidal volume (ml) |
480-460 |
450 |
|
PaCO2 (kPa) |
4.1 |
5.3 |
|
PaO2 (kPa) |
14 |
13.3 |