Final answer:
A normal PaCO₂ level in pregnant women can be concerning because it may indicate inadequate respiratory compensation, potentially leading to ventilatory failure. During pregnancy, lower PaCO₂ levels are expected due to physiological changes, so normal levels could suggest respiratory acidosis or other issues that need to be addressed.
Step-by-step explanation:
Pregnant women who present with a "normal" PaCO₂ level of 35 to 40 mm Hg (4.7 to 5.3 kPa) could be concerning because during pregnancy, there is an expected physiological change that includes an increase in respiratory rate to compensate for the increased oxygen demands of the fetus and the pregnant woman's increased metabolic rate. This results in a lower PaCO₂ than what is considered normal for non-pregnant individuals. Hence, a "normal" range PaCO₂ could indicate that the pregnant woman is not compensating adequately and could be at risk of ventilatory failure. Furthermore, with the growing uterus elevating the diaphragm, the tidal volume decreases, which can lead to compromised respiratory function and could trigger respiratory acidosis where the body increases bicarbonate in the blood to reestablish the correct acid-base balance. The clinician should look for signs of respiratory compromise or other conditions that could impair respiratory function, such as infections, morphine or barbiturate use, or other causes of hypoventilation that may lead to hypercapnia.