A comparative study of arterial oxygen saturation in pregnant and non-pregnant women

Abstract

Background: Pregnancy is a stressful condition with considerably altered physiological and metabolic functions. Several authors have reported that oxygen consumption increases by 30-40% during pregnancy. Maternal ventilation and blood gases undergo substantial changes in pregnancy. During pregnancy, the rib cage undergoes structural changes in response to progressive relaxation of the ligamentous attachments of rib increasing the subcostal angle from 68° to 103°. In pregnancy, the diaphragm is elevated by about 4 cm, and the lower ribcage circumference is increased by about 5 cm. Hence, the functional residual capacity (FRC) and residual volume are reduced in pregnancy. Decreased FRC with increased oxygen demand lowers oxygen reserve of the mother. The increased metabolic rate and low oxygen reservoir in the lung at end expiration make the pregnant women particularly susceptible to develop hypoxemia. The blood gas analyzers require blood sample from the patient, hence invasive and painful. Whereas, pulse oximetry is a non-invasive, inexpensive, bedside technique and an alternative for arterial blood gas measurement. There is conflicting evidence concerning arterial oxygen saturation during pregnancy, hence the present study was done. Aims and Objectives: The aim of this study is to assess and compare the arterial oxygen saturation in pregnant and non-pregnant women. Material and Methods: This study was done on 60 non-pregnant women and 60 pregnant women in each trimester of the age group 20-35 years. The arterial oxygen saturation was measured with pulse oximeter. Result: The arterial oxygen saturation did not show any statistically significant difference in pregnant women in any trimester as compared to non-pregnant women. Conclusion: The decreased FRC and increased oxygen demand does not affect the arterial oxygen saturation in pregnant women as progesterone mainly lowers the threshold of respiratory center and increases their sensitivity to carbon dioxide.