Early diagnosis and treatment of postspinal hypotension (PSH) in obstetric anaesthesia reduces the risk of maternofetal complications. In this study, the effect of EtCO2 and the integrated pulmonary index (IPI) in predicting PSH was investigated. Patients scheduled for cesarean section under spinal anaesthesia were included. The Capnostream 35 respiratory monitor (Medtronic, Inc., Dublin, Ireland) was used for EtCO2 and IPI. PSH developed in 52 (63.4%) of the 82 patients. EtCO2 and IPI values decreased significantly compared with baseline values in patients who developed PSH. There were statistically significant differences in EtCO2 (p = 0.001) and the IPI change (p = 0.045) in patients who developed PSH compared with those who did not. It was found that the EtCO2 difference had an independent effect on predicting PSH (p < 0.05), whereas the IPI difference did not (p > 0.05). One unit decrease in EtCO2 from the baseline increased the risk of PSH by 3.3 times. ROC curve analysis showed that the magnitude of change in EtCO2 was diagnostic for predicting PSH (AUC: 0.90 (0.83–0.97; p < 0.001)). IPI showed no predictive value for postspinal hypotension in cesarean section. However, EtCO2 monitoring, which is non-invasive and real-time monitoring, can be used to predict postspinal hypotension.