The pulse oximeter remains a valuable tool in the care of intensive care patients, but an awareness of its limitations is important in enhancing the quality of intensive care. We tried to determine the accuracy of pulse oximeter among Systemic Inflammatory Response Syndrome (SIRS) patients in the presence of various factors and also the reliability of predicting SaO₂ from subsequent SpO_2. Accuracy was analyzed by Bland-Altman analysis. Bias was found to be 2.5%. Subgroup analysis revealed hypoxia and acidosis significantly altered pulse oximeter accuracy. Regression analysis was done to assess reliability of predicting SaO₂ from subsequent SpO₂. Fluctuations in SpO₂ to SaO₂ difference indicated that SaO₂ could not be reliably predicted from SpO₂ after a single ABG analysis. A SpO₂ above 93% appears necessary to ensure a SaO₂ of 90%.