Role of Oxygen Saturation Index as a Noninvasive Surrogate Marker of Oxygenation in Intubated Critically Ill Adult Patients: A Prospective Observational Study.

BACKGROUND AND AIM: This study aims to compare the oxygenation saturation index (OSI), a noninvasive marker, with commonly used invasive markers of oxygenation [PaO2, PaO2 to FiO2 (P/F) ratio, oxygenation index (OI)] in critically ill patients requiring invasive mechanical ventilatory support after 48 hours of admission in a surgical intensive care unit (ICU).

PATIENTS AND

METHODS

A total of 91 intubated patients aged between 18 and 75 years admitted to the surgical ICU with preexisting or new onset respiratory failure were recruited as per predefined exclusion and inclusion criteria after being on the ventilator for 48 hours. Patients were enrolled in the study for 7 days or till extubation, tracheostomy, or death. The OSI was compared with other invasive and noninvasive markers to assess correlation.

RESULTS

Strong correlation of OSI with P/F ratio, SpO2/FiO2 (S/F) ratio, and OI individually was noted up to 7 days post 48 hours of intubation in critically ill patients, while it correlated with SpO2 on days 2, 3, 4, and 5 and PaO2 on days 2, 4, and 5, respectively. Correlation after natural logarithmic transformation was strongest for OI (r = 0.833), followed by S/F ratio (r = 0.686), P/F ratio (r = 0.409), SpO2 (r = 0.229), and weakest for PaO2 (r = 0.045).

CONCLUSION

Oxygen saturation index is a valid noninvasive marker of oxygenation in critically ill intubated patients and correlates well with invasive markers of oxygenation.

HOW TO CITE THIS ARTICLE: Koshy A, Kurian G, Jacob J, Vincent D, Rao SV, Subramani K, et al. Role of Oxygen Saturation Index as a Noninvasive Surrogate Marker of Oxygenation in Intubated Critically Ill Adult Patients: A Prospective Observational Study. Indian J Crit Care Med 2025;29(9):765-770.