Development and Validation of an Obstetric Organ Dysfunction Score to Predict Mortality in Intensive Care Unit: A Multicenter, Prospective, Cohort Study

INTRODUCTION The Sequential Organ Failure Assessment (SOFA) score was initially developed in a consensus meeting organized by the European Society of Intensive Care in 1996. The aim of the score was to quantify and objectively describe the degree of organ dysfunction or failure in critically ill patients (1). The SOFA score describes a continuum process from normality to dysfunction and failure for six organ systems (respiratory, hematologic, hepatic, cardiovascular, neurologic and renal) (1). Although primary objective of SOFA score was descriptive, numerous studies have proven its prognostic value as well. There is a strong association between SOFA, number of dysfunctions upon admission and SOFA trends in the first 48h and ICU mortality (2, 3).

The SOFA score is a key component of the last definition of sepsis. In 2016, the European Society of Critical Care and the American Society of Critical Care developed and validated a new definition of sepsis. Sepsis was then considered as a life-threatening organ dysfunction caused by a dysregulated host response to infection (3). SOFA score was chosen to identify organ dysfunction due to its simplicity and widespread use. Organ dysfunction was defined as a change in total SOFA score of ≥ 2 points (3). This definition was validated by many studies of different countries, including Argentina (4, 5).

The SOFA score was developed and validated in a population of adult critically ill patients. Thus, its calibration for other populations with particular physiological changes, such as children or obstetric patients, could be inadequate. While some scores, like the PELOD (6, 7) or modified SOFA (8) were developed and validated for pediatric patients, there is no one suitable for obstetric patients yet. General SOFA score was associated with mortality among obstetric patients (9-12) but its predictive validity could be improved if adjustments to pregnancy were performed. Although two groups proposed modified SOFA scores adjusted to obstetric patients, these scores presented clear deficiencies and were not validated (13, 14). The development of an adjusted and calibrated organ dysfunction score for obstetric patients, would improve the validity of the score to predict ICU mortality, and would provide a reliable tool to be incorporated into the definition of maternal sepsis (15, 16). Obstetric sepsis account for 11% of global maternal mortality and for 19%, when abortion-related deaths are added, as most of them are due to sepsis (17). Developing a validated instrument to define sepsis in this population, would improve its recognition and would eventually promote its early treatment, which is associated with better outcomes (18).

Barriers for using the non-adjusted SOFA score to diagnose sepsis in obstetric patients are mainly related to renal and cardiovascular systems. SOFA score sets a creatinine of ≥1.2 mg/dl as the lower cut-off point to identify kidney dysfunction (1). However, pregnant patients and those in early puerperium, present an increased in cardiac output, in renal plasma flow and in glomerular filtration rate, which in turn decrease normal creatinine levels to <0.9 mg/dl in any trimester of pregnancy (19, 20) and in the first 2 weeks postpartum (20-22). Thus, a non-adjusted SOFA score underestimates renal dysfunction in obstetric patients. In terms of cardiovascular dysfunction, mean arterial pressure (MAP) normally decreases during the second trimester of pregnancy, up to approximately 65 mmHg. However, for the general SOFA score any value of MAP ≤70 mmHg is considered abnormal, which will overestimate hemodynamic dysfunction during that trimester (1). In addition to the abovementioned required adjustments, respiratory evaluation of SOFA is usually lacking among obstetric patients. This evaluation is performed through the paO2/FiO2 ratio, which requires an arterial blood gas (ABG) extraction (23, 24). ABG measurement could be unavailable in some low-resource settings, but also could be missing due to a deliberate physician decision of avoiding arterial gas extraction in these patients (24). Using the relationship between the peripheral oxygen saturation over the inspired fraction of oxygen (spO2/FiO2) could address this deficiency. The spO2/FiO2 ratio is a validated, widely available and non-invasive surrogate of paO2/FiO2 ratio to evaluate respiratory performance (25, 26). The use of a paO2/FiO2 ratio surrogate, such as the spO2/FiO2, improves SOFA score specificity compared to the decision of considering the missing value as normal (24) and it is a key factor when SOFA score is used to define sepsis (15).

The main objective of this study is to develop and validate an organ dysfunction score adjusted to obstetric patients (SOFA-OBS) to predict ICU mortality among pregnant and early postpartum patients requiring ICU admission.