SOFA Score Insufficient for Predicting COVID-19 Mortality Before Intubation

The Sequential Organ Failure Assessment (SOFA) score is a poor way to accurately predict mortality prior to intubation among patients with novel coronavirus (COVID-19), according to a research letter published in JAMA.

Investigators from Arizona noted that in studies performed in 2016 and 2017, the SOFA score only provided a moderate discriminant accuracy when predicting survival of ICU patients with sepsis.

In August 2020, a survey identified 26 COVID-19 triage policies, the study authors also noted. Of those, 20 used some form of SOFA score.

Knowing that, they wanted to test whether the SOFA score might be less accurate in patients that required mechanical ventilation while fighting COVID-19 infection. These patients, according to the study authors, “generally have severe single-organ dysfunction and less variation in SOFA scores.”

The SOFA score ranges from 0 to 24 points, with a higher score indicating a worse organ function. Six organ systems are rated from 0 to 4 points based on ratio of PaO2 to fraction inspired oxygen, Glasgow Coma Scale score, mean arterial pressure, serum creatinine level, bilirubin level, and platelet count, the study authors explained.

The study authors gathered data from 2,546 adult patients treated between March 1 and August 31, 2020 at 18 ICUs across the Southwestern U.S. These were patients who had a diagnosis of COVID-19 pneumonia, received oxygen therapy for 4 hours or longer, and underwent endotracheal intubation.

The investigators calculated SODA scores using the worst observed values within 48 hours prior to intubation. They noted that this was the point in time in which the ventilator triage for a patient with COVID-19 pneumonia would occur.

Of the total patient cohort, 972 were intubated 4 hours or longer after receiving oxygen, the study authors noted; however, 297 did not have sufficient data to calculate the SOFA score.

For the 675 remaining patients, the median SOFA score was 6, with respiratory SOFA subscores ranging from 3 to 4 in the majority of patients, the study authors observed.

The investigators observed a SOFA subscore of 0 to 1 in the majority of the patients for the renal system (72 percent), the central nervous system (78 percent), coagulation (94 percent), the cardiovascular system (95 percent), and the hepatobiliary system (96 percent).

The study authors also noted that 400 patients, or about 60 percent, died or were discharged to hospice.

“The discriminant accuracy of the SOFA score for mortality prediction in patients prior to intubation for COVID-19 pneumonia was poor and significantly inferior to simply using age,” the study authors wrote.

They added that one possible explanation for this observation was that SOFA score was designed for sepsis patients. Moreover, only 3 of the 6 weighted organ system subscores (which include respiratory, renal, and hepatobiliary) are associated with mortality among COVID-19 patients.

COVID-19 populations, like the one in this analysis, had less variable SOFA scores with a lower proportion of patients with a cumulative score of 0 to 2, they also noted. These types of patients do not show severe organ system dysfunction and can be relatively accurately predicted to survive, the investigators wrote.

Finally, all the patients in this study required mechanical ventilation due to respiratory failure, which is the major cause of death among COVID-19 patients.

“The SOFA score possesses inadequate discriminant accuracy to be used for ventilator triage of COVID-19 patients,” the study authors concluded. “A better option is needed that incorporates variables specifically related to mortality in patients with COVID-19 pneumonia requiring mechanical ventilation.”