ORIGINAL ARTICLE |
https://doi.org/10.5005/jp-journals-10071-24165 |
Comparison of Sequential Organ Failure Assessment Score and Sequential Organ Failure Assessment Score with pH in Outcome Prediction among ICU Patients: A Prospective Observational Study
1Department of Anaesthesia and CCM, Rani Durgawati Medical College, Banda, Uttar Pradesh, India
2,5Department of Anesthesia, SN Medical College, Agra, Uttar Pradesh, India
3,4Department of General Surgery, FH Medical College and Hospital, Agra, Uttar Pradesh, India
Corresponding Author: Amrita Gupta, Department of Anesthesia, SN Medical College, Agra, Uttar Pradesh, India, Phone: +91 9837077784, e-mail: amritagupta78@gmail.com
How to cite this article: Agarwal AM, Gupta A, Saxena AK, Sahni R, Pandey A. Comparison of Sequential Organ Failure Assessment Score and Sequential Organ Failure Assessment Score with pH in Outcome Prediction among ICU Patients: A Prospective Observational Study. Indian J Crit Care Med 2022;26(4):479–483.
Source of support: Nil
Conflict of interest: None
ABSTRACT
Aim and objective: To examine if sequential organ failure assessment (SOFA) alone or SOFA in combination with pH is a better prognosis and mortality indicator.
Materials and methods: We conducted a prospective observational study in a total of sixty patients. The mortality of patients was predicted on the basis of a SOFA score alone or SOFA score in combination with pH, and the prediction by both was compared to the actual outcome. The comparison was based on the “standardized mortality ratio” and the “area under the receiver operating characteristic curve (AUROC).”
Result: At the time of admission, both the scores (SOFA and SOFA with pH) were equally effective in predicting mortality. At 48 hours, SOFA with pH proves to be slightly better in mortality prediction than SOFA score alone.
The discriminative power of both the scores was assessed by calculating AUROC. AUROC of the SOFA score was better than that of SOFA with pH at admission and at 48 hours, but statistically, both had the same level of discrimination, i.e., excellent.
Accuracy, sensitivity, specificity, positive predictive value, and negative predictive value were the same for both the scores at admission, but all parameters except specificity were better for SOFA with pH at 48 hours. Specificity was the same for both even at 48 hours.
Conclusion: At the time of admission, SOFA score and SOFA with pH were equally effective in outcome prediction, but after 48 hours, SOFA with pH proves to be better than the SOFA score alone.
The power of discrimination is the same for both the scores at admission and at 48 hours.
Keywords: pH, Respiratory acidosis, Scoring system, SOFA score.
INTRODUCTION
Various organ dysfunction along with the number of failing organs is correlated with ICU mortality. So, quantification of organ dysfunction is done to facilitate the description of severity in different groups of patients enabling comparison over time or among groups to classify patients for enrollment and to compare treatment groups.1 Various ICU scoring systems have been developed to estimate the severity of critical illness on an objective basis.2 A scoring system usually comprises two parts—a score in which higher the number more severe is the condition and a probability model (equation giving the probability of hospital deaths of patients).3 Old scoring systems like Acute Physiology and Chronic Health Evaluation (APACHE), Simplified Acute Physiology Score (SAPS), and Mortality Prediction Model (MPM) ignore many factors that may influence patient outcome beyond the first 24 hours.3 SOFA score collects data every day throughout the ICU stay and has demonstrated the relationship between organ failure and mortality.4,5 The SOFA score also requires a review data over a 24-hour period to identify the most abnormal value.
Our body functions in a relatively narrow alkaline environment (pH: 7.35–7.45). Maintenance of normal physiologic function is closely related to the maintenance of pH within this range. The two main mechanisms for this balance are respiratory and metabolic.6,7 The respiratory response is fast and activated within minutes, while compensation is slow and takes hours to days to get activated.8
pH is also a major component of the APACHE-II scoring system.
Rajawat et al.9 have shown that the blood pH (both acidemia and alkalemia, irrespective of the type, i.e., respiratory and metabolic) are an important factor influencing mortality and morbidity in ICU patients. Also, the rate of improvement of pH is an important contributing factor.
Since pH is seen to be an important predictor of outcome prediction, this study was taken to include pH as an additional measure in the SOFA score to see if this improves the prediction better than the SOFA score alone.
AIMS AND OBJECTIVES
Aims
To examine if SOFA alone or SOFA in combination with pH is a better prognosis and mortality indicator.
Objectives
To examine SOFA vs SOFA and pH to estimate the risk of hospital death.
To assess the prognosis of patients using defined scores like SOFA vs SOFA and pH.
To determine the sociodemographic profile, diagnosis, and characteristics of patients admitted to ICU.
MATERIALS AND METHODS
It is a prospective observational study done in the north Indian population after the approval by the institutional ethical committee (IEC/2021/64). The study was done in the ICU of SN Medical College, Agra, from November 1, 2018, to December 31, 2019, after taking the informed written consent from patients’ attendants. A total of sixty patients with age more than or equal to 18 years admitted into the ICU for more than 48 hours were included in this study, at 95% power and 5% level of significance.
Patients excluded were postoperative patients for elective ventilation, patients with acute coronary syndrome, burn patients, and patients with terminal cancer.
The SOFA score and pH score were calculated from the laboratory and patient characteristics mentioned in the ICU scoring data sheet, at 0 hours (at admission) and 48 hours.
The highest SOFA score of the day was recorded. The pre-sedation Glasgow coma score was used to evaluate the neurological status of patients under sedation.
The outcome based on the score used at 0 and 48 hours was calculated and correlated with the actual outcome, as survivors or nonsurvivors. The results were presented as mean ± standard deviation.
Statistical tests were applied as follows:
Quantitative variables were compared using Mann–Whitney test (as the data sets were not normally distributed) between the two groups, and Wilcoxon signed-rank test was used for comparison between the SOFA score alone and the SOFA score with pH.
Receiver operating characteristic (ROC) curve was used to find out the cutoff point of scores for predicting mortality.
A p-value of <0.05 was considered statistically significant.
Assessment of Scoring Systems
Two main properties are used to assess and validate the scoring system—model calibration and model discrimination.
Model Calibration
Calibration can be assessed by standardized mortality ratio (SMR) values. SMR = observed mortality rate/predicted mortality rate.
Calibration is considered to be good if the predicted mortality is close to the observed mortality.
Model Discrimination
This is done by calculating the area under the receiver operating characteristic (AUROC) curve which represents the number of patients who died.
Discrimination levels based on the AUROC.
AUROC | Level of discrimination |
---|---|
Perfect | 1.00 |
Excellent | 0.90–0.99 |
Very good | 0.80–0.89 |
Good | 0.70–0.79 |
Moderate | 0.60–0.69 |
Poor | 0.60 |
Method of Scoring and Observation
The SOFA scoring system and daily pH for each patient will be calculated using Table 1.
SOFA score | 0 | 1 | 2 | 3 | 4 |
---|---|---|---|---|---|
Respiration PaO2/FiO2 mm Hg | >400 | ≤400 | ≤300 | ≤200 | ≤100 |
Coagulation, platelets, ×103/μL | >150 | 101–150 | 51–100 | 21–50 | 0–20 |
Hepatic bilirubin, mg/dL | <1.2 | 1.2–1.9 | 2.0–5.9 | 6.0–11.9 | >12.0 |
CNS Glasgow Coma Score | 15 | 13–14 | 10–12 | 6–9 | <6 |
Cardiovascular MAP, mm Hg | >70 | 0–70 | Dopamine ≤5.0 or dobutamine (any dose) | Dopamine 5–14.9 Epinephrine ≤0.1 Norepinephrine ≤0.1 |
Dopamine ≥15 Epinephrine >0.1 Norepinephrine >0.1 |
Renal S. creatinine, mg/dL or urine output, mL |
<1.2 | 1.2–1.9 | 2.0–3.4 | 3.5–4.9 or <500 | >5.0 or <200 |
pH
Physiologic variables | +4 | +3 | +2 | +1 | 0 | +1 | +2 | +3 | +4 |
Arterial pH | ≥7.7 | 7.6–7.69 | 7.5–7.59 | 7.33–7.49 | 7.25–7.32 | 7.15–7.24 | <7.15 |
The following parameters were observed:
Age of patients.
Mean length of stay in ICU and hospital.
SOFA and SOFA with pH scores by measuring the following parameters at 0 and 48 hours:
–PaO2/FiO2 (%).
–Platelet count (103/mm3).
–Serum bilirubin (mg/dL).
–Mean arterial pressure (mm Hg).
–Presedation Glasgow coma scale.
–Serum creatinine (mg/dL).
Standardized mortality ratio (observed mortality rate/predicted mortality rate).
Sensitivity, Specificity, negative predictive value (NPV), positive predictive value (PPV), and accuracy of SOFA and SOFA with pH.
AUROC.
RESULTS
Table 2 shows the mean age of survivors was 44.30 ± 15.85 years.
Survivors | Nonsurvivors | p value | |
---|---|---|---|
Mean age | 44.30 ± 15.85 years | 48.85 ± 11.83 year | 0.20 |
Mean ICU stay | 5.96 ± 1.65 | 6.12 ± 3.01 | 0.80 |
Mean hospital stay | 14.34 ± 3.21 | 9.55 ± 3.57 | <0.01 |
The mean age of nonsurvivors was 48.85 ± 11.83 years.
The difference between them is not statistically significant (p-value <0.20). Of the sixty patients included in the study, 27 recovered and 33 succumbed to the disease.
The mean length of stay in ICU in survivors was 5.96 with an SD of 1.65 and in nonsurvivors was 6.12 with an SD of 3.01. The difference between them is not statistically significant (p-value = 0.80).
The mean length of stay in the hospital of survivors was 14.34 (SD 3.21) and of nonsurvivors was 9.55 (SD 3.57). The difference between them is statistically significant.
Table 3 shows the mean SOFA score and SOFA with pH score at the time of admission and 48 hours after admission was significantly higher in nonsurvivors than in survivors. The difference is statistically significant (p-value <0.0001). The mean SOFA score and SOFA with pH score showed a decreasing trend in survivors, and in nonsurvivors, it showed a slightly increasing trend.
Survivors (N = 27) | Nonsurvivors (N = 33) | p value | t value | |
---|---|---|---|---|
Mean SOFA 0 hour | 9.74 ± 1.46 | 12.36 ± 0.99 | <0.0001 | 8.254 |
SOFA 48 hours (mean) | 8.67 ± 1.44 | 12.42 ± 0.97 | <0.0001 | 12.006 |
SOFA + pH 0 hour (mean) | 16.99 ± 1.44 | 19.51 ± 0.99 | <0.0001 | 8.009 |
SOFA + pH 48 hours (mean) | 16.01 ± 1.42 | 19.60 ± 0.97 | <0.0001 | 11.597 |
Table 4 shows that at 0 hours, SMR of both SOFA score and SOFA score with pH was 1.14, i.e., both the scores underpredicted the mortality. While after 48 hours, the SMR of SOFA score alone was 0.96 and that of SOFA score with pH was 1, this means that SOFA score with pH was better for prediction at 48 hours.
0 hour | 48 hours | ||
---|---|---|---|
SOFA score | OMR | 0.55 | 0.55 |
PMR | 0.48 | 0.57 | |
SMR | 1.14 | 0.96 | |
SOFA score with pH | OMR | 0.55 | 0.55 |
PMR | 0.48 | 0.55 | |
SMR | 1.14 | 1 |
Table 5 shows that different statistical parameters show similar results between SOFA and SOFA with pH at the time of admission of patients.
Sensitivity (%) | Specificity (%) | PPV (%) | NPV (%) | Accuracy (%) | |
---|---|---|---|---|---|
SOFA 0 hour | 85.19 | 75.76 | 74.19 | 86.21 | 80 |
SOFA + pH 0 hour | 85.19 | 75.76 | 74.19 | 86.21 | 80 |
SOFA 48 hours | 92.59 | 96.97 | 96.15 | 94.12 | 95 |
SOFA + pH 48 hours | 96.30 | 96.97 | 96.30 | 96.97 | 96.67 |
At 48 hours, SOFA with pH had a significantly higher sensitivity (96.30%) than SOFA score alone (92.59%). The specificity of both the scores was similar (96.97%).
PPV is slightly better in SOFA with pH (96.30%) than SOFA score alone (96.15%). NPV is better in SOFA with pH (96.97%) than SOFA score alone (94.12%). SOFA score with pH had a better diagnostic accuracy (96.67%) than SOFA score alone (95%).
Table 6 shows the area under ROC curve for SOFA at 0 hour is 0.953 (Fig. 1) and SOFA score at 48 hours is 0.994 (Fig. 2). The area under ROC curve for SOFA score with pH at 0 hour is 0.927 (Fig. 3) and SOFA score with pH at 48 hours is 0.985 (Fig. 4). Both scores at 0 hour and 48 hours show excellent discrimination. Although SOFA score at 0 hour as compared to SOFA with pH at 0 hour offers slight advantage in terms of power of discrimination.
Fig. 1: ROC of SOFA score at 0 hour
Fig. 2: ROC of SOFA score at 48 hours
Fig. 3: ROC of SOFA with pH at 0 hour
Fig. 4: ROC of SOFA with pH at 48 hours
AUROC | |
---|---|
SOFA 0 hour | 0.953 |
SOFA + pH 0 hour | 0.927 |
SOFA 48 hours | 0.994 |
SOFA + pH 48 hours | 0.985 |
DISCUSSION
This study showed that at the time of admission both SOFA and SOFA with pH scores had equal SMR and both the scores underpredicted the mortality, but at 48 hours, the SOFA score with pH predicted mortality slightly better than the SOFA score.
SOFA score and SOFA with pH had similar statistics at the time of admission. Both had the same sensitivity, specificity, NPV, and PPV.
At 48 hours, SOFA with pH had a significantly higher sensitivity, PPV, and NPV) than SOFA score alone. The specificity of both the scores was similar.
None of the earlier studies has mentioned the sensitivity, specificity, NPV, and PPV of SOFA or SOFA scores with pH at variable time intervals.
Although AUROC for SOFA (0.953) was better than SOFA with pH (0.927) at 0 hour and marginally better at 48 hours, the power of discrimination of both the scores was statistically comparable and excellent.
Previous studies by Bale et al.10 like our study showed that the SOFA score was significantly higher in nonsurvivors than in survivors. Franz11 like our study mentioned that changes in pH had a better correlation with a magnitude of multiorgan failure.
The main drawback of our study was that the sample size was small.
CONCLUSION
Hence, SOFA score with pH seems to be superior to SOFA score alone in outcome prediction among ICU patients. But since this study was based on a single ICU and had a limited number of patients and limited resources, we propose that this study be done on a larger scale in order to achieve more accurate results.
ORCID
Atiharsh M Agarwal https://orcid.org/0000-0002-2459-3870
Amrita Gupta https://orcid.org/0000-0002-4668-2604
Avanish K Saxena https://orcid.org/0000-0001-9499-332X
Radhika Sahni https://orcid.org/0000-0001-5318-1229
Aviral Pandey https://orcid.org/0000-0002-4101-2855
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