Obstetric Early Warning Score for Prognostication of Critically Ill Obstetric Patient

INTRODUCTION

Childbirth is a major life event for women and their families. However, some women become critically ill during this time and it becomes important to provide critical care services to such patients who are young, otherwise healthy, and cornerstones of their families and society at large. It is estimated that about 830 women die each day worldwide from preventable causes related to pregnancy and childbirth with the majority of such deaths occurring in developing countries.¹ Critical care is required in about 2% of pregnant women; however, when required there is a high maternal mortality ranging from 3.4 to 14%.^2–4 The indications for admission to the critical care unit may be direct obstetric causes like preeclampsia-eclampsia, obstetric hemorrhage, and puerperal sepsis as well as indirect causes like heart disease and liver disorders.⁵

Predictive models are extremely important tools for prognosticating a critically ill patient in the ICU setting, which help not only in immediate allocation of resources but also in counseling of the relatives of the patient. Further improving or deteriorating scores on a daily basis can help in guiding the treatment of the patient. Prognostic scoring systems used in nonpregnant population are either based on organ dysfunction, such as sequential organ failure assessment (SOFA) score, multiple organ dysfunction score (MODS), logistic organ dysfunction score (LODS), or on acute physiology chronic health parameters such as acute physiology and chronic health evaluation (APACHE II) score.^6–9 Some others are based on physiological variables and age such as simplified acute physiological score (SAPS I-III).¹⁰

Pregnancy is associated with many physiological changes involving cardiovascular, respiratory, renal, and hematological system; thus, interpretation of these scores is more challenging in obstetric population. It has been seen that the use of these scores in obstetric patients often overpredicts mortality.^11,12 Overestimation of mortality risk by these scores in obstetric patients likely relates to pregnancy physiological changes that are not included in mortality scores, demographic characteristics, and lack of comorbidities in this population, and the significant and unique improvement in mortality that follows specific interventions in pregnancy. The standardized mortality ratio (SMR) is a ratio between observed number of deaths and number of deaths predicted by the score. It has been observed that the SMR of most of the prognostic scores used in obstetric population grossly overpredicts the maternal mortality.^9,11,13–16

However, since the concept of obstetric critical care is relatively new, there are no validated scoring systems for exclusive use in the critically ill obstetric patients. An obstetric specific statistically derived score is the Carle’s obstetric early warning score (OEWS), which was originally developed for triaging the obstetric patients in the labor wards; however, this has been recently described as a prognostic score in the ICU setting also with some modifications.^17,18 The major advantage of this score is that it uses the triggers according to the physiological changes of pregnant women and secondly does not require any laboratory value, as it is based on clinical parameters; hence, it is simple to calculate and less time-consuming. As there is only scant retrospective data and none from the Indian subcontinent, this study was conducted with the aim of prospectively comparing the OEWS with SOFA and APACHE II for prediction of mortality in a dedicated obstetric critical care unit (OCCU) of a tertiary care referral hospital.

MATERIALS AND METHODS

RESULTS

It was observed that indications directly related to complications of pregnancy represented the most frequent causes of OCCU admission such as hemorrhagic conditions (20%), followed by sepsis (18.8%) (puerperal sepsis 16%, septic abortions 2.8%), and hypertensive disorders (15.6%). It is noteworthy that anemia contributed to as many as 17.6% of the OCCU admissions (Table 1). The mean age of the patients was 25.07 ± 3.94 years. The mean SOFA score was 5.56 ± 4.42, whereas the mean APACHE II and OEWS were 11.14 ± 7.16 and 8.2 ± 5.22, respectively (Table 2). For the women who had mortality, the mean SOFA score was 10.69 ± 3.57, mean APACHE II was 19.37 ± 5.23, and mean OEWS was 13.57 ± 2.93. We observed a maternal mortality rate of 26% (65 out of 250). Sepsis contributed for maximum number of maternal deaths (23%), followed by acute kidney injury and eclampsia (Table 3).

The AUROC of OEWS was 0.894 (95% CI, 0.849–0.929) with p value <0.0001; cutoff of %3E;9 had a sensitivity (Sn) of 90.77% and specificity (Sp) of 78.92% with PPV 60.2% and NPV 96.1%; AUROC of APACHE II was 0.93 (95% CI, 0.891–0.958) with p value <0.0001; cutoff of >12 had a Sn of 93.85% and Sp of 82.16% with PPV 64.9% and NPV 97.4%, whereas the AUROC of SOFA score was 0.924 (95% CI, 0.884–0.954) with p value <0.0001; cutoff of >5 had a Sn of 92.31% and Sp of 76.22% with PPV 57.7% and NPV 96.6% (Fig. 2 and Table 4).

The standard mortality rate (SMR) of OEWS was 66.66%, which was comparable to that of APACHE II and SOFA, indicating that all the three scores were overpredicting maternal mortality (Table 5).

Unlike APACHE II and SOFA score, the OEWS was found to correlate significantly with the length of ICU stay and the number of hours on ventilation, which were the secondary outcomes in the study (Table 6).

DISCUSSION

The most common indications for admission to the obstetric CCU in this study were direct obstetric conditions like hemorrhage, sepsis, and preeclampsia. Sepsis contributed for maximum number of maternal deaths (23%), whereas hemorrhage was responsible for only around 8% of the deaths though being the commonest indication for admission to the critical care unit as seen in Tables 1 and 3, probably reflecting that aggressive management of postpartum hemorrhage (PPH) can save lives whereas sepsis especially after development of multiorgan dysfunction is the most challenging condition. It is noteworthy that most of the cases of puerperal sepsis had an unsupervised delivery and reported after the golden first hour, again reiterating the importance of institutional deliveries in our country, which is perceived as one of the most important intervention for decreasing maternal mortality.²⁰

We observed that all the three scores, OEWS, SOFA, and APACHE II, had a comparable predictive value for maternal mortality, which was statistically significant.

Although APACHE II and SOFA score were found to be useful as maternal mortality predictors, they needed to be calculated on the basis of lab parameters, some of which were available only after 6–8 hours. During the course of the study, we found that calculating the OEW score was very simple, less time-consuming, and did not require any lab report or any lengthy calculation. It was very user-friendly and we were able to prognosticate the patient immediately on admission. With a cut-off threshold of >9, it had a sensitivity of 90.7% and a specificity of 78.9% in predicting maternal mortality. Further, OEWS was found to significantly correlate with length of ICU stay (p = 0.029, R = 0.138) and number of hours on ventilation (p = 0.025, R = 0.228). However, APACHE II and SOFA score were not found to correlate with the length of CCU stay and number of hours of ventilation.

In a retrospective cohort study performed by Paternina-Caicedo et al. from January 2006 through December 2011 in Colombia, 702 pregnant or postpartum women who were admitted consecutively to the ICU were studied to determine the role of OEWS for prediction of maternal mortality. The AUROC of the OEWS in discrimination of maternal death was 0.84 (95% CI, 0.75–0.92). Peripartum women with normal values of obstetric early warning score had 0% mortality rate, while those with high obstetric early warning score values (>6) had a mortality rate of 6.3%. The overall predictive value of the obstetric early warning score was better when the main cause of admission was directly related to pregnancy or the postpartum state. However, the biggest limitation of this study was that it was retrospective in nature with resultant information bias. Moreover, they did not compare the performance of OEWS with the more intensively studied SOFA and APCHE II scores.¹⁸

Another interesting fact that we found during the analysis of the data was that whereas the NPV of APACHE II, SOFA, and OEWS was very good at 97.4, 96.6, and 96.1%, respectively, the PPVs of all the three scores were quite low at 64.9, 57.7, and 60.2%, respectively. The SMR for OEWS, SOFA, and APACHE II was 66.3, 62.5, and 69.15%, respectively. Hence, it can be seen that all the scores tend to overpredict the maternal mortalities, which has also been observed by others.^9,11,13–16 Thus, the OEWS, which is an obstetric specific score, did not fare better than other general scores in overprediction of outcomes. In another study Aarvold et al. compared four general scores with an obstetric specific score, “sepsis in obstetrics score” (SOS), which was originally developed for emergency settings but was modified by the authors for use in the ICU. They found that the obstetric specific score was not superior to the other general scores. The SOS, APACHE II, SAPS II, SOFA, and MODS scores gave AUROC curves of 0.67, 0.68, 0.72, 0.79, and 0.84 for prediction of mortality in the obstetric cohort, respectively. They concluded that the MODS is a simple organ-based score and performs well as a predictor in ICU even in the obstetric sepsis patients over the obstetric specific score.²¹

This study was primarily conducted to find a simple and accurate prognostic model, which could be used in the critically ill obstetric patients. We have been using the SOFA score but faced two major problems with it. First, we had to wait for the lab reports to determine the score, hence wasting precious time; and second, it overpredicted maternal mortality. The first problem can be overcome by using the OEWS; however, a more representative score for obstetric patients with a good SMR still evades us.

The strength of this study lies in that it was prospective in nature with a robust sample size and has been conducted in a dedicated OCCU. The main limitation was that these scores could not be assessed in nonpregnant, age-, and sex-matched controls as the number of nonpregnant young women in the general ICU was found to be very low.

CONCLUSION

Hence, it can be concluded from this study that Carle’s OEWS can stratify risk and predict mortality in critically ill obstetric patients as effectively as SOFA and APACHE II. Major advantage of OEWS is that it does not need any laboratory parameter and hence calculation is easy and less time-consuming. Thus, it can be done immediately on admission of patient and can help in early allocation of the appropriate manpower and other resources for optimum outcome. However, it was not found to be superior to other scores from the point of view of overprediction of maternal mortality in spite of its pregnancy-specific triggers.

CLINICAL SIGNIFICANCE

The clinical application of this study will help intensivists to prognosticate the critically ill obstetric patients immediately following admission to the critical care unit, which will help in optimizing the management.

To reduce maternal mortality, timely recognition and treatment of severe obstetric complications is crucial and provision of critical care is the need of hour. Obstetric critical care is an emerging topic and challenging too. Further research is warranted in developing prognostic scores for use in obstetric ICUs, which consider the physiological changes of pregnancy and do not overpredict maternal mortality.

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