The Revised-Risk Analysis Index as a predictor of major morbidity and mortality after abdominal surgery in elderly patients: a retrospective cohort study

Abstract

Background

The revised-Risk Analysis Index (RAI-rev) can accurately predict postoperative mortality risk. However, the association of RAI-rev with composite outcome of major morbidity and mortality (MMM) among elderly surgical patients is largely unknown. This study investigated the association between RAI-rev and postoperative MMM in older patients undergoing abdominal surgery. It also assessed the predictive value of RAI-rev combined with other preoperative risk factors.

Methods

This retrospective cohort study reviewed the medical records of all patients aged 65 and older who underwent abdominal surgery between January 2018 and December 2019. The primary outcome was the postoperative MMM during hospitalization, and its association with pre-operative RAI-rev scores was assessed using multivariable logistic regression analysis. The prediction of postoperative outcomes was used the receiver-operating characteristic curve analysis.

Results

A total of 2225 elderly patients were analyzed, and 258 (11.6%) developed postoperative MMM. After adjusting for confounders, each unit increase in RAI-rev scores resulted in a 2.3% increase in the MMM risk and a 3.0% increase in the odds of life-threatening complications and mortality (both P < 0.05). The area under the curves (AUCs) of RAI-rev scores in predicting MMM and life-threatening complications and mortality was 0.604 (95% CI: 0.567–0.640) and 0.633 (95% CI: 0.592 to 0.675), respectively (both P < 0.001); when the RAI-rev was combined with the American Society of Anesthesiologists (ASA) classification, operative stress, and urgency status of surgery (emergency or elective), the AUCs were 0.691 (95% CI: 0.656–0.726) and 0.739 (95% CI: 0.702 to 0.777), respectively (both P < 0.001).

Conclusions

Higher RAI-rev scores were independently associated with increased risk of MMM. When combined with the ASA classification, operative stress, and urgency status of surgery, RAI-rev has improved performance in predicting the risk of MMM, particularly the life-threatening complications and mortality.

Background

With a significant increase in life expectancy, the proportion of elderly adults (≥ 65 years) has increased dramatically over the past decades [1]. This has led to an increasing number of elderly people undergoing surgical procedures, which presents a huge challenge for clinicians. Despite improvement in perioperative medical care and management, elderly patients still have higher odds of postoperative complications and mortality than younger patients [2, 3]. Therefore, it is imperative for clinicians to accurately stratify the peri-operative risks among elderly patients and provide tailored clinical care to improve postoperative outcomes. Frailty, as a geriatric syndrome characterized by a combination of reduced physiologic reserve and multisystem deficit accumulation distinct from normal aging processes [4], has emerged as a key predictor for adverse outcomes in elderly surgical patients [2, 3, 5, 6].

Various screening tools have been proposed to measure frailty in the peri-operative settings, such as the Risk Analysis Index (RAI) developed by Hall and colleagues [7]. The RAI is an instrument based on the deficit accumulation model of frailty and comprises multiple frailty domains, including comorbidities, cognitive ability, social, nutrition, and functional status [7–9]. It represents a more comprehensive measure than other similar frailty instruments (e.g., modified frailty index [mFI]) [9, 10]. Initially, the validation of RAI was limited to the veteran surgical cohorts, with women in the minority [7, 11, 12]; several authors then validated it with external cohorts [9, 13, 14]. Among them, Arya et al. modified the original RAI and proposed the revised-Risk Analysis Index (RAI-rev); furthermore, they found that the RAI-rev had improved discrimination and calibration for mortality over the original RAI in peri-operative settings [9]. So far, there has been limited data on the association of RAI-rev with the postoperative complications and the predictive value of RAI-rev in predicting the composite outcome of major morbidity and mortality (MMM) in elderly surgical patients.

The current study aimed to determine the association between the RAI-rev scores and the risk of postoperative MMM in elderly patients undergoing abdominal surgery. Additionally, we sought to explore the predictive value of RAI-rev in predicting the occurrence of MMM when combined with other commonly-used risk factors (American Society of Anesthesiologists [ASA] physical status classification, type of surgery categorized by operative stress, and urgency status of surgery [emergency or elective]). We hypothesized that a higher RAI-rev score was associated with an increased odds of MMM and could accurately predict the occurrence of MMM when combined with other preoperative risk factors.

Methods

The study protocol was approved by the Biomedical Research Ethics Committee of Peking University Third Hospital, Beijing, China (Chairperson Prof Chunli Song) on April, 2022 (2022 [158-02]). Due to the retrospective design and that no patient follow-up was performed, the Ethics Committee agreed to waive the written informed consent from the patients. The investigators who performed the data collection were blinded to the objective of the study and received strict training sessions.

Patient selection

This retrospective cohort study reviewed the electronic medical records of elderly patients (≥65 years of age) who underwent abdominal surgery (including urologic and general surgical procedures) from January 2018 to December 2019, in Peking University Third Hospital. Patients with incomplete or missing peri-operative data were excluded. All personal information on patients was kept confidential.

Measurement of RAI-rev score 

RAI-rev score was calculated by evaluating 11 variables derived from the Veterans Affairs or American College of Surgeons National Surgical Quality Improvement Projects (VASQIP/ACS-NSQIP) datasets, i.e., age, sex, cancer, poor appetite, unintentional weight loss, renal failure, congestive heart failure, shortness of breath, residence other than independent living, cognitive decline, and functional status [7-9]. Total score ranges from 0 to 81, with higher scores indicating more severe frailty. Details on the weight of each item are listed in Supplemental Digital Content (SDC) 1. Ifa patient experienced more than one surgical procedure during the hospital stay and had multiple preoperative RAI-rev scores, only the first round of the surgery and the corresponding preoperative RAI-rev score were analyzed.

Other baseline characteristics not covered by the RAI-rev were gathered, including body mass index (BMI), smoking and drinking status, major comorbidities, ASA physical status classification, and main laboratory test results. Intra-operative factors were also extracted and included type of surgery categorized by operative stress [15], urgency status of surgery (emergency or elective), anesthetic methods, duration of surgery, estimated blood loss, and intra-operative blood transfusion. The operative stress levels of surgical procedures were stratified using the Operative Stress Score (OSS), i.e., OSS1, very low stress; OSS 2, low stress; OSS 3, moderate stress; OSS 4, high stress; and OSS 5, very high stress [15].

Postoperative outcomes 

The primary outcome was the occurrence of MMM during hospitalization, i.e., grade III or greater complications according to the Clavien-Dindo (CD) scoring system (SDC 2) [16]. For patients with multiple complications, we included the most severe complication for analysis. The diagnostic criteria for major complications are listed in SDC 3. The secondary outcome was the development of life-threatening complications and mortality, i.e., CD IV or greater complications. 

Statistical analysis

The baseline and perioperative variables were compared between patients with MMM and those without. Continuous variables were analyzed with the independent samples t-test or Mann-Whitney U test; the Kolmogorov-Smirnov test was performed to check for normality. Categorical variables were analyzed using c² tests, continuity-corrected c² tests, or Fisher's exact tests. Time-to-event variables were analyzed with Kaplan-Meier survival analysis ( Log-Rank test).

We used multivariable logistic regression models to investigate the association between RAI-rev scores and outcomes. Peri-operative variables that might be associated with the development of MMM were screened using univariable logistic regression analyses and tested for multicollinearity. Independent variables with P values <0.10 in univariable analyses and those considered clinically significant were entered into a multivariable logistic regression model to identify the association of RAI-rev scores with the MMM risk. Similarly, another multivariable logistic regression model was constructed to investigate the relationship between RAI-rev scores and life-threatening complications and mortality. The 11 variables included in the RAI-rev were not separately enrolled in either univariable or multivariable analyses. The Hosmer-Lemeshow test was used to confirm the goodness of fit of the multivariable logistic regression models. 

The predictive performances of RAI-rev scores alone and the combination of RAI-rev scores, ASA classification, operative stress, and urgency status of surgery were assessed using the receiver-operating characteristic (ROC) curve analysis. The area under the curve (AUC) and 95 % confidence interval (CI) were used to assess the discriminative power (ability to classify correctly) of these risk factors for outcomes. The relevant predictive parameters, including sensitivity, specificity, positive and negative predictive values (PPV and NPV), were calculated for different thresholds of RAI-rev scores. For all analyses, two-tailed P values<0.05 were considered significantly statistical. All statistical analyses were performed with the SPSS version 26.0 (IBM Corp., Armonk, NY, USA).

Although the sample size was not estimated in advance, 258 cases of MMM and 16 independent variables included in the corresponding multivariable logistic regression model, as well as 178 cases of life-threatening complications and mortality and 15 independent variables included in the corresponding multivariable model, meet the requirement of the "ten events per variable" rule [17]. Therefore, the sample size (2225) of our study was sufficient and could guarantee the reliability and validity of the regression estimates.

Results

Association Between Rai-rev Scores And Mmm

Univariable analysis showed that a higher RAI-rev score was associated with an increased risk of MMM, i.e., with every unit increase in the RAI-rev value, the odds of MMM increased by 5.3% (unadjusted OR: 1.053; 95% CI: 1.034 to 1.072; P < 0.001). After testing the multicollinearity, 15 other potential risk factors for MMM (P < 0.10) were identified (SDC 5 and Table 2).

After correcting for confounding factors, the rising RAI-rev score remained an independent predictor for an increased risk of MMM. The multivariable analysis showed that each unit increase in RAI-rev scores resulted in a 2.3% increase in the odds of MMM (adjusted OR: 1.023; 95% CI: 1.003 to 1.044; P = 0.026; Table 2).

Association Between Rai-rev Scores And Life-threatening Complications And Mortality

Univariable analysis revealed that with each unit increase in the RAI-rev score, the rate of postoperative life-threatening complications and mortality increased by 6.7% (unadjusted OR: 1.067; 95% CI: 1.044 to 1.091; P < 0.001). After testing the multicollinearity, 14 variables with P < 0.10 were identified by univariable analyses (see SDC 6 and Table 3). The multivariable logistic regression analysis indicated that rising RAI-rev scores predicted stepwise increased risk of life-threatening complications and mortality, i.e., every one unit increase in RAI-rev score predicted a 3.0% increase in the odds of this serious adverse outcome (adjusted OR: 1.030; 95% CI: 1.005 to 1.055; P = 0.017; Table 3).

Receiver-operating Characteristic Analysis For Mmm

The AUC of RAI-rev scores in predicting MMM was 0.604 (95% CI: 0.567 to 0.640; P < 0.001; Fig. 3A). The sensitivity, specificity, PPV, and NPV for different threshold values of RAI-rev scores are summarised in Table 4.

When combined with the ASA classification, operative stress, and urgency status of surgery, the predictive ability of RAI-rev scores was improved (AUC: 0.691; 95% CI: 0.656 to 0.726; P < 0.001; Fig. 3A).

Receiver-operating Characteristic Analysis For Life-threatening Complications And Mortality

The AUC of RAI-rev scores in predicting the occurrence of life-threatening complications and mortality was 0.633 (95% CI: 0.592 to 0.675; P < 0.001; Fig. 3B). The sensitivity, specificity, PPV, and NPV for different threshold values of RAI-rev scores are detailed in Table 4.

Compared with RAI-rev alone, the combination of RAI-rev scores with the ASA classification, operative stress, and urgency status of surgery had improved discriminative power (AUC: 0.739; 95% CI: 0.702 to 0.777; P < 0.001; Fig. 3B).

Discussion

This retrospective cohort study determined that rising RAI-rev scores were independently associated with stepwise increased risk of MMM in elderly patients after abdominal surgery. The AUCs of the RAI-rev scores ranged from 0.60 to 0.65 when predicting postoperative MMM or life-threatening complications and death. Compared with the RAI-rev alone, the combination of RAI-rev scores with additional predictors (i.e., ASA classification, operative stress, and urgency status of surgery) had significantly improved predictive value for MMM. Especially for the life-threatening complications and mortality, the combination of RAI-rev scores with the above predictors showed a moderate predictive value with an AUC of more than 0.70, which is clinically useful in the decision-making process.

It was revealed that postoperative deaths accounted for 7.7% of all deaths worldwide, making it the third leading cause of death [18]. Undoubtedly, major postoperative complications lead to a cascade of peri-operative adverse events, including death; furthermore, the occurrence of major complications is associated with poor long-term survival outcomes in the surgical patients [19, 20]. Therefore, prediction of MMM is the critical first step for clinicians to address the burden of postoperative mortality. In the current study, postoperative MMM occurred in 11.6% of our patients. In previous studies of patients undergoing abdominal surgery, the reported incidence of CD grade III or greater complications ranged from 9.7 to 13.2% [20–22]; the incidence of postoperative MMM in our study population was within this range.

Similar to the original RAI scoring system, the RAI-rev comprises more comprehensive frailty domains than mFI. The mFI is another well-known deficit accumulation model of frailty and includes merely the domains of comorbidity and functional status.¹⁰ Furthermore, unlike mFI, the RAI-rev is a weighted model with each item having different weights derived from a valid model [9]. When compared with the original RAI, the RAI-rev performed better discrimination and calibration in predicting postoperative mortality [9]. Although the RAI-rev scoring system offered higher weight on the male sex, Arya et al. revealed that it also performed robust validity in the female population, confirming its general applicability in clinical settings [9]. Compared with previous studies [8, 9], a larger proportion of patients in our study had high RAI-rev scores. This discrepancy might be attributed to the differences in target patients and clinical settings. To our knowledge, this study is the first to investigate the association of RAI-rev scores with the postoperative MMM, as well as the predictive power of RAI-rev scores for the MMM in older surgical patients.

Our results showed that higher RAI-rev scores were independently associated with increased risk of MMM in elderly patients after abdominal surgery. This finding reinforces the available evidence that pre-operative frailty is an important predictor of adverse postoperative outcomes [2, 3, 5, 6]. In addition, we found that BMI < 18.5 kg/m², ASA classification III or higher, surgery with moderate or greater operative stress, emergency surgery, and intra-operative blood transfusion were independently associated with a higher risk of MMM. We also determined that BMI < 18.5 kg/m², ASA classification III or higher, surgery with high or very high operative stress, emergency surgery, long duration of surgery, and hyponatremia (Na⁺<135.0 mmol/l) were independent predictors for increased risk of life-threatening complications and mortality. These results were in line with previous findings [3, 23–28].

This study also evaluated the predictive value of the RAI-rev scores in predicting the risk of postoperative complications. However, our results demonstrated that it lacked good discrimination for the MMM or CD IV or greater complications in elderly patients undergoing abdominal surgery (AUCs: 0.60–0.65). Previous findings from the studies that had used the frailty tools alone to predict postoperative complications were equally disappointing [14, 29, 30]. The poor predictive performance of preoperative frailty in the prediction of postoperative complications may be attributed to the fact that the etiology of postoperative complications is multifactorial and difficult to predict; the patient-level factors alone could not well explain the variation in complication risk. Thus, additional baseline characteristics or surgical-related factors should also be considered when predicting the risk of postoperative complications. Despite its poor discriminative ability, RAI-rev displayed high NPV at all thresholds; of course, this is also related to the low incidence of postoperative MMM. The high NPV indicated that the RAI-rev possesses a superior ability to exclude patients at low risk of major complications. In perioperative settings, the use of RAI-rev can facilitate the rapid identification of low-risk patients. For patients classified as 'non-frail', unnecessary medical modification or intervention (such as planned admission to the ICU after surgery) may be avoided, which can help prompt the efficient allocation of medical resources and improve the quality of peri-operative care.

As expected, the combination of RAI-rev with other commonly–used pre-operative factors (ASA classification, operative stress, and urgency status of surgery) had significantly improved performance to discriminate the risk of major complications, particularly the life-threatening complications and mortality (with an AUC above 0.70). A prediction model with AUC exceeding 0.70 may be considered to be useful in clinical decision-making [31]. Besides RAI-rev scores, high ASA classification, surgery with moderate or greater operative stress, and emergency surgery were identified as credible predictors for MMM and CD IV or greater complications in our multivariable analyses. ASA physical status classification is a traditional preoperative risk stratification tool based on the subjective estimate, reflecting a patient's physiologic reserve and his/her tolerance to surgical trauma stressors. Compared with elective surgery, emergency surgery constitutes an important predictor for poor postoperative outcomes due to acute disease processes and inadequate medical optimization before surgery [28]. The operative stress, represented by the OSS, categorized the surgical procedures based on different degrees of physiologic stress [15]. Considering the lack of an assessment of the urgency status of surgery in the OSS system, we added this important surgical-related factor into the combined model to predict postoperative complications. Based on our findings, the combination of RAI-rev scores with the above risk factors might help clinicians assess the expected risk of life-threatening complications and mortality in elderly surgical patients, despite its limited ability to predict the MMM risk.

Besides the retrospective nature, this study had some other limitations. First, our study did not include gynecological patients who underwent abdominal surgery due to the concern about the influence of the special sex distribution of those patients on the RAI-rev score calculation and the final results. However, this might lead to selection bias. Second, the primary endpoint was limited to in-hospital MMM; the occurrence of postdischarge MMM was not observed, which might confound the association between RAI-rev scores and outcomes. Finally, as single-center research, our results may not be extrapolated to patients from other institutions. Despite these, our study for the first time explored the association of RAI-rev scores with postoperative complications and the predictive value of RAI-rev for major complications.

Conclusion

In conclusion, this study demonstrated that higher RAI-rev scores were associated with an increased risk of postoperative MMM in older patients undergoing abdominal surgery. When combined with the ASA physical status classification, operative stress, and urgency status of surgery, RAI-rev might have better performance in predicting postoperative MMM, particularly the life-threatening complications and mortality. Our findings enable clinicians to better identify high-risk older patients and thus optimize perioperative care and management.

Declarations

Acknowledgments

We would like to thank Dr. Yang Bao and Dr. Linyu Ren (Department of Anaesthesiology, Peking University Third Hospital) for their help during the data collection.

Authors' contributions

Study design: Bin Wei, Yanan Zong, Mao Xu, Xiaoxiao Wang, Xiangyang Guo; Data collection: Bin Wei, Yanan Zong, Mao Xu; Data analysis: Bin Wei, Yanan Zong, Mao Xu, Xiaoxiao Wang; Manuscript preparation: Bin Wei, Yanan Zong, Mao Xu, Xiaoxiao Wang, Xiangyang Guo.

Funding

None.

Availability of data and materials

The data set used and analyzed during the current study is available from the corresponding author on reasonable request.

Ethics approval and consent to participate

The study protocol was approved by Peking University Third Hospital Science Research Ethics Committee, Beijing, China (2022 [158-02]). Due to the retrospective design and that no patient follow-up was performed, the Ethics Committee agreed to waive the written informed consent from the patients. In the study, all the methods were carried out in accordance with the relevant guidelines and regulations.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Authors' details

¹ Department of Anesthesiology, Peking University Third Hospital, Beijing, China; ² Clinical Epidemiology Research Center, Peking University Third Hospital, Beijing, China.

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