Introduction
Malnutrition is highly prevalent in patients treated in the intensive care unit (ICU) and varies from 39-50% depending on screening tools and patient groups [
1]. Poor nutritional status in critically ill patients is closely associated with negative clinical outcomes such as prolonged ICU stay, increased mortality, and infectious complications [
2,
3,
4]. Therefore, adequate nutritional support is an essential component in the management of critical illness and this should start with the identification of poor nutritional status of patients in the ICU [
5].
Over the past decade, nutrition screening and assessment have become an integral part of nutrition care, with a variety of tools and guidelines available to healthcare professionals [
6,
7,
8,
9]. Nutritional risk screening 2002 (NRS-2002) has been shown to have good predictive validity in various hospitalized patients, but conflicting views have been shown in critically ill patients [
10]. Since Heyland et al. introduced a severity index in the Nutrition Risk in the Critically Ill (NUTRIC) score [
11], the modified-NUTRIC (mNUTRIC) score was developed during the studies on critically ill patients and has been validated across many observational studies from different countries [
11,
12,
13,
14]. However, the mNUTRIC score does not include traditional variables of nutrition such as changes in food intake or body weight. Besides, studies regarding to nutritional therapy using mNUTRIC score are relatively lacking on Asians.
The nutritional status of patients admitted to the ICUs deteriorates rapidly even in the case of well-nourished patients [
4]. In fact, altered metabolism in critically ill patients exacerbates malnutrition, and the effects of inflammation on the nutritional status of patients is known [
15]. During acute inflammatory states, nutrition cannot reverse the loss of body cell mass completely. These conditions predispose critically ill patients to a high risk of malnutrition [
16]. For critically ill patients who are expected to stay in the ICU for more than 48 hours, providing early nutrition is recommended as the standard of care [
10,
17]. Several studies have reported that nutritional adequacy, such as total calorie and protein intake during the first week in ICU, improved prognosis. This included reduced mortality and shortened length of stay in the ICU [
18,
19,
20,
21]. Recently, the adequacy of nutritional supply has been evaluated according to the risk of malnutrition based on the mNUTRIC score [
22,
23]. When examining the pathophysiology of malnutrition across two main characteristics of critically ill patients, stress catabolism and inadequate nutritional intake, it is necessary to establish a nutrition screening strategy that considers metabolic changes in critically ill patients. However, such studies have not yet been conducted.
This study aimed to (1) assess the use of mNUTRIC score compared to traditional screening tools in Korean ICU patients, (2) evaluate the proper time to apply the mNUTIRC score to consider the metabolic characteristics of acute and recovery phases, and (3) identify critical nutrition strategies for improving 28-day mortality in the ICU.
Materials and Methods
Study design and patient enrollment
This prospective observational study included all adult patients (aged ≥ 18 years) eligible for nutritional screening within two days of medical ICU admission at the Seoul National University Bundang Hospital from September 2020 to February 2022. The exclusion criteria were as follows: patients who were not eligible for nutrition screening within 48 h of ICU admission due to death, transfer, insufficient data, and discharge or by the judgment of the attending physician. All data collection and analysis procedures were approved by the Institutional Review Board of the Seoul National University Bundang Hospital (No. B-2009-634-301). Informed consent was obtained from all the participants or their respective guardians.
Statistical analysis
Statistical analyses were performed using the SAS software version 9.4. Demographic characteristics were described using student’s t-test for continuous variables and chi-squared test for categorical variables. Continuous and categorical variables were summarized as mean ± standard deviation (median, interquartile range) and counts (percentile, %), respectively. Prognostic performance for predicting 28-day mortality among nutrition screening tools was compared using the area under the Receiver Operating Characteristic curve (ROC) by a logistic procedure. To evaluate sensitivity and specificity, the risk levels on days 2 and 7 were dichotomized according to nutritional status (high vs. low risk). The survival curves for 28-day mortality were derived using the Kaplan–Meier method, and the log-rank test was used for statistical comparison between high- and low-risk groups. The risk factors associated with the 28 day-mortality were evaluated using univariable and multivariable Cox proportional hazards regression. Multicollinearity among variables was tested, and multivariable regression was carried out based on the results of the univariable analyses. The final multivariable regression model was developed based on backward elimination. All statistical tests were two-sided, and the p-value of < 0.05 was considered statistically significant.
Results
Of the 515 patients admitted to the ICU during the study period, 490 patients were included on day 2, and we observed the prognosis such as the 28-day mortality in all of them. Finally, 266 patients, who were believed to be in the post-acute (recovery) phase, were evaluated on day 7 for the second implementation phase of nutrition screening. A flow diagram of patient selection is shown in
Figure 1.
The baseline characteristics of the enrolled patients, according to the timing of nutritional screening, are presented in
Table 1. The study population was predominantly male (64.7%), with a mean age of 67.9 (±15.0) and BMI 23.6 (±5.6). Sex, age, BMI, ICU admission sources, days from hospital to ICU, number of comorbidities, and 28-day mortality did not differ significantly between the two groups. The most common diagnoses at admission were respiratory and circulatory diseases, and neoplasms. Significant differences between days 2 and 7 were observed in the APACHE and SOFA scores, use of vasopressors, and routes of nutrition administration. Severity scores were lower on day 7 than on day 2 according to the mean APACHE score (from 28.6 on day 2 to 17.1 on day7, p<0.001) and mean SOFA score (from 7.5 on day 2 to 6.8 on day 7, p=0.012). However, the high risk as per the mNUTRIC score on day 7 was still 51.5%. Nothing by mouth (NPO) patients decreased on day 7, and availability of nutritional support through various routes increased both total caloric and protein supply. Hypocaloric feeding patients on day 7 decreased from 61% to 37.2%, but protein supply below 1.0 g/kg was still 62.4%.
Here,
Figure 2 shows the Kaplan-Meier survival function for the risk group stratified by NRS-2002, MNA-SF, and mNUTRIC scores on days 2 and 7, respectively. The NRS-2002 classified most patients as having a high risk of malnutrition, even on ICU day 7. Only the mNUTRIC score showed significant differences in nutritional risk stratification on days 2 and 7. In addition, comparison of the 28-day mortality prediction with nutrition screening tools using ROC analysis showed a good predictive value for the mNUTRIC score and was performed on day 7 (0.692, CI:0.631 – 0.752, p<0.001,
Figure 3).
Using univariate analysis as the first step to affirm risk factors, total calorie and protein amount, hypoalbuminemia (< 2.5 mg/dL), neoplasm, renal dialysis, use of vasopressors, hypocaloric supply, hypo-protein (< 1.0 g/kg, only on day 7) and mNUTRIC score (low and high risk) were identified as significant covariates that influenced 28-day mortality. Finally, the multivariate Cox proportional hazards regression showed that patients with neoplasm (adjusted hazard ratio, aHR=2.739, CI:1.504-4.990, p=0.001) and use of vasopressors on day 7 (aHR=1.993, CI:1.121-3.541, p=0.019) were associated with a significantly higher 28-day mortality. Hypoalbuminemia (aHR=2.552, CI:1.452-4.486, p=0.001) and hypo-protein supply (aHR=2.329, CI:1.185-4.577, p=0.014) on day 7 also negatively influenced 28-day mortality as nutritional factors. In particular, patients assessed as having high risk according to mNUTRIC score on day 7 were predicted to have the poorest survival result (aHR=4.708, CI:2.336-9.492, p<0.0001) (
Figure 4).
Discussion
We aimed to identify critical nutrition strategies using the mNUTIRC score and predict major prognosis such as 28-day mortality in Korean ICU patients. In addition, we sought to explore when it would be more appropriate to implement nutrition screening tools used in ICUs to reflect the patient's metabolic state. In this study, mNUTRIC score applying at ICU day 7 showed better in predicting 28-day mortality compared with others. Also, high risk by mNUTRIC score, use of vasopressor, hypo-protein supply below 1.0 g/kg/day and hypoalbuminemia (<2.5 mg/dl) in ICU patients going into a recovery phase were strongly associated with 28-day mortality.
Adequate timing to implement the mNUTRIC score in critically ill patients
The broad definition of nutrition screening focuses on the identification of patients who might be malnourished or are “at nutrition risk”. This simplifies the screening time at the time of hospitalization [
33,
34]. Most nutrition screening tools have been developed in outpatient or inpatient settings and do not include variables depending on the time of application [
6,
7]. In contrast, the mNUTRIC score integrates the severity of illness scores into its risk assessment calculations. Critically ill patients become metabolically/hemodynamically unstable during the acute phase, that is immediately after ICU hospitalization within 5-7 days [
10]. Therefore, we hypothesized that the timing of the mNUTRIC score for predicting prognosis would be more appropriate after the acute phase. Our results demonstrated that mNUTRIC on day 7 not only showed good predictive performance but also exhibited a significant probability of 28-day mortality at high risk (aHR=4.708, p<0.0001).
Even though the mNUTRIC score in the recovery phase was better than the acute phase, it was estimated less predictable than that of other studies (Heyland
et al., AUC 0.783, Manon
et al., AUC 0.768, and Majari
et al., AUC 0.806) [
11,
13,
31]. This difference can be explained as follows: First, the distinctive characteristic of the study subjects was that they had a higher average age (67.9 years) and severity scores than other studies. The period of this study corresponds to the period of the COVID-19 pandemic, and during this period, it was judged that the severity of the patient was higher than before due to limited ICU beds. Actually, the SOFA scores of our patients were much higher than those of studies conducted at tertiary hospitals of a similar size in Korea before COVID-19 [
35]. Second, it may be due to differences in the time of data collection related to the nutrition screening tool. In other studies, data for nutrition screening were obtained within 24 hours of admission to the ICU, whereas our study allowed 36-48 hours. During the hyperacute early phase, the patient status is characterized by more severe metabolic instability and an increase in catabolism [
10]. Thus, during our observation period, patients needed a more intensive treatment strategy. There existed a difference in the initial predicting ability due to the patient's unstable condition.
Nutrition support strategy for improving 28-day mortality
Inflammation during the acute ICU phase is usually associated with elevated CRP levels and hypoalbuminemia. Rapid loss of protein in ICU patients is most likely related to the proinflammatory state and severe catabolism due to an increase in stress-related cytokines and hormones. In one study, patients lost approximately 10~15% of their initial total protein content within 10 days of ICU stay, despite previous good nutritional status and adequate protein and energy intake [
36]. Our study population, as shown by demographics, had improved CRP and APACHE II levels but displayed a decrease in albumin levels during the acute and recovery phases. When examining the nutritional support on ICU day 7, 62.8% of patients were supplied with ≥ 70% of calculated calories, but hypo-protein was still 62.4%. Also, hypoalbuminemia and hypo-protein supply were significant factors as negative influence on the 28-day mortality. This shows that supplementation with lost protein in the acute phase is a very important nutritional support strategy for improving the prognosis of patients who enter the recovery period. Recent reports indicate that higher nutritional adequacy evaluated in terms of calorie intake may reduce 28-day mortality in patients with a high mNUTRIC score [
22,
23]. European Society of Parenteral and Enteral Nutrition guideline recommends that hypocaloric nutrition (below 70% estimated needs used predictive equation) should be preferred for the first week of ICU stay (10). We did not observe an association between hypocaloric feeding and 28-day mortality. As we applied strict calorie calculation including those from dextrose fluid and propofol, the impact of low calories intake could have been further identified if the only considered calories supplied through EN + PN as other studies. It also seems that the severity of patients enrolled in our study may have offset the beneficial effects of caloric intake.
New insights and limitations
This is the first prospective study of the mNUTRIC score considering the characteristics of critically ill patients who go through the acute and recovery phases in the ICU setting. Our results suggest that a nutritional intervention in those identified as greater risk by the mNUTRIC score at the recovery phase have a benefit to the 28-day mortality. One of the limitations of our study is that it was conducted in a single center in Korea. In addition, the recovery period (ICU day 7) applied in our study was based on commonly suggested metabolic characteristics without objective measurements such as inflammation indicators. Thus, it is thought that there will be actual differences in individual patients. Lastly, as this was a prospective observational study restricting any nutritional interventions, causality cannot be assumed. Therefore, further research is needed to compare the effects of aggressive nutritional support in patients who are identified to be at high risk by the mNUTRIC score.
Conclusion
The implementation of mNUTRIC score in the post-acute phase is the optimal time for considering metabolic characteristics. Hypo-protein intake (<1.0 g/kg/d) in post-acute phase patients with a high mNUTRIC score is associated with an increased risk of 28-day mortality.
Author Contributions
So hang Park, Hyung-sook Kim, Sung Yoon Lim, and Soo An Choi made substantial contributions to the conception or acquisition of data. Sunny Park, So hyang Park, Ye ju Kim, Geon Ho Lee, and Hyung-sook Kim collected the data. Sunny Park, So hyang Park, and Soo An Choi conducted the analysis and produced the first draft of the manuscript. Sung Yun Lim and Soo An Choi made critical supervision of important intellectual content. All authors gave the final approval for publication.
Funding
This study was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2020R1F1A1069046) and the National Research Funding of Korea, funded by the Ministry of Education, Science and Technology (NRF-2019R1A6A1A03031807).
Conflicts of Interest
The authors declare no conflict of interest.
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