The growing number of older patients referred to cardiac surgery is leading to a turning point. This changing population has new and unique features, such as frailty, that are not included in the traditional models used for risk scores calculation. Frailty has been proven to significantly influence surgical and non-surgical outcomes (2). As a consequence, the applicability of traditional risk assessment models to the current surgical population has been questioned (18). Chronic undernutrition is part of the constellation of alterations that define frailty and it is common in older patients, as its prevalence can vary from 20 to 78% depending on the scale used (11–12). Regardless of frailty, previous reports have highlighted the possibility that nutritional status may be useful for risk stratification but 1) an evaluation of patient’s nutrition-related risk of complications is not routinely performed and 2) doubts about the best and simplest tool to assess patient’s nutritional status still exist.

In this retrospective, single-center study we evaluated the impact of baseline nutritional status on outcomes in a sample of older patients undergoing isolated, elective heart valve surgery. Nutritional status can be measured in many different ways. The Mini Nutritional Assessment is a tool that has been recommended for detecting the risk of undernutrition in older adults. It includes a dietary questionnaire and physical and mental aspects that frequently affect the nutritional status of frail older patients (19). However, this tool does not include biological indicators and it may easily be biased in hospitalized older patients (13). Serum albumin alone was found to be inadequate to describe nutritional status because it is influenced by inflammation and hydration (20). The combination of serum albumin and weight loss has been shown to yield a higher prognostic value than serum albumin or body weight alone (13).

The GNRI has been proposed as a prognostic nutritional index able to quantify the risk of nutrition-related morbidity and mortality in older patients (13). It was developed as an adaptation of the Nutritional Risk Index (21) by replacing usual weight, which is difficult to determine in older adults, with ideal weight calculated with the Lorentz formula. In their study, Bouillanne et al. (13) demonstrated that the risk of mortality, infective complications, and bedsores was higher in older patients with low GNRI admitted to a geriatric rehabilitation care unit. Afterwards, other groups tested GNRI in different clinical settings, including cardiovascular disease (15–16). Shibata et al. (15) reported GNRI to predict worse survival after transcatheter aortic valve implantation in a large Japanese multicenter registry including more than 1600 patients. Authors found that 30-day mortality increased significantly across GNRI ≥ 92, GNRI 82 – 92 and GNRI ≤ 82 groups (0.9%, 2.3%, and 6.8%, respectively, p < 0.001). Similarly, 1-year all-cause mortality rates were significantly higher in the lower GNRI groups (16.4% and 36.4%, p < 0.001 for GNRI 82–92 and GNRI ≤82 respectively), although this difference was mainly driven by non-cardiovascular deaths.

More recently, Gürbak et al. (16) found GNRI ≤ 102.5 to be associated with higher 30-day, 1-year and follow-up all-cause mortality in 150 older patients who underwent surgical aortic valve replacement.

Interestingly, our results showed that GNRI < 92 was not associated with increased risk of 30-day mortality nor was it with mid-term mortality after isolated, elective mitral and/or aortic valve surgery. This opposing finding may have two possible reasons. Firstly, Shibata et al. (15) reported results from a large cohort of patients who underwent transcatheter aortic valve implantation. Surgical patients are different from those who are referred to percutaneous procedures. Indeed, 85% of patients included in the Japanese registry were older than 80 years. Moreover, 29%, 47.7%, and 59.1% of patients in the GNRI ≥ 92, GNRI 82 – 92 and GNRI ≤ 82 groups had STS score > 8%. Conversely, even if Gürbak et al. (16) described outcomes of patients who had heart valve surgery, their study population was different as it included younger patients who had isolated aortic valve replacement. These findings suggest that GNRI performance varies according to the type of heart valve disease. However, Cho et al. (22). recently concluded that malnutrition, identified by Controlling Nutritional Status score, Prognostic Nutritional Index and GNRI, was significantly associated with greater 1-year mortality in a retrospective cohort of 1927 patients undergoing different types of heart valve surgery (22).

Secondly, it must be acknowledged that the number of patients with GNRI < 82 in our study was small (3.6%). Although this group of patients is under-represented in many other previous studies, as patients with severe malnutrition are rarely considered for percutaneous or surgical procedures, this may have biased results.

On the other hand, patients with GNRI < 92 had more frequently acute kidney injury requiring dialysis, red blood cells transfusions, inotropes, and prolonged mechanical ventilation. Of note, this difference in postoperative complications was not predicted by STS score or EuroSCORE II, confirming that both these models have limitations when used in older, malnourished patients.

Similar results were found by Unosawa et al. (10) in a retrospective analysis of 287 patients who underwent elective cardiac surgery (aortic, valvular, or coronary surgery). Authors described more frequent pneumonia, prolonged mechanical ventilation (> 72 hours), and postoperative bedridden state in the malnourished group. Although other postoperative complications did not differ (new dialysis, stroke, sepsis, sternal osteomyelitis), longer intensive care unit and hospital stays were reported for patients with GNRI < 91. This prolonged hospitalization may be the consequence of a higher rate of postoperative complications as well as delayed rehabilitation, as highlighted by Ogawa et al. (23). In our study, intensive care unit and hospital stays were on average 3 and 6 days longer, respectivly, in patients with GNRI < 92.

Our study has several limitations. Firstly, the small number of patients with very low (< 82) GNRI scores limited the possibility to recognize the outcomes of this high-risk group. Secondly, we included both mitral and aortic valve patients and this mixed population may have biased the outcomes. Also, due to the limited number of events, our study was underpowered to detect clinically meaningful differences in outcomes between patients with preserved vs. low GNRI scores. Finally, we limited our analyses to postoperative mortality and morbidity, and we did not consider other outcomes, such as functional recovery or cost-effect impact, of poor preoperative nutritional status.