Immune status in chronic critical illness: a systematic review

INTRODUCTION: Currently, there is an increase in the number of patients who are classified as chronically critically ill patients. OBJECTIVE: The review is aimed at studying the indicators of the immune status of chronically critically ill patients. MATERIALS AND METHODS: PubMed and Google Scholar were used to identify relevant articles. The following 3 searches were performed: “chronically critically ill patients AND immune”, “chronic critical illness AND immune”, “persistent inflammation, immunosuppression, and catabolism syndrome AND immune”. The literature review was limited from 2012 to August 2022. The inclusion criteria were as follows: (1) patients with chronic critical illness (CCI) or persistent inflammation, immunosuppression and catabolism syndrome (PICS); (2) comparison groups are at least one of the specified — patients undergoing rapid recovery, healthy volunteers; (3) parameters of the immune status, inflammation and catabolism are the study endpoints; (4) original articles. To assess the validity of the results, a risk of bias assessment was performed for each study included in the analysis. The risk of bias in non-randomised studies of exposures (ROBINS-E) tool was used. The Delphi method was executed in two rounds by three researchers to assess bias. RESULTS: Chronically critically ill patients with the immunosuppressive status have reduced levels of HLA-DR and ALC and elevated sPD-L1 and IL-10 levels. The results of the studies were rated at ‘high’ and ‘moderate’ risk of reporting bias. Their findings should be considered as low-quality results. CONCLUSIONS: Chronic critical illness is a poorly understood condition that periodically occurs in patients in the ICU. The immune status of chronically critically ill patients is a debatable issue, as the current data are insufficient to draw a definitive conclusion. Based on the systematic review, further prospective trials are required to study the immune status of chronically critically ill patients.