Comparison of high and low protein intakes and clinical outcomes in critically ill patients: a systematic review and meta-analysis

Abstract

BACKGROUND: Protein is an important part of the critical care diet but the right amount has been a source of debate. Recent international guidelines recommend a high protein diet >1.2-2g/kg/d for adult critically ill patients. However, the grade of recommendations was low and mainly based on observational data and this has raised concerns about the quality of these studies. The aim systematically review the existing randomised control trials (RCTs) to assess the effect of higher vs lower protein administration on clinical outcomes in critically ill patients METHOD: MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) were searched up to 2021. Eligible studies included randomised control trials published in a peer-reviewed journal in the English language comparing higher protein intake >1.2g/kg/d versus lower protein intake among adult critically ill patients. Studies were only included if there was a statistically significant difference in the protein supplied between two intervention groups (P value less than 0.05). Studies including immune modulating nutrition in the intervention group were excluded due to the potential impact on clinical outcomes. To assess study quality, the Cochrane Risk of Bias Tool was utilised. To summarise and understand the findings, a narrative synthesis was used. Additionally, the risk ratio for dichotomised outcomes and mean difference for continuous outcomes were pooled using random effect meta-analysis. RESULTS: Out of 506 abstracts, 44 full-text publications were evaluated and 5 studies with a total of 420 patients satisfied the inclusion criteria. The mean difference of protein intake was an additional 0.52g/kg/d of protein delivered to the higher protein intake group. Higher protein intake did not significantly affect ICU mortality (RR 0.92, 95% CI 0.64–1.34, p= 0.68: I2= 0%), hospital mortality (RR 0.97, 95% CI 0.66–1.42, P= 0.88: I2= 0%) or other mortality at any point in time. Additionally, greater protein intake reduces the length of stay in ICU and hospital by 0.26 days and 2 days, respectively which is not statistically significant. The duration of mechanical ventilation was not statistically significantly affected by the amount of protein consumed (MD 0.55, 95% CI –1.88–2.98, p= 0.66: I2= 47%). CONCLUSION: The findings of this review are aligned with international guidelines regarding a high protein prescription for critically ill patients. Large, methodologically rigorous, randomised clinical trials evaluating protein provision within the guideline recommendations are required to inform clinical practise. It is also vital to investigate the optimal timing of protein dosage among critically ill patients.