Impact of Adequate Protein Intake on Morbidity and Mortality in Critically Ill Patients
The following text provides a summary of findings from clinical studies in the field of nutritional therapy for critically ill patients and its impact on protein metabolism and patient outcomes.
Inevitable Catabolic Process
Current studies indicate that a negative protein balance, secondarily caused by severe illness, is associated with higher patient morbidity. Severe illnesses inevitably lead to catabolism of skeletal muscle fibers, resulting in a loss of total body protein often despite aggressive nutritional therapy. The ubiquitin-proteasome system is considered the primary metabolic and biochemical mechanism involved in the degradation of unnecessary or damaged proteins, utilizing adenosine triphosphate (ATP) as an energy source.
Negative Protein Imbalance and Its Consequences
Stressful situations accompanying trauma, septic conditions, and advanced malignant diseases are associated with multisystem changes, deviations in macronutrient metabolism, endocrinological-metabolic processes, and immune responses. Stress reactions increase the demands on energy expenditure and simultaneously increase the utilization of protein reserves (primarily actin and myosin) in skeletal muscle proteins. Mobilization of these reserves is not a one-way process but rather a consequence of an imbalance between protein synthesis and degradation.
The intensity of both processes increases, potentially reaching > 45% of resting values for the synthesis of new proteins depending on the severity of the trauma, with protein degradation rising up to 80% compared to equilibrium states. The resulting negative protein imbalance is associated with immunosuppression, impaired wound healing, and muscle weakness in critically ill patients. This adverse state prolongs hospitalization and raises the financial costs of the healthcare system. It is assumed that maintaining a neutral protein balance in critically ill patients could improve their outcomes and reduce mortality.
Main Goals of Nutritional Therapy
The primary goal of nutritional therapy is to prevent the degradation of skeletal muscle and preserve lean body mass. These tissues not only contribute to oxygenation but also contain a high proportion of potassium and participate in the synthesis of acute phase proteins. In clinical practice, this goal is achieved by adding the correct amount of protein and adequate energy.
Determining Energy Expenditure and Adequate Protein Intake
It is crucial to determine the energy expenditure of the patient either through indirect calorimetry measurements or by using predictive equations (Harris-Benedict equation), although it is known that using these two methods may not yield identical values. It is reported that patients with a lower body mass index (BMI) have a higher fraction of metabolically active tissue, which would mean higher energy expenditure per kilogram of body weight for this group. According to some authors, this fact justifies an increase in daily protein supply by 20% (approx. 1.8–1.9 g/kg body weight) for patients with lower BMI.
Risks of Increased and Decreased Energy Supply
Supplying higher amounts of energy (hyperalimentation) results in increased fat tissue deposits with heightened systemic inflammatory activity and oxidative stress, a rise in infectious complications, and higher mortality. Reduced energy supply (underfeeding) leads to a negative energy balance with a demonstrably increased incidence of infections. Both conditions correlate with loss of anabolism and increased atrophy of skeletal muscle.
Conclusion
The authors concluded in their summary that based on study results and recommendations from professional societies, it is appropriate to provide critically ill patients with higher amounts of protein in parenteral nutrition (daily dose > 1.2 g of protein per kg of body weight). The administration of higher amounts of protein in nutritional therapy was associated with reduced morbidity and mortality in this patient population.
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Source: da Cunha H. F. R., da Rocha E. E. M., Hissa M. Protein requirements, morbidity and mortality in critically ill patients: fundamentals and applications. Rev Bras Ter Intensiva 2013; 25 (1): 49–55, doi: 10.1590/s0103-507x2013000100010.
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