Nutrition therapy is no longer a support method for critically ill patients but is considered an important treatment measure. Increasing the protein and energy available to patients in the intensive care unit (ICU) reduces infection and complications, increases ventilator-free days, increases long-term physical recovery, and lowers patient mortality Among critically ill patients, protein is the most important macronutrient because it promotes healing, improves immune function, and helps patients maintain their lean body mass. Growing evidence has shown that adequate protein intake may be more important than caloric intake in the body. In addition, reaching at least 80% of the prescribed protein intake rather than energy intake is related to improved survival rates in ICU patients.
Muscular atrophy is a common feature in patients with intensive care unit-acquired weakness (ICU-AW), and it can start in the early stages of critical illness (within hours of onset of the disease). Its development has been related to the acute inflammatory process and immobilization. Factors such as age, medications, comorbidities, nutrition, and nervous, and muscular damage before critical illness can contribute to the extent of atrophy and the muscular and functional recovery capacity.
It was believed that perhaps the respiratory muscles in humans were spared any loss of muscle protein during starvation because of their constant activity. In a necropsy study designed to assess the diaphragm in health and disease, it was found that alterations in body weight and muscularity profoundly affect the diaphragm muscle mass.
Mechanical ventilation (MV) is the most important life-sustaining measure for critically ill patients, Even if the MV is maintained for a short time, diaphragm fatigue may also occur owing to atrophy or decreased contractile function, which is known as ventilator-induced diaphragm dysfunction (VIDD). Pathophysiological changes of VIDD include muscle atrophy, structural damage, and fiber-type transformation and remodeling.VIDD is the main factor contributing to difficult weaning from long-term MV in critically ill patients. Prolonging the time of MV is associated with an increased risk of complications, long-term dysfunction, and death.
Muscles of the lower limb are more prone to early atrophy as they are weight-bearing compared to the muscles of the upper limb as shown in previous studies. The authors showed that the size of the flexor compartment of the elbow did not show any change in the first 10 days of admission, whereas the size of the anterior compartment muscles of the lower limb showed a greater decrease in thickness within the first 5 days. Thus, these muscles make a good choice for muscle mass assessment.
Point-of-care ultrasound (POCUS) is rapid, accurate, repeatable, nonexpensive, noninvasive, and without the risk of radiation. It can visualize a large muscle area and deeper-located muscles. It can be used in both stable and unstable patients. Performing repeated ultrasound examinations in critical patients is essential and improves the overall sensitivity of the examination, which has become a standard of care in critical care.
One of the unsolved problems for a reliable definition of protein goals is the optimal intake timing to reach predefined therapeutic goals. European Society for Clinical Nutrition and Metabolism (ESPEN) 2009 recommended protein dose to be 1.2 - 1.5 gm /kg/day, while recent ESPEN 2019 guidelines recommend a dose of 1.3 gm/kg/day. On the other hand, the American Society for Parenteral and Enteral Nutrition (ASPEN) 2016 and ASPEN 2022 recommend a dose of 1.2- 2 gm/kg/day.
Generally, it is well known that patients in the acute phase (ebb phase) of the stress response are less capable of utilizing nutrients, thereby implying that early high-dose protein administration might not be beneficial. In the later phase (flow phase) of metabolic stress, insulin sensitivity gradually improves, and the human body's capability to metabolize exogenous substrates increases accordingly.
