The Relation Between Quadriceps Muscle Layer Thickness and Nitrogen Balance for Nutrition Monitoring

Protein catabolism and proteolysis, mainly in the skeletal muscles is highly accelerated in critical illness with severe acute inflammatory processes, such as sepsis, burns, and polytrauma patients. The resulting catabolic state may be linked to immunosuppression, poor wound healing, and intensive care unit-acquired weakness (ICU-AW), which are associated with delayed recovery and increased mortality. In order to prevent muscle-protein depletion, several strategies have been proposed. One of them is adequate nutrition. Higher protein intake appears to be beneficial and could mitigate the negative catabolic state by increasing the availability of exogenous amino acids.

The adequacy of protein intake could only be optimized by appropriate monitoring. Nitrogen balance (NB) is the commonly used tool in this context. It is considered a good marker of adequate protein intake, easy, and available method of assessing the success of nutritional therapy as it reflects the gain or loss of total body proteins by calculating the difference between dietary nitrogen intake and nitrogen losses.

Moreover, a considerable reduction in muscle mass begins within the first 3 days of ICU admission and progressively worsens; therefore quantifying the muscle size may help in recognizing patients at risk of ICU acquired weakness and also may guide the interventions to prevent this complication. So, it may help in monitoring the adequacy of nutritional therapy and protein intake.

The primary methods that have been explored to measure musculature include computed tomography (C.T), magnetic resonance imagining (MRI), ultrasonography (US), and bioimpedance. Ultrasonography as a noninvasive, practical, readily available, and bedside technique could be considered the first option for the quantification of muscle size in these patients.

The quadriceps muscle is the most studied muscle found to have strong correlation with muscle mass and strength. Its size can be measured by either the quadriceps muscle layer thickness (QMLT) or the cross-sectional area (CSA). However, QMLT have greater practicability as measurements could be obtained rapidly and in real time as well as it easier to identify than CSA.

Since, monitoring is the key to individualize and optimize the critical protein intake. We hypothesized that QMLT evaluation by ultrasound could be used to guide nutritional protein intake and is correlated to conventional monitoring with nitrogen balance in critically ill trauma patients.

Inclusion criteria

• Anticipated to be mechanically ventilated to >48hour and expected to Stay in ICU > 4 days.
• No contraindication to early enteral nutrition.
• Enteral feeding in the first 24 hours after admission, with a minimum protein contribution of 1 gm / kg / day.
• We recruited only well nourished, previously healthy patients with no past history of nutritional problems.

Exclusion criteria

• Patients with preexisting neuromuscular pathology, lower limb amputation, skeletal fractures or immobilization in the previous 2years.
• Patients with relevant Co-morbidities (renal, liver or heart disease or COPD), previous immune abnormalities including those receiving corticosteroids, and those with past or recent history of cancer.
• Patients with anuria owing to the difficulty in evaluating excreted urea nitrogen
• Whose ultrasound data will be missing or incomplete
• Pregnancy
• Patients who will not reach the goal in enteral protein intake for any reason (gastrointestinal intolerance, contraindication to enteral feeding or repeated interruptions of enteral feeding due to multiple surgical procedures) or those who start parenteral nutrition.