Ultrasound, Nutritional Status, and Outcomes in Surgical ICU

The surgical intensive care unit (ICU) provides continuous preoperative and postoperative monitoring of hemodynamically unstable, critically or potentially critically ill patients whose treatment requirements exceed the scope of the competent surgical department. The most common reasons for admission to the ICU are older age, multiple comorbidities, sepsis, demanding and high-risk surgery, and complications during the procedure. The literature increasingly reports that patients' nutritional status and clinical frailty are predictors of ICU treatment duration and outcome. The nutritional status (NS) of patients in intensive care units (ICUs) is assessed using clinical and laboratory indicators, including body mass index (BMI), the clinical frailty score, and hemoglobin and albumin levels. It is quantified by rating scales such as NRS (Nutritional Risk Screening) and MUST (Malnutrition Universal Screening Tool).

Frailty syndrome is defined as a patient's reduced capacity to tolerate changes in physical, physiological, and cognitive body functions. Given the reduction in the organism's physiological reserves, the patient becomes vulnerable to stressors and acute complications associated with the health condition. Patient frailty is correlated with aging, and age is among the most important determinants of frailty. In the intensive care unit, patient frailty is an important predictor of the duration and outcome of treatment, the development of complications during hospitalization, and, as noted above, the consumption of available resources. Assessment of patient frailty enables the appropriate selection of therapeutic procedures and provides overall support to the patient, aiming to achieve optimal treatment outcomes. Patient frailty can be measured using clinical scales; the most commonly used are the Clinical Frailty Scale (CSF) and the modified frailty index (mFI).

Ultrasound is a diagnostic tool that, due to its non-invasiveness and ease of use, is increasingly used to assess the patient's condition and changes during treatment. The most commonly measured ultrasound indicators in intensive care are the presence of effusion or blood in body cavities, flow through blood vessels, and measurement of distance for puncture purposes.

Ultrasound has recently been used to assess the patient's nutritional status by measuring muscle thickness and echogenicity, most often of the upper leg muscles, such as the quadriceps. Muscle cross-sectional area and the thickness of the adipose tissue above it are often measured.

Studies on nutritional status and its relationship with muscle echogenicity in the surgical patient population are rare.

The prospective observational study will include consecutive patients of both genders admitted to the Department of Intensive Care of the Clinical Hospital Center in Osijek. The expected number of subjects is 50. The study will be conducted after approval by the ethics committee of the Clinical Hospital Center in Osijek, and before inclusion, the investigator will obtain informed consent from the patient or a guardian. Patients who have had surgery on their right leg, on which muscle thickness and echogenicity will be measured, patients for whom informed consent is not obtained, and patients who are paraplegic will not be included in the study.

Demographic data will be recorded from medical records and the hospital information system for each individual subject. Patient demographics (age, gender), comorbidities, laboratory parameters (hemoglobin, albumin, lactate), reason and duration of intensive care unit hospitalization, and time required to wean the patient from mechanical ventilation will be recorded. Patient frailty will be assessed during an interview. For patients who are unable to provide information, information will be collected from family members. For the purposes of this study, the CFS will be used, which categorizes patients from 1 (very active, physically strong) to 9 (very sick, not expected to survive more than 6 months). The examiner will perform an ultrasound examination of the thigh muscles (m. rectus femoris, m. vastus intermedius, m. vastus medialis, m. vastus lateralis) with a linear ultrasound probe for each subject within 48 hours of admission to the intensive care unit (ICU), measure the thickness of the muscle and the fatty tissue immediately above it, and display the dimensions in mm. Muscle echogenicity will be expressed numerically using image analysis. Signal intensity will be calculated in a standard 5 × 5 mm area, equal across all images, using the ImageJ/Fiji software. The average of 3 ultrasound measurements will be calculated. In addition to ultrasound measurements, laboratory indicators of the patient's nutritional status are also important. Hemoglobin and serum albumin are most often associated with nutritional status. Their values are usually reduced in patients with clinical frailty, and the finding of anemia and hypoproteinemia of varying degrees is common in people with limited mobility, malnutrition, or in people with specific nutritional deficiencies, e.g., in liver cirrhosis. The values will be compared computationally with clinical indicators such as patient frailty, hemoglobin, albumin and the patient's status assessment obtained by rating scales (CSF, NRS).

• Haemoglobin [Time frame: Day 1]
• Albumin [Time frame: Day 1]
• C-reactive protein (CRP) [Time frame: Perioperative]
• Lactate [Time frame: Day 1]