An Investigation of The Relationship Between Muscle Mass, Physiological Parameters, and Blood Gas Levels in Adult Patients Hospitalized in The Intensive Care Unit

Intensive care units are facilities where patients whose physiological balance has been disrupted due to life-threatening illnesses are monitored and treated. In these patients, critical illness disrupts homeostasis, affecting multiple organ functions; sepsis, prolonged mechanical ventilation, and immobilization are significant risk factors for ICU-acquired weakness . These conditions lead to a loss of muscle mass, which negatively affects metabolic reserve, respiratory muscle strength, and recovery capacity; prolongs the length of hospital stay; and increases the risk of mortality.

Muscle tissue not only enables movement but also plays a critical role in metabolic and systemic regulation through the secretion of myokines. Therefore, muscle loss is not limited to physical weakness but also affects metabolic and systemic functions .Muscle weakness is common in intensive care patients, and losses exceeding 10%-particularly in the first few weeks-are associated with functional impairments .

A decrease in muscle mass can weaken respiratory muscle strength, leading to reduced oxygen saturation, impaired circulatory function, and decreased organ perfusion; this may manifest as pulse variability, low oxygen saturation, and decreased urine output. In a study of patients intubated due to COVID-19-related pneumonia, it was observed that individuals with high muscle density had higher extubation success rates, lower complication rates, and reduced mortality. Similarly, post-discharge measurement of quadriceps muscle mass using BIA showed a positive correlation with long-term recovery.The relationship between muscle mass and respiratory function was examined using DXA, and significant associations were found between restrictive ventilatory dysfunction and muscle mass . These data indicate that muscle mass indirectly supports oxygenation and hemodynamic stability.

The risk of muscle loss increases with prolonged immobilization, mechanical ventilation, and the use of high doses of sedatives. For this reason, the assessment of muscle mass in intensive care patients is important both for monitoring clinical course and for investigating its relationship with physiological parameters such as SpO₂, blood pressure, pulse, diuresis, and blood gas values.

Following a review of the literature, no study was found that examined the relationship between anthropometric measurements of muscle mass and physiological parameters and blood gas values in adult patients admitted to the intensive care unit. In this context, the study was planned.

Type of Study: Observational Study Study Population: Patients admitted to the palliative care intensive care unit, pulmonary intensive care unit, and cardiovascular intensive care unit at Erzurum City Hospital will be included in the study.

Sample Size: In this study, as the primary analysis, the relationship between muscle mass and SpO₂ will be evaluated using a one-way Pearson correlation; similar studies in the literature have shown a moderate correlation (r ≈ 0.30) (Damanti et al., 2022; Lim et al., 2024).Under these assumptions, a power analysis conducted with a statistical power of (1-β) = 0.80 and a significance level of (α = 0.05) determined that a sample size of approximately 67 patients would be required to test the hypothesis that SpO₂ values increase as muscle mass increases. To account for potential data losses, the sample size was planned to be approximately 80 patients.

The criteria used in similar studies in the literature that examine the relationship between muscle mass, muscle strength, and clinical outcomes in intensive care patients will serve as the basis.

Collection of research data: The research data will include adult patients hospitalized in the palliative care, pulmonary, and cardiovascular surgery intensive care units at Erzurum City Hospital. Informed consent forms will be obtained from the patients or their first-degree relatives, as well as from the attending physician in the intensive care unit.

Edema Assessment: This is a routine measurement. It poses no risk to human health. Before measurements begin, patients' upper and lower extremities will be assessed for edema. The assessment will be based on the pitting edema test-performed by applying light pressure with the thumb for 2-3 seconds-and clinical observation. For edema assessment, measurements will be taken at the widest point on the medial surface of the calf, the anterior aspect of the thigh, the midpoint of the femur (midpoint of the SIAS and the patella), the anterior surface of the midpoint of the humerus (between the acromion and the olecranon), and the posterior surface of the midpoint of the humerus (between the acromion and the olecranon).

For grading: 0+: No indentation → No edema; 1+: Mild indentation, recovers quickly → Mild edema, 2+: Moderate indentation, persists for a few seconds → Moderate edema, 3+: Deep indentation, persists for up to 15 seconds → Severe edema, 4+: Very deep indentation, persists for >30 seconds → Very severe edema; these values will be used.

Anthropometric Measurements Patients' circumference measurements and skinfold measurements will be taken while they are lying on their backs. Muscles will be kept relaxed, and a non-elastic anthropometric tape and a Baseline brand skinfold caliper will be used. Measurements will be taken on the right side of the body whenever possible; if access is obstructed, the left or opposite side will be used, and this will be noted on the record form. All measurements will be taken in a single attempt and recorded with a precision of 0.1 mm. The researchers performing the measurements have received training in accordance with the ISAK protocol.

Circumference Measurements: Measurements will be taken at the calf, thigh, and biceps. For the calf, measurements will be taken at the widest point of the calf ; for the thigh, at the midpoint of the femur on the anterior aspect of the thigh and 10 cm above the patella; and for the biceps, from the midpoint of the humerus , and the results will be recorded in centimeters.

Skinfold Measurements: Measurements will be taken from the biceps, triceps, suprailiac region, abdomen, thigh, and calf. Biceps: measured vertically from the midpoint of the humerus; triceps: measured vertically from the midpoint between the acromion and the olecranon; suprailiac: measured obliquely just above the iliac crest; abdomen: measured vertically 2 cm to the right of the navel; thigh: measured vertically from the midpoint of the femur; calf: vertically from the widest point of the calf, and the measurements will be recorded in centimeters.

Measurements will not be taken from the subscapular region, as it is believed this would interfere with patient positioning.

Muscle Mass Calculation: The thigh cross-sectional area formula will be used to calculate muscle mass.

The muscle radius (r) will be determined using the formula: thigh circumference / 2.

Then, using π = 3.14, the formula for muscle cross-sectional area = π (r - (skinfold thickness / 2))² will be used.

Physiological Parameters and Blood Gases: On the day anthropometric measurements are taken, patients' SpO₂, pulse rate, blood pressure, and diuresis will be recorded.

In addition, arterial blood gas (ABG) values will be based on data obtained during routine clinical follow-up within ±12 hours of the measurement time; no additional blood samples will be drawn. Parameters to be recorded: pH, PaO₂, PaCO₂, SaO₂, HCO₃-, base excess (BE), lactate, as well as FiO₂ and ventilator parameters.

Measurement of diuresis: For patients with a urinary catheter: The urine volume collected in the urine bag over a 12-hour period or ±12 hours will be recorded. For patients without a urinary catheter: Urine output by the patient over a 12-hour period (using a soft catheter or urine bag) will be recorded. Unit: To be recorded as mL/12 hours.

All data will be used to evaluate the relationship between muscle mass and oxygen saturation, blood pressure, pulse, diuresis, and blood gas parameters in intensive care patients.

Statistical Analysis: The data obtained from this study will be analyzed using SPSS (The Statistical Package for the Social Sciences). The Shapiro-Wilk test will be used to determine whether the data are normally distributed. The Pearson test will be used for groups with a normal distribution, and the Spearman test will be used for groups without a normal distribution. Results will be evaluated at a significance level of 0.05.

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