General anesthesia is characterized by temporary loss of consciousness and decreased reflex activity without any change in vital functions. It can be performed with intravenous and/or inhalation agents. During general anesthesia, breathing is stopped and respiratory support is provided to patients with various respiratory equipment and ventilation modes on the anesthesia device. The most commonly used ventilation modes during anesthesia are volume controlled (VCV) and pressure controlled (PCV). In pressure-controlled ventilation, ventilation is provided with the airway pressure determined by the anesthesiologist throughout inspiration. While the pressure is constant during inspiration, the tidal volume is variable. In volume controlled ventilation, ventilation executed at the volume is set by the anesthesiologist. In other words, the determined volume is constant, but airway pressures vary.

In pediatric anesthesia practice modes have not been shown to have a clear advantage over each other. Both modes have advantages and disadvantages. With the development of modern anesthesia devices in recent years, safe ventilation can be provided even in very young children with volume controlled mode (VCV).

Atelectasis is the restriction of gas exchange due to complete or partial collapse of the lung. Atelectasis can be seen in 90 percent of patients receiving general anesthesia. This incidence is reported to be 68-100 percent in children.

Lung ultrasonography is an imaging method with many advantages for imaging lung-related diseases, such as not containing ionizing radiation, being inexpensive, and being performed at the bedside. Recently, its use by anesthesiologists has become widespread in many lung pathologies, including atelectasis. Traditional and modified lung ultrasonography scoring systems can be used to evaluate atelectasis in lung parenchyma with ultrasonography. In addition to the traditional system, modified scoring system also enables to evaluate small subpleural consolidations

In this study, it was aimed to compare the effects of volume controlled and pressure controlled ventilation modes used in general anesthesia in children on atelectasis with lung ultrasonography.

Traditional and modified lung ultrasonography scoring systems can be used to evaluate atelectasis in the lung parenchyma by ultrasonography. The modified scoring system also provides the opportunity to evaluate small subpleural consolidations in addition to the traditional system.

Lung tissue is evaluated between the intercostal spaces. On ultrasound, the pleural line can usually be seen as bright white due to the acoustic impedance difference between the aerated lung tissue and the surrounding tissues. Most of the ultrasound waves are reflected from this line. Due to the constantly reflected ultrasound waves between the pleural line and the transducer, hyperechoic lines parallel to the pleural line, called A lines, can be observed in the parenchyma. Vertical hyperechoic lines emerging from the pleural line in the lung ultrasound image are defined as B lines. B lines follow perpendicular to A lines. B lines accompany the sliding movement of the lungs along with the respiratory movement.

The patient is usually evaluated while lying in the supine position. The thorax is divided into 12 quadrants when evaluated with ultrasound for atelectasis. Midsternal line, anterior axillary line, posterior axillary line form the vertical boundaries of the quadrants. Each area is divided into two parts, upper and lower, by a line passing through its midpoint. Left hemithorax anterior upper, lateral upper, posterior upper, anterior lower, lateral lower, posterior lateral; The right hemithorax consists of 12 quadrants: anterior upper, lateral upper, posterior upper, anterior lower, lateral lower, and posterior lateral. The ultrasound probe is advanced transversely and each quadrant is examined. The patient may be asked to turn slightly to the side to evaluate the posterior quadrants. The ultrasound probe is placed vertically on the ribs and the lung parenchyma seen between the intercostal spaces is evaluated. Loss of ventilation is evaluated according to the modified lung ultrasonography scoring system for each quadrant. The score is collected by evaluating 12 quadrants from 0 to 3 and a value between 0-36 is obtained. For each quadrant, 0 represents the region with no ventilation loss and 3 indicates the region with severe ventilation loss. 0 indicates normal tissue with no loss of ventilation and 2 or fewer B lines are observed. 1 indicates little loss of ventilation, 3 or more B lines or one or more subpleural consolidations separated by a normal pleural line are observed. 2 indicates moderate loss of ventilation, observed as multiple fused B lines or multiple small subpleural consolidations separated by thickened or irregular pleural lines. 3 indicates severe loss of ventilation and is observed as consolidation or subpleural consolidation larger than 1x2 cm.

Each patient underwent transthoracic lung ultrasonography a total of 4 times: before laryngeal mask airway (LMA), at the 10th minute after LMA, before extubation and at the 10th minute after extubation. In addition, data on respiratory mechanics and hemodynamic parameters were recorded twice, at the 10th minute after LMA and before extubation.

Inclusion Criteria:

• Aged between 2 and 10 years old
• American Society of Anesthesiologists (ASA) Scoring I-II
• Elective surgery planned
• Cases that will undergo general anesthesia
• Surgical time is expected to be >30 minutes

Exclusion Criteria:

• Patients who are allergic to ultrasonography (USG) gel
• Known obstructive and restrictive lung disease
• Pulmonary infection in the last 3 months
• Having a history of surgery in the last 3 months
• A history of multiple trauma in the last 3 months
• Body Mass Index ≥30
• With diaphragmatic hernia
• Having undergone laparoscopic abdominal surgery