Effects of incrementally increasing tidal volume on the right internal jugular vein in pediatric patients

Twenty tree children between the ages of 7 and 12 yr, American Society of Anesthesiologists (ASA) physical status I and II, scheduled to undergo routine surgery under general endotracheal anesthesia, were studied. Patients with previous right internal juguler vein (IJV) catheterization, anatomical malformations of IJV, previous neck surgery, congenital heart disease, concurrent pulmonary disease that might influence the hemodynamics of the right heart, increased intracranial pressure, or preoperative hemodynamic instability were excluded from the present study. Fasting periods were in accordance with ASA guidelines. Anesthesia was induced with propofol (3 to 5 mg/kg) and remifentanyl (0.5 mcg/kg), and endotracheal intubation (with an appropriately sized tracheal tube) was facilitated using rocuronium. After induction, volume- controlled mechanical ventilation (tidal volume adjusted to 6 and 10 mL/kg with no application of positive end expiratory pressure and respiratory rates were adjusted to achieve an end-tidal carbon dioxide of 30 to 35 mm Hg.) was initiated. Anaesthesia was maintained using sevoflurane 1–2% in an oxygen / air mixture. Patients were placed in a supine position position with a roll under the center of the upper back to allow the head and the neck to be slightly extended. The size of the roll was adjusted to the children and not to be larger than the size of the neck. The head was positioned in a neutral position and then rotated 30 degrees to the contralateral side. The right IJV cross-sectional area (CSA) and the anatomical relationship with the carotid artery were assessed using a two-dimensional ultrasound machine with a 10 MHz linear probe. The ultrasound probe was placed perpendicular to the skin, and images of the right IJV and carotid artery (CA) were collected at the level of the cricoid cartilage. The transducer was applied with minimal pressure to ensure that the vein was not compressed. This measurement was repeated after increasing the inspiratory volume in 1 ml/kg increments from a TV of 6 ml/kg to 10 ml/kg. To eliminate the respiratory effect, the investigator selected the image showing the largest CSA at the end-inspiratory phase of the 5th respiratory cycle at every tidal volume (TV) after freezing the image on the screen. Peak inspiratory pressure (PIP), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP), heart rate (HR), and end tidal carbon dioxide (EtCO2) were recorded at all TV levels. One investigator with more than 3 years experience handling the ultrasound machine captured all the images. All ultrasonography images were stored, and measurements were performed later by different blinded investigator . On US images, the CSA of the right IJV were measured as previously described using a built in caliper. Transvers and sagittal diameter of the right IJV measured and the percentage overlap between the two vessels was calculated according to this formula [right IJV overlap of carotid artery (mm) / carotid artery diameter (mm)) × 100].