Comparison of the Ultrasonic Cardiac Output Monitor and Echocardiography for Hemodynamic Assessment in Pediatric Anesthesia

This prospective observational pilot study is designed to evaluate the agreement between Ultrasound Cardiac Output Monitor (USCOM) measurements and transthoracic echocardiography-derived hemodynamic parameters in pediatric patients undergoing elective surgery under standardized general anesthesia.

After anesthesia induction and airway management, patients are allowed to reach stable hemodynamic and ventilatory conditions. Heart rate, noninvasive blood pressure, peripheral oxygen saturation, tidal volume, respiratory rate, and positive end-expiratory pressure are documented to confirm comparable physiological conditions during all measurements.

All measurements are performed before surgical incision and under unchanged ventilator settings, anesthetic depth, and patient positioning. No fluid administration, vasoactive medication, or ventilatory adjustments are made between techniques.

USCOM measurements are obtained first using a suprasternal approach to acquire spectral Doppler signals. Device-derived parameters, including velocity time integral (VTI), stroke volume (SV), cardiac output (CO), stroke volume variation (SVV), systemic vascular resistance (SVR), and device-calculated aortic valve area (AVA), are recorded consecutively during spontaneous or controlled mechanical ventilation without apnea. Only Doppler signals with clearly defined spectral envelopes are accepted. Measurements with artifacts or poor signal quality are repeated until optimal tracings are achieved.

Immediately afterward, transthoracic echocardiography is performed using a pediatric probe. Suprasternal Doppler recordings are aligned as parallel as possible to blood flow in the ascending aorta, and angle correction is applied when required. VTI is measured from the largest and most clearly defined spectral Doppler envelope. The aortic annulus diameter is obtained from the parasternal long-axis view during midsystole, and aortic valve area is calculated. Stroke volume is derived as aortic valve area × VTI, and cardiac output is calculated as stroke volume × heart rate. Inspiratory and expiratory VTI values are recorded to determine respiratory variation and calculate SVV.

USCOM and echocardiography measurements are performed sequentially within a 1-2-minute time window to minimize the impact of temporal hemodynamic variability. Each parameter is measured three consecutive times, and the average value is used for statistical analysis.

All examinations are conducted by a single experienced operator who completed supervised echocardiography training and independently performed at least 30 validated measurements before study initiation to minimize interobserver variability.

The primary objective is to assess agreement between USCOM and echocardiography for stroke volume and cardiac output measurements. Secondary objectives include correlation of suprasternal VTI values, agreement in SVV measurements, comparison of USCOM-calculated versus echocardiography-derived aortic valve area, and Bland-Altman analysis of all paired hemodynamic parameters.

Inclusion criteria

• Pediatric patients aged 6 months to 15 years
• ASA physical status I-II
• Scheduled for elective surgery requiring general anesthesia
• Written informed consent obtained from parent(s) or legal guardian(s)

Exclusion criteria

• Intracardiac or extracardiac shunts
• Aortic valve disease
• Anatomical limitation preventing suprasternal Doppler assessment
• Required Doppler angle correction >20° during echocardiography evaluation
• Emergency surgery
• Inability to obtain informed consent