Effect of Continuous Positive Airway Pressure on the Measurement of Thoracoabdominal Asynchrony and Minute Ventilation in Children Anesthetized With Sevoflurane and Nitrous Oxide

Study objectives To quantify thoracoabdominal asynchrony (TAA) in children during anesthesia, and to measure the effect of continuous positive airway pressure (CPAP) on TAA, tidal volume (V t ), and minute ventilation ( V ˙ e ). Design Prospective, nonrandomized, controlled study. Setting Operating room of a university children's hospital. Participants Ninety children aged 2 to 9 years scheduled for elective outpatient day surgery who were enrolled prospectively. Methods Each subject was anesthetized with sevoflurane 3% in equal parts O 2 and N 2 O while breathing spontaneously through a facemask. Respiratory impedance plethysmography was used to calculate TAA indexes (phase angle [PA], phase relation in inspiration [PhRIB], phase relation in expiration, phase relation in total breath [PhRTB], and ratio of the inspiratory time to the total duration of the respiratory cycle [T i /T tot] ), V t , and V ˙ e . Tidal gas flows were measured with a dual-hotwire anemometer with the sensor inserted between the facemask and the Y-piece of the anesthetic breathing circuit. This enabled the volume calibration of the respiratory impedance plethysmography equipment. The following conditions were compared: (1) no CPAP, (2) CPAP of 5 cm H 2 O, and (3) CPAP of 10 cm H 2 O. Results Eighty-one children completed the study protocol. All measurements of TAA with an inspiratory component (PA, PhRIB, PhRTB, and T i /T tot ) decreased significantly from baseline with the addition of CPAP to the circuit. Application of CPAP of 10 cm H 2 O decreased significantly mean V t s and V ˙ e s compared with CPAP of 5 cm H 2 O and no CPAP. There were no differences in TAA for all conditions when comparing children scheduled for adenoidectomy with other surgical procedures. Conclusions With spontaneously breathing anesthetized children, TAA decreases with the application of CPAP. CPAP of 5 cm H 2 O was as effective as CPAP of 10 cm H 2 O in reducing PA, PhRIB, PhRTB, and T i /T tot . However, CPAP of 10 cm H 2 O also caused a significant decrease in V t and V ˙ e .