Expired tidal volumes measured by hot‐wire anemometer during high‐frequency oscillation in preterm infants

• DOI: 10.1002/ppul.20367
• Publication Date: 2006-03-17T22:16:50Z
• Authors: Magdalena Zimová‐...; Richard Plavka
• Keywords: 03 medical and health sciences; 0302 clinical medicine; Breath Tests; Infant, Newborn; Tidal Volume; High-Frequency Ventilation; Humans; Infant, Premature; 3. Good health

AbstractWe sought to determine the normocapnic values of expiratory tidal volume measured by hot‐wire anemometer, and to evaluate how often expiratory tidal volume exceeds estimated anatomical dead space during high‐frequency oscillatory ventilation (HFOV) in preterm infants. We also sought to determine the relationship between expiratory tidal volume and other respiratory parameters. The neonatal respiration monitor SLE 2100 VPM, a hot‐wire anemometer, was used to measure expired tidal volume (VT,E) in patients ventilated by the Sensormedics 3100A during routine clinical use of HFOV. Two hundred and fourteen simultaneous measurements of PaCO2, VT,E, fraction of inspired oxygen (FiO2), continuous distending pressure (CDP), frequency, and amplitude were obtained from 28 patients. The median birth weight was 852 g (range, 435–3,450 g), and median gestational age was 27.2 weeks (range, 23.3–41.0 weeks). One hundred and eighteen (55%) normocapnic measurements, 42 (20%) hypocapnic measurements, and 54 (25%) hypercapnic measurements were recorded in which the median VT,E was 1.67 ml/kg (95% confidence interval (CI), 1.55–1.79), 1.94 ml/kg (95% CI, 1.74–2.14), and 1.54 ml/kg (95% CI, 1.42–1.66), respectively. The measured VT,E exceeded 2.0 ml/kg in 30 instances of normocapnic VT,E (14%) and 54 of all VT,E (25%), and 3 ml/kg only in 7 (3%) and 11 (5%) instances of normocapnic and all VT,E. There was a significant difference in median normocapnic VT,E obtained when FiO2 was between 0.21–0.35, compared to values obtained when FiO2 was 0.36–1.0 (1.61 ml/kg (95% CI, 1.52–1.70) vs. 2.06 ml/kg (95% CI, 1.93–2.19), P < 0.002). The calculated values of PaCO2 between 35–47, using the calculated regression equation for prediction of PaCO2 (mmHg), correctly predicted normocapnic values in 60% of measurements. Values >47 should predict hypercapnia in 81% of cases. In conclusion, expired tidal volume measurement by heated double‐wire anemometer sensor is feasible, provides useful real‐time information about tidal volume changes, and may improve the clinical management of HFOV. Pediatr Pulmonol. 2006; 41:428–433. © 2006 Wiley‐Liss, Inc.