Comparison of the work of breathing imposed by three anaesthetic breathing systems in children

Abstract

Introduction There is concern that the resistance of the valves in circle systems may impose an unacceptable respiratory load in children (1). In this study we compared the work of breathing imposed by the Bain, Jackson Rees and the circle systems in anaesthetised spontaneously breathing children.Methods Following local ethics committee approval and the written informed consent of a parent, 12 children, aged 2–6 years, ASA grades I–II scheduled for routine genital surgery (e.g. circumcision) were recruited [Weight 14.4 ± 2.9 kg and age 3.02 ± 1.3 years (meant SD)]. Patients were premedicated with midazolam 0.5 mg·kg−1. Anaesthesia was induced by inhalation of 66% N2O in O2 and sevoflurane 8%, and the trachea was intubated. Caudal analgesia was provided using bupivacaine 0.25% in a dose of 0.5 mg·kg−1. Anaesthesia with spontaneous ventilation was maintained with 66% N2O in O2, and sevoflurane 2–4%. Routine monitoring consisted of ECG, pulse oximetry, capnography and non‐invasive blood pressure.When anaesthesia had been stable for at least 15 min, the patients were attached to three different breathing systems in random succession for 10 min: 1, a Circle (Draeger Julian); 2, a Bain; 3, a Jackson Rees system. At the end of these 10 min periods, work of breathing was measured using a computerised, portable respiratory monitor (CP‐100 Pulmonary Monitor, Bear Medical). Work of breathing (W) was calculated by measuring the area enclosed in the oesophageal pressure‐volume loop (2). Oesophageal pressure was measured using a disposable balloon catheter (Smartcath, Bear Medical) and flow was measured using a disposable flow transducer (Varflex, Bear Medical). All equipment was calibrated in accordance with the manufacturers instructions prior to use.The total work of breathing (W) was expressed as Joules per litre of ventilation (J·l−1). This was compared between breathing systems using anova. P < 0.05 was considered statistically significant.Results The results are presented in Table 1. Direct measurements and calculated variables (mean ± SD) Circle Bain Jackson – Rees Work of breathing (J·l−1) 0.34 ± 0.1 0.36 ± 0.07 0.34 ± 0.09 Peak inspiratory flow rate (l·s−1) 0.19 ± 0.03 0.20 ± 0.04 0.20 ± 0.04 Peak expiratory flow rate (l·s−1) 0.16 ± 0.03 0.14 ± 0.03 0.16 ± 0.03 Δ Poes(cmH2O) 5.5 ± 2.71 6.3 ± 1.49 5.9 ± 1.83 Minute ventilation (l·min−1) 2.9 ± 0.6 2.8 ± 0.7 2.9 ± 0.6 End‐tidal CO2 (kPa) 7.8 ± 0.9 7.7 ± 0.9 7.0 ± 2.4 Δ Poes = difference between end‐expiratory oesophageal pressure and lowest oesophageal pressure. Conclusions Our results indicate that there was no difference in the total work of breathing in children attached to a circle system compared to a Bain or Jackson Rees systems.Acknowledgements This work was supported by a grant from Draeger UK Ltd.