Carbon dioxide rebreathing caused by deformed silicon leaflet in the expiratory unidirectional valve
A four-year-old boy was scheduled for cleft palate repair, as the third patient on the list. After managing two adult patients earlier, the corrugated tubing of the circle breathing system was changed to the pediatric type and tested for leaks. Anesthesia was induced with sevoflurane using JRMATP. After tracheal intubation, the circle breathing system was used with pressure-controlled ventilation (PCV). After a few breaths, FiCO2 increased to 9 mmHg []. Soda lime was only partly discolored. The flow rate setting in the ventilator (i.e., the flow rate used to achieve the set inspiratory pressure, an equivalent of Pramp or ‘rise time’) was increased and FiCO2 became zero. With manual ventilation, FiCO2 increased whenever the tidal volume was delivered slowly and decreased with rapid delivery of tidal volume. We noted that the leaflet of the expiratory UDV was deformed and part of it remained open during inspiration []. The valve was closing fully with rapid delivery of tidal volume (or higher flow rate). The flow waveform on the ventilator showed minimal flow during inspiration []. The flow sensor was not direction sensitive, and was showing both the normal expiratory flow and the abnormal reverse flow on the same side of the Y-axis (the ventilator was not equipped with any alarm to indicate reverse flow). Later, the expiratory UDV was tested and found to be incompetent. The machine was used in subsequent patients after replacing the defective valve leaflet. The problem recurred after a few days and the new leaflet was also found to be deformed.\nOn checking all anesthesia machines with similar UDVs, the inspiratory UDVs were found to be deformed and incompetent in some machines, although no problem was reported during clinical use. The matter was reported to the manufacturer and they concluded that the problem was caused by the thinness of the valve leaflet (0.3 mm). All the leaflets in UDVs were replaced with thicker ones (0.5 mm). No similar problems have been reported since then.