ABSTRACT
The authors report a case of 66-year-old female patient, 55 kg, ASA I who, under general anesthesia in supine position, developed gradual hypoxemia [from a baseline PaO[2] of 250 to 91 mmHg], carbon dioxide build up [from a baseline PaCO[2] 31 to 41 mmHg] associated with gradual hyperthermia up to 38.3°C over seven hours, intra-operatively. These observations were noted while using a semiclosed carbon dioxide absorption circuit in conjunction with the Hygroster filter at a fresh gas flow of 4 1/min of 50% nitrous oxide in oxygen. While the ventilation pattern was unchanged throughout the procedure, there was a change in exhaled tidal and minute ventilation volume with a net decrease of 28 ml and 0.4 l/min respectively. Findings are probably the result of pulmonary atelecatasis under general anesthesia due to the use of a relatively high-inspired oxygen concentration [50%]. In addition, the use of a high humidity and temperature heat moisture exchanger [HME] filter [Hygroster] in conjunction with the circle absorber system may have resulted in over humidification and aggravated the pulmonary atelecatasis over the long operative time