Unidirectional valve malfunction by the breakage or malposition of disc - two cases report -
A 46-year-old-female was scheduled for laparoscopic subtotal hysterectomy due to uterine myoma in our hospital. The preoperative laboratory findings were all within the normal ranges except for low hemoglobin of 9.0 g/dl. The patient was premedicated with intramuscular injection of glycopyrrolate 0.2 mg and midazolam 2 mg 30 minutes before induction of anesthesia. When the patient arrived at the operating room, blood pressure was 140/80 mmHg, heart rate 90 beats/min, respiratory rate 18 times/min, and SpO2 98%. After a normal test of preanesthetic leak test by closing the pop-off valve, occluding the Y-piece, and pressurizing the circuit to 30 cmH2O with the oxygen flush valve and flow test by using the ventilator and a breathing bag attached to the "Y"-piece as described in the 1993 FDA Anesthesia Apparatus Checkout Recommendations [] on the breathing circuit, propofol 120 mg and rocuronium 30 mg were given intravenously, followed by uneventful endotracheal intubation. After intubation, SpO2 was 99% and end-tidal CO2 (ETCO2) measured through a previously calibrated side stream capnometer (S/5™ Anesthesia Monitor, GE Healthcare, Finland) was 34 mmHg. The anesthesia was maintained with O2 1.5 L/min, air 2.5 L/min, sevoflurane 2-3 vol%, and remifentanil 0.2-0.5 µg/kg/min. The anesthesia ventilator (Narcomed 2B, Dräger, Germany) was set at volume control mode (tidal volume 500 ml, respiratory rate 10 times/min, I/E ratio 1 : 2). Systolic blood pressure was maintained at 100-150 mmHg, diastolic pressure at 60-90 mmHg, heart rate at 50-90 beats/min. About 10 minutes after the anesthesia began, ETCO2 suddenly increased to 52 mmHg and PICO2 30 mmHg was noted (). It was the second general anesthesia of the day in this operating room. In addition, during the first 10 minutes, the capnography wave form was normal. Therefore, we initially suspected an erroneous capnometry reading and recalibrated. Breath sounds were clear and bilaterally equal. Since the core temperature measured using a Thermoscan® (infrared tympanic thermometer IRT4020, Braun, Germany) was normal range (36.4℃), malignant hyperthermia was ruled out. Carbon dioxide absorbent had not changed color. This implied the possibility of rebreathing. Blood pressure was 115/62 mmHg and heart rate was 85 beats/min. When the breathing system was rechecked, breakage of the expiratory unidirectional valve through transparent dome, which is divided into three pieces, was discovered (). After replacement of the broken disc by a new one, the capnogram waveform returned to normal. The surgery was completed smoothly and the patient had an uneventful recovery.