[Hypercapnea during thoracoscopic surgery under regional anesthesia]

A 23-year-old woman was supposed to undergo thoracoscopic surgery for the 10th pneumothorax that accompanied histiocytosis X. The past history included Lylle's disease, asthma, myocarditis, drug-induced leucocytopenia and bronchitis obliterans. The preoperative arterial blood gas analysis under receiving O2 at rate of 2 l.min-1 via a nasal cannula revealed normal values. General anesthesia and intubation with a double-lumen endotracheal tube would have been preferable, but regional anesthesia was chosen because of her medical history and positive results of the skin tests for vecuronium, pancronium, diazepam and midazolam. During the first 10 min of thoracoscopic procedure, her respiration became rapid and shallow and she was restless and comatose. The operation was cancelled. Arterial blood gas analysis under receiving O2 at rate of 4 l.min-1 via a face mask revealed: pH 7.025, PaO2 113.8 mmHg, PaO2 244.8 mmHg, HCO3- 29.7 mEq.l-1, BE-5.6, and O2 saturation 99.1%. Manual artificial ventilation with a mask and bag was initiated. Her spontaneous respiration and consciousness recovered in next 30 min. The postoperative course was uneventful. Tachypnea, caused from anxiety, dyspnea and stimulation of irritant receptors in the airway, were considered to be responsible for the event. The duration of inspiration became shorter as tachypnea developed, that made the tidal volume to decrease and hypercapnea ensued.