Background In patients undergoing abdominal radiotherapy or transurethral surgery, bladder perforations are a possible complication. Likewise, pleural effusions due to a pleuroperitoneal leak caused by either a congenital or acquired diaphragmatic defect can also occur. We report a case in which a saline solution, which migrated into the abdominal cavity from a bladder perforation during transurethral electrocoagulation, further formed bilateral pleural effusions and caused rapid ventilation failure. Case presentation A patient undergoing radiation therapy and hormone therapy for prostate cancer underwent emergency surgery for electrocoagulation due to hematuria and a rapid drop in hemoglobin. The surgery began under general anesthesia, and we first noticed an increase in airway pressure and a decrease in dynamic lung compliance, followed by abdominal distension. Based on readouts from the respiratory mechanics monitor, we suspected lung abnormalities and performed a pulmonary ultrasound, leading to a diagnosis of bilateral pleural effusions, which we then drained. Conclusions Respiratory mechanics monitoring is simple and can be performed at all times during anesthesia, and when combined with pulmonary ultrasound, diagnoses can be made quickly and prevent deaths.