a 55-year - old man was admitted to the general ward at a gyeongsang national university hospital with an obstructive hydrocephalus visualized by brain magnetic resonance imaging . a ventriculoperitoneal shunt had been placed 2 years earlier due to an obstructive hydrocephalus , but the physical examination was within the normal limits with the exception of an upward gaze disturbance . the laboratory studies including a complete blood count , electrocardiogram , liver and renal function tests were within the normal limits . the patient was premedicated with midazolam ( 2.5 mg ) and glycopyrrolate ( 0.2 mg ) . anesthesia was induced with 250 mg sodium thiopental and 50 mg rocuronium while he received oxygen ( 5 l / min ) through a face mask . fiberoptic orotracheal intubation was then accomplished using a reinforced endotracheal tube ( internal diameter : 7.5 mm ) . anesthesia was maintained with nitrous oxide in oxygen ( 50% : 50% ) and 6 vol% desflurane . the intraoperative end - tidal carbon dioxide tension was maintained within 30 - 35 mmhg . he received irrigation with approximately 3,000 ml normal saline at room temperature while introducing the neuroendoscope ( minop neuroendoscopy system , aesculap , center valley , pennsylvania , usa ) with a shaft diameter of 2.7 mm , a maximum infusion rate of 1,000 ml / min and a maximum pumping pressure of 500 mmhg . during the surgical procedure , irrigation fluid was naturally drained and the neuroendoscopic intracranial pressure was not measured because monitoring equipment was unavailable . two hours after beginning the procedure , his systolic blood pressure and heart rate increased from 100 mmhg to 170 mmhg and from 45 - 90 beats / min to 100 - 110 beats / min , respectively . intravenous hydralazine ( 10 mg ) and esmolol ( 10 mg ) was administered to control the increased blood pressure and heart rate . however , the increased heart rate persisted from 2 hours after beginning the procedure to the end of the operation . otherwise , the operation and anesthesia were uneventful . in order to rule out a postoperative hemorrhage , brain computerized tomogram taken immediately after the endoscopic third ventriculostomy revealed the external ventricular drainage catheter and pneumocephalus on the left frontal convexity . although he showed mild confusion , the patient was extubated after confirming adequate voluntary respiration . four hours after surgery , the respiratory rate increased to 50 - 66/min and he showed seizure - like movements . although administering intravenous diazepam ( 10 mg ) , haloperidol ( 3 mg ) and orfil ( 300 mg ) to treat the seizure - like movement , mild seizure - like activity such as myoclonal jerk persisted for 2 hours and was treated successfully with intravenous administration of another 10 mg diazepam used for endotracheal intubation . arterial blood gas analysis at that time revealed acute respiratory alkalosis ( table 1 ) . orotracheal intubation using a direct laryngoscope was then performed with the intravenous administration of 10 mg diazepam , and controlled mechanical ventilation ( assist - control mechanical ventilation mode : tidal volume ; 500 ml , respiratory rate ; 16/min , inspired oxygen fraction ; 40% ) was applied for 15 hours ( table 1 ) . the complication rate for endoscopic third ventriculostomy ranges from 6% to 8% , and is similar to the expected infection rate of a shunt . the complications of an endoscopic third ventriculostomy include cerebrospinal fluid leak , pneumocephalus , ventriculitis , subdural hematoma , injury to the periventricular structures ( hypothalamus , basal ganglia and brain stem ) , bradycardia , asystole , minor bleeding and hypokalemia . the etiology of respiratory alkalosis includes hypoxia , parenchymal lung disease , bronchial asthma , drug , mechanical ventilation , central nervous system disorder , metabolic causes and hyperventilation . the floor of the third ventricle is not a membrane but a part of the hypothalamus . massive or high - speed irrigation with normal saline has been associated with a hypothalamic dysfunction . as the neuroendoscope used in this patient was not equipped with device for a critical setting of infusion rate and pumping pressure , an unchecked maximum infusion rate ( 1,000 ml / min ) and pumping pressure ( 500 mmhg ) which produce a transient increase in pressure inside neuroendoscope may cause a transient injury of periventricular st ructures such as hypothalamus . a > 30 mmhg pressure inside the endoscope is associated with postoperative morbidity , particularly unexpected delayed recovery . first , considering the above reports , hypothalamic dysfunction caused by an unrecognized increased intracranial pressure due to the high - speed irrigation of normal saline during an endoscopic third ventriculostomy may contribute to the hyperventilation observed in the recovery room . a critical setting of infusion rate and pumping pressure during an endoscopic third ventriculostomy might help reduce pressure transferring to periventricular structures . therefore , we recommend that the neuroendoscopic intracranial pressure be monitored to prevent the complications associated with hypothalamic dysfunctions . second , this hyperventilation may be partially associated with csf acidosis induced by normal saline irrigation used during the procedure . the ph of the cerebrospinal fluid is 7.31 , whereas that of normal saline is 6.1 . a total of 3,000 ml normal saline used during the endoscopic third ventriculostomy would fill the enlarged lateral and third ventricles with normal saline instead of csf . after fenestrating the floor of the third ventricle , acidic normal saline in the enlarged lateral and third ventricles drained into the interpuduncular cisterna filled with csf , which might have led to a more acidic csf compared to normal csf . central lactate production of a meningeal tumor can also cause csf acidosis , which induces hyperventilation and respiratory alkalosis . the capacity of the male elderly lateral and third ventricle is 35.19  20.35 and 2.63  0.96 ml , respectively . our findings and those of previous reports [ 8 - 10 ] suggest that the ph in the csf and arterial blood should be measured simultaneously to confirm the respiratory alkalosis caused by normal saline irrigation - induced csf acidosis . the causes of peripheral hyperventilation , which include hypoxia , parenchymal lung disease , medication , mechanical ventilation , central nervous system disorder and metabolic disturbance , were excluded by a physical examination and laboratory tests . in conclusion , central neurogenic hyperventilation was developed in a patient receiving high - speed irrigation and large amount of normal saline ( maximum infusion rate of 1000 ml / min and maximum pumping pressure of 500 mmhg ) during an endoscopic third ventriculostomy , which may be ascribed to a transient hypothalamic dysfunction and/or acidic csf .
an endoscopic third ventriculostomy was performed in a 55-year - old man with an obstructive hydrocephalus due to aqueductal stenosis . 
 the vital signs and laboratory studies upon admission were within the normal limits . 
 anesthesia was maintained with nitrous oxide in oxygen and 6% desflurane . 
 the patient received irrigation with approximately 3,000 ml normal saline during the procedure . 
 anesthesia and operation were uneventful . 
 however , he developed postoperative hyperventilation in the recovery room , and arterial blood gas analysis revealed acute respiratory alkalosis . 
 we report a rare respiratory alkalosis that occurred after an endoscopic third ventriculostomy .