The Oxygen Reserve Index (ORi™) is a non-invasive variable that reflects oxygenation continuously. The aims of this study were to examine the relationship between arterial partial pressure of oxygen (PaO 2 ) and ORi during general anesthesia, and to investigate the usefulness of ORi as an indicator to avoid hyperoxia. Twenty adult patients who were scheduled for surgery under general anesthesia with arterial catheterization were enrolled. After induction of general anesthesia, inspired oxygen concentration (FiO 2 ) was set to 0.33, and arterial blood gas analysis was performed. The PaO 2 and ORi at the time of blood collection were recorded. After that, FiO 2 was changed to achieve an ORi around 0.5, 0.2, and 0, followed by arterial blood gas analysis. The relationship between ORi and PaO 2 was then investigated using the data obtained. Eighty datasets from the 20 patients were analyzed. When PaO 2 was less than 240 mmHg (n = 69), linear regression analysis showed a relatively strong positive correlation (r 2 = 0.706). The cut-off ORi value obtained from the receiver operating characteristic curve to detect PaO 2 ≥ 150 mmHg was 0.21 (sensitivity 0.950, specificity 0.755). Four-quadrant plot analysis showed that the ORi trending of PaO 2 was good (concordance rate was 100.0%). Hyperoxemia can be detected by observing ORi of patients under general anesthesia, and thus unnecessary administration of high concentration oxygen can possibly be avoided. KeywordsOxygen reserve index (ORi) • Arterial partial pressure of oxygen (PaO 2 ) • Hyperoxia • Hyperoxemia

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Application of buffers covering a range of acidic pH values activates and sensitizes nociceptors and produces pain. The purpose of this study was to determine whether a range of acidic pH in tissue produces mechanical hyperalgesia. Tissue acidosis was produced in the hindpaw of the rat by intraplantar injections of hyaluronic acid (HA) adjusted to pH 7.4, 6.0, 5.0, 4.0 or 3.0. Mechanical hyperalgesia was assessed by evaluating responses to application of a von Frey monofilament to the plantar surface before and after injection of HA. In separate experiments, magnitude of tissue acidosis produced by injection of HA was determined by measuring pH of intraplantar tissue using a pH microelectrode. Although needle stick alone produced mechanical hyperalgesia, intraplantar injections of HA at pH 6.0 or 5.0 produced significantly greater mechanical hyperalgesia. In contrast, mechanical hyperalgesia produced by injection of HA at pH 7.4, 4.0 or 3.0 was not different from that produced by needle stick. Although injection of HA at low pH produced tissue acidosis in a pH dependent manner, only a narrow range of tissue acidosis (pH = 6.38-6.00) produced mechanical hyperalgesia. Our data suggest that tissue acidosis induces mechanical hyperalgesia; however, the range of tissue pH that produces this effect is limited.

Background: Status epilepticus requires immediate treatment because treatment delay can cause permanent neurologic complications. Dexmedetomidine may be an option for the treatment of status epilepticus although its effect remains unclear with conflicting reports. Case presentation: A 64-year-old woman with epilepsy with complex partial seizures underwent total knee arthroplasty. After emergence from general anesthesia, she developed status epilepticus and was transferred to the intensive care unit. Following initial treatment using benzodiazepines, phenytoin, and levetiracetam, dexmedetomidine (0.37 μg/kg loading in 10 min followed by 0.6 μg/kg/h) was administered and seizures terminated in 20 min. Color density spectral array using Root® with SedLine® (Masimo, Irvine, CA, USA) showed an increase in power in high frequency band of the electroencephalogram during the seizure attacks. Conclusion: We described a case of status epilepticus which was treated with dexmedetomidine and monitored using color density spectral array.

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