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

The oxygen reserve index (ORi™) is a new parameter for monitoring oxygen reserve noninvasively. The aim of this study was to examine the usefulness of ORi for rapid sequence induction (RSI). Twenty adult patients who were scheduled for surgical procedures under general anesthesia were enrolled. After attaching a sensor capable of measuring ORi, oxygen (6 L/min) and fentanyl (2 μg/kg) were administered. After 3 min, propofol 2 mg/kg and rocuronium 1 mg/kg were administered without ventilation. Regardless of changes in ORi, tracheal intubation was performed either 2 min after administration of propofol or when percutaneous oxygen saturation (SpO) reached 98%. Ventilation was then provided with oxygen at 6 L/min, and trends in ORi and SpO during RSI were observed. Data from 16 of the 20 patients were analyzed. Before oxygen administration, the median SpO was 98% [interquartile range (IQR) 97-98] and ORi was 0.00 in all patients. At 3 min after starting oxygen administration, the median SpO was 100% (IQR 100-100) and the median ORi was 0.50 (IQR 0.42-0.57). There was an SpO decline of 1% or more from the peak value after propofol administration in 13 patients, and 32.5 s (IQR 18.8-51.3) before the SpO decrease, ORi began to decline in 10 of the 13 (77%) patients. The ORi trends enable us to predict oxygenation reduction approximately 30 s before SpO starts to decline. By monitoring ORi, the incidence related to hypoxemia during RSI could be reduced.

We evaluated the accuracy of noninvasive and continuous total hemoglobin (SpHb) monitoring with the Radical-7(®) Pulse CO-Oximeter in Japanese surgical patients before and after an in vivo adjustment of the first SpHb value to match the first reference value from a satellite laboratory CO-Oximeter. Twenty patients undergoing surgical procedures with general anesthesia were monitored with Pulse CO-Oximetry for SpHb. Laboratory CO-Oximeter values (tHb) were compared to SpHb at the time of the blood draws. Bias, precision, limits of agreement and correlation coefficient of SpHb compared to tHb were calculated before and after SpHb values were adjusted by subtracting the difference between the first SpHb and tHb value from all subsequent SpHb values. Trending of SpHb to tHb and the effect of perfusion index (PI) on the agreement of SpHb to tHb were also analyzed. Ninety-two tHb values were compared to the SpHb. Bias ± 1SD was 0.2 ± 1.5 g/dL before in vivo adjustment and -0.7 ± 1.0 g/dL after in vivo adjustment. Bland-Altman analysis showed limits of agreement of -2.8 to 3.1 g/dL before in vivo adjustment and -2.8 to 1.4 g/dL after in vivo adjustment. The correlation coefficient was 0.76 prior to in vivo adjustment and 0.87 after in vivo adjustment. In patients with adequate perfusion (PI ≥1.4) the correlation coefficient was 0.89. In vivo adjustment of SpHb significantly improved the accuracy in our cohort of Japanese surgical patients. The strongest correlation between SpHb and tHb values was observed in patients with adequate peripheral perfusion suggesting that low perfusion may affect the accuracy of SpHb monitoring.

Ultrasound-guided subcostal transversus abdominis plane block (TAPB) is widely used for abdominal surgery; however, arterial plasma concentration of the anesthetic ropivacaine after the blockade is still unclear. We evaluated ropivacaine concentration after subcostal TAPB in adult patients undergoing upper abdominal surgery. Twelve patients with American Society of Anesthesiologists physical status 1-2 were enrolled. They received ultrasound-guided subcostal TAPB with 0.45 % ropivacaine at 3 mg/kg. Arterial plasma samples were collected at 15, 30, 45, 60, 90, and 120 min after the blockade and analyzed for total ropivacaine concentration using liquid chromatography and mass spectrometry. At every time point, the maximum concentrations (C(max)), and time to the C max (T(max)) were recorded. The mean C(max) and T(max) were 1.87 (0.78) µg/ml and 31.3 (16.7) min, respectively. No adverse events or clinical symptoms indicating systemic toxicity were observed during this study. The study demonstrated that administration of ropivacaine at 3 mg/kg during subcostal TAPB led to rapid increases in plasma concentration of the anesthetic during the first 2 h after the blockade. C(max) nearly reached the threshold for systemic toxicity.

: Purpose of the studyThe measurement of stroke volume variation (SVV) using the FloTrac TM system (Edwards Lifescience, USA) is useful to estimate cardiac preload. We evaluated the benefits of SVV monitoring for adjusting fluid supplementation during laparoscopic adrenalectomy under anesthesia in patients with pheochromocytoma. Subjects and MethodsAmong 10 patients who underwent laparoscopic adrenalectomy for pheochromocytoma in our institution from June 2004 to December 2009, SVV was not monitored in 5 patients (group I) and in the other 5 patients (group II), SVV monitoring was performed. Subject age, height and body weight, total volume of fluid supplemented, blood loss, urine output and net fluid in -out balance during the procedure were retrospectively assessed. In those with SVV monitoring, infusion volume was adjusted for SVV less than 13%. ResultsThere were significant differences in the patient age and body weight between the two groups (group I : 64.2 years old and 55.1 kg ; group II : 43.6 years old and 71.7 kg). Both total infusion volume and urine output were significantly higher in group I compared with group II (5,610 vs. 2,400 ml and 1,125 vs. 750 ml, respectively). Total blood loss was similar between the two groups. Values of the net fluid balance divided by the body weight and total anesthesia period (hr) were significantly lower in group II compared with group I (I ; +13.2 in group I and +6.2 in group II, ml/kg/hr). ConclusionsThese data suggest that SVV monitoring is helpful to estimate the optimal volume for fluid supplementation and could prevent excessive fluid infusion during surgical procedures.