Cerebral oxygenation in the beach chair position before and during general anesthesia in patients with and without cardiovascular risk factors.

STUDY OBJECTIVES: To evaluate changes in cerebral tissue oxygen index (TOI) values under the beach chair position before and during general anesthesia in surgical patients with or without cardiovascular risk factors. DESIGN: Prospective study. SETTING: Operating room in the university hospital. PATIENTS: Ninety-one patients undergoing surgery, including healthy patients (n = 28), patients with 1 cardiovascular risk factor (n = 33), and those with more than 1 risk factor (n = 30). INTERVENTIONS AND MEASUREMENTS: Cerebral TOI the day before and during general anesthesia was evaluated using a near-infrared spectroscopy NIRO-200 (Hamamatsu Photonics, Hamamatsu, Japan) for each patient. The initial TOI measurement in the supine position after a 10-minute rest or 10 minute after the endotracheal intubation was followed by measurements in 30° and subsequent 60° upright position for 5 minutes. Phenylephrine 0.1 mg and/or ephedrine 4 mg was administered intravenously to maintain mean blood pressure above 60 mm Hg accordingly. MAIN RESULTS: The beach chair position decreased mean arterial blood pressure and heart rate under general anesthesia, although patients with more than 1 cardiovascular risk factor needed significantly more phenylephrine doses to maintain mean blood pressure above 60 mm Hg. Values of TOI were within the normal range of about 70% before and during anesthesia in all groups. CONCLUSIONS: The beach chair position under general anesthesia did not alter cerebral oxygenation in patients with or without cardiovascular risk factors showing normal preoperative cerebral TOI values when the mean blood pressure was maintained above 60 mm Hg. The careful management using the cerebral oxygenation monitoring appears to maintain cerebral perfusion in the beach chair position during general anesthesia.

[A case of upper airway obstruction associated with flexed cervical position after posterior occipito-cervical fusion--a retrospective radiographic analysis by the O-C2 angle].

A 71-year-old female developed upper airway obstruction due to flexed cervical position after posterior occipito-cervical fusion. After the operation, she was re-intubated with the air-Q intubating laryngeal airway. Revision surgery allowing the angle to return to the neutral position was performed to attenuate the overflexion of the cervical position. After revision surgery, the upper airway obstruction disappeared. From the retrospective radiographic analysis, we suggest that the decrease of 18 degrees in the O-C2 angle causes the upper airway obstruction. On the extubation after occipito-cervical fusion, we should take care of the possibility of re-intubation and its difficulty based on the O-C2 angle.

[Postoperative pain management by continuous intravenous infusion of fentanyl using the single-use continuous infusion device].

BACKGROUND: Continuous infusion of fentanyl for postoperative pain management is performed commonly. But the usage of traditional syringe pump or infusion pump sometimes makes medical staff confusing for its difficulties of handling. We have simplified the postoperative pain management system using the single-use continuous infusion device and the protocol for administration of fentanyl. METHODS: Single-use patient controlled analgesia (PCA) system was employed for the continuous administration of fentanyl. The amount of fentanyl was calculated by a concise chart. Numerical pain rating scale, frequency of bolus infusion and side effect were monitored by ward nurses. RESULTS: Twenty nine patients were included in this study, achieving good postoperative pain control. Seven cases of nausea, two cases of vomiting were observed as side effects, but no cases of over sedation or respiratory depression were reported. CONCLUSIONS: It is concluded that good postoperative pain management is possible with single use infusion device safely.

Comparison of bicarbonate and base excess values analyzed by four different blood gas analyzers.

Comparison of the calculation formula, reproducibility, correlation and variation of bicarbonate ion concentration (HCO(3) (-)), and base excess value (BE) among four blood-gas analyzers was performed. No HCO(3) (-) and BE values calculated from the formulas showed any clinically significant difference, and all analyzers showed good correlation on their measurements. On the actual measurement of a specific sample, however, BE values from the same sample ranged between -6.3 and -15.7, which might affect therapeutic strategy. Caution should be taken for the assessment of data if different types of blood-gas analysis devices are used in the same facility.

The effects of sevoflurane and propofol on QT interval and heterologously expressed human ether-a-go-go related gene currents in Xenopus oocytes.

Sevoflurane can induce prolongation of the cardiac QT interval by inhibiting the repolarization phase of the action potential. This may occur as a result of inhibition of the human ether-a-go-go related gene (HERG) channel. To clarify the mechanisms of anesthetics on HERG channels, we monitored the electrocardiogram and measured QT intervals in the guinea pig in the presence of sevoflurane and propofol. Sevoflurane (1%-4%) prolonged QTc dose-dependently (7.5%-21.2%), but propofol did not affect it. Furthermore, HERG channels were expressed in Xenopus oocytes and outward HERG currents were obtained on step depolarization from a holding potential of -70 mV. Repolarization to -70 mV from positive test potentials resulted in large outward tail currents. Sevoflurane (1%-4%), in a dose-dependent manner, inhibited the HERG outward tail currents (9.7%-26.6%), whereas steady-state currents were inhibited only at large concentrations. The time constant of the converging current was decreased in the presence of sevoflurane, but the inactivation and activation curves were not shifted. Propofol did not affect these currents within the clinically relevant concentration. In conclusion, compared with steady-state currents, sevoflurane was more potent in inhibiting the outward tail currents, suggesting that sevoflurane may modulate the HERG channel kinetics in its inactivated state.

[Mechanism of QT interval prolongation induced by sevoflurane in guinea-pig ventricular myocyte].

BACKGROUND: Sevoflurane causes QT interval prolongation clinically, but its precise mechanism has not been clarified. We examined the mechanism of QT interval prolongation induced by sevoflurane by means of electrophysiological technique in guinea-pig ventricular myocyte. METHODS: Electrocardiogram was recorded in guinea-pig and effect of sevoflurane (1, 2, 4%) was examined. Action potential (AP), delayed rectified potassium current (IKr), and L-type calcium channel current (ICa) were monitored as whole-cell current and by voltage clamp techniques in guinea-pig single ventricular myocytes. Sevoflurane was applied by bubbling into the bathing solution. RESULTS: Sevoflurane (1, 2, 4%) increased QTc value. Sevoflurane prolonged the duration of AP at 2%, but shortened it at 6%. IKr was reduced to 35% of control in the presence of 2% sevoflurane, but a higher concentration (6%) did not show further inhibition. ICa was reduced only to 87% of control in the presence of 2% sevoflurane and the reduction was dose-dependent (4, 6%). CONCLUSIONS: Sevoflurane 2% inhibited IKr, but it showed only slight inhibition on ICa. Because the duration of AP is regulated by ICa (plateau phase) and IKr (repolarization), greater inhibition of IKr than ICa could result in prolongation of AP. It is suggested that this mechanism may play a role in QT interval prolongation under sevoflurane anesthesia.

Effects of ropivacaine on membrane potential and voltage-dependent calcium channel current in single guinea-pig ventricular myocytes.

PURPOSE: This study was undertaken to assess the effects of ropivacaine on the membrane action potential and the voltage-dependent L-type calcium channel current ( I(Ca)) in guinea-pig single ventricular myocytes. METHODS: Single ventricular myocytes were prepared by enzymatic dispersion. Whole-cell current and voltage-clamp techniques were used to monitor membrane potentials and I(Ca). RESULTS: Ropivacaine (10(-5) and 10(-4) M) reduced the overshoot and shortened the duration of the action potential. Hyperpolarization of the resting membrane potential was observed in the presence of ropivacaine (10(-4) M). Ropivacaine (10(-5)-10(-3) M) reduced I(Ca) dose-dependently and reversibly, and the 50% inhibitory concentration (IC(50)) of ropivacaine was estimated as 4.3 x 10(-4) M. Furthermore, the inhibition of I(Ca) was not a use-dependent block. CONCLUSION: Ropivacaine has an inhibitory effect on I(Ca) in the guinea-pig single ventricular myocyte. It is concluded that the mild negative inotropic effect induced by ropivacaine can be attributed in part to shortening of the duration of the action potential, which is caused by inhibition of I(Ca).