The default-mode network (DMN) is a set of specific brain regions whose activity, predominant in the resting-state, is attenuated during cognitively demanding, externally-cued tasks. The cognitive correlates of this network have proven difficult to interrogate, but one hypothesis is that regions in the network process episodic memories and semantic knowledge integral to internally-generated mental activity. Here, we compare default-mode functional connectivity in the same group of subjects during rest and conscious sedation with midazolam, a state characterized by anterograde amnesia and a reduced level of consciousness. Although the DMN showed functional connectivity during both rest and conscious sedation, a direct comparison found that there was significantly reduced functional connectivity in the posterior cingulate cortex during conscious sedation. These results confirm that low-frequency oscillations in the DMN persist and remain highly correlated even at reduced levels of consciousness. We hypothesize that focal reductions in DMN connectivity, as shown here in the posterior cingulate cortex, may represent a stable correlate of reduced consciousness.

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Signal intensity changes in fMRI during rest caused by vasomotor fluctuations were investigated in this work. Resting‐state baseline fluctuations were evaluated in 12 children anesthetized with thiopental. Five subjects had fluctuations related to subvoxel motion. In seven subjects without significant motion, slow signal fluctuation at 0.025–0.041 Hz near one or more primary sensory cortices was observed. In each subject the amplitude and frequency of the fluctuations were stable. It is hypothesized that thiopental, which reduces blood pressure and flow in the cortex, alters the feedback in neurovascular coupling leading to an increase in the magnitude and a reduction in the frequency of these fluctuations. The use of anesthesia in fMRI may provide new insight into neural connectivity and the coupling of blood flow and neural metabolism. Magn Reson Med 44:373–378, 2000. © 2000 Wiley‐Liss, Inc.

The clinical and pharmacokinetic properties of ropivacaine and bupivacaine, both 5 mg/mL, used in axillary plexus block were compared in 60 patients in this randomized, double-blind, parallel-group study. The axillary plexus was identified with a nerve stimulator and 30, 35, or 40 mL of drug, depending on body weight, was injected into the perivascular sheath. In 20 patients, venous blood samples for the pharmacokinetic measurement were obtained over 24 h. The median onset times for anesthesia and complete motor block were in the range of 12-48 min and 5-20 min, respectively. Thirty-eight percent of patients in the ropivacaine group and 29% in the bupivacaine group needed additional nerve block(s) or supplementary analgesia and 7% in the bupivacaine group needed general anesthesia for surgery. Anesthesia was achieved in 52%-86% of the evaluated six nerves in the ropivacaine group and in 36%-87% in the bupivacaine group; the lowest figures were seen in the musculocutaneous nerve. In the pharmacokinetic study the mean peak plasma concentrations (Cmax) were 1.28 +/- 0.21 mg/L in the ropivacaine group and 1.28 +/- 0.47 mg/L in the bupivacaine group and the median times to peak plasma concentration (tmax) were 0.86 h and 0.96 h, respectively. The median terminal half-lives (t1/2) were 7.1 h and 11.5 h in the ropivacaine group and the bupivacaine group, respectively (P = 0.07). No statistically significant differences were found between ropivacaine and bupivacaine in either the clinical or the pharmacokinetic comparisons.

A leukocyte-depleting filter improves brain protection after a prolonged period of hypothermic circulatory arrest.