Using new electrofishing technology to amp-up fish sampling in estuarine habitats.

A prototype, boat-mounted electrofisher capable of operation in estuarine waters (where electrical conductivities often exceed 20 000 µS cm(-1)) was assessed. Electrofishing was compared to fyke and mesh netting in four riverine estuaries and to seining in a lagoonal estuary (consisting of a series of brackish coastal lakes separated from the sea by a barrier system of sand dunes). Fish assemblage composition, length distributions and the probability of detecting ecological fish guilds (relating to estuary use, position in the water column and body size) were compared among gears. The assemblage composition of electrofishing samples differed from those of fyke nets in all riverine estuaries and from mesh netting in two. The assemblage composition of electrofishing samples differed from those of seining in structured seagrass habitats of the lagoonal estuary. When all species were pooled, the electrofisher sampled a broader range of lengths than either fyke or mesh netting in riverine estuaries or seining in lagoonal estuaries. The bias of electrofishing and netting towards particular species and size classes affected the probability of detecting some ecological guilds, highlighting the potential implications of gear choice on understanding estuarine ecological function. The detection of guilds varied with gear type and environmental conditions, including stratification, water depth and surface electrical conductivity. Assessments with the aim to characterize the structure of fish assemblages will benefit from the use of multiple gears. Electrofishing shows immense promise for discretely sampling highly structured habitats to test hypotheses about their use.

Drotrecogin alfa (activated) in severe falciparum malaria.

Drotrecogin alfa (activated) is a drug licensed for the treatment of severe sepsis. We describe the care of a 61-year-old man who developed multi-organ failure secondary to severe falciparum malaria infection with parasitaemia levels of 40%. Included in his care were an exchange blood transfusion and an infusion of Drotrecogin alfa (activated). Within hours of starting the infusion of Drotrecogin alfa (activated), the patient's clinical condition stopped deteriorating. Steady improvement followed with weaning from ventilatory assistance on day 14 post admission. The patient made a full recovery and was discharged home following rehabilitation. The indications for Drotrecogin alfa (activated) and the appropriateness of its use in severe malaria with multi-organ failure are discussed. Drotrecogin alfa (activated) may be a useful treatment in patients with multi-organ failure resulting from severe malaria.

A method for producing the coherent frequency: a steady-state auditory evoked response in the electroencephalogram.

Transient and steady-state auditory evoked responses in the electroencephalogram are used to study the effect on the brain of graded changes in the concentration of general anesthetics. A method is described using modern signal processing techniques to improve the analysis of steady-state auditory evoked responses (SSAER). The SSAER was obtained using headphones to give 100-200 auditory click stimuli from 6.5 Hz.to 50.5Hz in 1-Hz steps. The resulting electroencephalogram signals were filtered and subject to Fourier analysis, after which a series of coherence indexes were derived based on waves with significant power in the fundamental but with minimal harmonic content. These were plotted against the range of stimuli and fitted with a third-order polynomial. The frequency at which the maximum coherence index was achieved (highest possible value = 1) was derived from polynomial interpolation. The repeatability of the method was examined in 10 awake subjects using runs of ascending then descending stimulating frequencies. The mean maximum coherence index was at 38 Hz, with the 95% confidence interval of 37.3 Hz-38.9 Hz. There was no difference between ascending and descending sweeps. The method provides an automatic analysis of the SSAER that obviates the need to make subjective decisions about which is the dominant wave, a major problem in the analysis of the transient auditory evoked responses.

The coherent frequency in the electroencephalogram as an objective measure of cognitive function during propofol sedation.

Ten volunteers were studied during six stages of propofol sedation, namely awake (no propofol), light sedation (small dose of propofol), deep sedation (large dose), deep sedation with stimulation of the ulnar nerve, then light sedation again (small dose), and awake (recovery). Light and deep sedation were defined in terms of performance on a test of cognitive function: the within-list recognition (WLR) test. At each stage, the steady-state auditory evoked potential was measured at different stimulating frequencies to derive the frequency needed to achieve the maximal coherence index. This frequency is called the "maximum coherent frequency". WLR performance correlated with infusion dose (r = -0.71), plasma propofol concentration (r = -0.75), and maximum coherent frequency (r = 0.75). When the correlations were examined for the propofol sedation stages only, there remained a strong correlation between WLR performance and maximum coherent frequency (r = 0.47, P < 0.005), but no significant correlations between infusion dose and WLR (r = -0.11) or infusion dose and plasma concentration (r = 0.13). These data suggest that maximum coherent frequency provides a better measure of depth of sedation than does the dose of propofol alone.