Recovery from sevoflurane anesthesia: a comparison to isoflurane and propofol anesthesia

BACKGROUND: Sevoflurane has a lower blood:gas partition coefficient than isoflurane, which may cause a more rapid recovery from anesthesia; it also might cause faster emergence times than for propofol-based anesthesia. We evaluated a database that included recovery endpoints from controlled, randomized, prospective studies sponsored by Abbott Laboratories that compared sevoflurane to isoflurane or propofol when extubation was planned immediately after completion of elective surgery in adult patients. METHODS: Sevoflurane was compared to isoflurane in eight studies (N=2,008) and to propofol in three studies (N=436). Analysis of variance was applied using least squares method mean values to calculate the pooled mean difference in recovery endpoints between primary anesthetics. The effects of patient age and case duration also were determined. RESULTS: Sevoflurane resulted in statistically significant shorter times to emergence (-3.3 min), response to command (-3.1 min), orientation (-4.0 min) and first analgesic (-8.9 min) but not time to eligibility for discharge (-1.7 min) compared to isoflurane (mean difference). Times to recovery endpoints increased with increasing case duration with isoflurane but not with sevoflurane (patients receiving isoflurane took 4-5 min more to emerge and respond to commands and 8.6 min more to achieve orientation during cases longer than 3 hr in duration than those receiving sevoflurane). Patients older than 65 yr had longer times to orientation, but within any age group, orientation was always faster after sevoflurane. There were no differences in recovery times between sevoflurane and propofol. CONCLUSIONS: Recovery from sevoflurane was 3-4 min faster than with isoflurane in all age groups, and the difference was magnified in longer-duration surgical cases (> 3 hr).     

Covariance matrix properties and multiple symbol/soft decisiondetection in slow flat Rician fading

For a small number of symbols N and slow flat fading channels, it is shown that covariance matrices encountered in practice have two nonnegligible eigenvalues, the first much larger than the second, with a symmetric eigenvector associated with the first eigenvalue, and a skew symmetric eigenvector associated with the second eigenvalue. The first eigenvector is well approximated by a conditional mean, and the second eigenvector represents a small drift about the mean. The eigenvalues and eigenvectors of the slow flat fading channel covariance matrix are shown to be strongly related to those of a certain conditional covariance matrix. The maximum likelihood (ML) rules for block hard decision and symbol-by-symbol hard decision, and a rule for soft decision detection of M-DPSK, all using multiple symbol information, are obtained for the Rician channel as a function of N. The eigenvalue-eigenvector results lead to practical implementations of all rules. For small to moderate N, it is shown that a simple open-loop algorithm, of complexity N log N, attains the performance of the ML decision rules for an E_s/N ₀ range of interest for several land mobile satellite systems. The ML decision rules are seen to give rapidly diminishing returns as N increases, showing that simple noncoherent techniques can have very effective performance for the Rician fading channel. Lastly, several conclusions are drawn about the asymptotic channel behavior, including the Rayleigh channel. The work is directly applicable to the Australian and North American land mobile satellite systems     

Codes based on a trellis cut-set transformation. I. Rotationallyinvariant codes

Let a trellis section 𝒯 generate a trellis code 𝒞. We study two trellis sections based on 𝒯, a “cut-set” trellis section 𝒯_cs and a “differential encoder” trellis section 𝒯_de. We show that 𝒯 can be transformed to a cut-set trellis section 𝒯_cs, which is equivalent to 𝒯 in the sense that both 𝒯 and 𝒯 _cs generate 𝒞 and both 𝒯 and 𝒯_cs have the same decoding complexity. A differential encoder trellis section is equivalent to the trellis section obtained by following 𝒯 with a differential encoder. It is shown that both 𝒯_cs and 𝒯_de have inverse transform trellis sections. A differential encoder trellis section generates a rotationally invariant (RI) code in a particularly simple and straightforward way. But an RI code need not have a differential encoder trellis section. However, for all of the RI codes examined here, we show that the cut-set trellis section can be arranged into a differential encoder trellis section. This means that these codes can be decomposed into an encoder followed by a differential encoder. Further we show that when 𝒯 is formed using a linear binary convolutional encoder and a mapping by set partitioning, then 𝒯 followed by a differential encoder gives an RI code which in some cases is as good as the best previously known codes, after applying the inverse transform to 𝒯_de